The microstructure, precipitates and properties of 25CrNiMoV (DZ2) steel for high-speed railway axles with different Nb contents were investigated by means of optical microscopy, scanning electron microscopy, electron back-scattering diffraction, transmission electron microscopy and physicochemical phase analysis. The results show that the grain size of the original austenite of the test steels decreases from 20.5 to 14.2 and 10.8 μm after adding 0.026 and 0.039 wt.% Nb to a 25CrNiMoV steel, respectively. Moreover, the block width of the tempered martensite in the test steels is refined from 1.91 to 1.72 and 1.60 µm, respectively. MC-type precipitates in 25CrNiMoV steel are mainly VC, while (Nb,V)C gradually precipitates when Nb is microalloyed, and the amount of precipitates increases with increasing Nb content. Through strengthening mechanism analysis, it is found that grain refinement strengthening is the primary way to increase the strength. The improvement in the yield strength with increasing Nb content is attributed to a significant increase in precipitation strengthening, grain refinement strengthening and dislocation strengthening.

通过光学显微镜，扫描电子显微镜，电子反向散射衍射，透射电子显微镜和理化相分析研究了不同Nb含量的25CrNiMoV（DZ2）钢用于高速铁路车轴的组织，析出和性能。结果表明，在25CrNiMoV钢中分别添加0.026和0.039 wt。％的Nb后，测试钢的原始奥氏体晶粒尺寸从20.5减小到14.2和10.8μm。此外，试验钢中回火马氏体的块宽分别从1.91精炼到1.72和1.60 µm。25CrNiMoV钢中的MC型析出物主要为VC，而当Nb微合金化时（Nb，V）C逐渐析出，且析出物的数量随Nb含量的增加而增加。通过强化机理分析发现，晶粒细化强化是提高强度的主要途径。随着Nb含量的增加，屈服强度的提高归因于沉淀强化，晶粒细化强化和位错强化的显着增加。