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

(Object) IF-based, continuously cast slab essentially freed from defects such as surface defects, difficult production and poor strength, etc. of the product that the IF-based sheet steels have; sheet steels and a process for producing the same are provided.P P (Structure) A continuously cast slab of extremely low carbon steel comprising not more than 1.5% by mass of Si, not more than 2.0% by mass of Mn, not ore than 0.15% by mass of P, 0.01-0.15% by mass of Al, and not more than 0.0050% by mass of N, where the surface layer further contains 0.01-0.08% by mass of C existing as a cementite and the inner layer further contains not more than 0.0050% by mass of C, and at least one of 0.02-0.10% by mass of Ti, 0.01-0.10% by mass of Nb, 0.02-0.10% by mass of V and 0.03-0.10% by mass of Zr, the carbon existing substantially as carbides of these elements, preferably both the surface layer and the inner layer further contain 0.0001-0.0015% by mass of B, the balance being Fe and inevitable impurities; an sheet steel made from the slab; and a process for producing the slab and the sheet steel, combined with continuously casting powder, an electromagnetic brake and an alloy-adding wire.PP(Effect) The IF steel and its high strong steel, which have been suffered from impaired mass production, lower production yield and incomplete product characteristics have been established as satisfactory basis metallic materials.