To see the other types of publications on this topic, follow the link: Austenite formation.
Dissertations / Theses on the topic 'Austenite formation'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 19 dissertations / theses for your research on the topic 'Austenite formation.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Azizi-Alizamini, Hamid. "Austenite formation and grain refinement in C-Mn steels." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/30513.
Full textAbstract:
The present work deals with grain refinement and austenite formation in a plain C-Mn steel with 0.17C-0.74Mn (wt pct). To improve the limited work hardening capability of ultrafine grained ferritic steels, new approaches were adopted to develop bimodal ferrite grain size distributions and ultrafine grained dual phase microstructures. The first approach is based on deformation and annealing of a ferrite-martensite microstructure. Ultrafine grained dual phase steels were obtained through rapid heating of very fine ferrite-carbide aggregates into the intercritical annealing region where partial austenite formation takes place. Hence, austenite formation was systematically investigated using a combination of microstructure characterization and detailed dilatometry analysis. The effect of initial structure and heating rate on austenite formation was examined. The resulting microstructure characteristics and mechanical properties of dual phase steels were also investigated. A multi-phase field modelling approach was adopted to simulate austenite formation from a variety of initial structures including ferrite-spheroidized carbide aggregates, fully pearlitic and ferrite-pearlite structures.
The results show that a bimodal distribution of ferrite grains negates the Lüdering effect, yet the improvement of work hardening rate remains marginal compared to fine grained ferrite structures. Very fine grained initial structure and rapid heat treatment cycle are essential parameters to achieve ultrafine grained dual phase steels with improved mechanical properties in the steel employed in this study. For austenite formation, dilatation data can be used to distinguish different stages of microstructure evolution upon heating into the single austenite phase region including ferrite recrystallization, pearlite to austenite and ferrite to austenite transformation. Heating rate has a pronounced effect on the size and morphology of austenite grains in the intercritical annealing region. It is shown that phase field modelling is capable of predicting microstructural changes during austenite formation. It is well suited to capture complex interaction between microstructure processes such as spheroidization, carbide dissolution and coarsening during austenite formation especially in fine grained structures where the length scale is comparable with carbon diffusion distance.
2
Chelladurai, Isaac. "Characterization of Phase Transformation and Twin Formation in Automotive Sheet Metal Alloys to Quantify and Understand Their Impact on Ductility." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8628.
Full textAbstract:
The motivation to use lightweight materials in the construction of the automotive structure is the resultant increased fuel efficiency. However, these materials possess certain drawbacks that make it challenging to adopt them into current automobile manufacturing processes. In this dissertation the microstructural response observed in a magnesium alloy, AZ31, and an advanced high strength steel alloy, QP1180, to uniaxial deformation is analyzed and the results are presented. In AZ31 the required slip modes are not activated at room temperature leading to its low ductility at room temperature. The resulting activity of these twins in response to uniaxial tension is analyzed and its correlations with the microstructure features is reported. Additionally, a neighborhood viscoplastic self-consistent model is developed that will allow more accurate simulation of twin response to outside deformation. Furthermore, activity of slip modes that are usually observed at high temperatures (>200°C) are also observed at lower temperatures (<125°C) and they are compared to the relative twin activity at these temperatures. It is observed that larger grains, with high schmid factors, longer grain boundaries and have misorientation with its neighboring grain greater than 27° are more favorable for twin formation and transmission in the AZ31 microstructure in response to uniaxial tension. The nature of retained austenite (RA) transformation into martensite that gives QP1180 its enhanced ductility, is not clearly understood primarily because of challenges present in characterization of these metastable RA. Further, a 2 dimensional characterization method does not provide the complete information of the RA grain. These challenges are overcome by characterization of a 3 dimensional volume element using serial sectioning and EBSD followed by reconstruction using DREAM3D. The influence of 3d morphology and orientation direction on RA transformation is studied using as-is and uniaxially deformed samples. A novel shear affinity factor is introduced as a metric to describe the ease of RA transformation under uniaxial tension. The 3d nature of the information collected allows a new classification of disk shape in addition to globular and lamellar shapes for RA. It is found that RA that are low volume laths and have low shear affinity factor transform later compared to disk shaped RA’s. Through these guidelines the preparation of a microstructure that is conducive to RA transformation under uniaxial tension is possible.
3
Tao, Xiao. "Investigations on the role of Cr, Mn and Ni on the formation, structure, and metastability of nitrogen-expanded austenite on Fe-based austenitic alloys under triode-plasma nitriding." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21957/.
Full text
4
Gyhlesten, Back Jessica. "Modelling and Characterisation of the Martensite Formation in Low Alloyed Carbon Steels." Licentiate thesis, Luleå tekniska universitet, Material- och solidmekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62369.
Full textAbstract:
The current work contains experimental and theoretical work about the formation of martensite from the austenitic state of the steel Hardox 450. Simulation of rolling and subsequent quenching of martensitic steel plates requires a model that can account for previous deformation, current stresses and the temperature history, therefore dilatometry experiments were performed, with and without deformation. Two austenitization schedules were used and in the standard dilatometry the cooling rates varied between 5-100 °C/s, in order to find the minimum cooling rate that gives a fully martensitic microstructure. Cooling rates larger than 40°C/s gave a fully martensitic microstructure. The cooling rate of 100 °C/s was used in the deformation dilatometry tests where the uniaxial deformation varied from 5-50 %. The theoretical work involved modelling of the martensite formation and the thermal/transformation strains they cause in the steel. Characterizations were done using light optical microscopy, hardness tests and electron backscatter diffraction technique. The parent austenite grains of the martensitic structure were reconstructed using the orientation relationship between the parent austenite and the martensite. Kurdjumov-Sachs orientation relationships have previously been proven to work well for low-carbon steels and was therefore selected. The standard implementation of the Koistinen-Marburger equation for martensite formation and a more convenient approach were compared. The latter approach does not require the storage of initial austenite fraction at start of martensite formation. The comparison shows that the latter model works equally well for the martensite formation. The results showed that the use of martensite start and finish temperatures calibrated versus experiments for Hardox 450 works better when computing thermal expansion than use of general relations based on the chemistry of the steel. The results from deformation dilatometry showed that deformation by compressive uniaxial stresses impedes the martensite transformation. The simplified incremental model works well for deformation with 5 % and 10 %. However, the waviness in the experimental curve for deformation 50 % does not fit the model due vi to large barrelling effect and the large relative expansion for the material that the sample holders are made of. Crystallographic reconstruction of parent austenite grains were performed on a hot-rolled as-received reference sample and dilatometry samples cooled with 60 °C/s and 100 °C/s. The misorientation results showed that the samples match with the Kurdjumov-Sachs orientation relationship in both hot rolled product and dilatometry samples. When misorientation between adjacent pixels are between 15° and 48°, then the boundary between them was considered as a parent austenite grain. The austenitic grain boundaries of the sample cooled at 100 °C/s is in general identical with the hot rolled sample when considering high angle boundaries (15°-48°). The results from the hardness tests showed that the rolled product exhibits higher hardness as compared to samples cooled by 100 °C/s and 60 °C/s. This can be attributed to the formation of transition-iron-carbides in the hot rolled product due to longer exposure of coiling temperature.
5
Javaheri, V. (Vahid). "Design, thermomechanical processing and induction hardening of a new medium-carbon steel microalloyed with niobium." Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526223582.
Full textAbstract:
Abstract This thesis has been made within the European Industrial Doctorate (EID) project called Mathematics and Materials Science for Steel Production and Manufacturing, abbreviated as MIMESIS, which has five partners: EFD Induction in Norway; SSAB, Outokumpu, and the University of Oulu in Finland; and Weierstrass Institute for Applied Analysis and Stochastics (WIAS) in Germany. The main aim of this work was to develop a steel composition and processing route suitable for making a slurry transportation pipeline with the aid of induction hardening, and to characterize the phase transformations and microstructures involved in the various stages of the processing route. A novel steel chemistry was designed based on metallurgical principles assisted by computational thermodynamics and kinetics. The designed composition is a medium-carbon, low-alloy steel microalloyed with niobium, in wt.% 0.40 C, 0.20 Si, 0.25 Mn, 0.50 Mo, 0.90 Cr, and 0.012 Nb. This was subsequently cast, thermomechanically rolled on a laboratory rolling mill to two bainitic microstructures, and finally subjected to the thermal cycles predicted to be encountered with the internal induction hardening of a typical pipe geometry. The phase transformations and microstructures found at various stages of the simulated production process have been characterized and algorithms developed to enable the optimization of microstructure and hardness through the pipe wall thicknessTiivistelmä Tämä väitöskirja on tehty osana Euroopan teollisuustohtori (European Industrial Doctorate, EID) -ohjelmaa projektissa eli Matematiikka ja materiaalitiede teräksen valmistuksessa ja käytössä (Mathematics and Materials Science for Steel Production and Manufacturing, MIMESIS). Ohjelmassa on viisi partneria: EFD Induction Norjasta; SSAB, Outokumpu ja Oulun yliopisto Suomesta; ja Weierstrass Institute for Applied Analysis and Stochastics (WIAS) Saksasta. Työn päätavoitteina oli kehittää teräksen koostumusta ja prosessointireittiä, jotka soveltuvat lietteen kuljetusputken valmistukseen induktiokarkaisun avulla, sekä karakterisoida prosessin eri vaiheiden aikana tapahtuvat faasimuutokset ja mikrorakenteet. Uusi teräskoostumus suunniteltiin metallurgisten periaatteiden pohjalta hyödyntämällä laskennallista termodynamiikkaa ja kinetiikkaa. Suunniteltu teräs on niobilla mikroseostettu, matalaseosteinen ja keskihiilinen, eli painoprosentteina 0,40 C, 0,20 Si, 0,25 Mn, 0,50 Mo, 0,90 Cr ja 0,012 Nb. Teräs valettiin, valssattiin ja jäähdytettiin termomekaanisesti laboratoriovalssaimella kahdeksi bainiittiseksi mikrorakenteeksi ja lopulta altistettiin lämpösykleille, joiden ennustettiin olevan tyypillisiä sisäisesti induktiokarkaistulle teräsputkelle. Simuloidun tuotantoprosessin eri vaiheissa havaitut faasimuutokset ja mikrorakenteet on karakterisoitu. Sen lisäksi on kehitetty algoritmit, jotka mahdollistavat mikrorakenteen ja kovuuden optimoinnin putken seinämän paksuuden läpi
6
Bellavoine, Marion. "Transformations de phases et recristallisation dans les aciers Dual Phase microalliés au titane niobium : étude expérimentale et modélisation." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0262.
Full textAbstract:
Les aciers multiphasés à très haute résistance mécanique destinés à l’industrie automobile font l’objet d’importantes activités de recherche et développement dans le contexte de l’allègement des structures. L’obtention de meilleurs compromis entre résistance et ductilité nécessite de comprendre l’influence du couple composition chimique nominale – paramètres du procédé d’élaboration sur la formation des microstructures.La présente étude s’inscrit dans cette démarche de compréhension et porte en particulier sur les mécanismes se produisant lors du recuit des nuances d’aciers Dual Phase de haut grade microalliés au Ti et au Nb, dont la microstructure initiale laminée à froid est composée de bainite et de martensite. Ces mécanismes (précipitation des éléments de microalliage Ti, Nb et Mo, recristallisation de la ferrite et formation de l’austénite) présentent des interactions complexes. Le scénario des évolutions microstructurales lors du recuit est caractérisé à l’aide d’une étude expérimentale s’appuyant sur des techniques d’analyses complémentaires à différentes échelles (DRX in situ, MEB, MET, SAT). L’influence respective des éléments de microalliage Ti, Nb et Mo et des paramètres du recuit sur ce scénario est clarifiée à l’aide d’une caractérisation systématique des évolutions microstructurales couplée à la mise en œuvre d’une démarche de modélisation des mécanismes et de leurs interactionsTo meet the need for weight reductions in the automotive industry, new advanced high-strength steels are being developed. The achievement of a better balance between high strength and high formability requires a deep understanding of both the effect of chemical composition and processing parameters on the formation of microstructures. The present work contributes to such an objective and deals with the mechanisms occurring during annealing of Dual Phase steels microalloyed with Ti and Nb. Microstructural changes during this stage include precipitation of microalloying elements, ferrite recrystallization and austenite formation. These mechanisms are investigated using complementary experimental techniques at different scales such as in situ XRD, SEM, TEM and APT in various Dual Phase steel grades having the same bainite-martensite initial cold-rolled microstructure. Using combined experimental and modeling approaches, the present work clarifies the separate influence of microalloying elements Ti, Nb and Mo and heating rate on the mechanisms occurring during annealing and their interactions
7
Marceaux, Dit Clément Arthur. "Interactions entre transformations de phases et recristallisation au recuit : influence de la microstructure initiale pour des aciers à 0,2 % de carbone." Electronic Thesis or Diss., Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0297.
Full textAbstract:
Les aciers à haute résistance sont très utilisés dans l’industrie automobile pour le bon compromis entre résistance et ductilité qu’ils offrent. D’intenses activités de recherche se poursuivent pour améliorer leurs propriétés de formabilité. Les chimies à fort taux de carbone peuvent aider à atteindre ces objectifs. Cette thèse porte sur les évolutions microstructurales au recuit de deux aciers à 0,2% pds de carbone microalliés au Ti et Nb, dont les microstructures initiales laminées à froid diffèrent (bainite-martensite et bainite-perlite). Les interactions entre la restauration, la recristallisation, la précipitation de cémentite, celle du microalliage et la formation d'austénite peuvent mener à la formation de microstructures finales très variées à l’issue du recuit. La genèse de microstructures en bandes, néfastes pour l’obtention de bonnes propriétés de formabilité et liées à la recristallisation incomplète des aciers lors de leur chauffe, est étudiéeHigh-strength steels are widely used in the automotive industry because of the good mechanical properties – formability ratio they offer. Numerous research activities are still ongoing to further improve their formability properties. High-carbon chemistries can help reach this goal. This thesis focuses on the microstructural evolutions during the annealing of two 0.2 wt.% carbon steels with Ti-Nb microalloy, for which cold-rolled initial microstructures are different (bainite-martensite and bainite-pearlite). Interactions between recovery, recrystallization, cementite precipitation, microalloying elements precipitation and austenite formation can lead to the formation of many kinds of final microstructures after annealing. The origin of banded microstructures, detrimental to good formability properties and linked to incomplete recrystallization during annealing, is studied
8
Esham, Kathryn V. "The Effect of Nanoscale Precipitates on the Templating of Martensite Twin Microstructure in NiTiHf High Temperature Shape Memory Alloys." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1494251602171757.
Full text
9
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.
Full textAbstract:
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-SIMSLightening 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
10
Bellavoine, Marion. "Transformations de phases et recristallisation dans les aciers Dual Phase microalliés au titane niobium : étude expérimentale et modélisation." Electronic Thesis or Diss., Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0262.
Full textAbstract:
Les aciers multiphasés à très haute résistance mécanique destinés à l’industrie automobile font l’objet d’importantes activités de recherche et développement dans le contexte de l’allègement des structures. L’obtention de meilleurs compromis entre résistance et ductilité nécessite de comprendre l’influence du couple composition chimique nominale – paramètres du procédé d’élaboration sur la formation des microstructures.La présente étude s’inscrit dans cette démarche de compréhension et porte en particulier sur les mécanismes se produisant lors du recuit des nuances d’aciers Dual Phase de haut grade microalliés au Ti et au Nb, dont la microstructure initiale laminée à froid est composée de bainite et de martensite. Ces mécanismes (précipitation des éléments de microalliage Ti, Nb et Mo, recristallisation de la ferrite et formation de l’austénite) présentent des interactions complexes. Le scénario des évolutions microstructurales lors du recuit est caractérisé à l’aide d’une étude expérimentale s’appuyant sur des techniques d’analyses complémentaires à différentes échelles (DRX in situ, MEB, MET, SAT). L’influence respective des éléments de microalliage Ti, Nb et Mo et des paramètres du recuit sur ce scénario est clarifiée à l’aide d’une caractérisation systématique des évolutions microstructurales couplée à la mise en œuvre d’une démarche de modélisation des mécanismes et de leurs interactionsTo meet the need for weight reductions in the automotive industry, new advanced high-strength steels are being developed. The achievement of a better balance between high strength and high formability requires a deep understanding of both the effect of chemical composition and processing parameters on the formation of microstructures. The present work contributes to such an objective and deals with the mechanisms occurring during annealing of Dual Phase steels microalloyed with Ti and Nb. Microstructural changes during this stage include precipitation of microalloying elements, ferrite recrystallization and austenite formation. These mechanisms are investigated using complementary experimental techniques at different scales such as in situ XRD, SEM, TEM and APT in various Dual Phase steel grades having the same bainite-martensite initial cold-rolled microstructure. Using combined experimental and modeling approaches, the present work clarifies the separate influence of microalloying elements Ti, Nb and Mo and heating rate on the mechanisms occurring during annealing and their interactions
11
Cho, Jae-Young. "Effect of [delta] ferrite on edge-crack formation during hot rolling of austenitic stainless steel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0027/MQ50595.pdf.
Full text
12
Cho, Jae-Young 1970. "Effect of [delta] ferrite on edge-crack formation during hot rolling of austenitic stainless steel." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21284.
Full textAbstract:
During planetary hot rolling of 304 austenitic stainless steel, cracks are formed along the plate edges. In order to explain the mechanism of edge cracking, the metallographical quantitative analysis of microstructural inhomogeneity of steel plates containing edge cracks of different intensities is performed. The austenitic matrix of the steel contained small amounts of delta ferrite inhomogeneously distributed across the width and the thickness of the plate. A correlation was found between ferrite content and edge cracking: the higher the ferrite content the longer the edge cracks. Among the chemical elements present in the steel, the most critical effect on delta ferrite content was exerted by carbon and nitrogen are a powerful gamma phase stabilizers at high temperature. To understand the effects of reheating parameters on the morphology and content of delta ferrite, the specimens selected from different locations of as-cast 304 stainless steel slab, were reheated according to the temperature profiles, which simulated the industrial reheating process before hot rolling. In general, reheating reduced the delta ferrite content, increased the size of the individual ferrite island and changed its shape to a more spherical. An increase of reheating time to 92 minutes caused drastic reduction in delta ferrite content and its further spherodization. Moreover, the size of the individual ferrite islands decreased. A possible, contribution of steel chemistry and reheating parameters to changes in the steel microstructure and the possibility of edge cracking, is discussed.
13
Westin, Elin M. "Microstructure and properties of welds in the lean duplex stainless steel LDX 2101." Doctoral thesis, KTH, Metallografi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-27387.
Full textAbstract:
Duplex stainless steels can be very attractive alternatives to austenitic grades due to their almost double strength at equal pitting corrosion resistance. When welding, the duplex alloys normally require addition of filler metal, while the commodity austenitic grades can often be welded autogenously. Over-alloyed consumables are used to counteract segregation of important alloying elements and to balance the two phases, ferrite and austenite, in the duplex weld metal. This work focuses on the weldability of the recently-developed lean duplex stainless steel LDX 2101® (EN 1.4162, UNS S32101). The pitting corrosion resistance of this grade is better than that of austenitic AISI 304 (EN 1.4307) and can reach the level of AISI 316L (EN 1.4404). The austenite formation is rapid in LDX 2101 compared to older duplex grades. Pitting resistance tests performed show that 1-2.5 mm thick laser and gas tungsten arc (GTA) welded LDX 2101 can have good corrosion properties even when welding autogenously. Additions of filler metal, nitrogen in the shielding gas, nitrogen-based backing gas and use of laser hybrid welding methods, however, increase the austenite formation. The pitting resistance may also be increased by suppressing formation of chromium nitrides in the weld metal and heat affected zone (HAZ). After thorough post-weld cleaning (pickling), pitting primarily occurred 1-3 mm from the fusion line, in the parent metal rather than in the HAZ. Neither the chromium nitride precipitates found in the HAZ, nor the element depletion along the fusion line that was revealed by electron probe microanalysis (EPMA) were found to locally decrease the pitting resistance. The preferential pitting location is suggested to be controlled by the residual weld oxide composition that varies over the surface. The composition and thickness of weld oxide formed on LDX 2101 and 2304 (EN 1.4362, UNS S32304) were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the AISI 300 series. A new approach to heat tint formation is presented; whereby evaporation of material from the weld metal and subsequent deposition on the already-formed weld oxide are suggested to contribute to weld oxide formation. This is consistent with manganese loss from the weld metal, and nitrogen additions to the GTA shielding gas enhance the evaporation. The segregation of all elements apart from nitrogen is low in autogenously welded LDX 2101. This means that filler wire additions may not be required as for other duplex grades assuming that there is no large nitrogen loss that could cause excessive ferrite contents. As the nitrogen appears to be controlling the austenite formation, it becomes essential to avoid losing nitrogen during welding by choosing nitrogen-containing shielding and backing gas.QC 20101213
14
Westin, Elin M. "Welds in the lean duplex stainless steel LDX 2101 : effect of microstructure and weld oxide on corrosion properties." Licentiate thesis, KTH, Materials Science and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9299.
Full textAbstract:
Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation.
15
Westin, Elin M. "Welds in the lean duplex stainless steel LDX 2101 : effect of microstructure and weld oxides on corrosion properties." Licentiate thesis, Stockholm : Industriell teknik och management, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9299.
Full text
16
Li, Wei. "An investigation into the effect of stress on the formation and stability of carbon s-phase on austenitic stainless steel." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/2894/.
Full textAbstract:
S-phase can be created in austenitic stainless steels by low-temperature thermochemical treatments, which greatly enhanced their hardness, wear resistance and fatigue properties because of the supersaturation by interstitials. One of the technological challenges associated with S-phase surface engineering is that the maximum layer thickness of the S-phase layers is very thin. The thickness of S-phase is restricted by its metastability and precipitation will occur as a result of prolonged treatment. In this project, the effect of in situ tensile stress on the formation of carbon S-phase on 316L austenitic stainless steel was investigated and it was demonstrated that the tensile stress thickened the S-phase layer by promoting the carbon diffusion in austenitic substrate. However, metastable carbides precipitated when applied tensile stress exceeded 40MPa. The thermo-mechanical stability of carbon S-phase was studied by creeping (tensile stress) and HIPping (compressive stress) tests. The results showed that the compressive stress retard the decomposition of S-phase by impeding the carbon diffusion; on the other hand, tensile stress promoted the carbon diffusion. The residual compressive and shear stresses in carbon S-phase was measured be 2.2 GPa and 132 MPa. The wear behaviour of carbon S-phase was studied by dry and oil lubricated reciprocating wear.
17
Bouquet, Nicolas. "Etude de la formation des joints soudés par diffusion : application aux échangeurs de chaleur compacts." Thesis, Dijon, 2014. http://www.theses.fr/2014DIJOS050/document.
Full textAbstract:
Les échangeurs compacts à plaques soudés-diffusés sont une solution prometteuse dans de nombreux domaines (nucléaire, (pétro-)chimie, solaire…) du fait de leurs performances. Ils sont envisagés pour le système de conversion d’énergie du réacteur nucléaire ASTRID. Pendant le soudage CIC, la problématique est double: maîtriser la déformation des canaux et l’évolution microstructurale du matériau tout en obtenant des interfaces résistantes. Cette thèse s’intéresse à la compréhension et à la maîtrise de la microstructure des assemblages pour définir des critères « procédé » permettant l’obtention d’interfaces non marquées par le procédé et le maintien d’une taille de grains fine. Après une caractérisation approfondie de leur surface et de l’évolution au chauffage de leur microstructure, le comportement au soudage de tôles en acier austénitique 316L a été étudié en faisant varier les paramètres liés au procédé (température et pression de soudage) et au format des tôles (épaisseur, état de surface…). Les résultats montrent que la formation de l’interface est associée à des mécanismes de croissance de grain classiques avec un ancrage interfacial plus ou moins marqué selon les caractéristiques des surfaces. Les propriétés mécaniques des assemblages ont été testées afin de déterminer la nocivité des défauts rencontrés. Si les pores constituent le défaut le plus pénalisant, l’influence d’autres hétérogénéités a été mise en évidence. Les étapes de formation des interfaces ont ensuite été identifiées par la réalisation de cycles de soudage interrompus. L’intérêt d’une approche numérique par la méthode Level-Set pour simuler les évolutions microstructurales est finalement discutéCompact diffusion bonded heat exchangers are an attractive option in many fields (nuclear, (petro-)chemistry, solar…) due to their performance. This type of concept is especially intended for manufacturing the energy conversion system of the ASTRID reactor. During diffusion bonding by HIP, the problem is twofold: the channel deformation and microstructure evolution must be controlled, while at the same time, highly resistant interfaces are desired. This thesis is focused on the understanding and the control of the bonded components microstructure prepared by HIP in order to define « process » criteria to achieve welds in agreement with specifications of components containing fluidic channels: interfaces unaffected by the process and small grain size. After a detailed characterization of their surface and microstructural evolution during heating, the behavior of AISI 316L austenitic steel sheets has been examined in a parametric study by varying the parameters related to process (diffusion bonding temperature and pressure) and welding material (thickness, surface finish…). The results show that the interface formation is driven by conventional grain growth mechanisms with an interfacial pining more or less marked depending on surface characteristics. The mechanical properties of assemblies have been tested to determine the influence of defects. Though pores are the most critical default, the influence of other heterogeneities has also been highlighted. The different steps of bond formation have been identified by performing interrupted diffusion bonding test. The interest of modeling approach by Level-Set method to simulate microstructure evolution has been finally discussed
18
Cho, Yeong-Bong. "The kinetics of austenite formation during continuous heating of a multi-phase steel." Thesis, 2000. http://hdl.handle.net/2429/10582.
Full textAbstract:
DP (Dual-Phase) and TRIP (Transformation Induced Plasticity) steels, also known as multiphase
steels, have been attracting a growing interest in the development of lighter
automobiles owing to their excellent combination of strength and ductility. TRIP steels can
usually be generated from a standard cold-rolled ferrite-pearlite grade by a two stage
continuous annealing process; continuous heating and intercritical annealing, followed by
subsequent cooling and austempering. The material is first intercritically annealed in the
ferrite/ austenite coexistence region, during which the ferrite matrix recrystallizes and
austenite is created. Austempering is then performed and some upper bainite is formed,
which, in turn, stabilizes the remaining austenite even down to room temperature.
Most studies have been focused so far on the second stage of the thermal scheme due to the
fact that the steel properties depend primarily on the transformation processes following
austenitization. However, the phase transformations occurring upon heating is of profound
importance. The state of the microstructure after heating; i.e., volume fraction, shape,
distribution and chemical composition of the austenite grains, has a great influence on the
kinetics of the phase transformation during cooling and on the subsequent mechanical
properties of the steel. Furthermore, the kinetics of the reverse transformation to austenite
determine the time and temperature required for either intercritical heat treatment or
normalization.
The objective of the present study is to characterize and understand the reaustenitization
kinetics from pearlite-ferrite structure during continuous heating. Futher, a mathematical
model based on the Avrami equation and the additivity principle has been adopted in
modeling the pearlite-ferrite to austenite transformation during continuous heating.
19
Yi-ShanHsu and 徐儀珊. "Effect of Austenite Grain Size and Cooling Rate on the Formation of Acicular Ferrite in SM570 Steel." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/37033585784391403993.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系
102
The study is divided into two parts experiment, first one is simulation of the heat affected zone of welding process and calculate the equation of austenite grain size and holding time. Second, simulate the different cooling rate and observe the acicular ferrite and calculate the volume proportion of each phase. The heat treatment process was designed to get the proper microstructure. OM analysis was checked the AF structure. EDS analysis identify the inclusion type. EBSD reconfirm the AF structure. By heat treatment experiment to simulate HAZ and observe growth of austenite grain size, we can construct the austenite grain growth equation of austenite grain size v.s holding time. Simulating various cooling rates, we can find that most appropriate cooling rate for the formation of acicular ferrite is air cooling. AF has a characteristic that the value of KAM will be relatively large, and the peak value at around 0.4.