钢轨闪光焊焊接接头轨面横向裂纹成因分析

Research on Transversal Cracks in the Tread of Flash Welding Joints of Rails

针对秦沈线17处钢轨闪光焊焊接接头轨面产生的横向裂纹,通过在伤损部位取样,分别进行洛氏硬度、金相组织和显微硬度等试验,结合焊轨生产的实际,分析裂纹形成原因。认为所检闪光焊焊接接头的裂纹起源于钢轨表面的白亮层马氏体组织,并在外力作用下扩展进入正常的珠光体组织区域,裂纹深度达到5mm。研究钢轨精磨方式与焊缝凸起之间的关系,得出:对矫直后具有明显焊缝凸起的焊接接头进行精磨时有可能因打磨中进刀量过大,引起钢轨局部机械热损伤,造成局部金属的急速高温和急速冷却,形成高硬度的脆性白亮层马氏体组织,是导致焊接接头轨面产生裂纹的根本原因。建议进一步研究钢轨焊接生产打磨工艺规范以及客运专线铁路钢轨的预打磨规范,避免钢轨及焊接接头出现马氏体组织。

In this paper, the cause of unusual transversal cracks in tread of seventeen flash welding joints of rails in Qin-Shen Line are analyzed through Rockwell hardness testing, microstructure checking and micro-hardness testing, combined with the actual situation of rail welding. Metallurgical specimens are cut from the damaged area of welding joints. The results show that the crack occurs in White Etching Layer （WEL）, which consists of brittle and hard martensite. With the effect of train dynamic forces, the crack grows into normal pearlitic area, and its depth is up to 5 mm. After investigating the relationship between rails final grinding procedure and the bump in welding joints, it is concluded that White Etching Layer which consists of brittle martensite is caused by improper final grinding procedure, and subsequently mi- crocracks are formed in WEL. When the crack size becomes sufficient, the crack will grow, leading to the failure of welding joints. The down-feed of grinding wheels may be excessive during grinding bump in welding joints, thus thermo-mechanical damages in part of rails are caused, which part of metal are heated and cooled rapidly, and subsequently hard and brittle WEL is formed. It is suggested that grinding procedure of rails welding joints and pre-grinding procedure of rails in passenger railway line should be further researched, so as to avoid appearing martensite in rails and welding joints.