• Title/Summary/Keyword: Transformation induced plasticity steel

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Grain Size Dependence of Tensile Deformation at Room Temperature of a Reversely Transformed Fe-Cr-Mn Transformation Induced Plasticity aided Stainless Steel (역변태 Fe-Cr-Mn계 변태유기소성 스테인레스강의 결정립 크기에 따른 상온인장변형 거동)

  • J. Y. Choi;K-T. Park
    • Transactions of Materials Processing
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    • v.32 no.2
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    • pp.53-60
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    • 2023
  • A wide range of grain size was achieved in a Fe-Cr-Mn austenitic stainless steel (STS) by cold rolling and reversion annealing. The tensile characteristics of the STS were analyzed in terms of the dependence of strain induced martensitic (SIM) transformation on the grain size. In the ultrafine grain regime, the steel showed a high yield strength over 1 GPa, a discontinuous yielding, and a prolonged yield point elongation followed by considerable strain hardening. By increasing the grain size, the discontinuous yielding diminished and the yield point elongation decreased. The microstructural examination revealed that these tensile characteristics are closely related to the suppression of SIM transformation with decreasing the grain size. Especially, the prolonged yield point elongation of the ultrafine grained STS was found to be associated with development of unidirectional ε martensite bands. Based on the microstructural examination of the deformed microstructures, the rationalization of the grain size dependence of SIM transformation was suggested.

Microstructural evolution of ultrafine grained TRIP low-carbon steel (초미세 결정립 TRIP 강의 미세조직 변화)

  • Lee, C.W.;Ko, Y.G.;NamGung, S.;Shin, D.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.263-266
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    • 2009
  • Transformation induced plasticity (TRIP) steel consisting of ferrite, austenite, and bainite phases was regarded as an excellent candidate for automotive applications due to the good combination of ductility and strength. The aim of the present study was to understand the microstructural characteristics of ultrafine grained (UFG) TRIP low-carbon steel fabricated via equal channel angular pressing accompanied with intercritical- and isothermal-annealing treatments. When compared to coarse grained counterpart, only the volume fraction of austenite phase in UFG TRIP steel remained unchanged, but all other microstructural variables such as size and morphology were different. It was found that UFG TRIP steel showed the homogeneous distribution of each constituent phase, which was discussed in terms of annealing treatments done in this study.

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Asymmetric Behavior and Springback of Transformation-Induced Plasticity (TRIP) Steels (TRIP강의 비대칭 거동과 스프링백)

  • Jun, S.;Jung, J.;Lee, H.S.;Kim, B.M.;Kim, J.H.
    • Transactions of Materials Processing
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    • v.26 no.6
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    • pp.333-340
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    • 2017
  • The cyclic hardening behavior of transformation-induced plasticity (TRIP) steels shows tension-compression asymmetry known to be attributed to transformation of retained austenite into martensite during deformation. In this work, YoshidaUemori hardening model was used to represent the asymmetric hardening behavior of TRIP1180 steel. Yoshida-Uemori hardening model parameters were obtained from three sets of data: tension-compression, compression-tension, and a combination of the two. Material models were validated for U-bending and springback.

Characteristics on the Warm Deep Drawability of Transformation-Induced Plasticity Steel Sheet (가공유기변태 강판의 온간 디프드로잉 성형 특성)

  • Kong K. H.;Choi C. S.;Choi Y. C.;Seo D. G.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2000.10a
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    • pp.162-167
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    • 2000
  • The warm deep drawability in square cup drawing is investigated about a newly developed high-strength steel sheet with retained austenite which is transformed into martensite during forming. For this investigation, six steps of temperature ranges, from room temperature to $250^{\circ}C$, and five kinds of drawing ratio, from 2.2 to 2.6 were adopted. As a result the maximum drawing force and the maximum drawing depth were affected by the elevated temperatures, and the more stable thickness strain distribution was observed to the elevated temperatures. But blue shortness happened over $200^{\circ}C$. The FEM analysis using the LS-DYNA code is adopted to compare the experimental results with the analytical results for thickness strain distribution.

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Manufacturing of Cold-rolled TRIP Steel by Reversion Process (역변태에 의한 냉연 TRIP강의 제조기술)

  • 진광근;정진환;이규영
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.08a
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    • pp.356-365
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    • 1999
  • The present study is aimed at developing the TRIP(transformation induced plasticity) aided high strength low carbon steel using reversion process. An excellent combination of elongation over 40% and tensile strength abut 100kgf/$\textrm{mm}^2$ achieved in processing of 0.15C-0.5 Si-6Mn steel by slow heating to intercritial temperature region and accelerated cooling into room temperature. This good combination is caused by TRIP phenomena of retained austenite in steels during deformation. The stability of retained austenite is very important for the good ductility and it depends on the diffusion of carbon and manganeses during heat treatment. The accelerated cooling after holding at annealing temperature retards the formation of pearlite and provides the carbon enrichment in retained austenite in steel, resulting in the increase in elongation of the cold-rolled TRIP steel. On the other hand, heat treating the steel at 600$^{\circ}C$ for 5 hour before cold rolling increases elongation but reduces the amount of retained austenite after reversion processing. It is accounted that the heat treating is effective for the increase in the stability of retained austenite.

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Elasto-Plastic Finite Element Analysis in Consideration of Phase Transformations (상변태를 고려한 탄소성 유한요소 해석)

  • Lee, M.G.;Kim, S.J.;Jeong, W.C.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.05a
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    • pp.334-336
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    • 2009
  • An elastic-plasticity model during the austenitic decomposition was derived and implemented to incorporate the two important deformation behaviors observed during the phase transformations: the volumetric strain and transformation induced plasticity due to the temperature change and phase transformation. To obtain transformed phase volume fractions during cooling, the fourth order Runge-Kutta method was used to solve the Kirkaldy's phase kinetics model which is function of temperature, austenitic grain size and chemical composition. The volumetric strain was calculated by considering the densities of constituent phases, while the transformation induced plasticity was based on the micro-plasticity due to the volume mismatch between soft austenitic phase and other harder phases. The constitutive equations were implemented into the implicit finite element software and a simple boundary value problem was chosen as a model problem to validate the effect of transformation plasticity on the deformation behavior of steel under cooling from high temperature. It was preliminary concluded that the transformation plasticity plays a critical role in relaxing the developed stress during forming and thus reducing the magnitude of springback.

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Investigation of Springback for the U-bending of Steel Sheets for Automotive body panels (차체 성형용 판재의 U 벤딩시의 스프링백에 관한 연구)

  • Kim S. H.;Shin J. M.;Chang S. H.;Seo D. G.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.10a
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    • pp.66-70
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    • 2001
  • The purpose of this paper is to investigate the characteristics of springback for the U-bending of steel sheets for automotive body panels. This study presents the experimental and analytical approach for the two kind of steel sheets, namely SCP1 and TRIP(Transformation-induced plasticity), the newly developed high strength steel. The adopted thicknesses are 0.8, 1.2 and 1.6 mm for SCP1, and 1.0 mm for TRIP. The punch profile radii are designed in 3, 6, 9, 12, and 15 mm. As results, the springgo aspect could be observed experimently in the small punch profile radius. The degree of springback for TRIP sheets was more than the SCP1 sheets.

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Springback for the Warm 2D Draw-bending of Steel Sheets (박판의 온간 2차원 드로오 벤딩에서의 스프링백)

  • Lee S. M.;Chang S. H.;Choi Y. C.;Heo Y. M.;Seo D. G.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.10a
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    • pp.75-80
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    • 2001
  • The purpose of this study is to investigate the characteristics of springback for various process conditions of the 2D draw-bending operation. The process variables are the forming temperature, the geometry of tools such as punch profile radius(Rp) and die profile radius(Rd). Especially, in order to control the springback, the use of the warm forming method is applied. For the warm draw-bending, five steps of temperature ranges, from room temperature to $200^{\circ}C$, were adopted. And two kinds of steel sheets, namely SCP1 and TRIP(transformation-induced plasticity), the newly developed high strength Steel, were adopted. As a result, the springback was affected by the elevated temperature and the geometry of tools in two kinds of steel sheets.

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Characteristics of the Warm Deep Drawability of a Transformation-Induced Plasticity Steel Sheet

  • 서대교;장성호;공경환
    • Transactions of Materials Processing
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    • v.8 no.3
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    • pp.221-221
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    • 1999
  • Warm deep drawability in a square cup drawing was investigated using a newly developed high-strength steel sheet with retained austenite that was transformed into martensite during formation. For this investigation, six different temperatures between room temperature and 250℃, and five different drawing ratios ranging from 2.2 to 2.6 were considered. The results showed that the maximum drawing force and the drawing depth were affected by the change in temperature, and a more stable thickness strain distribution was observed at elevated temperatures. However, blue shortness occurred at over 200℃. FEM analysis using the LS-DYNA code was used to compare the experimental results with the numerical results for the thickness strain distribution.

OPTIMIZATION OF WELDING PARAMETERS FOR RESISTANCE SPOT WELDING OF TRIP STEEL USING RESPONSE SURFACE METHODOLOGY

  • Park, Hyunsung;Kim, Taehyung;Sehun Rhee
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.366-371
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    • 2002
  • Because of the environmental problems, automotive companies are trying to reduce the weight of car body. Therefore, TRIP(TRansformation Induced Plasticity) steels, which have high strength and ductility have been developed. Welding process is a complex process; therefore deciding the optimal welding conditions on the basis of experimental data is an effective method. However, trial-and-error method to decide the optimal conditions requires too many experiments. To overcome these problems, response surface methodology was used. Response surface methodology is a collection of mathematical and statistical techniques that are used in the modeling and analysis of problems in which a response of interest is influenced by several variables and the objective is to optimize this response. This method was applied to the resistance spot welding process of the TRIP steel to optimize the welding parameters.

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