Study Of High-silicon Steel With Low Core Losses And High Magnetic Flux Densities Produced By Rolling Process And Its Coating

High-silicon steel is believed to be applicable to magnetic devices operating at high frequencies because its high permeability, low magnetocrystalline anisotropy, near-zero magnetostriction, low core loss, and low device noise. The high-silicon steel with low core losses and high magnetic flux densities produced by rolling process and its insulation coating have high industrial application values. A new type of non-oriented high-silicon steel sheets with low core losses and high magnetic flux densities along the rolling direction (RD) is produced by means of optimizing texture and grain size as well as controlling ordering degree. In addition, grain-oriented 6.5wt% silicon steel sheets with higher magnetic flux densities are produced by rolling and nitriding processes. The effects of texture and grain size on the magnetic flux density and core loss of cold-rolled high silicon steel sheets are investigated. Considering the more easily oxidized surfaces and poor punchability of high-silicon steel, a kind of environment friendly inorganic-organic insulation coating for high-silicon steel is prepared. Moreover, the punchability and punching fracture behaviors of high-silicon steel sheets are also studied, main conclusions are as follows:(1) More n-fiber textures (Goss texture as the main texture component) form in the subsurface of hot-rolled plates by using a large hot rolling reduction, and then are inherited. The coarse grains in warm-rolled plate are good for the formation of shear bands during the cold rolling. The high magnetic flux density along the RD is achieved after decarburization annealing due to the formation of strong{210}<001> and Goss texture which mainly nucleated and grew within shear bands of the deformed{111}<112> grains. The magnetic flux density is further improved because of the retention and enhancement of{310}<001> in n-fiber texture after annealing for a long time at high temperatures.(2) The value of B8 in cold-rolled high-silicon steel sheets is closely related to the volume fraction of η-fiber-oriented grains, while the value of B50 is closely related to the volume fractions of y-and X-fiber-oriented grains. The hysteresis loss of high-silicon steel can be greatly reduced by increasing its grain size and optimizing its texture. Although the increases in frequency decreased the effect of texture on core loss, the effect cannot be ignored. As annealing temperature and time increase, relative differences in core loss between the RD and transverse direction (TD) are maintained at higher frequencies because of the increases in grain size, the decreases in y-fiber texture intensity, and the maintenance of strong η-fiber textures. Texture and grain size jointly affect the high-frequency core loss of high-silicon steel.(3) The values of B & and B50 grain-oriented high-silicon steel produced by rolling and nitriding processes are higher than those of non-oriented high-silicon steel with strong η-fiber textures. The secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, and secondary recrystallized grain sizes become larger as well as the sharpness of Goss texture increases. Because more {110}<116> grains in the sub-surface and the central layer of sheets have a lot of 20-45° HE boundaries in addition to Goss grains,{110}<116> can be a main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. Increases in nitrogen content can increase the inhibitor intensity and hinder the abnormal growth of some of {110}<116> grains, and therefore enhance the sharpness of Goss texture.(4) The main components of oxide film formed on the surface of high-silicon steel during decarburization annealing process are SiO2, Fe2SiO4 and FeO. Comparing with the 3% silicon steel, more SiO2 form on the surface of high-silicon steel under the same conditions of decarburization annealing. It is necessary to reduce the thickness of oxide film before applying insulation coating, in order to increase the adhesion of coating. Under the condition of same coating amount, the cleaner and flatter the steel sheet, the thinner the oxide film, the better the adhesion quality of coating. The insulating coating has good adhesion, punchability and insulating properties when the coating weight per side is 0.8-1.2g/m2, the inter-lamination resistances are more than 5 Ω·cm2/piece.(5) The 0.2-0.3 mm thick cold-rolled sheets of high-silicon steel show good punchability under the condition of 0.01 mm punch-die clearance and at the temperature of 100 ℃; the punchability of annealed sheets with fine grain size is better than that of annealed sheets with coarse grain size. The major cleavage planes of annealed high-silicon steel sheets are{100} crystallographic planes on which brittle fracture occurs at low temperatures, and the cleavage systems include{100}<110> and{100}<100>, cleavage fracture takes place by one or both of them.The punchability of high-silicon steel sheets is influenced by punching temperature, grain size and ordering degree. Reducing ordering degree, increasing punching temperature, as well as refining grain size can improve the ductility and punchability of high-silicon steel sheets. Considering the punchability and industrial costs, the cold-rolled high-silicon steel sheets should be punched before annealing processes.