Research On The Deformation And Softening Behavior Of Fe-6.5%Si High Silicon Steel

It is well known that Fe-6.5%Si silicon steel is a kind of soft magnetic materials with higher permeability, lower iron loss and magnetostriction, which has broad application prospects. However, their room temperature brittleness caused by B2 and DO3 ordered phase in high silicon steel limits their development of their rolling technology. In this paper, the thermal deformation, the softening behavior during the hot rolling and warm deformation of high silicon steel were investigated by metallographic microscope, X-ray diffraction, microhardness test and transmission electron microscope, in order to lay a theoretical foundation for development of rolling technology of high silicon steel. Paper’s main work and achievements are shown as follows:(1) Through the single compression test on the thermal simulation experiment, the stress-strain curve of the high silicon steel is measured. The influence of the deforming temperature, deforming rate and deforming degree on the deformation resistance of the steel is researched, and the high silicon steel’s mathematical model of deformation resistance is established. The optimum technology parameters at different strains for hot rolling are determined based on dynamic material modeling theory and plastic instability criterion. The temperature of hot rolling experiment is determined at 850℃-1000℃.(2) According to the data obtained in thermal simulation compression experiment, through the hot rolling experiment of high silicon steel, the microstructure and the change of ordered phase is analyzed by metallographic microscope and X-ray diffraction. The ratio of intensity of diffraction peaks of DO3 decreases by water cooling after hot rolling. It means that the order phase decreases after water cooling. The microhardness decreases from 437.32HV to 390.28HV, and the work-hardening exponent also decreases through the result of microhardness test and surface morphologies of micro-indentations to investigate the softening behavior of high silicon steel caused by decrease of order degree. But the plasticity of the hot-rolled high silicon steel isn’t improved by decrease of order degree through the result of tensile experiment.(3) Through the result of heat treatment after hot rolling, the fiber structure disappears caused by recrystallization behavior at 650℃ by metallographic microscope. The result of X-ray diffraction shows that B2 phase transforms into DO3 phase above 700℃.Through the result of microhardness tests, the work-hardening exponent decrease by heat treatment above 700℃, the microhardness decreases caused by the transformation of B2 into DO3.(4) The change of work-hardening exponent is analyzed by the compression test of warm deformation at 600℃. It is found that the microhardness and work-hardening exponent decrease during warm deformation by microhardness test and surface morphologies of micro-indentations. The strain-softening behavior is investigated by transmission electron microscope which is caused by the decrease of the order degree.