Abstract
Final goal of this series of papers is to formulate a method to evaluate stress, or residual stress induced in the steel substrate in nitriding process. Non-equilibrium state is considered, in the first paper, to simulate nitrogen concentration successively by simple diffusion into α-Fe in the first stage of the process followed by formation of γ' and ε compounds associated with phase transformation due to crystallographic structure change. The volume dilatation by such diffusion and phase change processes is estimated, where emphasis is placed on that by considering the nitrogen dependence on lattice parameters for each unit cell. The volume dilatation thus evaluated is to be used to formulate elastic plastic strain and stress in the second paper.
