JPS6421017A - Continuous annealing method for thin steel strip - Google Patents

Abstract

PURPOSE:To efficiently anneal a thin steel sheet without oxidizing the sheet by heating a thin steel strip in a low temp. range and high temp. range respectively by direct fire reduction heating and laser beam, etc. at the time of subjecting said strip to continuous annealing. CONSTITUTION:The long-sized thin steel strip is annealed by the direct fire reduction heating method of <=1.0 air ratio while the oxidation of the thin steel strip is prevented in the low temp. range of <=650 deg.C at the time of subjecting the thin steel strip to the continuous annealing. The high temp. oxidation by CO2 and H2O is generated even by the direct fire heating of <=1.0 air ratio if the temp. exceeds 650 deg.C and, therefore, the heating and annealing in the high temp. range above 650 deg.C are executed by a CO2 laser or electron beam. The cooling of the thin steel sheet after the annealing treatment is executed between the final hearth roll passes of the heating by a liquid cooling, gas jet cooling, roll cooling or wet air cooling method, by which the annealing of the thin steel in an extremely short period of time is enabled without damaging the material quality of the thin steel sheet.