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对U71Mn钢轨闪光对焊接头的显微组织、硬度分布和微观断口形貌进行了分析,测试了焊接接头的断裂韧性,并分析了正火的影响。结果表明,U71Mn钢轨闪光焊接头中,焊缝区的金相组织为粗大的珠光体团,铁素体网沿晶界析出;热影响区全部为粗大的珠光体团;接头断裂韧性值较低。正火后接头晶粒组织得到细化,三点弯曲试验断口上的解理平台变小,组织的细化使得裂纹扩展的阻力变大,从而使断裂韧性值升高。分析表明,在落锤试验中,可以允许灰斑存在的临界尺寸大小约为4 mm,而在正火后达到了14 mm左右。
The microstructure, hardness distribution and microstructure of flash welded butt joint of U71Mn rail were analyzed. The fracture toughness of welded joint was tested and the influence of normalizing was analyzed. The results show that in the U71Mn rail flash welded joint, the microstructure of the weld zone is coarse pearlite, and the ferrite network is precipitated along the grain boundaries. The heat affected zone is all coarse pearlite group. The joint fracture toughness value is low . After normalizing, the grain structure of the joint was refined, the cleavage platform on the three-point bending test became smaller, and the refinement of the structure made the resistance of crack propagation larger and the fracture toughness value increased. Analysis shows that in the drop-hammer test, the critical size of the gray spot allowed to be about 4 mm, and after normalizing reached about 14 mm.