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페라이트계 스테인리스강의 재현 용접열영향부 열피로 특성
홍승갑,조민현,강기봉,Hong, S.G.,Cho, M.H.,Kang, K.B. 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.1
Ferritic stainless steel, which has been used as material for decoration parts in automobile, is recently used as material for the exhaust system due to its good performance at high temperature. To improve the fuel efficiency and purify automotive exhaust gas, it is needed to increase the temperature of exhaust gas. However, it is frequently reported that the rising of the temperature of exhaust gas increases thermal stress at exhaust manifold, which results in thermal fatigue failure in welded joints. Therefore, in this study, effects of chemical composition of steel and welding parameters on thermal fatigue properties of synthetic heat affected zone in ferritic stainless steel have been investigated. It has been found that thermal fatigue life in heat affected zone is affected by bead shape of welded joint and amount of soluble Nb in steel. Especially, Nb-Ti added steel has higher thermal fatigue life in comparison to Nb added steel, which is attributed to difference of precipitation behavior in both steels.
C-Mn-Si 계 변태유기소성강의 성형상에 미치는 베이나이트 변태 온도 및 응력상태의 영향
박찬경,전현조,오진후,홍승갑 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.9
The effects of TRansformation Induced Plasticity(TRIP) phenomena on the plastic deformation of 0.2C-1.5Si-1.5Mn multiphase steel have been investigated at various heat treatment and stress conditions. In order to estimate a deformation behavior under multi-axial stress rotate, the hole expansion(HE) tests were carried out. It is shown that the formability evaluation from the uni-axial tensile tests was quite different from the formability measured from multi-axial HE-tests because of different stress state. The formability in the multi-axial stress state decreased due to the extinction of the transformable retained austenite at relatively earlier deformation stage and the production of irregular α' martensite. The voids of TRIP steel were initiated exactly at the interface between transformed martensite and ferrite matrix regardless of stress state. In addition, new form of experimental formula is proposed in order to predict the multi-axial formability of the TRIP steel from the results of uniaxial tensile test.