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고내식 이상 SAF 2507 스테인레스강의 고온변형거동
정재영,방원규 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.12
The hot deformation behavior of cast SAF2507 super duplex stainless steel under hot working conditions in the temperature range of 900 to 1250℃ and strain rate range of 0.01 to 50s^(-1) has been studied using hot compression testing. The dynamic materials model has been used for developing the processing maps, which show the variation of the efficiency of power dissipation with temperature and strain rate. The processing map revealed a single domain with a peak efficiency of power dissipation of about 48% occurring at 1250℃ and 0.2s^(-1). These are the optimum conditions for hot working of SAF2507 and an elongated austenite phase divided into several equiaxed grains in microstructural observation. On the other hands, the material exhibits flow instability, manifested in the form of shear bands at strain rates higher than about 3s^(-1).
내부 변형변수 이론을 이용한 이상 스테인레스강의 초소성 변형 거동에 대한 연구
박재신,방원규,이형직,장영원 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.11
An internal variable theory has been used in this study to investigate quantitatively the major deformation mechanism of a duplex stainless steel. The flow curves obtained from load relaxation tests were found separable into two parts, viz. grain matrix deformation (GMD) curve and grain/phase boundary sliding (G/PBS) curve as was predicted by the internal variable theory. The major deformation mechanism of duplex stainless steel at high temperature is found to be a dynamic recrystallization (DRX) at an early stage of deformation, but grain/phase boundary sliding becomes the major deformation mechanism at the late stage of deformation. Additionally, x phase precipitated first by replacing Mo with W in duplex stainless steels appears to improve the superplastic deformation characteristics when it exists below a critical level. (Received May 19, 2004)