Influence of the parent phase on the bainitic transformation under large stress of manganese-boron steel 22MnB5
Diego Said Schicchi and Martin Hunkel
Volume: 151. Pages: 457--469
DOI: 10.1016/j.matchar.2019.01.025
Published: 2019
Abstract
22MnB5 steel grade is widely employed for manufacturing tailored tempered components in the automotive industry, where locally heated tools lead to bainitic microstructures in the whole or some regions of the formed parts. Because heat treatment and forming occur simultaneously, phase transformations evolve under the influence of high stresses and in pre-deformed austenite. Isothermal bainitic transformations at 450 °C under the influence of applied stresses in the range of 0–200 MPa are evaluated in this work. Material response is experimentally studied by means of a thermomechanical simulator using sheet specimens and an enhanced gas cooling device. Bainite morphology is studied with electron backscatter diffraction (EBSD) analysis. Austenite grains are reconstructed from the EBSD determinations, showing a good consistency between the calculations and the experimental results. These reconstructed parent phase distributions are further employed to analyze individual and general misorientation angles in both austenitic and bainitic states. Special attention is paid to the influence of the parent phase on the bainitic transformation kinetics. A displacive-based model, recently proposed by the authors, accounting for the variants selection, autocatalytic nucleation, and deformation related defects density is used in this investigation to account for the transformation kinetics, incorporating into consideration the reconstructed austenite.