Surface Nanocrystallization And Alloying Of Hot Rolled Silicon Steel

On the basis of stability in substrate chemical composite and apparent shape, a continuous transition nanocrystalline layer was prepared in the metal surface, which could improve the whole service performance of the material. The SNC was considered to be the development orientation in metal material modification, and has an extensive application prospects.The Fast Multiple Rotation Rolling (FMRR) device was adopted to treat the hot rolling non-orientation silicon steel. There was a discussion on the microstructure and the physical properties of SNCed silicon steel and alloying properties thereafter. The microstructure change was studied by metalloscope, X-ray diffractometer and scanning electron microscopy. The hardness was determined by microhardness tester. The results showed that the grain size in the surface layer is in nanoscale, about10nm, the size was a gradient distribution along the depth of the cross the depth, which was increase to the original grain size at last; It could improve the microhardness in the surface by75%. The microhardness decreased with the increasing of the depth, which was coinciding with the microstructure.Tensile properties and corrosion properties was studied by the normal contrast to the FMRRed sample. At room temperature, it showed the high yield strength and low workhardening capability in the nanometer crystal microstructure, which was indicated by the Hall-Petch relationship. The yield strength of the original sample is the58.0%of the sample treated at4.0MPa for60min by FMRR. The elongation of the original sample is the1.85times of the sample treated at4.0MPa for60min by FMRR. The Tensile Sample Fracture shows that the necking phenomenon in the FMRRed sample is shirked. The gliding fracture and the brittle failure were observed at the fracture, the later is dominated. The soft magnetic property was degenerated after FMRR. Ecorrare positive than the original sample, and the Icorrare raised.It indicated that the decay resistance properties ware lower than the original sample.Fe3Si type silicide infiltration layer was prepared in FMRRed sample by molten salt non-electrodeposition.The phase composition in the layer were determined by XRD.The apprearance and the chemical composition was determined by the SEM and the EDS.Contrary to the traditional coarse grain material,the diffusion velocity of FMRRed sample was higher, which indicated that the diffusion between iron and silicon is enhanced by the surface nanocrystalline layer.The average grain size in the surface is much smaller than the common silicide infiltration surface. The DO3type Fe3Si X-ray diffraction peak was much broader than the common. The silicon contents in the cross section of the silicide layer was much larger, the width and the pore in the Kirkendall pore band is bigger than the normal.It also illustrated that the silicon atom could be permeate the non-equilibrium grain-boundary much easily.The higher the silicide temperature the faster the infiltration layer grow.At the appropriate holding lime, the longer the time the thicker the infiltration layer.