Dissertations / Theses: 'HSLA (High Strength Low Alloy)'

1

Hu, Wei. "Data-driven metallurgical design for high strength low alloy (HSLA) steel." [Ames, Iowa : Iowa State University], 2008.

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2

Khoo, C. A. "Microstructure-mechanical property relationships in vanadium bearing high strength low alloy (HSLA) strip steels." Thesis, Swansea University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637790.

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High Strength Low Alloy (HSLA) strip steels have extensive applications in the automotive industry, due to their excellent combination of strength, toughness and suitable formability characteristics. The purpose of the present study is to study the control of austenite grain size via second phase particle additions, based on titanium and combine titanium-vanadium microalloy additions. Processing of HSLA strips steels aims to produce a fine austenite grain size resulting in the subsequent formation of a fine primarily ferritic product. Two experimental titanium and titanium-vanadium HSLA grades were studied as part of this comparative study. The present study confirmed that vanadium carbide precipitates successfully control the austenite grain size at low austenitisation temperatures <1000ºC by effectively pinning the austenite grain boundaries. However, at higher austenitisation temperatures >1000ºC rapid dissolution of vanadium carbides particles does occur and the importance of titanium nitride formation in controlling the austenite grain size in both experimental grades, becomes evident. The present study also identified the critical parameters in processing of the two novel HSLA grades studied as for the finishing hot rolling temperature, cooling rate between finishing and coiling temperature and coiling temperature concerned. Based on this study a recommendation for an optimised steel processing route in titanium-vanadium HSLA grade is made facilitating the production of enhanced quality hot rolled strip steel products.

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3

Rose, Scott Anthony. "The Effect of Cooling Rate of Friction Stir Welded High Strength Low Alloy Steel." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4181.

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The friction stir welding of steel has produced a hard zone in several different alloys. Despite its detrimental effects on weld toughness, the reasons behind neither its formation nor a method of reducing its size or effects have been explored. Recent advances in process control allow for direct heat input control, which combined with the use of backing plates of different thermal conductivity allows for an expansion of the process window. These control methods also affect the HAZ cooling rate by providing greater range (a 60% increase compared to a fixed backing plate) and control (five welds within 16 Â°C/s). This increased range produced microstructures consisting of various forms of ferrite at lower cooling rates and bainite at higher cooling rates. The hard zone was determined to be the result of the formation of the bainite at higher cooling rates and was avoided by keeping the cooling rate below 20 Â°C/s in HSLA-65.

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Talekar, Anjali S. "Oxidation behavior of Ni-base superalloys and high strength low alloy (HSLA) steels at elevated temperatures." abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3316371.

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5

Abbasi, Gharacheh Majid. "Microstructural Evaluation in Friction Stir Welded High Strength Low Alloy Steels." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/3099.

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Understanding microstructural evolution in Friction Stir Welding (FSW) of steels is essential in order to understand and optimize the process. Ferritic steels undergo an allotropic phase transformation. This makes microstructural evolution study very challenging. An approach based on Electron Backscattered Diffraction (EBSD) and phase transformation orientation relationships is introduced to reconstruct pre-transformed grain structure and texture. Reconstructed pre-transformed and post-transformed grain structures and textures were investigated in order to understand microstructural evolution. Texture results show that there is evidence of shear deformation as well as recrystallization in the reconstructed prior austenite. Room temperature ferrite exhibits well-defined shear deformation texture components. Shear deformation texture in the room temperature microstructure implies that FSW imposes deformation during and after the phase transformation. Prior austenite grain boundary analysis shows that variant selection is governed by interfacial energy. Variants that have near ideal BCC/FCC misorientation relative to their neighboring austenite and near zero misorientation relative to neighboring ferrite are selected. Selection of coinciding variants in transformed prior austenite Σ3 boundaries supports the interfacial-energy-controlled variant selection mechanism.

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6

Gonçalves, Hugo Miguel Dias. "Estudo de parâmetros de soldadura em aços HSLA." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/17011.

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Mestrado em Ciência e Engenharia de Materiais
Os ganhos de eficiência energética e a sustentabilidade estão na base do desenvolvimento de materiais com melhores propriedades específicas. Este é o caso das ligas leves e dos aços de baixa liga e elevada resistência (High Strength Low Alloy -HSLA- steels) que substituíram aços tradicionais, com teores mais elevados de elementos de liga. No caso da indústria automóvel, os aços HSLA têm utilização numa grande diversidade de componentes estruturais e permitem reduções significativas de peso e também de custo. O fabrico destes componentes envolve várias operações de enformação plástica e também de soldadura, estando esta última muitas vezes na origem de defeitos que podem ser detetados imediatamente ou, na pior situação possível, apenas após a entrada em serviço. É por isso fundamental identificar a contribuição de cada etapa do processamento para a origem destes defeitos. O estágio curricular foi realizado na empresa metalomecânica Epedal – Indústria de componentes metálicos S.A., que se dedica à produção de componentes para o sector automóvel. O presente trabalho teve como objetivo a identificação da origem de defeitos de soldadura por protuberâncias entre uma chapa de aço estampada (HX340LAD Zn100, com quatro protuberâncias produzidas por deformação plástica) e um bloco de aço (S355MC), ambos aços HSLA. O estudo efetuado teve como base o trabalho prévio realizado pela Epedal, que consistiu na alteração não sistemática de parâmetros do robot de soldadura até que o número de defeitos fosse diminuído. Neste trabalho estudou-se sobretudo o efeito da pressão e da intensidade de corrente aplicadas durante a soldadura. A caracterização consistiu na análise da forma das protuberâncias produzidas, antes e após aplicação da pressão, numa análise microestrutural das zonas soldadas, na sua caracterização mecânica através de microdureza Vickers (200 gf) e em ensaios mecânicos de arrancamento para avaliação da integridade estrutural das zonas soldadas. Uma tarefa nova consistiu na análise topográfica por microscopia ótica 3D através da técnica de variação de foco, das protuberâncias produzidas por deformação plástica da chapa metálica com 1,75 mm de espessura, antes e após a aplicação de pressão. Verificou-se que os topos das protuberâncias tal como produzidas não estavam centrados com a base circular das mesmas. Após a aplicação de pressão (2,5 bar, 4,5 bar e 6,0 bar) resultam áreas de contacto entre as quatro protuberâncias da chapa e o bloco de 5,09 mm2, 11,66 mm2 e 19,76 mm2, respetivamente. As pressões efetivas de contato foram obtidas após calibração da força aplicada com uma célula de carga. Conclui-se que no início da aplicação da corrente a tensão compressiva de contacto (1,07, 1,39 e 1,87 GPa) diminui com o aumento da pressão aplicada pela máquina, pois há maior deformação plástica da protuberância. Verificou-se também que as áreas de cada protuberância também não são iguais entre si, o que indica que durante a sua produção não se garantiu uma altura uniforme das mesmas. Foram realizadas várias soldaduras com intensidades de corrente de 17,5 kA, 35 kA e 44 kA, obtendo-se valores de densidade de corrente inicial entre 1,77 kA/mm2 e 6,88 kA/mm2. Mediram-se as áreas da zona termicamente afetada (ZTA) e o comprimento das mesmas, de acordo com o controlo de qualidade exigido pelo cliente. Através da análise microestrutural foi possível observar que as amostras produzidas com menor densidade de corrente apresentam maior teor em martensite, enquanto as amostras produzidas com densidade de corrente de 3,77 kA/mm2 e 6,88 kA/mm2 possuem mais austenite residual. A área da ZTA e o comprimento da união destas duas amostras são também as únicas que obedecem aos critérios mínimos do cliente das peças. Os perfis de microdureza mostram que estas duas amostras, tal como as restantes têm maior dureza nas zonas termicamente afetadas. As duas melhores amostras têm no entanto valores máximos na zona de fusão menores (~250 HV0.2) do que as restantes (~350 HV0.2), indicando que estas últimas terão uma soldadura mais frágil. Os ensaios de arrancamento mostraram que apenas as duas amostras com densidade de corrente de 3,77 kA/mm2 e 6,88 kA/mm2 obedecem inteiramente aos critérios de qualidade do cliente, o que não acontece com os parâmetros atuais da empresa. Chegou-se então à conclusão que a causa da falta de qualidade das peças soldadas ocorrida na Epedal estaria relacionada com a combinação inadequada de pressão de contacto e intensidade de corrente que resultariam em valores demasiado baixos de densidade de corrente. A geometria não uniforme das protuberâncias origina também densidades de corrente diferentes em cada protuberância, o que poderá resultar em protuberâncias com uma boa união com o bloco e outras sem qualquer transferência de material, numa mesma peça, agravando ainda mais o problema. Desta forma recomendou-se à Epedal a correção da ferramenta de estampar, por forma a proporcionar uma uniformização das protuberâncias. Identificou-se como densidade de corrente mínima pra a obtenção de uma boa soldadura o valor de 3,77 kA/mm2, que pode ser conseguido com uma intensidade de corrente de 35 kA para um valor de pressão mínima de 2,5 bar. Esta poderá ser aumentada para garantir a deformação completa da protuberância, mas garantindo sempre o valor mínimo da densidade de corrente.
Energy efficiency gains and sustainability are the base of the development of materials with increased specific proprieties. This is the case for light alloys and high strength low alloy (HSLA) steels, which replaced conventional steels, with higher levels of alloy elements. In the automobile industry, HSLA steels are used in a large diversity of structural components that account for significant reduction of the weight and also of material costs. The production of this components several plastic forming and welding operations. For the latter defects may appear immediately or, in the worst scenario, only after the entry into service. It is thus fundamental to identify the contribution of each step of the process in the origin of the defect. The internship was performed in a metalworking company named Epedal - Indústria de componentes metálicos S.A., whose main products are components for the automotive industry. The objective of the work was to identify the origin of projection welding defects between a HSLA steel sheet (HX340LAD Zn100, with four projections) and another HSLA steel block (S355MC). The study was performed based on previous work done by Epedal, which consisted on a non-systematic change of the robot’s welding parameters until the number of defects was reduced. In the present work the effect of pressure and current intensity applied during welding on the weld quality were assessed. The characterization consisted in the analysis of the shape of the projections produced before and after the application of pressure, a microstructural analysis of the welded areas, in the mechanical characterization by Vickers microhardness (200gf) measurements and by a mechanical pullout test for evaluating the structural integrity of the welded parts. A new task consisted in the topographical analysis by optical microscopy 3D using focus variation technique, of the projections produced by plastic deformation of the metal plate 1,75 mm thick before and after application of pressure. It was found that the tops of the projections produced were not centered with their circular base. After the application of pressure, 2,5 bar, and 4,5 bar 6,0 bar, the resulting contact areas between the four projections of the plate and the block are 5,09 mm2, 11,66 mm2 and 19,76 mm2, respectively. The effective contact pressures were obtained after calibration of the forces with a load cell. It was concluded that, just before current application, the actual contact pressure (1,07, 1,39 and 1,87 GPa) decreases with the increasing of the pressure applied by the machine, as there is a larger plastic deformation of the projections. It was also found that the areas of each projection are also not equal, which indicates that the stamping does not ensure neither the centering nor uniform height of the four projections. Several welding tests were carried out with current intensities of 17,5 kA, 35 kA and 44 kA, for initial current density values between 1,77 kA/mm2 and 6,88 kA/mm2. The areas of the heat affected zone (HAZ) and the joint length were measured, according to the quality control required by the customer. Through microstructural analysis it was observed that the samples produced with lower current density have a higher content of martensitic phase, while the samples produced with current density of 3,77 kA/mm2 and 6,88 kA/mm2 have more retained austenite. The area of the HAZ and the joint’s length of these two samples are also the ones that meet the minimum criteria of the customer’s requirements. Microhardness profiles showed that these samples, as well as the others, are harder in the heat affected zones. However this two samples have lower (~ 250 HV0,2) maximum values than the others (~ 350 HV0,2) in the melting zone, indicating that the latter weldings will be more brittle. The pullout tests showed that only two samples with current density of 3,77 kA/mm2 and 6,88 kA/mm2 fully satisfy the customer's quality criteria, which does not happen with the actual parameters used by the company. Finally, it can be concluded that the lack of quality of these welded parts at Epedal was related to an inadequate combination of contact pressure and current intensity that would result in too low values of current density. The non-uniform geometry of the projections also creates different current densities on each projection. So, in the same part, some projections may have a good bond with the block while for others there is no transfer of material, which can further worsen the problem. It was thus recommended to Epedal the correction of the geometry of the stamping tool in order to provide uniform projections. The minimum current density of 3,77 kA/mm2 was established for obtaining a good welding. This can be achieved with a current intensity of 35 kA for a minimum pressure value of 2,5 bar. The pressure can be increased to ensure complete deformation of the projection, but always guaranteeing the minimum value of the current density.

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Busso, Nicolangelo Del. "Caracterização microestrutural e mecânica em juntas soldadas por arco submerso em chapas de aço microligado API 5l x70 utilizadas em minerodutos." Universidade Presbiteriana Mackenzie, 2016. http://tede.mackenzie.br/jspui/handle/tede/1365.

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The present work investigates the possible changes that occur in the mechanical properties and microstructure of welded joints through the process of submerged arc in steel plates High Strength Low Alloy (HSLA) type API 5L X70, used in pipelines. These are usually constructed starting from calendered plates and welded through submerged arc process, forming 600 mm diameter pipes, with 12 m long. To reproduce faithfully the pipes manufacturing processes, for further characterization of test bodies were produced, welding plate supplied by USIMINAS, through the submerged arc welding, and withdrawing samples to perform the characterization of the regions of the weld metal (WM), the heat affected zone (HAZ) and the base metal (BM). Conventional tensile and Charpy V-Notch were performed to determine mechanical and impact properties of the tested materials, as well as macrograph tests and Optical microscopy (OM) and weld metal (WM), the heat affected zone (HAZ) and the base metal (BM). The metallographic examination showed banded microstructure consisting of polygonal ferrite, pearlite and bainite with small grain size. The results showed increased strength and hardness influenced by the presence of acicular ferrite. The fractography analysis after impact tests revealed ductile-brittle behavior. Impact tests were performed at temperatures of 0°C and -20°C, which exhibited significant toughness decrease, that is 260J to 202J for the BM, 106J to 81J for HAZ and 25J to 19J to the WM, while the Vickers hardness testing (HV10) was increased from the fusion zone to the base metal (194HV for WM, 202 HV for HAZ and 218 HV for BM).
O presente trabalho investiga as alterações que ocorrem nas propriedades mecânicas e na microestrutura em juntas soldadas por Arco Submerso, em chapas de aço ARBL (Alta Resistência e Baixa Liga) tipo API 5L X70, utilizadas em tubos de minerodutos. Estes são geralmente construídos a partir de chapas calandradas e soldadas de topo, pelo processo de Arco Submerso, formando tubos com diâmetro de cerca de 600mm, por 12 metros de comprimento. Objetivando reproduzir fidedignamente o processo de fabricação dos tubos, foram produzidos corpos de provas, soldando-se, pelo processo arco submerso, chapas fornecidas pela USIMINAS, e, destas foram retiradas amostras para se efetuar a caracterização das soldas, nas regiões da zona fundida (ZF), da zona termicamente afetada (ZTA), e do material base (MB). Foram efetuados os ensaios mecânicos de tração, dureza, dobramento e impacto, bem como a caracterização por macrografia e microscopias, ótica (MO) e de varredura (MEV). O exame metalográfico apresentou microestrutura bandeada, consistindo de ferrita poligonal, perlita e bainita com pequeno tamanho de grão. Os resultados obtidos mostraram o aumento da resistência mecânica e da dureza, influenciados pela presença de ferrita acicular. As análises fratográficas, após ensaios de impacto revelaram comportamento ductil-frágil. Os ensaios de impacto foram realizados às temperaturas de 0ºC e de -20ºC, onde apresentaram quedas significativas da tenacidade na região da solda, decrescendo da região do metal base (260J e 202J) para a zona termicamente afetada (106J e 81J) e para a zona fundida (25J e 19J), respectivamente, para 0ºC e -20ºC. Os resultados dos ensaios de dureza Vickers (HV10) apresentaram um ligeiro aumento da dureza, crescendo no sentido MB-ZTA-ZF (194 HV, 202 HV e 218 HV, respectivamente).

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Cruz, Magnus Geder Henz. "Estudo da substituição de aço convencional por aço de baixa liga e alta resistência (BLAR) em módulo estrutural." reponame:Repositório Institucional da UCS, 2006. https://repositorio.ucs.br/handle/11338/136.

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Foram estudados dois tipos de aços, aço convencional ZAR 230 (ZAR - Zincagem de alta resistência) e aço microligado ZSTE 380 (segundo norma SEW 093), sendo que foram avaliadas as suas propriedades mecânicas visando a substituição do aço convencional por aço microligado na estrutura tubular de uma carroceria para veículos de transporte coletivo de passageiros. O aço convencional vem sendo utilizado pela indústria de carrocerias há vários anos, já o aço microligado é utilizado basicamente em estruturas específicas que requeiram boas propriedades mecânicas e conseqüentemente redução de peso. A análise de viabilidade para a substituição de aço convencional por aço microligado em um módulo estrutural completo requereu uma série de ensaios: ensaios padronizados em laboratório foram executados para avaliação de suas principais propriedades mecânicas e químicas; ensaios de nós estruturais submetidos a uma carga forneceram informações para o uso em software de elementos finitos tanto para execução de cálculos estruturais, quanto para calibração de resultados. Os módulos estruturais foram preparados de acordo com as regulamentações ECE R66-00 (mercado europeu) e CONTRAN 811/96 (mercado brasileiro) e foram ensaiados exaustivamente até se obter o melhor resultado de deslocamento comparativamente aos dois materiais analisados. A validação da estrutura tubular foi obtida com a utilização do software Ansys Workbench 9.0 e a confecção de estrutura representativa de uma carroceria ensaiada conforme regulamentação CONTRAN 811/96.
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Two kinds of steel were studied, conventional steel ZAR 230 (a standard for high strength galvanizing) and microalloyed steel ZSTE 380 (according to the regulation SEW 093). The study of its mechanical properties aimed to replace the steel for microalloyed steel in bodywork s tubular structure for collective transport vehicles of passengers. The conventional steel has been used for the bodywork industry for years, and the microalloyed steel is basically used in specific structures, those who require good mechanical properties and mass reduction. The analysis of the feasibility for the replacement of conventional steel for microalloyed steel in a complete structural model requires a series of tests. Lab tests were done to evaluate their main mechanical and chemical properties. The tests of the structural nodes and the structural behaviour when subjected to a load provided information to be used in the finite elements method software to do structural calculation and to calibrate the results. The structural modules were prepared according to the regulations ECE R66-00 (European market) and CONTRAN 811/96 (Brazilian market) and these modules were tested exhaustively to achieve the best displacement between the two materials that were analysed comparatively. The validation of the tubular structure was obtained using the software Ansys Workbench 9.0 and the production of the representative structure of a bodywork tested according the regulation CONTRAN 811/96.

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Wynn, C. L. "Vanadium and niobium high strength low alloy steels for light gauge high strength strip." Thesis, Swansea University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636700.

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This thesis details the research work undertaken during the course of study for the Engineering Doctorate degree. The work is in the form of project which aims to develop knowledge about the rolling characteristics and properties of high strength low alloy (HSLA) steels with both singular and dual additions of niobium and vanadium. This aim has been achieved through extensive laboratory hot rolling studies of a range of steel compositions, mechanical testing and metallographic examination as well as detailed analysis of data recorded during the laboratory hot rolling process to determine mean flow stresses during the laboratory hot rolling process. The results highlight the occurrence of a temperature of non recrystallisation in the niobium grades and determine the necessary levels of vanadium required to obtain comparable properties to niobium based HSLA steels. Vanadium based HSLA steels could be used to slightly extent the gauge width matrix compared to existing niobium based HSLA steels. For higher strength products the effects of dual additions of niobium and vanadium at high, medium and low levels are observed and taking the properties, processability and cost into account suggested optimum combinations are highlighted.

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Donohoe, C. J. "Corrosion fatigue of a high strength low alloy steel." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322985.

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Punch, Rachel Bridget. "Toughness enhancement of high strength low alloy strip steels." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5143/.

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High strength strip steels with a yield strength of ~700 MPa are used in the yellow goods industry, with recent trends requiring thicker strips with an improved toughness. Strip steel was produced to thicknesses of 10 – 17 mm, with thinner strips showing improved Charpy impact toughness compared to the thicker strip. It was found that all samples (different thicknesses and test orientations) showed splits on the fracture surfaces in the upper transition region. The hot rolled strip steels showed a predominantly fine-grained (~4 µm ECD) ferrite microstructure, with some coarse grain patches (grains ≥5 µm grouped together). No significant differences were noted for the grain size, yield stress, tensile strength, hardness and texture for the different compositions. Splits were characterised and produced successfully by low blow Charpy testing with acoustic emission (AE) sensors indicating the presence of splits which occurred in the upper transition region predominantly without main crack propagation. Analysis by x-ray tomography and sectioning was carried out showing splits propagate by transgranular cleavage, preferentially following coarse-grained regions, with the 10 mm strip producing deeper splits which was related to elongated grains (high aspect ratio). Therefore the presence of deep splits improved toughness through a reduction of the impact transition temperature, which was achieved by ensuring the presence of a bimodal grain structure, containing coarse elongated grain patches.

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Wrigley, Nigel Stuart. "The fracture characteristics of a boron containing high strength low alloy steel." Thesis, University of Salford, 1994. http://usir.salford.ac.uk/43037/.

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This study is concerned with the fracture characteristics of RQT 701; a possible contender for the replacement of HY 100, the existing 690MNm-2 (100,000psi) strength level Naval quality steel. RQT 701 is a low nickel, boron containing quenched and tempered steel which is less expensive than HY 100 due to a lower nickel content. The hardenability is maintained by the boron addition. The preliminary testing of RQT 701 showed a variation in the impact transition temperature through the thickness of the plate. This study examines the possible causes of this variation in impact properties and makes a full assessment of the mechanical properties of RQT 701. A full metallographic investigation has been carried out using quantitative metallography, scanning electron microscopy and transmission electron microscopy. The effect of heat treatment on the steel's hardenability and mechanical properties has been studied so that suggestions to produce optimum properties of RQT 701 could be made. A full fractographic study has also been undertaken. The relationship between fracture characteristics, microstructure and hardenability has been discussed. A parallel investigation of HY 100 plate has been carried out. A comparison between the microstructures and fracture properties has been made and the relative merits of the two steels discussed.

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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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Laws, Paul. "Corrosion fatigue performance of welded high strength low alloy steels for use offshore." Thesis, Cranfield University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359541.

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15

Chen, Jhewn-Kuang. "Effects of alloying elements upon austenite decomposition in high strength low alloy steels." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-10102009-020227/.

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16

Pereira, Thiago Soares. "Bauschinger effect in macro and micro sized high strength low alloy pipeline steels." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7265/.

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The Bauschinger effects in X70, X80 and X100 high strength low alloy pipeline steels were presented. The microstructure of the as-received alloys was characterized. A variety of microstructures was present across the different alloys, ranging from a refined granular ferrite with small amounts of perlite to a bainitic structure containing martensite/austenite islands, retained austenite and small cementite constituents along with a small amount carbides. Similarly, the dislocation structures varied from homogeneously distributed across the ferrite grains to clusters/walls of dislocations. Mechanical tests on macro and micro sized samples were carried out up to 1% and 2% plastic strains. A micro-device for Bauschinger test was designed and manufactured using micro-electro-mechanical-system (MEMS) technology and was incorporated onto a FIB/SEM in order to prepare the micro sized samples and perform the micro Bauschinger tests. The Bauschinger stress parameter showed that the Bauschinger effect becomes more obvious in samples with higher yield strength and also with increasing pre-strain. In addition, the Bauschinger effect remained similar on the samples of different sizes in the current study. The results indicate that the cause of the early yielding during reverse loading of these alloys is dominated by the dislocation-dislocation interaction.

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17

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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18

Coimbatore, Dhandayuth Venkatesh. "Cerium chloride inhibition for high strength low alloy steel exposed to sulphide polluted seawater." University of Western Australia. School of Mechanical Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0134.

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[Truncated abstract] Corrosion of steel structures caused by sulphide is a common engineering problem encountered by many industries, such as the petroleum, chemical processing, mining and mineral processing industries. The control of sulphide corrosion is still a controversial topic among corrosion engineers. There is an absence of guideline for a reliable acceptable limit of sulphide level in service and each processing industry has its own empirical values. Selection of inhibitors in the sulphide environment depends on laboratory testing before its actual application in pipelines and reaction vessels. Many investigators have postulated the corrosion mechanisms due to sulphide based on operating envelopes such as pH, chloride, manganese, hydrogen sulphide, sulphate reducing bacteria levels and inhibitor concentration. It is recommended in the literature that the batch dosing of inhibitor and biocide needs to be evaluated in regards to sulphide reducing bacteria (SRB) level, which may produce sulphide concentrations up to 2000 ppm. Although sulphide scale formation may protect the base metal by providing a physical barrier, the detrimental effects of sulphide are often inevitable, such as stress corrosion cracking, hydrogen embrittlement, etc. Currently, there are many chemicals that are used as inhibitors to prevent corrosion by scavenging the sulphide from the environment. Cerium, a rare-earth element, is not used as inhibitor in the sulphide environment. Also, there are no previous research findings on the effects of compounds of rare-earth metals, such as cerium chloride (CeCl3), in sulphide environment. This research examines the corrosion behaviour of 0.4Mo-0.8Cr steel, a High Strength Low Alloy (HSLA) steel, in sulphide-polluted artificial seawater with the addition of CeCl3 and glutaraldehyde. ... It is postulated that the moderate inhibiting effect of CeCl3 is due to the scavenging effect thereby forming Ce2S3 complex. Further reaction of sulphide with steel resulted in ferrous sulphide, leading to an increased corrosion rate. It is also concluded that the CeCl3 interferes with both anodic and cathodic reactions in deaerated conditions. Addition of glutaraldehyde in the sulphide-polluted seawater was found to decrease the corrosion rate. According to the electrochemical measurements conducted, the concurrent addition of glutaraldehyde and CeCl3 appeared to have an added effect on reducing the corrosion of the steel, as evidenced by the increase of the open circuit potential during the short-term testing. From the weight loss measurements after 60 days, sulphide pollution in deaerated seawater was found to increase corrosion rate. This is attributed to the increase of sulphide activity whereby continual dissolution of steel was encountered. From the weight loss tests, it was found that the addition of CeCl3 and glutaraldehyde reduced the corrosion rate of the steel in the solutions containing 0-10 ppm sulphide. There is no noticeable corrosion rate decrease for the solution containing 100 ppm sulphide. The added effect of CeCl3 and glutaraldehyde to the SRB medium has resulted in lower corrosion rates. Further detailed experimentation is required to elucidate the corrosion reduction mechanism in glutaraldehyde-containing environments.

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19

Needham, William Donald. "Stress corrosion cracking and hydrogen embrittlement of thick section high strength low alloy steel." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/10945/22123.

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An experimental study was conducted to evaluate the corrosion performance of weldments of a high strength low alloy(HSLA) steel in a simulated seawater environment. This steel, designated HSLA80, was developed by the United States Navy for use in ship structural applications. Stress corrosion CRACKING(SCC) and hydrogen embrittlement(HEM) were investigated by conducting 42 Wedge-Opening load(WOL) tests as a function of stress intensity and corrosion potential and 33 Slow Strain Rate(SSR) tests as a function of strain rate and corrosion potential. The corrosion potentials were chosen to simulate the environmental conditions of free corrosion, cathodic protection and hydrogen generation. The results from this investigation indicated that HSLA 80 base metal and weldments were susceptible to hydrogen assisted cracking(HAC) in a seawater environment under conditions of continuous plastic deformation and triaxial stress in the presence of hydrogen. The heat-affected zone of the weldment was found to be the most susceptible portion of the weld joint. A lower bound was established for the critical stress intensity for stress corrosion cracking for HSLA 80 base metal and weldments.(Theses)

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20

Schroth, James Gregory. "Combined mode I - mode III fracture toughness of a high-strength low-alloy steel /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260859496482.

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21

Almansour, Mansour A. "Sulfide stress cracking resistance of API-X100 high strength low alloy steel in H2S environments." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/267.

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Sulfide Stress Cracking (SSC) resistance of the newly developed API-X100 High Strength Low Alloy (HSLA) steel was investigated in the NACE TM0177 "A" solution. The NACE TM0177 "A" solution is a hydrogen sulfide (H2S) saturated solution containing 5.0 wt.% sodium chloride (NaC1) and 0.5 wt.% acetic acid (CH3COOH). The aim of this thesis was to study the effect of microstructure, non-metallic inclusions and alloying elements of the X100 on H2S corrosion and SSC susceptibility. The study was conducted by means of electrochemical polarization techniques and constant load (proof ring) testing. Microstructural analysis and electrochemical polarization results for X100were compared with those for X80, an older generation HSLA steel. Uniaxial constant load SSC testing was conducted using X100 samples and the results were compared with those reported for older generation HSLA steels. Addition of H2S to the NACE TM0177 "A" solution increased the corrosion rate of X100from 51.6 to 96.7 mpy. The effect of H2S on the corrosion rate was similar for X80. The corrosion rate for X80 increased from 45.2 to 80.2 mpy when H2S was added to the test solution. Addition of H2S enhanced the anodic kinetics by forming a catalyst (FeHSads) on the metal surface and as a result, shifted the anodic polarization curve to more current densities. Moreover, the cathodic half cell potential increased due to the decrease in pH, from 2.9 to 2.7, which shifted the cathodic polarization curve to more current densities. The increase in both the anodic and cathodic currents, after H2S addition, caused the rise in the corrosion current density. In H2S saturated NACE TM-0177 "A" solution, the X100 steel corrosion rate was higher than the X80 steel by 20%. Longer phase boundaries and larger nonmetallic inclusions in the X100 microstructure generated more areas with dissimilar corrosion potentials and therefore, a stronger driving force for corrosion. Higher density of second phase regions and larger nonmetallic inclusions acted as an increased cathode area on the X100 surface which increased the cathodic current density and consequently, increased the corrosion current density. Proof ring tests on the X100 gave a threshold stress value, C5th, of 46% YS, 343.1 MPa(49.7 ksi). The main failure was caused by SSC cracking. SSC nucleated at corrosion pits on the metal surface and microcracks in the metal body and propagated perpendicular to the applied stress. Hydrogen Induced Cracking (HIC) was observed in the X100. HIC cracks nucleated at banded martensite-ferrite interfaces and propagated along the rolling direction parallel to the applied tensile stress through the softer ferrite phase. When compared to older HSLA grades, the X100 tested in this study had a high SSC susceptibility and therefore, is not be recommended for H2S service applications. The high X100 SSC susceptibility was caused by the material high corrosion rates in H2Smedia which formed corrosion pits that acted as crack initiation sites on the metal surface and provided more hydrogen that migrated into the steel. In addition, the X100 inhomogeneous microstructure provided a high density of hydrogen traps in front of the main crack tip which promoted SSC microcrack formation inside the metal. Microcracks in the metal body connected with the main crack tip that originated from corrosion pits which assisted SSC propagation.

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22

Liew, Heng Lee Henry. "Quantifying the economic and commercial potential of a high strength, low thermal coefficient super-alloy." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45387.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.
Includes bibliographical references (p. 54-55).
Inspired by the importance of having a favourable sheathing material for superconducting wires, a high-strength, low thermal coefficient (CTE) super-alloy has been developed. Known as Incoloy 908, this super-alloy's material properties have been extensively studied, and various mechanical, thermal, magnetic, and elastic properties of it have been researched for many years. In the pursuit of broader applications for this superior alloy, this project seeks to identify the most profitable and realistic applications where the fundamental advantages of this technology, due to its unique combination of properties relative to competitors, can create value and be commercialised. This work seeks to quantify the potential value of Incoloy-908 to the market, and on this basis, explore business strategies in which the value of the technology could be realised. The quantitative values assigned to the selected application as a saw blade in saw mills is optimistic in the perspective of the saw mill owner. However, business strategies to realise the potential value through start-up companies are challenging with long investment horizons. Recommendations for future work include developing a more refined estimate of the production costs, and exploring alternative business plans in the context of adopting the technology as an existing manufacturer.
by Heng Lee Henry Liew.
M.Eng.

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23

Haji, Hasan Abdalla. "An analysis of microstructure and crystallographic texture in friction stir welded high strength low alloy steel." Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589542.

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24

Millar, Peter G. "Corrosion fatigue crack propagation behaviour of a high strength low alloy steel in a synthetic sea water environment." Thesis, Cranfield University, 1986. http://dspace.lib.cranfield.ac.uk/handle/1826/4443.

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The corrosion fatigue crack propagation behaviour of a high strength low alloy steel, N-A-XTRA 70, in a synthetic sea water solution was tested using S. E. N. specimens subjected to a loading frequency of 0.1 Hz and a load ratio of 0.6. In order to simulate the conditions encountered by a thumbnail type crack several specimens from each of the microstructural types tested, namely parent plate, heat affected zone and heat treated material, had their crack sides covered by transparent plastic covers. Severe overprotection and slight underprotection conditions were produced using cathodic protection potentials of -1400, -1300, -1200 and -700 mV (S. C. E. ). The Paris relationship da/dN = CLKm was found to be a useful tool in describing the crack propagation rate data. Results obtained, presented in the form of plots of log da/dN against log AK, show that for parent plate, H. A. Z. and heat treated material, covering the crack sides of specimens produces enhanced corrosion fatigue crack propagation rates, at cathodic protection potentials of -1400 and -1300 mV (S. C. E. ), when compared to non covered specimens. This trend was also true for H. A. Z. specimens at a potential of -700 mV (S. C. E. ). For parent plate specimens, however, covering the crack sides at a potential of -700 mV (S. C. E. ) produced reduced crack propagation rates over non covered specimens. It is believed restriced oxygen access may account for these results. Plots of the Paris exponent m and constant C for the three microstructures tested produced three lines of the form m= alnC +b where a and b were found to be dependent upon material parameters. Comparison of results with BS 4360: 50D revealed that N-A-XTRA 70 exhibited superior fatigue performance when tested in air but behaved worse under conditions of free corrosion.

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25

Kilgallon, P. J. "The effect of sulphate reducing bacteria on the hydrogen absorption of cathodically protected high strength low alloy steel." Thesis, Cranfield University, 1994. http://dspace.lib.cranfield.ac.uk/handle/1826/7253.

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The hydrogen embrittlement of two HSLA steels was studied in conditions typical of the marine environment. Double cantilever beam specimens, heat treated to produce the microstructure in the heat affected zone of a weld, were tested in seawater containing sulphate reducing bacteria (SRB) over a range of cathodic protection (CP) potentials and the threshold stress intensities ([Threshold Stress Intensity]) were recorded. The hydrogen concentration absorbed by the steel ([Surface Hydrogen Concentration]) was measured and shown to be higher at more negative CP potentials and significantly increased when SRB were present. An inverse relationship was established between log [Threshold Stress Intensity] and [Surface Hydrogen Concentration]. It was concluded that crack propagation occurs by a single mechanism whether or not SRB are present. Three point bend specimens of both steels were machined from welded plate. Corrosion fatigue tests were carried out in seawater with and without SRB. The presence of active SRB caused increased crack growth rates. Sediment samples were collected from the River Mersey and the base of a North Sea platform. In addition, SRB were added as an inoculum to artificial seawater. SRB numbers were enumerated and their activities assessed by measuring the concentrations of sulphide generated. Hydrogen permeation tests were performed on steel held at a range of CP potentials and exposed to each environment. Measurements were also carried out in seawater containing chemically prepared sulphides. Hydrogen absorption was shown to be enhanced when SRB were present and to be related to the total sulphide (TS) concentration in the environment. High hydrogen concentrations were produced by chemically prepared sulphides and the nature and thickness of the sulphide film appeared to be important in determining the extent of hydrogen absorption. Chemically produced sulphide gave sustained levels of absorbed hydrogen, but those generated biogenically decayed rapidly unless the TS concentration was maintained in the solution.

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26

Drury, J. A. "An investigation into the fatigue and corrosion fatigue properties of two high strength low alloy steels and their HAZ's." Thesis, Cranfield University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332936.

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27

Alwaranbi, Maslat S. "Chloride pitting corrosion of API X-80 and X-100 high strength low alloy pipeline steels in bicarbonate solutions." Thesis, University of British Columbia, 2006. http://hdl.handle.net/2429/31557.

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The corrosion polarization behaviors of API X-80 (550 Grade) and API X-100 (690 Grade) pipeline steels in bicarbonate/chloride media were investigated by means of electrochemical techniques. In bicarbonate free chloride containing solutions, both steels revealed practically similar polarization behaviors exhibiting active/passive transitions with a varying number of distinct oxidation peaks. The bicarbonate concentration increase in the solutions was found to expand the passive potential region and result in more noble breakdown potentials. In contrast, the addition of small amounts of chloride ions evidently influenced the shape of the polarization curves where the corrosion rates were increased, the passive potential regions were narrowed in width, and the pitting potentials were shifted in the negative direction. The corrosion characteristics under the same prevailing experimental conditions of both steels indicated that API X-100 steel grade had lower corrosion rates in all tested bicarbonate solutions with and without the presence of chloride ions and better pitting corrosion resistance for the range of chloride concentrations investigated. This may have been attributed to the higher alloying content of molybdenum, nickel and copper in API X-100 steel over API X-80 grade and accordingly in the variance of the final microstructure formed for both steels which in turn could have made a change in the thickness and the protectiveness of the passive layers formed on the surfaces of the steels. Pitting morphology features such as the average diameter and density of active pits were examined by the Scanning Electron Microscopy (SEM). SEM observations showed that solutions of low bicarbonate concentrations (0.01 and 0.05M) resulted in a comparatively bigger size of pits, while solutions of higher bicarbonate concentrations (0.1 and 0.5M) showed no pits. This major difference may be due to the more stable passive films produced on the steel surfaces having higher bicarbonate concentrations. On the other hand, pit morphology as examined by the SEM technique for the bicarbonate solutions consisting of different concentrations of chloride ions indicated that the density and the average diameter of the stable corrosion pits increased with increasing the chloride concentrations in the test solutions.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

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28

Abosbaia, Alhadi Amar Salem. "Design and processing of low alloy high carbon steels by powder metallurgy : P/M processing and liquid phase sintering of newly designed low-alloy high carbon steels based on Fe-0.85Mo-C-Si-Mn with high toughness and strength." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4857.

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The work presented has the ultimate aim to increase dynamic mechanical properties by improvements in density and optimisation of microstructure of ultra high carbon PM steels by careful selection of processes, i.e. mixing, binding, alloying, heating profile and intelligent heat treatment. ThermoCalc modelling was employed to predict liquid phase amounts for two different powder grades, Astaloy 85Mo or Astaloy CrL with additive elements such as (0.4-0.6wt%)Si, (1.2-1.4wt%)C and (1-1.5wt%)Mn, in the sintering temperature range 1285-1300ºC and such powder mixes were pressed and liquid phase sintered. In high-C steels carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat-treated. To assist the breaking up of these continuous carbide networks, 0.4-0.6% silicon, in the form of silicon carbide, was added. The water gas shift reaction (C + H2O = CO + H2, start from ~500ºC) and Boudouard reaction (from ~500ºC complete ~930ºC) form CO gas in the early part of sintering and can lead to large porosity, which lowers mechanical properties. With the use of careful powder drying, low dew point atmospheres and optimisation of heating profiles, densities in excess of 7.70g/cm3 were attained. The brittle microstructure, containing carbide networks and free of cracks, is transformed by intelligent heat treatment to a tougher one of ferrite plus sub-micron spheroidised carbides. This gives the potential for production of components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains of up to 16 % were attained. Forging experiments were subsequently carried out for spheroidised specimens of Fe-0.85Mo+06Si+1.4C, for different strain rates of 10-3, 10-2, 10-1 and 1sec-1 and heated in argon to 700ºC, density ~7.8g/cm3 and 769 MPa yield strength were obtained.

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29

Abosbaia, Alhadi A. S. "Design and processing of low alloy high carbon steels by powder metallurgy. P/M processing and liquid phase sintering of newly designed low-alloy high carbon steels based on Fe-0.85Mo-C-Si-Mn with high toughness and strength." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4857.

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The work presented has the ultimate aim to increase dynamic mechanical properties by improvements in density and optimisation of microstructure of ultra high carbon PM steels by careful selection of processes, i.e. mixing, binding, alloying, heating profile and intelligent heat treatment. ThermoCalc modelling was employed to predict liquid phase amounts for two different powder grades, Astaloy 85Mo or Astaloy CrL with additive elements such as (0.4-0.6wt%)Si, (1.2-1.4wt%)C and (1-1.5wt%)Mn, in the sintering temperature range 1285-1300ºC and such powder mixes were pressed and liquid phase sintered. In high-C steels carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat-treated. To assist the breaking up of these continuous carbide networks, 0.4-0.6% silicon, in the form of silicon carbide, was added. The water gas shift reaction (C + H2O = CO + H2, start from ~500ºC) and Boudouard reaction (from ~500ºC complete ~930ºC) form CO gas in the early part of sintering and can lead to large porosity, which lowers mechanical properties. With the use of careful powder drying, low dew point atmospheres and optimisation of heating profiles, densities in excess of 7.70g/cm3 were attained. The brittle microstructure, containing carbide networks and free of cracks, is transformed by intelligent heat treatment to a tougher one of ferrite plus sub-micron spheroidised carbides. This gives the potential for production of components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains of up to 16 % were attained. Forging experiments were subsequently carried out for spheroidised specimens of Fe-0.85Mo+06Si+1.4C, for different strain rates of 10-3, 10-2, 10-1 and 1sec-1 and heated in argon to 700¿C, density ~7.8g/cm3 and 769 MPa yield strength were obtained.
Libyan Education Ministry Office

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30

Wei, Lingyun 1972. "Investigating correlations of microstructures, mechanical properties and FSW process variables in friction stir welded high strength low alloy 65 steel /." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3195.pdf.

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31

Wei, Lingyun. "Investigate Correlations of Microstructures, Mechanical Properties and FSW Process Variables in Friction Stir Welded High Strength Low Alloy 65 Steel." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2032.

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The present study focuses on developing a relationship between process variables, mechanical properties and post weld microstructure in Friction Stir Welded HSLA 65 steel. Fully consolidated welds can be produced in HSLA 65 steel by PCBN Convex-Scrolled-Shoulder-Step-Spiral (CS4) tool over a wide range of parameters. Microstructures in the nugget center (NC) are dominated by lath bainite and a few polygonal/allotriomorphic grain boundary ferrites. FSW dependent variables are related to FSW independent variables by non-linear relationship. Heat input is identified to be the best parameter index to correlate with microstructures. With increasing heat input, the volume of bainite is reduced, the shape of bainite is more curved and grain/lath size become coarser. A linear relationship was established between heat input and semi-quantitative post-weld microstructures based on the optical microstructures. Further analysis has been applied on the NC to obtain more fundamental understanding of FSW. The new approach via Orientation Imaging Microscopy (OIM) was developed to acquire quantitative microstructural data including bainite lath/packet and prior austenite grain size (PAG). A linear relationship between heat input and quantitative microstructural features in the NC have been established. Mechanical properties exhibits linear relationship with heat input. These correlations can be utilized to determine FSW weld parameter to get desired mechanical properties welds.

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32

Talbot, Diane. "The effects of plate processing parameters on the microstructure, mechanical properties and precipitation characteristics of niobium-containing high strength low alloy steels." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251877.

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33

Trippner, Ian George. "The effect of thermo-mechanical treatments on the micro-structure and mechanical properties of high strength low alloy steels micro-alloyed with vanadium." Thesis, University of Canterbury. Mechanical Engineering, 1990. http://hdl.handle.net/10092/6467.

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A series of vanadium micro-alloyed high strength low alloy steels were tested to evaluate the effect thermo-mechanical treatments had on their mechanical properties. The properties under consideration were the mechanical strengths and strain ageing propensity, as defined by the standard tensile test, and the fracture mode transition temperature, as defined by the Charpy impact test. Ferrite grain size was also evaluated, as was the portion of the interstitial nitrogen in the steel which was present in the form of a micro-alloy precipitate. Cooling rate was found to be the most significant factor in determining the ferrite grain size of the steel. Steel chemistry was found to be the primary factor in determining precipitation strengthening, this being independent of thermo-mechanical history. Carbon rich vanadium carbo-nitride precipitates in the steel were found to coarsen more rapidly than nitrogen rich precipitates, and a vanadium to nitrogen atomic ratio of less than 2:1 was, therefore, required to avoid loss of precipitation strengthening as a result of this effect. The effect of vanadium carbo-nitride precipitates on the fracture mode transition temperature of the steel was found to be essentially independent of cooling rate. It was dependent on the vanadium concentration of the steel, and on whether the carbo-nitride precipitates were coherent or non-coherent with the ferrite lattice. Strain ageing was found to be significantly reduced (less than 15 MPa) if the atomic ratio of vanadium to nitrogen was greater than 1.8:1. The fine precipitate present in the samples were found to be dissolved by standard acid dissolution nitrogen analysis techniques. As a result of this an alternate analysis technique was developed and shown to be more accurate in determining the concentration of nitrogen rich precipitates in the steel samples.

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34

Malheiros, Livia Cupertino. "Study of Structure, Hydrogen Diffusion and Trapping, Plasticity and Fracture towards the Comprehension of Hydrogen-Assisted Cracking of High-Strength Low-Alloy Martensitic Steels." Thesis, La Rochelle, 2020. http://www.theses.fr/2020LAROS022.

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Le défi que représente le développement d'aciers pour oil country tubular goods (OCTG) avec une résistance mécanique de plus en plus élevée tout en maintenant une résistance suffisante au sulfide stress cracking (SSC) motive cette recherche vers une meilleure compréhension de la fragilisation par l'hydrogène des aciers martensitiques revenus faiblement alliés. La caractérisation structurale est réalisée par de multiples techniques,notamment le MEB-EBSD, le MET, la DSC, la DRX synchrotron et conventionnelle. Les résultats sont liés aux paramètres de diffusion et de piégeage provenant de la perméation électrochimique (EP) et de la spectroscopie de désorption thermique (TDS). Ils sont principalement examinés en termes de densité de dislocation, de concentration de lacune, de limite d'élasticité, de composition et de température de revenu pour dix aciers martensitiques. Des essais de traction, de charge-décharge et de relaxation des contraintes sont réalisés sans hydrogène, après pré-chargement et désorption de l'hydrogène, et sous flux d'hydrogène pour évaluer l'impact du piégeage et de la mobilité de l'hydrogène dans les interactions hydrogène-plasticité. Pour l'essai sous flux d'hydrogène, une cellule de perméation électrochimique est construite sur une machine de traction, ce qui permet de surveiller en continu le flux global d'hydrogène et la charge mécanique pendant l'essai de traction des éprouvettes entaillées et non entaillées. En faisant varier les géométries des entailles et les densités de courant de polarisation cathodique, nous avons testé la susceptibilité des aciers à la fissuration assistée par l'hydrogène sous différentes intensités de flux et de concentration d'hydrogène pour plusieurs états mécaniques. Les essais sur des échantillons pré-chargés ont révélé que l'hydrogène profondément piégé a un impact mineur sur le comportement mécanique et la rupture, tandis que l'hydrogène mobile entraîne une rupture fragile par quasi clivage aux surfaces d'entrée de l'hydrogène. Les résultats de l'essai de perméation sous charge de traction sont intégrés dans la modélisation par éléments finis (FEM). Les conditions macroscopiques et locales (issues de la FEM) pour le développement de la rupture par quasi-clivage assistée par l'hydrogène sont évaluées, ainsi que la sensibilité de ces conditions de seuil (contrainte, déformation plastique, flux et concentration d'hydrogène) à l’intensité de la polarisation cathodique appliquée
The challenge of developing steels for sour service oil country tubular goods (OCTG) with mechanical strengthhigher and higher maintaining a sufficient resistance to sulfide stress cracking (SSC) motivates this researchtowards a better understanding of the hydrogen embrittlement of low-alloy tempered martensitic steels. Structuralcharacterization is performed by multiple techniques including SEM-EBSD, TEM, DSC, synchrotron andconventional XRD. The results are related to diffusion and trapping parameters from electrochemical permeation(EP) and thermal desorption spectroscopy (TDS), being mostly discussed in terms of dislocation density, vacancyconcentration, yield strength, composition and tempering temperature for ten martensitic steels. Tensile, loadingunloadingand stress-relaxation tests are completed without hydrogen, after hydrogen pre-charging and desorption,and under hydrogen flux to evaluate the impact of hydrogen trapping and mobility on the hydrogen-plasticityinteractions. For the test under hydrogen flux, an electrochemical permeation cell is built on a mechanical testingmachine, which allows continuous monitoring of the global hydrogen flux and mechanical loading during thetensile test of notched and unnotched specimens. By varying the notch geometries and the cathodic polarizationcurrent densities, we tested the susceptibility of the steels to hydrogen-assisted cracking under various intensitiesof hydrogen flux and concentration for several mechanical states. Tests on pre-charged specimens revealed thatdeeply trapped hydrogen has a minor impact on the mechanical behavior and fracture, whereas mobile hydrogenleads to brittle quasi-cleavage fracture at the hydrogen entry surfaces. The permeation test under tensile loadingresults are incorporated into finite elements modelling (FEM). Macroscopic and local (from FEM) conditions forthe development of hydrogen-assisted quasi-cleavage fracture are evaluated, as well as the sensitivity of thesethreshold conditions (stress, plastic strain, hydrogen flux and concentration) to the severity of the applied cathodicpolarization

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Wolf, Jason. "INVESTIGATION OF CHIP-FORM AND TOOL-WEAR IN TURNING OF HARDENED AF9628 ALLOY UNDER VARIOUS COOLING AND LUBRICATION CONDITIONS." UKnowledge, 2019. https://uknowledge.uky.edu/ms_etds/10.

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Next generation defense and commercial applications for structural steels require new alloys that eliminate or reduce critical elements from their composition to lower cost and improve manufacturability, while maintaining or exceeding high strength and toughness requirements. A new alloy, denoted as AF9628, has recently been developed for this purpose and its manufacturing characteristics and the material response in component manufacturing must be fully understood. In the present study, hardened AF9628 alloy was turned with a coated carbide cutting tool under fixed cutting speed, feed rate, and depth of cut parameters. This work focuses on chip-form and tool-wear analysis to understand, for the first time with AF9628, these fundamental aspects of the turning process and their relationship to productivity and part quality. Current industry standard practice of flood-cooled machining for AF9628 was used during machining experiments. Dry, minimum quantity lubrication (MQL), and cryogenic machining were investigated as alternative cooling and lubrication conditions. High-speed imaging during AF9628 turning experiments provides a new insight into the chip formation process, while the use of optical microscopy and scanning white light interferometry allowed for further characterization of chip-form and tool-wear. Chip-form is favorable as short, arc-shaped chips with new tools under all of the tested cooling and lubrication conditions. As a result of rapid wear at the end of the tool-life in all of the experimental conditions, chip-form evolves to unfavorably long, snarled ribbon-like chips and the resultant cutting force increased by as much as 64% under flood-cooled conditions. Tool-wear types that were observed during experiments include a combination of nose wear, built-up edge, plastic deformation, and groove wear on the rake face. Due to the fixed cutting parameters and cutting tool selected for this study, which were designed for flood-cooled machining in a prior study, undesirable failure of the cutting tools under dry, MQL, and cryogenic machining occurred. Future work requires experimentation across a wider processing space, and with different cutting tools, to thoroughly evaluate alternative cooling and lubrication techniques for machining AF9628.

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Mezzomo, Tiago. "Estudo comparativo do efeito de diferentes arames de adição em juntas soldadas de aços de fase dupla no comportamento em fadiga por flexão." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/135006.

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Atualmente, no setor de máquinas agrícolas o uso de aços de alta resistência está começando a ganhar espaço e cada vez mais lembrado nos projetos estruturais; para atender as necessidades citadas acima e também para redução de emissão de poluentes. A utilização dos aços de alta resistência na indústria de implementos agrícolas está focada nos aços DP (Dual Phase), sendo este o objeto de estudo desta presente pesquisa. Este trabalho visa analisar o comportamento mecânico, priorizando a análise de resistência à fadiga em flexão de uniões soldadas através do processo de soldagem de metal de gás ativo (GMAW) utilizando dois tipos de arames como material de adição. Neste estudo foram utilizadas chapas metálicas de aços de alta resistência da marca DOCOL 1000 fabricado pela SSAB e os arames de adição fornecidos pela ESAB, sendo um usado largamente na indústria de maquinas agrícolas e o outro um fio especial desenvolvido para soldagem de aços de alta resistência e baixa liga. O processo de solda robotizada foi adotado para assegurar a homogeneidade dos cordões das juntas durante a obtenção das amostras. Para a análise das características mecânicas das amostras foi realizado o ensaio de flexão estático, caracterização macroestrutural, perfil de microdureza e ensaios de fadiga de flexão em quatro pontos. Os resultados mostraram que a vida em fadiga, por flexão em quatro pontos, nas juntas soldadas com o material de adição para aço carbono comum obteve uma melhor resposta em relação ao material de adição especial para soldagem de aços de alta resistência, porém pode-se verificar que ambas as curvas de fadiga respeitaram a curva de projeto conforme norma.
Nowadays, in the agricultural industry the use of high strength steels is being used each day more and more as well and increasingly coming in our mind in structural designs, to meet the requirements mentioned above and also to reduce the emission of pollutants. The highstrength steels application in the agricultural machinery industry is focused on the DP steels (Dual Phase), which is the subject of this present study. The focus of this work is analyze the mechanical behavior, prioritizing the deflection fatigue strength analysis on welded joints by Gas Metal Arc Welding (GMAW) process using two welding wire types. In this study it was used high strength steels sheet metal called DOCOL 1000, manufactured by SSAB and solder wires supplied by ESAB, and one widely used in the agricultural machinery industry for carbon steel welding and other a special wire developed for high strength. The robotic welding process was used to ensure the homogeneity of the weld bead on the samples manufacture process. For the mechanical characteristics analysis was done the static bending test, macrography, microhardness profile and deflection fatigue tests by four points. The results showed that the fatigue life, four-point bending, at welded joint used welding wire to carbon steel achieved a better result regarding a special welding wire to high strength steel, however, both fatigue curve respected project curve as British Standard.

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Carlesso, Rodrigo. "Estudo do comportamento mecânico de juntas soldadas de um aço de alta resistência mecânica." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/169810.

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A aplicação de aços de alta resistência está fortemente difundida na indústria mecânica, principalmente em aplicações onde a redução de peso é importante, como por exemplo, a indústria de implementos rodoviários e maquinários agrícolas. Esta dissertação visa analisar a influência de diferentes aportes térmicos no comportamento microestrutural e mecânico de juntas soldadas através do processo MAG de modo a obter juntas com propriedades otimizadas. Para este estudo foram utilizadas chapas metálicas com espessura de 3 mm do aço de alta resistência e baixa liga USI LNE700. Os parâmetros nominais de energia de soldagem foram variados de acordo com os valores descritos pelo fornecedor SSAB. O processo de soldagem foi realizado com o auxílio de um sistema robotizado para manter a homogeneidade ao longo da junta, distância e posicionamento correto no comprimento total da junta soldada. Os ensaios para verificação do comportamento microestrutural e mecânico foram realizados com auxílio de microscopia ótica, perfis de microdureza e ensaios de tração. Buscaram-se utilizar aportes térmicos reduzidos para minimizar os efeitos de revenimento da martensita presente no metal de base, um dos principais responsáveis pela redução das propriedades mecânicas da junta soldada. Os resultados não mostraram significativa variações na microestrutura e propriedades de tração do material, porém o preenchimento da junta soldada formada apresenta um comportamento diretamente proporcional à energia de soldagem.
The application of high strength steels is strongly diffused in the engineering industry, especially in applications where weight reduction is important, such as the industry of agricultural machines and trailers industry. This investigation aims to analyze the influence of different heat inputs on microstructural and mechanical behavior of joint welded by GMAW in order to obtain joints with optimized properties. Sheet metal with a thickness of 3 mm high strength low alloy steel LNE700 (supplier Usiminas) were used. The welding energy was varied around the nominal value informed by the steel supplier SSAB for this study. The welding process was made using robotic system to maintain homogeneity along the joint, right distance and position during the total weld joint length. The microstructural and mechanical behaviors were performed with the optical microscope, microhardness profile and traction test. We attempted to use lower heat inputs to minimize the effects of tempering of martensite present in the base metal, a major contributor to the reduction of the mechanical properties of the welded joint. The results did not show significant microestructural and tensile properties variation, however, when the welding energy is increased, the welded joint penetration formed was increased as well.

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Alves, Gabriel Godinho. "Recristalização do aço ARBL microligado ao nióbio CSN 2336." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-27092012-120450/.

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No presente trabalho estudou-se a recristalização do aço de alta resistência baixa liga (ARBL) microligado ao nióbio (160 ppm em peso) da Companhia Siderúrgica Nacional 2336 utilizado na fabricação de reforços estruturais para a indústria automobilística. A grande utilização deste tipo de aço pelas indústrias tem motivado o desenvolvimento de novas ligas capazes de atender a requisitos críticos de estampagem combinado com alta resistência mecânica. Amostras deste aço no estado laminado a quente foram deformadas posteriormente a frio em escala piloto com reduções de 50 e 70%, reduções típicas na indústria, e recozidas em banho de sal em temperaturas variando entre 600 e 700ºC em diferentes tempos. A evolução microestrutural das amostras no estado encruado e na condição recozida foi acompanhada utilizando-se as técnicas de microscopia ótica e eletrônica de varredura. As texturas de deformação e de recristalização foram determinadas via difração de raios X. A fração volumétrica recristalizada (Xv) e o tamanho de grão foram determinados com o auxílio de metalografia quantitativa nas amostras recozidas. Medidas de microdureza Vickers foram utilizadas para construir as curvas de encruamento e da cinética de amolecimento em função da temperatura de recozimento e comparadas com curvas construídas pelo primeiro método. Os resultados mostram que a recristalização ocorre em temperaturas acima de 650°C. Com auxílio de um gráfico de Xv contra A (fração amolecida), podemos observar a ocorrência de um desvio da idealidade a 650°C e 700°C. A explicação mais provável é a ocorrência de precipitação, especialmente para o aço menos deformado. Os valores do expoente de Avrami obtidos a partir das duas abordagens (medidas de microdureza e metalografia quantitativa) são apresentados e discutidos.
The recrystallization of a high strength low alloy steel (HSLA) containing niobium (160 wt-ppm) was investigated. The HSLA steel, named CSN 2336, is used in the manufacture of structural parts for automotive industry. The increasing use of this application type of steels in automotive industries has motivated the development of new alloys able to gather the critical requirements for deep drawing combined with high strengths. Samples of this steel in hot-rolled condition were cold-rolled with reductions of 50% and 70%, commonly used in most of applications, and isothermally annealed in salt bath at temperatures between 600 and 700ºC. The microstructure of the samples in both coldworked and annealed states was imaged using light optical (LOM) and scanning electronic microscopies (SEM). Deformation and recrystallization textures were determined by X-ray diffraction. The recrystallized volume fraction (Xv) and the mean grain size were determined by quantitative metallography in the annealed samples. Vickers microhardness testing was used to determine the work hardening and the softening kinetics behaviors. The results show that recrystallization occurs at temperatures above 650°C for the most deformed steel. By plotting Xv against A (softening fraction), we observe the occurrence of a deviation from ideality at 650°C and 700°C, likely caused by solid-state precipitation, especially for the less deformed steel. The values of n (Avrami exponent) obtained from both approaches (softening curves and quantitative metallography) are presented and discussed.

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Falcão, César Augusto de Jesus. "Avaliação da tenacidade à fratura na zona termicamente afetada de soldas múltiplos passes em um aço ARBL." Universidade de São Paulo, 1997. http://www.teses.usp.br/teses/disponiveis/18/18136/tde-17012011-161430/.

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O presente trabalho avalia e compara os resultados da tenacidade à fratura da zona termicamente afetada (ZTA) de soldas múltiplos passes por meio de ensaios de CTOD. Para este estudo, foi utilizado um aço alta resistência e baixa liga (ARBL) resistente à corrosão ambiental. As soldas foram realizadas com insumo de calor de 30 e 50 kJ/cm em um chanfro 1/2 K. Os resultados dos ensaios de CTOD mostraram que a solda produzida com maior insumo de calor apresenta tenacidade à fratura mais elevada. A análise microestrutural revelou que as microestruturas de elevada dureza e baixa tenacidade, formadas na ZTA de granulação grosseira, para a condição de 30 kJ/cm, deram lugar às microestruturas de tenacidade mais elevada, para o insumo de calor de 50 kJ/cm.
In this work the fracture toughness results of the heat affected zone (HAZ) in a multiple pass welds using a crack tip opening displacement (CTOD) concept were evaluated and compared. It was used an ambiental resistent high strengh low alloy steel. The welds were carried out using a heat input of 30 and 50 kJ/cm in a bevel preparation 1/2 K. The results of CTOD testing showed that increasing heat input, caused an improvement in the weldments fracture toughness. Microstructural analysis revealed that the high hardness and low toughness microstructures formed at coarse grain HAZ, near fusion line, for welding condition 30 kJ/cm were changed to higher toughness microstructure using a heat input of 50 kJ/cm.

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Ogata, Paulo Henrique. "Caracterização microestrutural do aço para tubo API 5L-X65 em diferentes regiões da chapa como laminada e após austenitização e resfriamento sob diversas taxas de resfriamento." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-22102009-180225/.

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Este trabalho tem por objetivo caracterizar e comparar as microestruturas de diferentes regiões de uma chapa de aço microligado para tubo API 5L X65, empregado no transporte de gás natural e petróleo, como recebido e submetido a tratamentos térmicos de austenitização e resfriamento contínuo sob diferentes taxas de resfriamento. O aço em estudo apresenta uma linha de segregação central, originada durante o processo de produção do aço. Corpos de prova de dilatometria foram usinados da região central e de outras regiões da chapa. As amostras foram previamente austenitizadas a 1200°C e temperadas em água, visando solubilizar grande parte dos precipitados presentes no aço. Após este tratamento, as amostras foram austenitizadas em um dilatômetro de têmpera a 950°C por 180s, e em seguida resfriadas nas seguintes taxas de resfriamento: 0,5°C/s, 1°C/s, 5°C/s, 10°C/s, 20°C/s, 30°C/s, 40°C/s, 50ºC/s e 60ºC/s. Valores de temperatura e tempo correspondentes a inflexões da curva dilatométrica foram obtidas e correlacionadas com a microestrutura, para cada taxa de resfriamento. Com base nesta análise foi traçado um diagrama de Transformação por Resfriamento Contínuo (TRC) do material.
This work aims to characterize and compare the microstructures of different regions of a plate of microalloyed pipeline steel that conforms to API 5L X65, employed in the transportation of natural gas and oil, as received and after being subjected to heat treatments of austenitization and continuous cooling under different cooling rates. The steel under study presents a central line of segregation that was originated during production. Specimens for dilatometry were machined from the central region and from different regions of the plate. The samples were austenitized at 1200°C and in quenched in water, with the purpose of solubilizing most of the precipitates in the steel. After the preliminary heat treatment, the specimens were austenitized at 950°C for 180s and cooled under the cooling rates: 0.5°C/s, 1°C/s, 5°C/s, 10°C/s, 20°C/s, 30°C/s, 40°C/s, 50ºC/s and 60ºC/s in a quench dilatometer. Values of temperature and time correspond of transformation for each rate of cooling were used for the determination of the Continuous Cooling Transformation (CCT) diagram.

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Amaral, Thiago de Souza. "Atlas microestrutural para otimização de procedimentos de soldagem." Universidade Federal de Uberlândia, 2016. https://repositorio.ufu.br/handle/123456789/15004.

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More complex and bigger structures have increased the applicability of low alloy high strength steels due to weight and cost reductions in these projects. One of the requirements for the use of these materials is the preservation of performance after welding. Meanwhile, the norms on which the Welding Procedures Specifications (WPS) are based have not yet considered the development of modern steel and its new production process, resulting in unnecessary welding costs that diminish the profits of the application of this type of steel. This thesis aimed to develop and evaluate an experimental methodology to guide the creation and control of welding procedures for structural steel through a microstructural atlas of the heat affected zone (HAZ) in a thermomechanical control process (TMCP), 65 ksi steel (ASTM A572 Grade 65). This steel was used in the project of an industrial building for CBMM in Araxá, Minas Gerais, Brazil. It is proposed that through a microstructural atlas of a given steel, it is possible to determine the range of cooling rates that the steel may suffer during welding without affecting mechanical properties and without risking cold cracks. When comparing the microstructure of steel welds performed in field conditions, it is possible to determine the heat input range for a given process in the preparation of a WPS. The selected case study is from a high strength low alloy class 65 ksi steel (ASTM A572 Grade 65) that was used in the structure of an industrial building. The steel was produced using TMCP. The atlas was created via the construction of a continuous cooling transformation diagram using physical simulation (dilatometer and Gleeble) of the coarse grain HAZ (GCHAZ). The characterization of the simulated region was performed by metallography and mechanical tests. The microstructure of real welds made by a qualified WPS were compared to the atlas in order to certify the correct use of parameters and to validate the method. The methodology was also qualified and the potential economic benefits were quantified (based only on the reduction of consumables used and the increased availability of the welding process machine) for the selected industrial project. The mapped microstructures varied from martensite (at high cooling rates) to pearlite/ferrite with large grain size (at low cooling rates). There was remarkable prevalence of bainitic microstructure in a wide range of cooling rates, consistent with the chemical composition of the steel studied. Comparisons with real weld microstructures showed the atlas is compatible with them, and that it can more accurately describe the effective thermal cycle xi that occurs in the coarse grain region of the HAZ (other regions were not included). The application of this methodology in the development of new WPS would allow greater flexibility in the welding procedures, including welding without preheating. In this respect alone, it was possible to forecast savings of approximately R$200,000.00, 1,000 hours of processing and 172 tonnes of carbon equivalent emissions.
Estruturas cada vez mais complexas e de maiores dimensões vêm aumentando a aplicabilidade de aços de baixa liga e alta resistência, devido à redução de peso e custo dessas estruturas. Um dos requisitos para o uso desses materiais é a manutenção do desempenho após soldagem. Entretanto, as normas em que se baseiam as Especificações de Procedimentos de Soldagem (EPS) ainda não consideram aços mais modernos em termos de rota de fabricação, o que pode fazer com que custos desnecessários de soldagem minimizem os ganhos da aplicação desses aços. Este trabalho teve como objetivo o desenvolvimento e avaliação de uma metodologia para, experimentalmente, orientar a elaboração e o controle da aplicação de procedimentos de soldagem para aços estruturais, através de atlas microestrutural de regiões da zona afetada pelo calor (ZAC). Propõe-se que, através de um atlas microestrutural de um dado aço, seja possível determinar a faixa otimizada de energia de soldagem para um dado processo na elaboração e aplicação da EPS e, consequentemente, as velocidades de resfriamento que o aço possa sofrer durante a soldagem, sem perder as propriedades mecânicas e sem colocálo em risco quanto a trincas a frio. Tomou-se como estudo de caso o aço produzido por laminação controlada de classe de resistência de 65 ksi (ASTM A572 Grau 65), utilizado em um projeto de um prédio industrial na empresa CBMM. Trata-se de um aço fabricado pelo processo TMCP com resfriamento acelerado. A elaboração do Atlas se deu através da construção de um diagrama CCT, por simulação física (dilatômetro e Gleeble), da região de grãos grosseiros da zona afetada pelo calor (ZAC GG). Foram feitas caracterizações metalográficas e mecânicas das regiões simuladas. Microestruturas de soldas realizadas com EPS qualificadas foram comparadas com as do Atlas para se certificar da adequabilidade dos parâmetros utilizados e validação da abordagem. Foram realizadas ainda a qualificação e quantificação de potenciais benefícios econômicos no citado projeto industrial, obtidos pelo uso desta metodologia. As microestruturas apresentadas no mapa variavam de martensíta, para altas taxas de resfriamento, até perlita/ferrita de tamanho de grão elevado, para baixas taxas de resfriamento. Observou-se notável predominância da microestrutura bainítica em uma larga faixa de taxas de resfriamento, compatível com as propriedades e composição do aço estudado (alta soldabilidade). As comparações com as microestruturas de soldas reais mostraram que o Atlas pode descrever de forma precisa o ciclo térmico efetivamente imposto ix na ZAC GG. Concluiu-se que a aplicação desta metodologia na elaboração de novas EPS permitiria uma maior flexibilidade nos procedimentos de soldagem, admitindo inclusive soldagem sem pré-aquecimento. Em relação a não necessidade de pré-aquecimento, podese prever uma economia significante de custos e redução de emissão de gases que provocam efeito estufa.
Mestre em Engenharia Mecânica

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Kgomari, Lerato Criscelda. "Microstructural characterization of laser formed high-strength-low-alloy (HSLA) steel." Thesis, 2010. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000591.

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Thesis (MTech. : Engineering Metallurgy.)--Tshwane University of Technology, 2010.
Establish a qualitative and quantitative comparison between the parameters of the laser used in manufacturing a 120 mm curvature in HSLA steel parts and the micro-structural changes in the steel part. Subsequently, the final microstructure will be used to determine the reason for the poor fatigue performance of the HSLA steel after laser forming.

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Khan, Mohammad Ibraheem. "Spot Welding of Advanced High Strength Steels (AHSS)." Thesis, 2007. http://hdl.handle.net/10012/2777.

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Efforts to reduce vehicle weight and improve crash performance have resulted in increased application of advanced high strength steels (AHSS) and a recent focus on the weldability of these alloys. Resistance spot welding (RSW) is the primary sheet metal welding process in the manufacture of automotive assemblies. Integration of AHSS into the automotive architecture has brought renewed challenges for achieving acceptable welds. The varying alloying content and processing techniques has further complicated this initiative. The current study examines resistance spot welding of high strength and advance high strength steels including high strength low alloy (HSLA), dual phase (DP) and a ferritic-bainitic steel (590R). The mechanical properties and microstructure of these RSW welded steel alloys are detailed. Furthermore a relationship between chemistries and hardness is produced. The effect of strain rate on the joint strength and failure mode is also an important consideration in the design of welded structures. Current literature, however, does not explain the effects of weld microstructure and there are no comprehensive comparisons of steels. This work details the relationship between the joint microstructure and impact performance of spot welded AHSS. Quasi-static and impact tests were conducted using a universal tensile tester and an instrumented drop tower, respectively. Results for elongation, failure load and energy absorption for each material are presented. Failure modes are detailed by observing weld fracture surfaces. In addition, cross-sections of partially fractured weldments were examined to detail fracture paths during static loading. Correlations between the fracture path and mechanical properties are developed using observed microstructures in the fusion zone and heat-affected-zone. Friction stir spot welding (FSSW) has proven to be a potential candidate for spot welding AHSS. A comparative study of RSW and FSSW on spot welding AHSS has also been completed. The objective of this work is to compare the microstructure and mechanical properties of Zn-coated DP600 AHSS (1.2mm thick) spot welds conducted using both processes. This was accomplished by examining the metallurgical cross-sections and local hardnesses of various spot weld regions. High speed data acquisition was also used to monitor process parameters and attain energy outputs for each process.

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Wu, Chao Peng Paul. "Inclusion Characterization in High Strength Low Alloy Steel." Thesis, 2009. http://hdl.handle.net/1807/19003.

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The cleanliness of high strength low alloy (HSLA) steel was assessed qualitatively and quantitatively. The determination of inclusion type and inclusion morphology were carried out using Selective Potentiostatic Etching by Electrolytic Dissolution (SPEED) method allowing in-situ examination of inclusion morphology by analytical techniques such as SEM/EDS. Inclusion size analysis mainly involved a combination of an analytical technique to provide images of the sample surface and an image analysis system to accurately measure the inclusion size. Four analytical methods were compared in order to evaluate their suitability for subsequent quantitative analysis. It was found that images taken with backscattered electron imaging mode from the scanning electron microscope provides the most accurate representation of inclusion distribution. The various techniques were used to evaluate HSLA steel grades of similar chemistry produced with and without gas shrouding. The results confirmed that with reoxidation minimized by gas shrouding between ladle and tundish, the steel cleanliness was significantly improved.

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Hu, Nien-Tzu, and 胡念慈. "Wear-Corrosion Behavior of High Strength Low Alloy Steel." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/8528cw.

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碩士
國立臺灣大學
工程科學及海洋工程學研究所
107
Due to its superior yield strength, toughness and weldability. high strength low alloy steels have been widely used in the marine engineering and defense industry. However, for the high strength low alloy steels used in marine engineering, we should consider not only their mechanical properties, but also the corrosion resistance of materials. Because of the high content of chloride ions in the marine environment, oxygen concentration, temperature, pH and marine micro－ organisms cause serious corrosion problems and decrease the strength of material. And in the real industrial application, the occurrence of corrosion is usually not so simple. When a material is in a corrosive environment and sliding, due to mechanical and electrochemical interactions that result in material loss or surface damage, we are referred to as tribocorrosion. In this experiment found that the new designed NiCu alloy steel exhibit a better corrosive wear performance than S690Q alloy steel. In second part, the tempering temperature of 660°C increases the corrosion resistance of NiCu steel, but reduces its wear resistance, while the tempering temperature of 780°C decreases the corrosion resistance of NiCu but increases its wear resistance. In the different tempering temperature after heat treatment, found that NiCu_660 has better corrosive wear performance than NiCu_780.

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46

Chen, Cheng-Kang, and 陳正剛. "High Strength High Ductility Die Casting Al Alloy with Low Iron Content." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/58121244653596728973.

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碩士
大同大學
材料工程學系(所)
103
An investigation on the development of high strength high ductility die casting Al alloys with low-none iron content, based on a ADC3 Al alloy (Al-9.5Si-0.8Fe-0.4Mg), was carried out in this study. The first part of this study was to examine the microstructures and the mechanical properties of a series of ADC3-base alloys with different iron content and modified alloy compositions. The second part of this study utilized a T5 and a spheroidization heat treatments to further improve the mechanical properties of the modified ADC3-base alloys. The results show that, when iron content in gravity cast ADC3-base alloys was reduced from 0.8% to 0.4%, the amount of plate-like iron-rich compound with sharp edges was found decreased significantly. As such, the ductility of the low-iron ADC3-base alloys increase accordingly. Among the low-iron ADC3-base alloys studied the ADC3S2 alloy containing Cr and Zr (Al-9.5Si-0.4Fe-0.4Mg-0.3Cr-0.3Zr-0.02Sr) exhibited the best combination of high mechanical strength and high ductility. While in the iron-free ADC3-base alloys studied the non- heat–treatable ADC3S7 alloy (Al-9.5Si-0Fe-0Mg-0.6Mn-0.3Cr-0.3Zr- 0.02Sr) exhibited the best combination of high mechanical strength and high ductility. In comparisons of mechanical properties in the as-cast condition of die casting ADC3 (0.8 Fe), ADC3S2 (0.4 Fe) and ADC3S7 (Fe-free) alloys, the mechanical properties of low-iron ADC3S2 and iron-free ADC3S7 Al alloys are very similar and better than that of ADC3 (0.8 Fe). The YS, UTS and ductility values of as-cast ADC3S2 and ADC3S7 alloys are in the range of 190~192 MPa, 296~298 MPa and 8.1~8.2%, respectively. When subjected to a T5 treatment at 175oC for 8 h, the die cast ADC3S2 exhibited far better mechanical properties than the other two alloys, with YS, UTS and ductility of 260 MPa, 339 MPa and 7.8%, respectively. However, when subjected to the spheroidization treatment at 350oC for 0.5 h, the mechanical properties of three die cast alloys are very alike. The YS, UTS and ductility values in the die casting ADC3 (0.8 Fe), ADC3S2 (0.4 Fe) and ADC3S7 (Fe-free) alloys are in the range of 146~158 MPa, 224~245 MPa and 12.3%~15.0%, respectively.

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47

Kao, Fang-Hsin, and 高芳歆. "Precipitation Strengthening of Nanometer-Sized Copper Particles and Alloy Carbides in High Strength Low Alloy Steels." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/73284743085662263406.

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博士
國立臺灣大學
材料科學與工程學研究所
97
Most microalloyed steels contain small amounts of one or more strong carbide forming element. It is known that copper does not form intermetallic compounds with other microalloying elements, so copper precipitates can also contribute a strengthening mechanism. There has recently been considerable interest in the use of low carbon, copper containing, high strength, low alloy (HSLA) steels for application in heavy engineering, where strength, toughness and deformability are the most important requirements. The hardening effect depends both on the aging temperature and aging time; hence, it is worthy of study. On the other hand, in order to modify the mechanical properties of the tempering martensitic steels, HSLA steels contain multi-microalloy elements that form complex carbides with slower growth or coarsening rates compared to single component carbides. Therefore, the complex carbides in the martensite matrix are effective in temper-softening resistance during long duration tempering. Secondary precipitation hardening in martensitic steels, which occurs during tempering treatment, is widely used in many engineering applications, such as turbine blades, heat transfer tubes, and the nuclear industry; steels in these applications must have superior creep rupture strength and impact properties at high temperatures of about 600℃. In the present work, nano-sized cooper precipitates in the ferrite matrix were formed in low carbon steels containing 0.5 and 1.0 copper (wt %) during isothermal aging at various temperatures and times. The corresponding transmission microscopy and microhardness for the different aging temperatures and times of these two copper-containing steels have been investigated. It can be found that both interface precipitation and supersaturated precipitation are present in the ferrite grain under certain isothermal treatment conditions. The precipitation of enriched-copper particles can take place in the ferrite matrix in 1 wt % copper containing steel, and the maximum hardness can be obtained in this steel by aging at 615℃ for 90 min. A lower transformation temperature can cause a great amount of nano-sized precipitation in ferrite due to the lower diffusivity of microalloying elements and large driving force for precipitation. Interphase precipitation is also observed in these two steels. This phenomenon depends on the austenite/ferrite boundary migration rate being reduced. It is also found that the sheet spacing of interphase precipitation decreases with aging temperature; however, the interface precipitation displays the lightness and non-uniformity that cause scattered mechanical properties. HSLA steels contain Ti, Ti-Mo and Ti-Nb elements that form complex carbides in the martensite matrix during long-term tempering, leading to temper-softening resistance. Comparing the TiC carbides, (Ti,Mo)C complex carbides and (Ti,Nb)C complex carbides, (Ti,Mo)C complex carbides have a lower growing rate. However, (Ti,Nb)C complex carbides appear late, even with tempering at 600℃ for 560 h, which is why the temper-softening resistance appears after 560 h in Ti- Nb steel. This phenomenon differs greatly from those of Ti steel and Ti-Mo steel. From the hardness curves of Ti steel, Ti-Mo steel and Ti-Nb steel, it is clear that Mo addition results in the best temper-softening resistance when combined with Ti. HSLA steels containing Ti-Mo-0.5Cu and Ti-Mo-1.0Cu (wt %) elements form different types of complex carbides in the martensite matrix during long-term tempering. In Ti-Mo-0.5Cu (wt %) steel, TiC carbides, (Ti,Mo)C complex carbides and Cu rich complex carbides can be observed; however, when the precipitates form in Ti-Mo-1.0Cu (wt %) steel, the Ti, Mo and Cu elements tend to combine with each other. The abilities of temper-softening resistance in these two steels are similar before tempering for 560 h. However, the addition of 1.0 wt % copper is unfavorable to further tempering for 1150 h because the complex carbides that coarsen rapidly in the grain boundary lead to temper-softening. From comparing the hardness curve of Ti-Mo steel and Ti-Mo-0.5Cu (wt %) steel, it is known that Ti-Mo steel can produce effective temper-softening resistance during long-term tempering; however, Ti-Mo steel with a further 0.5 wt % copper addition has extended temper-softening resistance. Therefore, Cu addition is favorable for temper-softening resistance when combined with Ti and Mo.

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48

Huang, Wei-Hsuan, and 黃韋瑄. "Effect of alloy elements and heat treatment on the corrosion resistance of high strength low alloy steels." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/4mh738.

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碩士
國立臺灣大學
工程科學及海洋工程學研究所
106
High strength low alloy steels have been widely used in the marine engineering and defense industry due to their superior yield strength, toughness and weldability. Although these materials have superior mechanical properties, the corrosion resistance is the other important issue especially when they are used in the marine environment. In this study, we investigated the effect of nickel and copper addition on the corrosion resistance of high strength low alloy steels in the marine environment, and the effect of heat treatments on the corrosion resistance of the new designed NiCu steel. The potentiodynamic polarization curve was conducted using a Gamry Reference 600 potentiostat to evaluate the corrosion performance of two high strength low alloy steels. The surface morphology and composition of corrosion products formed on the material surface after corrosion treatment were analyzed using scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The preliminary electrochemical measurement and surface analysis results showed that higher amount of Ni and Cu addition can improve the corrosion resistance of high strength low alloy steels. In the EPMA analysis, it was found the corrosion layer of higher Cu and Ni containing alloy was enriched with copper. The new designed NiCu steel have the best corrosion resistance at tempering temperature of 660 oC.

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49

Zhu, Ruixian. "Microstructure Design of Low Alloy Transformation-Induced Plasticity Assisted Steels." Thesis, 2013. http://hdl.handle.net/1969.1/149351.

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The microstructure of low alloy Transformation Induced Plasticity (TRIP) assisted steels has been systematically varied through the combination of computational and experimental methodologies in order to enhance the mechanical performance and to fulfill the requirement of the next generation Advanced High Strength Steels (AHSS). The roles of microstructural parameters, such as phase constitutions, phase stability, and volume fractions on the strength-ductility combination have been revealed. Two model alloy compositions (i.e. Fe-1.5Mn-1.5Si-0.3C, and Fe-3Mn-1Si-0.3C in wt%, nominal composition) were studied. Multiphase microstructures including ferrite, bainite, retained austenite and martensite were obtained through conventional two step heat treatment (i.e. intercritical annealing-IA, and bainitic isothermal transformation-BIT). The effect of phase constitution on the mechanical properties was first characterized experimentally via systematically varying the volume fractions of these phases through computational thermodynamics. It was found that martensite was the main phase to deteriorate ductility, meanwhile the C/VA ratio (i.e. carbon content over the volume fraction of austenite) could be another indicator for the ductility of the multiphase microstructure. Following the microstructural characterization of the multiphase alloys, two microstructural design criteria (i.e. maximizing ferrite and austenite, suppressing athermal martensite) were proposed in order to optimize the corresponding mechanical performance. The volume fraction of ferrite was maximized during the IA with the help of computational thermodyanmics. On the other hand, it turned out theoretically that the martensite suppression could not be avoided on the low Mn contained alloy (i.e. Fe-1.5Mn-1.5Si-0.3C). Nevertheless, the achieved combination of strength (~1300MPa true strength) and ductility (~23% uniform elongation) on the low Mn alloy following the proposed design criteria fulfilled the requirement of the next generation AHSS. To further optimize the microstructure such that the designed criteria can be fully satisfied, further efforts have been made on two aspects: heat treatment and alloy addition. A multi-step BIT treatment was designed and successfully reduced the martensite content on the Fe-1.5Mn-1.5Si-0.3C alloy. Microstructure analysis showed a significant reduction on the volume fraction of martensite after the multi-step BIT as compared to the single BIT step. It was also found that, a slow cooling rate between the two BIT treatments resulted in a better combination of strength and ductility than rapid cooling or conventional one step BIT. Moreover, the athermal martensite formation can be fully suppressed by increasing the Mn content (Fe-3Mn-1Si-0.3C) and through carefully designed heat treatments. The athermal martensite-free alloy provided consistently better ductility than the martensite containing alloy. Finally, a microstructure based semi-empirical constitutive model has been developed to predict the monotonic tensile behavior of the multiphase TRIP assisted steels. The stress rule of mixture and isowork assumption for individual phases was presumed. Mecking-Kocks model was utilized to simulate the flow behavior of ferrite, bainitic ferrite and untransformed retained austenite. The kinetics of strain induced martensitic transformation was modeled following the Olson-Cohen method. The developed model has results in good agreements with the experimental results for both TRIP steels studied with same model parameters.

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50

Ni, Randolph. "Cracking tendencies of restrained welds in high strength low alloy steels under hyperbaric conditions." Thesis, 1987. http://hdl.handle.net/10945/22714.

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