Grain Refinement of Ferrite-pearlite Structure of Low Carbon Steel through the Controlled Rolling Process

Abstract

A 0.1%C-1.35%Mn-0.03%Nb steel was hot rolled in 1 pass up to 83% reduction in thickness at a temperature between 790 and 1050 °C and deformation of austenite was examined metallographically in detail. It was found that annealing twins were formed abundantly in the austenite during heating before rolling, or during recrystallization which occurred during rolling when the rolling temperature was high. Rolling at a temperature below the recrystallization temperature of austenite resulted in severe deformation of these annealing twins. At the same time, heavy local deformation was introduced into the regions near the boundaries of these annealing twins, and also into the regions near austenite grain boundaries. Such local deformation was found to enhance the formation of ferrite nuclei in these regions during ferrite-pearlite transformation. It was suggested that this effect was most essential in the grain refinement of control-rolled steel.