Yijian Zhang

This study aims to investigate the effects of slag chemical composition on the smelting reduction behavior and microstructural evolution of chromite at 1525–1550 °C, thereby providing theoretical guidance for optimizing the smelting reduction process. Through high-temperature melting experiments combined with Scanning Electron Microscope - Energy Dispersive Spectrometer(SEM-EDS) microstructural characterization and thermodynamic calculations, the influences of basicity, MgO content, and Al₂O₃ content on chromium reduction behavior, slag physicochemical properties, and spinel evolution mechanisms were systematically analyzed. The results indicate that a basicity of 1.2 effectively promotes the dissolution and reduction of chromium spinel, whereas excessively high basicity hinders the reduction process when using graphite as the reducing agent. Although increasing MgO content initially improves slag fluidity and reaction rates, it promotes the formation of a Mg-Al-rich solid product layer during the later stages of the reaction; this restricts the intra-phase diffusion of Cr³⁺ and causes the reduction process to stall. High Al₂O₃ content significantly increases system viscosity and impairs mass transfer, thereby reducing the degree of reduction. Under optimized conditions, specifically an Al₂O₃ content of 14 wt% and a temperature of 1550°C, the degree of reduction approaches 93%. Thermodynamic calculations further reveal that the efficiency of chromite smelting reduction is synergistically controlled by factors such as slag viscosity, liquid-phase behavior, and spinel equilibrium phase mass. The favorable slag composition identified in this study, basicity of 1.2, MgO content of 10 wt%, and Al₂O₃ content of 14 wt%, provides favorable physicochemical conditions for the efficient smelting reduction of chromite.

The increasing utilization of low‐grade iron ores poses significant challenges to the stable and efficient operation of blast furnaces. The gangue components in the ore affect slag fluidity and the permeability of the burden to gas and liquid. In this study, the coupled influence of slag properties, burden dripping behavior, and blast furnace performance was systematically investigated based on the principles of low‐grade burden smelting and long‐term industrial verification. The results show that with a burden ratio of 78% sinter + 14% pellet + 8% lump, the optimal coupling between the molten layer thickness and gas flow resistance is achieved, resulting in the minimum characteristic value S and improved gas–liquid permeability in the softening and melting zone. Increasing Al ₂ O ₃ content significantly increases slag viscosity and reduces superheating, thus narrowing the thermal operating window. When the Al ₂ O ₃ content is above 16 wt%, adding an appropriate amount of TiO ₂ up to 1.5 wt% can effectively compensate for the adverse effects of Al ₂ O ₃ . Applying the proposed slag and burden design scheme in a commercial blast furnace showed that when the ore grade decreased from 57.5% to 56.5%, the blast furnace maintained stable operation with good permeability, lower fuel consumption, and higher production efficiency. This provides guidance for the efficient and stable smelting of Al ₂ O ₃ ‐TiO ₂ ‐containing low‐grade iron ore in modern blast furnace ironmaking.

Traditional research has primarily focused on the performance of slag, but there is little research on the allowable composition fluctuation range of slag. In this study, an innovative approach, utilizing the critical circle radius to represent the slag composition range. The results show that as the Al ₂ O ₃ content increases from 13 to 16 wt%, the proportion of the liquid‐phase area expands from 25.9 to 28 wt%. Critical circle analysis reveals that at 1480 °C, when the MgO content reaches 8 wt%, the critical circle radius is maximized, indicating the largest composition fluctuation range. Under low Al ₂ O ₃ conditions, basicity is the primary limiting factor for the inscribed circle radius. As Al ₂ O ₃ content increases from 10 to 25 wt%, the optimal slag basicity initially rises and then declines. With the decrease of liquid‐phase temperature from 1480 to 1440 °C, the slag's capacity to tolerate Al ₂ O ₃ decreases, and the optimal critical Al ₂ O ₃ content reduces. Increasing MgO content enhances the slag's tolerance to Al ₂ O ₃ . When the liquid‐phase temperature is lowered to 1420 °C, the optimal critical Al ₂ O ₃ content is 12.5 wt%, and the MgO content is controlled to be 5 wt%. The corresponding critical circle radius is the largest.

Titanium ore furnace protection is an important means to ensure the safe production of blast furnace. Based on the industrial test of titanium ore furnace protection in the hearth of a cast vertical blast furnace in China, this paper analyzes the influence of titanium ore furnace protection on the fuel consumption of blast furnace, explores the reasonable titanium load suitable for smelting, and analyzes the unsteady process of titanium deposition. The relationship between Ti content and C, Si, and S content in molten iron is clarified, and the reasonable titanium content range for controlling Ti (C, N) precipitation is established. It is found that the fuel ratio is reduced by about 5 kg/t during the industrial test, and the titanium load should be maintained at 6–8 kg/t. Since the titanium ore is put into the furnace, the titanium deposition process has a delay of 6–7 days, and the unsteady period of the whole furnace protection process is 10 days. The Ti content in molten iron will increase with the increase of C content and Si content, and decrease with the increase of S content. Under the condition of Ti (C, N) precipitation, when the Ti content in molten iron is greater than 0.074%, the Si content is greater than 0.42%, and the S content is less than 0.061%, a better furnace protection effect can be obtained.