A microstructural model for predicting hardness profiles of Fe-Cr alloys after nitriding

Abstract

A model is developed to describe the kinetics of the development of the diffusion zone during gaseous nitriding of Fe-1 at.% Cr and Fe-2at.% Cr alloys. The model is based on the simultaneous diffusion of nitrogen and chromium and is directly linked to the microstructure which develops during nitriding. The model calculates the fraction of chromium atoms that precipitates as a function of time and position. To verify the model, nitrogen concentration and hardness profiles were measured. To compare the hardness profiles with the calculated profiles, a relation is derived between the hardness increase and the fraction of atoms precipitated. This relation is based on microstructural parameters and a cubic arrangement of plate-like precipitates. A satisfactory agreement between calculations and experimental nitrogen concentration and hardness profiles is obtained.