Grain Growth after Intercritical Rolling

The distribution of the characteristic texture components between the ferrite grains of different size classes has been studied in a steel with 0.082%C, 1.54% Mn, 0.35% Si, 0.055%Nb and 0.078%V after different rolling schedules with a final rolling temperature above or below Ar3. Microstructures and textures were characterized by means of optical microscopy and orientation microscopy. A strong grain refining effect together with a bimodal grain size distribution was observed in the steel both after final rolling in the intercritical region or in the austenite region, close to the Ar3 temperature. The differences in grain size were interpreted on the basis of three potentially acting mechanisms: (i) transformation-induced recrystallization, (ii) increased mobility of specific grain boundaries and (iii) fast nucleation of ferrite grains on specific sites of the parent austenite microstructure. The experimental data clearly favoured the third of these assumptions as the responsible mechanism for the observed bimodal grain size distributions.