Incomplete Recrystallization and Subsequent Microstructural Evolution during Intercritical Annealing in Cold-rolled Low Carbon Steels

Microstructural evolution during intercritical annealing after rapid heating of cold rolled low carbon steels was investigated by EBSD and TEM. When the specimens were heated to above the Ac(1) temperature before the completion of the primary recrystallization of alpha and then annealed, remarkable retardation of the primary recrystallization was observed, resulting in non-uniform grain size distribution of alpha. Because of the retardation, subgrains formed in non-recrystallized alpha are not consumed by recrystallized alpha and are thus able to gradually grow with annealing, and finally the grain size distribution of alpha becomes uniform. The analysis based on the r(n)-r(0)(n) = kt equation has shown that the subgrain growth in non-recrystallized alpha from the holding period of 100 to 1 000 s follows n = 3, indicating that the subgrain growth is controlled by the volume diffusion of Mn at alpha and gamma interfaces. The transition of n from 3 to 2, observed at the holding time of longer than 1 000 s, may be due to the gradual disappearance of the smaller gamma phase at subgrain boundaries.