Inclusion Removal Efficiency Research Articles

Effect of Pouring Techniques and Funnel Structures on Crucible Metallurgy: Physical and Numerical Simulations

In the planar flow casting process of amorphous strips, the flow behavior of molten metal and the inclusion content in the crucible are crucial to the morphology and magnetic properties of the material. This study conducts a comparative analysis of the effects of non-immersed and immersed funnels, as well as various funnel structures, on the fluid flow and inclusion removal efficiency in the crucible by integrating numerical and physical models. The findings reveal that for the same pouring flow rate, the diameter of the liquid column in non-immersed pouring conditions is smaller than that of the funnel outlet, leading to a faster injection flow velocity. As a result, the melt in the crucible is subjected to severe impacts, accompanied by an increased possibility of slag entrapment. Conversely, immersed pouring substantially reduces the velocity of the molten metal at the funnel outlet, thereby extending the residence time in the crucible and diminishing the volume of the dead zone. Additionally, the molten metal backflows due to the negative pressure formed in the inner chamber of the funnel. The design of a trumpet-shaped funnel increases the effective volume while reducing the height of the backflow fluid, consequently reducing the velocity of the molten metal at the funnel outlet and prolonging the residence time. Compared to the conventional pouring process with the non-immersed funnel, the outlet velocity is reduced from 1.1 m/s to 0.12 m/s by adopting the immersed funnel with an inverted trapezoidal trumpet structure. This reduction results in a stable flow state, a 9.69% reduction in the dead zone volume fraction, and a 22.96% increase in average inclusion removal efficiency. These improvements demonstrate that a crucible funnel with a well-designed structure and the implementation of an immersion process can significantly improve the metallurgical effects in the planar flow casting process.

Cleansing the molten steel due to the dispersed in situ phase induced by the composite sphere explosion reaction II. Inclusion removal

Industrial trials have been carried out on the base of the former experimental research and the CaCO3 proportion in composite sphere, feeding amount, and composite sphere feeding mode have been investigated. The fine inclusion removal mechanism has been analyzed. The results indicate that feeding composite sphere in RH degasser is a novel process and small inclusion in the molten steel can be removed effectively. CaCO3/CaO ratio in composite sphere has a great effect on the inclusion removal efficiency. More feeding times and a little feeding amount can increase the composite sphere utilization efficiency. Compared with the conventional inclusion removal technology, the number density of the oxide inclusion can be decreased to a lower level and the inclusion size becomes much finer. Using this novel process, T.O. in the as-cast slab can approach to 6 ppm.

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.

Flow Behavior of Liquid Steel in Fewer Strands Casting of Six-Strand Bloom Tundish

In continuous casting, it is common to close single or multiple submerged nozzles of multi-strands tundish to adapt to production rhythm due to insufficient liquid steel or equipment failure. However, the closure of the nozzle will change the flow field in the tundish and further affect the removal efficiency of inclusions in the tundish. For this reason, based on numerical simulation, the flow behavior of liquid steel and the removal of inclusion in tundish with different nozzle closed were studied, and the optimal nozzle closing scheme was obtained, which provided a basis for the selection of nozzle closing in tundish. At the same time, the gas curtain is set in the tundish to alleviate the negative effects such as the increase of dead zone caused by closing nozzle. The results show that the removal rate of inclusions with sizes 10, 30, 50, 70, and 90 μm change from 12.4%, 39.1%, 74.2%, 93.3%, and 95.6% to 14.7%, 36.4%, 76.4%, 85.3%, and 93.8%, respectively. The volume of the tundish dead zone is increased after closure of nozzle, the dead zone of the tundish is improved when the gas is installed, and the dead zone volume was reduced from 14.8% and 16.4% to 13.9 and 14.1%.

Investigation of Inclusion Removal at Steel–Slag Interface toward a Small‐Scale Criterion for Particle Separation

Interactions between inclusion particles and the steel–slag interface directly affect the inclusion removal efficiency and thus influence steel cleanliness. Herein, the three‐phase interactions are resolved using the volume of fluid (VOF) method coupled with a dynamic overset mesh. The simulation is able to capture the instantaneous interface deformation and predict the particle motion driven by capillary force. The model validity is first demonstrated by comparison with analytical results. Then, a parameter study is conducted to examine the most influential factors governing the separation process. The results show that the system's wetting condition and the slag viscosity have a decisive effect on particle behavior at the interface (separation or entrapment). From an energy perspective, a better wetting condition generates more energy sources, and the interfacial energy is efficiently transformed into the particle's kinetic energy within a less viscous environment, thus leading to better separation. Besides, a criterion for predicting particle behavior is developed based on a modified Reynolds number (, relevant to fluid properties) and a quantity related to particle dynamics (ζ). The current work brings insights into the interfacial phenomenon during inclusion removal, which can be incorporated into large‐scale simulations to estimate the removal efficiency more accurately.

Development of model-based simulation and optimization software for electron beam melting and refining

In this paper the development of a software for electron beam melting and refining (EBMR) of different materials is presented. It has the following functional characteristics: simulation of the temperature distributions in the cast ingots, investigation and optimization of the form of the liquid pool during the process of EBMR and estimation of the inclusion refining rates, depending on the EBMR process parameters. The temperature distributions in the cast ingots are simulated by the implementation of quasi steady-state two-dimensional heat model and three-dimensional time-dependent thermal model for different refined metals. Empirical models are estimated, integrated in the developed software and used for the investigation of the molten pool geometry parameters, the content of impurities after the electron beam refining process, refining rate, overall inclusion removal efficiency and the material losses. The influence of EBMR process parameters such as electron beam power, casting velocity, refining time, and electron beam radius are considered. Multicriterial optimization software functions can be implemented for solving concrete technological requirements for each practical use-case.

Simulation of Fluid Flow and Inclusion Removal in Five-Flow T-Type Tundishes with Porous Baffle Walls

To solve the instability of liquid steel in the continuous casting process and the inconsistent flaw detection of heavy rail steel, steel flow control was studied numerically in a tundish with a porous baffle wall by using the fluid dynamics software Fluent. The opening plan of the baffle wall was improved through orthogonal optimization of the design of the holes in the porous baffle wall. The test condition was set to a left inclination angle of α1 = 22°, a right inclination angle of α2 = 48°, an upward elevation angle of β = 30°, and an aperture of d = 70 mm. The simulation results of the optimization scheme showed that the uniformity of the flow and temperature fields had been significantly improved, and the flow in each strand became consistent. The maximum temperature difference was 21 K in the tundish, and the maximum temperature difference of three outlets was only 1.7 K. Dead zone volume was reduced by 10.0% compared to the original tundish, and plug flow volume was increased by 14.2%. Comparing the removal efficiency of Al2O3 inclusions of different size, the results showed that the removal efficiency of 10 μm and 30 μm smaller inclusions was above 87%. The removal rate of ≥50 μm larger inclusions also remained about 95%.

Carbides refinement and mechanical properties improvement of H13 die steel by magnetic-controlled electroslag remelting

The effect of an axial static magnetic field (ASMF) on the carbides and mechanical properties of electroslag remelted H13 die steel was studied in current work. Optical microscope (OM) and scanning electron microscope (SEM) were used to analyze the solidification structure and carbide morphology of electroslag remelting (ESR) ingots. The FEI Aspex Explorer was utilized to detect the inclusions in H13 ESR ingots. Compared with conventional ESR, the application of ASMF in this study made the metal molten pool shallower and flatter, resulting in shorter local solidification time and uniform distribution of solute atoms, which alleviated the element segregation degree, and further inhibited the formation of primary carbides. The magnetic-controlled electroslag remelting (MC-ESR) process not only refined the dendrite structure (tended to grow parallel to the ingot axis) and the carbides, but also improved the inclusion removal efficiency and mechanical properties of H13 ESR ingots.

Multi‐Stage Enhanced Removal of Inclusions During Electroslag Remelting Process by a Static Magnetic Field

An axial static magnetic field (ASMF) is superimposed during the electroslag remelting (ESR) process to regulate the inclusion removal (GCr15 bearing steel) in the current study. After applying a 50 mT ASMF, the metal pool of the ESR ingot becomes shallower and the solidified dendritic structure tends to grow axially, together with a higher inclusion removal efficiency. The number of inclusions in ESR ingot decreases, and the inclusion with larger size (>10 μm) is almost eliminated. By tailoring the morphology of the liquid melt film (LMF), droplet, and metal pool, the ASMF applied in this study strengthens the kinetic conditions (inclusion migrated to slag/metal interface) for the inclusion removal, thus realizing the multi‐stage enhanced removal of inclusion during ESR process.

Numerical Investigation on Motion and Removal of Inclusions in Continuous Casting Tundish with Multiorifice Filter

A fluid–solid‐coupled numerical model is established on the motion and removal of inclusions in the continuous casting tundish with a multichannel filter. The flow field, heat transfer, and motion of inclusions in continuous casting tundish are simulated. The erosion of the lower part of the weir and filter is the most serious; at the casting speed of 2.2 m min−1, the maximum displacements in the upstream and downstream directions are 4.25 and −3.81 mm, respectively. The casting speed effect on the flow pattern and removal of inclusions is investigated. The weir and filter erosion increases with increased casting speed, the total removal efficiency is raised, and the dead zone fraction is reduced. After the casting speed exceeds 2.2 m min−1, the total removal efficiency of inclusions starts to decline. When the casting speed is raised from 1.4 to 3.0 m min−1, the share of inclusions removed by the filter drops from 8.2 to 2.5%, which is nearly 70%.

Motion and removal behavior of inclusions in electrode tip during magnetically controlled electroslag remelting: X-ray microtomography characterization and modeling verification

• Detailed 3D microtomography characterizations of inclusions in electrode tip are performed. • Motion/removal behavior of inclusions in electrode tip are clarified based on experimental results and simulation verification. • The number and size of the inclusions in LMF are decreased due to the applied ASMF. • The mechanism is that the ASMF enhances the kinetic conditions for inclusion migrating to LSI and removal in LMF. Detailed three-dimensional (3D) microtomography characterizations of inclusions in electrode matrix, mushy zone (MZ) and liquid melt film (LMF) were performed to elucidate the motion and removal behavior of inclusions in electrode tip during magnetically controlled electroslag remelting (MC-ESR) process. A transient 2D numerical model was also built to verify the experimental results and proposed mechanisms. The number and size of inclusions exhibited an obvious increasing trend from edge to mid region in LMF, while remained almost the same in electrode matrix and MZ. The inclusions in LMF migrated from edge to mid region of LMF, accompanied with removal process. In addition, the kinetic conditions for inclusion migrating to LMF/slag interface (LSI) were enhanced during MC-ESR process, thereby improving the inclusion removal efficiency in LMF. This work highlights the 3D characterization and motion/removal mechanisms of inclusions in electrode tip, as well as sheds new light on preparing high purity materials.

Oxygen distribution between phases during ladle processing of aluminum killed bof steels

The modern state of secondary metallurgy is characterized by the sustainable development of technologies that ensure high metal quality by reducing the number of non-metallic inclusions, the which is closely related to the oxygen content in steel after smelting. Therefore, the issues of regularities of oxygen distribution between phases at the stage, BOF - CCM. Purpose. The aim of the research was to determine the conditions of redistribution of oxygen dissolved in the metal depending on the stages of steel processing, to determine the degree of approach of deoxidation processes to thermodynamic equilibrium. Methodology. Research was carried out in industrial scale. Steel grades 34Cr and 36CrB were smelted in BOF of 170-t capacity. Processing of crude steel was carried out in a LF unit with further vacuum degassing and wi thout it and transfer of steel to CCM. At each stage of steel treatment, metal and slag samples were taken using an automatic sampler to determine the chemical composition, and the temperature. Oxygen content were monitored using a "Celox" analyzer. Findings. The carried-out studies showed that before the end of metal processing in the ladle, it is possible to detect individual reoxidation processes caused by unwanted ingress of oxygen from the air and from ladle slag oxides. Accor ding to calculations, in the second half of processing in the ladle and during casting, there is a slight deoxidation of steel with aluminum due to a decrease in temperature. Even if during this time due to the exchange reaction between steel and slag, a small amount of Mn and Si is recovered from the ladle slag, while its composition is practically constant throughout the period of steel processing in the ladle, while the metallurgical reactions proceed in the region of thermodynamic equilibrium. Originality. It has been determined that oxygen activity in steel varies unevenly over time and decreases to 3 ppm by the end of treatment in the ladle. While in each case it is in the Fe – a[O] – Al system near the calculated values of thermodynamic equilibrium. Practical value. The use of the obtained regularities makes it possible to obtain the specified content of aluminum in steel for the studied assortment and to predict the burning of deoxidizers and alloying elements, ensuring the reliability of obtaining the required chemical composition of steel with a high degree of purity. Key words: reoxidation, deoxidation, oxygen activity, slag, metal, non-metallic inclusion After blowing end in the converter, the oxygen activity in steel is in the range of 1000-1500 ppm [1-3]. After tapping from the vessel to a teeming ladle, the oxygen content in the metal is reduced by secondary metallurgy processes in order to provide high-quality of continuously cast billets and high purity of steel. At this stage steel reaches necessary temperature and chemical composition. Important for theory and practice are patterns of oxygen distribution between phases at each stage of secondary metallurgy, studied directly under production conditions. This distribution determines the removal efficiency of harmful impurities, non-metallic inclusions and gases from the steel. It is advisable to compare the measured oxygen contents with equilibrium states, which can be easily achievable in practice, and their calculation can be carried by metallurgical scientists.

Numerical study of influence of casting speed on fluid flow characteristics in the four strand tundish

Steel maker companies attempt to achieve high production quality and decrease production costs due to high competition of the global steel industry. Steel cleanliness plays a significant role in the steel quality which is the key success factor for the steelmaker. In order to optimize the steel cleanliness in the continuous casting process, flow characteristics were studied to enhance the inclusion removal efficiency in four strand tundish. The purpose of this research is to study the effect of casting speed on the flow characteristics of molten steel inside a four-strand tundish. The investigation was carried out by using the commercial computational fluid dynamic (CFD) software ANSYS 18.2. A 1:3 water model tundish based on process parameters from Millcon Steel PLC were employed in this study. The simulation results were validated with the physical water model. The residence time distribution (RTD) curves were applied to analyze the flow characteristics of the tundish. The results of this study show the different casting speeds have an effect on the flow characteristics inside the tundish. The start point of RTD curve of the flow in the tundish with casting speed of 3.0 m/min is the shortest amongst all casting speeds used (1.7, 2.0, 2.3 and 3.0 m/min). A short time period of the start point of RTD curve increases the chance of inclusion contamination in the casting mould and leads to low quality products. Furthermore, the outlet positions affect the minimum residence time of RTD curves and the tracer concentration directly. The RTD start point of the middle outlet located close to the inlet position is faster than that of the far outlet located far from the inlet. The results obtained from the study contributes to the optimization of productivity and quality of the example plant.

Physical and mathematical modeling of inclusion behavior in a tundish with gas curtain

Gas injection in the tundish has been considered as an alternative to optimizing inclusion removal from steels. In the present study, physical and mathematical modeling were used to investigate the effect of gas injection in the tundish on the inclusion removal efficiency. The physical model is a 1/3 reduced scale of an industrial two-strand tundish of 40 tons. The inclusion removal efficiency was quantified using the APS III probe, which counts particles leaving the tundish during the test. Different locations for the gas injection plug were evaluated. Additionally, a mathematical model was developed using commercial CFD software CFX. The predictions of the mathematical model were validated by the physical model results, comparing the efficiency of inclusion removal. The proposed model includes a new boundary condition to describe the behavior of the particles at the free surface, implemented by a special subroutine. The model enabled the identification of appropriate conditions: plugs located at 0.56 or 0.84m from the tundish inlet with gas injection with the flow rate of 3NL/min.

Microstructure Evolution and Mechanical Properties Improvement in Magnetic-controlled Electroslag Remelted Bearing Steel

The transverse static magnetic field (TSMF) was introduced into the electroslag remelting (ESR) process to produce GCr15 steel ingots and the microstructure, non-metallic inclusions, chemical composition and mechanical properties of the ingots were analyzed to investigate the effect of TSMF during the ESR process. The transverse section of the ingots indicated that the application of a 130 mT static magnetic field resulted in a refined dendritic structure. The coverage ratio of the homogeneous crystallites area in the center of the transverse section increased to 52%. The metallic solid-liquid interface with different magnetic flux density (MFD) was recorded during ESR process. The depth of the metallic molten pool was 44.2 mm without the TSMF. When a 130 mT TSMF was applied, the molten pool became noticeably shallower (14.2 mm). And the oxide inclusions count in the scan area of 5.117 mm2 decreased to 239 from 1212. When the TSMF implemented, the tensile, friction and wear and Rockwell hardness properties of ingots showed a significant improvement. These results showed that the application of TSMF during the ESR process of GCr15 steel not only refine the dendritic structure, but also improve the efficiency of inclusion removal and mechanical properties.

Enhancement of removing inclusions from liquid melt film during the ESR process assisted by a static magnetic field

Magnetic-controlled Electroslag Remelting (MC-ESR) process has been proposed to improve the inclusion removal efficiency in recent years. In this study, the effects of transverse static magnetic field (TSMF) on liquid melting film (LMF) and inclusion removal during this period in ESR process of GCr15 steel were studied by a series of MC-ESR experiments. The thickness of the characteristic position of LMF was reduced by 27.2%∼80.5% due to the accelerated dynamic process (LMF aggregating to form droplet and droplet falling) after applying a 65mT TSMF. In addition, the kinetic conditions for inclusion removal in LMF were also enhanced by the TSMF, leading to decrease in the number and size of inclusions in LMF. A numerical simulation of the inclusion migration in LMF was then carried out to verify the experimental results to some extent.

Effects of Axial Static Magnetic Field on Inclusions Removal in the Liquid Melt Film During Electroslag Remelting Process

Magnetic-controlled Electroslag Remelting (MC-ESR) process has been proposed to improve the inclusion removal efficiency in recent years. In this study, the effects of axial static magnetic field (ASMF) on liquid melting film (LMF) and inclusion removal during this period in ESR process of GCr15 steel were studied by a series of MC-ESR experiments. The thickness of the characteristic position of LMF was reduced by 18.6 to 90.3 pct when a 50 mT ASMF was applied. The number and size of the inclusions in LMF were also decreased. In addition, the mechanisms of LMF thinning and inclusion removal efficiency improvement enhanced by the ASMF were interpreted in detail. Furthermore, a numerical simulation of the inclusion migration in LMF was also carried out to support the proposed mechanisms to some extent.

Removal of Alumina Inclusions from Molten Steel by Ceramic Foam Filtration

The efficiency of removal of solid alumina inclusions by filtration and the distribution of inclusions captured through the thickness of the filter was investigated for an aluminum killed 316 stainless steel casting. A mold design was developed using modeling software to produce two castings that fill simultaneously, one with a filter and the other without a filter. The design was optimized to produce the filtered casting and unfiltered casting from a single ladle pour, while also matching the fill rates and avoiding turbulence and reoxidation during pouring. Samples from the filters and the castings were analyzed using an SEM with EDS and automated feature analysis to measure the efficiency of inclusion removal for a 10 ppi zirconia foam filter. Results showed that inclusion removal efficiency depends strongly on the initial inclusion concentration and that the alumina inclusions are captured within the filter at the filter web-steel interface. This study also documented that inclusion floatation inside the mold cavity plays a role in reducing the inclusion concentration in the casting. The distribution of alumina inclusions captured through the filter thickness was quantified using elemental mapping and the inclusion distribution was found to decrease exponentially, following first-order capture kinetics.

Evolution of Nonmetallic Inclusions with Varied Argon Stirring Condition during Vacuum Degassing Refining of a Bearing Steel

In the current study, industrial trials are performed to investigate the effect of argon stirring conditions on nonmetallic inclusions of a bearing steel during vacuum degassing (VD). Three argon stirring modes, including strong stirring, moderate stirring, and weak stirring during the last 10 min of the high‐vacuum period, are compared. The removal fraction of >1 μm inclusions and >5 μm inclusions is the highest with the moderate stirring mode, reaching 15.7% and 42.2%, respectively. Inclusions of MgO·Al2O3 are easier to remove than CaO–Al2O3 and entrained CaO–Al2O3–SiO2 ones as MgO·Al2O3 inclusions have a higher coagulation coefficient, a higher contact angle, and a lower adhesion work between the inclusion and the molten steel. Meanwhile, the removal efficiency of inclusions in the bearing steel is in the order of Al2O3 > MgO·Al2O3 > solid CaO–Al2O3 > liquid CaO–Al2O3 and entrained CaO–Al2O3–SiO2. Liquid CaO–Al2O3 inclusions with >5 μm size originate from slag entrainment and can be efficiently removed from the molten steel by the moderate stirring mode.

Numerical Analysis of RTD Curves and Inclusions Removal in a Multi-Strand Asymmetric Tundish with Different Configuration of Impact Pad

To effectively remove non-metallic inclusions from the steel during the flowing in a five-strand asymmetric tundish, the novel configuration of the impact pad was developed. For analysis, complex numerical modelling in the programme ANSYS Fluent was used. The Lagrangian Discrete Phase Model of inclusion tracking was applied. The distribution of inclusions, with sizes ranging from 2 µm to 100 µm and density from 2500 to 3500 kg·m−3, was considered only through the shroud tube. The residence time distribution (RTD) curves and inclusion removal efficiency were used for evaluation of steady state steel flow character depending on internal configuration of a tundish with an impact pad in two design modifications (Modification 1—M1, Modification 2—M2). The preliminary results showed that in the case of asymmetric geometry plays a role the computational mesh independency. The assembly method with cut cell approach was satisfactory even when the tundish geometry was changed. The RTD curves with an M1 showed a huge dead volume in the tundish. In the case with an M2, the RTD curves are more or less uniform for all casting strands, and the removal of inclusions to slag increased from about 55% up to 70% in comparison with M1.