Zhaohui Zhang

The metallurgical tasks at different stages of converter blowing are different. The process operation and physical properties of molten baths are also different. It is very important to determine the flow characteristics of molten baths at different blowing stages for optimizing process operation. In this paper, a three-dimensional, full-scale model of a 120 t top–bottom combined blowing converter is established. Based on the parameters of oxygen lance position, bath temperature, bottom blowing intensity, and bath physical properties at different blowing stages, the changes in bath flow field, turbulent kinetic energy, impact depth, impact area, and wall shear force with blowing process are studied. The results show that at the initial stage of blowing, the lance position is high, the impact depth of the molten bath is 0.23 m, the impact area is 5.06 m², the dead zone area of the longitudinal section is 0.40 m², and the high-speed zone area is 2.73 m². As the blowing time increases, the lance position decreases, the impact depth of the molten bath increases, the impact area decreases, and the internal velocity of the molten bath increases. In the later stage of tuyere blowing, the lance level decreases to its lowest, the impact depth increases to 0.42 m, the impact area decreases to 2.83 m², the dead zone area of longitudinal section decreases to 0.18 m², and the high-speed area increases to 3.34 m². The area with the highest wall shear stress is situated within the gas–slag–metal three-phase region, where the lining experiences the most significant erosion. The fluctuation in the slag–metal interface is small, and the wall shear force is 2.80 Pa at the initial stage of blowing. From the early to late stages of blowing, the lance position decreases, the fluctuation range of the slag–metal interface increases, and the erosion of the furnace lining increases. In the later stage of blowing, the maximum wall shear force is 3.81 Pa.

Ultrahigh-speed continuous casting is a critical element in achieving high-efficiency continuous casting. In the present work, a three-dimensional model of a 160 mm × 160 mm billet ultrahigh-speed continuous casting mold was developed for use in studying the influences of different casting parameters on molten steel flow. The results showed that the flow pattern in the mold was not associated with its casting speeds, submerged entry nozzle (SEN) immersion depths, or inner diameters. Variation in casting speeds significantly affected the liquid level of the steel–slag interface. Its liquid level fluctuation was reasonable at an SEN immersion depth of 80 mm. Its impact depth reached the shallowest point, which was conducive to upward movement within high-velocity and high-temperature regions, and accelerated the floating of non-metallic inclusions. Expanding the inner diameter of the SEN could effectively weaken the initial kinetic energy of the jet. However, it may cause a deeper impact depth and a degree of upward movement in the raceway, which exhibited the shallowest impact depth in the jet and the most reasonable behavior of molten steel at a liquid level for which the inner diameter of the SEN was 40 mm.

In order to study the effect of the change of MgO/Al₂O₃ on the viscosity and thermodynamic properties of the chlorinated blast-furnace slag, the CaO-SiO₂-MgO-Al₂O₃-TiO₂-CaCl₂ slag system was taken as the research object, and the viscosity change rule of the chlorinated high-titanium slag was studied by using the rotating cylinder method. The thermal stability of the chlorinated high-titanium slag was quantitatively analyzed by calculating the extreme heat release rate (EHRS) of the chlorinated high-titanium slag. At the same time, the qualitative and quantitative analysis of the high-titanium slag containing chlorine was carried out by combining FTIR and Raman spectroscopy, and the mechanism of the influence of MgO/Al₂O₃ on the viscous flow characteristics of the high-titanium slag containing chlorine was revealed. The results show that when the alkalinity (R₂) of the fixed slag is 1.15, when MgO/Al₂O₃ is in the range of 0.40–0.66, the viscosity of the high-titanium slag containing chlorine presents a significant decreasing trend with the gradual increase of MgO/Al₂O₃, and the viscous flow activation energy of the slag decreases from 98.75kJ · mol⁻¹ to 95.21kJ · mol⁻¹. The heat capacity and enthalpy change of slag decrease with the increase of MgO/Al₂O₃, but the change rule of slag extreme heat release is opposite to that of heat capacity and enthalpy change. When MgO/Al₂O₃ increases, the slag extreme heat release increases from 13.413 kJ to 15.172 kJ. The content of simple structural units Q⁰ and Q¹ of silicate tetrahedron in the slag gradually increases, the content of complex structural units Q² and Q³ gradually decreases, and the average amount of non-bridging oxygen decreases from 1.94 to 1.79, indicating that Al₂O₃ acts as a network maker in the internal network structure of the slag. The increase of MgO/Al₂O₃ destroys the complex silicate tetrahedron structure in the slag, reducing the degree of polymerization of the slag silicate network. In addition, the transmissivity of [SiO₄]⁴⁻ tetrahedron, [AlO₄]⁴⁻ tetrahedron and T-O-T bond bending vibration band in the slag shows a decreasing trend. Within the scope of the experiment, the increase of MgO/Al₂O₃ can effectively improve the fluidity of the chlorine-containing blast-furnace slag and improve the thermal stability of the chlorine-containing blast-furnace slag.

The melting temperature and viscosity of magnesium reduction slag were calculated by using Factsage thermodynamic software. The composition range of the magnesium-slag-based dephosphorizing agent was analyzed by drawing a multiphase diagram of the slag system. The Box–Behnken high-temperature dephosphorization experiment was designed to study the effect of different composition of magnesium-slag-based dephosphorizers on the dephosphorization rate of the steelmaking process. The results show that magnesium slag can be used as a slag-forming agent for smelting low-silicon hot metal to promote slagging, and the effect of each factor on the phosphorus removal rate is ranked, and the results are ω(Fe₂O₃) > basicity > ω(Al₂O₃): ω(Al₂O₃) has no significant effect on the rate of phosphorus removal. When the basicity was 2.8, ω(Fe₂O₃) was 25.94%, ω(Al₂O₃) was 6.73%, and ω(MgO) was 6%, the dephosphorization rate reached a maximum of 96.7%, and the error was experimentally verified to be 2.6% from the predicted value, indicating that the model can be optimized to determine the best magnesium-slag-based dephosphorization agent and has a good prediction of dephosphorization effect.

To study the evolution of non-metallic inclusions in 27SiMn steel, the 27SiMn steel produced using the LD-LF-CCM process was sampled in various stages in a steel factory. The evolutionary behavior of inclusion in various processes was systematically analyzed by scanning electron microscopy (SEM-EDS), and the total oxygen content and nitrogen content in 27SiMn steel were measured at various production steps. On the basis of the calcium treatment for 27SiMn steel, the equilibrium reactions for Ca-Al were calculated according to the thermodynamic equilibrium model. The results showed that the types of inclusions at the start of LF stations are mainly Al₂O₃-FeO and MnS-Al₂O₃. Before calcium treatment, the inclusions are mostly calcium aluminate and CaO-MgO-Al₂O₃. Compared with the process after soft blowing, the number density of inclusions in tundish increased by 77.88%, possibly due to secondary oxidation. From the soft blowing process to the continuous casting round billet, the inclusions translate into spherical CaO-MgO-Al₂O₃-SiO₂, and a large number of CaS were observed. One part of the CaS precipitated separately, the other part was semi-wrapped with the composite inclusions. At the same time, calcium treatment increases the number density, mean diameter, and the area fraction of inclusions. The mass fraction of T.O. (total oxygen content) increased significantly after soft blowing, and the N content increased greatly from station to tundish. The change trend of N content in steel was basically consistent with that of T.O. content. It was necessary to prevent the secondary oxidation of molten steel during calcium treatment and the casting process. When the liquidus temperature of liquid steel is 1873 K, w[Al] = 0.022%, and w[Ca] in steel is controlled between 1.085 × 10⁻⁶ and 4.986 × 10⁻⁶, the Al₂O₃ inclusion degeneration effect is good.

Electric arc furnace dust (EAFD) presents a contamination hazard due to its heavy metal leachability. The traditional disposal methods of landfill or stacking not only pose a threat to the environment but also waste metal resources. This paper adopted vacuum carbothermic reduction to dispose of EAFD and the zinc metal could be obtained as a product. The reduction ratios of the EAFD were carried out under various reaction temperatures and times at 20 Pa. Furthermore, the kinetics of the reduction process was also studied. The reduction ratio of the reaction process can be facilitated through increasing the temperature or lengthening the time and can reach up to 99.6% under the condition of 1373 K with 60 min. The zinc ferrite and zinc oxide were reduced first and then iron oxide reduction occurred. The reduction process could be divided into three stages: Stage 1 involved the direct reduction of zinc ferrite and zinc oxide, and the control step was the phase boundary reaction with the apparent activation energy of 48.54 kJ/mol; Stage 2 involved the reduction of zinc oxide and iron oxide, and the control step was also the phase boundary reaction with the apparent activation energy of 56.27 kJ/mol; Stage 3 involved the escape of gas phase products and the control step was diffusion with the apparent activation energy of 105.3 kJ/mol.

Ultrahigh‐speed casting is the most remarkable feature of billet high‐efficiency continuous casting. The transient fluid flow, heat transfer, and solidification behavior under different casting speeds, submerged entry nozzle (SEN) parameters, and mold electromagnetic stirring (M‐EMS) are investigated using a 3D transient mathematical model. The results show that a typical roll flow pattern is generated for all casting speeds, while a third small recirculation zone developed near the solidified shell at the casting speed of 6.0 m min⁻¹. When the casting speed increases, the impact depth of the molten steel increases from 0.748 to 0.844 m, the velocity and level fluctuation at the steel/slag interface increases, the high‐temperature zone moves downward, and the shell thickness is reduced from 16.2 to 11.1 mm. As the SEN inner diameter and immersion depth increases, the impact depth increases, the velocity and level fluctuation at the steel/slag interface decreases, and the shell thickness at the mold exit is ≈11.0 mm. When the SEN immersion depth and inner diameter are 120 and 40 mm, respectively, the flow and temperature fields in the mold are the most appropriate. In addition, the M‐EMS have a great effect on the fluid flow and heat transfer behavior.

Recently, the proportion of electric furnace steelmaking has increased rapidly, and the content of electric arc furnace dust has increased. Through comprehensive recovery of electric arc furnace dust, the harm of metallurgical solid waste can be reduced and economic value can be created. In this paper, it gives a common outline about the known recycling techniques from electric arc furnace dusts and presents the carbothermal reduction under vacuum. The evolution in reduction products in the process of vacuum carbothermal reduction of zinc-containing electric arc furnace dust is studied using the X-ray diffraction (XRD) phase and micro-morphology analysis. The thermodynamic conditions for reduction are computed using Factsage 7.1 program. Through thermodynamic study, it is found that the initial temperature of reducing zinc oxide decreases as the pressure of the system drops. In the process of the vacuum carbothermal reduction experiment, the type of reducing agent, reduction temperature, carbon content, and reaction time are studied. According to the test results, the optimum process parameters are determined as follows: reduction time 30 min, reduction temperature 1273 K. The dezincification effect of electric arc furnace dust can reach over 99%.

A converter slagging agent was prepared using converter precipitator dust and oxide scale as raw materials and bentonite, calcium oxide, and soluble glass as binders. The influence of different binders on the strength of the converter slagging agent was studied. The optimum ratio of bentonite, calcium oxide, and sodium silicate was determined by orthogonal experiments. The chemical composition, strength, moisture content, alkalinity, and other indicators of the prepared converter slagging agent met the requirements for converter smelting. The drop intensity of the green pellet was 3.7 times, and the compressive strength of the dry pellet could reach 988.72 N/m ² . Therefore, the sustainable utilization of converter precipitator dust and oxide scale could be realized by the preparation of a converter slagging agent.