JPS6428313A - Production of silicon-contained cast iron - Google Patents

Abstract

PURPOSE:To stably produce a spheroidal graphite cast iron which is a raw material for castings having excellent mechanical strength and toughness by subjecting the molten iron tapped from a blast furnace to hearth desiliconizing, desulfurizing and dephosphorizing treatments, then adjusting the contents of carbon and silicon and spheroidizing graphite with Mg. CONSTITUTION:The molten iron 23 tapped from the blast furnace is predesiliconized by blowing a desiliconizing agent 25 such as mill scale, etc., on a blast furnace hearth 22. This molten iron 23 is put into a molten iron ladle 27 and molten slag 26 is scraped out. A CaO flux is then added to the molten iron to slag off and remove S in the molten iron as CaS and to desulfurize the molten iron to about 0.001%. After the molten slag of this time is discharged, a dephosporizing agent consisting of fluorite and millscale is added to the molten metal and oxygen is blown to remove P in the molten iron as P2O6-contg. molten slag. The content of C is adjusted to 3.4-3.8% and thereafter, metal silicon or ferrosilicon is added to the molten iron and oxygen is blown to increase the temp. of the molten metal by the oxidation heat of Si and simultaneously to adjust the content of Si to >=0.5% with the unoxidized Si, following which an Mg graphite spheroidizing agent is added to the molten iron to spheroidize the graphite shape of the molten iron to a flake or spheroidial shape. This molten iron is cast into a casting mold, by which the spheroidal graphite cast iron casting having the excellent strength and toughness is produced.