典型生产工艺对无碳化物贝氏体钢轨组织与性能的影响

Effect of Typical Production Process on Microstructure and Properties of Carbide-Free Bainitic Rail Steels

基于矫直、回火和在线热处理3种典型钢轨生产工艺,采用不同工艺组合工业试制5种无碳化物贝氏体钢轨;基于扫描电子显微镜、透射电子显微镜、背散射电子衍射法和X射线衍射法,分析无碳化物贝氏体钢轨的微观组织;采用布氏硬度、单轴拉伸、锯切应变片法、冲击韧性、断裂韧性和疲劳裂纹扩展速度测试等试验,研究典型生产工艺对无碳化物贝氏体钢轨组织和力学性能的影响。结果表明:矫直使无碳化物贝氏体钢轨中的残余奥氏体体积分数自12.44%降至10.6%,有利于促进亚稳态残余奥氏体的转变;回火稳定残余奥氏体,提升冲击韧性20%以上;在线热处理降低残余奥氏体体积分数,提高屈服强度19%以上,尤其能提高抗拉强度和冲击韧性,对轨底残余应力的影响不大。据此,为了综合提升无碳化物贝氏体钢轨的耐磨性和抗接触疲劳性能,在提高屈服强度和抗拉强度的同时增大残余奥氏体体积分数,以提升加工硬化能力和塑性。

Based on the three typical steel rail production processes of straightening,tempering and on-line heat treatment,five kinds of carbide-free bainitic rails were industrially trial-produced with different process combinations.The microstructures of carbide-free bainitic rails were analyzed based on the scanning electron microscope,transmission electron microscope,backscattered electron diffraction method and X-ray diffraction method.By means of Brinell hardness,uniaxial tension,sawing strain gauge method,impact toughness,fracture toughness and fatigue crack growth rate tests,the effect of typical production process on the microstructure and mechanical properties was studied.The results show that straightening reduces the volume fraction of retained austenite in carbide-free bainitic rail from 12.44%to 10.6%,which is beneficial to promote the transformation of metastable retained austenite.Tempering can stabilize the retained austenite and improve the impact toughness by more than 20%.On-line heat treatment can reduce the volume fraction of retained austenite and increase the yield strength by more than 19%,especially improve the tensile strength and impact toughness,but it has little effect on the residual stress at rail foot.Therefore,it is recommended to take into account the wear resistance and contact fatigue resistance of carbide-free bainitic rails synthetically to improve the yield strength and tensile strength while increasing the volume fraction of retained austenite to improve the work hardening ability and plasticity.