30NiCrMoV12和EA4T材质高速动车组车轴服役性能

为全面掌握高速动车组30NiCrMoV12和EA4T两种车轴材质的服役性能，分别实测了新、旧车轴的化学成分、常规力学性能、标样疲劳特性、冲击性能、断裂韧性、疲劳裂纹扩展门槛值和疲劳裂纹扩展速率等，并对其金相组织进行观测，综合评价分析两种材质车轴服役性能. 结果表明:（1） 与EA4T材质相比，30NiCrMoV12材质车轴中Ni含量高10倍，Mo、V含量高2倍，C含量略高，抗拉强度高34%，屈服强度高54%，疲劳强度高30%；（2） 断裂损伤性能对比中，30NiCrMoV12材质车轴比EA4T材质车轴的常温冲击功约低12%，断裂韧性约高34%，EA4T材质新轴疲劳裂纹扩展门槛值比30NiCrMoV12新轴的高21%，旧轴时两者相当；（3） 当应力强度因子幅度小于50 MPa?m1/2时，30NiCrMoV12材质车轴裂纹扩展速率大于EA4T材质车轴，反之，30NiCrMoV12材质车轴裂纹扩展速率小于EA4T材质车轴；（4） 30NiCrMoV12材质车轴整个截面组织均为晶粒细小的贝氏体和回火马氏体，淬透性较好，制造工艺性能好；EA4T车轴在表面约30 mm深度范围为均匀的贝氏体和回火马氏体，后随深度增加逐渐出现铁素体，距表面60 mm为珠光体和铁素体，并以铁素体为主. 

Service Performance of High-Speed EMU Axles Made of 30NiCrMoV12 and EA4T

In order to gain insight into the mechanical behaviors of China’s high-speed EMU (electric multiple unit) axles made of 30NiCrMoV12 and EA4T, both the in-serving and over-served axles were examined in their chemical composition, conventional tensile strength, fatigue, impact toughness, fracture toughness, the threshold value and rate of fatigue crack growth and the metallographic structure. The final results are shown as follows: (1) The 30NiCrMoV12 axles had 10 times higher Ni element content, 2 times higher Mo and V elements content, and slightly higher C element content than the EA4T axle. The conventional tensile strength, yield strength and fatigue strength were increased by 34%, 54%, and 30%, respectively. (2) Compared with the EA4T axle, the conventional impact energy of the 30NiCrMoV12 axle at room temperature decreased by 12%; however, its fracture toughness increased by 34%. The EA4T axle had a 12% higher threshold value of fatigue crack growth than the 30NiCrMoV12 axle, and as for the two types of the old axis, this feature are quite similar. (3) When the stress intensity factor was less than 50 MPa?m1/2, the crack growth rate was greater than the EA4T axle; However, when it was larger than 50 MPa?m1/2, it was on the contrary. (4) The grain size of the full section microstructure of the 30NiCrMoV12 axle was fine bainite and tempered martensite with good hardenability and manufacturing performance. However, the section of the EA4T axle was composed of uniform bainite and tempered martensite within the depth of 30 mm from surface, and the ferrite gradually appeared with depth increasing. When the depth increased to 60 mm, the microstructure consisted of pearlite and ferrite, meanwhile the volume fraction of ferrite was significantly higher than that of pearlite.