Effect of Finishing Hot-Working Temperature on Microstructure of Thermomechanically Processed Mn-Al Multiphase Steels

The study was devoted to the hot-working behavior and the microstructure evolution of four thermomechanically processed Mn-Al-alloyed multiphase steels. Determination of the hot deformation resistance of investigated steels was carried out on the basis of continuous compression, double-hit compression, and seven-step compression tests simulating conditions of hot strip rolling. The experiments were carried out using the Gleeble 3800 thermomechanical simulator. The physical simulation of hot strip rolling consisted of seven deformation steps characterized by decreasing strain, temperature, and interpass time whereas the strain rate values were gradually increased. A special attention was paid to the effect of Nb microaddition on the hot-working behavior and microstructure evolution with the finishing hot-working temperature varying in a range from 950 to 750 degrees C. Morphological features of a bainite-based matrix and retained austenite were identified using light microscopy and scanning electron microscopy techniques. A fraction of retained austenite was determined by X-ray diffraction. The increase in the Mn content increases the softening kinetics of austenite. It was also found that the best conditions for thermal stabilization of retained austenite occur at 950 degrees C for the steels containing 3% Mn.