Continuously Cast Slab of Extremely Low Carbon Steel with Less Surface Defects in Steel Sheet-Producing Step; Extremely Low Carbon Sheet Steel; and Process for Producing the Same

摘要

To provide a continuously cast IF slab and a thin IF steel sheet in whichdrawbacks encountered in a thin IF steel sheet, such as surface defect,manufacturing difficulty and a low strength are fundamentally eliminated, anda method of manufacturing the same slab and steel sheet. A continuously castslab of extremely low carbone steel containing Si = 1.5 %, Mn = 2.0 %, P =0.15 %, Al = 0.01 - 0.15 % and N = 0.0050 % in mass ratio, a superficiallayer containing 0.01 - 0.08 % of C as cementite, an inner layer containing C= 0.0050 % and one or not less than two kinds of elements out of Ti = 0.02 -0.10 %, Nb = 0.01 - 0.10 %, V = 0.02 - 0.10 % and Zr = 0.03 - 0.10 %, thecarbon existing substantially in the form of carbides of these elements, thesuperficial layer preferably further containing B = 0.0001 - 0.0015 %, therest comprising Fe and unavoidable impurities, and a thin steel sheet producedfrom the same slab; and a method of manufacturing the same slab and thin steelsheet combined with continuous casting powder, an electromagnetic brake or analloy-adding wire. The IF steel and high-strength IF steel, which have beenunable to be mass-produced, and unable to attain a high yield and perfectperformance, have been improved and recognized as reliable basic metalmaterials.