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Degradation in Steels: Transformation Plasticity
조이길,한흥남 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.1
Super-plastic deformation that originates from transformation plasticity has favorable aspects for steels with improved strength and ductility. However, it also causes undesirable deformation of products or specimens, leading to their degradation. This article reviews recent investigations of transformation plasticity. A combination of newly suggested models, numerical analyses, and novel experiments has attempted to reveal the mechanism. Since the nature of the transformation plasticity is still unclear, there are significant challenges still to be solved. Fundamental understanding of transformation plasticity will be essential for the development of advanced steels.
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.
김동완(Dong-Wan Kim),김문조(Moon-Jo Kim),조이길(Yi-Gil Cho),이재복(Jae-Bok Lee),이원범(Won-Beom Lee),한흥남(Heung-Nam Han) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
In this work, a carburizing process of automobile gear under low pressure mode has been analyzed. Carburizing of automotive annulus gear was performed at a temperature range of 830~930℃. An effect of carburizing on the surface hardening was observed by the measuring hardness and the microstructural analysis. Profile of carbon concentration along the thickness direction was measured by glow discharge spectrometer (GDS) system. A numerical analysis of carbon diffusion on the annulus gear was performed by finite element method (FEM) and the results were compared with experimentally measured distribution of carbon concentration.