Preparation method of glassless grain-oriented silicon steel and product thereof

A preparation method of glassless grain-oriented silicon steel, comprising processes of steelmaking and continuous casting to obtain a casting slab, casting slab heating, hot rolling, normalizing, cold rolling, decarburization annealing, nitriding, separator coating, annealing, and hot stretch flattening and coating;

• wherein:
• during the decarburization annealing, a dew point is between 38-58° C. and a heating temperature is between 800-850° C. wherein a thickness of an oxide film formed on a surface of strip is between 1.5-2.5 μm;
• and an atomic weight ratio of Si element and Fe element in the oxide film satisfies:
• Si/(Si+Fe) ≥0.76;
• during the separator coating, a separator comprises:
• a component A, a component B, a component C, and a component D;
• wherein:
• the component A is MgO, or a mixture containing MgO and Al2O3;
• the component B is one or more selected from a group consisting of NaCl, KCl, MgCl2, ZnCl2, BaCl2, SrCl2, MnCl2, CaCl2), BiONcoCl, SbOCl, Bi(NO3)2, Cu(NO3)2, NaNO3, and NO3NH4;
• the component C is a low-melting-point compound with a melting point ≤820° C.;
• and the component D is CaO or Ca(OH)2;
• wherein in the separator, a mass ratio of the component A, the component B, the component C, and the component D is 100:(0.5-6):(0.6-3):(0.6-5.3);
• during the annealing, a cooling stage comprises sequentially:
• a) cooling from a temperature of 1200° C. to 500° C. with an inner cover, wherein a protective gas is a mixed gas containing nitrogen and hydrogen, and a volume percentage of the hydrogen in the mixed gas is >3%;
• b) cooling from a temperature of 500° C. to 200° C. with the inner cover, wherein the protective gas is nitrogen;
• and c) cooling in air by removing the inner cover when temperature is <200° C.;
• during the hot stretch flattening and coating, a four-step washing process is used, and the four-step washing process comprises sequentially:
• a) washing with water;
• b) acid-washing with a mixed solution containing sulfuric acid with a mass concentration of 1%-10% and nitric acid with a mass concentration of 1%-5%;
• wherein a temperature of the acid-washing is between 50-80° C.;
• c) washing with a mixture containing water and a complexing agent for Fe ions, wherein in the mixture, a mass concentration of the complexing agent for Fe ions is between 0.5-5%;
• and d) washing with water;
• wherein the casting slab comprises, in mass percentage, C:
• 0.05-0.09%, Si:
• 2.9-4.6%, Mn:
• 0.05-0.20%, S:
• 0.005-0.020%, Als:
• 0.0225-0.0325%, N:
• 0.0045-0.0145%, Sn:
• 0.01-0.30%, Sb:
• 0.002-0.15%, Cr:
• 0.01-0.5%, and Cu:
• 0.01-0.8%, and remainder:
• Fe and inevitable impurity elements.