Effect of temperature and deformation histories on grain coarsening in medium carbon steel

Abstract

Hot rolling of medium carbon steel bars using a prototype mill and numerical analyses were carried out to examine quantitatively the effect of temperature and strain throughout rolling on the final grain size of the product. Cross-sections of the rolled bars were subjected to optical microscopy to investigate the effect of the instantaneous decrease in temperature owing to contact with the roll groove on grain coarsening in the vicinity of the bar surface. By analysing the grain size after rolling, the temperature history throughout rolling, and the equivalent plastic strain after rolling, it was found that the instantaneous decrease in temperature owing to contact did not affect grain coarsening unless the final values of the temperature and strain fell within a narrow band of values meeting the criteria for grain coarsening. Referring to both the present results and the authors' previous studies, criteria have been established for the prevention of grain coarsening in steel bar sizing operations.