Study On Effects Of Austenitizing Temperature And Undercooling On Phase Transition Of High Strength Bainitic Steel

A kind of high strength carbon bainitic steel without noble metals was designed in thiswork. The CCT curve of the test steel was investigated by dilation data on Gleeble1500thermal simulator and metallographic microstructures. The dynamic process of austenite graingrowth and bainite transformation were in situ observed using laser scanning confocalmicroscope. In addition, the effects of austenitizing temperature and undercooling on bainitephase transition were dividually researched, while the comparison result was simultaneouslystudied.It indicates that pearlite transformation can be avoided in the designed steel whencooling rate is above0.5℃/s, resulting in good hardenability. The bainite transformation inthe test steel can react during210℃~450℃; and the austenite grain coarsening temperature is1100℃. Moreover, longer and more bainite sheaves were obtained within the larger austenitegrains due to the austenitizing temperature. With the same austenitizing temperature, thedecreasing bainite isothermal temperature provides greater driving force, leading to asignificant increase of bainite fraction.Comparing the influence of austenitizing temperature and undercooling on bainitetransformation, it can be found that the influence of undercooling on bainite phase transitionis more significant than that of austenitizing temperature. The relative increase of bainitetransformation is16.1%after100℃increase of austenitizing temperature, while the relativeincrease of bainite transformation is87.5%with50℃decrease of isothermal transformationtemperature.