Study on Factors Affecting Efficient Dephosphorization in Hot Metal Pretreatment by the Converter Double-Slag Process

Given the increasing demand for low-phosphorus molten iron in high-value-added steel production and the rising phosphorus content in raw materials caused by the use of high-phosphorus ores in blast furnaces, the traditional converter single-slag process faces challenges such as high dephosphorization pressure, high slag consumption, and unstable endpoint control. This study systematically investigates the process principles and key influencing factors of the converter double-slag method (MURC process) as an efficient pretreatment technology for molten iron. Through thermodynamic analysis combined with industrial tests, the core process parameters affecting dephosphorization efficiency were identified, including temperature, slag basicity (R), iron oxide (T.Fe) content, and bottom-blowing stirring intensity. The results show that the optimal temperature during the dephosphorization stage is 1350–1400 °C, with slag alkalinity controlled at 1.6–2.0 and T.Fe content maintained at 19–23%. During the decarburization stage, the optimal temperature is 1620–1640 °C, and the final slag alkalinity should be increased to above 3.5. After applying the optimized “low-high-low” oxygen supply pattern and enhanced bottom-blowing stirring (0.04–0.20 Nm3/(t·min)), significant improvements were achieved in industrial practice on 180-t and 60-t converters. Lime consumption was reduced by more than 30%, the average endpoint phosphorus content decreased by approximately 0.005%, the phosphorus removal rate remained stable at above 90%, and the oxygen content in molten steel at the endpoint decreased by 50–100 ppm. This study provides a systematic theoretical basis and practical guidance for efficient and stable dephosphorization using the converter double-slag process.