CAST SLAB, HOT ROLLED STEEL SHEET, COLLED ROLLED ANNEALING STEEL SHEET OF ULTRALOW CARBON STEEL AND METHOD FOR PRODUCING THE COLLED ROLLED ANNEALING STEEL SHEET

摘要

An extra-low carbon thin steel sheet that through avoiding of inclusion aggregates in molten steel and through fine dispersing of inclusions in the steel sheet, realizes secure prevention of surface flaws and cracking at press molding, and that through promoting of re- growth of crystal grains at continuous annealing, realizes high r-value (r-value = 2.0) and elongation (total elongation = 50%); and a process for producing the same. There is provided an extra-low carbon thin steel sheet excelling in surface properties, moldability and workability, comprising, by mass, 0.0003%=C=0.003%, Si=0.01%, Mn=0.1%, P=0.02%, S=0.01%, 0. 0005%=N=0.0025%, 0.01%=acid-soluble Ti=0.07%, acid-soluble Al=0.003%, 0.002%=La+Ce+Nd=0.02% and the balance of iron and unavoidable impurities, characterized in that at least cerium oxysulfide, lanthanum oxysulfide and neodymium oxysulfide are contained in the steel sheet. ® KIPO & WIPO 2008