高温渗碳轴承钢旋弯疲劳裂纹萌生与扩展行为

 为了提高航空轴承的服役寿命,借助QBWP-10000X型旋转弯曲疲劳试验机,研究了高温渗碳轴承钢的旋转弯曲疲劳性能和裂纹萌生扩展行为。结果表明,钢的中值疲劳强度达到913.3 MPa。有效渗层中大量M₂₃C₆和少量M₆C碳化物显著提高了试验钢的表面硬度,渗层不同碳浓度导致马氏体先后发生相变而形成408 MPa表面压应力,进而提高了钢的疲劳性能。疲劳裂纹主要萌生在表面缺陷和次表面碳化物,分别占比71.4%和 28.6%。萌生裂纹缺陷特征尺寸及承载应力对应力强度因子和循环次数影响显著,深犁沟形状由于涉及应力集中而直接影响疲劳循环次数,承受相同加载应力碳化物特征尺寸越大,循环次数越低。裂纹萌生后沿渗碳层碳化物边界快速扩展同时向芯部缓慢扩展,最后在试样疲劳源对侧近边缘区域发生准解理和韧性混合断裂。

Fatigue crack initiation and propagation behavior of high temperature carburized bearing steel during rotary bending

In order to improve the service life of aviation bearing, with the help of QBWP-10000X rotary bending fatigue testing machine,the rotary bending fatigue properties and crack initiation and propagation behavior of high temperature carburized bearing steel were studied. The results show that the median fatigue strength of the steel reaches 913.3 MPa. A large amount of M₂₃C₆ and a small amount of M₆C carbides in the effective carburized layer significantly improve the surface hardness of the test steel. Different carbon concentrations in the carburized layer lead to martensite transformation successively and form 408 MPa surface compressive stress,which further improves the fatigue property of the steel. The fatigue cracks mainly originate from surface defects and subsurface carbides,accounting for 71.4% and 28.6% respectively. The results show that the characteristic size of crack initiation and the bearing stress have a significant effect on the stress intensity factor and the number of cycles. The shape of deep furrow directly affects the number of cycles due to the stress concentration. The larger the characteristic size of carbide under the same loading stress,the lower the number of cycles. After the crack initiation,it propagates rapidly along the carbide boundary of carburized layer and slowly to the core. Finally,quasi cleavage and ductile mixed fracture occur near the edge of the specimen on the opposite side of the fatigue source.