The Effect of Stress on Bainite Transformation, Microstructure, and Properties of a Low-Carbon Bainitic Steel

The effects of applying external stress on bainite transformation, microstructure, and mechanical properties are investigated by metallography, dilatometry, etc. Results show that compressive stress during bainite transformation accelerates the bainite transformation and increases the final bainite amount due to the additional mechanical driving force. The lath-like bainite becomes shorter, and smaller blocky martensite/austenite islands form under stress during the bainite reaction. Different from the results with stress during bainite transformation, applying stress after bainite transformation during isothermal holding cannot increase the volume fraction of bainite, and no obvious change in bainite morphology is observed. In addition, the subsequent martensite transformation is promoted during the cooling process. Moreover, the less amount of retained austenite (RA) but more carbon content in RA is obtained with applying stress after the bainite reaction. Finally, the tensile strength increases, while the elongation decreases when the external stress is imposed after bainite transformation.