Patent ID: 6818079
Filing Date: 2004-11-16
Classification: C21D

Abstract:
A method for manufacturing steel sheet comprising the steps of:continuously casting a steel consisting essentially of 0.04 to 0.2% C, 0.25 to 2% Si, 0.5 to 2.5% Mn, and 0.1% or less Al, by weight, to form a slab; and applying hot-rolling by rough-rolling the slab to form a sheet bar and finish-rolling the sheet bar, the finish-rolling being carried out with the reductions in thickness at the final stand of less than 30%, and the finish-rolling being completed at temperature range of from Ar3 transformation point to (Ar3 transformation point +60Â° C.); primary-cooling the hot-rolled steel sheet starting the primary cooling within 1.0 second after the completion of hot-rolling and conducting the cooling at cooling speeds of higher than 200Â° C./sec down to the temperature range of from (Ar3 âˆ’30Â° C.) to Ar1 transformation point; applying slow cooling or air-cooling the primary-cooled steel sheet in a temperature range of from Ar3 âˆ’30Â° C. transformation to Ar1 transformation point at cooling speeds of 10Â° C./sec or less for 2 seconds or more; secondary-cooling the steel sheet after the slow cooling or the air-cooling at cooling speeds of 30Â° C./sec or more; and coiling the secondary-cooled steel sheet at temperatures of 300Â° C. or less.