Method for producing grain-oriented electrical steel sheets or strips having a very high magnetic induction

Claim 1

In a method for producing grain-oriented electrical steel sheets or strips having a very high magnetic induction, in which method a forsterite ceramic coating is deposited on a sheet of silicon steel raw material composed of not more than 0.06% of C, 2.0-4.0% of Si, 0.01-0.20% of Mn, 0.005-0.10% of a total amount of at least one of S and Se and the remainder being Fe, the sheet of silicon steel raw material is hot rolled to a thickness of 2-5 mm, the hot rolled sheet is subjected repeatedly to annealings and cold rollings to prepare a cold rolled sheet having a final gauge of 0.1-0.5 mm, the cold rolled sheet is subjected to a decarburization annealing to decrease the carbon content to not more than 0.005%, and then the decarburized sheet is subjected to a series of final annealing steps, the improvement which comprises the cold rolled sheet containing substantially no Sb and Al, prior to being subjected to the final annealing steps, so as to prevent the deterioration of the forsterite ceramic coating formed on the sheet during the final annealing steps, the cold rolled sheet consisting of not more than 0.06% of C, 2.0-4.0% of Si, 0.01-0.20% of Mn, 0.005-0.10% of a total amount of at least one of S and Se and the remainder being substantially Fe, and containing not more than 0.0045% of N, and the final annealing steps consisting of a step for developing in the sheet fully secondary recrystallized grains, having (110) [001] orientation at a temperature of 800°-900° C., and a step for effecting a purification annealing of the sheet at a temperature of not lower than 1,000° C., so as to form a highly adhesive ceramic coating on the surface of the sheet.