Study On Desulphurization For Low Carbon-Silicon-Aluminum Steel In Refining Process

This paper deals with the desulphurization in refining process for low carbon-silicon- aluminum steel in MoSi2 furnace and medium-frequency induction furnace in laboratory. The main investigation contents include: (1) the effect of slag deoxidizers on reduction velocity of slag and contents of C, Si, Al in steel; (2) the effect of steel deoxidizers on desulphurization; (3) the effect of adding BaO into slag on desulphurization; (4) the effect of magnesium-based desulphurizer on desulphurization and inclusions in steel.The results of experiments conducted in MoSi2 furnace showed that: (1) The increase of C, Si, Al contents in steel could be controlled effectively by using mixed slag deoxidizer containing aluminum and calcium carbide. Increasing basicity properly of slag, or decreasing SiO2 content could restrain the increase of Si content in the steel. (2) When 10wt% BaO was added into slag to replace CaO, the desulphurization ability of slag could be improved obviously. (3) Desulphurization ratio could be improved by using magnesium predeoxidation. But if the quantity of addition of magnesium were large, it could result in heavily boiling in molten steel. However, using mixed deoxidizer could restrain molten steel to boil.The results of desulphurization of steel by feeding magnesium-cored wire in medium- frequency induction furnace showed that: (1) Deep desulphurization could be reached by feeding magnesium-cored wire, the sulfur contents in steel could be decreased from 100~175×10-6 to 46~72×10-6 and the desulphurization ratios were over 52% during magnesium-cored wires treated, which were Mg-Fe cored wire, Mg-CaO-CaF2 cored wire and Mg-BaO-CaO-CaF2 cored wire. (2) Most inclusions in steel treated with magnesium were fine granules, whose sizes were less than 5μm. Contrasted with Mg-Fe cored wire, the inclusion in steel treated with Mg-CaO-CaF2 cored wire was decreased obviously. (3) The results of SEM showed that most inclusions in steel were Al2O3 and (Fe-Mn)S and a few were complex of (Fe-Mn)O and (Fe-Mn)S. After treated with magnesium, a few complex oxide inclusions containing magnesium were brought into the steel. However, MgO and MgS inclusions were not found in steel.