Search

This study analyzed the impact of gas flow rate, oil layer thickness, and purging plug position on oil eye area and oil entrapment depth during ladle refining. To this end, a single-plug stirred water model system was used to experimentally investigate the dynamics of slag entrapment, which plays a vital role in purifying molten steel. High-definition cameras captured oil eye images and processed them through binarization. Oil eye area data were obtained using pixel point counting, establishing a database correlating slag-eye area with oil entrapment depth. The dataset was divided into 90 pct training and 10 pct validation data. The best hyperparameter combinations and established decision tree (DT) model were determined using grid search and cross-validation methods. The DT model successfully realized the prediction function for both parameters and achieved a high accuracy of 97.318 pct for the oil eye area and 90.624 pct for oil entrapment depth based on experimental data. A thermodynamic diagram and feature importance were employed to analyze these factors' effects on the experimental results. Furthermore, the decision-making process of the model was explored through Individual Conditional Expectation (ICE), Partial Dependence Plot (PDP), and Shapley Additive Explanations (SHAP) diagrams. The proposed DT model's feasibility was validated, exhibiting its strong adaptability in predicting oil entrapment and proving its effectiveness for practical applications within a plant setting. [ABSTRACT FROM AUTHOR]

To enhance the comprehension of the corrosion mechanism of refractories induced by molten slag, a 2D numerical model was developed in the present work. This model simulates the penetration of CaO–Al2O3–MeO slag into Al2O3–MgO refractory, considering capillary forces, as well as viscous and inertial resistances within the porous matrix acting on the molten slag. Experimental observations and measurements were conducted to validate the accuracy of the model. Through simulation, we visually represented the slag penetration process, highlighting the metamorphic reaction resulting from the diffusion of slag components. Notably, small aggregate particles had minimal impact on slag penetration. Instead, they were entirely enveloped by molten slag, subsequently peeling off from the refractory. The depth of penetration (αslag = 0.05, αslag represents the volume fraction of liquid slag) exceeded three times the corrosion depth (αslag = 0.99). Within the region penetrated by molten slag, a portion of the refractory matrix underwent metamorphosis into the liquidus phase. Significantly, reducing porosity emerged as an effective strategy to control molten slag penetration. A 44.7 pct reduction in corrosion depth was achieved by decreasing porosity from 0.28 to 0.14. This numerical model offers valuable insights into the factors influencing refractory corrosion and presents a quantitative approach for optimizing refractory designs to enhance resistance against slag penetration. [ABSTRACT FROM AUTHOR]

Strict requirements on low-carbon and environmentally friendly steelmaking process promote the application of the novel microporous magnesia with excellent thermal insulation as a promising refractory. This study performed static and dynamic slag resistance tests of the microporous magnesia in two tundish covering fluxes to explore its erosion and corrosion behaviors under different conditions. The fused magnesia castable was used as the control group. The phenomena were thoroughly analyzed according to macroscopic and microscopic morphology observations, supplemented with thermodynamic calculation and CFD simulation. The results showed that, castables were severely damaged through wear and peeling in the dynamic slag resistance tests, which process was enhanced by the fast dissolution of MgO. The microporous magnesia possessed stronger slag resistance since its occurrence time for wear was delayed over 5 minutes compared to fused magnesia castable, and the wear rate was lower. In addition, the microporous magnesia was less affected by the dissolution of MgO due to the formation of a spinel layer on the surface, which hindered the slag penetration and mass transfer. Finally, a Sherwood correlation was obtained based on the experimental data, which allowed one to calculate the wear rate of MgO castable at slag line in actual tundish. [ABSTRACT FROM AUTHOR]

The objective of this study was to create a novel 3D coupled numerical model that explores the impact of electromagnetism on the fluctuation of the slag/steel interface during the LF refining process. To evaluate the effects of alternating current power, an AC phasor was introduced to examine the Lorentz force and Joule heating phenomena. Turbulent motion was represented using the large eddy simulation technique, while the volume-of-fluid approach was utilized to illustrate the deformation of the air/slag/steel interface. The discrete phase model and the two-way coupled Euler–Lagrange technique were employed to track the motion of gas bubbles, accounting for bubble collision, coalescence, and breakup. By comparing the simulated results with experimental data, the model's fundamental validity was confirmed. The findings emphasized the importance of concurrently considering both the electromagnetic field and the bubbly flow in the investigation of the LF refining process. It was observed that the Lorentz force played a crucial role in promoting the fluctuation of the slag/steel interface, potentially leading to the absorption of carbon by the molten steel. [ABSTRACT FROM AUTHOR]

A quantitative evaluation method for the magnesia refractory deterioration in the smelting process is proposed based on analysis of static and rotating finger tests to study the dissolution behavior. A transient 3D fluid-solid coupled numerical model was then developed, including the two-phase gas/slag flow pattern, temperature profile, MgO content distribution, solid refractory dissolution, and sample shape change. A kinetic degradation model was introduced to calculate the refractory overall wear rate determined by the coupled effect of the flow-induced erosion and chemical-induced corrosion. The shape change of the solid refractory sample was characterized via the dynamic mesh technique. A close correlation between the simulated results and the experimental data gives confidence in the fundamental validity of the developed numerical model. The results indicate that the flow would increase the overall wear rate by one or two orders of magnitude depending on the velocity. Therefore, flow-induced erosion must be accounted for in estimating the refractory wear rate. The flow-induced erosion and chemical-induced corrosion could be quantified via the wall shear stress and a modified Arrhenius's law, respectively. [ABSTRACT FROM AUTHOR]

To realize an industrial production of a cerium‐treated electroslag remelted H13 steel, electroslag remelting (ESR) of H13 steel using a CaF2–CeO2–CaO–Al2O3 system slag combined with a Si–Ca reductant addition is studied. The influence of the Al2O3 content in the slag on the cerium treatment effect of cerium‐oxide‐containing slag is investigated to determine the appropriate slag. A 52.2 wt% CaF2–26.7 wt% CeO2–17.8 wt% CaO–3.3 wt% Al2O3 slag (RE‐Slag) is employed for the industrial ESR production of H13 steel. An H13 steel remelted by a 70 wt% CaF2–30 wt% Al2O3 slag (CA‐Slag) is used for comparison. Al2O3 can suppress the reduction of cerium oxide by changing the activities of slag components. ESR with RE‐Slag achieves a cerium treatment of H13 steel. However, an uneven distribution of Ce is obtained due to the limitation of the reductant addition method. The H13 steel remelted with RE‐Slag (RE‐Slag‐H13) has higher cleanliness, finer dendritic structures, and finer primary carbides than those of the steel remelted with CA‐Slag (CA‐Slag‐H13). Compared to the forged CA‐Slag‐H13 steel, the banded segregation of the RE‐Slag‐H13 steel is suppressed, and the impact toughness is increased by 30%. [ABSTRACT FROM AUTHOR]

This study examined the effects of micropores and nanosized zirconia (ZrO2) addition in a novel lightweight magnesia castable on the slag resistance. To this end, static and rotating finger tests were conducted to investigate the degradation of the novel lightweight and convectional fused magnesia castables in a high-basicity slag. A 3D transient numerical model was also established to assess wall shear stress distribution in the rotating finger tests. The corrosion process of the lightweight magnesia castable could be subdivided into the following three stages. In Stage 1, the slag penetrated into the castable through cracks and dissolved components, destroying the castable's structure and reducing its strength. In Stage 2, wear and peeling occurred, and the weight of the castable decrease a nearly constant rate. In Stage 3, the shear stress dropped with the castable diameter reduction, and corrosion rate decreased, and the penetration and dissolution in Stage 1 become restrictive link again. The analysis revealed the effects of micropores and nanosized ZrO2 on the slag penetration and microstructure evolution: micropores alleviated cracks and absorbed slag, and the formed CaZrO3-ZrO2 provided stronger bonding. [ABSTRACT FROM AUTHOR]

Surface tension is an important physical property of molten metallurgical slag. In recent years, the determination of slag surface tension by pendant drop method has received increasing attention, but the corresponding density data are required during its calculation. For this reason, researchers have to use the density data from literature or other experiments, which limits the application of the pendant drop method. In this work, a novel ring-shaped pendant drop forming device was made of PtIr alloy. A 40 pct CaO–40 pct SiO2–20 pct Al2O3 (mass percentages) slag was taken as an example, the density and surface tension data of the slag at high temperatures were tried to obtain in one experiment by the pendant drop method under different atmospheres including high-purity argon, air, and purified argon. In the temperature range of 1450 °C to 1650 °C, the measurement results are comparable with literature data of the slags with the same or similar compositions, which confirms that it is feasible to obtain the slag density and surface tension in one experiment by the pendant drop method based on the pendant drop forming device. The measured density of the molten slag slightly decreases with an increase in temperature, while the surface tension slightly increases; the temperature coefficients of both the density and the surface tension are relatively small. In addition, it is found that the obtained density values under the three atmospheres are highly consistent at the same temperature, and the surface tension values under high-purity argon and purified argon are also relatively consistent; however, the surface tension value under air is slightly larger than that under argon. [ABSTRACT FROM AUTHOR]

The application of BOF slag in the field of building materials is limited by its volume expansion during natural aging, which is mainly attributed to the hydration reaction of free calcium oxide in slag. In this study, the influence of SiO2 addition and atmosphere on the mineral modification of typical industrial converter slag, as well as, the dissolution kinetics of SiO2 in slag were explored. The results show that added SiO2 reacts with the free calcium oxide in slag to form dicalcium silicate. Ferrous oxide is oxidized to iron oxide under air atmosphere, which combines with free calcium oxide to form calcium aluminoferrite. Therefore, the amount of SiO2 required for complete digestion of free calcium oxide under air atmosphere is less than that under argon atmosphere. Based on the results of the immersion experiments of quartz rods, the dissolution model of spherical quartz sand was developed, which can be used to predict dissolution curves of quartz sand with different particle sizes in converter slag. The corrosion of magnesia crucible contacted with the molten slag in air atmosphere is more serious than argon atmosphere, which should attract more attentions. [ABSTRACT FROM AUTHOR]

The apparent contact angles between the molten steel with different [Al] contents (w[Al]) from 0.002% to 0.831% (mass fraction) and the microporous MgO (MM) substrates are measured at 1823 K using the sessile drop method. In particular, the contact angles of No. 1 (w[Al] = 0.002%) and No. 5 (w[Al] = 0.831%) molten steels gradually increase with time at the initial stage. As w[Al] increases from 0.002% to 0.831%, the transformation route of interfacial products between molten steel and the MM substrate is MgO–FeO → MgO·Al2O3 → CaO·2Al2O3 + MgO·Al2O3. The w[Al] of No. 1 molten steel is small, and the dissolution of CaO·ZrO2(s) in the substrate is mainly affected by FeO. As w[Al] increases gradually, [Al] consumes the (MgO) contained in CaO·MgO·SiO2 (CMS), and turns the CMS into (CaO·SiO2) slag layer, which promotes the CaO·ZrO2(s) dissolving and thus increasing the interaction area percentage. When w[Al] is 0.831%, [Al] can react with (CaO·SiO2) slag layer or CaO·ZrO2(s) to form CaO·2Al2O3(s). [ABSTRACT FROM AUTHOR]

The vaporization and crystallization of CaF2–CaO–Al2O3 slags with different MgO contents for electroslag remelting were investigated by various analytical methods. The results show that the main volatiles from investigated slag with 8.8 mass% MgO content at 1723 K are CaF2 and AlF3 and contain trace MgF2. The mass loss of CaF2–CaO–Al2O3–(MgO) slag decreases with the increase of MgO content. The addition of MgO within 8.8 mass% has little effect on the viscosity of investigated slag, implying that the viscosity change is not the reason to inhibit the fluoride vaporization. At 1723 K, the vapor pressures of CaF2 and AlF3 decrease with the increase of MgO content; thus, fluoride vaporization becomes weak. The fluoride vaporization of slag with MgO addition under vacuum at 1823 K is also inhibited. The MgO addition can decrease the crystallization temperature of 11CaO·7Al2O3·CaF2, but excessive MgO addition can lead to the precipitation of MgO. [ABSTRACT FROM AUTHOR]

The technological development and indexes of advanced specification grain-oriented (GO) silicon steels are evaluated. The influences of inclusions and precipitates on the magnetic properties of GO silicon steels are summarized. The research progress on controlling inclusions and precipitates to improve the properties of GO silicon steels is reviewed based on the current manufacturing technology. The results indicate that impurity and inclusions can be efficiently reduced by selecting a suitable deoxidizer, optimizing the refining slag composition and smelting process. The precipitates are controlled by optimizing composition design of inhibitor-forming elements or grain boundary segregation elements, adjusting rolling and heat-treating operation conditions during the manufacturing process. The problems existing in the manufacture process of GO silicon steels are analyzed. The development trend of the GO silicon steels is pointed out to provide a reference for low-cost manufacturing of advanced GO silicon steels for manufacturing larger capacity, higher voltage, better energy-saving and emission reduction transformers. [ABSTRACT FROM AUTHOR]

The corrosion of refractory is generally related to the wetting between slag and refractory. Investigating the wetting and corrosion characteristics of refractory by molten slag has a positive significance to elucidating the corrosion mechanism and understanding the slag resistance. In this work, the apparent contact angles of the CaO–Al 2 O 3 –SiO 2 –(MgO) molten slags on microporous magnesia aggregate (MM) and fused magnesia (FM) substrates were respectively measured by sessile drop method under Ar atmosphere at 1550 °C. The dissolution of the MM substrate and the slag penetration behavior were investigated by combining the theoretical calculation of the FactSage thermodynamic software with the examination of SEM-EDS. The results show that MM substrate had a better slag resistance than FM substrate. The final apparent contact angles (θ f) of slags with the CaO/SiO 2 values of 3, 5 and 11 on MM substrate were 15.8°, 21.4°, and 9.2°, respectively, and that with the MgO content of 3, 6 and 9 mass% were 11.1°, 14.2°, and 52.5°, respectively. The larger the CaO/SiO 2 value of the slag, the more beneficial it was to slowing down the dissolution of MM and FM substrates; the original slag with MgO was also beneficial to lessening the dissolution of the MM substrate, which was better than that with a high CaO/SiO 2 value. The formation of MA could inhibit the slag from penetrating. In addition, for slags with different CaO/SiO 2 values, the effects of surface tension and viscosity on slag penetration were more significant than that of contact angle; for slags with different MgO contents, the effect of contact angle on slag penetration was more significant than those of surface tension and viscosity. [ABSTRACT FROM AUTHOR]

The effect of vacuum treatment on the cleanliness of low Ti steel treated with low basicity refining slag was studied by analyzing the change of oxygen content and inclusions characteristics in the steel after the interaction between different basicity slags and GCr15 bearing steels and after vacuum treatment. The results show that the oxide inclusions in the steel are mainly MgO·Al 2 O 3 after slag-steel interaction. The low basicity slag refining is beneficial for decreasing the harm of TiN inclusions due to the better low Ti content control. However, the oxygen content and the number of inclusions in the steel increase with the decrease of slag basicity (CaO/SiO 2 mass ratio), which means that the decrease in the basicity is disadvantageous to the cleanliness of steel. Typical inclusions in the steel transform into smaller MgO inclusions and MgS–MgO-(MnS) composite inclusions after vacuum treatment, and the oxygen content of steel is decreased to the same level. Furthermore, the size and number density of inclusions are significantly decreased after the vacuum treatment. It indicates that the combined process of low basicity slag refining and vacuum carbon deoxidation can realize the TiN inclusion control and cleanliness improvement of GCr15 bearing steel. • Low basicity slag refining is beneficial for reducing the harm of TiN inclusions on the performance of bearing steel. • Vacuum carbon deoxidization can significantly improve the cleanliness of the liquid steel. • TiN inclusion and cleanliness control of bearing steel can be realized by low basicity slag refining and vacuum treatment. [ABSTRACT FROM AUTHOR]

The motion and distribution of lime particles in a basic oxygen furnace (BOF) is explored using the proposed 3D comprehensive numerical model taking into account the supersonic oxygen jet, bottom-blowing bubble, melt flow, temperature distribution, and lime particle movement. The gas/slag/metal three-phase flow and interface fluctuation are described using the volume of fluid approach. The two-way coupled Euler–Lagrange method is employed to evaluate the rising of bottom-blowing bubbles. In contrast, the one-way coupled Euler–Lagrange method is adopted to represent the motion of lime particles, which are shown to continuously descend under the effect of gravity after feeding on the top surface. Upon touching the molten slag, the particles first move towards the furnace wall, turning back from both sides, and then travel to the middle from both ends. The particles finally gradually disperse to the whole molten slag layer because of the large- and small-scale vortices. [ABSTRACT FROM AUTHOR]

To predict slag corrosion numerically, a transient 3D mathematical model that considers the fluid flow, heat, and mass transfer was developed. A dynamic corrosion experiment using the rotating immersion approach was carried out to assess the overall corrosion activation of the MgO-C refractory. An expression for the corrosion rate was determined based on the wall shear stress, slag viscosity, sample size, overall corrosion activation, and difference in MgO content. A greater corrosion rate was observed at the bottom corner of the refractory sample compared to other parts, and it was concluded that higher temperatures and speeds encourage slag corrosion. The averaged corrosion rates at the sample wall with different rotating speeds and holding periods were compared. The relative error varied from 1.92% to 12.19%, which is within the acceptable range. It is expected that the proposed computational framework can be potentially extended to other refractory corrosion scenarios in metallurgical reactors. [ABSTRACT FROM AUTHOR]

Demand for energy saving in steelmaking process, lightweight refractories have attracted great attentions for the excellent thermal insulation. Herein, the corrosion behavior of the lightweight magnesia in the high basicity tundish slag is explored, and compared with that of fused magnesia. The results show that the impurities in the fused magnesia cause more dissolution of magnesia into slag after 60 min. Different from fused magnesia, the penetration layer is found in the lightweight magnesia, where the intercrystalline CaZrO3–ZrO2 phases are dissolved by the slag. The micropores in the lightweight magnesia provide passages for slag infiltration, but also accelerate the supersaturation of slag in refractory and impede the mass transfer. Furthermore, the residual CaZrO3–ZrO2 phases in transition layer hinder the further slag infiltration. After 60 min holding, the MgO content in molten slag contacted with lightweight magnesia is lower, implying that the lightweight magnesia is the promising refractory for tundish lining. [ABSTRACT FROM AUTHOR]

To reduce the Mn vaporization during recycling rejected electrolytic manganese metal by electroslag remelting, it is proposed to reduce the temperature of molten slag pool, but which leads to the degradation of slag desulfurization. The desulfurization by interaction between CaF2–CaO–Al2O3–Na2O slag and rejected electrolytic manganese metal scrap was studied from the view of thermodynamics in this study. The results show that sulfur distribution ratio decreases with increase of CaF2 content, and increases with the increase of Na2O content and temperature. Na2O increases sulfur distribution ratio of slag by increasing CaO activity. Na2O addition in CaF2–CaO–Al2O3–Na2O slag can enhance desulfurization ability of slag due to the larger sulfur distribution ratio and lower viscosity. Thus, sulfur content in test of slag T3 bearing 45.8 wt% CaF2-23.2 wt% CaO-22.7 wt% Al2O3-8.3 wt% Na2O is much lower than that of slag without Na2O, implying that 45.8 wt% CaF2-23.2 wt% CaO-22.7 wt% Al2O3-8.3 wt%Na2O slag is the promising slag for recycling rejected electrolytic manganese metal by ESR. [ABSTRACT FROM AUTHOR]

Ladle refining is an efficient process for improvement of quality of steel on secondary metallurgy under harsh conditions. Magnesia refractories with high purity are important raw materials for ladle lining in high‐quality steel production. However, the penetration by CaO–MgO–SiO2 slags damages magnesia refractories, which considerably limits their service life. Abundant grain boundaries in magnesia create channels for slag penetration and lead to the destruction of the structure. The effect of the microstructure on the slag corrosion behavior of magnesia aggregates requires further systematic investigation. In this study, a corrosion model was established to describe the slag penetration process of magnesia aggregates. The effects of the grain‐boundary size and slag CaO/SiO2 mass ratio (C/S ratio) on slag penetration were investigated, and the possibility of the microstructure optimization of magnesia aggregates was discussed. The results indicated that magnesia aggregates exhibited excellent slag resistance for slag with a C/S ratio above 1.5 or even 2.0. When the slag C/S ratio was lower than 1.5, the dissolution rate of magnesia decreased more rapidly with the increase in the slag C/S ratio. In addition, the much smaller grain‐boundary size increased the slag penetration resistance by promoting the formation of a dense isolation layer and inhibiting further penetration processes. The calculation results agreed well with the experimental results, suggesting that the corrosion model is promising for predicting slag corrosion. [ABSTRACT FROM AUTHOR]

Abstract: To improve the utilization and evaluation of metallurgical solid waste, the investigation of slag has become a focused research subject in the recent years. However, when slag with various compositions was smelted to produce high value-added products in the slag furnace, the SiO2-MgO based slag caused serious damage to the refractory lining material of the furnace compared to the common CaO-Al2O3-SiO2 based slag. The tabular alumina, lightweight alumina, silicon carbide, mullite and brown fused alumina aggregates were selected for testing. The static crucible method was used to investigate the SiO2-MgO based slag corrosion and comparative analysis was performed. The results show that mullite-silicon carbide or tabular alumina-silicon carbide refractories are promising for the use as lining materials of SiO2-MgO slag smelting furnaces. [ABSTRACT FROM AUTHOR]

Multi-hole ceramic filter is regarded as an effective and cheap method of additional flow control device in tundish. In order to evaluate the performance of the ceramic filter, a transient three-dimensional (3D) comprehensive numerical model has been developed to study the flow pattern, temperature distribution and residence time of the molten steel, as well as the elimination of inclusion in a full size two-strand tundish. One-way coupled Euler–Lagrange approach with random walk model was adopted to track the inclusion motion trajectory. The gravity, buoyancy, drag, virtual mass, lift, pressure gradient, and rebound forces were included. The inclusion Reynolds number was utilized for the judgment of the inclusion separation at the slag-steel interface and the internal surface of the filter hole. Besides, the residence time distribution curve has been analyzed for figuring out the macroscopic mixing of the molten steel. The results indicate that the ceramic filter increases the flow resistance of the molten steel in the tundish, resulting in a longer residence time and a higher temperature drop. Except removed by the covering molten slag, the inclusion could also be trapped by the filter hole when the molten steel travels through the ceramic filter. The elimination of the smaller inclusion is significantly improved. The removal ratio of the 1 μm inclusion in the tundish without ceramic filter is only 59.3 pct, while the value is improved to 65.3 pct if we apply the ceramic filter with slenderness ratio of 3 to the tundish. And with the slenderness ratio changing from 3 to 5, the removal ratio of the 1 μm inclusion increases from 65.3 to 72.0 pct. Additionally, the ceramic filter could counteract certain side effects of the increasing inclusion density on the removal, especially for the smaller inclusion. With the inclusion density increasing from 3990 to 5000 kg/m3, the removal ratio of the 1 μm inclusion decreases by 14.5 pct in the tundish without ceramic filter, and after using the ceramic filter, the removal ratio decreases by 13.0, 7.4, and 5.0 pct with the slenderness ratio varies from 3 to 5. [ABSTRACT FROM AUTHOR]

The relationship of inclusions and primary carbides in H13 ingot processed by ESR with ANF-6 slag was investigated. It is found that inclusions in H13 ESR ingot are Al2O3, MnS and calcium-aluminate inclusions. The Al2O3 and MnS inclusions are found to be the nucleation cores of the primary carbides, whereas the calcium-aluminate inclusions are not. In order to study the effect of slag on inclusions and primary carbides of H13 steel further, the characteristics of inclusions and primary carbides in steel remelted by ANF-6 and ANF-8 slags were analyzed, and compared to the steel remelted without slag. After being remelted with the ANF-6 (70 mass% CaF2 + 30 mass% Al2O3) and ANF-8 (60 mass% CaF2 + 20 mass% CaO + 20 mass% Al2O3) slags, Al2O3 and CaO contents in calcium-aluminate inclusions increase, respectively. The ANF-8 slag shows stronger desulfurization ability than ANF-6 slag, which contributes to the delay of MnS inclusions precipitation and the decrease of inclusion number, and finally helps to inhibit the precipitation of primary carbides. It implies that the ANF-8 is the promising slag for the ESR process of H13 steel. [ABSTRACT FROM AUTHOR]

Effects of the basicity and the CaF2 content on viscosity of CaF2–CaO–SiO2 slag with high CaF2 content for electroslag remelting process were investigated by the rotating cylinder method in the temperature ranging from 1773 to 1533 K. The relationship between the structure and the viscosity variation of the slag was also clarified by the Fourier transform infrared (FT-IR) spectroscopy of water-quenched slags. The results show that the viscosity gradually decreases with the increase in the basicity of the slag from 1 to 3 under the present experimental conditions. It is found that the CaO does not depolymerize all silicate complex anions for the slag with the basicity of 1 at 1773 K and there are still some bridging oxygens. With the increase in the basicity to 3, the silicate complex anions are almost completely depolymerized to simple ions. As the CaF2 content increases from 40 to 80 mass%, the viscosity of the slag decreases due to the dilution of CaF2 for the concentration of the silicate complex anions in unit volume of the slag. Moreover, the effect of the temperature on the viscosity is not remarkable. The activation energy of viscous flow exhibits the decrease from 40.4 to 26.7 kJ · mol−1 with the increase in the basicity from 1 to 3, and also the decrease from 66.6 to 31.0 kJ · mol−1 with the increase in the CaF2 content from 40 to 80 mass%. [ABSTRACT FROM AUTHOR]

Five heats were carried out to study the effects of SiO2 containing slag for electroslag remelting (ESR) on inclusion characteristics of 42CrMo steel. Fluoride vaporization at elevated temperature from slags was also explored by thermogravimetric analysis. The results show that fluoride vaporization is dominated by slag viscosity and component activities in the melt. Slag composition has an important effect on the composition of the oxide inclusion. For 70 wt% CaF2–30 wt% Al2O3 slag, the compositions of oxide inclusions in remelted steel show no obvious differences compared with the virgin steel. Whereas, SiO2 content in oxide inclusions of steel processed by slag bearing SiO2 show an increasing trend with increase of SiO2 content in 50 wt% CaF2–CaO–SiO2 slag, and the MgO · Al2O3 inclusions are modified to (Al,Ca,Mg,Si)O inclusions with low melting temperature. Al2O3 contents in oxide inclusions are also closely related to the Al2O3 concentration in the molten slag, which increase with the addition of Al2O3 in slag bearing SiO2. In testing various slags, the incorporation of slag T2 with 50 wt% CaF2–30 wt% CaO–20 wt% SiO2 shows the highest cleanliness in remelted steel. This implies that slag T2 can be a promising slag for ESR process of alloy steel requiring Al content refinement due to less fluoride vaporization from slag and better inclusions modification. [ABSTRACT FROM AUTHOR]

The interaction between slag and GCr15 steel under argon and vacuum were investigated by laboratory experiments. The results show that the maximum and average size of inclusions, and the proportion of large inclusions decrease after slag-steel interaction. Compared with the test under argon, inclusion size of the steel in the test under vacuum is smaller and more uniform, which is attributed to that vacuum promotes the reaction of C and O in molten steel to form CO. The La content increase from 0 to 0.0022 wt% in the steel processed by La 2 O 3 containing slag after for 5 min holding at 1873 K under 0.5 kPa. Thermodynamic calculation reveals that the La 2 O 3 in molten slag can be reduced by dissolved C in liquid steel to form dissolved La under vacuum due to the relatively higher carbon content of GCr15 steel and appropriate vacuum condition. The microstructure and primary carbides of the tested steel under vacuum are finer than that under argon. The present study provides a theoretical basis for the homogenized La treatment of GCr15 steel under vacuum, which shows a promising prospect in vacuum electroslag remelting of high-end bearing steel. • Proposed a novel method for on homogenized La treatment of GCr15 steel. • The La treatment by interaction between La 2 O 3 containing slag and dissolved C in steel under vacuum is feasible. • The distribution of dissolved La in liquid steel by this method would be even due to the even distribution of reactans. [ABSTRACT FROM AUTHOR]

The slag corrosion and penetration behaviors of MgAlO, MgAlO-ZrO, MgAlO-ZrO-CaO, AlO, and AlO-ZrO-SiC refractories were investigated using the static crucible method at 1873 K for 2 h. The above refractories all displayed excellent slag corrosion resistance, and their corrosion depth was less than 1.10 mm. AlO material was hardly corroded by the molten slag, and its corrosion depth was only 0.05 mm. Their penetration depth ranged from 13.79 to 24.48 mm. Among them, AlO-ZrO-SiC refractories displayed good slag penetration resistance with a penetration depth of 13.79 mm. [ABSTRACT FROM AUTHOR]

The vaporization and crystallization of CaF 2 –CaO–Al 2 O 3 slags with different La 2 O 3 contents for electroslag remelting were investigated by various analytical methods. The results show that the main volatiles from investigated slag within 7.4 wt% La 2 O 3 content at 1723 K are CaF 2 and AlF 3. The weight loss of CaF 2 –CaO–Al 2 O 3 -(La 2 O 3) slags decrease with increase of La 2 O 3 content in both thermo gravimetric experiment and vacuum condition. The addition of La 2 O 3 within 7.4 wt% reduces the viscosity and breaking temperature of investigated slag, and the change of viscosity is not the main reason to inhibit the fluoride vaporization. The vapor pressure of CaF 2 and AlF 3 at 1723 K decreases with increase of La 2 O 3 content because of the changes in component activity. Thus, fluoride vaporization becomes weakened. The crystalline phases of CaF 2 –CaO–Al 2 O 3 slag are 11CaO·7Al 2 O 3 ·CaF 2 and CaF 2 , while the crystalline phases of slag within 7.4 wt% La 2 O 3 content are (CaLa)Al 3 O 7 , La(AlO 3) and CaF 2. The La 2 O 3 addition can decrease the crystallization temperature of CaF 2 and prevent the precipitation of 11CaO·7Al 2 O 3 ·CaF 2. • The vaporization and crystallization of CaF 2 –CaO–Al 2 O 3 -(La 2 O 3) were analyzed by TG-DSC. • The viscosity of CaF 2 –CaO–Al 2 O 3 -(La 2 O 3) slag was measured. • The crystalline phases ((CaLa)Al 3 O 7 , La(AlO 3)) were found in CaF 2 –CaO–Al 2 O 3 -7.4wt% La 2 O 3 slag. [ABSTRACT FROM AUTHOR]

In the present study, the experiments for the phosphorus equilibrium partition between CaO-SiO2-Fe tO-P2O5 slags with Na2O or K2O addition and solid pure iron foil were performed at 1573, 1623, and 1673 K, respectively. The experimental results showed that both Na2O and K2O addition can enhance the dephosphorization ability of CaO-SiO2-Fe tO-P2O5 based slags and they have similar dephosphorization ability under the same temperature and main slag composition. The phosphorous partition ratio between slag and carbon-saturated hot metal increased with the increase of basicity with a peak value in the range of R around 1.3-1.5. The phosphorous partition ratio decreased with the increasing of ( w(CaO) + w(Na2O))/ w(Fe tO) value in slags. The dephosphorization ability of CaO-SiO2-Fe tO-P2O5 based slags was relatively higher when the ( w(CaO) + w(Na2O))/ w(Fe tO) values fell in the range of 0.5-0.8. The phosphorous partition ratio decreased with the temperature increase. The linear relationships between the logarithm phosphorous partition ratio and the reciprocal of temperature were obtained for CaO-SiO2-Fe tO-P2O5 based slags with Na2O. The information provides by present study would be useful for optimization of dephosphorization in hot metal pretreatment. [ABSTRACT FROM AUTHOR]

The microporous magnesia aggregates show a promising application prospect as tundish lining, due to the excellent thermal insulation. In this study, the effect of nano-sized Al 2 O 3 addition on the corrosion resistance of microporous magnesia aggregates against tundish slag is explored. The results show that the addition of nano-sized Al 2 O 3 deteriorates the slag resistance of microporous magnesia aggregates, which is mainly because that the apparent porosity of aggregates increases with the addition of nano-sized Al 2 O 3. Furthermore, MgO·Al 2 O 3 spinel is formed in situ at the grain boundaries of Al 2 O 3 -bearing aggregates and the dissolution of MgO·Al 2 O 3 spinel into molten slag damages the structure of aggregates. For the Al 2 O 3 -free microporous magnesia aggregates, as expected, the penetration of high basicity slag (CaO/SiO 2 = 9, mass ratio) into refractory is slighter than that of low basicity slag (CaO/SiO 2 = 4, mass ratio). But, for the Al 2 O 3 -bearing microporous magnesia aggregates, the corrosion of refractory by high basicity slag is severer. This is mainly because that MgO·Al 2 O 3 spinel is more unstable in high basicity slag. Therefore, it is not suitable to add nano-sized Al 2 O 3 for the preparation of microporous magnesia as tundish lining. [ABSTRACT FROM AUTHOR]

The viscosity of slag is a key factor affecting metallurgical efficiency and recycling, such as metal-slag reaction and separation, as well as slag wool processing. In order to comprehensively clarify the variation of the slag viscosity, various data mining methods have been employed to predict the viscosity of the slag. In this study, a more advanced dual-stage predictive modeling approach is proposed in order to accurately analyze and predict the viscosity of slag. Compared with the traditional single data mining approach, the proposed method performs better with a higher recall rate and low misclassification rate. The simulation results show that temperature, SiO2, Al2O3, P2O5, and CaO have greater influences on the slag's viscosity. The critical temperature for onset of the important influence of slag composition is 980 °C. Furthermore, it is found that SiO2 and P2O5 have positive correlations with slag's viscosity, while temperature, Al2O3, and CaO have negative correlations. A two-equation model of six-degree polynomial combined with Arrhenius formula is also established for the purpose of providing theoretical guidance for industrial application and reutilization of slag. [ABSTRACT FROM AUTHOR]

In order to clarify the effect of graphite content on the corrosion behavior of MgO–C refractories immersed in MnO-rich slag, the MgO–C refractory samples bearing 5 wt%, 10 wt% and 15 wt% graphite were prepared, and exposed in the slag composed of 40 wt% CaO, 40 wt% SiO 2 and 20 wt% MnO. The results show that metallic Mn particles and (Mg,Mn)O solid solution are formed at the slag/refractories interface. Whereas, no dense layer is formed by (Mg,Mn)O solid solution at the interface. The decrease in MnO content of slag is mainly attributed to the reaction with graphite to form liquid Mn. The graphite is found in the slag, and dissolved in the form of oxidation. The poor wetting limits the contact area of graphite and slag, reducing graphite oxidation and decarburized area. The graphite does not become the passage for slag to penetrate into the refractories due to the oxidation. On the contrary, the dissolution of MgO in slag is faster than graphite, thus is mainly responsible for the degradation of refractories. As a result, MnO and MgO contents change less in the slag contacted with the refractories bearing higher graphite content. [ABSTRACT FROM AUTHOR]

Abstract In this study, five types of CaF 2 CaO Al 2 O 3 slags with varying CaO/Al 2 O 3 mass ratio and CaF 2 content were selected for investigating the vaporization behavior of slag bearing high CaF 2 content by thermo gravimetry and ion and molecule coexistence theory. The results show that the volatile product of slag is the AlF 3. The vaporization rate is affected by the vapor pressure of AlF 3 , mole number of complex molecules and the viscosity of slag. For all slags, the vaporization rate of slag bearing approximately 70 wt% CaF 2 and 30 wt% Al 2 O 3 is the fastest due to the ultra-high vapor pressure of AlF 3. In the test of slags containing 70 wt% CaF 2 , vaporization rate firstly decreases, then increases with CaO/Al 2 O 3 mass ratio increasing from 0.05 to 1.10 and 2.00. In the case of slags containing same CaO/Al 2 O 3 mass ratio, vaporization rate firstly increases, then decreases with CaF 2 content decreasing from 68.9 wt% to 48.1 wt% and 28.7 wt%. Slag T5 bearing approximately 30 wt% CaF 2 , 33.9 wt% CaO and 36.1 wt % Al 2 O 3 has lower electrical conductivity, slower vaporization rate and larger sulfide capacity, which will be economical, environmentally friendly and suitable for vacuum electroslag remelting. Highlights • Volatile product of CaF 2 CaO Al 2 O 3 slag bearing high CaF 2 content is the AlF 3. • The vaporization rate is affected by mole number of complex molecules and the viscosity of slag. • Vaporization behavior of slag bearing high CaF 2 content is firstly studied by ion and molecule coexistence theory. [ABSTRACT FROM AUTHOR]

The wetting and corrosion behavior of the corundum substrate anode by CaO–SiO 2 –MgO molten slag was investigated via the joint application of the sessile drop method with applied voltage and SEM-EDS technique. The slag drop exhibited a good wettability on the corundum substrate. The apparent contact angle at zero voltage slightly exceeded that at a 1 V applied voltage but was lower than those at 1.5 V and 2 V ones. Low applied voltage of 1 V had little effect on the corundum substrate's direct dissolution corrosion processes; high ones of not less than 1.5 V caused the electrode reaction to occur. The stirring effect of O 2 bubbles from the anode reaction aggravated the substrate's direct dissolution and physical stripping. It was found that the applied voltage could inhibit the slag penetration, and the apparent contact angle had no obvious relation with the direct dissolution thickness and penetration depth. A thin but almost continuous MgO⋅Al 2 O 3 (MA) layer could form at the slag/substrate interface at the applied voltage of 1.5 V. These results indicate the positive effect of applied voltage on the distribution of interfacial products and the molten slag penetration in reducing the corrosion of corundum anode under certain conditions. However, when the applied voltage was too high, the vigorous electrode reaction could aggravate the direct dissolution and physical stripping of the corundum anode, and damage the continuation of the formed interface product layer with a high melting point. [ABSTRACT FROM AUTHOR]

Chemical attacks and structural spalling dominated the degradation process of the refractory lining in refining ladle. In the present work, we have fabricated a cement-free gel-bonded corundum-spinel castables and examined the degradation behavior in contact with the molten steel/slag. Further, the role of infiltrated steel/slag associated with cracks on the spalling behavior were elucidated. The stress cracks formed on the corroded interface, providing a permeation pathway for molten corrosive species and acting as a sub-surface for further corrosion. Infiltrated steel contributed to the formation of composite (Mg, Fe)Al 2 O 4 spinel and led to an additional corrosion and induced a large structural spalling. Besides, macro-scale structural spalling of the refractory lining and microscale spalling of aluminate aggregates were discussed in detail, respectively. [ABSTRACT FROM AUTHOR]

In order to explore the slag with less fluoride vaporization for vacuum electroslag remelting of Ce-bearing steel, the fluoride vaporization behavior of CaF 2 –CaO–Al 2 O 3 -(Ce 2 O 3) slag was investigated by thermo gravimetry analysis at 1673 K. For the purpose of figuring out the mechanism of the Ce 2 O 3 effect on fluoride vaporization in slags, the viscosity of slags was measured, and the activity of components in molten slag was calculated based on the ion and molecule coexistence theory. The fluoride vaporization of slag under vacuum condition at 1823 K was also studied. The results show that the fluoride vaporization products are CaF 2 and AlF 3. The weight loss caused by fluoride vaporization reduces with increasing Ce 2 O 3 content. The Ce 2 O 3 addition lowers the breaking temperature of viscosity, which leads to the decrease of viscosity at 1673 K with the increase in Ce 2 O 3 content. It implies the viscosity change is not the reason inhibiting fluoride vaporization because a lower viscosity will promote the fluoride vaporization. The vapor pressure of CaF 2 and AlF 3 decreases with increasing Ce 2 O 3 content due to activity change, which contributes to the suppression effect on the fluoride vaporization in investigated slags. The fluoride vaporization of slag under vacuum is inhibited because of Ce 2 O 3 addition as well. • Weight loss of CaF 2 –CaO–Al 2 O 3 -(Ce 2 O 3) slag due to fluoride vaporization was determined by thermo gravimetry analysis. • A thermodynamics model used for estimating the activity of components in CaF 2 –CaO–Al 2 O 3 -(Ce 2 O 3) slag based on the ion and molecule coexistence theory is proposed. • Effect of Ce 2 O 3 on fluoride vaporization CaF 2 –CaO–Al 2 O 3 -(Ce 2 O 3) slag is explained by its influences on the viscosity of slag and activity of components. • Fluoride vaporization behavior of CaF 2 –CaO–Al 2 O 3 -(Ce 2 O 3) slag under vacuum condition was investigated. [ABSTRACT FROM AUTHOR]

The development of high value-added products prepared by slag has been restricted by the severe damage to refractories occurring during SiO 2 –MgO-based slag melting. In the current study, the Al 2 O 3 –SiC–C refractories were selected to conduct static resistance tests with SiO 2 –MgO-based slag in air and reducing atmospheres. The results show favorable corrosion resistance but poor permeability resistance in both atmospheres. The poor permeability can be attributed to the cracking of brown fused alumina aggregates caused by volume expansion during the formation of magnesium aluminate spinel. In addition, a model of crack growth for the aggregate is proposed to illustrate the corrosion mechanism of the Al 2 O 3 –SiC–C refractories. It is indicated that the crack growth of the aggregate proceeds mainly along the normal direction based on the calculation of the radial and normal lengths of the crack. [ABSTRACT FROM AUTHOR]

Lightweight microporous magnesia aggregates with closed porosity of 6.2%, apparent porosity of 2.1% and median pore size of 2.36 μm were fabricated by introducing nano-sized ZrO 2 combined with magnesite decomposition and sintered at 1780 °C. The sintering properties and microstructure revealed that nano-sized ZrO 2 promoted the sintering and formation of closed intragranular pores by increasing abundant crystal defects and producing cation vacancies (V M g ' ' ) raising the migration rate of grain boundaries, which induced a change in porosity type from large open pores to small closed pores. The nano-sized ZrO 2 changed the bonding of magnesia grains from single CaO–SiO 2 –MgO phases bonding to composited CaO–SiO 2 –MgO phases-CaZrO 3 phases bonding, significantly enhancing the slag penetration resistance. The closed porosity played a more important role in reducing the thermal conductivity compared with total porosities. The microporous magnesia aggregates and thermal conductivity of 8.994 W (m K)−1 at 800 °C exhibit potential for application in wear lining refractories. [ABSTRACT FROM AUTHOR]

[Display omitted] • Micro-closed pores relieved the thermal stress and deflected cracks propagation. • The transgranular cracks propagation owing to CaZrO 3 consumed great fracture energy. • The synergistic effect of pores and CaZrO 3 increased the interfacial dihedral angle. • Slag penetration and thermal shock resistances were enhanced by microporous magnesia. As the low thermal shock and slag-penetration resistance of the magnesia castables cause the premature failure of tundish flow-control devices leading to the pollution of steel, the microporous magnesia with high closed porosity and intergranular CaZrO 3 phase was utilized for simultaneously enhancing the high-temperature performance. The thermomechanical stress and slag corrosion tests indicated that since the micro-closed pores effectively relieved the thermal stress and CaZrO 3 absorbed massive crack-propagation energy, the cold modulus of rupture and residual strength ratio respectively reached 14.4 MPa and 73.4% after thermal shock cycles, nearly half higher than that of the fused magnesia based castables. Meanwhile, the synergistic effect of micro-closed pores and intergranular CaZrO 3 phase significantly reduced the slag-wettability, improved the interfacial energy and dihedral angle, leading to the decline of slag penetration indice (decreased by ∼34.8%). This study suggests a potential approach to generate new magnesia based castables in tundish for making clean steel. [ABSTRACT FROM AUTHOR]

• Slag corrosion experiments were performed under a static magnetic field at 1400∼1600 °C. • The slag corrosion resistance of lightweight magnesia with micro- and nano-sized pores was analyzed. • A static magnetic field can enhanced the slag corrosion resistance of lightweight magnesia-based refractories. Slag corrosion resistance of lightweight magnesia-based refractories with micro/nano-sized pores under a static magnetic field is investigated. They exhibited excellent slag resistance under static magnetic field of 8.5 mT with an isolation layer composed of solid phases formed at the refractory/slag interface. The static magnetic field generated a "magnetic brake effect" that suppressed the infiltrating flow of the molten slag and decreased the dissolution rate of MgO grains. Moreover, it also limited the thickness of the isolation layer by reducing the extent of the refractory-slag interaction, which can be applied to further improve the slag resistance of refractories. [ABSTRACT FROM AUTHOR]