Morphology of intergranular cementite arrays in nitrided chromium-alloyed steels

Preferential alignment of cementite precipitates at grain boundaries in nitrided steels is shown to be related to their orientation with respect to the residual stress axis. A scheme is proposed allowing one to estimate the number of precipitate-bearing boundaries for each given boundary orientation corresponding to a definite stress state, with a special emphasis on the kinetic aspect. The key parameter is the nucleation rate, which depends on the Gibbs energy of cementite formation, on shear and normal components of the residual stress and on the cementite-ferrite and ferrite-ferrite interface free energy. A satisfactory agreement between calculated and experimental data is obtained.