U71Mn钢轨闪光焊接头轨底伤波成因分析

Research on Defect Wave of Rail Bottom of Flash Welded Joints of U71Mn Rails

针对U71Mn钢轨在闪光焊后,焊接接头轨底部位探伤出现大量伤波的现象,采用金相显微镜、扫描电镜、磁粉探伤等对钢轨母材和焊接接头进行检验分析以查找出现伤波的原因。结果表明:U71Mn钢轨母材全断面化学成分及非金属夹杂物等符合标准要求;焊接接头金相检验结果显示,在探出伤波的位置,焊接头轨底熔合线两侧晶界部位存在大量裂纹,且宏观肉眼可见,裂纹微观内部无夹杂物等缺陷。这种缺陷为焊接过烧缺陷,系焊接时热输入偏大造成的,且此种缺陷无法通过正火消除。同时研究了过烧缺陷的分布情况,发现缺陷主要集中在轨底下表面及轨底上坡面的近表层附近。流线分析表明,缺陷所在的原始部位为轨底的内部中间区域,经焊接热挤压后流变到近表层。对U71Mn钢轨闪光焊工艺进行优化,降低焊接热输入,可以消除此类过烧缺陷。

Aiming at the phenomena that a large number of defect waves appeared in the welded joint of rail bottom of U71 Mn rail after flash welding, the base metal and welding joints of the rail were examined and analyzed by metallographic microscope, scanning electron microscope and magnetic particle inspection to find out the cause of the defect waves. The results show that chemical composition of full-section and non-metallic inclusions of the U71 Mn rail meet the standard requirements. The metallographic examination results of welding joints show that there are a lot of cracks at the grain boundary on both sides of the fusion line of welding joint at rail bottom corresponding to the location of defect waves. The cracks are visible and there are no inclusions in the interior of the cracks. The crack is a kind of welding overburning defect which is caused by large heat input during welding, and the defect cannot be eliminated by normalizing. At the same time, the distribution of overburning defects was studied. It is found that the defects mainly concentrated near the surface of the rail bottom and the slope of the rail bottom. The streamline analysis shows that the original position of the defects is the central area of the rail bottom, and it moves to the near surface by hot extrusion during welding. By optimizing flash welding process of U71 Mn rail and reducing welding heat input, such overburning defects can be eliminated.