Features of ladle desulfuration of pipe steel with low sulfur content

Abstract

At the present time the sulfur content in pipe steel is strictly regulated. Under conditions of PJSC “Magnitogorsk Iron and Steel Works” the metal is smelted in BOF shop with preliminary desulfurization of molten iron, treatment of tapping steel by a solid slag-forming mixture and final desulfurization in the “Ladle-Furnace” unit (LP-unit). In order to increase the efficiency of the sulfur removal process, the influence of the covering slag composition on metal desulfurization is considered. Statistical processing of production data array consisting of 14 melts of steel grade 10Г2ФБЮ with K60 strength class was performed. The dependences of the sulfur content in the metal after desulfurization in the LP-unit on the oxidizing ability, covering slag basicity and the content of magnesium oxide was established: it is shown that the amount of sulfur removed during the ladle treatment process increases with the increase of the covering slag basicity and with the decrease of the magnesium oxide content in slag. For describing this dependence, a new parameter was proposed – the ratio of slag basicity to MgO content in it, %–1. A high content of magnesium oxide in the “white” slag was revealed. This fact indicates a significant amount of converter slag getting into the ladle due to its poor cut-off in the process of metal tapping from the unit. The study of the influence of the coating “white” slag composition on the metal desulfurization process in the LP-unit showed, that for the effective sulfur removal, it is necessary to provide not only welldeoxidized slag with a total content of iron and manganese oxides of less than 1%, but also to ensure the ratio of its basicity to the magnesium content in this slag not less than 0.60–0.65%–1.