Influence of Mn on Cementite Coarsening and Ferrite Grain Growth During Annealing of a Cold Rolled Medium Carbon Steel

Abstract

To improve the formability of cold‐rolled medium carbon steels, the grain growth of ferrite with pinning of cementite particles during soft‐annealing was investigated through experiments and simulations in a hypoeutectoid Fe–0.29 mass%C–0.51 mass%Mn steel.Between the annealing times of 1.8 × 10 4 (5 h) and 3.6 × 10 5 s (100 h) the number of cementite particles decreased to less than one‐tenth, and the ferrite grain size increased by ∼50%. In addition, nearly 90% of cementite particles accumulated at the grain boundaries. Simulations were carried out using the local equilibrium theory of cementite coarsening in alloy steel by Björklund et al., and the statistical model of grain growth by Abbruzzese and Lücke, incorporating the pinning effect of cementite particles. It is likely that all cementite particles within the ferrite grains and at the grain boundaries coarsened by Mn volume diffusion while Mn grain boundary diffusion accelerated the coarsening of grain boundary cementite particles. The trapping of cementite particles by migrating grain boundaries appeared to be the main mechanism for the accumulation of cementite at grain boundaries, while carbon volume diffusion likely played a major role in plain carbon steel, as previously reported.