THE MANUFACTURING METHOD FOR COLD ROLLING STEEL SHEET WITH EXCELLENT THICKNESS PRECISION

摘要

PURPOSE: Provided is a method for manufacturing cold rolled steel sheets having low thickness deviation even after continuous annealing which is suitable to drop forging and black plate. CONSTITUTION: In a manufacturing method of cold rolled steel sheets where a steel slab comprising C 0.01wt.% or less, Mn 0.50wt.% or less, P 0.10wt.% or less, S 0.020wt.% or less, Al 0.06wt.% or less, N 0.008wt.% or less, solid-solution B 0.0005-0.0015wt.%, a balance of Fe, and other inevitable impurities is homogenizing heat-treated at 1100deg.C or higher; finish hot rolled in the temperature range of 870 to 930deg.C; coiled in the temperature range of 600 to 750deg.C; cold rolled at a reduction rate of 60% or more; and then continuous annealed at over 780deg.C, recrystallization completion temperature, the present invention is characterized in that Ti content of the steel slab is 0.05% or less and also the amount of solid solution B is 0.0005-0.0015% in case of Ti-1.5S3.43N. Further, in the case that either Ti-1.5S3.43N or Ti element is not added to the steel, the amount of solid solution B comes to be within the follow range: 0.77£N-(Ti-1.5S)/3.43|+ 0.0005B0.77£N-(Ti-1.5S)/3.43|+ 0.0015.