钢轨闪光焊接头心部马氏体的成因及对策

Causes and Countermeasures of Martensite in the Center of Rail Flash Butt Welding Joint

采用光学显微镜、显微硬度计、激光光谱原位分析仪(LibsOpa)和扫描电镜(EDS)能谱分析了U71Mn和U75V钢轨闪光焊接头心部马氏体与基体在组织、硬度、成分分布和含量上的差异。采用JMatPro软件模拟了2种成分下冷却曲线的变化。结果表明:U75V和U71Mn钢轨闪光焊接头热影响区中存在Mn和Si元素偏析,其中Mn元素是产生高硬马氏体的主要诱因。产生机理是Mn元素增强了过冷奥氏体的稳定性并导致C曲线右移,使其部分越过珠光体转变而发生马氏体转变;同时Mn偏析将偏析区域马氏体转变的最小冷速分别降低了4℃/s和3℃/s,显著提高了偏析区域的淬透性。解决方法一是从源头上改善钢轨生产工艺,减少元素偏析;二是调整焊后正火工艺,在保证接头硬度的前提下,适当降低接头冷却速率或者提高喷风结束温度后空冷(缓冷)。

The differences in microstructure,hardness,composition distribution and content between the core martensite and matrix of U71Mn and U75V rail flash butt welding joints were analyzed by optical microscope,microhardness tester,laser spectrum in situ analyzer(libsopa)and energy spectrum.JMatPro software was used to simulate the change of cooling curve under two components.The results show that Mn and Si segregation exist in the heat affected zone of U75V and U71Mn rail flash butt welded joints,in which Mn is the main inducement to produce high hardness martensite.The mechanism is that Mn enhances the stability of undercooled austenite and causes the C curve to shift to the right,making it partially cross pearlite transformation and martensite transformation.At the same time,Mn segregation reduces the minimum cooling rate of martensitic transformation in the segregation region by 4℃/s and 3℃/s respectively,which significantly improves the hardenability of the segregation region.The first solution is to improve the rail production process from the source and reduce element segregation.Second,adjust the post weld normalizing process,appropriately reduce the joint cooling rate or increase the end temperature of air spraying on the premise of ensuring the joint hardness.