Improvement of Gas Nitriding Process by Prior Surface Quality Control

Abstract

Thermochemical processes for metal surface modification such as nitriding and nitrocarburising are sequences of physicochemical, chemical, and metallurgical reactions. The heterogeneous reaction in particular (formation of atomic nitrogen at the surface, from adsorbed ammonia in nitriding or from nitrogen in plasma nitriding) is not yet fully understood. Nevertheless, the nitriding and nitrocarburising processes are broadly applied, especially in the automotive industry, to form wear and corrosion resistant surfaces for motor and gear components. Steel manufacturing affects not only the shape of a workpiece but also its surface structure and composition. Different steels and metal compounds (oxides and phosphates), as exist in the form of surface layers on industrial parts after machining, have been nitrided in several gas atmospheres to explore possible mechanisms of reaction inhibition or acceleration with the aim of developing a more reproducible nitriding process. For most materials examined, functionally clean reference specimens seldom showed the highest nitrogen concentrations.