Changes of Structure and Physical-Mechanical Properties in Alloy Steels Thermochemically Treated by Plasma Nitriding

Abstract

Plasma nitriding is a method of surface modification using a glow discharge technology to introduce nitrogen into the surface of a metal, which subsequently diffuses into the material. The main advantages of plasma nitriding over conventional nitriding processes are: reduced cycle time, controlled growth of the surface layer, elimination of white layer, reduced distortion, no need of finishing, pore-free surfaces and mechanical masks instead of copper plating. The process is especially suitable for complex parts that are intensively solicited by wear, fatigue, contact pressure, shocks, possibly also to corrosion. It is applied in order to bring the metallic products in a state favourable from the point of view of structure, chemical composition and internal stress state. The paper presents an analysis of the structures and characteristics of a widely used structural steel 39 - CrAl6. As a result of plasma nitriding, a surface layer with high wear and fatigue resistance was created on the surface of the material. Also, between the surface layer and the base material was interposed a hard substrate with high wear resistance having a bainitic / martensitic structure.