Search Results (6)

In the process of continuous casting, especially high-speed continuous casting, the inflow state of the mold flux is particularly important. The fluxing agent is one of the most important factors affecting the flow state. The influence of the typical fluxing agent B₂O₃ on the viscous characteristics and melt structure of the fluorine-free CaO-SiO₂-M₂O (M = Li, Na) system was analyzed. The following conclusions were drawn. In the CaO-SiO₂-Na₂O slags, with the increasing addition of B₂O₃, the viscosity, breaking temperature, and polymerization degree of the slag show a gradually decreasing trend. When the mass fraction of B₂O₃ increased from 0 to 10%, the increase in two-dimensional [BO₃] structural units played a dominant role. When the mass fraction of B₂O₃ reached 15%, the network was affected by the increase in [BO₃] and the low-polymerized [SiO₄] tetrahedrons. The CaO-SiO₂-Li₂O slag system had a lower breaking temperature due to the formation of phases such as Li₂O·2B₂O₃, of a low melting temperature. The initial degree of depolymerization of the network was high. Upon increasing the addition of B₂O₃, the relative proportion of the network modifier structural units significantly increased, resulting in the enhanced instability of the network structure. As a result, the effect of [SiO₄]-polymerization was stronger than that of [BO₃]-depolymerization in maintaining the stability of the network structure. Full article

In this experiment, a quaternary fluorine-free refining slag system of CaO-SiO₂-Al₂O₃-MgO was selected, with basicity ratios of 2, 4, and 6 and calcium-aluminum ratios of 1.5, 2.1, and 3. High-temperature “slag-steel equilibrium” experiments were conducted to investigate the influence of different basicity ratios and calcium–aluminum ratios on the morphologies, compositions, sizes, and quantities of the inclusions in H13 steel, aiming to improve the cleanliness of H13 steel to meet practical industrial requirements. The experimental results showed that with the increase in the basicity ratio and the calcium–aluminum ratio, the morphologies of the inclusions changed from elliptical to regular circular, with more regular edges. As the basicity ratio increased from 2 to 6, the densities of the inclusions showed a decreasing trend, with values of 40, 35, 30, 25, 32, and 30 inclusions/mm². When the basicity ratio remained the same, the average size of the inclusions in the steel decreased first and then increased with the increases in the calcium–aluminum ratios, with sizes of 1.59 μm, 1.23 μm, and 1.38 μm, respectively. Among these, when the basicity ratio was 6 and the calcium–aluminum ratio was 2.1, the control effect on the densities and sizes of the inclusions was the best, yielding an inclusion density of 25 inclusions/mm² and a size of 1.15 μm. Additionally, reducing the Al₂O₃ content in the slag could reduce the Al₂O₃ contents in the inclusions, which also promoted improvements in the elastic deformation capacities of the inclusions. With increases in the calcium–aluminum ratios in the slag system, the masses of the inclusions decreased due to the reduced Al contents in the steel. The Al contents in the steel also had an impact on the compositions of the inclusions. Full article

Liquid accelerating agents have the advantages of simple operation and fast construction, and have become indispensable admixtures in shotcrete. However, most liquid accelerating agents in the market at present contain alkali or fluorine, which adversely affect concrete and seriously threaten the physical and mental health of workers. Therefore, in view of the above deficiencies, it is necessary to develop a new type of alkali-free fluorine-free liquid accelerating agent. In this paper, the polyaluminum sulfate early strength alkali-free liquid accelerator is prepared using polymeric aluminum sulfate, diethanolamine, magnesium sulfate heptahydrate and nano-silica. The influence of this agent on the setting time of fresh cement paste and compressive strength of the corresponding cement mortar is determined. Thermogravimetric analysis curves, X-ray diffraction and scanning electron microscopy images are obtained to investigate the mechanism. Findings show that the initial setting time and the final setting time of cement paste are 2 min 30 s and 7 min 25 s. The compressive strengths of cement mortar cured for 1 d, 28 d and 90 d are 2.4 MPa, 52.2 MPa and 54.3 MPa respectively. Additionally, the corresponding flexural strengths are 3.4 MPa, 9.8 MPa, 11.8 MPa. When the mass rate of accelerator is 7%, the mechanical strengths of cement mortar are the highest. The additions of fly ash and blast furnace slag can affect the mechanical of cement mortar mixed with accelerator. When the mass ratio of the fly ash and blast furnace slag is 15%, the mechanical strengths of cement mortar reach the highest. Moreover, the hydration heat release rate of cement is increased by the accelerator and the corresponding time of hydration heat peak is decreased by the accelerator. The accelerator can decrease the amount of needle-like hydration products and improve the compactness. The mechanical strengths are improved by consuming a large amount of Ca(OH)₂ and forming more compact hydration products. It is recommended that the optimum dosage range of the polyaluminum sulfate early strength alkali-free liquid accelerator is 7%. Full article

Fluorine-bearing refining slag (FBS) is used to produce axle steel for electric multiple unit vehicles. To avoid environmental pollution caused by fluorine, a fluorine-free ladle furnace slag (FFS) was designed based on an industrial FBS. The effects of main components on the physical and metallurgical properties of slag were investigated via theoretical analysis and laboratory tests. The composition range of components of the designed FFS are w(CaO) = 40–55 wt.%, w(SiO₂) = 2–6 wt.%, w(Al₂O₃) = 30–40 wt.%, w(MgO) = 6–8 wt.%, and w(CaO)/w(Al₂O₃) = 1.25–1.50. Industrial-scale test results indicate that the FFS has similar deoxidation and desulfurization capabilities to industrial FBS. Full article

In this study, the structure, viscosity characteristics, and crystallization behavior of CaO-SiO₂-B₂O₃ based melts were studied combining molecular dynamics (MD) simulation, Fourier transform infrared (FTIR) spectroscopy, rotating viscometer test, and FactSage thermodynamic calculation. The results showed that, in the ternary CaO-SiO₂-B₂O₃ glass system, stable structural units of [SiO₄]⁴⁻ tetrahedral, [BO₃]³⁻ trihedral and [BO₄]⁵⁻ tetrahedral were formed, and the Si-O and B-O structure depolymerize with the basicity increase from 1.15 to 1.25, then the B-O structure become complex with the basicity further increase to 1.35. In fluorine-free mold fluxes, with the basicity increases, the viscosity at 1300 °C increases, the liquidus temperature decreases and then increases, the network structure polymerizes, it indicates that the structural complexity rather than the melting property change plays a predominant role in increasing the viscosity at 1300 °C. Moreover, due to the changes in crystallization phase and solid solution ratio, the viscosity-temperature curve of fluorine-free slag shows the characteristics of alkaline slag and the break temperature increase with the basicity increase. The MD simulation, FTIR experiment, viscosity test, and FactSage calculation results are verified and complemented each other. Full article

In order to reduce the amount of fluorite during the steelmaking process for environmental protection, it is essential to investigate the fluorine-free slag system. Thus, high-basicity CaO–SiO₂–FeO_x–MgO slag with B₂O₃ content from 0% to 15% was designed, and its melting characteristics and viscosity were investigated. The influence of B₂O₃ content on the phase diagram of the slag system was calculated using FactSage 7.3, and the break temperature was determined from the curves of temperature-dependent viscosity. The results show that, with the increase in B₂O₃ content, the melting characteristics of the CaO–SiO₂–FeO_x–MgO/B₂O₃ slag system, including liquidus temperature, flow temperature, softening temperature, and hemispheric temperature, all decreased; the main phase of the slag system transformed from Ca₂SiO₄ into borosilicate, and finally into borate; the viscous flow activation energy reduced from 690 kJ to 130 kJ; the break temperature reduced from 1590 °C to 1160 °C. Furthermore, the melting characteristics and the break temperature of the slag system with 5% and 8% B₂O₃ content were found to be the closest to the values of fluorine-containing steel slag. Full article