Optimization of gaseous nitriding of steels by multi-physics modeling

Gaseous nitriding is controlled by temperature, time and surface nitrogen potential. Tuning these parameters lead to the expected mechanical properties (hardness, residual stress) and durability of treated mechanical parts. In this paper, a methodology is proposed to optimize nitriding parameters by using a multi-physics modeling of the nitriding treatment (microstructure, diffusion/precipitation mechanisms, hardness and residual stress generation). This model is particularly suited to the diffusion layer and does not apply to the compound layer. The scope concerns low-alloyed carbon steels and gaseous nitriding. The role of carbon is clearly established and taken into account in the proposed methodology.

The model is firstly compared to experimental investigations carried out on a 32CrMoV13 steel grade nitrided for short times (5-30h) at several temperatures (between 480 and 560 °C) and nitriding potentials (from 0.3 to 8 atm^-1). The convenience of the model is then tested according to technical specifications (nitriding depth, hardness and residual stresses of nitride layers).