Abstract
Failures of case-hardened components appear to be responsible for a greater part of service failures of machines. Electron fractography is being used widely for failure analysis and, actually, it is successful for determining the causes of some failures. However, on high hardness materials, especially on case-hardened materials, the relationship between fracture modes and fracture mechanisms has been rarely investigated.
In this paper, the characteristics of fracture surface of case-hardened materials broken in service were examined by means of fractography. From the results of examination, it was clarified that, in the hardened layer of carburized materials, dimple fracture occured at high cycles (3.4×109 cycles) and intergranular fracture occured under impact stress. Also the microcharacteristics of hardening cracks in induction hardened materials were clarified.
