贝氏体钢轨母材轨头核伤原因分析

通过断口宏观与微观形貌观察、扫描电镜及能谱分析、金相显微组织分析等方式对3根贝氏体钢轨母材轨头核伤的原因予以分析,发现伤损均为氢致裂纹引起的轨头内部横裂型核伤。断口中心区域存在粗大的非金属夹杂物是导致钢轨中的氢在此处富集并形成裂纹的主要原因。贝氏体钢轨氢致裂纹型核伤的主要特征有:伤损位于轨头内部踏面下方4～10 mm处,断口中部存在粗大夹杂物;断口附近的低倍样中观察不到微细裂纹。通过采取改进生产工艺、降低钢中的氢含量(将钢水氢含量控制在1.7×10-6以下)、减少钢中的粗大夹杂物等措施,再上线的贝氏体钢轨未出现该类伤损。

Analysis on Cause of Rail Head Transverse Cracks of Bainite Rail Base Metal

By means of macroscopic and microscopic morphology observation of fracture,scanning electron microscope and energy dispersive spectrometer analysis,metallographic microstructure analysis,the causes of rail head transverse cracks of three Bainite rail base metal were analyzed.It was found that the damage is transverse cracks in the rail head caused by hydrogen induced cracks and the main reason for hydrogen enrichment and crack formation in the rail is the presence of large nonmetallic inclusions in the center of fracture.The main characteristics of hydrogen induced cracktype tache oval of Bainite rail are as follows:the damage is 4~10 mm below the internal tread of the rail head,there are coarse inclusions in the middle of fracture,and no micro-cracks are observed in the macrostructure samples near the fracture.By improving the production process,reducing the hydrogen content in the steel(controlling the hydrogen content below 1.7×10^-6 in the molten steel),reducing the coarse inclusions in the steel and other measures,the laid Bainite rail does not have such type of cracks any more.