PLASMA-NITRIDING OF TOOL STEELS FOR COMBINED PERCUSSIVE IMPACT AND ROLLING FATIGUE WEAR APPLICATIONS

Plasma-nitriding is a flexible, multifunctional case-hardening technol ogy. In the present investigation, this technique was applied to incre ase the compound percussive impact and rolling contact fatigue resista nce of steel-plant hot-rolling-mill components, made out of AISI H13 a nd D2 grades of tool steel. Plasma-nitrided layers were characterized by optical and scanning electron microscopy, microhardness measurement s, and phase analysis and residual stress determination using X-ray di ffraction techniques. The service life of the components was determine d in the real plant operation. Plasma-nitriding improved the service l ife by two- to 3.6-fold, depending upon the type of steel and the comp onents' contact surface geometry. Redesigning of the surface/subsurfac es by plasma-nitriding coupled with appropriate selection of substrate enhanced the service life of the component by up to sevenfold. The se rvice life was examined in relation to nitrided layer characteristics, and the importance of residual stresses and surface microstructure ar e highlighted. (C) 1998 Elsevier Science S.A. All rights reserved.