The work addresses physical simulation and dilatometric study of one-step and double-step heat treatments of medium-Mn steel designed for automotive sheets. The conventional one-step isothermal bainitic transformation was applied as the reference heat treatment. The newly implemented heat treatment consisted of isothermal holding in a bainitic region followed by additional holding of the material at reduced temperature also in the bainitic range. This step was added to refine the microstructure, which led to the stabilization of the retained austenite. Calculations of equilibrium state and non-equilibrium cooling and simulations of the developed thermal cycles were performed using the thermodynamic JMatPro software. The physical simulations of the heat treatment were performed in the dilatometer. The obtained samples were subjected to microscopic observations using light and SEM microscopy. One- and two-step heat treatments allowed to obtain bainitic structures with high contents of retained austenite. Lowering the temperature of one-step isothermal holding resulted in the bainite refinement and adjacent retained austenite. The increased Mn content in steel increased its susceptibility to form coalesced bainite resulting in the partial formation of thicker plates despite a decrease in a process temperature.

该工作涉及为汽车板材设计的中锰钢的一步和两步热处理的物理模拟和膨胀学研究。将常规的一步等温贝氏体转变用作参考热处理。新近实施的热处理包括在贝氏体区域等温保持，然后在贝氏体范围内将材料在降低的温度下额外保持。添加该步骤以细化微观结构，这导致残留奥氏体的稳定化。使用热力学JMatPro软件进行了平衡状态和非平衡冷却的计算以及模拟的热循环。在膨胀计中进行热处理的物理模拟。使用光和SEM显微镜对获得的样品进行显微镜观察。通过一阶段和两阶段的热处理，可以获得具有高残留奥氏体含量的贝氏体组织。降低一步恒温保持的温度导致贝氏体细化和相邻的残余奥氏体。尽管过程温度降低，钢中锰含量的增加也增加了其形成聚结贝氏体的敏感性，从而导致部分形成了较厚的钢板。