Dissertations / Theses: 'Dual Phase steel - DP'

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Falk, Johannes. "Fracture prediction of stretched shear cut edges in sheets made of Dual-Phase steel." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-13956.

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Dual-Phase (DP) steels, part of the group of Advanced High Strength Steels (AHSS), are used by car manufactures due to its large strength to weight ratio. The high strength of the DP steel does have a negative impact on the formability during sheet metal forming and stretch forming, e.g. fractures often appear in shear cut edges during forming of blanks made of DP steel. The main objective with this thesis is to develop a new punch for Volvo Cars that concentrates the strain to the sheared edges of a test specimen made from different types of DP steel. This is done to be able to measure and obtain maximum fracture strain during stretch forming tests in a press. The newly developed test method is called CTEST (Concentrated Trim Edge Strain Test). The tests are performed with DP steel specimens with three different qualities of the shear cut edges; fine cut, medium cut and worn cut. DP steels tested are DP600GI, DP600UC and DP800GI from three different suppliers. 10 different types of DP steels are tested in this study with different thickness. Thickness of specimens tested are 1 mm, 1.1 mm, 1.5 mm and 2 mm and all specimens tested have a lengthwise (RD) rolling direction. The quality of the sheared cut edge has a great impact to the formability and maximum fracture strain of the specimen. A specimen with a fine cut endures higher fracture strain than medium cut and a worn cut for all types of DP steel with different thickness. A 1 mm thick specimen endures a lower fracture strain than 1.5 mm and 2 mm specimen for all cut qualities. Further, the impact of the orientation of the burr zone of a shear cut edge is studied. With the burr zone facing upwards from the CTEST punch the formability of the specimens is decreased compared to a burr zone facing downwards, especially for a worn cut specimen with micro cracks and imperfections in the edge surface. ARAMIS Digital Image Correlation (DIC) system is used to analyze the specimen edges during press experiments. The ARAMIS results unveil that several small fractures appear in the sheared edges of a specimen just before the specimens split into two pieces. This phenomenon was seen for specimen with worn and medium shear cut qualities. Finite Element (FE) simulations of the CTEST is performed in AutoForm to determine maximum values of the true strain for the three different cut qualities. The simulation in AutoForm does show a slightly higher value of the force and press depth than the value from the press test before maximum fracture strain in reached. The small fractures seen in ARAMIS just before the specimen split into two pieces cannot be seen in the simulation in AutoForm.

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Zanluchi, Jeferson Jorge Dallagnol. "Avaliação de retorno elástico para processos de estampagem à frio dos aços bifásicos DP 600 e DP 800." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/127900.

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Este trabalho procura avaliar o retorno elástico em aços avançados de alta resistência utilizados em processo de dobramento. Para isso, foram usadas chapas de aço bifásico DP 600 e DP 800, ambas revestidas. Foram empregados dois métodos de medição a fim de abordar e avaliar o retorno elástico. O primeiro método abordado foi à conformação de tiras em U e o segundo método foi à realização do ensaio Dobramento Sob Tensão, aos quais possibilitaram a coleta de dados para aplicação em cálculo de coeficiente de atrito no processo de dobramento. Em ambas as avaliações foram utilizadas duas diferentes condições de lubrificação para o processo de dobramento, visando variar a condição de atrito no processo. A primeira foi à aplicação de um lubrificante em forma de pasta, de nome comercial Clarus Desmoldax DCP 35 e a segunda foi à aplicação em forma líquida, denominado Clarus Desmoldax DCP 35X. Para analisar o retorno elástico, foram utilizadas como critério de avaliação as medições de abertura da parede da tira conformada, permitindo desta forma considerar o atrito por intermédio da variação do tipo lubrificante. As análises realizadas nos corpos de prova conformados em formato U evidenciaram um retorno elástico menor para as amostras do aço DP 600, se comparadas com as amostras do aço DP 800. Não existiu relevância na variação dos lubrificantes quanto ao retorno elástico nas amostras de um mesmo tipo de aço. As análises realizadas nos corpos de prova submetidos ao ensaio de dobramento sob tensão, também evidenciaram um retorno elástico menor para as amostras do aço DP 600 se comparadas com as amostras do aço DP 800. Comparando as amostras com base nos dados coletados e aplicados ao cálculo de coeficiente de atrito, percebeu-se que as amostras que tiveram um retorno elástico menor, também possuíam coeficientes de atrito menor, constatando assim que quanto menor o coeficiente de atrito, menor é o retorno elástico.
This piece of work seeks to evaluate the springback effect on advanced high strength steel used in the bending process. For this, biphasic steel plates DP 600 and DP 800, both coated, were used. Two methods of measurement were used to approach and asses the springback effect. The first method approached was the conformation of strips in U and the second method was the preformance of the Bending Under Tension test, which enabled the data collect for the application in calculation of the friction coefficient in the bending process. In both assessments two different lubricant conditions for the bending process were used with the aim of varying the condition of friction in the process. The first one was the application of a paste lubricant, with the brand name Clarus Desmoldax DCP 35 and the second one was the application of a liquid lubricant, called Clarus Desmoldax DCP 35X. To analyze the springback effect the measurements of the opening of the wall of the conformed strip were used, thus allowing to consider the friction through the variation of the type of lubricant. The assessments carried out in the specimens in U shape showed a smaller springback effect for the steel samples DP 600 in comparison with the DP 800 ones. There was no relevance in the range of lubricants as the springback effect in the samples of the same type of steel. The analyzes carried out in the specimens subjected to bending under pressure test also showed a smaller springback effect for the steel samples DP 600 compared with the DP 800 ones. Comparing the samples based on the data collected and applied to the calculation of the friction coefficient, it was noticed that the samples that had a smaller springback effect also had lower friction coefficients, therefore verifying that the lower the friction coefficient is, the lower the springback effect.

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Hou, Yuliang. "Modelling of plasticity and fracture behaviors of dual-phase steel." Thesis, Compiègne, 2016. http://www.theses.fr/2016COMP2302/document.

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L’acier à double phase (DP) a été développé par l'industrie automobile pour le but de réduire le poids, l'amélioration de la performance de la sécurité et l'efficacité énergétique. Habituellement, l'acier DP contient des îlots de martensite dure noyée dans une matrice de ferrite doux. La synergie entre ces deux phases avec la microstructure inhomogène présente d'excellentes propriétés mécaniques. Les propriétés mécaniques (comportements de plasticité et de dégâts) d'acier DP sont principalement dérivés de sa microstructure, par exemple, la fraction de volume, la taille, la distribution et la morphologie de chaque phase constituante. Les approches micromécaniques sont largement appliquées pour prédire la plasticité et d'autres propriétés mécaniques de l'acier DP selon divers scénarios de chargement. Dans ce travail, la modélisation micromécanique de l'acier DP a été réalisée en utilisant des microstructures réelles ou artificielles. Une véritable microstructure est obtenue à partir de l'image métallographique, tandis qu'un générateur de microstructure artificielle à l'aide d'un algorithme d'affectation de phase améliorée basée sur l'optimisation de la topologie matériau est proposé d'étudier les propriétés mécaniques. Dans ce générateur artificiel, un processus d'affectation de phase est réalisé sur une mosaïque de Voronoï modifié pour obtenir une mesure représentative de l'élément de volume (VER) avec une bonne convergence. La méthode proposée comprend également une réduction appropriée décomposition orthogonale (POD) des courbes de débit (instantanés), qui sont calculés en utilisant le schéma asymptotique homogénéisation d'extension (AEH), pour identifier le contrôle des paramètres optimaux pour l'acier DP. Cette méthode numérique est vérifiée en utilisant DP590 et DP980 aciers qui indiquent un bon accord avec la contrainte d'écoulement à partir de mesures et prédiction de RVE basés sur de vraies microstructures. Les prédictions des modèles de déformation plastique, y compris des bandes de cisaillement en utilisant la microstructure artificielle ressemblent étroitement le comportement mécanique réel dans des conditions de chargement similaires. En outre, une interpolation a été adoptée pour obtenir une corrélation entre ces paramètres de contrôles basés sur l'identification des différents aciers DP. En outre, un modèle de substitution bi-niveau réduit est élaboré et présenté pour identifier les paramètres matériels du critère de rupture de Mohr-Coulomb (MMC). En utilisant cette méthode, le processus d'identification devient possible avec un nombre limité de tests Expérimentaux. La méthode combine des éléments critiques locaux associés à des modèles globaux. Le modèle de substitution de la souche de fracture construit en utilisant l'approximation diffuse et les éléments locaux, réduit le coût de calcul pour la recherche des paramètres matériels. Des simulations de fracturation sont effectuées globales pour mettre à jour la déformation à la rupture de la cible et pour calculer le déplacement de l'apparition de la panne correspondante. Des résultats probants sont obtenus par application successive de la conception de l'expérience (DOE) et l'amélioration des algorithmes de transformation de l'espace de conception. Le protocole d'identification proposée est validé avec de l'acier DP590. Robustesse de la méthode est confirmée par des valeurs initiales différentes. Ces investigations numériques fournissent nouvelle direction pour les simulations multi-échelles de la plasticité et de dégâts des comportements d'acier DP. De plus, ils contribuent efficacement à combler le fossé entre la recherche scientifique et à l'application de l'ingénierie des matériaux hétérogènes
Dual-phase (DP) steel has been developed by automotive industry for the purpose of weight reduction, improvement in safety performance and fuel efficiency. Usually, DP steel contains hard martensite islands embedded in a soft ferrite matrix. Synergy between these two phases with the inhomogeneous microstructure exhibits excellent mechanical properties. The mechanical properties (plasticity and damage behaviors) of DP steel are mostly derived from its microstructure, e.g., volume fraction, size, distribution and morphology of each constituent phase. Micromechanical approaches are vastly applied to predict plasticity and other mechanical properties of DP steel under various loading scenarios. In this work, micromechanical modelling of DP steel has been performed using real or artificial microstructures. A real microstructure is obtained from metallographic image, while an artificial microstructure generator with an enhanced phase assignment algorithm based on material topology optimization is proposed to investigate the mechanical properties. In this artificial generator, phase assignment process is performed on a modified Voronoï tessellation to achieve the tailored representative volume element (RVE) with a good convergence. The proposed method also includes a proper orthogonal decomposition (POD) reduction of flow curves (snapshots), which are computed using the asymptotic extension homogenization (AEH) scheme, to identify the optimal controlling parameters for DP steel. This numerical method is verified using DP590 and DP980 steels that indicate a good agreement with the flow stress from measurements and RVE prediction based on real microstructures. Predictions of plastic strain patterns including shear bands using the artificial microstructure closely resemble the actual mechanical behavior under similar loading conditions. Moreover, an interpolation has been adopted to obtain a correlation between these controlling parameters based on the identification for various DP steels. Additionally, a bi-level reduced surrogate model is developed and presented to identify the material parameters of the Mohr-Coulomb (MMC) fracture criterion. Using this method, the identification process becomes feasible with a limited number of experimental tests. The method combines local critical elements associated with global models. The surrogate model of fracture strain constructed using the diffuse approximation and the local elements, reduced the computational cost for searching material parameters. Global fracture simulations are performed to update the target fracture strain and to compute the corresponding failure onset displacement. Convincing results are obtained via successive application of design of experiment (DOE) and enhanced design space transformation algorithms. The proposed identification protocol is validated with DP590 steel. Robustness of the method is confirmed with different initial values. These numerical investigations provide new direction for multiscale simulations of the plasticity and damage behaviors of DP steel. Moreover, they efficiently contribute to bridge the gap between scientific research and engineering application of heterogeneous materials

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Sung, Ji-Hyun. "The Causes of “Shear Fracture” of Dual-Phase Steels." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1268039436.

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Olsen, Eric Michael. "Friction Stir Welding of High-Strength Automotive Steel." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/951.

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The following thesis is a study on the ability to create acceptable welds in thin-plate, ultra-high-strength steels (UHSS) by way of friction stir welding (FSW). Steels are welded together to create tailor-welded blanks (TWB) for use in the automotive industry. Dual Phase (DP) 590, 780, and 980 steel as well as Transformation-Induced Plasticity (TRIP) 590 steel with thicknesses ranging from 1.2 mm to 1.8 mm were welded using friction stir welding under a variety of processing conditions, including experiments with dissimilar thicknesses. Samples were tested under tensile loads for initial determination if an acceptable weld had been created. Acceptable welds were created in both TRIP 590 and DP 590 at speeds up to 102 centimeters-per-minute. No acceptable welds were created in the DP 780 and DP 980 materials. A series of microhardness measurements were taken across weld samples to gain understanding as to the causes of failure. These data indicate that softening, caused by both excessive heat and insufficient heat can result in weld failure. Not enough heat causes the high concentration of martensite in these materials to temper while too much heat can cause excessive hardening in the weld, through the formation of even more martensite, which tends to promote failure mode during forming operations. Laser welding is one of the leading methods for creating tailor-welded blank. Therefore, laser welded samples of each material were tested and compared to Friction Stir Welded samples. Lower strength and elongation are measured in weld failure while the failure location itself determines the success of a weld. In short, an acceptable weld is one that breaks outside the weld nugget and Heat Affected Zone (HAZ) and where the tensile strength (both yield and ultimate) along with the elongation are comparable to the base material. In unacceptable welds, the sample broke in the weld nugget or HAZ while strength and elongations were well below those of the base material samples.

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Rosado, Diego Belato. "Comparação do efeito da fragilização por hidrogênio em aços com resistência à tração acima de 1000 MPa." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/37374.

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Este trabalho tem por objetivo avaliar os efeitos do hidrogênio em três diferentes tipos de aços de alta resistência mecânica. São descritos os fenômenos de introdução, difusão e aprisionamento de hidrogênio (H) dentro dos metais, em conjunto com os diferentes tipos de danos provocados devido à presença do hidrogênio. Os materiais de estudo são aços da família Advanced High Strength Steels (AHSS): aços Dual Phase (DP 1000 e DP 1200) e aço Martensítico (M 190). A introdução de hidrogênio nos materiais foi realizada através de carregamento catódico, o qual é representativo para as condições industriais a que se destinam. De modo a avaliar a influência do H nas propriedades mecânicas dos aços, os seguintes ensaios foram propostos: ensaio de carregamento com H, para determinar o conteúdo total de H (saturação) e conteúdo de H difusível (suscetibilidade a fragilização); ensaio de tração ao ar, para determinar a tensão no final da região elástica e resistência à tração na região do entalhe e ensaio de tração com carga constante em ambiente hidrogenado, para avaliar os efeitos provocados pela presença do H e determinar o patamar abaixo do qual o H não apresenta efeito crítico sobre o material. Os efeitos provocados pela aplicação de diferentes densidades de correntes (0,2 – 1,0 mA/cm²) foram avaliados nos ensaios de quantificação de H difusível. Conforme os resultados obtidos todos os aços apresentaram perdas na resistência mecânica à tração quando em ambiente hidrogenado, ou seja, sofreram fragilização por H. Os aços DP 1200 e M 190 (de microestrutura predominantemente martensítica) foram fortemente afetados, conforme evidenciado pela notável queda nos valores de tensão necessários para provocar a falha. Por outro lado, o aço DP 1000, de menor resistência mecânica, demonstrou menor suscetibilidade à fragilização, o que é atribuído a menor permeabilidade do H na microestrutura austenítica.
This work aims to evaluate the effects of hydrogen in three high- strength steel grades. The phenomena of hydrogen (H) entry, transport and trapping inside the metals, together with the different types of damages due to the presence of hydrogen are presented. The study materials are a range of AHSS steel grades: Dual Phase Steel (DP 1000 and DP 1200) and Martensitic Steel (M 190). The hydrogen entry was performed by cathodic charging, which is suitable for industrial applications. In order to evaluate the influence of H on the steel mechanical properties, the following tests were done: H charging, to measure total H content (saturation point) and diffusible H content (embrittlement susceptibility); uniaxial tensile test of uncharged samples to determine notched tensile strength values and the strength levels at the end of elastic region and constant load tensile testing carried out in hydrogen environment, to determine the threshold values where hydrogen has an effect on the material. DP 1200 and M 190 were strongly affected by H pre-charging, as shown by the significant drop in stress required to break them. On the other hand, DP 1000 showed a lower embrittlement susceptibility, which is attributed to its lower mechanical strength. The current densities effects (0.2 up to 1.0 mA/cm²) were evaluated during H charging to measure diffusible H content. All steels showed a drop in the tensile strength i.e. experienced hydrogen embrittlement. Steels with higher tensile strength, as DP 1200 and M 190, showed a much bigger drop that is related to the favorable characteristics of martensitic microstructure regarding to the hydrogen permeability and diffusivity.

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Piao, Kun. "An Elevated-Temperature Tension-Compression Test and Its Application to Mg AZ31B." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316096630.

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Mallick, Dwaipayan. "Hydrogen behavior in first and second generation of advanced high strength steels." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI052.

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Les aciers AHSS sont largement utilisés pour les caisses des véhicules, en raison de leurs bonnes propriétés mécaniques et de leurs capacités à réduire l'empreinte carbone. Toutefois, leur utilisation est limitée par leur sensibilité à la fragilisation par l'hydrogène (HE). La présente étude vise à comprendre l'influence de l'hydrogène sur quatre aciers AHSS : deux biphasés (DP), un phase complexe (CP) et un à plasticité induite (TWIP). Les résultats montrent une forte susceptibilité à l’HE pour les aciers DP et TWIP par rapport aux aciers CP. Le comportement de CP est attribuée à une microstructure plus homogène, une densité de piège plus petite (mais à énergie élevé) et une concentration en H plus faible. Dans les aciers DP, la forte densité de pièges à faible énergie et la forte absorption de H augmentent la susceptibilité à l’HE. Les dislocations et les joints de grains sont les principaux sites de piégeage pour tous ces aciers, ainsi que la cémentite dans les aciers CP et les particules AlN et l’austénite pour les aciers TWIP. Sous chargement mécanique, la désorption de l'hydrogène s’accélère avec l'expansion du réseau cristallin et les mouvements des dislocations (jusqu'à la limite d'élasticité), alors qu'elle diminue en raison de la génération de défauts dans la domaine plastique. Pour l'acier CP, l'hydrogène piégé fortement désorbe à l'UTS alors que dans l'acier TWIP, la génération de défauts libère l'hydrogène. Pour l’acier DP galvanisés, la couche de Zn se comporte une couche barrière à l’hydrogène sous polarisation fortement cathodiques, tandis qu'à potentiels cathodique plus faible, elle favorise la perméation de l'hydrogène en raison de sa dissolution
Advanced High Strength Steels (AHSS) are increasingly used as fabrication material for vehicle Body In White (BIW), owing to their superior properties and ability to reduce carbon footprint. However, its susceptibility to hydrogen embrittlement (HE) restricts the use of AHSS. The present study aims to understand the H influence on four commercial-grade AHSS steels, two Dual Phase (DP), one Complex Phase (CP), and one Twinning Induced Plasticity (TWIP) steel. Results show high HE susceptibility for DP and TWIP steel compared to CP steel. The superior HE resistance in CP steel was attributed to a more homogeneous microstructure, smaller yet stronger trap density, and lower H concentration. In DP steels, a high density of weak traps and high H uptake increased HE susceptibility. During charging, H preferentially adsorbed along the grain boundaries and interfaces for all steels along with grain interior in TWIP steels. Dislocations and grain boundaries were the main trap sites for all steels, along with cementite particles in CP steels and AlN particles and austenitic grain interior in TWIP steels. For all steels under stress, hydrogen desorption increased up to yield point due to lattice expansion and dislocation movement, whereas decreased in the plastic region due to defect generation. For CP steel, strongly trapped hydrogen desorbed at UTS whereas in TWIP steel, generation of deformation twinning released hydrogen. The study of the galvanized layer showed that at higher cathodic overpotential, the Zn layer behaved as a barrier layer protecting the steel, while at a lower potential, it increased the HE susceptibility due to Zn layer dissolution. Overall, CP steel was the most resistant steel to HE, followed by TWIP and DP steels

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Sun, Shoujin. "Directionally structured dual phase steel composites." Thesis, University of Canterbury. Mechanical Engineering, 1998. http://hdl.handle.net/10092/8134.

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Manganese partitioning and mechanical properties of dual phase steels have been examined. The manganese partitioning coefficient increases to a limit with increasing isothermal holding time, and the final equilibrium partitioning coefficient decreases with increasing annealing temperature. The combination of diffusion equations in austenite and ferrite plus mass balance and austenite growth can give the manganese distribution in austenite and ferrite respectively, and the manganese partitioning coefficient at any isothermal holding time. The introduction of rolling during annealing or at the end of annealing can strengthen dual phase steels by elongating austenite and introducing internal stresses and dislocations, the magnitude of which depends on finishing rolling temperature and the timing of rolling during annealing. The tensile properties of as-rolled dual phase steels are strongly influenced by finishing rolling temperature and martensite volume fraction because of internal stresses and dislocation density, whereas those of post-rolling annealed steels depend on only martensite volume percentage. To model the heat-treatment for producing dual phase steels (“in-situ” dual phase steel), a steel-steel composite is produced by incorporating high strength steel-wires into ductile steel sheets through hot-rolling (“artificial” dual phase steel). The properties of the reinforcing wire, matrix steels, interfacial strength between wire and matrix steels and steel-steel composite are affected by the surface condition of wire, finishing rolling temperature, preform holding time at rolling temperature before rolling, and heat-treatment after fabrication of composites. Mileiko’s theory can predict the relationship between the steel-steel composite strength and the volume fraction of wire. But for dual phase steels, Mileiko’s theory can be applied only when martensite volume fraction is over 30% because the residual stress, high dislocation density and carbide are produced at low temperature, at which low martensite volume fraction is obtained. Continuous wire composites can simulate the as-rolled dual phase steel when the reinforcement content is over 30%, but discontinuous wire composites can not simulate the post-rolling annealed dual phase steel.

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Cochrane, Hal. "Formable dual-phase steels." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329964.

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Rieger, Florian [Verfasser]. "Work-hardening of dual-phase steel / Florian Rieger." Karlsruhe : KIT Scientific Publishing, 2016. http://www.ksp.kit.edu.

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Els-Botes, Annelize. "Material characterisation of laser formed dual phase steel components." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/176.

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The nature and scope of this thesis can be divided into four categories: • FORMING PARAMETERS • Identification of various laser forming parameters in order to produce specimens of similar dimension (radius of curvature). • TEMPERATURE AND MICROSTRUCTURE • To study the effect of maximum temperature reached during the forming operation on the microstructure of the various specimens. • FATIGUE LIFE • Compare the fatigue life of the specimens produced by various laser parameters to that of the original material, and also the fatigue life of mechanical formed specimens. • RESIDUAL STRESS PROFILE Determine if the laser forming process induces detrimental residual stress magnitudes in the specimens. The main objective of this thesis was to gain an understanding of the way in which laser forming affects the fatigue performance and residual stress magnitude / distribution of dual phase steel. Although lasers have been used successfully in various manufacturing processes (welding, cutting, marking, etc.), little information is available on the influence of laser forming on many automotive alloys such as dual phase steel. The first part of the work involved a literature review of the process and factors affecting the laser forming process. It became clear from the literature overview that laser forming of sheet material thicker than 1mm is complex in nature. The variables that can influence the process are complicated and their interaction with each other is not easily controlled. The main parameters that were thus controlled in this study are as follows: • Laser power (P) • Laser head travel speed (v) • Laser beam size (mm) The chapters that follow the literature review, deals with the laser forming process of dual phase steel and the production of fatigue specimens using various laser parameters. It was found that the following laser parameters resulted in specimens with approximately the same radius of curvature: Laser power KW Beam diameter mm Interval spacing % Overlap Scanning velocity m/min Line Energy J/m 5 20 10 50 2,5 2000 3,1 14 10,5 25 2 1550 1,5 7,5 7,5 0 1,2 1250 From the results obtained from fatigue testing specimens produced with the above settings, it is clear that the laser forming process has the potential to be employed as a production stage in the manufacture of wheel centre discs while maintaining adequate fatigue strength. Large beam diameters which cause heat penetration through the thickness of the specimen and hence microstructure breakdown should be avoided, since it was shown that these specimens exhibited impaired mechanical properties than those produced with a smaller laser beam diameter. The microstructural changes observed during the forming process needs to be considered since the mechanical properties of the material changes with a change in microstructure. A dramatic change in microstructure was observed; therefore it is of crucial importance that microstructural evaluation plays an important part in deciding optimum laser parameters for the forming process of ferrous alloys. During residual stress analysis, trends were observed between measurements taken at the same location of the samples; regardless whether measurements were taken on the laser irradiated side or the reverse side of the specimen. The only difference was the magnitude of the relieved residual stress. In most cases the obtained relieved residual stress was much smaller in magnitude than that of the original plate (in the bulk of the material). The surface indicated a slight tensile residual stress for most samples evaluated. A good correlation in distribution profile was obtained between microhardness and relieved residual stress distribution at the ‘middle of sample’ location. This indicates that an increase in hardness indicates an increase in residual stress magnitude for the laser formed specimens. In conclusion, this research has proved that it is possible to deform metal plate of a 3,5mm thickness with a CO2 laser system. The research also established the effect of process parameters on the final product’s shape/bend angle and characterised the effect of the laser forming process on the material’s mechanical properties and structural integrity.

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Mesmari, H. R. A. "Strength and fatigue behaviour of dual phase steels." Thesis, University of Strathclyde, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382450.

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Jamwal, Ranbir Singh. "Microstructural origins of variability in the tensile ductility of dual phase steels." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39477.

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Quantitative relationships among processing parameters, microstructure, and material properties are of considerable interest in the context of development of robust processing routes that optimize the required material properties. As a result, the scientific literature contains a large number of experimental and theoretical studies on microstructure-properties relationships. Fracture sensitive mechanical properties such as ductility, ultimate tensile strength, fatigue life, and fracture toughness depend on the average microstructural parameters as well as the distributions of microstructural parameters and their extrema.Development of quantitative relationships between such material properties and microstructural distributions and extrema has received considerably less attention, particularly in the wrought metals and alloys. Accordingly, an important objective of this research is to perform a systematic investigation in this direction. The dependence of the fracture-sensitive mechanical properties on the microstructural distributions and extrema often leads to substantial variability in these properties: a set of specimens having the same average chemistry, the same average processing history, and the same average microstructural parameters such as volume fractions of different constituents can exhibit substantially different material properties. The present research (i) is concerned with high strength (~ 1000 MPa) high martensite (>50%) dual phase steel where the martensite is a topologically continuous phase (matrix) containing a dispersion of islands of ferrite, and (ii) focuses on understanding the microstructural origins of the variability in fracture sensitive mechanical properties, in particular variability in the room temperature uniaxial tensile ductility. The research involves quantitative microstructure characterization using stereology and digital image processing and quantitative fractography using scanning electron microscopy (SEM) and fracture profilometry. The analysis of the quantitative fractographic and microstructural data obtained in this research leads to useful guidelines for reducing the variability in the tensile ductility of the dual phase steel under investigation.

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Rieger, Florian [Verfasser], and T. [Akademischer Betreuer] Böhlke. "Work-hardening of dual-phase steel / Florian Rieger. Betreuer: T. Böhlke." Karlsruhe : KIT-Bibliothek, 2015. http://d-nb.info/1100529683/34.

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Gruben, Gaute. "Ductile Fracture in Dual-Phase Steel : Theoretical, Experimental and Numerical Study." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19445.

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The thesis is focused on quasi-static ductile fracture in the low range of stress triaxiality of the dual-phase steel Docol 600DL. The study includes mechanical testing, theoretical aspects of ductile fracture and numerical simulations. Ductile fracture in the low range of stress triaxiality is an interesting topic since experimental data from various studies suggests that the ductility of the material is not only governed by the hydrostatic stressstate, but is also influenced by the deviatoric stress-state. The thesis consists of four journal articles bound together by a synopsis, where the introduction gives the motivation for the work and a state-of-the-art of the topics examined in this study. After the introduction, the objectives for the study are given followed by a summary of the work, conclusions and suggestions for further work. Finally the four articles are given. The articles are referred to as parts as they give detailed information of the different parts of the study. In Part I and Part II the experimental side of the study is described. These parts give detailed information regarding the material, test set-ups, specimen geometries and optical measurement procedures. The results from the experiments in form of the minor versus major principal strain as well as the stress triaxiality, the Lode parameter, and the equivalent strain at fracture are presented and used to describe the material’s fracture characteristics. Macroscopically the material displayed typical ductile behaviour with large strains before fracture. This was confirmed by scanning electron microscopy of selected specimens since all showed ductile dimples. Further, the material displayed a significant drop in ductility when exposed to plane-strain loading; an observation that suggests that the material’s fracture properties are Lode dependent. In Part III several uncoupled criteria for ductile fracture which explicitly take into account the effect of the Lode dependence were assessed. One of the criteria, the modified Mohr-Coulomb criterion, was taken from literature, while two of the criteria, the extended Cockcroft-Latham criterion and the extended Rice-Tracey criterion are augmented versions of existing criteria. The data given in Part I and II were used in evaluating the various criteria and it was found that the proposed extended Cockcroft- Latham criterion managed to give accurate predictions on the equivalent strain at fracture, while a somewhat larger spread was observed for the modified Mohr-Coulomb criterion and the extended Rice-Tracey criterion. Part IV focuses on numerical modelling of ductile crack propagation. Here the experimental tests from Part I were used in assessing the extended Cockcroft-Latham and modified Mohr-Coulomb criteria on crack propagation. Additionally the effects of using a high-exponent yield surface and material softening were investigated. It was found that the different fracture criteria as well as a change of yield function had little effect on the crack propagation. By including material softening through damage coupling, slant shear fracture as observed in some of the experiments was captured, but this did not alter the global response in form of the force-displacement curves.

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Ajmal, Mohammed. "Thermomechanically processed dual-phase steel : effects on hardenability and mechanical properties." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328761.

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Mazinani, Mohammad. "Deformation and fracture behaviour of a low-carbon dual-phase steel." Thesis, University of British Columbia, 2006. http://hdl.handle.net/2429/30951.

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The primary goal of this study was to evaluate the effect of martensite plasticity on the deformation and fracture behaviour of an intercritically annealed commercial low carbon (0.06 wt.%) dual phase steel. The volume fraction and the morphology (banded and almost equiaxed) of the martensite phase were systematically varied by control of the intercritical annealing temperature and the heating rate to this temperature. It was observed that the yield and tensile strengths were dependent on the martensite content but not on the martensite morphology. On the other hand, the true uniform strain, fracture strain and fracture stress were found to have a significant dependence on martensite morphology. An Eshelby based model, which allowed for the calculation of the stress in the martensite islands, was employed in order to rationalize the tensile properties of the dual-phase steel samples with different martensite contents and morphologies. In addition, by comparing the calculated stress in the martensite with an estimate of yield stress, it was possible to examine the conditions under which martensite plasticity occurs. The work hardening behaviour and the fracture properties of the steel samples were rationalized by the implications of martensite plasticity. For the cases where martensite showed significant plasticity (or co-deformed with the ferrite matrix), the void nucleation rate during post-necking deformation decreased considerably and hence, the final fracture properties were dramatically improved. The deformation of martensite in different dual-phase steel samples was examined both qualitatively (using optical micrographs of the undeformed and deformed sections of fractured tensile samples) and quantitatively (through image analysis of the microstructures before and after tensile deformation). The tensile stress-strain responses of different dual-phase steel samples were modeled using the modified Eshelby method. This approach was found appropriate for modelling the stress-strain behaviour of the steels with equiaxed morphology and martensite contents below approximately 30%. In the case of banded morphology, the stress-strain behaviour of the steel sample with 17% martensite was successfully predicted by the model. However, the model overestimated the flow stress of the steel with 30% martensite. For the martensite contents greater than 30%, the overestimation of the flow stress of the steel samples with banded morphology was greater than that for the equiaxed samples. Finally, the void formation process during tensile deformation was examined quantitatively through image analysis of the fracture surface of the steels. The experimental results showed very little void growth during ductile fracture of the steel samples with 17% and 41% martensite. Modelling the void formation process in these steels assuming no void growth stage resulted in the same observation. This confirmed the quantitative observation that void nucleation is the dominant effect during ductile fracture of these steels.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

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Rudnizki, Jenny [Verfasser]. "Through-process model for the microstructure of dual-phase steel / Jenny Rudnizki." Aachen : Shaker, 2011. http://d-nb.info/1071528130/34.

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Kulakov, Mykola. "Microstructure evolution during intercritical annealing of a Mn-Cr dual-phase steel." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44695.

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A model was developed to describe the microstructure evolution during intercritical annealing of a low-carbon steel suitable for industrial production of dual-phase steels (DP600 grade) on a hot-dip galvanizing line. The microstructure evolution model consists of individual submodels for recrystallization, austenite formation in a fully recrystallized material and austenite decomposition after partial austenization. These submodels were developed using the Johnson-Mehl-Avrami-Kolmogorov approach and the additivity principle. The model parameters were obtained based on the results of systematic experiments addressing the effects of initial microstructures and processing conditions on the microstructure evolution in the course of intercritical annealing. The initial microstructures included 50 pct cold-rolled ferrite-pearlite, ferrite-bainite-pearlite and martensite. If heating to an intercritical temperature was sufficiently slow, recrystallization was completed before austenite formation, otherwise austenite formed in a partially recrystallized microstructure. The recrystallization-austenite formation interaction accelerated austenization in all three starting microstructures by providing additional nucleation sites and enhancing growth rates; this complex process could not be accounted for with the current modelling approach. A variety of austenite morphologies was produced by using different initial microstructures and/or by means of the interaction of recrystallization and austenite formation. Following the complete intercritical annealing cycle, the final microstructure was composed of ferrite, bainite and martensite; the latter two components inherited the distribution and morphology of those for intercritical austenite. The microstructure evolution model was validated using simulated industrial thermal paths for intercritical annealing. Laser ultrasonics was employed for in-situ monitoring of phase transformations to facilitate the validation of the microstructure evolution model.

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Mahmoody, Sam. "Micromechancal modeling of dual-phase steel using a rate-dependent crystal plasticity model." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99778.

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Dual-phase (DP) steels consisting of a ferrite matrix with dispersed martensite particles have attracted a significant interest due to their combination of high work hardening and ductility. A great deal of experimental work has been done to obtain a better comprehension of the relation of their mechanical behaviour to their microstructural characteristics. In the present work, a micromechanical study of ferrite-martensite DP steels is conducted. The deformation of ferrite is described by a rate-dependent crystal plasticity theory, which relates the stress-strain field equations on the grain level to the macroscopic behaviour of the material. The crystal plasticity theory assumes that slip is the only deformation mechanism. Martensite, on the other hand, is considered an elastic-plastic isotropic solid. The interfaces of the grains are taken into account through an idealized form of grain boundaries. A FORTRAN program was coupled with the finite element method to solve the stress equations of the crystal plasticity. Including the grain boundaries made it possible to examine the effect of ferrite grain size on the strength of the material. It is shown that by decreasing the grain size, the yield stress increases according to Hall-Petch equation. Additionally, the effects of the volume fraction of martensite (Vm) on the onset strain, i.e. the strain at which martensite deforms plastically, and of the distribution of martensite on the stress are studied. The former showed that the onset strain of the DP steel declines linearly with increasing Vm up to 36%, beyond which the onset strain becomes independent of V m. The latter revealed that when martensite particles are formed as islands in the ferrite grains, the material exhibits higher strength and hardening rate; compared to when martensite is distributed as large blocks among the ferrite grains.

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Viardin, Alexandre. "Modélisation par champ de phases de la croissance de la ferrite allotriomorphe dans les aciers Fe-C-Mn." Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL014N/document.

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La ferrite allotriomorphe est une des morphologies de la ferrite dont la répartition spatiale influe fortement sur les propriétés mécaniques dans les aciers dual-phase. En fonction des traitements qu'ils subissent, la ferrite peut s'y répartir suivant les bandes de ségrégation en manganèse, issues de l'étape de solidification. Pour établir le rôle que joue le processus de croissance de la ferrite allotriomorphe sur la mise en place de la structure en bandes, nous avons développé un modèle de champ de phases possédant deux spécificités originales, imposées par le problème. D'une part, ce modèle est capable de reproduire les différents régimes cinétiques observés dans les alliages ternaires Fe-C-X, pilotés par la présence concomittante du carbone diffusant rapidement,et d'un élément substitutionnel X diffusant lentement. Nous avons ainsi mis en évidence la transition d'un régime initial rapide de paraéquilibre vers une croissance lente en orthoéquilibre, en bon accord avec des résultats expérimentaux de la littérature. D'autre part, notre modèle incorpore de manière économe la présence des joints de grains austénitiques, dont le rôle dans l'élimination des structures en bande est souligné par nos calculs. Nous observons ainsi qu'il existe un seuil d'intensité deségrégation en manganèse en dessous duquel le mouillage de la ferrite le long des joints de grain de plus grande énergie peut contrecarrer la croissance dans les bandes ségrégées négativement
The growth of allotriomorphic ferrite plays a major role in the formation of martensite bands in Dual-Phase steels. We have thus developed a phase field model to study the ferritic growth in different ternary Fe-C-X alloys, incorporating two necessary features. First, we have paid a particular attention to recover the different growth regimes due to the huge difference between the diffusion rates of Cand X substitutional species. Our calculations have exhibited a transition from fast paraequilibrium to slow orthoequilibrium in good agreement with experimental measurements in the literature. Second, austenite grain boundaries have been included in the model because they can conterbalance the manganese segregation bands, as shown in our calculations. Indeed, our results show that the bands can be broken bythe wetting of ferrite along the austenite grain boundaries, provided that the segregation is below a threshold value, and provided that the grain boundary energies are sufficiently high

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Philcox, Ann E. "The influence of elemental partitioning on hardness in a 12% chromium dual-phase steel." Master's thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/22213.

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Bibliography: pages 96-102.
During the annealing treatment in the production of dual phase steels, partitfoning of alloying elements can occur depending on competitive solubility in the ferrite and austenite for the specific partitioning species. An investigation of the partitioning of substitutional elements was considered paramount in understanding certain anomalies that had been identified by previous researchers in various studies of a dualphase 12% Chromium steel, designated 3CR12. These anomalies concerned observed increases in bulk hardness that could not be attributed to changes in the volume fraction of martensite produced after exposure to a range of temperatures within the dual phase field. Subsequent experiments revealed an unexpected increase in the microhardness of the martensite phase prOduced by heat treatment in the temperature range of interest. In this thesis conventional analytical measurements using Energy dispersive X-ray analysis facilities attached to a Scanning Electron microscope have been utilised to determine the compositions of the two phases in the alloy. A range of temperatures in the dual phase region have been investigated at holding durations of 1, 4 and 20 hours. It was found that partitioning of substitutional elements was occurring, however no changes were observed as a function of holding time. Further empirical data was obtained using dilatometric methods. This strongly suggested that interstitial concentrations were increasing as a function of annealing time and clarified the anomalies observed during previous studies on 3CR12. Further study includes that of substitutional element partitioning in the prior states of the commercially produced hot-rolled and annealed 3CR12 alloy. These include the as cast slab and the hot-rolled slab, as well as the final hot-rolled and annealed slab. Segregation was found to occur in the as cast slab. Subsequent investigation showed the presence of δ-ferrite in the final processing stages of the hot-rolled and annealed product.

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McGrath, PJ, DG Hattingh, and MN James. "Correlation between Fatigae of Automotive Wheel Centre - Discs and Hour-glass Laboratory Specimen." R & D Journal, 2009. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000876.

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Fatigue testing of complete automotive wheels is carried out on rotary bendmachines. These commercial mac hin e s s imulnt e h ar d - c o rn e rin g c o n ditio n s an d mainly testthefatigue performance of the central section of an automotive wheel' . This paper develops a relationship for predicting the fatigue performance of the wheel,based onfatigue tests of hourglass specimens machinedfrom centre discs. This is more economical of material and, in principle, also allows the effect on fatigue performance of change inproduction parameters or starting alloy to be assess ed, by c o n sid e rin g a limit e d numb e r of w h e e I blanks take n from each stage of the production process. This is p ote ntially a v ery u s eful to ol in optimisin g mat e rial selection, wheel design and production parameters. The p arti c ular c e ntr e - dis c un d e r c o n s id e r atio n i s manufactured from a dual-phas e ste eI (DP S)2 . Good c o rr elatio n w as achie v e d b e tw e e n S - lr.' data fr o m th e automotiv e w he els qnd that from the ho urglas s (H G) specimens.

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Ennis, Bernard. "The effect of chemical segregation on phase transformations and mechanical behaviour in a TRIP-assisted dual phase steel." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/the-effect-of-chemical-segregation-on-phase-transformations-and-mechanical-behaviour-in-a-tripassisted-dual-phase-steel(89d5c774-cb2e-49f7-9b85-981a68323acb).html.

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In the drive towards higher strength alloys, a diverse range of alloying elements is employed to enhance their strength and ductility. Limited solid solubility of these elements in steel leads to segregation during casting which affects the entire down-stream processing and eventually the mechanical properties of the finished product. The work presented in this PhD shows that segregation of alloying elements during casting, particularly aluminium, leads directly to banding in the final product. It has been demonstrated that no significant homogenisation is possible in this alloy within practical time constraints of the industrial thermo-mechanical process. A through-process model was developed to design a thermo-mechanical treatment aimed at reducing the effects of segregation on the formation of banding. A new polynomial function for calculating the local phase transformation temperature (Ae3) between the austenite + ferrite and the fully austenitic phase fields during heating and cooling of steel is presented. Material was produced both with and without banding and used to study the effect upon the mechanical properties. The banded steel variants show a significant reduction in tensile strength for a similar level of ductility compared to non-banded variants. In situ measurement under uniaxial loading using high-energy synchrotron diffraction allowed direct quantification of the impact of the mechanically induced transformation of metastable austenite on the work- hardening behaviour. The results reveal that the mechanically induced transformation of austenite does not begin until the onset of matrix yielding and the experimental evidence demonstrates that the austenite to martensite transformation increases the work-hardening rate of the ferrite phase and delays the onset of Stage-III hardening until the yield point of austenite. The increase in work-hardening rate (and thus work required) supports a driving force approach to transformation induced plasticity. The transformation work required leads to an increase in the macroscopic work-hardening rate after matrix yielding which offsets the decrease in the work-hardening rate in the ferrite and martensite phases up to the UTS. Steels with a high degree of banding do not show this extra contribution due to the more dominant anisotropic effect of martensite bands on the work-hardening of ferrite coupled to increased mechanical austenite stability as a result of increased carbon content. A list of revisions as requested by the examiners is produced on pages 18 and 19 of the thesis for examination. Abstract: In the drive towards higher strength alloys, a diverse range of alloying elements is employed to enhance their strength and ductility. Limited solid solubility of these elements in steel leads to segregation during casting which affects the entire down-stream processing and eventually the mechanical properties of the finished product. The work presented in this PhD shows that segregation of alloying elements during casting, particularly aluminium, leads directly to banding in the final product. It has been demonstrated that no significant homogenisation is possible in this alloy within practical time constraints of the industrial thermo-mechanical process. A through-process model was developed to design a thermo-mechanical treatment aimed at reducing the effects of segregation on the formation of banding. A new polynomial function for calculating the local phase transformation temperature (Ae3) between the austenite + ferrite and the fully austenitic phase fields during heating and cooling of steel is presented. Material was produced both with and without banding and used to study the effect upon the mechanical properties. The banded steel variants show a significant reduction in tensile strength for a similar level of ductility compared to non-banded variants. In situ measurement under uniaxial loading using high-energy synchrotron diffraction allowed direct quantification of the impact of the mechanically induced transformation of metastable austenite on the work- hardening behaviour. The results reveal that the mechanically induced transformation of austenite does not begin until the onset of matrix yielding and the experimental evidence demonstrates that the austenite to martensite transformation increases the work-hardening rate of the ferrite phase and delays the onset of Stage-III hardening until the yield point of austenite. The increase in work-hardening rate (and thus work required) supports a driving force approach to transformation induced plasticity. The transformation work required leads to an increase in the macroscopic work-hardening rate after matrix yielding which offsets the decrease in the work-hardening rate in the ferrite and martensite phases up to the UTS. Steels with a high degree of banding do not show this extra contribution due to the more dominant anisotropic effect of martensite bands on the work-hardening of ferrite coupled to increased mechanical austenite stability as a result of increased carbon content.

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Allam, Tarek [Verfasser], Wolfgang [Akademischer Betreuer] Bleck, and Brita Daniela [Akademischer Betreuer] Zander. "Direct hot rolled dual phase weathering steel / Tarek Allam ; Wolfgang Bleck, Brita Daniela Zander." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1127051385/34.

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Alharbi, Khaled. "Damage investigation in dual-phase 1000 steel and behaviour prediction using microstructure based modelling." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/12700/.

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Dual phase (DP) steels are advanced high strength steels that are being progressively used in the automotive industry in order to reduce weight while enhancing safety. The development of the next generation DP steels requires better understanding of the deformation and damage development at the scale of their microstructure in order to predict their mechanical response, especially work-hardening up to the Ultimate Tensile Strength and elongation to fracture. A combined methodology of experimental measurements and modelling at micro-scale was used in this project to investigate deformation and damage in DP1000 steels. A digital image correlation (DIC) experimental technique was used to measure deformation of the microstructure. The displacement results of DIC were extracted and used as boundary conditions for microstructure simulation. The uniqueness of this method is to ensure deformation of modelling matches the actual deformation, which thus allows further investigation for strain and stress values at the damage locations. The method was then used to investigate a crack initiation criterion in the martensite phase and predict crack propagation. A critical maximum principal stress value of 1700 MPa is suggested to initiate damage in the martensite phase of DP1000 steel. Additionally, a continuum-based damage model, namely Gurson, was used for the ferrite phase in order to predict the stress/strain curve of the material. A new approach based on microstructure simulations was used to adjust the Gurson damage parameters. The transferability of these parameter values was examined using different specimen geometries with different stress triaxiality, including a notch bar of DP1000 steel. The results showed a reasonable agreement between stress predictions from microstructure simulations and experimentally measured true stress values. The method of using combined DIC results and microstructure simulation for damage initiation criterion in the martensite and for calibrating damage model parameters for the ferrite phase is then discussed, and the significance of the results obtained in this work for the prediction of overall stress/strain curves of advanced high strength steels is then drawn.

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Kaplan, Mucahit. "Characterization Of Dual Phase Steels By Using Magnetic Barkhausen Noise Analysis." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607604/index.pdf.

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The aim of this work is to nondestructively characterize the industrial dual phase (ferritic-martensitic) steels (DPS) by the Magnetic Barkhausen Noise (MBN) method. By quenching of AISI 8620 steel specimens having two different starting microstructures, from various intercritical annealing temperatures (ICAT) in the ferrite-austenite region, the microstructures consisting of different volume fractions of martensite and morphology have been obtained. The microstructures, strength properties and hardness values were determined by conventional metallographic and mechanical tests. The measurements of the Magnetic Barkhausen Noise (MBN) were performed by using both Rollscan and &
#956
SCAN sensor connectors. A good correlation between the martensite volume fraction, hardness and MBN signal amplitude has been obtained. MBN emission decreased as the ICAT, therefore the volume fraction of martensite increased. Moreover, MBN emission decreased as the martensite morphology become thinner. It has been concluded that MBN method can be used for nondestructive characterization of industrial dual phase steels.

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Myeong-Heom, Park. "Effect of Grain Size on Mechanical Properties of Dual Phase Steel Composed of Ferrite and Martensite." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225592.

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Yan, Dingshun Verfasser], Alexander [Akademischer Betreuer] Hartmaier, and Dierk [Akademischer Betreuer] [Raabe. "Micromechanically guided design of graded ultrafine-grained dual-phase steel / Dingshun Yan. Gutachter: Alexander Hartmaier ; Dierk Raabe." Bochum : Ruhr-Universität Bochum, 2016. http://d-nb.info/1082425834/34.

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Yan, Dingshun [Verfasser], Alexander Akademischer Betreuer] Hartmaier, and Dierk [Akademischer Betreuer] [Raabe. "Micromechanically guided design of graded ultrafine-grained dual-phase steel / Dingshun Yan. Gutachter: Alexander Hartmaier ; Dierk Raabe." Bochum : Ruhr-Universität Bochum, 2016. http://d-nb.info/1082425834/34.

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Liu, Shibo. "Numerical and experimental study on residual stresses in laser beam welding of dual phase DP600 steel plates." Thesis, Rennes, INSA, 2017. http://www.theses.fr/2017ISAR0003/document.

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Le procédé de soudage laser est largement utilisé dans les travaux d'assemblage, en particulier, dans ledomaine de l'industrie automobile. L'acier dual phase DP600 est un acier à haute résistance qui permet deréduire le poids de l'automobile dans le cadre de l'allègement des structures. Notre travail s' estessentiellement basé sur l'évaluation des contraintes résiduelles générées dans l'acier DP600 lors du soudagepar laser. Deux approches ont été réalisées. L'approche expérimentale a été réalisée à l'aide de méthodes derayon X et par neutrons pour calculer les contraintes résiduelles. L'approche de simulation a été réalisée parcouplage de différentes formulations numériques.Numériquement, le formalisme de la mécanique continue a été utilisé par des simulations par éléments finis(FEM) pour analyser et évaluer les contraintes résiduelles. Sur la base de tests de traction expérimentaux, lemodèle constitutif élasto-thermo-plastique de l'acier DP600 a été identifié. L'écrouissage du matériau a étéétudié par la loi de Ludwik et de Voce. A partir de résultats experimentaux, un modèle a été proposé et lesrésultats analysés en utilisant une loi de mélange martensite (écrouissage Ludwik) et ferrite (adoucissementde Voce). De même, nous avons étudié la sensibilité à la température en utilisant plusieurs modèles :Johnson-Cook, Khan, Chen. A partir de cette étude, nous avons proposé un modèle de sensibilité à tatempérature. Enfin, un modèle de sensibilité à la déformation plastique, à la vitesse de déformation issu destravaux d'A.Gavrus et un modèle d'anisotropie planaire définit par la théorie de Hill ont été ajoutés.Une méthode d'automate cellulaire (CA) 2D a été programmée pour simuler l'évolution de la microstructurelors de la solification liée au processus de soudage laser. Dans ce modèle, les phénomènes de nucléationavec prise en compte de l'orientation de la croissance, de la concentration et de la vitesse de croissance àl'interface solide/liquide, l'anisotropie de la tension de surface, de la diffusion, ainsi que la fraction desphases en présence ont été pris en compte. De plus, les équations de conservation ont été étudiées en détail etanalysés. Les résultats ainsi que le champ de température issu du modèle FEM ont été importés dans lemodèle CA. En comparant la simulation et les résultats expérimentaux, de bonnes concordances ont ététrouvées.Par la suite, nous avons réalisés un couplage des deux modèles CA et FEM. Concernant le procédé laser, lesrésultats du modèle par éléments finis ont été analysés. La géométrie de l'échantillon, la source de chaleur,les conditions aux limites, le comportement thermo-mécanique de l'acier dual phase DP600 telles que laconductivité, la densité, la chaleur spécifique, l'expansion, l'élasticité et la plasticité sont introduites. Lesmodèles d'analyse du terme d'écrouissage, de la sensibilité à la vitesse de déformation, de la sensibilité à latempérature, de l'anisotropie plastique et de l'anisotropie élastique ont été simulés. Les fractions volumiquesconcernant ta nature des deux phases en présence ont été également étudiées.Les résultats numériques finaux tes contraintes résiduelles ont été étudiées. Les comparaisons avec desmesures experimentales ont montré à la fois quels phénomènes étudiés sont prépondérants et tes effets moinsinfluents sur l'évaluation des contraintes résiduelles. Les résultats tes plus probants ont montré des bonnesconvergences entre l'approche numérique et expérimentale. Ces résultats confortent la robustesse du modèlenumérique developpé
Laser welding process is widely used in assembly work of automobi le industry. DP600 dual phase steeis a high strength steel to reduce automobile weight. Residual stresses are produced during laser weldingDP600. Continuum mechanics is used for analyzing res idual stresses by finite element simulation.Based on experimental tensile tests, the DP600 steel constitutive model are identified. The hardening termaccording to Ludwik law, Voce law and a proposed synthesis model are studied. The temperature sensitivityof Johnson-Cook, Khan, Chen and a proposed temperature sensitivity model are investigated. The strain ratesensitivity model proposed by A. Gavrus and planar anisotropy defined by Hi ll theory are also used.Cellul ar Automaton (CA) 20 method are programed for the simulation of solidification microstructureevolution during laser welding process. The temperature field of CA are imported from finite element analysimodel. The analysis function of nucleation, solid fraction, interface concentration, surface tension an isotropy,diffusion, interface growth ve locity and conservation equations are presented in detail. By comparing thesimulation and experimental results, good accordances are found.Modelling by a finite element method of laser welding process are presented. Geometry of specimen, heatsource, boundary conditions, DP600 dual phase steel material properties such as conductivity, density, specifiheat, expansion, elasticity and plasticity are introduced. Models analyzing hardening term, strain ratesensitivity, temperature sensitivity, plastic an isotropy and elastic an isotropy are simulated.The numerical results of laser welding DP600 steel process are presented. The influence of hardening term,strain rate sensitivity, temperature sensitivity and anisotropy on residual stresses are analyzed. Comparisonwith experimental data show good numerical accuracy.Keywords: Laser Welding, DP600, Residual Stress, Cellular Automaton, Hardening, Temperature sensitivity,Strain Rate Sensitivity, Anisotropy, Mixture dual phase law

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Li, Hongxing. "Mechanical Properties of Dual Phase Alloys Composed of Soft and Hard Phases." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215959.

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Vajragupta, Napat [Verfasser]. "The artificial microstructure model and its applications on plasticity and damage of the dual phase steel / Napat Vajragupta." Aachen : Shaker, 2015. http://d-nb.info/1080763031/34.

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Ollat, Mélanie. "Characterization and modeling of microstructural evolutions during the thermal treatment of cold-rolled Dual-Phase steels." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI097/document.

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Les aciers Dual-Phase (DP) sont des aciers à très haute résistance mécanique (AHSS) fortement utilisés pour des applications automobiles en raison de leur très bon compromis résistance mécanique/ductilité ainsi que par leur habilité à répondre aux multiples exigences industrielles (bas prix, assemblage, revêtement etc.). A l'heure actuelle, le développement d'aciers DP apparait durable pour la caisse-en-blanc des structures automobiles. La microstructure ferrite-martensite, caractéristique des aciers DP, est obtenue par un traitement thermique complexe composé de différentes étapes au cours desquelles différents mécanismes métallurgiques entrent en jeux. Les principales difficultés de production sont liées au fait (i)que les évolutions microstructurales sont influencées par les différents paramètres de traitement thermique (vitesse de chauffe, température ...), (ii) que les différentes étapes de traitement sont interconnectées et que (iii) les évolutions microstructurales peuvent se chevaucher et, part conséquent, interagir entre elles. Ces travaux de thèse ont pour objectif d'améliorer la compréhension des évolutions métallurgiques entrant en jeux lors des traitements thermiques des aciers DP, et notamment d'améliorer la compréhension de l'influence des paramètres de traitement. Les différentes évolutions métallurgiques ont été, dans un premier temps, caractérisées en couplant un ensemble de techniques expérimentales (dilatométrie, dureté, TPE ...) et grâce à un protocole assurant de décorréler les mécanismes se superposant et interconnectés. A titre d'exemple, les deux principaux mécanismes entrant en jeux lors de l'étape de recuit intercritique ont été, dans un premier temps, étudiés séparément ((1) la recristallisation a été étudié en dessous de la température de formation d'austénite et (2) la formation d'austénite a été étudié sur un acier pré-recristallisé) avant de se concentrer sur le cas des aciers laminés à froid où la recristallisation et formation d'austénite se superposent. Le projet avait également pour objectif de développer des outils de prédictions permettant de décrire les évolutions microstructurales basés sur des approches empiriques (loi de JMAK) ainsi que vers des modèles à base plus physique (mixed-mode modèle et modèle diffusif). Une attention particulière a été dédié à discuter de la fiabilité, l'adaptabilité, des forces et limitations des différentes approches développées
Dual-Phase steels (DP) are one of the most used Advanced High Strength Steels (AHSS) for automotive applications because they present good strength/ductility compromise and they adapt to number of industrial constraints (low price, shaping, welding, coating etc.). Nowadays, the development of DP steels seems to be promising and sustainable for the body-in-white structure. The typical ferrite-martensite microstructure, characteristic of DP steels, are obtained by a thermal treatment composed of different stages during which metallurgical evolutions occur. Major difficulties of their processing are due to the fact that (i) microstructural evolution kinetics are influenced by cycle parameters (heating rate, annealing temperature etc.), (ii) different stages are interconnected and (iii) some microstructural evolutions may overlap and, therefore, interact. This PhD-work aimed at getting a better understanding of microstructural evolutions during the thermal cycle of DP steel and, namely, the influence of cycle parameters. Different microstructural evolutions occurring during the thermal cycle were first characterized coupling different experimental techniques (dilatometry, hardness, TPE etc.) and with a particular protocol in order to decorrelate overlapping and interconnected phenomena. As example, two major evolutions occurring during the intercritical annealing were first studied individually ((1) recrystallization was investigated below austenite formation temperature and (2) austenite formation was investigated on prior recrystallized steels) before investigated cold-rolled steel case where recrystallization and austenite formation overlap. The study was then attached to develop some predictive tools to describe microstructural evolutions based on phenomenological approaches (JMAK law) towards more physical based models (mixed-mode, diffusive models). A particular care was attached to discuss on model reliability, versatility, strengths and limitations

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Iacoviello, Francesco. "Fragilisation par l'hydrogène de l'acier inoxydable austéno-ferritique Z2CND22 05 : rôle de la microstructure." Châtenay-Malabry, Ecole centrale de Paris, 1997. http://www.theses.fr/1997ECAP0536.

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Les aciers inoxydables austéno-ferritiques sont caractérisés par des propriétés mécaniques élevées et par une bonne résistance à la corrosion, notamment à la corrosion sous contrainte et par piquration. En revanche, leur structure duplex montre une sensibilité à la fragilisation par l'hydrogène. Parmi les aciers inoxydables austéno-ferritiques, la nuance z2cnd22 05 s'est progressivement imposée comme nuance de base et elle est la plus répandue des nuances austéno-ferritiques actuellement utilisées. Dans cette étude, nous avons analysé le comportement mécanique en traction et la cinétique de fissuration par fatigue de l'acier inoxydable austéno-ferritique z2cnd22 05, chargé ou non en hydrogène après différents traitements thermiques de revenu. Les températures et les durées des traitements thermiques de revenu ont été choisies avec la double finalité de fournir une caractérisation la plus complète possible de l'influence de toutes les phases secondaires, carbures et nitrures et, en plus, d'analyser d'une façon plus approfondie les températures critiques connues par la bibliographie et les résultats des essais de traction. De plus, nous avons perfectionné une technique d'évaluation du coefficient de diffusion, solution alternative à la mesure par perméation. Par ailleurs, nous avons utilisé la technique de l'analyse thermique pour mesurer l'énergie d'activation des pièges présents dans l'acier à l'état de livraison. Les résultats obtenus permettent d'établir les conclusions suivantes : - les joints de grains et les dislocations ont une influence négligeable sur le processus de diffusion de l'hydrogène - la quantité d'hydrogène absorbé dépend de la microstructure : la présence d'autres phases secondaires, carbures et nitrures dans la ferrite diminue fortement cette quantité. Cette diminution est probablement due a une variation de la solubilité et de la diffusivité de l'hydrogène - le chargement en hydrogène de l'acier duplex implique une forte diminution de #m% pour toutes les températures de revenu, sauf a 1050c ou la densité des dislocations est très basse et toutes les phases secondaires, carbures et nitrures, sont dissoutes. - le chargement en hydrogène de l'acier duplex n'induit pas de variation de r#e, tandis que la diminution de r#m dépend de la microstructure. L'indice fragilisation f permet de mettre en évidence l'influence positive de la décomposition spinodale et de la précipitation de la phase G. L'utilisation de l'indice de fragilisation % permet de montrer que la précipitation de la phase implique une fragilisation par l'hydrogène plus élevée, malgré des quantités inferieures d'hydrogène absorbe - l'acier duplex a l'état de livraison, charge en hydrogène, présente la possibilité de récupérer complètement ses propriétés mécaniques grâce a un traitement thermique de revenu à basse température (< 250°C) - la fissuration par fatigue a l'air ne varie pas avec la fréquence (entre 10 et 50 Hz) ni avec la direction de charge (lt ou Tl). Les modifications microstructurales dans la ferrite après revenu a 475c ou a 800c modifient la vitesse de fissuration dans les stades ii et iii, mais pas sur le stade de seuil - la fissuration de l'acier duplex sous chargement d'hydrogène en conditions potentiostatiques dans l'eau de mer n'a pas lieu - la fissuration de l'acier duplex sous chargement en conditions potentiostatiques dans une solution aqueuse d'acide sulfurique a lieu avec des vitesse plus élevées dans les trois stades de propagation, car outre la fragilisation de la ferrite, il y a un début de fragilisation de l'austénite. L’importance de l'influence de l'hydrogène est différente suivant les valeurs de k. La formation des stries a toujours lieu dans l'austénite et dans la ferrite, avec une distance entre stries qui dépend de la vitesse macroscopique, du libre parcours moyen de l'hydrogène dans la ferrite et dans l'austénite et de la dimension de la zone plastique réversible.

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Lester, Charles Gilbert IV. "Analysis of fatigue behavior, fatigue damage and fatigue fracture surfaces of two high strength steels." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42795.

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Building fuel efficient automobiles is increasingly important due to the rising cost of energy. One way to improve fuel efficiency is to reduce the overall automobile weight. Weight reductions using steel components are desirable because of easy integration into existing manufacturing systems. Designing components with Advanced High Strength Steels (AHSS) has allowed for material reductions, while maintaining strength requirements. Two Advanced High Strength steel microstructures investigated in this research utilize different strengthening mechanisms to obtain a desired tensile strength grade of 590MPa. One steel, HR590, utilizes precipitation strengthening to refine the grain size and harden the steel. The other steel, HR590DP, utilizes a dual phase microstructure consisting of hardened martensite constituents in a ferrite matrix. The steels are processed to have the same tensile strength grade, but exhibit different fatigue behavior. The central objective of this research is to characterize and compare the fatigue behavior of these two steels. The results show the dual phase steel work hardens at a low fatigue life. The precipitation strengthened microstructure shows hardening at low strain amplitudes, softening at intermediate strain amplitudes and little to no effect at high strain amplitudes. These different fatigue responses are characterized and quantified in this research. Additionally, observations showing the fracture surfaces and the bulk microstructure are analyzed.

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Torabiandehkordi, Noushin. "High and very high cycle fatigue behavior of DP600 dual-phase steel : correlation between temperature, strain rate, and deformation mechanisms." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0020/document.

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Ce travail vise à améliorer notre compréhension du comportement en fatigue à grand et très grand nombre de cycles d’un acier ferrito-martensitique dual phase, notamment les effets de la température et de la vitesse de déformation résultant de chargements cycliques à haute fréquence. L'effet de la fréquence sur la réponse en fatigue de l'acier DP600 a été étudié en effectuant des essais de fatigue sur une machine ultrasonique travaillant à 20 kHz et sur une machine conventionnelle travaillant à des fréquences inférieures à 100 Hz. Des études de fractographie et des observations microscopiques à la surface des échantillons ont été effectuées pour étudier les mécanismes de déformation et de rupture. De plus, la thermographie infrarouge in situ a été utilisée pour étudier la réponse thermique et les mécanismes dissipatifs du matériau lors des essais de fatigue. Les courbes S-N ont été déterminées à partir de chargements de fatigue ultrasoniques à 20 kHz et d’essais conventionnels à 30 Hz. La durée de vie pour une amplitude de contrainte donnée est plus élevée dans le cas de la fatigue ultrasonique bien que la limite de fatigue soit identique dans les deux cas. L’augmentation inévitable de la température en fatigue ultrasonique à fortes amplitudes de contraintes, ainsi que le comportement dépendant de la vitesse de déformation de la ferrite, en tant que structure CC, ont été trouvés comme les paramètres clés expliquant le comportement observé en fatigue, et la réponse thermique sous les fréquences faibles et ultrasoniques. Les écarts observés entre l’essai de fatigue conventionnel et celui ultrasonique ont été évalués à travers les mécanismes de mobilité des dislocations vis dans la phase ferritique de structure cubique centrée (CC). La durée de vie plus élevée et l’amorçage de la fissure principale sur une inclusion observés en fatigue ultrasonique ont été attribués au vieillissement dynamique résultant du fort auto-échauffement du matériau aux fortes amplitudes de contraintes. L'existence d'une transition du régime thermiquement activé au régime athermique avec l’augmentation de l'amplitude de contrainte a été mise en évidence. Au-dessous de la limite de fatigue, la déformation a lieu dans un régime thermiquement activé alors qu'elle est dans un régime athermique au-dessus de la limite de fatigue. En fatigue conventionnelle, la déformation est athermique pour toutes les amplitudes de contrainte. Une carte de transition a été produite en utilisant les résultats expérimentaux pour l'acier DP600 ainsi que les données disponibles dans la littérature pour d'autres aciers à base de ferrite, montrant ainsi la corrélation entre le mouvement des dislocations vis thermiquement activé et l'absence de rupture en fatigue à très grand nombre de cycle
This work is an attempt towards a better understanding of the high cycle and very high cycle fatigue behaviors of a ferritic-martensitic dual-phase steel, with a regard to temperature and strain rate effects, resulting from accelerated fatigue loading frequencies. The influence of frequency on fatigue response of DP600 steel was investigated by conducting ultrasonic and conventional low frequency fatigue tests. Fractography studies and microscopic observations on the surface of specimens were carried out to study the deformation and fracture mechanisms under low and ultrasonic frequencies. Moreover, in situ infrared thermography was carried out to investigate the thermal response and dissipative mechanisms of the material under fatigue tests. The S-N curves were determined from ultrasonic 20-kHz fatigue loadings and conventional tests at 30 Hz. Fatigue life for a given stress amplitude was found to be higher in the case of ultrasonic fatigue whereas the fatigue limit was the same for both cases. Moreover, crack initiation was always inclusion-induced under ultrasonic loading while under conventional tests it occurred at slip bands or defects on the surface. The inevitable temperature increase under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a body centered cubic (BCC) structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. The discrepancies observed between conventional and ultrasonic fatigue tests were assessed through the mechanisms of screw dislocation mobility in the ferrite phase as a BCC structure. The higher fatigue life and inclusion-induced crack initiations in the case of ultrasonic loading were attributed to the dynamic strain aging, which resulted from the high temperature increases at high stress amplitudes. The existence of a transition in deformation regime from thermally-activated to athermal regime under ultrasonic fatigue loading by increasing the stress amplitude was confirmed. Below the fatigue limit, deformation occurred in thermally-activated regime while it was in athermal regime above the fatigue limit. Under conventional loading deformation occurred in athermal regime for all stress amplitudes. From the analysis of the experimental data gathered in this work, guidelines were given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue

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Landron, Caroline. "Ductile damage characterization in Dual-Phase steels using X-ray tomography." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00738820.

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Dans le cadre du développement de nuances d'aciers toujours plus performantes en termes de résistance à l'effort et à l'endommagement, les aciers Dual-Phase (DP) présentent un bon compromis résistance/ductilité. Cependant, il est nécessaire de disposer de meilleures connaissances concernant les mécanismes menant à la rupture de tels aciers. Les mécanismes d'endommagement ont ainsi été étudiés dans cette thèse à l'aide de la tomographie aux rayons X. Des essais de traction in-situ ont été réalisés sur plusieurs nuances d'aciers DP, un acier ferritique et un acier martensitique afin de caractériser chaque étape de l'endommagement ductile. Des observations qualitatives et des données quantitatives concernant la germination de l'endommagement, la croissance des cavités et la coalescence ont été recueillies lors de ces essais. Ces données quantitatives ont ensuite été utilisées pour le développement et/ou la validation de modèles d'endommagement. Une prédiction de la cinétique de germination a ainsi été proposée et la version du modèle de croissance de cavités de Rice et Tracey corrigée par Huang et prenant mieux en compte l'effet de la triaxialité a été validée expérimentalement. L'étape de coalescence des cavités menant à la rupture des matériaux a pour la première fois été caractérisée de façon quantitative dans un matériau industriel et des critères de coalescence ont été appliqués localement sur les couples de cavités présentes dans le matériau. L'utilisation de ces modèles analytiques a permis une meilleure compréhension des propriétés agissant sur les phénomènes mis en jeu. L'effet de la part cinématique de l'écrouissage sur la germination et la croissance de l'endommagement a notamment été souligné et validé par des essais de chargements complexes.

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Paula, Emerson Bertaglia de. "Estudo sobre a aplicação de aços dual phase na indústria automotiva com o objetivo de redução de massa em amortecedores estruturais." Universidade Presbiteriana Mackenzie, 2014. http://tede.mackenzie.br/jspui/handle/tede/1341.

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Made available in DSpace on 2016-03-15T19:36:41Z (GMT). No. of bitstreams: 1 Emerson Bertaglia de Paula.pdf: 2673349 bytes, checksum: 7ced38cf4db0e9c40ec1a57cbdf6bf07 (MD5) Previous issue date: 2014-02-13
Universidade Presbiteriana Mackenzie
McPherson shock absorber is a metallic structure that is used to link body to wheels of vehicles, most part of shock absorbers are produced using carbon steel low alloy of medium strength, because in this way it has a lowest cost. Due to the continuous change of market requirement, it is necessary that it be created an alternative to performance improvement and reduce fuel consumption and one possibility, it is reduce the weight of shock absorbers. There are many type of materials, metallic and no metallic that can reduce the weigh, however, dual phase steel shows an interesting alternative to substitute carbon steels, because dual phase steel does not change or demand new investments to current production process. Dual-phase steel has high mechanical properties that allow significant weight reductions. In this study there is a comparison between carbon steel and dual-phase steels, performed with current loads case used for approve McPherson shock absorbers and components. Components of shock absorber was analyzed by analytical and finite element methods. Result of this study showed that it is possible use dual-phase steel with a weight reduction of 10% to 24% for each component studied and a reduction of 7,23% for strut shock absorber.
Amortecedores McPherson são estruturas metálicas que servem de ligação entre a carroceria e as rodas do veículo e a grande maioria dos amortecedores produzidos mundialmente utilizam aço carbono de baixa liga e média resistência, pois desta forma apresentam um menor custo. Com as contínuas mudanças das exigências do mercado consumidor, é necessário que seja apresentado uma alternativa para a redução de massa dos amortecedores, pois somente desta forma tem-se um melhor desempenho com uma redução no consumo de combustíveis. Há diversos tipos de materiais metálicos e não metálicos que podem proporcionar esta redução de massa, porém o aço dual-phase apresenta uma interessante alternativa para substituição dos aços carbono, pois não gera modificações e investimentos significativos no atual processo produtivo. O aço dual-phase possui elevadas propriedades mecânicas possibilitando reduções significativas de massa. Neste estudo foi realizado um comparativo entre os aços carbono e o aço dual-phase em condições de carregamento normalmente utilizada para aprovação dos amortecedores McPherson. Os componentes estudados, foram analisados pelos métodos analítico e de elementos finitos, o resultado deste estudo mostra que é possível utilizar o aço dual-phase com uma redução de massa de 10% a 24% para cada componente estudado e uma redução no amortecedor estrutural de 7,23%.

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Mathevon, Alexandre. "Characterization and modelling of microstructural evolutions and mechanical properties during the thermal treatments of Dual-Phase steels." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI120.

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L'objectif de cette thèse était de contribuer au développement et à la compréhension des phénomènes physiques pilotant les évolutions microstructurales et les propriétés mécaniques des aciers Dual-Phase. Dans un souci d'utilisation sur les lignes de production industrielle, le développement d'outils numériques à champ moyen a été retenu, utilisables pour une large gamme de compositions chimiques et de cycle thermique. Une calibration des modèles sur des aciers ternaires provenant de coulées de laboratoire a été effectuée avant leur validation sur deux nuances industrielles. Un modèle de prédiction de la cinétique de recristallisation (MiReX) a été développé à partir de la composition chimique, du taux de réduction par laminage à froid et de leur état de précipitation prévu en utilisant un couplage avec un logiciel de prédiction de la cinétique de précipitation (Preciso). Un modèle pour la transformation de phase entre la ferrite et l'austénite, basé sur la minimisation de l'énergie du système global (GEM), a été proposé pour les traitements isothermes et anisothermes. Il reproduit la cinétique de la formation de l'austénite sur un cycle thermique industriel comprenant une rampe de chauffage et un maintien pour les systèmes quaternaires en tenant compte de la dissolution de la cémentite. Un modèle permettant de prédire la température du début de la transformation martensitique a également été développé pour les aciers bi-phasés, en tenant compte de la taille des grains austénitiques et de l'enrichissement en carbone et en manganèse à l'interface. Enfin, une nouvelle loi d'interaction basée sur les observations lors d'un essai de traction ex-situ a permis d'améliorer une prédiction modèle des propriétés mécaniques des aciers DP. La considération de l'étape de revenu de la martensite sur les propriétés des aciers DP a été proposée après l'analyse des mécanismes métallurgiques impliqués dans le revenu par des mesures de pouvoir thermoélectrique et de dureté
The aim of this thesis was to contribute to the development and understanding of the physical phenomena driving the microstructural evolutions and the mechanical properties of Dual-Phase steels. In a concern of use on industrial production lines, the development of physics-based mean-field numerical tools was retained, usable for a wide range of chemical composition and thermal cycle parameters. A calibration of the models on ternary steels from laboratory castings was carried out before their validation on two industrial grades. A model for predicting recrystallization kinetics (MiReX) was developed based on the chemical composition, the reduction ratio by cold rolling and their predicted precipitation state using a coupling with a software for predicting precipitation kinetics (Preciso). A model for the phase transformation between ferrite and austenite, based on the minimization of the global system energy (GEM), has been proposed for isothermal and anisothermal treatments. It reproduces the kinetics of austenite formation on an industrial thermal cycle including a heating ramp and holding for quaternary systems taking into account the dissolution of the cementite. A model for predicting the temperature of the beginning of martensitic transformation has also been developed for two-phase steels, taking into account austenitic grain size and carbon and manganese enrichment at the interface. Finally, a new interaction law based on observations during an ex-situ tensile test has allowed the improvement of a prediction model of the mechanical properties of DP steels. A consideration of the tempering step of martensite on the mechanical properties of DP steels has been proposed after the analysis of metallurgical mechanisms involved in tempering bythermoelectric power and hardness measurements

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Thompson, Alan. "High Strain Rate Characterization of Advanced High Strength Steels." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2831.

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The current research has considered the characterization of the high strain rate constitutive response of three steels: a drawing quality steel (DDQ), a high strength low alloy steel (HSLA350), and a dual phase steel (DP600). The stress-strain response of these steels were measured at seven strain rates between 0. 003 s^-1 and 1500 s^-1 (0. 003, 0. 1, 30, 100, 500, 1000, and 1500 s^-1) and temperatures of 21, 150, and 300 °C. In addition, the steels were tested in both the undeformed sheet condition and the as-formed tube condition, so that tube forming effects could be identified. After the experiments were performed, the parameters of the Johnson-Cook and Zerilli-Armstrong constitutive models were fit to the results.

In order to determine the response of the steels at strain rates of 30 and 100 s^-1, an intermediate rate tensile experiment was developed as part of this research using an instrumented falling weight impact facility (IFWI). An Instron tensile apparatus was used to perform the experiments at lower strain rates and a tensile split-Hopkinson bar was used to perform the experiments at strain rates above 500 s^-1

A positive strain rate sensitivity was observed for each of the steels. It was found that, as the nominal strength of the steel increased, the strain rate sensitivity decreased. For an increase in strain rate from 0. 003 to 100 s^-1, the corresponding increase in strength at 10% strain was found to be approximately 170, 130, and 110 MPa for DDQ, HSLA350, and DP600, respectively.

The thermal sensitivity was obtained for each steel as well, however no correlation was seen between strength and thermal sensitivity. For a rise in temperature from 21 to 300 °C, the loss in strength at 10% strain was found to be 200, 225, and 195 MPa for DDQ, HSLA350, and DP600, respectively for the 6 o?clock tube specimens.

For all of the alloys, a difference in the stress ? strain behaviour was seen between the sheet and tube specimens due to the plastic work that was imparted during forming of the tube. For the DP600, the plastic work only affected the work-hardening response.

It was found that both the HSLA350 and DDQ sheet specimens exhibited an upper/lower yield stress that was amplified as the strain rate increased. Consequently the actual strength at 30 and 100 s^-1 was obscured and the data at strain rates above 500 s^-1 to be unusable for constitutive modeling. This effect was not observed in any of the tube specimens or the DP600 sheet specimens

For each of the steels, both the Johnson-Cook and Zerilli-Armstrong models fit the experimental data well; however, the Zerilli-Armstrong fit was slightly more accurate. Numerical models of the IFWI and the TSHB tests were created to assess whether the experimental results could be reproduced using the constitutive fits. Both numerical models confirmed that the constitutive fits were applied correctly.

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Kubecka, Petr. "Etude du comportement d'alliages passivables, acier duplex et alliage fer-nickel, soumis a l'action combinée du frottement et de la corrosion." Châtenay-Malabry, Ecole centrale de Paris, 1998. http://www.theses.fr/1998ECAP0584.

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La tribocorrosion est le processus conduisant a la dégradation d'un matériau métallique sous l'action conjuguée du frottement et de la corrosion. Le travail décrit dans ce mémoire a deux objectifs complémentaires : - mettre au point un essai de tribocorrosion permettant a la fois des études appliquées et des recherches approfondies a caractère fondamental sur les mécanismes de tribocorrosion. Dans ce but, nous avons mis en œuvre un tribometre de type pion-disque apte a travailler en milieu corrosif et permettant d'utiliser toutes les techniques électrochimiques d'étude de la corrosion. Étudier les mécanismes de tribocorrosion de deux aciers passivables, un alliage fer 29% nickel et un acier inoxydable duplex z2 cndn 22-05 (22% cr 5% ni 3% mo). Nous avons en particulier étudié les réactions de dissolution anodique et de passivation, et les interactions de ces réactions avec le frottement. Les mesures électrochimiques ont permis d'étudier la contribution des phénomènes de corrosion et de passivation dans le comportement en tribocorrosion des alliages étudiés, ainsi que l'influence du frottement sur la réactivité électrochimique de la surface. Nous avons ainsi pu mettre en évidence l'influence de la convection d'électrolyte provoquée par le mouvement relatif des deux surfaces en contact. Nous avons montré que l'écrouissage ne modifie pas sensiblement la réactivité de la surface métallique frottée. Enfin nous avons montré que la destruction des couches superficielles par le frottement, active la dissolution du métal. Nous avons utilise un modèle simple de tribocorrosion pour expliquer cet effet. Nous avons aussi montre expérimentalement que la présence de ces couches modifie les conditions mécaniques du frottement (coefficient de frottement). En complément, afin de caractériser de la manière la plus précise possible les propriétés superficielles et en volume des matériaux étudiés et de comprendre les mécanismes d'endommagement, nous avons mis en œuvre, avant et après l'essai de tribocorrosion, différentes méthodes d'analyse. Nos travaux ont montre la nécessité de développer une description plus fine, au niveau local, de l'état électrochimique, mécanique et structural, de la surface frottée, et décrivant également les interactions entre les différentes parties de la surface.

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Gallo, Giulliano Batelochi. "Influência do tratamento térmico sobre a tenacidade de um aço com AISI SAE 1045 com médio teor de carbono, avaliada por ensaios de impacto /." Guaratinguetá : [s.n.], 2006. http://hdl.handle.net/11449/97094.

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Orientador: Marcelo dos Santos Pereira
Banca: Humberto Lopes Rodrigues
Banca: Pedro Paulo de Campos
Resumo: Estudos de novos materiais, mais resistentes, econômicos e de menor densidade, são de grande interesse para aplicações estruturais em projetos de Engenharias. Propriedades mecânicas antes obtidas principalmente por meio de adição de elementos de ligas, como por exemplo elevada dureza, tenacidade e resistência mecânica, podem ser atingidas atualmente com variações no processamento térmico e termomecânico. Estas alterações têm proporcionado a formação de estruturas multifásicas nos aços, e como elemento deste estudo, os aços bifásicos. Neste trabalho, buscou-se entender os efeitos que processamentos térmicos possuem sobre as microestruturas dos aços de médio teor de carbono (SAE 1045), assim como a sua influência sobre as propriedades mecânicas, especialmente sobre a tenacidade, evidenciada por meio de ensaios de impacto. O material tratado termicamente obteve, sua estrutura transformada, visando à formação de estrutura bifásica (ferrita e martensita) e de estrutura formada por martensita revenida, sendo comparadas com a condição do material como fornecido (ferrita e perlita). A caracterização microestrutural foi realizada para determinação das fases presentes, assim como das frações volumétricas respectivas. Ensaios de tração e de impacto foram realizados visando a determinação das propriedades mecânicas do aço. Os resultados mostraram que a interação entre ferrita e martensita, gerada na condição bifásica, possue forte influência nos resultados referentes à tenacidade, assim como a temperatura em que o material foi ensaiado. Comparando-se três estruturas, comprova-se que a estrutura bifásica possui resistência mecânica e tenacidade mais elevadas que os aços temperados e revenidos, e tenacidade proxima a do aço com médio teor de carbono, sem tratamento térmico.
Abstract: Studies of new materials, more resistance, cheaper costs and lower density, have high interest for structural use in engineering projects. Mechanical properties adquired in the past by alloyes adition, for example igher hardness, toughness and mechanical strenght, nowadays can be reached using controlled thermo mechanical process. These changes have provided the multiphase structures formation in steels, for example the dual phase steel, subject of the present study. In this work it was researched the effects of heat process in microestructure of medium carbon steels (SAE 1045) and the influence over mechanical properties, specially in toughers, realized by impact analysis. The heat treatment material has its structure transformed in dual-phase structure (ferrite and martensite) and compared with supplied material (ferrite and perlite). The microestructural characterization was done to determine the present phase, and the respective volumetric fraction of martensite. Tension and impact analysis were done to determine the steel mechanical properties. Results have shown that the interaction between ferrite and martensite generated in dual-phase condition, has higher influence, related the materials toughness, so the temperature that material was analysed comparing the three structures, verifies that the dual-phase struture has level of mechanical resistence and toughness, higher than quenched and tempered steels, and toughness near of medium carbon steel that has not received heat treatment in higher or lower temperatures.
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45

Ebbinghaus, Michael. "Untersuchung der Verarbeitungseigenschaften von Kupferbasiszusatzwerkstoffen im MIG- und Laserlötprozess an Stahlblechen mit unterschiedlichem Festigkeitsverhalten." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-152166.

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In der Arbeit werden spezielle Kupferlote im MIG- und Laserlötverfahren an Stählen mit unterschiedlichem Festigkeitsverhalten untersucht. Die Ergebnisse sollen dazu beitragen, den Lötprozess durch den Einsatz spezieller Kupferbasislote zu optimieren und durch reduzierten Energieeintrag ein homogeneres Eigenschaftsfeld im Bereich der Fügestelle zu erzeugen. Den Verarbeitern dieser Werkstoffe soll die Möglichkeit gegeben werden, diese Werkstoffe rationeller und mit höherer Effektivität zu verarbeiten. Im Ergebnis der Arbeit sollen Verbesserungen der Eigenschaften der Lötnähte erzielt werden, die besonders in der Dünnblechverarbeitung mit Schwerpunkt Karosseriebau Anwendung finden. Wesentliche Ziele sind die Erhöhung der Festigkeitseigenschaften, eine Erhöhung der Fügegeschwindigkeit, die Verbesserung des Phosphatierungsverhaltens sowie eine Reduzierung der eingebrachten Wärmeenergie. Die Vielfältigkeit dieser Anforderungen macht es notwendig, die Versuche sowohl im Laser- als auch im MIG-Lötverfahren durchzuführen. Die Lötverfahren werden in der Praxis für unterschiedliche Anforderungen innerhalb der Karosserie eingesetzt. Das Fügen von hochfesten Strukturelementen oder Außenhautbauteilen erfordert in Abhängigkeit von den Anforderungen die Verwendung ausgewählter Zusatzwerkstoffe. Die Vielfältigkeit der Werkstoffe und der Anforderungen spiegelt sich in den Untersuchungen der vorliegenden Arbeit wieder. Für weitergehende Untersuchungen, speziell im hochfesten Blechbereich, soll die Arbeit entsprechende Grundlagen bieten. Als Vorlage für die Erarbeitung von experimentellen und theoretischen Methodiken der Prozessbetrachtung werden neben typischen Kupferloten neu entwickelte Lotlegierungen verwendet. Bei der Betrachtung der Kupferlegierungen werden die unterschiedlichen Einflüsse auf den Fügeprozess definiert und beschrieben. Es wird festgestellt, dass niedrig schmelzende Lote mit ausgewählter Legierungszusammensetzung im Gegensatz zu Eisenbasis-Schweißdrähten einen geringeren negativen Einfluss auf das Gefüge der Bleche im Nahtbereich ausüben. Um die thermische Beanspruchung, besonders in der Wärmeeinflusszone, während des Fügeprozesses gering zu halten, kann zusätzlich eine geeignete Stromquellentechnik zum Einsatz kommen. Mit Hilfe des „kalten“ Lichtbogens ist es möglich, die eingebrachte Streckenenergie weiter zu reduzieren. Faktoren, die den Energieeintrag beeinflussen, werden in der vorliegenden Arbeit in experimentellen und theoretischen Untersuchungen hinsichtlich ihrer Wirkung auf das Festigkeitsverhalten betrachtet. Es werden durch geeignete Legierungskombinationen die Einflüsse auf die Steigerung der Lötgeschwindigkeit und auf eine Verbesserung des Phosphatierungsverhaltens untersucht. Die Ergebnisse dieser Untersuchungen liefern die Informations- und Beweisbasis für die erarbeiteten Legierungssysteme und ermöglichen es, den optimierten Lötprozess an hochfesten Stahlblechen wissenschaftlich zu betrachten. Die Auswertung der wissenschaftlichen Experimente, dargestellt in den angefügten ausführlichen Tabellen, stellen die Zusammenhänge zwischen der Legierungsauswahl und der eingebrachten Streckenenergie dar. Die Erkenntnisse aus der vorliegenden Arbeit sollen für das Fügen von hochfesten Blechen die Entscheidung über die Auswahl geeigneter Zusatzwerkstoffe erleichtern. Die Ergebnisse der theoretischen Untersuchungen anhand mathematischer Modelle zur Beschreibung der physikalischen Prozesse der Wärmezufuhr durch Verwendung eines ausgewählten Lotes in Kombination mit geeigneter Stromquellentechnologie sind die Grundlage für die Optimierung des Lötprozesses. Die vorgeschlagenen Modelle zur Entwicklung und Optimierung von Lichtbogenlötprozessen mit neu entwickelten Lotlegierungen wurde im Rahmen der vorgelegten Arbeit an realen Blechqualitäten angewendet und überprüft. In den Ergebnissen hat sich bestätigt, dass die Verwendung spezieller Kupferlote zu verbesserten Verarbeitungseigenschaften führen, und damit Konzepte zum wirtschaftlich verbesserten Fügen angeboten werden.

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46

Diawara, Bandiougou. "Caractérisation quantitative de la microstructure de l'acier 16MND5 des cuves de réacteurs nucléaires à eau pressurisée." Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENI063.

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Ce travail de thèse concerne l’acier 16MND5 des cuves des Réacteurs à Eau Préssurisée (REP).L’étude vise à caractériser de manière quantitative la microstructure et à comprendre l’effet desparamètres influents (vitesse de refroidissement, température de revenu …) sur sa formation. D’unpoint de vue expérimental, l’étude est menée grâce à l’utilisation des techniques d’observationcomme la métallographie, le MET, MEB et l’EBSD, et la réalisation de traitements thermiquescontrôlés (dilatométrie notamment).Ces observations visent à identifier les différents constituants de l’acier et de déterminer lesgrandeurs quantitatives les caractériser (tailles, fractions volumiques des différentes phases ainsique leurs orientations cristallographiques).Nous avons dans un premier temps caractérisé de manière complète et quantitative, lamicrostructure de l’acier 16MND5 à l’état de réception (trempé et revenu). L’étude a permis demontrer qu’il existe un gradient de microstructure entre la peau interne et le coeur de l’épaisseur dela virole. La microstructure à coeur est constituée de ferrite proeutectoïde, de bainite et d’amas decarbures, tandis qu’en peau interne on est en présence de bainite et d’amas de carbures.Une campagne d’essais de dilatométrie a été réalisée afin de simuler la microstructure brute detrempe de l’acier 16MND5 et d’observer l’effet de la vitesse de refroidissement, des températuresde transformation sur la microstructure des aciers de cuve. Ces essais ont révélé que lamicrostructure de l’acier 16MND5 après refroidissement est constituée de bainite, d’îlots demartensite et d’austénite résiduelle (M-A) enrichie en carbone. Ce sont ces îlots M-A qui donnentnaissance aux amas de carbures lors du revenu final.L’effet de la composition chimique de cet acier a été étudié grâce à l’utilisation d’une tôle ayant unecomposition chimique plus riche en carbone et en éléments d’alliages. Ce travail a montré quel’augmentation des teneurs en carbone et en éléments d’alliages modifiaient la morphologie et lacristallographie de la ferrite.L’étude des comportements mécaniques des constituants présents en peau interne, quart épaisseur etmi épaisseur a été réalisée grâce à des essais de résilience sur des éprouvettes de mini charpy. Cetteétude a permis de montrer qu’à basse température (-120°C) la peau interne présente de meilleurespropriétés de résilience que le quart et la mi épaisseur de la virole. Des examens de la surfacelatérale des éprouvettes de Charpy ont montré que la présence de ferrite proeutectoïde favorise lagermination de micro-fissures de clivage
Reactor pressure vessel is the second security barrier of the nuclear reactor and it is elaboratedwith a low carbon steel ( C-0.16%). Due to the large size of the ferrule there is temperatureand cooling rate gradient, which lead to microstructure gradient. To develop predictive modelit is necessary to well describe the microstructure which depend to the processing parameters.We focuse our work in investigating the effect of the processing parameters (cooling rate,chemical composition...) on the final microstructure during phase transformation.To get these informations and better describe the microstructure, we have used someexperimental technics like SEM, EBSD, TEM and Optical Microscopy. The steel used is alow carbon steel with a composition of C-0.16%, Mn-1.32%, Ni-0.72%, Mo-0.49%, Si-0.23%, Cr-0.23%, P-0.010%, S-0.004%. The material has been tempered in the range 635°C-660°C after cooling. Three positions have been chosen for examinations, because the coolingrate is not the same between the center and the edge of the material. The results of theobservations made in the different scale, indicate that the microstructure is mainly baniticwith bainitic ferrite and cementite precipitates. Examinations of the precipitates withextractive replicas in TEM reveal that morphology of cementite particles is complex they arecylinder-shaped particles, short bars particles and skeletal particles. OrientationsRelationships (OR) have been determined between ferrite and cementite particles with thinfoils in TEM by using Selected Area Diffraction, in a large number areas the Isaichev andBagaryatskii OR have been observed, a little Pitsch Petch OR have been obtained. The EBSDmap shows that the bainitic ferrite morphologies are both lath like and polygon. Themisorientations inside the laths are very small (0.5° misorientation point to point) andbetween laths we have the range 49-60° misorientation. The profile of misorientationsbetween point to point indicates higher frequency for the range 49-60°. Charpy test have beenperformed to analyze the effect of the microstructure on the fracture energy at lowtemperature. The results show that the fracture energy decreases when the content ofproeutectoid ferrite is high

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Gallo, Giulliano Batelochi [UNESP]. "Influência do tratamento térmico sobre a tenacidade de um aço com AISI SAE 1045 com médio teor de carbono, avaliada por ensaios de impacto." Universidade Estadual Paulista (UNESP), 2006. http://hdl.handle.net/11449/97094.

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Made available in DSpace on 2014-06-11T19:28:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-02-07Bitstream added on 2014-06-13T18:57:57Z : No. of bitstreams: 1 gallo_gb_me_guara.pdf: 1706567 bytes, checksum: 597ea250f08f8ddc714ee7df53e7829b (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Estudos de novos materiais, mais resistentes, econômicos e de menor densidade, são de grande interesse para aplicações estruturais em projetos de Engenharias. Propriedades mecânicas antes obtidas principalmente por meio de adição de elementos de ligas, como por exemplo elevada dureza, tenacidade e resistência mecânica, podem ser atingidas atualmente com variações no processamento térmico e termomecânico. Estas alterações têm proporcionado a formação de estruturas multifásicas nos aços, e como elemento deste estudo, os aços bifásicos. Neste trabalho, buscou-se entender os efeitos que processamentos térmicos possuem sobre as microestruturas dos aços de médio teor de carbono (SAE 1045), assim como a sua influência sobre as propriedades mecânicas, especialmente sobre a tenacidade, evidenciada por meio de ensaios de impacto. O material tratado termicamente obteve, sua estrutura transformada, visando à formação de estrutura bifásica (ferrita e martensita) e de estrutura formada por martensita revenida, sendo comparadas com a condição do material como fornecido (ferrita e perlita). A caracterização microestrutural foi realizada para determinação das fases presentes, assim como das frações volumétricas respectivas. Ensaios de tração e de impacto foram realizados visando a determinação das propriedades mecânicas do aço. Os resultados mostraram que a interação entre ferrita e martensita, gerada na condição bifásica, possue forte influência nos resultados referentes à tenacidade, assim como a temperatura em que o material foi ensaiado. Comparando-se três estruturas, comprova-se que a estrutura bifásica possui resistência mecânica e tenacidade mais elevadas que os aços temperados e revenidos, e tenacidade proxima a do aço com médio teor de carbono, sem tratamento térmico.
Studies of new materials, more resistance, cheaper costs and lower density, have high interest for structural use in engineering projects. Mechanical properties adquired in the past by alloyes adition, for example igher hardness, toughness and mechanical strenght, nowadays can be reached using controlled thermo mechanical process. These changes have provided the multiphase structures formation in steels, for example the dual phase steel, subject of the present study. In this work it was researched the effects of heat process in microestructure of medium carbon steels (SAE 1045) and the influence over mechanical properties, specially in toughers, realized by impact analysis. The heat treatment material has its structure transformed in dual-phase structure (ferrite and martensite) and compared with supplied material (ferrite and perlite). The microestructural characterization was done to determine the present phase, and the respective volumetric fraction of martensite. Tension and impact analysis were done to determine the steel mechanical properties. Results have shown that the interaction between ferrite and martensite generated in dual-phase condition, has higher influence, related the materials toughness, so the temperature that material was analysed comparing the three structures, verifies that the dual-phase struture has level of mechanical resistence and toughness, higher than quenched and tempered steels, and toughness near of medium carbon steel that has not received heat treatment in higher or lower temperatures.

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Philippot, Clément. "Etude des mécanismes de précipitation, de recristallisation et de transformation de phases dans les aciers Dual Phase microalliés au titane niobium lors du recuit." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4342.

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L’allégement des véhicules est l’un des objectifs prioritaires des constructeurs automobile pour répondre aux directives environnementales d’émission de CO2. Le développement des aciers multiphasés à très haute résistance mécanique est l’une des solutions communément adoptées pour réduire l’épaisseur des tôles dans les véhicules tout en conservant leur capacité à assurer la sécurité des passagers. La présente étude porte sur l’optimisation des paramètres du procédé de production industrielle de l’une des ces familles d’aciers : les aciers Dual Phase microalliés au titane et au niobium de haut grade ; c'est-à-dire possédant une résistance à la rupture supérieure à 800MPa.A partir d’une microstructure initiale bainite + martensite laminée à froid, les différents phénomènes se produisant au cours du recuit, de la chauffe jusqu’à la fin du maintien intercritique, sont caractérisés. L’influence des paramètres du recuit comme la vitesse de chauffe, la température et le temps de maintien est étudiée. Le système d’interactions triple entre la précipitation des éléments de microalliage, la recristallisation et la formation de l’austénite est au cœur du problème. Un scénario des évolutions microstructurales a été établi à partir de la caractérisation des divers phénomènes. La finesse de la microstructure étudiée (sub-micrométrique) a nécessité l’emploi combiné de techniques de caractérisation multi-échelles : MEB, MET, sonde atomique tomographique, nano-SIMS
Lightening the weight of vehicles is one of the main challenging objectives of the automotive industry to reach the environmental regulation in term of CO2 emissions. The development of multiphase high strength steels is a common solution to reduce the thickness of sheet steel used in vehicles while keeping the same level of passenger’s safety requirements. The present study deals with the optimization of industrial process parameters applied to obtain one of these steels: the high strength microalloyed Dual Phase steels; i.e. with ultimate tensile strength superior to 800MPa.From an initial cold rolled microstructure made of bainite + martensite, the phenomena occurring during the annealing are characterized since the heating up to the end of the intercritical holding. The influence of process parameters as the heating rate, the holding temperature and the holding time are studied. The triple interactions system between the precipitation of microalloying elements, the recrystallization and the austenite formation is the core of the problem. A scenario of microstructural evolutions has been established based on the characterized phenomena. The studied fine microstructure (sub-microns) requires the combination of multiscale characterization techniques: SEM, TEM, atom probe tomography, nano-SIMS

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Uran, Matthias [Verfasser], Axel [Gutachter] Klawonn, Oliver [Gutachter] Rheinbach, and Jörg [Gutachter] Schröder. "High-Performance Computing Two-Scale Finite Element Simulations of a Contact Problem Using Computational Homogenization - Virtual Forming Limit Curves for Dual-Phase Steel / Matthias Uran ; Gutachter: Axel Klawonn, Oliver Rheinbach, Jörg Schröder." Köln : Universitäts- und Stadtbibliothek Köln, 2020. http://d-nb.info/1215837089/34.

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Amorim, Marcelo Soares. "Estudo da influência do tratamento térmico a laser nas características dos aços avançados de alta resistência dual phase 600 e transformed induced plasticity 750 /." Guaratinguetá, 2016. http://hdl.handle.net/11449/138039.

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Orientador: Fernando de Azevedo Silva
Resumo: Os aços avançados de alta resistência são de importância na indústria moderna da mobilidade. Na indústria automobilística, por exemplo, é previsto que o uso destes materiais cresça de maneira acentuada nos próximos anos. Algumas características destes materiais podem ser melhoradas por meio de tratamento térmico, seja ele em toda a extensão do produto ou em partes específicas para as quais se deseja um dado comportamento mecânico. Neste trabalho se propôs a investigação inicial do efeito de um tratamento térmico local por radiação laser, uma forma controlada de adição de energia, nas propriedades mecânicas e na microestrutura de dois destes materiais. Os materiais estudados foram os aços dual phase (DP 600) e o transformed induced plasticity (TRIP 750), e a contribuição pretendida aqui foi prover informações sobre a interação entre a radiação laser e os materiais de estudo, dentro de determinados parâmetros de processamento térmico. Para a caracterização dos materiais, conforme recebidos e após os tratamentos térmicos a laser propostos, foram realizados ensaios metalográficos, de difratometria de raios-X, de dureza e de tração. Verificou-se que, para a faixa de parâmetros de processo experimentada, houve mudanças significativas nas características dos materiais estudados, notadamente um aumento na dureza superficial, alcançando valores correspondentes ao dobro dos relativos aos materiais sem tratamento, nos limites de escoamento, com aumentos de até 15% com relação ao materia... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The advanced high strength steels are of importance in modern mobility industry. In the automotive industry, for example, it is anticipated that the use of such materials will be increased in the near future. Some characteristics of these materials can be improved through heat treatments, considering the entire mass of the product or in specific regions of a part, for which it is necessary a particular mechanical behavior. This work focused on the initial investigation of a local heat treatment by laser radiation, a controlled form of energy addition, in the mechanical properties and microstructure of two of these materials. The studied materials are the dual phase steel (DP 600) and the transformed induced plasticity steel (TRIP 750), and the desired contribution here was to provide information about the interaction between the laser radiation and the studied materials for a given range of thermal processing parameters. To characterize the materials as received and after proposed laser heat treatments, metallographic evaluation, X-ray diffraction, and hardness and tensile tests were performed. It was found that, for the range of process parameters investigated, there were significant changes in the characteristics of the materials, notably an increase in surface hardness, reaching values corresponding to twice of those for materials without treatment, in the yield limits, with increases of up to 15% with respect to the base material, and strength limits, with increases up to... (Complete abstract click electronic access below)
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