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Fe-20Mn-12Cr-1Cu 제진합금의 고온가스 질화처리
성지현 ( Jee Hyun Sung ),김영희 ( Yeong Hee Kim ),성장현 ( Jang Hyun Sung ),강창룡 ( Chang Yong Kang ) 한국열처리공학회 2013 熱處理工學會誌 Vol.26 No.3
The microstructural changes of Fe-20Mn-12Cr-1Cu alloy have been studied during high temperature gas nitriding (HTGN) at the range of 1000℃ in an atmosphere of nitrogen gas. The mixed microstruc-ture of austenite and ε-martensite of as-received alloy was changed to austenite single phase after HTGN treat-ment at the nitrogen-permeated surface layer, however the interior region that was not affected nitrogen permeation remained the structure of austenite and ε-martensite. With raising the HTGN treatment temperature, the concentration and permeation depth of nitrogen, which is known as the austenite stabilizing element, were increased. Accordingly, the depth of austenite single phase region was increased. The outmost surface of HTGN treated alloy at 1000℃ appeared Cr nitride. And this was in good agreement with the thermodynamically calcu-lated phase diagram. The grain growth was delayed after HTGN treatment temperature ranges of 1000℃∼1100℃ due to the grain boundary precipitates. For the HTGN treatment temperature or 1150℃, the fine grain region was shown at the near surface due to the grain boundary precipitates, however, owing to the depletion of grain boundary precipitates, coarse grain was appeared at the depth far from the surface.This depletion may come from the strong affinity between nitrogen and substitutional element of Al and Ti leading the diffusion of these elements from interior to surface. Because of the nitrogen dissolution at the nitrogen-permeated surface layer by HTGN treatment, the surface hardness was increased above 150 Hv compared to the interior region that was consisted with the mixed microstructure of austenite and ε-martensite. (Receivied March 11, 2013, Revised April 18, 2013; Accepted May 5, 2013)
장원석(Won Seok Jang),서창희(Chang Hee Suh),오상균(Sang Kyun Oh),김동배(Dong Bae Kim),성지현(Jee Hyun Sung),정윤철(Yun-Chul Jung),김영석(Young Suk Kim) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.10
열간성형된 보론강판은 고강도특성이 필요한 자동차 부품에 널리 적용되고 있으며, 최근에는 샤시부품에도 점차로 적용되고 있다. 샤시 부품으로 적용되기 위해서 고강도 특성뿐만 아니라 내피로특성이 동시에 요구되고 있어, 본 연구에서 열간성형된 보론강판의 저주기 피로특성을 연구하였다. 저주기 피로시험결과, 총변형률 진폭이 낮은 영역에서는 열간성형된 보론강의 피로수명이 현저히 높았지만, 높은 총변형률 진폭에서는 열간성형된 보론강의 마르텐사이트 조직특성인 낮은 연성과 파괴인성으로 인해서 보론강 원소재의 피로수명이 더 높음을 확인할 수 있었다. Boron steel sheet is suitable for fabricating automobile parts because it is very strong and has low weight. Recently, many car makers are investigating the feasibility of fabricating the chassis part of automobiles using boron steel. In order to use boron steel sheets to fabricate the chassis part of automobiles, much better material property of low cycle fatigue life as well as high formability during hot stamping is required. Therefore, the low-cycle fatigue life of hot-stamped quenched boron steel was investigated in this study. The fatigue life observed at low strain amplitude was longer than that of an as-received boron steel sheet. However, the fatigue life reduced at high strain amplitude because of the low ductility and low fracture toughness of martensite, which was produced as a result of hot stamping.