利用热变形和两步淬火配分(quenching and partitioning, Q&P)工艺的复合作用制备低碳合金钢试样, 设计不同的热变形温度, 研究加载(获得30%变形量)引起的应力和塑性变形对Q&P工艺下马氏体相变开始温度(M_s), 残余奥氏体含量和力学性能的影响. 结果表明, 与传统两步Q&P工艺相比, 复合作用下显微组织细化, 尤其是随着变形温度的降低细化更明显, 马氏体板条呈现弯曲形貌. 随着变形温度升高, M_s升高, 但马氏体转变量却有所下降, 其原因是应力引起的位错多在奥氏体母相晶界处出现, 成为马氏体相变优先形核的位置, 而一旦发生相变, 一定的塑性应变将提高晶内奥氏体的稳定性, 从而促进残余奥氏体含量增加. 复合作用下试样的力学性能也有所提高, 在650 ℃变形时试样的硬度最高, 而在750 ℃变形时试样的塑性最好.

A combined process of hot deformation with different deformation temperatures plus two step quenching and partitioning (Q&P) treatment was applied to low carbon alloyed steel. The effect of stress (30% plastic deformation) on the start temperature of martensite transformation (Ms), volume fraction of retained austenite and mechanical properties was analyzed. It found that comparing with specimen treated by conventional two-step Q&P process, the microstructure of steel treated by combined process was finer and finer with the decreasing hot deformation temperature, and the typical curved micromorphology of martensite exists. Moreover, the Ms of specimen treated by combined process is increased with the increasing of deformation temperature. The effect of stress on the Ms can be attributed to the effect of stress on the grain boundaries of austenitic parent phase, where a large amount of dislocation induced by the stress is prior to occur so as to promote formation of martensite. However, the stability of untransformed austenite was improved by the plastic deformation when matensite transformed so as to get the more retained austenite (the highest volume fraction of retained austenite obtained by combined process of hot deformation at 750 ℃ is 17.2%). Moreover, the mechanical properties were improved by the combined process, namely, the highest hardness of specimen were obtained when hot deformation at 650 ℃ and the highest plasticity were obtained when hot deformed at 750 ℃.