A potential hot stamping process for microstructure optimization of 22MnB5 steels characterized by asymmetric pre-rolling and one- or two-step pre-heating

In this paper, a study on the innovative hot stamping process and the typical microstructures is presented, aiming to clarify insights into the influence of processing variables (asymmetric rolling temperature, rolling reduction, pre-heating method, and so on) on the evolution of microstructure, in order to evaluate the feasibility of the new process to improve properties of 22MnB5 steels. TEM investigations of asymmetrically rolled samples indicate different morphologies of dislocation density and pearlite with altering the rolling reduction, velocity ratio (VR) and rolling temperature. And the study demonstrates that asymmetric rolling before hot stamping process greatly promotes the austenite transformation during the pre-heating stage, especially when the rolling temperature is lowered to liquid nitrogen temperature (LNT) and the velocity ratio is higher than 1.5. And two-step pre-heating with induction heater and roller hearth furnace contributes positively to the austenite grain refinement in pre-deformed 22MnB5 steel. Another relevant conclusion is that the cooling microstructures can also be adjusted by changing the pre-deformed temperature of the samples.