Study Of Bainitic Microstructure Control Process In Steels

The bainite morphologies and formation mechanism of bainite in 60Si2Mn and T10 steels under quench hot(970℃) were studied by optic microscope,transmission electron microscope(TEM) and micro-character. The bainite morphologies and formation mechanism of bainite were compaired with normal quench(870℃). The bainitic morphologies and bainitic transformation in tow steels were influenced with austenization temperature and austenization time. Some martensite-like bainites,such as regular triangular, crossed,"N"- and butterfly-type were observed in the alloys. The bainite microstructure and morphologies in steels under different isothermal temperature and isothermal time condition were investigated.The hardness of steels were investigated by the sclerometer. The transition characteristics of bainite phase transformation were discussed from perspective of self-organization theory.The results show that bainite phase transformation in the middle temperature area is transitive,and it has double character of the pearlite decomposition and the martensite transformation,transition characteristics.The valence electron structures of austenite and the critical resistance of bainitic transformation in bainite phase transformation area of Fe-C alloy are calculated by the empirical electron theory of solid and molecules.The effect on bainite phase transformation by elements Si, Mn is discussed.Since the behaviour of elements Si and Mn during isothermal transformation depends on the segregation force of C-S, C-Mn, the complexity of the microstructure and morphology are appeared.Based on the empirical electron theory of solids and molecule,this paper sets up the valence electron structure of bainitic crystal cells in Fe-C alloys and analyses the effect of alloying elements Mn,Si etc,on strength and toughness in bainitic steels.It shows that there are segregation structure units of C-Si and C-Mn in the alloying bainitic steels which have higher bond strength and more hamper on the diffusion of carbon than Fe-C alloys, then make the strength and the toughness of bainitic steels are more superior.