Patent ID: 6395104
Filing Date: 2002-05-28
Classification: C21D,C23C,H01F

Abstract:
In a process for producing a grain-oriented electrical steel sheet comprising the step of conventionally treating a slab comprising up to 0.10% of C, 2.0 to 7.0% of Si in terms of weight %, up to 400 ppm of Al, a conventional inhibitor component, and the balance Fe and unavoidable impurities and rolling to form a steel strip having a final product thickness, the step of decarburization annealing the steel strip, the step of final finishing annealing the steel strip, and the step of conducting an insulating coating treatment, said process comprising:the steel strip is rapidly heated to temperatures of at least 800Â° C. at a rate of at least 100Â° C./sec by subjecting the steel strip to a heating stage in the decarburization annealing step in a rapid heating chamber which is connectively provided to a decarburization annealing furnace through a throat portion while the PH2O/PH2 ratio is held at 0.20 to 3.0 and the residence time of the steel strip at temperatures of at least 750Â° C. is set less than 10 sec in the rapid heating chamber; and the steel strip is decarburization annealed in a decarburization annealing furnace provided with an exhaust vent near the entry side which exhausts the atmosphere of the rapid heating chamber and that of the decarburization annealing furnace, while the PH2O/PH2 ratio is held at 0.25 to 0.6 in the decarburization annealing furnace; wherein the PH2O/PH2 ratio in the rapid heating chamber is more than the PH2O/PH2 ratio in the decarburization annealing furnace so as to provide improved oxide film adhesion.