Analysis of nitrided H13 steel in rotating bending fatigue

Abstract

Abstract Fatigue behavior of tool steels like AISI H13 needs to be investigated since these materials undergo heavy surface loading conditions during mechanical working operations such as forging, extrusion, etc. Nitriding is one of the methods employed to improve the surface hardness if the materials have to face surface contact or surface loading as the cracking might begin from the surface especially if there is fatigue loading pattern. This work involves heating the H13 steel specimens to 1020 °C, quenching in oil thereafter double tempering at 520 °C for two hours. The nitriding was performed at 550 °C in the atmosphere of atomic nitrogen for two hours to get the effective case depth of 200 µm. These specimens were subjected to rotating bending fatigue at room temperature conditions at a speed of 3000 rpm and constant amplitude loading. The H13 specimens were characterized for hardness, surface roughness and fractured specimens were investigated with scanning electron microscope. It was established nitrided H13 specimens indicated reduced fatigue life which could be attributed to initiation of fatigue cracks from the specimen surface or interface between the nitrided layer and the core matrix.