Effect of subgrain structure on the kinetics of phosphorus segregation in grain boundaries

• We model phosphorus segregations taking into account the sub-grain structure.
• The volume diffusion of phosphorus is assumed to be a limiting process.
• Diffusion problem for a subgrain has to account the phosphorus depletion in the bulk.

The effect of steel microstructure, in particular the grain fragmentation onto subgrains, on the kinetics of phosphorus segregation in grain boundaries is considered. Assuming that intergranular phosphorus redistribution happens much faster than bulk diffusion, the segregation process is controlled by phosphorus transport toward the subgrain surfaces. The diffusion problem for a subgrain, allowing the phosphorus depletion in the subgrain volume, is proposed to describe the segregation kinetics. This model is applied to the pressure vessel steel 15Kh2NMFA-A and weld metal Sv-10KhGNMAA of the nuclear power reactor WWER-1000. It was shown that this model provides better fitting of the experimental data than the conventional Langmuir–McLean equation.