Investigation On The Microstructure,Texture And Magnetic Property Of Twin-roll Strip Casting 4.5wt.%Si Steel

With the continuous enhancing requirements in the efficiency of using resources and energy,large amounts of non-oriented electrical steel suitable for serving under high-frequency environment are in demand.Increasing the silicon concentration and reducing the thickness are effective methods to reduce the iron loss under high-frequency.The increasing of the content of the silicon,however,will lead to a sharp increase in the hardness and brittleness.It will be difficult to achieve thickness reduction by conventional rolling process.Further improvements of the properties should be sought by controlling techniques of the texture and employing advanced manufacturing technologies to produce high Si steel.Looking for advanced manufacturing technologies and appropriate silicon concentration will be extremely essential for the development of the high-frequency motor industry.The targets of this study are focused on the development of the manufacture technology and the upgrade of the properties of products.By the twin-roll strip casting technology,4.5 wt.%Si steel sheet with excellent magnetic properties was produced.The characteristic and evolution of the microstructure and texture during the preparation process were studied.This study also puts focus on the recrystallisation behaviours and the nucleation mechanism,trying to provide technical supports and theoretical basis for the high efficient production of non-oriented silicon steel and the regulation of the microstructure and texture.The twin-roll strip casting technology was utilised into the development of the high silicon steel which is based on the content of 4.5 wt.%silicon.By the design of composition and the test of strip casting,the preparation parameters were obtained.Through exploring the microstructure and the hardness of the as-cast strip,the advantage of the 4.5 wt.%Si steel manufactured by rolling were investigated.The morphology of the precipitation,the segregation of the elements,the brittle ordered phase and other related issues were analysed.The evolution of the microstructure and texture during the whole processing were studied.By comparing the magnetic properties,the advantages of the twin-roll strip casting 4.5 wt.%Si steel were demonstrated.The evolution of the texture forming the nucleation to the end of recrystallization by EBSD and XRD was compared,and the reasons were analysed for the elimination of the orientation which belongs to the preferential nucleation and the enhancement of orientation which belongs to minor nucleation.At the start of the recrystallisation,the{100}<001>,{100}<001>and {111}<112>were preferred nucleation,however,the{411?<148>oriented nucleation was random distribution.It was pointed out that the orientation pinning and selective growth mechanism are responsible for the formation of the sharp {411}<148>component.The {411}<148>texture has no obvious relationship with the plastic instability of the {100}<011>oriented deformed grains.The 4.5 wt.%Si ultra thin strips with no edge cracks and good shape can only be produced by warm rolling and cold rolling.The microstructure and texture of the three different thicknesses(0.05mm,0.1mm and 0.2mm)thin strips were analyzed.The texture of the 0.05mm ultra thin strip is the least obvious,and the new nuclei were random distributed during the recrystallization annealing.The magnetic induction of the 0.2mm thick ultra thin strips can reach up to 1.686T(B50).The iron loss of the 0.05mm ultra thin strips is 8.13W/kg(W5/1000).The influences of the thickness on the microstructure,texture and magnetic properties were obtained.The 4.5 wt.%Si as-cast strip with equiaxed grain and,texture was firstly manufactured by optimizing the composition and processing.The magnetic properties of the product can reach up to 1.712T(B50),23.77W/kg(W5/1000).Utilizing the EBSD,the nucleation sites were found for the {100}<013>new grains.The results show that the oriented nucleation mechanisms are responsible for the formation of the sharp{100}<013>component.The evolutions of the dislocation and substructure during recovery and nucleation were investigated by TEM.And the characteristics of the grain boundary and shear bands during recrystallization were explored by EBSD.It is really helpful for deeply understanding the process of recrystallisation.