渗碳钢疲劳内裂纹的萌生和扩展

Initiation and Propagation of Internal Fatigue Cracks in a Carburized Steel

本文对淬火加回火渗碳钢的拉伸一拉伸疲劳断口进行了内裂纹的分析和研究。实验结果表明:内裂纹会出现在渗碳层与芯部之间的交界处,并朝与试样的轴向相平行和相垂直的两个方向扩展。从内裂纹的最终形态判断,它的萌生和长大经历了若干阶段,即夹杂物或渗碳体粒子处空位的萌生和长大、微空洞的形成和合并等。定性分析表明:内裂纹的存在改变了主裂纹前缘的应力场,并使主裂纹在内裂纹处扩展时呈跳跃式前进,增加了主裂纹的扩展速率。

Internal fatigue cracks occurred in the fracture of a quenched and tempered carburized steel specimen under tension-tension fatigue loads are discussed in this paper. It has been observed that the internal cracks had occurred between the carburized case and the core of specimen and extended in the direction both parallel and perpendicular to the axis of the specimen. It has been shown that an internal fatigue crack forms in some steps,i. e, initiation and growth of voids,formation and coalescence of inner-holes, and so on. Quantitatively, the presence of internal cracks changes the stress field in front of a main crack and enhances the fatigue crack propagation rate because of the jumping forward of the main crack over an internal fatigue crack.