Inclusions In Molten Steel Research Articles

Dynamic interaction between refractory and low‐carbon low‐silicon Al‐killed steel

AbstractTo investigate the dynamic interaction between refining refractory and low‐carbon low‐silicon Al‐killed steel, the “refractory‐molten steel‐inclusion” system was analyzed using dynamic erosion experiments and the FactSage database. This study discussed the formation of interfacial layers between various refining refractories and molten steel, as well as the transformation of nonmetallic inclusions in steel. The findings indicate that the interaction between refractories and molten steel produces a distinct interface layer. The influence of various refining refractories on inclusions varies significantly. MgO‐C refractory promotes the formation of MgO·Al2O3 inclusions in steel, while Al2O3‐MgO refractory leads to the formation of SiO2‐MnO‐Al2O3 inclusions. Both Al2O3‐SiC refractory and Al2O3‐MgO‐C refractory result in Al2O3 inclusions with trace levels of MgO. Steel refined with Al2O3‐MgO‐C refractory has increased MgO content within Al2O3 inclusions but still does not reach the stoichiometric ratio of MgO·Al2O3. As the initial Al content increases, the influence of MgO‐C refractory inclusions becomes increasingly noticeable. The average MgO content within the inclusions rises with the reaction duration, achieving as high as 62.9%. The transition path of Al2O3 inclusions in molten steel follows “Al2O3→MgO·Al2O3→MgO.”

Effect of ladle slag composition on the cleanliness of Al-Ti deoxidized interstitial-free steel

The effect of slag composition on the cleanliness of Al-Ti deoxidized interstitial-free steel produced via basic oxygen furnace (BOF)-ladle furnace (LF)-Ruhrstahl-Heraeus (RH)-continuous casting (CC) process was investigated by the systematic samplings and analyses for four heats in a steel plant in China. Oxygen/nitrogen analyzer, automatic scanning electron microscope, field-emission scanning electron microscope, and energy spectroscopy analysis were used to analyze the variations of number, size, type, and morphology of inclusions in molten steel from RH to tundish, and X-ray fluorescence was used to analyze the slag composition. The relationship between slag composition and inclusion characteristics in molten steel was investigated. The effect of slag composition on the oxygen mass transfer from the slag–metal interface to liquid steel was also studied through a theoretical calculation. The results showed that the cleanliness of molten steel was greatly affected by the slag composition. The deterioration of steel cleanliness was mainly arisen from a serious reoxidation of molten steel by oxidizing components like (T.Fe + MnO) in top slag during RH refining process. A weak ability to absorb inclusions of top slag with high CaO/Al2O3 and CaO/SiO2 mass ratios was confirmed from the inclusions analyses. The size and number of Al2O3 inclusion clusters were larger, and Ti content in Al2O3-TiO x inclusions was higher from RH to tundish in the case of serious reoxidation. The reduction of FeO content and keeping the CaO/Al2O3 and CaO/SiO2 ratios at about 1.6 and 4–7, respectively, in top slag during RH refining process was beneficial to minimize the reoxidation of Al and Ti and increase the inclusion absorption ability of top slag.

Periclase-magnesium aluminate spinel ceramics filter with excellent purification efficiency on molten steel prepared from Mg(OH)2: Effect of fused MgO content

Reticulated ceramic filters are widely used in the field of steel purification to improve the quality of steel products. In this work, periclase-magnesium aluminate spinel ceramic filters with microporous MgO coating were fabricated by using Mg(OH)2 as raw material. The effect of fused MgO content on the microstructures, mechanical properties and filtration capacity of filters on Al2O3 inclusions in molten steel was comparatively studied. The results indicate that the particle packing and liquid phase sintering cooperated to promote the formation of neck connections between microporous MgO particles, which increased the cold compressive strength and thermal shock resistance of the filters. Furthermore, the results from the immersion test in molten steel demonstrate that an appropriate amount of high-temperature liquid phase and the relatively microporous structure of filter skeleton were favorable for filters to filtrate Al2O3 inclusion in molten steel. Overall, the filter with 30 wt% fused MgO had the best comprehensive performance with a cold compressive strength of 0.68 MPa, a residual retention of cold compressive strength after three thermal shock recycles of 79.07 % and a filtration efficiency of 79.06 % in reducing the total oxygen content of the steel.

Phase equilibria of CaO–Al2O3–CaO·TiO2 system at 1500 °C in hydrogen atmosphere

The phase diagram of CaO–Al2O3-TiOx system is of great importance in guiding the design of metallurgical slag systems for Al–Ti alloy steel, controlling Ti-bearing inclusions in molten steel, and regulating the mineral phase of vanadium-titanium magnetite. In the present work, the high temperature equilibration-quench technique was adopted, and the types and compositions of equilibrium phases were identified by Electron Probe Micro Analysis (EPMA) and X-ray diffraction (XRD). The isothermal section of CaO–Al2O3–CaO·TiO2 system at 1500 °C in H2 atmosphere was constructed for the first time. There are 7 three-phase fields, 10 two-phase fields, and a single liquid phase field. On this basis, according to the theoretical analysis of the crystal structure, the formation energy analysis based on first-principles calculations, and the related theories of defect chemistry, the formation mechanisms of CaTiO3 and Ca3Ti2O7 solid solution with were determined, respectively. Additionally, the experimental phase diagram was utilized to discuss the dissolution type and the equilibrium solubility of typical inclusions (Al2O3, Ti3O5, and CaO·TiO2) in Al–Ti alloy steel.

Evaluation of inclusion agglomeration behavior in molten steel based on the modified model of cavity bridge force

Inclusion agglomeration behavior in molten steel is a key factor that affecting steelmaking process and steel quality. In this work, the modification on the Laplace pressure of cavitation interaction between inclusions has been made according to the calculation model of cavity bridge force. The effects of the distance between inclusions, the diameter of inclusions, the surface tension of molten steel, and the contact angle between inclusions and molten steel on the cavity bridge force were quantitatively investigated by using this modified model. The results show that the contact angle between inclusions and molten steel has a significant influence on inclusions agglomeration. The inclusions cannot agglomerate by cavity bridge force when the contact angle is less than 90°. Subsequently, the agglomeration tendency of different inclusions was calculated and compared. The order of cavity bridge force and critical agglomeration distance of inclusions in molten steel is MgO·Al2O3 < CaO < MgO < Ti2O3 < AlN < Al2O3. Then the high temperature experiments were carried out to investigate the evolution of inclusions sizes in molten steel. It is found that the average size of Al2O3 is larger than that of AlN, which indicates that the agglomeration tendency of AlN inclusions is much weaker than that of Al2O3 inclusions. This calculation model can accurately evaluate the agglomeration behavior of inclusions and provide theoretical guidance for inclusions control.

Effect of steel-refractory reactions on inclusion modification in lanthanum-, cerium-, and yttrium-added steels

The reactions of rare earth elements (REEs) with refractory materials significantly affect their effective concentrations and inclusion modifications in molten steel. This study investigated the influence of steel-refractory reactions on the modification of inclusions in lanthanum-, cerium-, and yttrium-added steels utilizing three types of commonly used crucibles as smelting vessels. Steel-refractory reactions were found to strongly affect inclusions with different outcomes for smelting in MgO, Al2O3, and MgO·Al2O3 crucibles. The RE-crucible reactions affected the evolution and size of inclusions in molten steel by influencing the content of [Mg] and [Al]. The RE-MgO crucible reactions increased [Mg] content, leading to more MgO inclusions and a smaller average size. The RE-Al2O3 crucible reactions increased [Al] content, resulting in more REAlO3 inclusions and a bigger average size. The reactions of La, Ce, and Y with MgO·Al2O3 crucibles had varying effects on the evolution of inclusions. La and Ce selectively eroded the crucible, mostly reacting with the Al2O3 component and generating REAlO3 inclusions. In contrast, the slow reaction rate of Y with the crucible and the formation of the dense Y2O3 layer at the steel/crucible interface made it react almost simultaneously with both MgO and Al2O3 components, and the modification of inclusions was dominated by [Mg] rather than [Al]. The above conclusions provided more information on how the reactions between rare earth elements and refractory materials affected inclusions in rare earth steels during smelting. They also enriched the theory of inclusion control in steel and offered new controlling strategies.

Impact of functional coatings on microstructure and properties of periclase-magnesium aluminate spinel ceramic filter and its purification capacity on molten steel

Reticulated ceramic filters play an important role in the reduction of non-metallic inclusions in molten steel, which can improve the quality of steel products. In this work, periclase-magnesium aluminate spinel ceramic filters with Al2O3 and TiO2 functional coatings were fabricated by using microporous MgO powder, respectively. The effects of the functional coatings on their microstructure, properties and purification capacity on molten steel were studied. The filter with Al2O3 functional coating exhibited the best mechanical properties owing to the good rheological properties of the coating slurry, as well as the formation of in-situ spinel layer connection between the Al2O3 functional coating and the microporous MgO layer of the filter substrate. Compared with the filters without functional coating or with TiO2 functional coating, the filter with Al2O3 functional coating made more Al2O3 inclusions deposit on the filter surface by physical adsorption due to the same chemical composition between the functional coating and inclusions, which significantly improved the adsorption capacity of filter for Al2O3 inclusions in molten steel. Overall, the filter with Al2O3 functional coating had the highest cold compressive strength of 1.4 MPa, a residual retention of cold compressive strength after thermal shock of 65.71 % and an efficiency of 36.56 % in reducing the total oxygen content of the steel.

Effect of Silicon–Manganese Deoxidation on Oxygen Content and Inclusions in Molten Steel

In order to improve the cleanliness of steel, non-aluminum deoxidation processes have begun to replace aluminum deoxidation processes. Although the aluminum deoxidation process can reduce the oxygen content in steel to &lt;10 × 10−6, this deoxidation method causes fatigue failure resulting from the formation of large-grained spherical (Ds-type) inclusions composed of calcium–aluminate. It also tends to lead to nozzle blockage during casting. Given the above problems, this study conducted an in-depth investigation of silicon–manganese deoxidation. Thermal experiments and thermodynamic calculations were used to assess the impact of different Mn–Si ratios on the oxygen content and inclusion characteristics during the deoxidation process of molten steel with different initial oxygen contents. The experimental samples were analyzed using an oxygen–nitrogen–hydrogen analyzer, a direct reading spectrometer, and an automatic scanning electron microscope. After that, the samples were electrolyzed to observe the 2D morphology and 3D morphology of the inclusions using scanning electron microscopy. Finally, thermodynamic calculations were carried out using FactSage to verify the experimental results. The results indicated that, regardless of the initial oxygen content, silicon–manganese deoxidation maintained the total oxygen content at 35 × 10−6. It effectively managed the plasticization of inclusions in molten steel, predominantly yielding spherical silicates while minimizing Al-containing inclusions. Nevertheless, as the initial content of [O] increased, the size and density of the silicate inclusions in the steel also increased. An optimal point in the number and size of inclusions was observed with an increased Mn–Si ratio. Moreover, the combined utilization of silicon–manganese deoxidation, diffusion deoxidation, and vacuum deoxidation enabled ultra-low oxygen content control of molten steel.

Study on Influence of Rare Earth Ce on Micro and Macro Properties of U75V Steel.

Non-metallic inclusions in steel have great influence on the continuity of the steel matrix and the mechanical properties of steel. The precipitation sequence of Ce inclusions in molten steel is predicted by thermodynamic calculations. The results show that Ce content will affect the precipitation sequence of rare earth inclusions in molten steel, and the formation of CeO2, Ce2O3 and CeAlO3 will be inhibited with the increase in Ce content. Our laboratory smelted the test steel without rare earth additive and the test steel with rare earth Ce additive (0.0008%, 0.0013%, 0.0032%, 0.0042%). It was found that the MnS inclusions and inclusions containing Al, Ca, Mg and Si oxides or sulfides in the steel after rare earth addition were modified into complex inclusions containing CeAlO3 and Ce2O2S. The size of inclusion in steel was reduced and the aspect ratio of inclusion was improved. The addition of Ce also improved the grain size of U75V steel and significantly refined the pearlite lamellar spacing. After mechanical property testing of the test steel, it was found that when Ce is increased within 0.0042%, the tensile and impact properties of U75V steel are also improved.

Effect of types of calcium-containing alloy on non-metallic inclusions in high-Al steel

The influence of different calcium-containing alloys on inclusions in high-Al steel is investigated in the current study. The effects of SiCa, AlCa20, AlCa75 and FeSi alloys on the modification of solid inclusions in molten steel are compared, and the mechanism of inclusion evolution is revealed based on the non-uniform distribution of elements and the lattice mismatch between the inclusion particles. The results show that the Ca yield of FeSi alloy is 26%, which is significantly higher than that of other alloys (&lt;5%). In addition, the calcium treatment by FeSi alloy causes less aspiration of molten steel, which is conducive to avoiding the increase of AlN in high-Al steel. After calcium treatment, the primary Al2O3 particles in steel are transformed into CaO-Al2O3-CaS and CaO-Al2O3-MgO complex inclusions, while AlN can only be precipitated in the form of a single particle, or precipitated from the transformed CaO · 2Al2O3 oxide. In general, FeSi alloy has the best effect on the modification of Al2O3 inclusions, which can maximize the transformation of solid particles into liquid inclusions in steel liquid without introducing too much impurities.

Motion behaviour of solid inclusions at the steel–slag interface in high-Al steel

ABSTRACT In the steelmaking process of high-Al steel, solid inclusions will accumulate in the slag phase near the steel–slag interface, and it is crucial to eliminate the residual Al-containing inclusions in molten steel. In the present study, the film-rupture and drainage models were applied to clarify the characteristics of the inclusion detachment motion. The analysis of parameters was carried out and their impact on the inclusion motion was further discussed. It was found that the micro-size inclusions are prone to remain at the interface or rebound back into the steel. According to the models, the motion of the solid inclusion in the drainage stage is solely influenced by the steel density and the interfacial tension between steel and slag. The decrease of the steel–slag interfacial tension is beneficial to the transfer of the inclusions, while the low-density of the high-Al steel will promote the rebound of the inclusions.

Microstructure and properties of ceramic filter containing porous MgO coating and its filtration of Al2O3 inclusions in molten steel

Reticulated ceramic filters can be used to remove non-metallic inclusions in molten steel and improve the quality of steel products. In this work, three kinds of new reticulated ceramic filters were prepared by using spinel (MgAl2O4), ZrO2 and SiC reticulated ceramic filters as preforms, respectively, which were all coated with porous MgO coating on their surfaces. The effect of preform type on the phase composition, microstructures, mechanical properties and interaction with molten steel of the filters was studied. The results show that the filter fabricated by spinel preform exhibited the best mechanical properties, which related to the formation of better interface bonding between the spinel preform and the porous MgO coating. Compared with the filters containing ZrO2 and SiC preforms, the porous MgO coating on the surface of the filter containing spinel preform had the highest roughness, which significantly improved the contact area between the filter and the Al2O3 inclusions, thus promoting the adsorption capacity on Al2O3 inclusions. Overall, the filter with spinel preform had the highest cold compressive strength of 0.86 MPa and flexural strength of 0.96 MPa, excellent thermal shock resistance against to molten steel, as well as the best adsorption capacity on Al2O3 inclusions.

Formation and aggregation behavior of inclusions in Ni-based alloys with different Mg contents

Large non-metallic inclusions affect the mechanical properties and service life of nickel-based superalloys. This study investigates the effects of magnesium elements on non-metallic inclusions in K4169 nickel-based superalloys, exploring the formation mechanisms and aggregation relationships of the inclusions. Four gradients of the magnesium content were used to simulate the erosion of MgO refractories on inclusions in the vacuum induction melting of nickel-based superalloys. The observed inclusions mainly comprised MgO, TiN, MgAl2O4, and MgAl2O4–TiN composites. To study the formation mechanism of inclusions in Ni-based alloys with different Mg contents, the predominance diagram of Mg–Al–Ti–O inclusions in nickel-based superalloy systems was calculated using Factsage thermodynamics software and classical thermodynamics separately. The aggregation behavior of MgAl2O4 and MgO inclusions on the surface of molten nickel-based superalloys was observed in situ under a high-temperature confocal laser scan microscope. The capillary force acting on inclusions in nickel-based superalloys was calculated using the Kralchevsky–Paunov model (K–P model), the calculation was verified with experimental results, and the influencing factors were analyzed. The capillary force acting on inclusions on the surface of molten nickel-based superalloys weakened in the order of MgAl2O4 > MgO > Al2O3, which is the opposite of the order for the force acting on inclusions in molten steel. Minimizing the magnesium content in the alloy is crucial to preventing the formation of large inclusions in nickel-based superalloys, and the use of magnesium-containing materials in the smelting process should thus be avoided.

Transient evolution of non-metallic inclusions in molten high aluminum and high manganese steel contacting with slag and crucible: experimental investigation and FactSage macros modeling

In this work, high temperature experiments of high Al molten steel contacting with crucible and slag were performed to investigate the effect of crucible–slag–steel reaction on transient evolution of inclusions in the high Al molten steel. Processing samples were taken for the chemical compositions of steel and also the inclusions have been characterized by using SEM and EDS AZtec. FactSage macros have been applied to simulate the evolution of molten steel composition and inclusions in molten steel during steel-slag reaction and comparing to the experimental results. Due to the steel–crucible–slag reactions especially under the condition of the high Al molten steel, the Ca and Mg transferred from slag and crucible to the molten steel and then subsequently led to the evolution of Mg and Ca-containing inclusions. The Mg inclusions transferred from MgAl2O4 to MgO inclusions while Ca transferred to steel and modified MgAl2O4 at crucible interface to form CaMgAl2O5 phase. The FactSage macros modeling did agree reasonably well with the experimental results.

Research Status of Numerical Simulation of Nonmetallic Inclusions Interfacial Removal

The removal of inclusions in liquid steel has always been the focus of research, and the removal of inclusions is mainly through the process of the inclusion through the slag–steel interface. The inclusion removal process can be subdivided into inclusions in molten steel grew up rise, in steel–slag interface through separation, adsorb dissolved in molten slag 3 steps. Based on the microscopic process of three steps, this article summarizes and discusses the mathematical model, fluid mechanics model, and experimental verification method of inclusion removal process, analyzes limiting and influencing factors of inclusion removal process, and comprehensively describes the numerical simulation research progress of inclusion removal process. With the development of numerical simulation techniques and experimental equipment, some progress has been made in the study of interfacial removal of inclusions. The inclusion interface removal behavior can be analyzed semiquantitatively based on dynamic force model. The computational fluid dynamics model has advantages in studying the phenomena of the inclusion interface, and the phase‐field method is often used to simulate the removal process of the inclusion interface. The combination of water model and numerical simulation, high‐temperature laser confocal method, and other methods is of great help to explore the interface behavior of inclusions.

Effect of Slag Basicity on Non-Metallic Inclusions and Cleanliness of 15-5PH Stainless Steel

Few reports exist on the effect of the basicity of refining slag on inclusions in 15-5PH stainless steel and its removal efficiency. In this study, the effects of various basicities on the formation and removal efficiency of inclusions in molten steel were investigated. To investigate the effect of the chemical makeup of slag on the non-metallic inclusions in liquid steel, laboratory experiments and thermodynamic calculations were conducted on CaO-MgO-SiO2-Al2O3-CaF2 slag with various slag basicities and 15-5PH stainless steel. In the steel samples that had reacted with high-basicity slag samples, the magnesium content and aluminum yield were higher. Thermodynamic findings according to the ion and molecule coexistence theory showed that log (aSiO23/aAl2O32) decreases as slag basicity increases. This increases the Al concentration in liquid steel while decreasing the Si content. Log (aMgO3/aAl2O3) also increases, increasing the Mg content of the molten steel. With this, the transformation order of oxide inclusions is Al2O3 → MgAl2O4 → MgO. High-basicity slag increases the attachment of slag to inclusions and generates MgAl2O4 inclusions that are more easily adsorbed by inclusions in molten steel, thereby improving the cleanliness of molten steel.

Effect of Molten Steel Composition on Inclusion Modification by Calcium Treatment in Al-Killed Tinplate Steel

The effects of oxygen, magnesium, and sulfur content in Al-killed tinplate steel on the “liquid zone” of inclusion modification by calcium treatment were clarified through industrial experiments and thermodynamic calculation, and the characteristics of inclusions modification were studied. The results show that the inclusions in molten steel before calcium treatment are mainly Al2O3 inclusions. The inclusions in molten steel are CaO·Al2O3 after calcium treatment with a holding time of 10 min, while the inclusions are mainly 3CaO·Al2O3 with a holding time of 30 min. And 12CaO·7Al2O3 inclusions are observed in molten steel when T.O content increases to 40 ppm after calcium treatment with a holding time of 30 min. As the increase of T.O content from 10 ppm to 40 ppm, the difference between the upper and lower limits of the critical calcium content corresponding to the “liquid zone” increases from 5 ppm to 17 ppm. The increase of T.O content in molten steel will enlarge the “liquid zone” range of inclusion modification by calcium treatment, and increase the critical calcium content. With the increase of magnesium content in molten steel, the liquid phase ratio of inclusions modification by calcium treatment decreases. To obtain the liquid phase ratio of inclusions at least 50% in molten steel, not only the calcium content in steel should be strictly controlled, but also the magnesium content in steel should not be larger than 15 ppm. With the increase of sulfur content in molten steel, the “liquid zone” range of inclusion modification by calcium treatment becomes narrow.

Effect of Slag Adjustment on Inclusions and Mechanical Properties of Si-Killed 55SiCr Spring Steel

The effects of the Al2O3 content and basicity of CaO–SiO2–Al2O3–10 wt.% MgO refining slag on inclusions removal in 55SiCr spring steel were investigated. The viscosity of slag was studied using a viscometer, while the microstructure investigation involved using a water-quenching furnace and a Fourier-transform infrared spectrometer. The influence mechanism of the slag adjustment on inclusions was explored through thermodynamic calculations and kinetic analysis. The results indicated that the viscosity of the molten slag increased gradually with the content of Al2O3 increasing due to it increasing the degree of polymerization of the slag network structure, especially the [AlO4]5− and [Si-O-Si] structures. In contrast, the viscosity of molten slag experienced the opposite pattern, with the basicity of molten slag increasing. This was due to the fact that Ca2+ can significantly reduce the degree of polymerization of a slag network structure, especially the percentages of the [SiO4]4−, [AlO4]5− and [Si-O-Si] network structures. Finally, the changes in physical properties and structure of slag significantly affected the removal effect of the inclusions in molten steel. As a result, the number, size distribution, composition distribution and morphology of the inclusions displayed significant changes when the content of Al2O3 increased from 3 wt.% to 12 wt.% and the basicity of the slag gradually increased from 0.5 to 1.2.

Formation and Removal Mechanism of Nonmetallic Inclusions in 42CrMo4 Steel during the Steelmaking Process

Nonmetallic inclusions are harmful to the quality of 42CrMo4 steel. Therefore, the formation and removal mechanism of inclusions in 42CrMo4 steel during the steelmaking process is investigated by industrial trials. The characteristics of inclusions in specimens were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The main type of inclusions in molten steel in the early stage of ladle furnace (LF) refining is MgO-Al2O3 inclusions of irregular shape. CaO begins to appear in MgO-Al2O3 inclusions in the middle and late stages of LF. In the vacuum degassing (VD) refining stage, the inclusions in molten steel completely change into low-melting-point CaO-MgO-Al2O3 inclusions. The existence of [Mg] in molten steel is the fundamental reason for the formation of a large number of MgO-Al2O3 inclusions. Thermodynamic calculation shows that the refractory mainly transfers [Mg] to the liquid steel in the LF refining stage, whereas the slag mainly transfers [Mg] to the liquid steel in the VD refining stage. Kinetic calculation indicates that MgO-Al2O3 inclusions could be removed from molten steel faster than low-melting-point CaO-MgO-Al2O3 inclusions. The fundamental reason for the different removal behavior of the two types of inclusions is that the interfacial tension between the low-melting-point CaO-MgO-Al2O3 inclusions and the liquid steel is 50% lower than that of the MgO-Al2O3 inclusions.

Kinetics on Formation, Growth, and Removal of Alumina Inclusions in Molten Steel

Kinetics on Formation, Growth, and Removal of Alumina Inclusions in Molten Steel