Alloying Factors and Parameter of Alloying Elements for Carbon and Nitrogen Uptake during Carbonitriding as Basis for Simulation

Abstract

Abstract Carbonitriding serves to increase the strength and wear properties of steel components. The carbon and nitrogen concentration and the depth distribution decisively determine the resulting properties. Optimal profiles create an ideal microstructure of martensite, residual austenite, finely distributed nitrides, carbonitrides and inherent compressive stress in the surface zone. The reliability of carbonitriding heat treatment process is strongly dependent on the possibilities of process control. Previous investigations aimed at measuring the nitrogen potential of the atmosphere by means of an ammonia sensor in the exhaust gas as well as by a wire sensor. Carbon potential is conventionally controlled using an oxygen probe. In order to further increase the process reliability of carbonitriding, simulation of the carbon and nitrogen profiles and of any precipitation of carbides and nitrides are necessary. The first step is the determination of interdependent alloying influences on the carbon and nitrogen contents. The carbon and nitrogen activities in the atmosphere and the alloy surface are near equilibrium after long-time carbonitriding. Depending on the composition of the material, significantly different effects can be described. These influences must be considered. In addition to the reached equilibrium content, the diffusion, the position of phase boundaries in the phase diagrams and the formation of precipitation with influence of carbon and nitrogen as well as interactions with other alloying elements are to be worked out in order to further develop controlled carbonitriding for the reliable adjustment of the heat treatment results.