轻质高强中锰钢(含 3%~12%Mn，质量分数)是第三代汽车用钢的典型代表，充分利用其中亚稳奥氏体在塑性变形中的孪晶诱导塑性 (TWIP)与相变诱导塑性(TRIP)效应耦合作用，可使其获得优异的强度与塑性。然而目前关于双相中锰钢的低温变形特性与断裂行为尚不清晰。本文对一种高性能双相中锰钢在低温环境下的力学行为、变形机制以及韧脆转变特性进行研究。实验钢屈服强度(TS)与抗拉强度(UTS)随变形温度降低而逐渐升高，但总延伸率(TE)逐渐下降。其综合力学性能在0℃下达到峰值，强塑积为72.97 GPa%。奥氏体的TRIP效应对中锰钢低温力学性能起到关键作用，对此构建了低温变形条件下α′-马氏体转变动力学模型，其中变形温度降低使应变诱导马氏体转变(SIMT)速率加快。对于马氏体形核机制，其20℃下表现为γ→twins与γ→ε→α′多种机制共同作用，即TWIP与TRIP效应耦合。而随变形温度降低至0℃，TWIP效应受到抑制，γ→ε→α′成为主要的变形机制。随变形温度再次下降(-40℃)试样表现为γ→α′直接形核方式，α′-马氏体在形变初期快速增长。另外，随变形温度下降双相中锰钢的断裂模式出现韧脆转变特征。通过SEM与EBSD测试方法对裂纹周围微观组织表征显示20℃下中锰钢的裂纹源出现在铁素体/马氏体(α/α′)界面位置，并沿α/α′或α′/α′界面扩展。而在低温环境下，其裂纹萌生位置相同，在α/α′界面位置。但由于α′-马氏体在低温下脆性增强，裂纹扩展直接穿越α′-马氏体内部，导致试样发生脆性断裂。

The lightweight and high-strength medium manganese steel (MMnS with 3%-12% Mn, mass fraction) is a typical representative of the third-generation steels for automotive applications, which can achieve excellent strength and plasticity by fully utilizing the coupling effect of metastable austenite, induces twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effect during plastic deformation. However, the low-temperature deformation characteristics and fracture behavior of dual-phase MMnS remain unclear at present. The mechanical properties, deformation mechanism and the ductile-to-brittle transition characteristics of dual-phase MMnS are investigated under low-temperature conditions The yield strength (TS) and ultimate tensile strength (UTS) of the MMnS increase, whereas the total elongation (TE) decrease as deformation temperature decrease form 20℃ to -60℃. The comprehensive mechanical properties of the samples reach peak value at 0°C, with an excellent combination of strength and ductility (72.97 GPa%). The TRIP effect of metastable austenite(γ) plays a crucial role in the low-temperature mechanical properties of MMnS. This paper established a quantitative kinetic model of strain-induced martensite transformation (SIMT) under low-temperature deformation progress, which indicated SIMT rate is faster at lower deformation temperatures. The α′-martensite nucleation mechanism is characterized by the combined action of γ→twins and γ→ε→α′ mechanisms at 20°C. This indicates that both the TWIP and TRIP effects are acting together at 20°C. As the deformation temperature decreases to 0℃, the TWIP effect was inhibited, and the γ→ε→α′ transformation dominated the SIMT. The sample demonstrates a direct nucleation mechanism from γ→α′ as the deformation temperature decreases to -40℃, leading to a rapid increase in the content of α′-martensite. In addition, the fracture mode of MMnS exhibits a ductile-to-brittle transition as the deformation temperature decreases. As characterized by SEM and EBSD analysis of the microstructure surrounding the crack, the crack initiation in MMnS was primarily due to damage at the ferrite/martensite (α/α′) interface at 20°C. Crack propagation along the α/α′ or α′/α′ interface. The α′-martensite impedes crack propagation, resulting in ductile fracture of the sample. The crack initiation location is the same at α/α′ interface in low-temperature environments. However, the crack rapidly propagates through the α′-martensite due to the increased brittleness of α′-martensite at low temperatures. This results in brittle fracture of the sample in low-temperature deformation.