采用双相区保温+奥氏体化淬火+低温退火的热处理工艺, 研究了合金元素配分行为对C-Si-Mn系高强钢微观组织和力学性能的影响. 结果表明, 在760 ℃随着保温时间的延长, 双相区中奥氏体相的体积分数逐渐增多直至达到饱和, 而铁素体向奥氏体扩散的Mn元素含量也逐渐增多直至在两相间达到化学势平衡, 后加热至930 ℃保温120 s, 再淬火至220 ℃, 配分过程中发生了C从马氏体向奥氏体中的扩散偏聚. 经该工艺处理后实验用钢的抗拉强度为1310 MPa, 延伸率可达12%, 强塑积达到15720 MPa.%, 相比传统淬火+碳配分工艺, 双相区保温+奥氏体化淬火+低温退火的热处理工艺过程中Mn配分和C配分共同作用能够显著提高钢中残余奥氏体的含量和稳定性, 从而提高高强钢的室温成形能力.

The C content in high strength steel must be controlled at a lower level for the good weldability. However, the lower level of C content will reduce the C partitioning efficiency and influence the stability of retained austenite, which leads to the decrease of the product of tensile strength and elongation of high strength steel. A novel preparation mechanism of high strength steel is to employ some kind of substitutional alloying elements, for example Mn, instead of C to partitioning to enhance the austenitic stability, which would not remarkably reduce the weldability of the steel. One low alloy C-Si-Mn steel was used in present work. The Mn partitioning behavior and its effect on the stability of the retained austenite and the mechanical property were studied by means of intercritical annealing, subsequent austenitizing, then quenching and partitioning process (I&Q&P). The results show that in the process of intercritical annealing at 760 ℃, by extending the annealing time, austenite volume fraction increases gradually until it reaches the saturation, meanwhile the Mn partitioning behavior occurs and Mn content increases gradually from ferrite to austenite until it reaches the chemical potential balance in two phases. The sample is heated to 930 ℃ for 120 s, then rapidly quenching to 220 ℃, the carbon diffuses from martensite to austenite phase in the process of partitioning. After I&Q&P process, the tensile strength of experimental steel is 1310 MPa, elongation up to 12%, the product of strength and elongation up to more than 15000 MPa.%. The steel only contains a small amount of retained austenite by only C partitioning after traditional Q&P process, while the steel contains more Mn-rich retained austenite after I&Q&P process. Hence, the content and stability of retained austenite of steel can be improved significantly, which enhance the formability at room temperature.