润滑条件下中低碳空冷贝氏体钢的滚动滑动接触疲劳行为

Lubricated Rolling-Sliding Contact Fatigue Behavior of Air Cooled Bainitic Steels with Low/Medium Carbon Contents

研究了三种高强度或超高强度高韧性空冷贝氏体钢在油润滑条件下的接触疲劳行为。发现引起麻点剥落的疲劳裂纹不仅可在接触表面 ,也可以在距表面一定深度下的亚表面萌生 ,亚表面萌生裂纹的深度比理论计算最大剪切应力所在深度小近一个数量级 ,裂纹萌生由塑性变形和剪应力共同作用产生 ,一端向接触表面扩展 ,到达表面后润滑油被挤压进入裂纹中产生支点效果 ,另一端向最大剪应力深度扩展 ,最后在外力和润滑油支点共同作用下 ,由裂纹包围的金属屑被折断 ,形成疲劳剥落坑。钢的初始硬度或强度在低接触应力下对接触疲劳寿命影响不明显 ,在高接触应力下影响显著 ,初始硬度越高 ,接触疲劳寿命越长。

The rolling sliding contact fatigue (RCF) behavior of three high and/or ultrahigh strength high toughness air cooled bainitic steels has been inverstigated under oil lubricated condition. The rsults show that the RCF cracks leading to pitting may nucleate at surface and subsurface. The depth of subsurface initiated crack formed by plastic deformation and shear stress is one order of magnitude less than that calculated according to the elastic theory. One tip of subsurface nucleated crack propagates towards contact surface and another tip goes to where maximum shear stresses exist. The oil is entrapped into crack and acts as fulcrum when the crack reaches surface. Finally the debris embraced with carck is broken off by the action of both contact stress and oil fulcrum after the crack propagates to a certain length and leaves surface a pit. The initial hardness or strength has little effect on RCF life under lower contact pressure, but its influence is considerable at higher contact stress. The higher the initial hardness, the longer the RCF life.