Influence of Tertiary Carbides on Improving Fatigue Limit of H13 Die Steels

Forging dies are subjected to fatigue failures for which different surface treatments are used as most of the failures begin from the surface. In this work, the influence of cryogenic treatment on fatigue limit of die steels has been discussed with hardening of fatigue specimens of AISI H13 die steels at 1020 A degrees C, oil quenching, double tempering at 500 A degrees C, cryogenic treatment at minus 185 A degrees C for 16 h followed by soft tempering at 100 A degrees C. The fatigue limit analysis had been carried out with constant amplitude rotating bending fatigue testing at room temperature, at 3000 rpm with load variations which indicated improved fatigue limit for 16 h cryogenically treated specimens in the high cycle fatigue regime. This has been attributed to decreased surface roughness, increased hardness and precipitation of finer tertiary carbides as an influence of microstructure. The minimum value of fatigue strength exponent, in Basquin equation, has also depicted the increased fatigue limit for cryogenically treated H13 specimens.