研磨加工层对高碳铬轴承钢超长寿命疲劳行为的影响

EFFECT OF GROUND LAYER ON ULTRA LONG LIFE FATIGUE BEHAVIOUR IN HIGH CARBON CHROMIUM BEARING STEEL

为了阐明磨石研磨加工层对高碳铬轴承钢JIS SUJ2超长寿命疲劳行为的影响,分别使用经砂纸研磨和电解研磨的砂漏形试样,在室温空气环境下进行旋转弯曲疲劳试验。砂纸研磨试样被除去部分磨石研磨层,电解研磨试样被除去了全部的磨石研磨层。结果表明,两种试样的S-N曲线由位于短寿命区的表面破坏模式和位于长寿命区的内部破坏模式的两条组成,表面破坏模式的S-N曲线受表面粗糙度和表面压缩残余应力的影响。内部破坏模式的S-N曲线不受表面条件的影响,是材料固有的特性。砂纸研磨试样表面破坏模式的疲劳极限最高,是电解研磨试样1．11倍和磨石研磨的1．20倍。表面压缩残余应力对表面破坏模式疲劳极限的影响可以用修正Goodman图表示。还讨论裂纹的萌生和扩展条件,推定超长寿命的疲劳极限。

In order to investigate the effect of ground layer on fatigue behavior of high carbon chromium bearing steel JIS SUJ2 in ultra-long life regime, rotating-bending fatigue tests are performed in laboratory air at room temperature using hourglass-shaped emerized and electro-polished specimens. The emerized specimen and the electro-polished one are obtained by removing a partial ground layer with surface roughness and the whole ground layer from ground ones, respectively. The results show that S-N curves are composed of surface fracture mode curve in the region of short life and internal fracture mode curve in the region of long life. The S-N curves for surface fracture mode are affected by surface roughness and compressive residual stress. The S-N curves for internal fracture mode are not affected by surface conditions, which is an inherent characteristic of the material. For the surface fracture mode, the emerized specimen shows the largest fatigue limit, about 1.11 times larger than for the electro-polished one and 1.20 times larger than for the ground one. The fatigue limits of surface fracture mode affected by the surface compressive residual stress can be expressed by modified Goodman diagram. Furthermore, conditions for internal crack initiation and propagation are discussed. The fatigue limit in ultra-long life regime is estimated.