Failure analysis of cryogenically treated H13 specimen in rotating bending fatigue

The fatigue failures start at the surface mostly in case of forging die steels like AISI H13. The aim of this work is to analyse the effect of cryogenic treatment on delayed failure of H13 steel specimens subjected to rotating bending fatigue. The specimens were hardened at 1020 degrees C, double tempered at 500 degrees C for 2 h, followed bycryogenic treatment in a cryo-chamber at minus 185 degrees C for 16 h and soft tempering at 100 degrees C. The room temperature fatigue test was carried out on rotating bending fatigue testing machine at 3000 rpm with constant amplitude loading. X-ray diffraction studies were carried out along with microstructural details. It was established that fine grained structure, precipitation of fine carbides in the tempered marten site, increased carbide density and harder structure were responsible for the delayed crack propagation and thereby increasing the fatigue life of the cryogenically treated H13 steel in comparison with the conventionally treated specimens in high cycle fatigue regime.