Effect of alloying elements addition on coarsening behavior of pearlitic cementite particles after severe cold rolling and annealing

The coarsening kinetics of cementite (θ) particles in severely cold-rolled and annealed pearlite in Fe–0.8 mass% C alloys with various contents of Cr, Mn and Si were investigated, and the effect of alloying elements was discussed. The results showed that severely cold-rolled pearlitic cementite spheroidized rapidly during annealing at 923 K in the Fe–0.8C alloys, and the coarsening of θ particles is strongly suppressed by the addition of Cr, Mn and Si. The coarsening kinetics of θ particles obeys the relationship, d = ktn, and the staged change appears on the coarsening kinetics curves. In Fe–0.8C alloy, the solute atoms diffused mainly along dislocations at the first stage, but they diffused mostly along the grain boundaries during the subsequent annealing. The addition of Cr or Mn restrained coarsening of θ particles due to decrease of diffusivity of carbon atoms, but this suppression effect weakened after a long-time annealing (more than 3 h). The addition of Si accelerated exclusion of carbon atoms from the rolled α-Fe, thus it changed the diffusion pattern of solute atoms and increased the n value at the initial annealing stage (∼0.6 ks). During the subsequent annealing (0.6–10.8 ks), the addition of Si suppressed the coarsening of θ particles pronouncedly.