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성장모델과 유한요소법의 연계해석을 통한 변태소성 전산모사
조이길(Y.-G. Cho),김진유(J.-Y. Kim),차필령(P.-R. Cha),이재곤(J.K. Lee),한흥남(H.N. Han) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
Transformation plasticity is that when a phase transformation of ferrous or non-ferrous alloys progresses even under an extremely small applied stress compared with a yield stress of the material, a permanent deformation occurs. One of widely accepted description for the transformation was proposed by Greenwood and Johnson [1]. Their description is based on an assumption that a weaker phase of an ideal plastic material could deform plastically to accommodate the externally applied stress and the internal stress caused by the volumetric change accompanying the phase transformation. In this study, an implicit finite element model was developed to simulate the deformation behavior of a low carbon steel during phase transformation. The finite element model was coupled with a phase field model, which could simulate the kinetics for ferrite to austenite transformation of the steel. The thermo-elasto-plastic constitutive equation for each phase was adopted to confirm the weaker phase yielding, which was proposed by Greenwood and Johnson [1]. Form the simulation, the origin of the transformation plasticity was quantitatively discussed comparing with the other descriptions of it.
초경량 Fe-27Mn-12Al-0.8C 이상조직강의 상온인장변형특성
하민철(M. C. Ha),황시우(S. W. Hwang),구진모(J. M. Koo),이재곤(J. G. Lee),박경태(K.-T. Park) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.10
Room temperature tensile deformation behavior of a low density Fe-27Mn-12Al-0.8C duplex steel was investigated to understand for plastic deformations with constituent phases. Various ordered phases were formed by quenching of the steel after annealing at the (austenite + ferrite) two phase region. The B2 domains were formed in disordered ferrite matrix. In addition to the B2 domains, fine D0 phases were evenly distributed through both B2 domains and disordered ferrite matrix. The nano-sized k-carbides were precipitated in austenite. The steel exhibited the relatively high yield strength and the low strain hardening rate initially, leading to the moderate elongation. Deformed structure of ferrite is manifested by short, straight segments of paired superdislocations. In austenite, a single planar dislocation glide was dominant at low strains and multiple planar slip occurred at high strains. Based on these microstructural observations, it is suggested that strain hardening of the steel is dominated mainly by shearing of the ordered phases by superdislocations (in ferrite) and planar gliding dislocation (in austenite).