Annealing behavior of submicrometer grained ferrite in a low carbon steel fabricated by severe plastic deformation

The annealing behavior of submicrometer grained ferrite in a low carbon steel processed by equal channel angular pressing (ECAP) was investigated. In particular, the effect of the ECAP strain on the annealing behavior of submicrometer grained ferrite was studied by examining the microstructural changes of the samples processed by two different ECAP strains, 4 and 8, during static annealing. Contrary to the general belief that more severely worked materials exhibit faster kinetics of microstructural evolution related to annealing, i.e. recovery, recrystallization and grain growth, the steel subjected to higher ECAP strain exhibited more sluggish recovery and recrystallization kinetics. The more sluggish recovery and recrystallization kinetics with increasing the ECAP strain is associated with the carbon dissolution from pearlitic cementite during ECAP. The grain growth kinetics of submicrometer grained ferrite was analyzed by the non-ideal grain growth law. The grain growth exponent was about 0.2 and the apparent activation energy for grain growth was 170–180 kJ mol−1. Neither value was influenced by the ECAP strain.