Crystallographic Analysis Of High Temperature Phase Transition Of Medium Carbon Alloy Steel

This paper aims the crystallographic orientation characteristics and magnetic induced mechanism of diffusion-controlled phase transformation for 50Si2Mn3 steel under different magnetic intensities. Crystallographic orientation characteristics under different magnetic intensities have been investigated, including nucleation, growth and crystallographic, etc., and discussed that the influence of different magnetic intensities on starting points and the maximum temperatures of MIP phase transformation. In addition, build up the curve about the phase transformation starting point and magnetic intensity-isothermal temperature-magnetic time.The nucleation and growth of MIP in Si-Mn casting steel under 12 T shows that pearlite ferrite (PF) along with<110>//ND components have priority to nucleation and growth at the early stage of phase transformation, as compared with other texture components, such as<111>//ND and<100>//ND, which indicates PF has an obvious preferred orientation during nucleation and growth by the applied high magnetic field; With the low transformed fraction of MIP increasing, the initial nucleation PF maintain its preferred crystallographic orientation to grow up, while new phase suffer not only the comprehensive influence from interfacial energy, volume free energy and the magnetic free energy, but also accumulated elastic strain energy of parent gradually, resulting in multidirectional space orientation and further losing preferred direction on<110>//ND; 100 percent transformation of sample continued to extend the magnetic processing time don’t perform any micro texture features.The research of higher magnetic field focuses on:ferromagnetic PF may present preferred direction along with easy magnetization direction<001> or still continue growth regularity of 12 T. Considering the size of sample and isothermal furnace hearth, magnet effective cavity and experimental manipulation, the highest magnetic field intensity is 20 T, but the actual field intensity is 19.8 T. The crystallographic orientation variation of MIP during its microstructure evolution in 19.8 T demonstrated that it is closely related to the isothermal temperatures and the applied magnetic time during the process of MIP formation. The<100> easy magnetization direction in MIP colonies is strengthened with the time within the certain transformed fraction of MIP (fMIP) at the relatively lower temperature (983 K) above the eutectoid temperature, while this special orientation tends to be weakened at a relatively higher temperature (995 K); For the same magnetic time, the higher the temperature, the relatively larger proportion in <100> orientation for MIP colonies at the early growth stage; These results have demonstrated that the change of<100> orientation of MIP is closely related to the growth rate of PF, and strengthened mainly at early transformation stage. When fMIP reaches some value, the growth rate of MIP at other crystallographic orientations, such as<110>, even the hard magnetization direction, turns to present speed-up.According to different fMIP under different magnetic intensities, the starting points and maximum temperatures of MIP phase transformation have been studied, and build up the curve about the phase transformation starting point and magnetic intensity-temperature-time, which shows the influence of magnetic field on the maximum phase transformation temperatures is not linear; Magnetic field promotes <100>-oriented grains nucleation and growth at early transformation stage, Cem with granular or short rod precipitate discontinuously from the block ferrite, and the increased amount of MIP is mainly from that P preferentially formed grew up, rather than the increasing nucleation amount.