INFLUENCE OF HOT DEFORMATION ON CONTINUOUS COOLING BAINITIC TRANSFORMATION IN A LOW CARBON STEEL

The influence of hot deformation conditions on continuous cooling bainitic transformation has been investigated for a low carbon microalloyed steel. The CCT diagrams show that deformation in unrecrystallized austenite region can accelerate transformation process. Bainitic transformation in intermediate transformation temperature region is prominent, and the proeutectoid polygonal ferrite transformation at elevated high temperature is suppressed. According to optical and TEM analyses, low carbon bainitic ferrite is characterized by granular and lathlike ferrite, based on the cooling rate and deformation conditions. For nondeformation, groups of coarse parallel ferrite lath form from the prior austenite grain boundaries with the same crystallographic orientation. For heavy deformation, cell structure within the austenite grains due to the high dislocation density formed, which provides more nucleation sites for bainite ferrite. So deformation can discontinue the growth of ferrite laths and decrease the length of ferrite laths. (Steel composition in wt%: 0.10C, 1.6Mn, 0.31Si, 0.012P, 0.0107N, 0.28Mn, 0.038Nb, 0.081V, 0.018Ti.)