采用完全淬火+两相区淬火+临界区淬火的三步热处理方式,利用SEM、EBSD、XRD、TEM和EPMA等手段研究了0.12C-3.0Mn低碳中锰钢组织演变规律和力学性能,并对0.12C-3.0Mn钢进行了-40~-196 ℃的系统低温冲击实验研究。结果表明,三步热处理后0.12C-3.0Mn钢的组织为临界铁素体、马氏体/贝氏体和残余奥氏体,残余奥氏体呈块状和条状分布在原奥氏体晶界上和马氏体/贝氏体板条界上,残余奥氏体主要通过临界淬火富集C和Mn元素达到稳定,室温下稳定的残余奥氏体含量最高可达到15%。由于残余奥氏体的应变诱导塑性(TRIP)效应,0.12C-3.0Mn钢具有良好的塑性和优异的低温韧性：断后总延伸率高于30%,均匀延伸率高于16%,-80 ℃下冲击功可达到200 J。
Low carbon and low alloy steels require good combination of strength and ductility to ensure safety and stability of structures, and the low temperature toughness has become more significant to low carbon low alloyed high performance steel recently. Retained austenite plays a great role in a multiphase system to improve the toughness of steel as a result of the deformation induced transformation of retained austenite when the steel deformed. In this work, the characterization of multiphase microstructure including retained austenite, tempered martensite and intercritical ferrite which obtained by a three-step intercritical heat treatment in a low carbon medium manganese steel were studied, and the low-temperature impact toughness evolution from -40~-196 ℃ during the process were analyzed. The results showed that C and Mn distributed unevenly after intercritical quenching and were benefit to martensite inverse transformation to austenite, and the enriched C and Mn elements can improve the stability of reverted austenite during the tempering process. The impact energy of the steel is 200 J at -80 ℃ during the processes at intercritical quenching temperature 720 ℃ and tempering temperature 640 ℃, and the energy of impact crack formation and propagation at different temperature were also analyzed.
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