Study On Phase Transition And Microstructure Of Super Bainitic Steel

A kind of super bainite steel without noble metals such as Mo and Ni were designed, andusing thermal dilation method and metallographic observation, the continuous coolingtransformation curve (CCT) of this steel was measured and plotted. At the same time, Thestructure and hardness in various cooling speed were analyzed, which prove that the designedsteel is reasonable and feasible. Then, combined thermal simulation experiment with hightemperature laser confocal microscopy experiment, the effect of austenitizing temperature onbainite phase transformation was researched, and discussed which heating process would shortenthe incubation, speed up the bainite transformation. Through in-situ observation, the change ofaustenite grain and the regulation of nucleation and growth of bainite phase transformation wereobserved, meanwhile, microcosmic causes heating process effect bainite transformation wasgiven.The results show that the designed steel has good hardenability, when cooling speed isabove0.5℃/s, the steel can avoid transformation of high temperature austenite, this is good forindustrial production. The austenite grain coarsening temperature is more than1000℃, theprocess of austenite grain growth is grain boundary expansion and migration, when it migrates,small grain is combined by the big grain nearby, moreover, there is secondary grew up in thegrain growth. The higher austenitizing temperature is, the shorter the bainite transformationincubation period is, the faster the transformation is, the more quantity of bainite transformationwe can get. The nucleation of bainite ferrite initiates on grain boundary, following in the grainand on the pre-formed bainite. When bainite is growing, if without effect of other bainite, itwon’t stop until meeting grain boundary, or they will interplay and form short and small bainitelath in the grain.