Texture Optimization Principles And Technical Exploration In The Electrical Steels In Medium-high Frequency Application

In the current word,needs for environment protection and stable energy supply are constantly driving the demand for energy conservation.Motors and electrical control systems,as indispensable elements in power and telecom industry,are called the heart of electricity sector.This "heart" is in turn driven by core materials used in motors,which play a key role in improving motor efficiency and achieving low energy consumption.According to statistics,the power loss generated from iron cores accounts for 6%of total power.Reducing the iron loss of electrical steel not only helps to save a large amount of electrical power but also simplifies the complicated cooling devices and significantly extends the service life of motors and transformers.Besides,with the development of electronic technologies,high-frequency applications in electrical and electronic machines represented by converter control are also growing quickly.Thin-gauge,miniaturization and high-frequency have become a major development direction in current electrical steel industry.In this paper,two methods,i.e.reducing the thickness of strip steel and increasing the silicon content,are adopted to reducing the iron loss of electrical steels.On this basis,the preparation techniques and relevant mechanisms of ultra-thin grain-oriented electrical steels and high silicon steels which applied in medium-high frequency are investigated and analyzed,thus providing technical guidance for the commercial production of electrical steels.Primary recrystallization method is adopted to prepare ultra-thin grain-oriented electrical steels.By exploring the effect of cold rolling reduction and initial Goss orientation on the texture evolution and magnetic properties of ultra-thin grain-oriented electrical steels,the production process of ultra-thin grain-oriented electrical steels can be optimized.For the research of non-oriented high-silicon steels,the columnar grains with strong {100} texture are adopted and cold rolled in ND direction to summarized the behavior of deformation and recrystallization.This will facilitate identification of the control method and theories of cube texture,which is beneficial for the preparation of new type non-oriented or double grain-oriented high-silicon steels.For the development of high-silicon grain-oriented electrical steels,both inhibitor method and without inhibitor method(surface energy method)are adopted to prepare high-silicon grain-oriented electrical steels with higher magnetic properties along the rolling direction,which provides new methods and theories for industrial production of high-silicon grain-oriented electrical steels.The main conclusions are as following:(1)The cold rolling reduction and sharpness of Goss orientation have a major impact on texture evolution and magnetic properties of ultra-thin grain-oriented electrical steels.As the cold rolling reduction increases and the thickness decreases,recrystallized grains sizes gradually increase,the strength of?(<001>//RD)texture first increased,and then decreased.At 70%cold rolling reduction,? texture is the sharpest with the best magnetic properties.When the cold rolling reduction increases to 75%,grain orientation has a tendency to rotate along the ND axis.The occurrence of deviated {210}<001>oriented grains weaken the texture of ?(<001>//RD).The 70%cold rolling reduction is recommended to prepare ultra-thin grain-oriented electrical steels by taking the grain size and ?(<001>//RD)texture into consideration.(2)The effect of initial Goss orientation on magnetic properties of ultra-thin grain-oriented electrical steels is due to the different deformation and recrystallization behaviors between Goss grains and deviated Goss grains.After 70%cold rolling,the grain-oriented electrical steels with high grade formed sharp{111}<112>deformation texture,while the grain-oriented electrical steels with low grade formed a texture somewhere between {111}<112>and {111}<110>.Due to Goss texture formed during primary recrystallization result from Goss grains in the initial strips,the high-grade grain-oriented electrical steel with high intensity of Goss texture generated sharper Goss texture after primary recrystallization annealing.At the stage of secondary recrystallization annealing,the two grades of grain-oriented electrical steels exhibited different secondary recrystallization behavior.The high-grade grain-oriented electrical steels presented the inhibitory effect of Goss texture,which deteriorated the sharpness of Goss texture.The low-grade grain-oriented electrical steels revealed strong surface-energy induction effect,which enhanced the intensity of Goss texture.During cold rolling of thin silicon steel strips,the surface shear behavior should not be neglected.The origin of {113}<361>grains are related to surface shearing behaviors of the cold-rolled thin strips,and such orientation in surface was result from initial deviate Goss grains.The {113}<361>grains can swallow up the small grains with Goss orientation during the secondary recrystallization by taking the advantage of lower grain boundaries energy,which led to degradation of sharp Goss texture formed in primary recrystallization.(3)The ultra-thin strips made of high-grade grain-oriented electrical steels exhibited better low frequency magnetic properties at primary recrystallization temperature,while those made of low-grade grain-oriented electrical steels exhibited better high-frequency magnetic properties at secondary recrystallization temperature.By controlling the process of secondary recrystallization annealing,the texture of low-grade grain-oriented electrical steels can be significantly optimized,the magnetic properties can be improved,thus achieving conversion from low-grade oriented electrical steel products to high-grade products.(4)Through hot rolling,warm rolling,cold rolling,and high-temperature recrystallization annealing of ND high-silicon columnar grains,0.27mm thick non-oriented high-silicon electrical steels with excellent magnetic properties are obtained by taking advantage of heredity of {100} texture.The texture of finished products is dominated by cube texture with 41%percentage.The strong cube texture in the finished sheets is related to the heredity of columnar grains during deformation and recrystallization.Attribute to the coarse {100}<001>deformed grains in center and preferred cube nucleation in deformed {113}<361>areas in subsurface in cold rolled plate,the cube oriented grains have significantly nucleation advantages in recrystallization annealing.As the {113}<361>grains are related to initial cube oriented grains,the heredity of initial {100} columnar grains is also reflected.(5)The high silicon grain-oriented electrical steels with strong Goss texture can be prepared by the inherent inhibitor(CU2S)combined with additional inhibitor(AIN)method.The nitriding time has great effects on the secondary recrystallization structure.In those samples without additional nitrogen,the secondary recrystallization does not occur.With the nitriding time of 60s,as the inhibitor is insufficient,the percentage of secondary recrystallization structure is about 80%.With the nitriding time of 120s,the inhibitor is excessive,and the percentage of secondary recrystallization structure is only 30%.When the nitriding time is 90s,the complete secondary recrystallization structure with strong Goss texture enables the finished products to have excellent magnetic properties.The preferential growth behavior of Goss oriented grain mainly depends on the high mobility of high-energy grain boundaries.With the increase of annealing temperature,the frequency of 20°?45° high-energy grain boundaries with Goss grains gradually increases.At the temperature of secondary recrystallization(1000?),the frequency of 20°?45° high-energy grain boundaries with Goss grains is 62.7%,providing favorable conditions for abnormal growth of Goss grains,led to a secondary recrystallization structure dominated by strong Goss texture.(6)The double grain-oriented high-silicon steel products with sharp cube texture are prepared by three-stage rolling method combined with the surface energy.The cube texture component of finished products originates from the deformed cube grains existed in center layer of hot rolled sheet.During three-stage warm rolling and intermediate annealing,the cube texture component was further enhanced.At the stage of primary recrystallization annealing,the strong cube texture with 28.1%percentage is formed by taking advantage of preferred cube nucleation.With the increasing of annealing temperature,the grain size exceeds the plate thickness,the surface energy effect is prominent,both the components of Goss and cube texture enhanced.After high temperature annealing for a long time,the cube oriented grains abnormally grow up by taking advantage of the grain size and frequency of cube grains.The secondary recrystallization microstructure consisting of strong cube texture is formed,which significantly improved the magnetic properties of high silicon steel sheet.