地铁线路钢轨闪光焊接头轨头下颚伤损原因分析

Damage Cause Analysis of Flash Butt Welded Joint of Metro Rail Jaw

国内某地铁线路在服役2年多后,钢轨的闪光焊接头出现了多起轨头下颚伤损,裂纹从轨头下颚焊筋边缘处发生,并快速发展为严重缺陷,最后导致接头断裂。通过对该受损接头进行外观检验,采用光学显微镜、扫描电镜等设备对裂纹的断口形貌、金相组织等进行检验,找到了下颚伤损的具体原因:该轨头下颚处推瘤后焊缝余高超标,推瘤与母材形成的夹皮未打磨干净,由此形成了明显的尖角,导致应力集中;加上该处在焊后正火过程中脱碳,形成了大量的铁素体组织,导致钢轨疲劳强度降低;列车运行中,在轮轨反复作用力下,轨头下颚推瘤夹皮与母材尖角处形成裂纹源,并逐渐扩展形成疲劳核伤,裂纹进一步扩展后导致接头断裂。

After certain domestic metro line serving for over 2 years,numeral cases of rail jaw damage at the flash butt welded joints have appeared,and the cracks all occurred from the weld seam of rail jaw,quickly developing into serious defects,which finally leads to joint fracture.Through appearance inspection of the damaged joint,optical microscope and scanning electron microscope,the fracture morphology and metallographic structure of the crack are inspected.Specific reasons for jaw damage are found:weld reinforcement exceeding standard after beading trimming at rail jaw,and obvious sharp angle is formed due to the skin formed between the welding beadings and the base metal being not polished clean,which leads to stress concentration.Large amount of ferrite structure was found due to the decarburization during the normalizing process after welding,which reduces the rail fatigue strength.In the process of train operation,under the repeated force of wheel and rail relative effects,the crack source is formed at the sharp corner of the skin and the base metal,which gradually expands to form the fatigue transverse cracks,and further expands leading to joint fracture.