CONTINUOUS CASTING METHOD FOR SLAB FOR THIN COLD ROLLED SHEET OF DEAD SOFT STEEL WITHOUT BLISTER DEFECT IN ANNEALING STAGE

摘要

PURPOSE:To prevent the blister defect of a thin sheet by using a gaseous mixture composed of Ar limited to a specific amt. and the balance N2 to constitute a gas to be diffused into a molten steel and controlling the quantities of the pinholes larger than a prescribed size to a specific range. CONSTITUTION:An immersion nozzle 1 is disposed in a mold 2. the nozzle 1 is constituted of anupper nozzle (a), a sliding plate (b), a lower nozzle (c) and an immersion pipe (d). The gaseous mixture composed of Ar and N2 is diffused through pores, etc. of a porous brick into the molten steel 3 to avert the precipitation of inclusions in the molten steel. The gaseous mixture is formed by limiting the gaseous Ar per ton of the molten steel 3 to =4Nl and the balance N2. The clogging of the nozzle is prevented by the incorporation of the gaseous N2 and the number of the pinholes sized 1mmphi in the slab is decreased to within 10 pieces per on by limiting the content of the gaseous Ar. The blister defect of the thin sheet in the stage of annealing is prevented by the above-mentioned method.