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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.
냉연 TRIP 강의 미세조직과 성형성에 미치는 베이나이트 변태온도의 영향
洪三永,全現助,朴晟浩,姜信煥,朴贊卿 대한금속재료학회 2001 대한금속·재료학회지 Vol.39 No.12
TRIP steels exhibits low formability under multi-axial stress condition. The purpose of the present study is to suggest a way of improving the formability of TRIP steels under plane strain mode. For this purpose, the formability under different stress states and their relationships with the microstructure of the secondary phases have been investigated in the cold rolled 0.2C-1.5Si-1.5Mn TRIP steels experienced with various bainitic isothermal transformation at 300, 350, 400 and 450℃. Two kinds of mechanical tests were conducted to evaluate the formability: the tensile test under uni-axial stress condition, and the Limiting Dome Height(LDH) test for the plane strain mode under multi-axial stress condition. The formability of the present TRIP steels strongly depends on the isothermal bainitic transformation temperatures. The discrepancy between EL and LDH at 350℃ could be explained by the stability of the retained austenite and the distribution of the secondary phases. Consequently, this study revealed that effects of the microstructure on the formability were different depending on the deformation modes in TRIP steels. In order to improve the EL property, the stability of RA should be controlled, and in order to improve the LDH property, the continuously networked RA and the fine bainite should be formed.
Fe3Al 금속간화합물의 항복강도 이상거동과 변형기구 고찰
박찬경,장영원,전현조 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.8
It is well known that Fe₃Al intermetallic compound shows an anomalous peak of the yield strength at about 500℃. That is, the yield strengths increase with increasing deformation temperature in the range of 300℃-500$quot;℃, and then decrease at higher temperatures. The dislocation structure was examined by transmission electron microscopy, and high temperature mechanical properties were examined by tensile and load relaxation tests. The flow stress curves obtained from lead relaxation bests were then analyzed in terms of internal variable deformation theory. It was found that the flow curves consisted of three micro-deformation mechanisms i.e inelastic deformation mode, plastic deformation mode and dislocation creep deformation mode, depending on both dislocation structure and deformation temperature. The flow curves could be well described by the constitutive equations of these three micro-deformation mechanisms based on the internal variable deformation theory.