Plasma-nitriding of tool steels for combined percussive impact and rolling fatigue wear applications

Abstract

Plasma-nitriding is a flexible, multifunctional case-hardening technology. In the present investigation, this technique was applied to increase the compound percussive impact and rolling contact fatigue resistance of steel-plant hot-rolling-mill components, made out of AISI H13 and D2 grades of tool steel. Plasma-nitrided layers were characterized by optical and scanning electron microscopy, microhardness measurements, and phase analysis and residual stress determination using X-ray diffraction techniques. The service life of the components was determined in the real plant operation. Plasma-nitriding improved the service life by two- to 3.6-fold, depending upon the type of steel and the components' contact surface geometry. Redesigning of the surface/subsurfaces by plasma-nitriding coupled with appropriate selection of substrate enhanced the service life of the component by up to sevenfold. The service life was examined in relation to nitrided layer characteristics, and the importance of residual stresses and surface microstructure are highlighted.