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研究了经临界退火和不同温度回火后多相组织低合金钢中残余奥氏体对塑性和韧性的影响. 结果表明, 实验钢经两相区临界退火和不同温度回火后, 获得了临界铁素体、回火马氏体/贝氏体以及体积分数分别为2%, 5%, 10%的残余奥氏体多相组织. 含有不同体积分数残余奥氏体的多相组织钢强度差异不大, 其屈服强度介于540~590 MPa, 抗拉强度介于720~780 MPa. 残余奥氏体含量对塑性和韧性影响显著. 随着残余奥氏体含量的增加, 实验钢的均匀延伸率和断后延伸率分别从10.3%和23.8%提高到20.4%和33.8%. 塑性的提高主要是由于残余奥氏体在拉伸过程中逐步发生马氏体相变, 从而提供持续的加工硬化能力, 推迟颈缩的发生. 残余奥氏体对韧性的改善随着冲击测试温度的降低变得更加显著. 冲击温度高于-60 ℃时, 不同体积分数的残余奥氏体实验钢的冲击功均在120 J以上, 当冲击实验温度为-80 ℃时, 残余奥氏体含量仅2%的实验钢的冲击韧性仅14 J, 而含有残余奥氏体体积分数约10%的实验钢在-80和-100 ℃的冲击功仍然保持在60~80 J. 残余奥氏体的存在有利于提高低温冲击过程中的塑性变形能力, 延迟起裂, 提高起裂功, 从而有利于获得优异的低温冲击韧性.

High performance steels require not only high strength, but also the combination of high ductility, high toughness and good weldability. Retained austenite in multi-phase steels has been widely reported to be helpful for obtaining high strength, high ductility and high toughness. In this work, steel with multi-phase microstructure consisting of intercritical ferrite, tempered martensite/bainite and different volume fractions retained austenite was obtained by intercritical annealing and tempering at 600~680 ℃. The volume fractions of retained austenite were 2%, 5%, 10% for samples tempered at 600, 650 and 680 ℃, respectively. The effect of retained austenite on ductility and toughness was studied in detail. Results showed that there was no obvious change in strength by varying the volume fraction of retained austenite, yield strength of the steel was 540~590 MPa, tensile strength was 720~780 MPa. Retained austenite could largely improve both the ductility and toughness of the steel. With increasing the volume fraction of retained austenite from 2% to 10%, the uniform elongation and total elongation were enhanced from 10.3% and 23.8% to 20.4% and 33.8%, respectively. The underlying reason for the improvement of ductility was attributed to the transformation induced plasticity of retained austenite by providing sustainable high work hardening rate. The improvement of toughness by retained austenite became more obvious when testing temperature was lower. When impact test temperature was higher than -60 ℃, the Charpy impact energy of samples with 2%~10% retained austenite were larger than 120 J. When test temperature was -80 ℃, Charpy impact energy of sample with 2% retained austenite decreased to 14 J, while that of sample with 10% retained austenite remained as 60~80 J when test temperature was as low as -80 and -100 ℃. Results from instrument impact test indicated that retained austenite was helpful for enhancing plasticity before crack initiation at low temperature, leading to improvement of crack initiation energy, resulting in excellent low temperature toughness.