Reducing Dephosphorization of Molten Stainless Steel by Metallic Calcium

Abstract

Dephosphorization of molten stainless steel by the addition of metallic calcium has been studied by using a laboratory scale high frequency furnace and an industrial scale electric arc furnace. Safety treatments of dephosphorization slag have also been examined. The results obtained are summarized as follows:(1) From the laboratory scale test, it is found that there is a relation between the activities of carbon and oxygen (aC and aO) in molten steels and dephosphorization ratios. Favorable conditions under which the dephosphorization ratio exceeds 50% are aC<0.92 and aO<4×10-4 at 1480°C.(2) For an efficient dephosphorization of 18Cr8Ni steel, it is necessary to control the carbon and oxygen contents of molten metal in the range of 0.3%<C<1.0% and O<60ppm at 1480°C.(3) The dephosphorization ratio and the desulfurization ratio determined by the industrial scale experiment of 13Cr5Ni steel are 33% and 55%, respectively, when the addition of calcium is 10.6kg/t steel.(4) The concentrations of PH3 and H2S gases generated from the dephosphorization slag have been measured. The maximum concentrations are 160ppm/g for PH3 and 400ppm/g for H2S before safety treatment. After safety treatment, the maximum concentrations decrease to 2ppm/g for PH3 and 11ppm/g for H2S.