Bainite isothermal transformation of Si–Mn–Mo alloy by phase structure factor calculation under different rare earth contents

The effect of rare earth (RE) on bainite transformation mechanism is not yet unified in the academia. Therefore, further studying the effect of RE on bainite transformation mechanism will have important guiding significance for the development of bainite steels. In this paper, using differential dilatometer (DIL805A/D), heat treatment was performed and C-curve was drawn. The effect of phase structure factor on bainite transformation under two different fractions of RE in Si–Mn–Mo bainite steels was investigated by the empirical electron theory (EET) of solids, molecules, dilatometry, and metallography. Experimental results show that RE makes Fe–C-RE segregation structural unit of Si–Mn–Mo bainite steels increase, i.e., the values of phase structure factor (n _A, F _C ^D ) increase, and delay bainite transformation due to the drag effect resulting from the segregation of RE ferrite island interphase and the retardation of RE to carbon diffusion in Si–Mn–Mo bainite steels. Beside this, C-curve is shifted to right and down, and microstructures of bainite ferrite and substructures are finer.