Study Of Structure And Crystallography Texture Of Fe-3%Si Steel Sheet Produced By TSCR

In recent years, the research of silicon steel, especially oriented silicon steel, produced by a short process has attracted more attention in world steel industry, because of the questions of traditional process such as a long process and the high cost. The success of this technology development and industrialization will bring about a profound change in the electrical steel production.For the present Fe-3%Si steel, a series of laboratory tests were performed by a thermomechanical simulator including compression, soaking and quenching tests with different processing parameters. The evolution of microstructure and grain orientation during high-temperature processing in this coarse grained ferrite material was investigated by analyzing the characteristics of true strain-true stress curve, microstructure and recrystallization kinetics. Under laboratory conditions, smelting, casting, hot rolling and cold rolling were carried out to simulate thin slab cast rolling (TSCR) of Fe-3%Si steel, which mainly includes the designs of mould and chemical component, the selection of inhibiter, the determination and optimization of processing parameters in hot rolling (e.g. soaking temperature, time of ingot, reduction and cooling schedule), cold rolling and annealing etc.. The precipitation of inhibiter, formation of microstructure and texture and their influence factors in Fe-3%Si steel produced by TSCR were studied systematically. The results can provide the necessary guidance for the production and application of oriented-silicon steels using a short process. The main contents and results are as follows.(1) The true stress-strain curves with different stain, strain rate and deforming temperature and as-quenched microstructure for Fe-3%Si steel were analyzed. The true stress-strain curve shows that dynamic recovery is the dominant softening mechanism, and the recovery rate is far faster than austenite materials. Initial austenite content increases with heating temperature, the continuous-dynamic recrystallizing grains can be observed from in Fe-3%Si material by heavy deformation. The presence of minor austenite, acting as second phase, plays an important role in pinning the grain boundary and preventing grain growth.(2) The recrystallization behavior and microstructure feature of Fe-3%Si steel have been analyzed using samples which were deformed and subsequently quenched after annealing for different times. The volume fraction of recrystallization increase quickly with annealing time, and in coarse grained material, retardation of recrystallization resulted in the appearance of a plateau in the recrystallization curves. The microstructure mainly consists of recovery and recrystallization grain, and dislocation line and subgrain can be observed in optical micrographs for samples quenched immediately after deformation.(3) In coarse-grained ferrite materials, the activation energy for static recrystallization was determined using the time of 30% recrystallization. For the deformation conditions investigated, original grain boundaries, particularly triple points of boundaries are preferential nucleation sites for new recrystallized grains, boundaries, whereas some intragranular nucleation also occurs when austenite is present. As a result of rapid recovery in ferrite, growth rate falls by more than two orders of magnitude during recrystallization and driving pressure for growth of recrystallizing regions also falls with annealing time. The sizes of recrystallizing grains depend on initial microstructure, such as grain size and austenite content, and deforming parameters, such as strain, strain rate and temperature.(4) Under laboratory conditions, the proportions of equiaxed grains and columnar grains are observed to be close to 35% and 65% respectively in as-quenched macrostructure of ingot after it is pulled out from the mould, and the desired volume fraction of Goss texture and texture gradient in thickness are obtained for hot-rolled slab with reheating furnace entry temperature greater than 1000℃. There are significant differences between the microstructures of head and middle of hot-rolled sheets for ingots soaked at 1175 and 1150℃respectively. The microstructure has no clear differnce between head and middle of steel sheets when holding for 30min at 1200℃, which is very similar to that of GO steel produced by traditional process in metallography.(5) The TEM observation of as-quenched samples of ingot,3 pass and 7 pass hot rolling sheets, as-rolled and as-normalized samples, shows that it is very important that ingot maintains uniform and high temperature distribution in length, width and thickness direction before hot rolling for inhibitor precipitation with small-sized and homogenous-distributed particles in TSCR process. Minor and coarse precipitates formed in casting can be re-dissolved at 1200℃, and then precipitated once again with fine-grained and homogenous-distributed particles during hot rolling, and the particle size of copper sulfide is less than that of MnS particles. The precipitates are mainly distributed within grain, at dislocation, grain boundary and subgrain boundary, whose proportion is closely relate to rolling schedule.(6) Base onφ2=45°sections of the X-ray ODFs analysis, the subsurface texture of hot -rolled sheet consists of s TD//<110> fibers. But, the texture of cold-rolled sheet mainly consists ofα(<110>//RD) and y(<111>//ND) fibers, and Goss texture ({110}<001>) disappears. The Goss texture is translated to{111}<112> orientation from 1/8 and 1/4 thickness firstly. The hot rolling texture has a certain effect on the cold rolling texture. Al- or Sn-containing silicon steels are more suitable for one-stage cold rolling.{111}<112> orientation density mainly is dependent on diameter of working roll and reduction schedule of cold rolling.