A finite difference model was developed for the simulation of C segregation to grain boundaries during the continuous annealing of ultralow-C bake-hardening steels. Continuous cooling experiments, using various soaking times and cooling rates, were performed, and the solute C content was measured via internal friction techniques. The simulation results were in good agreement with experimental results when using a maximum grain-boundary C-site density of 4/a2. Here, a was the unit-cell length of body-centered cubic Fe. This value was about 4 times higher than the published value, and implied that far more C could be stored in grain boundaries than had formerly been expected. The competition between C diffusion to grain boundaries and to dislocations, during subsequent strain aging, was modelled using Monte Carlo simulations. Upon using the same parameter values for the grain boundary site density as those used during continuous annealing, the simulations were also found to be in good agreement with strain-aging experiments.

Competition between Grain Boundary Segregation and Cottrell Atmosphere Formation during Static Strain Aging in Ultra Low Carbon Bake Hardening Steels. B.Soenen, A.K.De, S.Vandeputte, B.C.De Cooman: Acta Materialia, 2004, 52[12], 3483-92