Surface hardening of iron and steels-nitriding and nitrocarburizing

This chapter describes microstructure evolution of the diffusion zone and the compound layer during gaseous nitriding and nitrocarburizing. The microstructural features described are representative for all nitriding and nitrocarburizig treatments. Firstly, the thermodynamics of gas-solid interactions are summarized. Hereafter the kinetics of microstructure evolution is systematically dealt with for compound layer and diffusion zone, respectively. Compound layer evolution is treated for iron and iron-carbon substrates (as a model alloy for carbon steel), while diffusion zone evolution is described for nitriding steels and stainless steels. The chapter closes with a brief discussion of the various possibilities for numerical simulation of the kinetics of microstructure evolution.