55NiCrMoV7 hot-work die steel is mainly used to manufacture heavy forgings in the fields of aerospace and automobile. This study aims to clarify the effects of heat treatment on the microstructural evolution and mechanical properties of the steel, in order to find out an optimal heat treatment scheme to obtain an excellent balance of strength, ductility and toughness. The steel was quenched at temperature from 790 °C to 910 °C followed by tempering treatments of 100–650 °C for 5 h. The mechanical property tests were carried out by tensile, impact toughness and hardness. Optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to observe the austenite grains, lath martensite, carbides and fracture morphology. The results show that the quenching temperature mainly influences the austenite grain size and the volume fraction of undissolved carbides (UCs), while the tempering temperature mainly influences the size and morphology of the martensite with a body centered cubic (BCC) and the carbides with a face centered cubic (FCC). The mechanical properties of the steel, including yield and tensile strength, ductility, impact toughness and hardness, get an excellent balance at a quenching range of 850–870 °C. As the tempering temperature increases, the yield and tensile strength and hardness decrease, while the ductility and impact toughness increase. These variation trends can be further verified by fracture SEM observation and analysis. Combined with a macro-micro coupled finite element (MMFE) modeling technique, the cooling rate, microstructural evolution and yield strength of the steel were predicted and compared with the tested data.

55NiCrMoV7热作模具钢主要用于制造航空航天、汽车等领域的重型锻件。本研究旨在阐明热处理对钢的显微组织演变和力学性能的影响，以找出最佳热处理方案，以获得强度、延展性和韧性的良好平衡。钢在 790°C 至 910°C 的温度下淬火，然后在 100-650°C 的温度下进行 5 小时的回火处理。力学性能测试通过拉伸、冲击韧性和硬度进行。用光学显微镜(OM)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)观察奥氏体晶粒、板条马氏体、碳化物和断口形貌。结果表明，淬火温度主要影响奥氏体晶粒尺寸和未溶解碳化物（UCs）的体积分数，而回火温度主要影响体心立方（BCC）马氏体和碳化物的尺寸和形貌。面心立方 (FCC)。钢材的力学性能，包括屈服强度和抗拉强度、延展性、冲击韧性和硬度，在 850-870°C 的淬火范围内得到了很好的平衡。随着回火温度的升高，屈服强度和抗拉强度和硬度降低，而塑性和冲击韧性增加。这些变化趋势可以通过断口扫描电镜观察和分析进一步验证。结合宏观-微观耦合有限元（MMFE）建模技术，冷却速度，