钢轨厂焊接头焊缝轨腰轨底圆弧过渡区缺陷检测及分析

Detection and Analysis of Defects in Arc Transition Zone of Waist and Bottom of Rail Factory Welding Joint Weld Seam

U71MnG钢轨厂焊接头焊缝轨腰轨底圆弧过渡区超声波探伤回波超标,表面磁粉探伤显现出缺陷形貌。针对这一问题,采用光学显微镜、扫描电镜和能谱对缺陷进行了分析。结果表明:缺陷为钢轨焊缝表面裂纹,微观下以大小孔洞的形态分布在焊缝正中心及其两侧,长约12 mm,宽约2 mm,深度至少1.2 mm;断口存在沿晶断裂和烧蚀孔洞形貌,能谱未发现晶粒及晶界有明显的元素偏析。该缺陷是闪光焊弧坑裂纹,形成过程是焊接顶锻前出现异常的大体积过梁爆破形成端面弧坑,大体积弧坑在顶锻瞬间未被液态金属完全填充而形成密闭孔洞,孔洞周围高温液态金属自由凝固形成大小不同的微小孔洞,在高温和组织应力作用下晶界产生少量的晶间裂纹。建议检查焊接设备的机械和电气状态,优化焊接工艺参数。

The ultrasonic detection echo of the arc transition zone at the waist and bottom of the U71MnG rail factory welding joint exceeds the standard,and the surface magnetic particle flaw detection shows defect morphology.In response to this issue,optical microscopy,scanning electron microscopy,and energy spectrum were used to analyze the defects.The results show that the defect is a surface crack on the rail weld seam,which is distributed in the form of small and medium-sized holes at the center and both sides of the weld seam at the micro level,with a length of about 12 mm,a width of about 2 mm,and a depth of at least 1.2 mm.The fracture surface exhibits intergranular fracture and ablative pore morphology,and no significant elemental segregation was observed in the grains and grain boundaries by energy spectrum.The defect is a flash welding crater crack,which is formed by an abnormal large volume lintel explosion before welding and forging,and formed an end face crater.The large volume crater is not completely filled by liquid metal at the moment of forging,forming a closed hole.The high-temperature liquid metal around the hole solidifies freely to form small holes of different sizes,and a small amount of intergranular cracks are generated at the grain boundary under the action of high temperature and structural stress.It is recommended to check the mechanical and electrical status of welding equipment and optimize welding process parameters.