Evolution Behavior And Control Mechanism Of Microstructure And Texture Of Strip Casting Grain-oriented Silicon Steel

The exploratory study was carried on the evolution of microstructure,texture and inhibitor and the control mechanism of strip casting grain-oriented silicon steels in this paper.This study mainly focused on the origin and evolution of Goss texture,microstructure and texture evolution during secondary recrystallization and the effect of primary recrystallization microstructure and texture on the abnormal growth of Goss grains.The main research conclusions are as follows:(1)The formation mechanism of solidification microstructure and texture under the condition of sub-rapid solidification was investigated.The formation mechanisms of Goss texture during strip cating were revealed.The microstructure and texture of ?-ferrite can be effectively controlled by changing the melt superheat.The final solidification texture was mainly determined by the orientations of initial ?-ferrite grains and whether the as-cast strip was subjected to hot rolling deformation by the casting rolls.With the absence of deformation,the as-cast strips composed of fully equiaxed grains,outer columnar grains with inner equiaxed grains and fully columnar grains can be successively produced by improving the superheat from 15?to 100?.The equiaxed grains and columnar grains corresponded to random texture and strong {100}<0vw>fiber texture,respectively.In case of relatively low melt superheat,small Goss oriented 8-ferrite grains can be formed due to random nucleation during solidification.When the as-cast strip is deformed by two cast rolls,Goss texture is formed in the subsurface because of shear deformation.(2)The influences of solidification microstructure,hot rolling reduction and hot rolling method on the hot rolled microstructure and texture of grain-oriented silicon steels were investigated.The methods to control the hot rolled Goss texture on the condition of strip casting process were clarified.The microstructure of grain-oriented silicon steel was composed of 8-ferrite grains and austenite at hot rolling temperature.The 8-ferrite grains were only subjected to recovery during hot rolling and the phase transformation was limited during the cooling stage after hot rolling.Thus,the hot rolled texture was mainly determined by recovered 8-ferrite grains and it was significantly influenced by the initial solidification microstructure,hot rolling reduction and hot rolling method.Under the condition of symmetrical hot rolling at 1150?,when the hot rolling reduction was less than 50%,only a few Goss grains were formed in the subsurface layer as a result of limited shear deformation.When the hot rolling reduction was increased up to 50%,relatively strong Goss texture was formed in the hot rolled sheet.And,stronger Goss texture was generated in the coarse-grained hot rolled sheet.When the grain-oriented silicon steel was subjected to asymmetrical hot rolling at 1150?,relatively strong Goss texture was produced with the aid of additional shear deformation even if the hot rolling reduction was only 35%?When the hot rolling temperature was reduced,only weak Goss texture was generated due to limited of shear deformation.(3)The microstructure,texture and inhibitor evolution along the whole process of strip casting grain-oriented silicon steel with MnS as the inhibitor were investigated.The origin and evolution of Goss texture was clarified.The results showed that only a few Goss grains were generated in the hot rolled sheet because of limited rolling reduction and they grew to large sizes during normalizing.The pearlite,martensite and carbides in the matrix greatly increased the work hardening of coarse 8-ferrite grains during first cold rolling.This promoted the formation of homogeneous intermediate annealed microstructure and the elimination of harmful {100}<0vw>fiber texture.After primary recrystallization annealing,a homogeneous recrystallization microstructure with small Goss grains and lots of fine MnS precipitates was generated.The accociated texture was characterized by relatively strong?-fiber texture and Goss grains were surrounded by high-frequency 20-45° boundaries.With the increasing of second cold rolling reduction,the {111}<112>component was enhanced.After high temperature annealing,the perfect secondary recrystallization microstructures were produced.The highest magnetic induction B8 was up to 1.86 T.(4)The microstructure,texture and inhibitor evolution along the whole process of strip casting high-permeability grain-oriented silicon steel with AIN and MnS as the inhibitors were investigated.The evolutions of microstructure,texture and grain boundary distribution characteristics during high temperature annealing were investigated.The results showed that the Goss oriented ?-ferrite grains in the as-cast strip grew to large sizes after hot rolling and normalizing.After cold rolling and primary recrystallization annealing,a fine and homogeneous microstructure with {111}<112>component and {hll}<1/h 1 2>texture was produced.A few small Goss grains and a large number of fine AIN and MnS precipitates were distributed in the matrix.The cold rolling reduction exhibited significant influences on the primary recrystallization texture and thus on secondary recrystallization behaviors.When the cold rolling reduction was 88.5%,the {h11}<1/h 1 2>texture in the primary recrystallization annealed sheet was relatively weak and Goss grains were surrounded by high-frequency 20?45° boundaries.The frequency of this kind of boundary was further improved during high temperature annealing,resulting in the formation of perfect secondary recrystallization microstructure.The magnetic induction was as high as 1.94 T.(5)The evolutions of microstructure,texture and inhibitor along the whole process of strip casting low-carbon grain-oriented silicon steel were investigated.The relation between the evolution of primary recrystallization microstructure and texture and secondary recrystallization behavior was established.The results showed that Goss orientation within the shear bands in some a and y deformed grains preferentially nucleated during intermediate annealing,resulting in strong Goss texture.Although the 8/y transformation and hot rolling were eliminated,a large number of fine and dispersed AIN and MnS precipitates were still produced by controlling the cooling process after solidification and normalizing.The assignment of cold rolling reductions showed remarkable effects on primary recrystallization microstructure and texture and thus affected the abnormal growth of Goss grains.When the single-stage cold rolling or inappropriate two-stage cold rolling process were applied,lots of coarse and elongated ?-and a-oriented grains were produced.These grains blocked the abnormal growth of Goss grains during high temperature.In case of appreciate two-stage cold rolling process,a perfect secondary recrystallization microstructure was produced and the magnetic induction B8 was as high as 1.82?1.85 T.