Influence of plasma and gas nitriding on fatigue resistance of plain carbon (Ck45) steel

Abstract

In this research the structure and fatigue properties of plasma and gas nitrided Ck45 steel were evaluated and compared with a standard nitriding steel. Plasma treatments were carried out using a semi-industrial size furnace in appropriate nitrogen–hydrogen mixtures and a rotating–bending fatigue machine was employed to obtain the fatigue limits. The microhardness profiles were obtained and used to demonstrate the case depth. The structures of surface layers and diffusion zone were examined by optical and scanning electron microscopy and X-ray diffraction. It was found that thermochemical processing significantly increased the microhardness and fatigue limit of Ck45 steel; increasing the fatigue limit to more than 50% was noticed after 70-h gas nitriding, similar improvements were achieved using plasma treatment in a 5-h cycle. XRD results indicated that the compound layer formed in plasma nitriding was mono-phased and thinner than the two-phase layer formed by the gaseous method which also contained iron oxide.