U71Mn钢轨闪光焊接头马氏体组织成因及处理措施

Causes and countermeasures of martensitic structure formation in flash welded joint of U71Mn steel rail

马氏体组织作为U71Mn钢轨闪光焊接头中的异常组织,会影响接头的安全性能,故需对其产生原因和处理措施进行研究。以未经正火处理的U71Mn钢轨闪光焊接头为研究对象,利用Gleeble-1500D热模拟试验机对其进行一次正火处理和二次正火处理,利用光学显微镜和扫描电镜对其热处理前后的显微组织和元素成分进行分析,探讨了马氏体组织在U71Mn钢轨闪光焊接头的分布规律和产生原因,提出了相应的处理措施,并进行了现场验证。结果表明,U71Mn钢轨闪光焊接头中马氏体的分布规律与C和Mn元素偏析具有一致性,马氏体主要出现在富锰富碳区,其中Mn含量可达母材的两倍以上;闪光焊会加剧U71Mn钢轨中的Mn元素偏析,正火处理对U71Mn钢轨闪光焊接头中Mn元素偏析的改善效果并不明显,但可加速C元素的扩散,从而在一定程度上减轻马氏体的出现程度;降低U71Mn钢轨中的Mn含量,并配以合适的正火处理,能够极大消除甚至避免闪光焊接头中马氏体的出现。

Martensite,as an abnormal microstructure in U71Mn steel rail flash welded joint,will decrease the safety of the joint,so it is necessary to study its formation causes and countermeasures.Taking U71Mn steel rail flash welded joint as the research object,the single normalizing treatment and dual-normalizing treatment were carried out by Gleeble-1500D thermal simulation testing machine.The microstructure and element composition before and after normalizing treatment were analyzed by means of optical microscope and scanning electron microscope.The distribution law and formation causes of martensite microstructure in the U71Mn steel rail flash welded joint were discussed,and the corresponding countermeasures were put forward and verified on the spot.The results show that the distribution of martensite in the flash welded joint of the U71Mn steel rail is consistent with the segregation of C,Mn element.The martensite in flash welded joint mainly occurs in the manganese rich and carbon rich area,in which the content of Mn element is more than twice that of the base metal.Flash welding will aggravate Mn element segregation in the U71Mn steel rail.Normalizing treatment has no obvious effect on Mn element segregation in U71Mn steel rail flash welding joint,but it can accelerate the diffusion of C element and reduce the occurrence of martensite to a certain extent.By reducing the content of Mn in U71Mn steel rail and providing proper normalizing treatment can greatly eliminate or even avoid the occurrence of martensite.