Carbon segregation behavior during continuous annealing and cooling, and the subsequent strain aging behavior of an ultra low carbon bake hardening steel have been evaluated as a function of grain size and cooling rate after annealing. Numerical simulations agree with the experimental strain aging experiments and internal friction results when a maximum grain boundary carbon site density of 2/a~2 was used, with (a) the lattice unit cell length of bcc-Fe. Within the grain size range studied, increased grain size and cooling rate can significantly increase the solute carbon content in the matrix, thereby increasing the bake hardening level of the ULC BH steel. The effects of grain size and cooling rate are opposite to what is noticed in the case of low carbon BH steels. This is explained by the presence of the cementite particle distribution between grain boundaries and matrix in the latter steel.
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