Study on the Melting Temperature of CaF2-CaO-MgO-Al2O3-TiO2 Slag under the Condition of a Fixed Ratio of Titanium and Aluminum in the Steel during the Electroslag Remelting Process

During the process of electroslag remelting (ESR) of steel containing titanium and aluminum, the activity ratio between titania and alumina in CaF2-CaO-MgO-Al2O3-TiO2 slag must be fixed in order to guarantee the titanium and aluminum contents in the ESR ingots. Under the condition of fixed activity ratio between titania and alumina in the slag, the melting temperature of slag should be investigated to improve the surface quality of ESR ingots. Therefore, this paper focuses on finding a kind of slag with low melting temperature that can be used for producing steel containing titanium. In the current study, the thermodynamic equilibrium of 3[Ti] + 2(Al2O3) = 4[Al] + 3(TiO2) between SUS321 steel and the two slag systems (CaF2:MgO:CaO:Al2O3:TiO2 = 46:4:25:(25 − x):x and CaF2:MgO:CaO:Al2O3:TiO2 = 46:4:(25 − 0.5 x):(25 − 0.5 x):x) are studied in an electrical resistance furnace based on Factsage software. After obtaining the equilibrium slag with fixed activity ratio between titania and alumina, the melting temperatures of the two slag systems are studied using slag melting experimental measurements and phase diagrams. The results show that the slag systems CaF2:MgO:CaO:Al2O3:TiO2 = 46:4:25:(25 − x):x, which consists of pre-melted slag S0 (CaF2:MgO:CaO:Al2O3 = 46:4:25:25) and pre-melted slag F1 (CaF2:MgO:CaO:TiO2 = 46:4:25:25), can not only control the aluminum and titanium contents in steel, but also have the desired low melting temperature property.

The Concurrent Sintering-Crystallization Behavior of Fluoride-Containing Wollastonite Glass-Ceramics

The fabrication of well densified wollastonite with smooth appearance by direct sintering method is still a challenge due to the competitive behaviors between sintering and crystallization. In this study, the coarser glass frits with a size of 1–4 mm are subjected to heat treatment at different temperatures. An attempt of integrating differential thermal analyzer with a slag melting temperature characteristic tester was exploited to monitor the heat and geometry changes during the heating. The results showed that the addition of CaF2 can significantly promote the crystallization of wollastonite at 940 °C, while hindering the sintering ability. At higher temperature, the increase of CaF2 acts as flux and favors the formation of eutectics, leading to a decline in the precipitation amount of wollastonite. The predominated liquid sintering brought fast shrinkage. It was found out that high content of CaF2 narrows the dense sintering temperature range and results in uneven surfaces. In order to obtain wollastonite glass-ceramics with smooth appearance, the maximum content of CaF2 in sintering glass-ceramics should be limited to 2 wt.%.

Strength Properties of Steel Slag Concrete Prepared with Partial Replacement of Cement with Silica Fume

Concrete is a very versatile material. The rapid growth of the industry produces a large amount of by-products and waste, which can be used as SCM machines for ash, silica fume, slag, melting of granular soil, iron slag, etc. This waste is used to improve concrete structures with a new blending framework. Cement, sand and aggregate were mixed in a certain ratio. The proportion began to maximize the strength of the concrete mixture. In real time, the mixture could be easily nourished on construction projects, so it took a certain amount of time to achieve sustainable benefits. It is usually 28 days to get a full booster for the production of the mixture. Aggregates and silica fume were mixed at specific levels of 0%, 5%, 10%, 15% and 20%. This inclusion was tested and produced the strongest distribution at any given time. Analyzes of compressive strength, insulation tension, flexural strength, and shear strength tests were performed on concrete mixtures from M-0 to M-20. This paper examines the aforementioned tests on various compositions of the material.

Effect of ZnO/PbO and FeOX/SiO2 ratio on the viscosity of lead smelting slags

The effect of ZnO/PbO and FeOX/SiO2 on the viscosity of the PbO-ZnO-Fe3O4-SiO2-CaO slag was measured using the rotating spindle method. The slag viscosity decreased with decreasing ZnO/PbO mass ratio because of the depolymerization of the silicate structures. The viscosity decreased with increasing FeOX/SiO2 mass ratio as the experimental temperature was above 1623 K, while the viscosity increased significantly with the increase of FeOX/SiO2 as the experimental temperature below 1623 K because of the phase transition and the change of slag melting point. According to XRD analysis of as-quenched slag, the spinel and the zincite phase increased with increasing FeOX/SiO2. Increasing ZnO/PbO and FeOX/SiO2 could enhance the crystallization capacity of the slag. FTIR analysis revealed that the degree of polymerization of the as-quenched slags decreased with decreasing ZnO/PbO and increasing FeOX/SiO2. The temperature dependencies of the viscosity on ZnO/PbO and FeOX/SiO2 were investigated, and the apparent activation energies of each system were found to be between 169.5 to 227.4 KJ/mol, and 151.1 to 676.4 KJ/mol, respectively.

Decomposition behavior and kinetics of limestone in early converter slag

The decomposition of limestone in converter slag directly determines the speed of slag melting for lime that has a strong effect on the steelmaking process of the converter. In this paper, a high temperature furnace was used to study the decomposition behavior of cylindrical limestone samples in the converter early slag at the temperatures of 1250 °C, 1300 °C, and 1350 °C under laboratory conditions, and macro-dynamics equation was used to determine the rate-determining step for limestone decomposition in the converter early slag. The results show that when the limestone is decomposed in the early converter slag, the heat transfer from the slag through the lime layer to the unreacted core is the rate-determining step. The limestone decomposition rate in converter slag is slightly lower than that in hot metal. Finally, the suitable grain size of the limestone added into the converter was determined. Thus, this study provides theoretical guidelines for practical use of converter steelmaking in industrial production.

The influence of the volatiles on the slag composition for the heating process

The physicochemical properties of slag are of great importance in pyrometallurgy. If there is a volatile component in the slag, evaporation will inevitably occur. As a result, the slag composition will change, and the measured results will be inconsistent with the original slag composition. Therefore, the traditional methods can be applied to determine the properties of slag, however, the change in slag composition will lead to the inaccuracy of the results. Two typical kinds of slag ESR slag with higher CaF2 and Pb smelting reduction slag with higher PbO were chosen, and melting point measurements were taken as an example to demonstrate the new method in practice. Weight loss measurements and evaporation test with thermogravimetric (TG) analysis, as well as high-temperature mass spectrometer (MS) tests were carried out to identify the volatiles. It was found that CaF2 and MgF2 is the main volatiles with a small amount of AlF3 to ESR slag and PbO is the main volatile with a small amount of ZnO. Based on these points and the weight loss, the slag melting points measured with traditional method and the slag chemical composition were modified to fit the melting point value. This way is proved to be feasible in theory and practice. Some suggestion for further research are proposed. The work will be of significance for both slag and molten salt with volatiles.

Reduction Smelting Low Ferronickel from Pre-concentrated Nickel-Iron Ore of Nickel Laterite

The research of smelting low ferronickel from pre-concentrate nickel-iron ore with 2.76 % Ni and 38.00 % Fetotal was carried out to find an effective way for stainless steel enterprises to use the low-nickel laterite reasonable. The results show that Ni and Fe both have a certain degree of enrichment, and impurities and harm elements have different degrees of reduction after pre-concentration of nickel-iron ore. Most valuable metal did not compound with impurities which greatly accelerated the speed and extent of melt separation reduction. Good alloy of 6.58 % Ni with the overall recoveries of 93.38 % and 89.95 % Fetotal with the overall recoveries of 89.57 % was manufactured under the following conditions: 10 % coke, 1.0 binary basicity, 18 % MgO and 3 % Al2O3 in slag, melting at 1,550 °C for 10 min. The product can be used for the feed of producing stainless steel.

Study on Control of Inclusion Compositions in Tire Cord Steel by Low Basicity Top Slag

Top slag melting experiment was conducted in a silicon molybdenum furnace with tire cord steel billet. The influence of top slag composition on the plasticity of CaO–Al2O3–SiO2–MgO inclusion and inclusion plasticization conditions was calculated by thermodynamic software FactSage. Use the thermodynamic calculation to guide the laboratory experiments to study slag compositions influence inclusions composition. Then industrial experiments were conducted based on the theoretical calculation and results of laboratory experiments. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to determine the morphology and composition of inclusions in steel. All studies show that in the CaO–Al2O3–SiO2–10% MgO diagram, when CaO = 8–48%, SiO2 = 35–75%, Al2O3 = 0–32%, inclusions are in the plastic area. When basicity of top slag is certain, Al2O3 content in inclusions increases with the increase of Al2O3 content in the slag, and the distribution of inclusions becomes scattered with the increase of Al2O3 content in slag. Inclusion plasticization can be achieved when the binary basicities of top slag are 0.6, 0.8–1.2, 1.4 and corresponding w(Al2O3)s are 2–15%, 2–10%, <2%. According to industrial experimental results, when top slag basicity decreases from 1.5 to 0.67–0.9 and Al2O3 content decreases below 10 wt%, the inclusion falls into plastic area. It is feasible in practice to control the CaO–Al2O3–SiO2–MgO inclusions plastic through adjusting Al2O3 content in slag.