A detailed microscopic analysis of fracture surfaces of 42CrMo4‐hardened steel after ultrasonic fatigue testing revealed globular and cylindrical particles located in ridges along the crack propagation direction. Observed particles could be easily taken for non‐metallic inclusions; however, chemical analysis showed that they are of the same composition as the steel matrix. The formation of such round‐shaped debris was found to be a result of cutting out the matrix fragments by ‘en passant’ cracks interaction and their subsequent fretting burnishing. Possible correlation of the parameters of ridges and debris with cyclic plastic zone width and martensite structure is discussed.

中文翻译：

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关于42CrMo4钢沿内部疲劳裂纹扩展的脊和磨屑的形成

在对42CrMo4淬硬钢进行超声疲劳测试后，对断裂表面进行了详细的显微镜分析，结果表明，沿着裂纹扩展方向，球状和圆柱状颗粒位于脊中。可以很容易地将观察到的颗粒用于非金属夹杂物。然而，化学分析表明它们的成分与钢基质相同。发现这种圆形碎屑的形成是通过“过路”裂纹相互作用及其随后的微动磨光来切出基体碎片的结果。讨论了脊和碎片参数与循环塑性区宽度和马氏体结构的可能相关性。