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

Hot rolling of medium carbon steel bars using a prototype mill and numerica l analyses were carried out to examine quantitatively the effect of tempera ture and strain throughout rolling on the final grain size of the product, Cross-sections of the rolled bars were subjected to optical microscopy to i nvestigate the effect of the instantaneous decrease in temperature owing to contact with the roll groove on grain coarsening in the vicinity of the ba r surface. By analysing the grain size after rolling, the temperature histo ry throughout rolling, and the equivalent plastic strain after rolling, it was found that the instantaneous decrease in temperature owing to contact d id not affect grain coarsening unless the final Values of the temperature a nd strain fell within a narrow band of values meeting the criteria for grai n coarsening. Referring to both the present results and the authors' previo us studies, criteria have been established for the prevention of grain coar sening in steel bar sizing operations. I&S/1418.