Effect of Thermomechanical processes on the Refinement of ferrite grains

Controlled thermomechanical processing is used to refine the ferrite grains which increase the strength without eliminating toughness. The present research deals with the effect of thermomechanical processing on the refinement of ferrite grains. The controlled thermomecahnical processing consisted of three stages; simultaneous deformation and recrystallization of austenite, deformation of austenite with partial recrystallization and deformation in the two phase region (α+γ). C-Mn steel was used as a raw material in this experimental work. The effect of thermomechanical processing was studied during controlled rolling at temperatures of 825 o C, 925 o C and 1025 o C using the austenizing temperature 1050 o C. Various reductions from 10% to 25% were given at 1025 o C, 925 o C and 825 o C. It was confirmed with the help of metallurgical microscope that the refinement of ferrite grains was achieved. The refinement was resulted from the increased nucleation of ferrite on intergranular sites such as dislocation substructure and deformation bands as well as elongated austenite grain boundaries during rolling. The hardness, tensile and impact strength of rolled steel showed that the strength was increased by the refinement of ferrite grains.