Clean Steel Production Research Articles

Sustainable Production of Hydrogen through High-Temperature Molten Salt Electrolysis

The green and cost-effective production of strategic materials, including steel on a large scale is pivotal for fostering sustainable industrial development. Hydrogen emerges as a key component for clean steel production, but its sustainable and economical generation remains a barrier to widespread utilization in iron and steelmaking, as well as other applications. Conventional water electrolysis, a common method for carbon-free hydrogen production, faces economic challenges, equipment corrosion, and the use of expensive catalysts with high over-potentials, limiting its viability. Additionally, the transportation of hydrogen from the electrolyzer to utilization units poses cost and safety concerns. Addressing these challenges, this presentation discusses the electro-generation of hydrogen in high-temperature molten salts. The generated hydrogen can then be utilized in situ for the production of metals, alloys, and other commercially valuable materials. Leveraging high temperatures improves the thermodynamic potential and efficiency of the water-splitting process. Remarkably, electrolytic hydrogen produced in molten salts, operating at a potential of around 1 V, has the capacity to facilitate the production of a diverse range of materials such as Fe, Mo, W, Ni, and Co-based alloys. References K. Xie, A.R. Kamali*, Energy Convers. Manag. 251 (2022) 114980D. Qiao, K. Xie, A.R. Kamali*, Mater. Adv. 1 (2020) 2225K. Xie, A.R. Kamali*, Int. J. Hydrogen Energy 44 (2019) 2 4353A.R. Kamali*, RSC Advances 10 (2020) 36020A.R. Kamali, US2021009415 (2023)K. Xie, A.R. Kamali*, Green Chem.21 (2019)198

Effect of flow modifiers on the fluid flow characteristics in a slab caster tundish

ABSTRACT In a slab caster tundish, controlling liquid steel flow is of paramount importance for clean steel production. A conventional tundish design consists of a pouring box, a weir and a dam. To improve the overall performance of a 40 ton slab caster tundish, three different arrangements by incorporating additional flow modifiers have been examined. A three-dimensional steady state fluid flow model has been developed using a RANS (Reynolds-Averaged Navier-Stokes) approach. Subsequently, transient scalar-transport equations were solved to obtain the C-curve of the tundish. A different approach has been followed to evaluate the inlet boundary condition to mimic the process conditions more accurately. The CFD predictions were validated with the results of the water model. Mean residence time, dead volume fraction and flow structures have been considered for evaluating tundish performance. All the proposed configurations have shown improvements in comparison to the base case. The mean residence time of the fluid was found to be the highest for the case having two pairs of weir and dam. However, the insights derived from the flow structures specifically plug flow in zone 2 and near the tundish outlet region suggest that that having a single weir and two dams is the optimal choice.

Effect of carbon nanofibers fabricated from electrospun PAN precursors on the characteristics and densification of MgO–CaO ceramic systems

MgO–CaO composites are basic materials with high melting points, high chemical resistance to alkaline environments, clean steel production, environmental friendliness, and abundant sources. In the current work, carbon nanofibers (CNFs) with diameters between 150 and 270 nm were prepared at different temperatures (up to 1200 °C) by carbonization of electrospun polyacrylonitrile (PAN) precursors. Then, the MgO–CaO composites were prepared in two steps. First, 3 wt% CNFs carbonized at different temperatures were added to the composite to determine the optimal carbonization temperature. Subsequently, the physical properties (apparent porosity and bulk density) and mechanical properties (flexural strength (FS) and cold crushing strength (CCS)) of the MgO–CaO-CNF composites were investigated. X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDS), and thermogravimetric analysis (TGA) were used to analyze the composition, morphology, and structure of the CNFs powders and composite samples. Based on the results obtained, such as the percentage graphitization, length, average diameter, and morphology of the CNFs, 1000 °C was determined as the appropriate carbonization temperature for the next steps of this study. In a second step, the CNFs synthesized at 1000 °C were added to the MgO–CaO with different wt% (0, 0.5, 1, 1.5, 2, 2.5, and 3 wt%). It was found that by adding CNFs (up to 1.5 wt%) into the MgO-CaO composites, the physical properties increased due to the improvement of densification, and mechanical properties improved due to the activation of reinforcing mechanisms, the reduction of surface defects and the creation of a dense body. However, these properties decreased from 1.5 to 3 wt% due to the agglomeration and poor dispersion of the CNFs. Finally, the results illustrated that adding CNFs, even in small amounts, significantly improved the features of MgO-CaO compounds; the ideal content was 1.5 wt% CNFs.

Advancements in the Understanding of Single‐Bubble Dynamics: Integrated Experimental and Simulation Studies

Because of wake instability, bubbles always ascend along an unstable path, which is not considered when simulating their movement in steel refining and continuous casting systems. Utilizing the 3D shadow image method, a quantitative characterization of the bubble trajectories is conducted to establish a bubble path oscillation model considering the zigzag lateral movement of bubbles due to asymmetric wake shedding. This model is incorporated into a rectilinear bubble motion model within the Lagrangian framework and then used to simulate the free ascent of single bubbles within the 2.15–2.55 mm range. The predicted bubble ascent velocities and trajectories agree well with the experimental. The spatial position, velocity, acceleration, forces, volume swept by bubbles, and bubble residence time are discussed. The results shown that the dominant force in the horizontal direction is the lateral force, followed by the drag and virtual mass force. Compared to the rectilinear path model, the volume swept by bubbles with initial diameters of 2.15, 2.25, 2.34, 2.45, and 2.55 mm in this model increases by 30.8%, 32.0%, 34.0%, 31.5%, and 29.6%, respectively. These findings help accurately predict the path of bubbles and also may contribute to a better understanding of bubble dynamics in bubble metallurgy and clean steel production.

Effects of YSZ and CA6 additives on densification and thermal shock resistance of Al2O3-MgO-CaO-Y2O3 refractories

To achieve high-quality and stable production of modern clean steel, novel Al2O3-MgO-CaO-Y2O3 refractories with enhanced sintering properties and thermo-mechanical properties were synthesized by introducing YSZ and CA6 as the reinforcers. A sintering reaction mechanism involving the Al2O3-MgO-CaO-Y2O3 quaternary system is proposed. The results show that the sintering process in the Al2O3-MgO-CaO-Y2O3 quaternary system was characterized by the sequential formation of Al5Y3O12→YAlO3→Y4Al2O9→Y2O3 in three distinct stages, resulting in the predominant phases of Al5Y3O12 and MgAl2O4. The YSZ addition on Al2O3-MgO-CaO-Y2O3 refractories promotes the complete reaction between Y2O3 and CaAl4O7, fostering the formation of additional Al5Y3O12, which significantly enhances the densification, leading to improvements in both compressive strength and thermal shock resistance. The addition of CA6 promotes the generation of more Al5Y3O12, which forms numerous pores during the three stages of the sintering process, and the distribution of these pores is uncontrollable. Therefore, based on the sintering reaction mechanism of the Al2O3-MgO-CaO-Y2O3 quaternary system, a low-cost and enforceable reinforcement strategy for Al2O3-MgO-CaO-Y2O3 refractories is proposed, which is expected to focus on the application of YSZ in Al2O3-MgO-CaO-Y2O3 refractories for clean steel smelting.

Simulation of the effect of continuous casting tundish filter on removing inclusions in steel

The control of inclusions in clean steel production is one of the key processes and a key factor determining the quality of high-end steel materials. The inhomogeneous hydrodynamic equations have been numerically solved to obtain a transient and multiphase field inside the caster tundish with filter to predict the inclusion movement track and percentage of inclusion removal during continuous casting process. The simulation result is validated with the samples taken during casting continuous process in X steelworks. The method of bulk-sample-electrolysis is taken to analyze the percentage of inclusion removal of the samples. The results imply: the inclusions through the filter are influenced on velocity and separated from liquid steel with high turbulence. Thus the inclusions’ residence time in tundish is prolonged, which causes the probability of inclusion removal increasing. The fluctuations on percentage of inclusion removal are found when the diameter of inclusions is less than 80μm. However, the fluctuation is not so severely for the inclusions of more than 100μm. The percentage of inclusion in tundish as 100 tones remaining in ladle is larger than that as 200 tones remaining in ladle. The percentage of inclusion removal is proportional to time. The filter can reduce the irregular inclusions to improve the quality of product.

Reoxidation Phenomena of Liquid Steel in Secondary Refining and Continuous Casting Processes: A Review

This review article reports the critical issue of reoxidation in clean steel production during secondary refining and continuous casting processes. Reoxidation presents substantial challenges to process stability and final product quality. Various sources of reoxidation, including exposure to oxidizing gases, reducible oxides in slag and refractories, and the presence of ferroalloys are explored. Fundamental reactions and their consequences, such as changes in steel composition, inclusion composition/morphology, and the formation of reaction products at the interface between liquid steel and refractory materials, are reviewed. High oxygen partial pressure on the refractory side is identified as a significant factor, particularly in tundish and continuous casting processes. To address reoxidation effectively, the review discusses modeling approaches like computational fluid dynamics and thermodynamic/kinetic modeling. In the industrial context, reoxidation in the tundish is mainly attributed to open‐eye formation in the tundish flux and reducible oxides like SiO2 in an insulating cover powder, for example, rice hust ash. Maintaining precise tundish flux control is crucial for steel cleanliness. In conclusion, this review highlights the multifaceted nature of reoxidation challenges in clean steel production. A comprehensive understanding of reoxidation mechanisms and the implementation of effective strategies are essential for achieving cleaner steel production.

Physical and chemical calculations of steelmaking processes and predictive models for the production of clean steel

The results of physicochemical calculations of steelmaking processes for the production of clean steels deoxidized with aluminum are presented. The efficiency of the calculations was achieved using as the main scientific idea the position on the leading role of the oxidation potential in the metal – slag – gas system, while controlling the external supply of oxygen from the atmosphere, materials, slag and refractories. The advantage of this idea lies in the fact that thanks to it it provides a quick identification of critical points in developed and existing technologies, and determines effective ways to solve emerging quality problems in clean and ultra-clean steels. An approach is considered to improve the technology of clean steel production, including elements of mathematical and thermodynamic models, as well as algorithmic approaches for building static models using machine learning technology to improve efficiency in steelmaking technologies. For the application of the presented approach it is necessary to prepare the data set before-hand, as well as to carry out the interpretation of the results of machine learning, based on fundamental laws and physical and chemical processes occurring in steelmaking production. As a result of the thermodynamic calculations performed in the STM program, measures were developed for the production of clean steels. On the examples of the production of thin slabs and billets search and confirmation of significant technological parameters in the formation of steel-making defects due to non-metallic inclusions was carried out using methods of in-depth analytics and machine learning

Numerical Simulation of Bubble Size Distribution in Single Snorkel Furnace (SSF) with Population Balance Model (PBM)

Single Snorkel Furnace (SSF) vacuum refining furnace is a novel external refining equipment for high clean steel production. RH is a molten steel refining technology developed by Rheinstahl-Heraeus company. Compared with the traditional RH furnace, the SSF furnace has the advantages of a simple structure, high refining efficiency, and low production cost. However, because the upward flow and the downward flow are in a single snorkel, the flow phenomenon is more complex than that in the RH device. Therefore, the gas–liquid two-phase flow law in SSF furnaces plays an important role in improving equipment efficiency and accurate control. In addition, the evolution and movement behavior of bubbles have an important influence on the two-phase flow. In this study, the Population Balance Model (PBM) model is employed to study the bubble properties, taking into account the effect of bubble coalescence and breakup on the flow field. The simulation results with this model are consistent with the experimental values, and the comparison with the results of the model without the PBM is revealed to be closer with less error. The results show that with the PBM model the flow field is more homogeneously distributed, the flow velocity is more stable, and the area distribution of the upward flow and downward flow in the snorkel is more symmetrical. In the case of this study, as the fluid level rises, the bubble diameter will increase due to the decrease in hydrostatic pressure.

Design Improvement of Four-Strand Continuous-Casting Tundish Using Physical and Numerical Simulation.

The flow pattern is vital for the metallurgical performance of continuous casting tundishes. The purpose of this study was to design and optimize the flow characteristics inside a four-strand tundish. Numerical simulations and water model experiments were validated and utilized to investigate the flow behavior. The effect of different flow rates in the original tundish was evaluated; two modified retaining walls and a new ladle shroud were designed for optimization. The molten steel inside the original tundish tends to be more active as the flow rate increases from 3.8 L/min to 6.2 L/min, which results in a reduction in dead volume from 36.47% to 17.59% and better consistency between different outlets. The dead volume and outlet consistency inside the tundish are improved significantly when the modified walls are applied. The proper design of the diversion hole further enhances the plug volume from 6.39% to 13.44% of the tundish by forming an upstream circular flow in the casting zone. In addition, the new trumpet ladle shroud demonstrates an advantage in increasing the response time from 152.5 s to 167.5 s and alleviating the turbulence in the pouring zone, which is beneficial for clean steel production.

Physical properties and corrosion resistance of magnesia-calcium hexaaluminate refractories to molten steel

The continuous casting tundish serves as the final vessel for molten steel in the smelting process. Resistance to steel corrosion and penetration is critical for clean steel smelting and the durability of working linings. In this study, calcium hexaaluminate (CA6) was selected to gradually replace the commonly used MgO refractory. We analyzed the phase composition, cold modulus of fracture, cold crushing strength, bulk density, porosity, and resistance to molten steel corrosion and penetration of MgO–CA6 refractories. It was observed that the mechanical properties of the material were reduced by the addition of CA6; however, a certain percentage of CA6 and MgO formed a small amount of MgO·Al2O3 at high temperatures to retain its high performance. The materials are less likely to react with [Mn], [Si] and other alloying elements in steel after the addition of CA6 and it exhibits excellent resistance to steel corrosion, which is important for clean steel production and the durability of working linings.

Uncovering temperature-tempted coordination of inclusions within ultra-high-strength-steel via in-situ spectro-microscopy

Despite the common challenge of investigating non-metallic inclusions within ultra-high-strength-steel (UHSS) at sub-micrometer scale via conventional methods, probing nitride inclusions at elevated temperatures is vital for guiding steel’ performance. Herein, an in-situ spectro-microscopic determination using advanced Synchrotron X-ray absorption spectroscopy (XAS) coupled with photoelectron emission microscopy (PEEM) is employed to explore the local structure and electronic properties of selective h-boron nitride (h-BN) containing inclusions (A1 and A2) embedded within steel matrix. While the variation in the relative intensity of π∗/σ∗ excitonic peaks at spatially different locations refers to the polarization and or thickness effects. Several minute features observed in the 192–195 eV energy range show oxygen (O) substituted nitrogen (N) defects (ON,2N,3N), which are more dominant in A2 inclusion. The observed dominance further explains the relatively high intense π∗ peak in A2 due to increased localization. Weak shoulder on the left side of π∗ peak in both room and high-temperature XAS spectra is ascribed to the interaction between h-BN and the local environment, such as Ca-based inclusion or steel matrix. Defects are commonly found in h-BN, and precise identification of the same is vital as they affect the overall physical, chemical, and mechanical properties. Moreover, significant changes in high-temperature B K-edge XAS spectra, such as relative intensity of π∗/σ∗ excitonic peaks at the same location and reduced intensity of defects, suggest the adjusting nature of BN inclusion, complicating their precise prediction and control towards clean steel production.

Design of Clean Steel Production with Hydrogen: Impact of Electricity System Composition

In Europe, electrification is considered a key option to obtain a cleaner production of steel at the same time as the electricity system production portfolio is expected to consist of an increasing share of varying renewable electricity (VRE) generation, mainly in the form of solar PV and wind power. We investigate cost-efficient designs of hydrogen-based steelmaking in electricity systems dominated by VRE. We develop and apply a linear cost-minimization model with an hourly time resolution, which determines cost-optimal operation and sizing of the units in hydrogen-based steelmaking including an electrolyser, direct reduction shaft, electric arc furnace, as well as storage for hydrogen and hot-briquetted iron pellets. We show that the electricity price following steelmaking leads to savings in running costs but to increased capital cost due to investments in the overcapacity of steel production units and storage units for hydrogen and hot-briquetted iron pellets. For two VRE-dominated regions, we show that the electricity price following steel production reduces the total steel production cost by 23% and 17%, respectively, as compared to continuous steel production at a constant level. We also show that the cost-optimal design of the steelmaking process is dependent upon the electricity system mix.

Mathematical modelling and plant trial on slagging regime in a ladle furnace for high-efficiency desulphurization

ABSTRACT Intelligent iron/steel manufacturing has been drawing increasing attention in recent years. Slagging is of importance for clean steel production in the ladle furnace (LF) refining process. In this study, a calculation model of slag-making materials was established based on the actual LF refining conditions, the metallurgical mechanism model and the production data model of the sulphur distribution ratio. In order to test the slag-making model, the data of 50 heats from historical production were examined by using the model; as a result, 49 heats successfully reached the target sulphur content when the error of the lime weight is within the range of ±40 kg. Meanwhile, plant trials were carried out to validate the slag-making model; the results demonstrated that 45 out of 48 tested heats successfully reached the required level of desulphurization by adding slag-making materials at one time.

Application of microcrystalline complex modifiers for steel ladle treatment. Part 1. The role of nonmetallic inclusions in steel quality forming

Contamination of steel by nonmetallic inclusions (NI) has a negative effect on mechanical characteristics of metal used under no favorable conditions. Conditions of NI forming in the process of steel smelting, ladle treatment and casting considered. It was shown that it is impossible to get rid of many NI. However, the task of forming less “harmful” NI having minimal effect on the decrease of finished products indices is quite practicable. To refine steel of NI it is reasonable to accomplish operations in a melt to modify NI morphology from dangerous acute-angled aluminous to globular oxide-sulphide. This task can be solved by introduction into metal complex modifiers comprising calcium, barium, strontium and rare earth metals. Addition of complex modifiers is a good alternative to complicative and long-time operations to decrease NI general content to lower levels, for example, by long-time metal ladle treatment. Application of the method enables in some situation to avoid expensive operations related to deep metal desulphuri zation and its dehydronization. Clean steel production becomes considerably easier at application of multicomponent alloys, obtained by a technology of accelerated crystallization. Application of such compositions results in forming globular oxide and oxide-sulphide compounds, as well as eutectics with low-melting point, which are comparatively quickly removed out of liquid metal. At that due to decreasing of liquation processes forming in the liquid metal, higher quality of large ingots and work-pieces, obtained from 420 t mass ingots can be reached.

Effect of Zr Additions on Non-Metallic Inclusions in X11CrNiMo12 Steel

The production of clean steel is associated with high-quality steel grades for demanding applications. The formation of oxide inclusions mainly depends on the deoxidation practice; it is usually carried out through Al additions, but alumina inclusions can have detrimental effects. An alternative zirconium inclusion modification was used in a creep-resistant steel to improve the cleanliness of laboratory-made steel. The thermodynamics behind the inclusion modification are presented, the reaction products are identified and the steel cleanliness improvement is quantified. The resulting influence of zirconium addition on non-metallic inclusions and mechanical properties is discussed. While the Zr additions drastically reduce the non-metallic inclusion size and area, additions above a certain amount result in the formation of zirconium nitrides that ultimately soften the martensitic steel due to the depletion of nitrogen in solid solution.

Modeling and computational simulation of fluid flow, heat transfer and inclusions trajectories in a tundish of a steel continuous casting machine

Currently, the continuous casting process is the main route used in the integrated steelmaking process. The tundish is an essential component of the caster machine and plays an important role in the control of inclusion in the production of the clean steels. Thus, viable methodologies and predictive models to evaluate this metallurgical reactor efficiency are important technological allies to improve the clean steel production. The main goal of the present study is to develop a computational tool to analyze the turbulent fluid flow, temperature distribution and inclusions removal during the continuous operation of the tundish of an industrial facility to improve its internal configuration. New configurations using weirs and dams are proposed which improve the steel quality. We used the Ansys CFX® software based on the element-based finite-volume method (EbFVM) to solve the coupled turbulent flow and heat transfer model equations in an Eulerian flame. A random nucleation mechanism for the inclusions generation and a modified Lagrangian model with a random walking model (RWM) to account for the effect of turbulence on the inclusions trajectories were proposed. The flow pattern was successfully validated with experimental data. The results were presented in terms of velocity and temperature fields and residence time distribution (RTD) curves. Then, the model was used to investigate new scenarios and enhanced geometry configurations.

Physical Simulation of Molten Steel Homogenization and Slag Entrapment in Argon Blown Ladle

Argon stirring is one of the most widely used metallurgical methods in the secondary refining process as it is economical and easy, and also an important refining method in clean steel production. Aiming at the issue of poor homogeneity of composition and temperature of a bottom argon blowing ladle molten steel in a Chinese steel mill, a 1:5 water model for 110 t ladle was established, and the mixing time and interface slag entrainment under the different conditions of injection modes, flow rates and top slag thicknesses were investigated. The flow dynamics of argon plume in steel ladle was also discussed. The results show that, as the bottom blowing argon flow rate increases, the mixing time of ladle decreases; the depth of slag entrapment increases with the argon flow rate and slag thickness; the area of slag eyes decreases with the decrease of the argon flow rate and increase of slag thickness. The optimum argon flow rate is between 36–42 m3/h, and the double porous plugs injection mode should be adopted at this time.

Slag carry-over and the production of clean steel

Slag carry-over and the production of clean steel

Production of Clean Steel Using the Nitrogen Elevating and Reducing Method

Nitrogen Elevating and Reducing Method (NERM) is a new technology developed to remove inclusions and oxygen in molten steel. The principle that underlies it is that nitrogenizing molten steel under low or normal pressure initially elevates the nitrogen content. Then, when the vacuum treatment is started, the nitrogen bubbles can nucleate on the surface of the inclusions and carry them to slag, reducing the number of inclusions in steel significantly. The removal effects between the new method and the conventional method were compared by industrial trials in this paper. The results show that the average oxygen content of the billet produced by the conventional method was 16 ppm, while that produced by the new method dropped to 11.5 ppm. Besides, the new method shows better removal effect of inclusions, and the number of inclusions decreased by 52.8% compared to the conventional method. The new method has obvious removal effects on inclusions in different sizes. In addition, the differences between NERM and the Pressure Elevating and Reducing Method (PERM) were compared, and the mechanism of each method was analyzed in this paper.