60N U71MnG钢轨轨头裂纹成因分析  

Cause Analysis of Cracks in the 60N U71MnG Rail Head

作　　者：许鑫 徐超 张倩 梁旭 李锦 吕晶 杨其全 曹欣旺 XU Xin;XU Chao;ZHANG Qian;LIANG Xu;LI Jin;LÜJing;YANG Qiquan;CAO Xinwang(Metals and Chemistry Research Institute,China Academy of Railway Sciences Corporation Limited,Beijing 100081,China;Department of Engineering,China Railway Shenyang Group Co.,Ltd.,Shenyang Liaoning 110001,China;Laboratory of Metal Research,Beijing Advanced Material Technology Co.,Ltd.of CARS,Beijing 100081,China)

机构地区：[1]中国铁道科学研究院集团有限公司金属及化学研究所,北京100081 [2]中国铁路沈阳局集团有限公司工务部,沈阳110001 [3]北京中铁科新材料技术有限公司金属研究室,北京100081

出　　处：《中国铁道科学》2023年第5期47-57,共11页China Railway Science

基　　金：国家重点研发计划项目(2021YFB2601000);中国铁道科学研究院集团有限公司院基金课题(2021YJ224)。

摘　　要：对线路探伤检查发现的60N U71MnG重伤钢轨进行磁粉检测复核,在钢轨轨头工作边侧表面发现了裂纹。为查明裂纹产生的原因,人工压断裂纹钢轨并取样,对裂纹处断口进行宏观形貌观察、扫描电镜观察及能谱分析,以获得裂纹断口的形貌特征和伤损特点;对试样进行显微组织观察和维氏硬度检验,以分析裂纹的成因和机理,并在考虑温度拉应力和列车动弯应力作用下,对钢轨受力及裂纹萌生机理进行仿真分析。结果表明:钢轨轨头工作边侧表面裂纹为冷态下形成的外伤,裂纹及其附近部位曾受到过剧烈摩擦产生高温并发生相变产生了马氏体组织;当轨温为-33℃时,在温度拉应力和列车产生的动弯应力的共同作用下,白层马氏体表面中心偏下位置的拉应力为417.6 MPa,裂纹易从钢轨表面中心萌生,其尖端应力强度因子KI为28.9 MPa·mm^(1/2),高于钢轨断裂韧性KIC的最小单值,因此钢轨在经历很短的循环载荷周次后便从白层马氏体处发生裂纹失稳扩展。A re-examination of the magnetic particle testing was conducted for the severely damaged 60N U71MnG rail discovered during the line flaw detection inspection.A crack was identified on the surface of the rail head on the working side.In order to find out the causes of cracks,the cracked rail was manually fractured and sampled.The morphology observation,scanning electron microscope observation and energy spectrum analysis of the crack fracture were applied to obtain morphological characteristics and damage characteristics of the crack fracture.Microscopic observation and the Vickers hardness test were conducted to analyze the cause and mechanism of the crack.Considering the temperature tensile stress and dynamic bending stress of the train,the simulation analysis of the stress and crack initiation mechanism of the cracked rail was carried out.The results showed that the crack on the the rail head surface on the working side was a result of external bruising that occurred during cold conditions.The crack and its adjacent parts experienced intense friction,resulting in elevated temperatures and a phase transformation leading to the formation of a martensite structure.At a rail temperature of-33℃,the combined action of temperature-induced tensile stress and vehicle dynamic bending stress resulted in a tensile stress of 417.6 MPa at a lower position just below the center of the martensite surface.The crack initiated easily from the center of the rail surface and had a stress intensity factor(KI)of 28.9 MPa·mm^(1/2) at the crack tip.This value exceeded the minimum fracture toughness value(KIC)of the rail,indicating that after a short cycle of cyclic loading,crack instability propagation occurs at the white martensite of rail.

关 键 词：U71MnG钢轨 外伤 裂纹 马氏体组织 温度拉应力 动弯应力 

分 类 号：U213.46[交通运输工程—道路与铁道工程]