轮轨硌伤诱发滚动接触疲劳机制的材料影响

Influence of Wheel/Rail Material on Initiation of Local Rolling Contact Fatigue from Indentations

利用GPM-30滚动接触疲劳磨损试验机,在油润滑条件下试验研究轮轨材料对丝锥硌伤诱发局部滚动接触疲劳(LRCF)的影响,涉及ER8高速车轮钢、U71MnG高速钢轨钢,以及1280 MPa和1380 MPa级的贝马复相、PG4、PG5等4种新开发的重载钢轨钢。发现硌伤诱发的剥离掉块仅发生在硬度低于300 HV的ER8和U71MnG高速轮轨材料,且只有在硌伤深度超过150~200μm的临界值时发生,对于硬度高于400 HV的重载钢轨材料,表面硌伤不太可能诱发局部滚动接触疲劳。试样表面和剖切观测显示,初始疲劳裂纹可萌生于硌伤内部和前、后沿,底部萌生的裂纹更容易导致包含深裂纹和大块剥离的局部滚动接触疲劳,后沿比前沿更容易萌生初始裂纹。与U71MnG高速钢轨相比,硬度更低的ER8高速车轮钢试样上硌伤引发剥离掉块的可能性更高,但U71MnG钢轨钢试样上萌生的初始裂纹可扩展得更宽、更深,更易引发大块剥离,局部滚动接触疲劳造成的后果更严重。

A scaled twin-disc test rig GPM-30 was employed to experimentally study the influence of wheel/rail material on the initiation of local rolling contact fatigue(LRCF)from indentations under oil lubrication,for which high speed wheel/rail steel of ER8 and U71MnG was considered together with four kinds of heavy haul rail steel developed recently,namely,Bainitic-Martensitic(1280 MPa and 1380 MPa),PG4 and PG5.It is found that significant spalling defects,cracks and LRCF only occur on ER8 and U71MnG steel with average surface hardness less than 300 HV when the depth of the indentations exceeds a critical value of 150~200μm.In contrast,indentation is unlikely to induce LRCF for heavy haul rail steel with hardness higher than 400 HV.Observations of surface appearance and sections of the specimens show that cracks can initiate from the interior,front and rear edges of the indentations.Cracks initiating from the bottom are more likely to result in LRCF including deep cracks and large spalling defects,with the rear edge more likely to initiate the initial crack than the front edge.Compared with the U71MnG rail steel,the indentations of the ER8 wheel steel specimens with lower hardness are more likely to cause spalling defects while the initial cracks initiating on U71MnG specimens can propagate wider and deeper,and are more likely to cause larger spalling defects with more serious consequences caused by LRCF.