Subcritical thermomechanical treatments of eutectoid steel

Abstract

The kinetics of annealing of eutectoid steel which was 75% cold rolled and then annealed at temperatures of 400, 500, and 600°C have been examined using measurements of microhardness, X-ray textures and line broadening, scanning and transmission electron microscopy, and positron annihilation. The controlling process appears to be the diffusion of Fe along Fe3C/α Fe interfaces. The polygonization of ferrite, the formation of recrystallized ferrite grains, and the spheroidization of Fe3C were observed. Major changes in positron and X-ray line breadth parameters within the first 10–100 s indicate very rapid initial recovery but it is not clear if subsequent changes in those two parameters are a result of recrystallization only or of overlapping recovery and recrystallization processes. Although some degree of spheroidization was involved in each of the anneals, the positron and X-ray line broadening were selective in that they detect changes in the ferrite only.