Effect of Fine Particle Peening Treatment prior to Nitriding on Fatigue Properties of AISI 4135 Steel

Abstract

In this study, a new hybrid surface modification process, fine particle peening (FPP) treatment prior to nitriding, was proposed. In order to clarify the effects of FPP treatment prior to nitriding on the fatigue strength of notched AISI 4135 steel with a stress concentration factor K_t of 2.36, fatigue tests were conducted at room temperature using a rotational bending fatigue testing machine. Hardness and residual stress distributions were measured in order to characterize the surface-modified layer. As a result, the surface hardness of the FPP-treated specimen before nitriding was higher than that of the nitrided specimen. The surface microstructures of treated specimens were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The crystal structure of the compound layer of the FPP-treated specimen before nitriding was different to that of the nitrided specimen. The compound layer of the FPP-treated specimen was dense. This suggests that FPP treatment prior to nitriding is very effective for improvement of the fatigue strength of steel.