Composition Design Of Strip Casting Grain Oriented Silicon Steels And Microstructure Texture Regulation Mechanism

Twin-roll strip casting with the characteristics of short process and rapid solidification has a distinctive advantage on simplification grain oriented silicon steel production process and inhibitors control.Based on the rapid solidification characteristic of strip casting process,the composition,subsequent rolling and annealing process of grain oriented silicon steel were adjusted and optimized.The microstructure and texture evolution and the dissolve and precipitation behaviors of inhibitors were systematic investigated during single-stage hot rolling,one-stage cold rolling and two-stage cold rolling processes.The effect of Nb-particles as grain growth inhibitors on the microstructure,texture and magnetic properties of conventional grain oriented silicon steels and strip casting grain oriented silicon steels was.comparative studied.The reason of Nb-particels cannot be acted as inhibitors of silicon steels produced by conventional process were explained.Finally,the effect of inhibitor strength and texture distribution on the secondary recrystallization kinetics of grain oriented silicon steel was discussed,and the rapid annealing process of grain oriented silicon steels by using twice secondary recrystallization phenomenon was proposed.The main innovative results are as follows:(1)Based on the rapid solidification characteristic of strip casting process,the composition system of ultra-low carbon oriented silicon steel was proposed and the subsequent decarburizing annealing process was cancelled,leading to the further simplify the production process.The conventional process through a tedious technology that addition carbon during smelting and then decarburization' before subsequent high temperature annealing successfully solved the contradiction between the controls of precipitation distribution by introduced the austenite phase during the hot rolling and normalization processes,and the requirements of high temperature annealing process in the single ferrite area.In the strip casting process,the refinement of solidified structure by carbon addition was ineffective.The austenite phase was distributed at the grain boundary.However,the solidified structure and texture can be effectively controlled by changing the thermal conductivity between molten pool and cast rollers.On the other hand,Due to the rapid solidification advantages of strip casting,the second phase particles were supersaturated solid solution or fine and dispersion precipitated,and then the main precipitation can be precisely controlled in the subsequent annealing process.It is not necessary to add carbon and introduce of the austenite phase and use the y/a transformation controlling the solid solution and precipitation behaviors of inhibitors.(2)The effect of single hot rolling process on the microstructure,texture,inhibitors and magnetic properties of ultra-low carbon grain oriented silicon steels was clearly explained.The results shown that the nose temperature of the PTT curve of AIN is 1090 ? and with the increase of hot rolling reductions,the hot rolled microstructure was refined and the Goss texture gradually increased,but because of the reduction limitation of the single hot rolling process,the hot rolled Goss texture was significantly lower than that of the conventional hot rolled sheets.After cold rolling and primary annealing,the amount of Goss texture was almost the same with that of the conventional annealed sheets.The optimal hot rolling process was 1100? and 35%reduction,the magnetic induction of B8 was 1.85 T.(3)The effect of normalization after strip cast on the microstructure,texture and inhibitors was studied based on one-stage cold rolling process.It was shown that without normalization process,the MnS was precipitated during primary annealing,and the precipitation behavior was started before the primary recrystallization.The distributions of MnS particles were inhomogeneous in different deformed grains,leading to the inhomgenetiy of the microstructure of primary annealed sheets.AIN particles were precipitated during high temperature annealing.The per-precipitates MnS was coarsening and failure the inhibited effect of grain growth before the beginning of AIN particles was precipitated,leading to no secondary recrystallization.When the normalization was introduced before cold rolling process,the MnS and AIN particles was precipitated homogeneous during normalization,and the primary annealed microstructure was also homogeneous.The.AlN particles have been existed before MnS particles became coarsening,which can continually inhibit the grain growth,promoting the secondary recrystallization during high temperature annealing.The optimal magnetic induction of B8 was 1.75T(4)The origin of Goss texture and its development in strip casting grain oriented silicon steel and the inhibitors solid solution and precipitation behaviors were studied based on the two-stage cold rolling process The results showed that the two stage cold rolling process could significantly improved the inhomogeneity of cold rolling and subsequent annealing microstructure caused by the coarse initial solidification structure.The primary recrystallization grain size can be controlled in the range of 5?15 ?m.The effective Goss seed was originated at the shear bands formed in the cold deformed y-grains,and which distributed homogeneous along the thickness direction of intermediate annealed sheets.The Goss texture intensity of intermediate sheets was increases with the first cold rolling reduction increased.The control strategy of inhibitor solid solution and precipitation behaviors was completely different from that of the conventional process by hot rolling and normalizing.Due to the sub-rapid solidification and subsequent cooling process,the inhibitor elements can be supersaturated solid solution in the as-cast strip and then a large number of inhibitors can be precipitated fine and dispersed in the subsequent intermediate annealing process.The size and density of inhibitors can be precisely controlled by changing the first stage cold rolled reduction and annealing temperature.This control strategy can overcome the inherent problems of AIN precipitated inhomogeneous in the conventional grain oriented silicon steel bearing carbon.The utilization efficiency of the inhibitor elements was significantly improved,and a 0.18 mm thickness grain oriented silicon steel can be successfully prepared.The magnetic induction of B8 was more than 1.9 T.(5)The microstructure and texture evolutions in strip casting grain oriented silicon steels and conventional process grain oriented silicon steels with Nb-particles as grain growth inhibitors was comparatively studied.In the conventional process,the formation of hot rolled Goss texture was inhibited by Nb-particles.The Goss seeds were less in quantity and smaller in size during the stage of high temperature annealing,there was no secondary recrystallization or non-Goss {113}<110>texture was abnormal growth.The phenomenon of{113}<110>abnormal growth can be explained by CSL grain boundary theory.In the strip casting process,the Goss seed was originated in the cold rolling and subsequent annealing process,the introduction of the Nb-particles could not lead to a drop in Goss seeds.Therefore,Goss could occur secondary recrystallization,and the magnetic induction of B8 was 1.85?1.89 T.(6)The effects of inhibitor strength and texture distribution on the secondary recrystallization kinetics of grain oriented silicon steel were analyzed.The rapid high temperature annealing process of grain oriented silicon steel using twice secondary recrystallization phenomenon was proposed.It was shown that the growth rate of abnormal Goss grain was changed.At the early stage of secondary recrystallization,the grain boundary migration was higher,while the growth rates were gradually slowed as the proceeding of grain growth.The in situ observation experiments by high temperature scanning confocal microscope shown that abnormal grain growth rate is about 40?1300 m/min.The addition of Nb as grain growth inhibitor and using twice secondary recrystallization phenomenon could significantly improve the growth rate of abnormal grains.The first abnormal grain growth was obtained during high temperature intermediate annealing.Due to the strong Goss texture inherited form first abnormal grain growth,and the low temperature Nb inhibitor was obtained during the cooling process of intermediate annealing,the subsequent second abnormal grain growth accelerated,and the final magnetic induction of B8 was 1.75 T.