Comparison between Static and Metadynamic Recrystallization. An Application to the Hot Rolling of Steels.

Abstract

An investigation has been performed to simulate the microstructural evolution during the hot strip rolling of steels. During this research, the controlling softening and recrystallization mechanisms after the hot deformation of austenite were first determined using single-hit and double-hit compression techniques. Based on the experimental flow and softening data, several mathematical expressions have been proposed to quantify the boundary conditions and overall kinetics for static and metadynamic recrystallization, respectively. The static model is expressed as a function of initial grain size, strain, strain rate and temperature, while the metadynamic one only depends on the strain rate and temperature. Together with industrial mill processing parameters, these models were incorporated into an integrative analysis of the hot rolling of plain carbon steel strips. The simulation results indicate that metadynamic recrystallization is dominant and leads to the full softening during rough rolling, where processing temperatures are high and strain rates relatively low. Metadynamic recrystallization can also occur between the initial finishing stands, when larger reductions are applied to the steel band. In general, however, static recrystallization becomes more and more important in the finishing mill. Partial static recrystallization may take place in the later stages of finish rolling, which can be attributed to the decreasing processing temperatures, reduced stand strains and much shorter interstand times. The evolution of the austenite microstructure during hot rolling can be characterized by the grain refinement associated with recrystallization and the subsequent grain growth. Although grain growth is significant during rough rolling, grain refinement with minimum interstand grain growth plays a key role during finish rolling.