Research On Fabrication Of6.5wt%High Silicon Steel By Composite Technique

6.5wt%high silicon steel, as an excellent soft magnetic material, exhibits near-zero magnetostriction, high permeability, low coercive force, low iron loss and so on. It has huge superiorities in high frequency fields, because of its advantages in reducing the consumption of energy and noise pollution. However, it is impossible to fabricate thin sheets of this alloy by the conventional casting-rolling process by virtue of its unsolved problems of brittleness and difficult-to-process at room temperature, which limits its industrial application seriously. Therefore, fully understanding its brittleness essence and deformation mechanism, imposing active control on microstructure and property of this material during preparation and processing and creating a special approach to product this alloy effectively are the crucial scientific foundations for efficiently fabricating Fe-6.5wt%Si alloy strips by rolling process.In this work, according to the characteristics of laminar composite, the protection of outer layer to the inner layer and variation of the field of stress, the6.5wt%high silicon steel thin sheet, which is hard to process because fo its uncommonly brittleness at room temperature, has been fabricated by the composite technique. This presentation is consisted of clad casting, stages of deformation, heat treatment, distribution of elements, variation of interfaces, microstructure and magnetic properties, and the main conclusions as followed:(1) The inner layer and out layer, which are10-12wt%Si alloy and3wt%Si, respective, are conceived by coat casting according to the design of elements and constructure. The silicon element was disappearing in a large account due to the high temperature, and construction of the composite was changed after hot forged.(2) Hot rolling was made after considering the theory of hot rolling of high silicon steel composite sheet. Thickness of this sheet is near2.5mm at the end of hot rolling generation. The proportion of two layers is almost1:1. More phases like Fe2SiO4,FeSiO3,Fe1.6SiO4and SiO2are detectived and also D03ordered phase by the way of X-ray diffraction. That means the silicon element lost tremendous in high temperature.(3) The high silicon composite plate was not opened after cooling in the way of pollution of water and15wt%NaCl at the end of heat treatment, before that the composite alloy was heat at850℃during an hour. Hardness of the inner layer is from556HV falling to482HV. The ordered phase D03was changed to the big B2ordered phase and the composite material is becoming soften and the B20phase is found in the same period, that was observed by X-ray diffraction.(4) It is not hard to process during the middle temperature by warm rolling, especially at690℃, and the micro structure is like the thin fibers. That means continuous processing goes well after the phase order is low and thickness of this plate is0.5mm. Finding the difference of silicon element during the stage of warm rolling using the Scanning Electric Microscope, the results shows silicon element dot not lose under750℃The heat treatment of eliminating the second hard and residual stress is better under the temperature of second recrystallation.(5) The composite after warm rolling could not be processed by cold rolling, after that, more cracks emerged after cold rolling. Thickness of the composite will be getted as0.2mm after treatment of medium temper. If the composite thin sheet was treated by the special heat treatment before cold rolling, it could be formed continuously at the end of that stage, thickness of this strip is near0.05mm.(6) The third-layer constructure of the composite thin sheet is observed clearly at the beginning of cold rolling section, and also the transition layer is clear during the two layers. The transition is becoming dark gradually as well as the deformation is bigger than before. In the beginning of cold rolling, more deformation is showed by outer layer. However, the deformation of inner layer is raising up as the second harding appearing as well, and the microstructure of composite thin sheet after cold rolling is like the long fibers, all of that is observed by Scanning Electric Microscope.(7) The composite thin sheet after warm rolling which thickness is0.8mm is getted diffusion treatment, the results show that there is almost no diffusion happening at1100℃, Si element begin to move to another place but its speed is so limited at1150℃, during a short time at1200℃, Si moving in a common fast and silicon element of the whole composite is average which is near6.41wt%. Another composite thin sheet which thickness is0.5mm is in the same condition when it was heated at1200℃and after75min.(8) The magnetic properties are investigated when the diffusion stage finished, P15/50, B8and B50of0.8mm thin sheet is3.906W/Kg,1.297T, and1.584T, respectively. P15/50, B8and B50of number three0.5mm thin sheet is2.833W/Kg,1.371T, and1.628T, respectively. P15/50, B8and B50of number one0.5mm thin sheet is3.327W/Kg,1.332T, and1.609T, respectively.