A new twin-disc test was performed using discs containing all microstructures of the heat-affected zone (HAZ) of flash-butt welded rails. It was observed that the lower hardness regions (spheroidized cementite in a ferritic matrix) at the HAZ boundary underwent a local deformation, generating valleys and reproducing a common defect type observed in rail welds: double squat-like defect. Longer crack lengths or crack clusters were observed in the HAZ boundary and central weld regions. The cross-section metallography showed that these cracks are directly related to the microstructure of spheroidized cementite at the HAZ edges or pro-eutectoid ferrite at the central region. The decrease in surface roughness before the cracks, the presence of oxide on the bottom crack surface, and superior spheroidized cementite microstructure in the upper crack region suggest that these larger/cluster cracks are predominated by extrusion of the softer material above the harder material (pearlitic/base metal).

中文翻译：

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闪光对焊钢轨双盘试验HAZ显微组织对RCF的影响

使用包含闪光对焊钢轨热影响区 (HAZ) 所有微观结构的圆盘进行了一项新的双圆盘测试。据观察，热影响区边界处的较低硬度区域（铁素体基体中的球化渗碳体）发生局部变形，产生凹谷并再现钢轨焊缝中观察到的常见缺陷类型：双蹲状缺陷。在热影响区边界和中心焊缝区域观察到较长的裂纹长度或裂纹簇。截面金相显示，这些裂纹与热影响区边缘球化渗碳体或中心区域先共析铁素体的显微组织直接相关。裂纹前表面粗糙度的降低、底部裂纹表面上氧化物的存在以及上部裂纹区域中优良的球化渗碳体微观结构表明，这些较大/簇状裂纹主要是由于较软材料在较硬材料（珠光体）上方的挤压而形成的。 /基本金属）。