Competition between grain boundary segregation and Cottrell atmosphere formation during static strain aging in ultra low carbon bake hardening steels

Abstract A finite differences model has been developed for simulation of carbon segregation to grain boundaries during continuous annealing (CA) of ultra low carbon bake hardening steels. Continuous cooling experiments with variation of soaking times and cooling rates were performed. The solute carbon content was measured by internal friction. The simulation results are in good agreement with the experimental results, using a maximum grain boundary carbon site density of 4/a2, with a the unit cell length of bcc-Fe. This value is about four times higher than the literature value reported by McLean and implies that far more carbon can be stored in grain boundaries than formerly expected. Competition between carbon diffusion to grain boundaries and to dislocations during subsequent strain aging of the material was modelled with Monte-Carlo simulations. Using the same parameter values for the grain boundary site density as during CA, the simulations were also in good agreement with strain aging experiments.