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유위도(Wee Do Yoo),나영상(Young Sang Na),이종훈(Jong Hoon lee) 한국주조공학회 2002 한국주조공학회지 Vol.22 No.1
N/A Hot deformation behavior of GCD-50 cast iron has been investigated by employing the compressive test. Phenomenological deformation behaviors, which were modeled based on the dynamic materials model and the kinetic model, have been correlated with the microstructural change taken place during compression. Microstructural investigation revealed that the adiabatic shear band caused by the locallized deformation was taken place in low temperature and high strain rate. On the other hand, the wavy and curved grain boundaries, which repersent the occurrence of dynamic microstructure change such as dynamic recovery and dynamic recrystallization, were observed in high temperature and low strain rate. Deformation model based on hyperbolic sine law has also been suggested.
이종훈(Jong-Hoon Lee),유위도(Wee-Do Yoo) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
The several failure cases which occur frequently in the heat treatment processing of the heat treatment companies were introduced in this study. The case study about heat treatment failure analysis was especially focused on the induction surface hardening of the machinery parts. The general analysis method is as follows. Ⅰ) Visual exam i na t ion. Ⅱ) Fracture surface observation. Ⅲ) Microstructural examination around crack. Ⅳ) Evaluation about mechanical and chemical properties of material.
슈퍼 듀플렉스 스테인레스강의 미세조직 및 기계적 특성에 미치는 열처리 후 냉각속도의 영향
권기현 ( Gi Hyoun Kwon ),나영상 ( Young Sang Na ),유위도 ( Wee Do Yoo ),이종훈 ( Jong Hoon Lee ),박용호 ( Yong Ho Park ) 대한금속재료학회(구 대한금속학회) 2012 대한금속·재료학회지 Vol.50 No.10
Abstract: The aim of this study was to analyze the effect of the cooling rate after heat treatment on the microstructure and mechanical properties of 2507 duplex stainless steels. Heat treatment was carried out at 1050℃ for 1 hr, followed by controlled cooling. The cooling rates were 175.6 × 10-3℃/s, 47.8 × 10-3℃/s, 33.3 × 10-3℃/s, 16.7 × 10-3℃/s, 11.7 × 10-3℃/s, 5.8 × 10-3℃/s and 2.8 × 10-3℃/s, which resulted in variations of the microstructure, such as the fractional change of the ferrite phase and sigma phase formation. Fatigue, hardness, impact and tensile tests were performed on the specimens with different cooling rates. The precipitation of the σ phase caused a hardness increase and a sharp decrease of toughness and tensile elongation. The fatigue limit of the sample with a cooling rate of 5.8 × 10-3℃/s was 26MPa higher than that of the sample with a cooling rate of 175.6 × 10-3℃/s. Our observations of the fracture surface confirmed that the higher fatigue resistance of the specimen with a cooling rate of 5.8 × 10-3℃/s was caused by the delay of the fatigue crack growth, in addition to higher yield strength.