Subcritical Spheroidization Annealing of Cold-Rolled Cr-Mo Microalloyed Medium-Carbon Steel with Different Initial Microstructure

According to the industrial production process of fine-blanking steel (including hot rolling, cold rolling, and spheroidization annealing), a Cr-Mo-microalloyed medium-carbon steel is taken as the research object for laboratory simulation in this paper. The ferrite+pearlite (F + P) and ferrite+bainite (F + B) are obtained by changing coiling temperature during hot rolling conduct cold rolling with 25%, 50%, and 75% total reduction and subcritical annealing at 740 degrees C for 1-8 h. Microstructure evolution during spheroidization annealing is studied and analyzed by an electron probe microanalyzer, electron back-scattered diffraction, DICTRA simulation, transmission electron microscopy, and microhardness tester. Compared with F + P, the dislocation density distributed to the ferrite of F + B during cold rolling is higher. The cold-rolled F + B microstructure shows the rapid spheroidization annealing behavior, which leads to the uniform distribution of finer spherical carbides and the full recrystallization of the ferrite matrix. In addition, properly increasing the reduction of cold rolling can also speed up the spheroidization process of carbide. Herein, a 50% reduction is determined to be the most suitable cold-rolling process parameter for carbide spheroidization. Moreover, the recrystallization of ferrite is enhanced with the increase of cold-rolling reduction.