In this study, the austenite transformation behaviour in a medium-Mn (MMn) steel is investigated during heat treatments that replicate those occurring in low-temperature hot stamping (LTHS), with the aim of better understanding this behaviour to optimise heat-treatment design. The austenitisation behaviour and critical phase transformation temperatures during the LTHS heating process and their dependence on heating conditions are investigated using dilatometry with a Gleeble 3800 thermal-mechanical simulator, covering heating rates of 1–25 °C s⁻¹ and soaking temperatures of 630–900 °C. Both a higher heating rate and higher soaking temperature are found to be beneficial to shorten the time required for obtaining a given austenite fraction. The martensite start temperature (M_s) shows a rapid increase with increasing soaking temperatures when austenitisation is partial, and a slower increase after full austenitisation. Excellent ultimate tensile strength values of around 1750 MPa and total elongation values of around 9.3 % are obtained for the material after the LTHS heating process. A physically based model describing the austenitic transformation under these conditions has been adopted and calibrated. The model shows good agreement with austenitic transformation diagrams constructed from experimental data, and thus can function as a guide for selecting optimum heat-treatment parameters for LTHS.

在这项研究中，研究了中锰 (MMn) 钢在热处理过程中的奥氏体转变行为，这些行为复制了低温热冲压 (LTHS) 中发生的那些行为，目的是更好地了解这种行为以优化热处理设计. LTHS 加热过程中的奥氏体化行为和临界相变温度及其对加热条件的依赖性通过 Gleeble 3800 热机械模拟器使用膨胀法进行研究，加热速率为 1–25 °C s ^-1，均热温度为 630– 900℃。发现较高的加热速率和较高的均热温度有利于缩短获得给定奥氏体分数所需的时间。马氏体起始温度 ( M _s) 在部分奥氏体化时随着均热温度的升高而迅速增加，在完全奥氏体化后缓慢增加。在 LTHS 加热过程后，材料获得了约 1750 MPa 的优异极限拉伸强度值和约 9.3% 的总伸长率值。已经采用并校准了描述这些条件下奥氏体转变的基于物理的模型。该模型与根据实验数据构建的奥氏体转变图显示出良好的一致性，因此可以作为选择 LTHS 最佳热处理参数的指南。