Advances in Modeling the Nitriding of Tempered Martensitic Steels

During the nitriding of quenched and tempered martensitic steels a compound layer comprised of ε and γ’ iron nitrides is formed on the surface of the alloy while a diffusion zone forms in the steel due to the diffusion of nitrogen into the steel. The simulation of the nitriding process predicts the thickness and phase composition of the compound layer as well as the nitrogen and hardness profiles in the diffusion zone. The input to the simulation model is the alloy composition and initial microstructure of the tempered martensite, the nitriding potential in the nitriding atmosphere, and the temperatures and times of the nitriding process. In this paper recent advances in improving the software will be presented and discussed including: incubation time calculation for compound layer formation, compound layer phase composition and growth kinetics, alloy specific Lehrer diagrams, nitrogen flux determination as a function of time, and nitrogen diffusivity in tempered martensite. The results of these models are compared with experimental results.