道岔轨头内部伤损形貌及组织的研究分析

Research and analysis of damaged morphology and structure on the head of switch rail

高速道岔是高速铁路轨道结构的关键,其结构与状态对列车运行安全和运行品质具有重大影响。道岔尖轨的制造涉及到锻压、热处理、机加工等多个环节,是影响道岔平顺性以及安全性的关键部件。因此,对尖轨伤损的形貌及组织进行分析,对处理今后线路上类似的伤损问题具有指导意义。根据超声波探伤发现,某铁路道岔直尖轨轨头内部存在重伤,实验主要从宏观和微观两个方面进行了检验分析。通过对伤损的宏观形貌观察,利用扫描电子显微镜(SEM)、能谱成分分析仪及金相显微镜等设备对伤损组织进行了微观观察及分析,缺陷区域可看到清晰的晶界及大量的细小孔洞,孔洞边缘光滑,有金属熔融特征,在断口表面还分布着一些融化后再凝固形成的枝晶形貌,枝晶上条状析出物的S、Mn元素含量非常高,为以MnS为主的夹杂物,在缺陷区域还存在沿过烧组织晶粒开裂的裂纹。缺陷区域金相组织的晶粒粗大不均,其中粗晶粒组织晶粒度大小为4.5级,细晶粒组织晶粒度大小为7.5级。以上实验分析结果表明:在伤损直尖轨的加工过程中,由于温度控制不当导致跟端变形过渡区的轨头内部组织出现了过热及局部过烧现象,最终形成重型伤损。

High speed turnout is the key of track structure for the high speed railway.Its structure and state have a great influence on the operation safety and quality of trains.The manufacture of turnout switch rail involves many steps,including forging,heat treatment,machining and so on.The switch rail is a key component influencing the ride comfort and safety of turnouts.Therefore,the analysis of damaged morphology and structure of switch rail has guiding significance to deal with the similar damage problems in the future.According to the ultrasonic detection,serious internal damage existed on the head of one switch rail.The check analysis was mainly conducted from both macro and micro aspects.Through macro morphology observation,the scanning electron microscope(SEM),energy spectrum composition analysis and metallographic microscope were employed for the microscopic observation and analysis of damaged structure.Clear grain boundary and a large number of fine voids could be observed in the defected area.The edge of voids was smooth with metal melting characteristics.Moreover,there were some dendritic crystals on the fracture surface.These dendritic crystals were formed by melting and resolidification.The contents of S and Mn were very high in stripped precipitates on the dendritic crystal.The inclusion was mainly composed of MnS.In addition,the cracks along the overburnt grains also existed in the defected area.The grains of metallographic structure in the defected area were coarse and uneven.The grain size of coarse grain structure was grade 4.5,and the grain size of the fine grain structure was grade 7.5.The results above showed that in the manufacturing process of switch rail,the improper temperature control caused the overheating and partial overburning on the head in the deformation area of the rail.Finally,a serious damage was formed.