Optimization of RPC technique for refining the intermediate transformation microstructure

The influence of processing parameters of relaxation-precipitation-controlling phase transformation (RPC) technique, finish rolling temperature, reduction ratio and relaxing time on the microstructure was studied by thermo-simulation for a low carbon Nb and Ti containing micro-alloyed steel. The microstructure was investigated by optical microscope, transmission electron microscope and electron back scatter diffraction (EBSD). The statistical results of the packet size were calculated. It shows that, after RPC process, the steel is a composite microstructure of bainite and matensite. The best thermo-simulation process for refinement in this experiment is deformation for 30% at 850℃, and then relaxing at this temperature for 60 s to 200 s. Increasing the reduction ratio from 30% to 60% or decreasing the deformation temperature to 800℃ would cause the best relaxation time to become shorter, increasing the deformation temperature to 900℃ would cause the refinement effect to be weak.