Abstract
The effects of hot rolling condition and chemistry of the steels on the onset temperature of γ-α transformation after hot rolling were investigated using the thermal analyzer developed for measurment of Ar3 temperature after hot rolling. The changes of Ar3 temperature and austenitic microstructure with the reheating temperature, the rolling temperature and the rolling reduction were investigated in the Si-Mn and Nb-bearing steel. These results were analyzed based on the changes of the effective interfacial area per unit volume(SV) that included the recrystallized or unrecrystallized γ grain boundary and deformation band as a nucleation site for ferrite. Although the SV value increased with the refinement of recrystallized γ grain or the increase of rolling reduction below recrystallization temperature of austenite, the latter resulted in much greater rise of Ar3 temperature in Nb steel. This was considered to be due to the reduction of the amount of dissoluted Nb atom around the grainboundary or deformation band through the strain induced precipitation of Nb(CN).
The effects of chemistry and the plate thickness on Ar3 temperature after controlled rolling were studied in the large number of the steels with the different chemistry, and the relation of Ar3 temperature and each element was quantitatively established based on the multiple regression analysis.
