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- 저자 : 장영원 ( Hwan Jin Sung (검색결과 3 건)
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김기수,장영원,성환진 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.1
The purpose of present study is to establish a new inelastic deformation theory based on dislocation mechanisms and grain boundary sliding applicable at high temperature. The basic concept of this theory is that the grain boundary sliding accomodated by grain matrix deformation plays a major role in the large superplastic deformation. Expanding the unified internal variable theory of inelastic deformation, new constitutive parameters and mechanical equation of state for grain boundary sliding are proposed from the consideration of dislocation kinetics. A series of load relaxation tests were then conducted to verify for the existence of mechanical equations of state for 7475 Al alloy. The stress-strain rate curves obtained from the load relaxation tests of 7475 Al alloy were found to fit well to the proposed state equations. The combined effect of temperature and grain size on the behavior of grain boundary sliding is also shown to be well characterized by the two structural parameters ∑_g and σ in the proposed state equations. A modification of the Hall-Petch equation is also suggested to replace the flow stress σ by σ. Finally, the conventional strain rate sensitivity parameter should also be replaced by new parameters defined by the internal state variables.
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Fe-C-Si-Mn 강의 변형유기 마르텐사이트변태 현상
신홍철,김성규,정진환,장영원 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.2
Deformation induced martensitic transformation in a steel containing retained austenite(γ_R) has been studied to elucidate the relationship between the stability of retained austenite and the flow behavior depending on the various bainite transformation conditions. The operation of plasticity induced transformation is viewed here as an effective relaxation mechanism of internal strain energy accumulated during plastic deformation. A new kinetics equation for deformation induced transformation has been formulated, based on this relaxation concept of internal strain energy as, f/f_s=1-exp(-βε^n), with the parameter β characterizing the stability of retained austenite, n a deformation mode parameter and f_s denoting the saturation value of transformed martensite. The deformation mode parameter, n is found to be n=1.0 for this steel regardless of heat treatment conditions. The maximum elongation was obtained in a specimen annealed at 400℃ for 5min, corresponding to the minimum value of β. It is therefore concluded that the minimum value of β provides the steady transformation rate during plastic deformation resulting in the best combination of strength and ductility in high strength sheet steel.
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