Refractories for vacuum degassing of steel

Abstract

The metallurgists of our country have mastered new processes including vacuum degassing of steel by such methods as degassing in the ladle, vacuum degassing of the stream of metal in a continuous casting machine with treatment with synthetic slag and pouring of large ingots, cyclic and circulation flow vacuum degassing from an open ladle, and refining in ladles with arc heating (ASEA-SKF).It is planned to place in service new equipment for outside-the-furnace treatment of steel including argon-oxygen refining units, circulation flow vacuum degassingun~ts, units for outside-the-furnace treatment of steel in the ladle with electric arc heating (AOST), and others, primarily of domestic construction.Based on the specific problems of the steel industry the following refractories have been developed and are being produced: magnesia from enriched natural raw material, including high-temperature fired from fused and sintered periclase and periclase-chromite powders (PKhP, PKhPU, and PKhV) and unfired from sintered periclase with chemical binders;periclase-carbon from fused and sintered periclase powders; magnesia from synthetic spinel and fused and sintered periclase (PShKh) and periclasechromite and periclase (PShPKh) powders; corundum from sintered powders and fused cast blocks; high-alumina from natural raw material and alumina; unformed from fused periclase, periclase-chromite, and corundum powders (ramming compounds, mortars, slag neutralizers); lightweight thermal insulation.In addition, in ladles for outside-the-furnace treatment of steel periclase-lime (magnesia-dolomite) heat-treated parts, forsterite parts including with the addition of carbon, and rammed and semidry vibrocompacted compounds, sometimes in combination with chromiumcontaining magnesia parts in the bottom and slag belt, are starting to be used in the USSR and abroad.The production of magnesia refractories for outside-the-furnace treatment involves the use of enriched raw material including flotation concentrates of magnesites, periclase from sea water, bischofites MgCI2"6H20 , or synthetic obtained by a chemical method such as hydrochloric acid treatment of natural raw material (magnesite, carnallite). In connection with the shortage of lump chrome ores free of silica large-scale production of refractories is oriented toward the use of finely dispersed chrome concentrates which in briquetted form are fired at 2000~ or are oxidation electrofused into blocks [1][2][3]. In the steel industry the use of bauxites with 60-88 wt. % AI203 is increasing for the production of ladle parts and ranching compounds, the use of which in ladles for outside-the-furnace treatment makes it possible to obtain high-quality steel with minimum expenditures of energy for preliminary heating of the lining and heating between heats with a sufficiently long life (30-70 heats) [4].Therefore the development of outside-the-furnace treatment has determined the directions of developments of new forms of refractories such as the use of primarily pure and frequently synthetic magne...