Patent ID: 7736444
Filing Date: 2010-06-15
Classification: C21C,C21D,C22C,H01F

Abstract:
1. A process for producing grain oriented electrical steel comprising: i) forming molten liquid steel; ii) removing carbon from the molten liquid steel, the amount of carbon remaining in the molten liquid steel being not more than about 0.05% by weight, based on the weight of the molten liquid steel; iii) adjusting the chemical composition of the molten liquid steel before or after removing carbon therefrom so that the amount remaining in the molten liquid steel is not more than about 0.05% by weight, the amount of Cu is up to about 1%, the amount of Al is up to about 0.5%, the amount of N is up to about 0.05%, the amount of Mn is up to about 0.3% and the amount of Si is up to about 5%, by weight, based on the weight of the molten steel, the Cu to N weight ratio being at least about 40; iv) continuously casting a thin slab from the molten liquid steel of step iii), said thin slab having a finished thickness of between about 10 and 80 mm in an inert gaseous atmosphere to minimize interference with the molten liquid steel by the surrounding environment; v) controlling the casting speed to between about 2 and 10 meters/min; vi) bending the thin slab from a vertical plane to a horizontal plane within a radius of from about 2 to 6 meters; vii) solidifying the thin slab of step vi) within a period of time not greater than about 120 seconds from initiating continuous casting in step iv); viii) descaling the solidified thin slab of step vii) with an aqueous liquid; ix) heating the solidified thin slab of step viii) up to a temperature of not more that about 1250° C. to facilitate hot rolling; x) hot rolling the solidified thin slab of step ix) to a thickness of about 1 to 3 mm at a finishing temperature of between about 950° C. to 1050° C. to form a thin strip of steel; xi) rapidly cooling the thin strip with water, the cooled thin strip comprising grains, including up to about 25% cube-on-edge grains, based on the total amount of said grains; xii) maintaining the thin strip of step xi) at a temperature of from about 1050° C. to 1150° C. and removing scales from the thin strip of step xi); xiii) first cold rolling of the thin strip of step xii) to a thickness of about 0.1 to 0.9 mm; xiv) removing carbon by decarburizing the thin strip of step xiii) at a temperature of between about 800° C. to 900° C. for about 5 to 7 minutes in an atmosphere of water vapor; xv) adjusting a ratio of a partial pressure of water to a partial pressure of hydrogen with respect to the atmosphere of step xiv) to between about 0.1 to 0.26 to form a mixture of iron oxide and silicon oxide particles on and below the exposed outer surface of the thin strip of step xiv); xvi) annealing the thin strip of step xv) for growing iron crystals at a temperature of about 800° C. to 900° C. for a period of time from about 5 to 7 minutes; xvii) second cold rolling of the thin strip of step xvi) to a thickness of up to about 0.35 mm; xviii) coating the thin strip of step xvii) with a slurry of MgO; xix) drying the coated thin strip of step xviii); xx) controlling the rate of heating of the coated thin strip of step xix) to about 50° C./hour at a temperature of between about 700° C. to 1000° C. to complete the formation of a Cu-based grain growth inhibiting species; xxi) annealing the coated strip of step xx) at a temperature of between about 1100° C. and 1300° C. in a gaseous hydrogen atmosphere to grow oriented crystalline grains in the coated thin strip and to form a grain oriented thin strip; xxii) straightening the grain oriented thin strip of step xxi) under tension; and xxiii) applying an insulative coating comprising phosphoric acid, MgO and aluminum hydroxide to the grain oriented thin straightened strip of step xxii).