Microstructure-Properties Regulation Mechanism During Deformation And Heat Treatment Of Strip Cast Non-oriented Silicon Steel

Non-oriented silicon steel is produced and used as core material of electrical machines such as motors and generators.In view of energy crisis,raising motor efficiency by improving the magnetic properties of silicon steel is of great significance for promoting sustainable development of economy and society.However,the conventional processing characterized by heavy hot rolling process severely limits the controllability of texture and the room for improvement of magnetic properties.Therefore,in this work,the twin-roll strip casting,a form of near net shape casting process,was employed to prepare silicon steel.Based on the deformation and heat treatment process,the preparation method of non-oriented silicon steel with superior properties and the related mechanism was studied.The evolution mechanism of specific texture during deformation and annealing was clarified,and the effect of hot rolling,warm rolling and annealing process on microstructure evolution and magnetic properties was analyzed,and the method and mechanism of texture control for thin-gauge product was explored.It provided a new way for the production technology of high-quality non-oriented silicon steel.The main contents and results are as follows:（1）The deformation behavior of Cube grains in non-oriented silicon steel was studied,and the recrystallization process of grains with specific orientation and the formation theory of recrystallization texture was analyzed.The results show that Cube grains have three kinds of rotation routes during deformation: the one is rotating along {001 }<120>,{001 }<110> and a-orientation line;the second is rotating along {114}<841>,{112}<571>;the third is rotating along {013}<031>,{012}<021>,{110}<110> and {110}<221>.New Cube grains mainly nucleate at the deformation bands between {110}<110> ～{110}<221 > oriented deformation bands,and at {114}<841> deformation bands and at {111}<112> deformed grains,where the first two regions contribute the largest fraction of Cube nuclei.This recrystallization process is related to the heredity of Cube structure.In addition,part of the blocky Cube deformation micro structure can be retained in the annealed micro structure by recovery.During annealing,the growth rates of all new grains are almost the same regardless of orientation.The nucleation of Cube and Goss grains dominates the recrystallization process by virtue of nucleation density.The formation of recrystallization texture is attributed to the oriented nucleation mechanism.Moreover,the “orientation pinning effect” caused by the colony distribution of Goss and Cube grains and the recovery of large-sized Cube deformation microstructure has a great effect on the orientation density distribution of the recrystallization texture.（2）Dynamic strain aging（DSA）behavior and its effect on deformation microstructure and texture during warm rolling of Fe-2.8%Si steel was studied.The influence of warm rolling process on recrystallization textxire and magnetic properties was discussed.It is found that with the increase of rolling temperature in the range of 50～300 ℃,the DSA behavior is gradually strengthened,and the fraction of shear bands in warm rolled sheet is increased,and y-fiber deformation texture is weakened whereas the a-fiber texture is enhanced.After optimizing the warm rolling process,the Goss recrystallization texture is gradually increased,whereas the Cube texture is gradually weakened.It is related to the increased nucleation of Goss grains at shear bands.The average magnetic induction B₅₀ between rolling direction and transverse direction of the annealed sheet increases from 1.72 T to 1.75 T,but the core loss also increases because of the decreased grain size.（3）The deformation microstructure and recrystallization behavior was controled through the regulation of hot rolling and cold rolling process.A preparation method of complete {100}recrystallization texture was proposed based on the characteristic microstructure evolution.The results show that with the increase in hot rolling reduction and decrease in hot rolling temperature,the grain size of hot rolled Fe-1.3%Si sheet and the fraction of shear bands in cold rolled microstructure gradually decrease.Meanwhile,the a-fiber textoe of the cold rolled sheet is gradually weakened,and the y-fiber texture is gradually enhanced.In the case of 900 ℃ hot rolling with reduction of 55%,complete {100} texture and weak Goss texture is formed in the annealed sheet.During this process,the {100} deformation microstructure increases significantly and the fraction of shear bands decreases significantly so that the nucleation and retention of {100} grains dominate the recrystallization process.Ultimately,the magnetic inductions at 30～75° direction are increased by 0.01 ～0.04 T,and the circumferentially average values of magnetic induction B₅0 as 1.72 T with anisotropy of 2.4%and core loss P_15/50 as 4.20 W/kg with anisotropy of 3.7％ are obtained.（4）The pre-recovery annealing process and intermediate-recovery annealing process were designed to optimize {100} recrystallization texture.The efifect of recovery annealing process on recrystallization texture was clarified through the characterization of microstructure and texture under different annealing routes.It is found that the recovery annealing process releases the stored energy,thereby decreasing the driving force of boundary migration of new grains into {100} deformation microstructure and increasing the retention of{100} deformation microstructure in the final annealed sheet.After introducing recovery annealing process,the Cube,{001}<120> and {001}<110> grains with size of greater than200 jxm in final annealed sheet are gradually increased,resulting in the enhancement of {100}recrystallization texture.The area firaction of {100} grains in the final annealed Fe-3.0%Si sheet increases from 14.6% to 38.5%.However,excessively long recovery annealing process leads to poor microstructure uniformity,and it increases non-{100} oriented microstructure in annealed sheet,which is detrimental to optimization of recrystallization texture.（5）0.20 mm-thick non-oriented electrical steel with high magnetic induction and low core loss was successfully processed by microstructure heredity and shear band control technology.The microstructure and texture evolution along the whole processing routes was investigated.The results show that the cold-rolled microstructure processed by one-stage rolling with reduction of 91% is composed of heavily elongated and fragmented grains with little shear bands.The cold-rolled sheet exhibits strong a-fiber texture,and strong{111}<112> and {223}<110> recrystallization texture are formed after annealing.Two-stage rolling process significantly enhances the fraction of shear bands and the retention of Cube and Goss microstructure in cold rolled sheet.After annealing,the y-fiber and a-fiber recrystallization texture is obviously weakened,whereas the r(-fiber texture is significantly enhanced.The average values of core loss as 2.09 W/kg and magnetic induction as 1.72 T is obtained,which displays an improvement by 0.07 T compared with the conventional product.