In-depth understanding of the impact mechanism of nitrogen on tempering behavior of hot-working die steel is still limited. In present work, the microstructural evolution and mechanical property change of new nitrogen-alloyed Cr–Mo–V hot-working die steel during long-term tempering were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), eletron backscattered diffraction technique (EBSD) and 3D atom probe tomography (3DAP). The impact mechanism of nitrogen on tempering stability were discussed in detail. The results reveal that whether nitrogen is beneficial to the tempering stability of steel varies with quenching temperature. Trace nitrogen exerts a significant effect on the allowed quenching temperature and metastable M₃C carbides, affecting the coarsening rate and transformation of M₂₃C₆ carbides during tempering process. Tempering stability was improved by nitrogen mainly by enhancing precipitation hardening and grain refinement strengthening, which account for about 70% of total yield strength. Improving effect of nitrogen in precipitation hardening is more distinct with the increase of tempering time. These results are helpful for understanding the mechanisms of nitrogen in steels worked at high temperatures.

对氮对热作模具钢回火行为的影响机理的深入了解仍然有限。在目前的工作中，通过扫描电子显微镜（SEM），高分辨率透射电子显微镜（HRTEM）研究了新型氮合金化Cr-Mo-V热作模具钢在长期回火过程中的组织演变和力学性能变化。 ，电子背散射衍射技术（EBSD）和3D原子探针层析成像（3DAP）。详细讨论了氮对回火稳定性的影响机理。结果表明，氮是否有利于钢的回火稳定性随淬火温度的变化而变化。微量氮对允许的淬火温度和亚稳M ₃产生重大影响C碳化物，影响回火过程中M ₂₃ C ₆碳化物的粗化率和相变。氮主要通过增强沉淀硬化和晶粒细化强化来改善回火稳定性，约占总屈服强度的70％。随着回火时间的增加，氮在沉淀硬化中的改善作用更加明显。这些结果有助于理解高温下钢中氮的机理。