Thermodynamic Analysis on Slag/Metal Reactions in Steelmaking Process Using Direct Reduced Iron and Steel Scraps

Abstract

Hydrogen reduction processes of iron ores are being developed to achieve carbon neutrality. However, high-grade iron ore pellets used in the current direct reduction process will be depleted in the future. On the other hand, steel scraps recovered from society are usually contaminated with tramp elements, which are difficult to remove in the current steel refining processes. To produce high-quality steel from DRI and steel scraps, molten steel composition in the melting process should be optimized considering the impurities originating in iron resources and conditions such as temperature and oxygen potential. In this study, the equilibrium of slag/metal reactions in the steelmaking process using DRI and steel scraps were thermodynamically analyzed, and the effect of using scrap on the composition of molten steel and slag and the conditions to produce low-phosphorous molten steel from high-P content DRI and steel scrap were discussed. The use of steel scrap showed such advantages as a decrease in the concentrations of Si, S, and P originating from high-P DRI, a decrease in the amount of slag, and a reduction in the amount of limestone required to maintain slag basicity. Moreover, the P content of iron can be decreased to 13 mass ppm at 1873 K and P_O2 = 10⁻¹⁰ atm even when the high-P DRI is used in combination with steel scrap. The thermodynamic analysis showed the potential for carbon-free steel by optimizing the hydrogen reduction process and the melting process of DRI with steel scraps.