采用化学成分分析、力学性能测试、金相检验和断口分析等方法, 分析了U75V钢轨闪光焊接头轨腰拉伸断后伸长率不合格的原因。结果表明: 钢轨接头和钢轨母材轨腰大量密集分布MnS夹杂物(评级达到3.0级), 长条状的MnS夹杂物经闪光焊顶锻后, 随金属流线偏转45°方向, 当与拉伸过程中的45°最大剪切应力平行时, 相当于MnS夹杂物受到横向拉伸剪切, 裂纹容易在夹杂物中开裂和扩展, 故断后伸长率很低。

Using chemical composition analysis, mechanical properties testing, metallographic examination and fracture analysis to find out the reason of substandard elongation after fracture of U75V rail web of flash welding joint. The results showed that there were numerous dense inclusions (MnS ratings reached 3.0 grade) in rail joint and rail web, the long stripe of MnS inclusion after welding upsetting, was deflected with the metal flow, and the deflecting direction was 45°, when it was parallel to the tensile process of 45° maximum shear stress, that means was the MnS inclusion subjected to transverse tensile shear, the cracks was so easy dehisced and expanded in MnS inclusion, elongation properties was so low.