STEEL SHEET SUPERIOR IN SURFACE PROPERTIES, HOT-DIP GALVANIZED STEEL SHEET, AND METHOD FOR CONTINUOUSLY CASTING SLAB FOR USE IN MANUFACTURING STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To provide a steel sheet for plating, which does not produce streaky irregularities and has superior surface properties; a hot-dip galvanized steel sheet; and a method for continuously casting a slab for use in manufacturing the steel sheet.;SOLUTION: (1) The steel sheet for plating superior in the surface properties comprises, by mass%, 0.0005 to 0.0040% C, 1.5% or less Si, 0.05 to 2.0% Mn, 0.06% or less P, 0.02% or less S, 0.005% or less N, 0.005 to 0.1% sol. Al, 0.005 to 0.05% Ti, 0.04 to 0.2% Nb, and the balance Fe with impurities. In the surface layer of 10 μm or less deep from the surface of the steel sheet, Ti nitrides have an average particle size of smaller than 10 nm, and carbosulfides of Ti containing 5 mass% or less Nb have an average particle size of smaller than 20 nm. The hot-dip galvanized steel sheet is also disclosed. (2) The method for continuously casting the slab for use in manufacturing the steel sheet includes cooling the slab at a cooling rate of 4°C/s or more while a central area in the width direction of the slab is in a range of 1,200°C or higher to 900°C or lower, in a secondarily cooling zone in which mist is sprayed from an outlet side of a mold of a perpendicularly-bending-type continuous casting machine.;COPYRIGHT: (C)2009,JPO&INPIT