中碳贝氏体支承辊钢低应力牵引滚动接触下的疲劳短裂纹行为

研究了中碳贝氏体支承辊钢在低应力、水润滑和牵引滚动条件下的接触疲劳裂纹萌生与扩展特征，发现了表面起源的垂直短裂纹和棘齿短裂纹．疲劳10^4cyc时，垂直短裂纹就在接触表面大量出现，且在萌生后立即进行高速初始扩展，其后绝大多数停止长大；棘齿短裂纹出现较晚．两种短裂纹长大到一定深度时均停止扩展．在疲劳失效寿命的70％-80％时，垂直短裂纹恢复扩展，并随即加速长大．几乎同时，两种短裂纹在亚表层以转折的方式重新扩展．在表面损伤出现之前，两种短裂纹的萌生和扩展行为始终局限在近表面薄层内．

BEHAVIOR OF SHORT FATIGUE CRACKS IN MEDIUM CARBON BAINITIC BACK-UP ROLL STEEL UNDER MILD TRACTIVE ROLLING CONTACT

The surface-initiated rolling contact fatigue (RCF) behavior of the medium carbon bainitic back-up roll steel has been investigated at low contact pressure and under water lubricated and tractive rolling conditions. Two types of surface originated RCF short cracks, i.e. vertical short cracks and ratcheting short cracks were observed. The former occur on contact surfaces in numbers at as early as 104 cyc. Viewed from surfaces, they propagate initially with high growth rates immediately after initiation, and then most of them stop growing. The latter nucleate far later. The two types of short cracks stop propagating on reaching some depth. Vertical short cracks on surfaces resume propagating till 70-80 percent of the total RCF failure lives and then are accelerated to propagate, almost synchronously, the two types of short cracks resume growing with a turned mode in subsurface. The behavior of the initiation and propagation of the two types short cracks is confined to a thin surface layer prior to surface damage.