The fatigue properties of two pearlitic rail steel with different Cr contents were determined using a SincoTec electromagnetic resonance high-frequency fatigue testing machine.The effects of heat treatment process and the Cr contents on the fatigue crack propagation behavior of the rail steels were studied by analyzing the fatigue crack propagation rate curves,fracture morphologies,inclusions and precipitates at the fracture surfaces.The results show that the optimal heat treatment process for the low-Cr steel is cooling at a rate of 8 ℃/s to 560 ℃ and then isothermal holding for 30 s,which increases the fatigue life of the low-Cr steel from 788 000 cycles in as-rolled state to 914 000 cycles,by 16.0％.While under the same heat treatment conditions,the fatigue life of the high-Cr steel is increased from 812 000 cycles in as-rolled state to 1 043 000 cycles,by 28.4％.The fatigue performance improvement of the tested steels resulted by optimized heat treatment process and higher Cr content is attributed to the significant reduction in the interlamellar spacing and cluster size of pearlite.On one hand,the microstructure refinement increases the crack propagation resistance,reduces the distance between fatigued striations,and increases the number of fatigue steps.On the other hand,it hinders the primary crack growth,and increases the grain orientations to obtain higher possibility of secondary cracks.Moreover,the higher Cr content promotes(Fe,Cr)3C second-phase particle precipitation during stage Ⅱ cracking zone,which impedes dislocation motion and thus reduces crack propagation rate during fatigue loading.
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