Research On Hardanability Of25CrMo Axle Steel Used In High-Speed Rail

With China’s railway sixth speed increase, there are higher and more strictrequirements for the railway and trains. The train axle is the important part ofhigh-speed rail for its walk, and its quality determines the speed of trains running andthe security of transport, therefore, the performance of axle is critical. The mechanicalproperties of axle is determined by the composition and heat treatment process. Whilethe hardenability is the key to design heat treatment process. In this paper, the study onhardenability of25CrMo axles steel using in high-speed rail was carried out by usinghardness measurement, metallographic analysis, quantitative metallography, scanningelectron microscopy. The main contents are as follows.1. According to high-speed axle technical standard for the control of C, Si, Cr, Mo,Mn, Ni,Cu,V alloy element in axle steel, the25CrMo axle steel used in high-speed axlewas designed. The inclusions and fatigue were also analyzed, the resules show that themetallurgical quality is well and its mechanical properties meet the requirements oftechnical standard.2. Based on the traditional end-quenched test method, an improved end-quenchedtest was put forward in the experiment, in which the advantage is to force the heat totransfer along axial direction, and avoid edge effects.3. Effect of heat treatment process on microstructure and hardness of25CrMo steelwas also studied. The results show that the ability of bainite formation for25CrMo steelis strong. The bainite can form even if under air-cooled condition. The final heattreatment process was choosen as tempering temperature at870℃followed byquenching at380℃, then cooling in water.4. Effect of element on hardenabilitywas investigated with different content of C,Cr, Mn, Mo, Ni, Cu, V in axle steel25CrMo. C, Cr, Mn and Mo have a big impact onthe hardenability of25CrMo steel. The end quenching curve shifts up, and the hardness value increases significantly. The hardenability values can reach over15mm. Fromsurface to the center of sample, the microstructure is of martensite, martensite withbainite, bainite respectively.5. Based on the end quenching models and test data, the mathematical model for25CrMo axle steel was developed by nonlinear fitting. Quantitative relationshipbetween the chemical composition and hardenability coefficients was also determinedfor the25CrMo axle steel.