Secondary Steelmaking Research Articles

Weathering Behavior of Newly Developed Highly Fluxed DRI

The weathering behavior of highly fluxed and reduced iron ore pellet (DRI-Direct Reduced Iron) having 4, 6, and 8 basicity and 65–98% R (R-reduction) are given in this paper. The primary objective has been to solve weathering issues related to DRI and fresh lime used in the secondary steelmaking process. Experimental studies indicated that the addition of lime during pellet making and its subsequent reduction in coal bed yielded weather-resistant fluxed DRI with lime present in combined state. Such fluxed DRI exposed to 10 days open air (85% humidity) resulted in only 2 wt% moisture adsorption. The 30 days of air exposure caused 6 wt% moisture adsorption within acceptable limits for industrial acceptance. This low moisture adsorption by fluxed DRI was perhaps due to the presence of lime in combined form.

Computer Simulation of Continuous Casting Processes: A Review

Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium, and vanadium are added to produce the exact steel required. Modern steelmaking processes are broken into two categories: primary and secondary steelmaking. Primary steelmaking uses mostly new iron as the feedstock, usually from a blast furnace. Secondary steelmaking uses scrap steel as the primary raw material. Gases created during the production of steel can be used as a power source. Steelmaking is presently a grounded innovation driven by plant, exploratory and computational examination. The continuous casting process comprises many complicated phenomena in terms of fluid flow, heat transfer, and structural deformation. The important numerical modeling method of the continuous casting process has been discussed in reference in this work. With the recent advancement in metallurgical methods, the continuous casting process now becomes the main method for steel production. To achieve efficient and effective production, the manufacturers of steel keep on searching for new methods which increase productivity. The present work describes molten steel flow, heat transfer, solidification, electromagnetic applications, formation of the shell by solidification and coupling, etc.

Optimization of AISI 443 Stainless Steel Cleanness during Secondary Steelmaking Process

Optimization of AISI 443 Stainless Steel Cleanness during Secondary Steelmaking Process

The Impact of the Production Stages of Grade D Steel on its Contamination and the Chemical Composition of Nonmetallic Inclusions

Optical and electronic microscopy methods are used to evaluate the contamination of grade D carbon steel with nonmetallic inclusions in steel samples taken at various stages of steelmaking (electric arc furnace (EAF) discharge -> ladle furnace (LF) -> vacuum deoxidation (VD) -> continuous casting) at an electric furnace melting shop. Steel contamination with nonmetallic inclusions and inclusion chemical composition are assessed. It is demonstrated that the aluminum deoxidation of the semiproduct leads to the formation of corundum nonmetallic inclusions (Al2O3) in molten steel. The total amount of corundum reaches 52% for all the stages of steelmaking process. The identification and evaluation of nonmetallic inclusions demonstrates that deoxidation performed at all the stages of secondary steelmaking reduce the amount of inclusions. After vacuum deoxidation and adding Al and SiCa, corundum inclusions become globular in shape with a particle size less than 6 urn. When the continuously cast billet has solidified, the total amount of nonmetallic inclusions does not change, whereas silicate inclusion content decreases and corundum contamination grows, with corundum inclusions being of an irregular shape. A heavy corundum contamination is caused by aluminum secondary deoxidation during steel casting as well as by the fact that the molten residue in the pouring nozzle is carried into the solidifying continuously cast billet.

A Review of Steel Processing Considerations for Oxide Cleanliness

Control of non-metallic inclusions is essential for the production of high-quality steel. This review summarizes processes that change inclusion compositions and concentrations during secondary steelmaking—slower changes are limited by reaction between bulk steel and slag or refractory, and faster changes involve direct additions to the steel bath. An example of the former is conversion of alumina inclusions to spinels during ladle treatment, while reoxidation and calcium treatment are typical exemplars of the fast changes. For the slower changes, inclusions approach equilibrium with the liquid steel and conceptually simple kinetic models correctly describe inclusion evolution during ladle treatment. Disequilibrium from faster changes persists for several minutes under typical ladle conditions, with small-scale inhomogeneity in the steel. Fast scanning electron microscopy with microanalysis has facilitated detailed study of these inclusion evolution processes by providing information on inclusion composition, size, and shape. Machine learning methods are likely to be increasingly important in analysis of the results. Such methods have already shown promise to improve classification of inclusions and recognizing inclusion clusters, from analyses of polished sections. Several unresolved issues that require future study are noted.

Numerical and Physical Investigation of the Mixing Process in Gas Stirred Ladle System

Secondary steelmaking or ladle metallurgy is one of the important processes that adjust and homogenize the chemical compositions and the temperature. In this process, argon gas is injected into the melt through porous plugs to accelerate the chemical reaction and the mixing. One of the indicators for the mixing efficiency is “the mixing time”. The purposes of this study were to investigate the effects of gas flow rate and purging system on the mixing time and flow characteristics by using numerical and physical investigation and to predict the velocity magnitude acting on the refractory wall by analyzing the effects of gas flow rate. A 1:5 scaled water model and a full-scale ladle model of Millcon steel PLC were used in the study. The numerical simulation modelling was carried out by using CFD commercial software Flow-3D. The results from the numerical simulation were in consistence with the experiment results. The simulation results showed that with the highest gas flow rate the reduction of the mixing time was around 36% and the velocity magnitude increased to approximately 44% in comparison with the lowest gas flow rate in the full-scale model. The area at the ladle wall near the liquid surface has a higher chance of the damage than other areas. Besides, employing the dual-plugs system led to approximately 33–49% shorter mixing time compared to the single-plug system. The results show that the gas flow rate affects the turbulent kinetic energy directly. However, high turbulent kinetic energy leads to open-eye size which results in re-oxidation and contamination. Therefore, it is important to optimize the flow rate to achieve both productivity and steel cleanliness.

Structural Transformation of Molten CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub>–Fe<i><sub>x</sub></i>O Slags during Secondary Refining of Steels

According to the variation of compositions during steel secondary refining process, the ice-quenched samples of CaO–SiO2–FexO–Al2O3 system were prepared, the structure were detected via the method of Raman spectroscopy, and the evolution of structural units were further analyzed. The results showed that, for the Fe3+ cation, two types of units of tetrahedral fourfold coordination ([FeO4]) and octahedral sixfold coordination ([FeO6]) coexisted in the molten slag, and the ratio of [FeO6]/[FeO4] increases with the decreasing ratio of CaO/(SiO2+Al2O3). For the Al3+ cations, four types of aluminum units of Q2Al, Q3Al, Q4Al coexisted in the molten slag and the lower polymerized units Q2Al transform into the higher polymerized Q3Al and Q4Al along with the ratio of Al/(Al+Si) increasing from 0.41 to 0.85. For the Si4+ cations, Q0Si, Q1Si and Q2Si are the main types of [SiO4]-tetrahedral units, the Ca2+ cations of oxygen coordination in [SiO4]-tetrahedral units are gradually replaced by Al3+, which just act as network modifier, with the increase of Al/(Si+Al) ratio. Accordingly, the degree of polymerization of molten slag presented in NBO/T increases with the process of secondary steelmaking.

Green Castable Using Steelmaking Slags: A Sustainable Product for Refractory Applications

Continuous focus on capacity growth and increase in productivity by the manufacturing sector has led to the generation of a huge quantity of solid waste as by-product and depletion of the natural resources including refractories. The present study focuses on a sustainable approach to develop a low-cost castable intended for low-temperature applications by utilizing steelmaking slags as the raw materials. Firstly, the ladle slag generated after the secondary steelmaking process was used in the range of 50–70% as a complete source of CaO to develop a calcium-aluminate cement. The slag was used as a 100% replacement of limestone and partial replacement of Al2O3 source in the cement. Thus, it was possible to eliminate the CO2 emission associated with dissociation of limestone during the clinker making process. The castable was prepared using primary steelmaking slag as the aggregate and developed slag cement as the binder. CA and CA2 were formed as the primary phases in the slag cement, with Gehlenite, C12A7, and ‘Q’ phases as the secondary phases. Slag cement with 60% slag content exhibited superior strength as compared to commercial calcium-aluminate cement of medium purity. Further, the 110 °C and 1000 °C crushing strengths were found to be better for slag cement-added castable than the commercial cement-added one. Thus, it was possible to develop a green castable by using by-products of the steelmaking process that would not only help in reducing the carbon footprint, but also reduce the manufacturing cost and address the environmental concerns.

Numerical Modeling for Simulation of Compaction of Refractory Materials for Secondary Steelmaking.

The purpose of this work is to simulate the powder compaction of refractory materials, using the discrete element method (DEM). The capability of two cohesive contact models, implemented in different DEM packages, to simulate the compaction of a mixture of two refractory materials (dead burnt magnesia (MgO) and calcined alumina (Al2O3)) was analyzed, and the simulation results were compared with experimental data. The maximum force applied by the punch and the porosity and final shape quality of the compact were examined. As a starting point, the influence of Young’s modulus (E), the cohesion energy density (CED), and the diameter of the Al2O3 particles (D) on the results was analyzed. This analysis allowed to distinguish that E and CED were the most influential factors. Therefore, a more extensive examination of these two factors was performed afterward, using a fixed value of D. The analysis of the combined effect of these factors made it possible to calibrate the DEM models, and consequently, after this calibration, the compacts had an adequate final shape quality and the maximum force applied in the simulations matched with the experimental one. However, the porosity of the simulated compacts was higher than that of the real ones. To reduce the porosity of the compacts, lower values of D were also modeled. Consequently, the relative deviation of the porosity was reduced from 40–50% to 20%, using a value of D equal to 0.15 mm.

Optimization of AISI 443 Stainless Steel Cleanness during Secondary Steelmaking Process

Nonmetallic inclusions formed during the Ti‐stabilized 443 stainless steelmaking process can cause the clogging of submerged entry nozzle (SEN) and surface defects of cold‐rolled steel. The formation mechanism of oxide inclusions in 20Cr stainless steel is investigated by industrial experiment and FactSage thermodynamic calculation. After Al deoxidized and calcium treatment, the main types of inclusions in three heats are different, including irregular MgO–Al2O3 and spherical CaO–MgO–Al2O3, which is due to the different Ca and Al contents in samples. Combined with FactSage thermodynamic calculations, the calcium contents which can effectively modify oxide inclusions in 443 stainless steels with different Al contents are obtained. The initial calcium and aluminum contents in molten steel affect the main type of oxide inclusions formed during Ti addition process. High‐melting‐point Ca–Ti–O inclusions are observed in the sample containing high Ca content and low Al content. The experimental results and FactSage thermodynamic calculation results show that reducing Ca content and increasing Al content before Ti addition can reduce the formation of high‐melting‐point perovskite inclusions.

Inclusions Absorbed by Slags in Interstitial‐Free Steel Production

The nonmetallic inclusions absorbed by ladle slags during secondary steelmaking operations and in the tundish and mold during casting are crucial to the production of interstitial‐free (IF) steel. However, little to no research has been conducted on the separation and dissolution of inclusions along with a focus on IF steel. Herein, a theoretical study of the separation of solid alumina at the steel–slag interface is conducted. The dissolution of alumina particles is observed in situ in different IF steel slags, and the dissolution mechanism is analyzed. The results show that the interfacial tensions and slag viscosity have a large influence on the predicted displacement, but for IF steel production, the dissolution of inclusions in the slags has a greater influence on the removal of inclusions than on inclusion separation. Using ladle slags with a proper CaO wt%/Al2O3 wt% is the most effective way to remove the Al2O3 inclusions compared with the other slags in IF steel production.

Electrification of Industry: Potential, Challenges and Outlook

Industry is one of the most difficult sectors to decarbonize. With the rapidly falling cost of solar PV, wind power, and battery storage, industry electrification coupled with renewable electricity supply has the potential to be a key pathway to achieve industry decarbonization. This paper summarizes the latest research on the possibility of electrification of the industry sector. The transition to industry electrification would entail major changes in the energy system: large scale increases in renewable electricity or nuclear power supplies, the expansion of electricity transmission and distribution networks, completely different end-use technologies for process heating, and new infrastructure for distributing and dispensing hydrogen. Thus, aggressive and sustained supportive policies and much wider research, development, demonstration, and deployment activities are required to meet net zero carbon emissions goals in the industrial sector. Existing economically competitive electrified industrial processes (such as electric arc furnaces for secondary steelmaking from scrap steel), coupled with zero-carbon electricity sources can sharply reduce greenhouse gas emissions (GHG) compared to manufacturing processes that rely on fossil fuels. Fuel switching in industry from fossil fuel–based process heating to electrified heat can offer many product and productivity benefits, but operating costs in general are much higher than fossil fuel-based heating. Either much lower costs of electricity and energy storage are required and/or new, cost-competitive electric-technology applications are needed to enable further electrification of industry. Indirect electrification i.e., hydrogen production via water electrolysis is another complimentary technology reliant on electricity. Hydrogen can be used as an energy carrier, industrial feedstock for products and fuels, or for long-duration energy storage, and thus can also play a key role in industry decarbonization when the hydrogen is produced from zero-carbon electricity and/or with carbon capture and storage. As with direct electrification, cost is the key barrier for the deployment of hydrogen resources.

Development of the Metal Temperature Prediction Model for Steel-pouring and Tundish Ladles Used at the Casting and Rolling Complex

A model has been developed for predicting the metal temperature in the specified superheat range above the liquidus temperature inside the tundish of a continuous casting machine (CCM) depending on the last temperature measurement in the steel-pouring ladle (prior to casting), as well as ladle history and secondary steelmaking process under the conditions of the Casting and Rolling Complex (CRC) of the JSC “Vyksa Metallurgical Plant” (VMZ). It is suggested to predict the superheat temperature of steel at the CRC by using statistical models considering the specifics of technological process. During the first stage, the model itself has been developed by integrating the following two approaches: a machinelearning algorithm and probabilistic graphical model (PGM and Bayesian networks). The first approach provides the point estimate of the intermediate and final temperatures of the specific melting, while the second approach allows evaluating the probability distribution. The PGM-approach is very promising in the situations involving missing, incorrect, or undefined input data, which are quite common at the metallurgical plants. During the first stage, the achieved level of accuracy of tundish temperature prediction was 6.0°C. During the second stage, the model was integrated into the shop automated process control system, which allowed increasing the prediction accuracy and ensuring a real-time control of the process parameters. The model is used as a guidance (master) tool for the process personnel operating the ladlefurnace and vacuum degasser equipment.

Major determinant of service life in magnesia-graphite slagline refractory lining in secondary steelmaking ladle furnace

Magnesia-carbon (MgO-C) refractory bricks are used for slagline lining in secondary steelmaking to withstand the harsh basic slag and high temperature environment. In an operation using bottom purging ladle furnaces, preliminary study of residual bricks after lining failures shows less than 50 vol. % of the MgO-C bricks is typically used before the linings would fail. Slag basicity, high temperature oxidation and erosion are known as root causes of different degradation modes in this application. This work, presented in part herein, seeks to identify the dominant cause for this resource utilization inefficiency. Slag basicity excursions and thermal fluctuations versus service lives and residual thicknesses of each MgO-C brick after lining failure, were studied for five ladle linings. Optical and electron microscopy were also used in further post-mortem of the residual bricks. The operation data that showed thermal spikes above 1600 °C and acidic slags with basicity usually below the ideal of 1.67. Micrographs from the slag-refractory interfaces indicated effect of this operational extremes showing thermal shock cracking, slag penetration and evolution of phase due to the slag-refractory interactions. However, bricks evidencing these effects were not the most worn. Slag basicity attack and high temperature oxidations are diffusion controlled and did not proceed aggressively by themselves. Rather, least residual thicknesses were found in bricks from columns adjacent to the two purging gas entry points at the bottom of the ladle. Up to 86 % wear were obtained at such points, in contrast to 24 % for bricks farthest from this effect. Turbulence from the purging gas is thus responsible for localized and highest lining consumption rate that decimates lining life in these ladles. Without this purging turbulence, such as in induction stirring, it can be projected that the lining life can triple, with obvious economics and environmental advantages. While the MgO-C refractory is well able to withstand the chemical and thermal extremes of secondary steelmaking slag environment, bottom purging ladle furnace design deserves a review to improve refractory utilization.

Recycling Ladle Furnace Slag as Flux in Steelmaking: A Review

The use of synthetic fluxes in secondary steelmaking not only improves the properties of top slag and steel quality but also increases the production cost. Ladle furnace (LF) slag can be used as a replacement to synthetic fluxes owing to its chemical and mineralogical compositions. Valorization of LF slag helps in sustainable steelmaking and also reduces steel production cost. In spite of beneficial composition, valorization of LF slag is difficult due to its disintegration phenomenon. The present paper reviews on the importance of ladle flux usage, various methods available to prevent disintegration of LF slags, and possibilities to recycle LF slags as a flux in the steelmaking. The paper helps steel plant operators to select a suitable option for recycling LF slags as a flux in steelmaking.

Microtexture Performance of EAF Slags Used as Aggregate in Asphalt Mixes: A Comparative Study with Surface Properties of Natural Stones

Steelmaking industries produce a large amount of solid wastes that need to be adequately managed in order to ensure environmental sustainability and reduce the impact of their disposal on earth pollution. Electric arc furnace (EAF) slags are those wastes deriving from secondary steelmaking production; these slags can be re-used and recycled in many industrial applications such as the production of asphalt mixes. In this paper authors investigate the surface performance of EAF slags used as second-hand aggregate in asphalt mixes. In particular, slags behavior under polishing is compared to other types of aggregate commonly used for asphalt concrete such as limestone, basalt, and kinginzite. Several devices (skid tester, laser profilometer, polishing machine) were used to collect experimental data; the analysis of microtexture was carried out by comparing aggregate surface performance before and after polishing. Results show that EAF slags are positively comparable to basalt as concerns the polishing behavior; good correlations between skid resistance and some microtexture indicators are also carried out.

Evaluating slag–metal deoxidation equilibrium in secondary steelmaking

Steel–slag reactions are important in steelmaking, in special in secondary steelmaking. Currently, desulfurization, deoxidation and inclusion removal are mostly performed during ladle refining. The extent to which these reactions proceed is governed by the initial state of the material reaching the ladle, the additions made to the ladle and by undesired interactions such as reoxidation and steel-refractory reactions. In this work, the extent to which equilibrium is approached for the different deoxidation reactions is Al-killed and Si–Mn deoxidized steel is evaluated using thermodynamics. These results are compared to measurements performed in industrial ladle furnaces. The comparisons make possible evaluating the efficiency of the deoxidation process. The results indicate that reoxidation by air caused by agitation probably play a key role on the ability to approach equilibrium, reaching low oxygen content in steel. It is also concluded that relatively long treatments with controlled agitation are needed to achieve steel–slag equilibrium.

Physical and CFD Modeling of the Effect of Top Layer Properties on the Formation of Open‐Eye in Gas‐Stirred Ladles With Single and Dual‐Plugs

In secondary steelmaking, the optimal size and position of open‐eye is important for effective alloying practice. In the current work, the effect of the top layer thickness and density on the formation of open‐eye in a gas stirred ladle was investigated. A one‐fifth scale water model of 150‐ton ladle was established with single and dual plug configurations for the physical modeling measurements. Air, water and three different oils were used to simulate the argon, liquid steel and slag in the water model, respectively. A transient Computational Fluid Dynamics (CFD) model based on Eulerian Volume of Fluid (VOF) approach was developed for numerical modeling of the fluid flow behavior. The physical modeling results show that the relative open‐eye area decreases from 46.7 to 5.6% when top layer thickness was increased from 0.75 to 7.5 cm using a gas flow rate of 7.5 NL min−1. The effect of the number of plugs on the open‐eye area for the same range of top layer thickness mentioned above was also studied. The relative open‐eye area generated due to the gas injection through the dual plugs decreased from 49.9 to 5.8%. To study the effect of top layer properties, rapeseed oil, castor oil and paraffin oil were employed for studying the effect of density and dynamic viscosity on the open‐eye formation. The results revealed that a larger open‐eye is formed when the density is increased. Furthermore, it was found out that the density of the upper phase dominates the open‐eye formation while dynamic viscosity has only minor effect. The results obtained from numerical simulations and physical modeling were found to be in good agreement.

Numerical Investigations on the Effect of Gas Flow Rate in the Gas Stirred Ladle with Dual Plugs

Ladle or secondary steelmaking is an essential metallurgy process in which the steel is adjusted to the chemical compositions required in the final product. The objective of this study was to predict 95% mixing time curve using CFD simulation in order to investigate the possibility to optimize the gas flow rate in gas stirred ladle systems. The commercial software, Flow-3D, was used in this study. This study was divided into three parts. The first two parts of the study was the investigation of the effects of bubble sizes and diffusion coefficient on the mixing time by setting constant-volume gas flow rate. The last part was the study of the effect of gas flow rate on the mixing time. The ladle geometry and operation condition from the example steel plant, Millcon Steel PLC were used in this study. The simulation results indicated that different sizes of bubble have minor effects on the mixing time. The investigation of the effect on the mixing time with and without diffusion coefficient showed that the diffusion coefficient has no significant influence on the mixing time but has significant effects on the characteristics of the plume regions and the velocity flow field. Finally, it was found that gas flow rate has significant effects on turbulent kinetic energy, the mixing time and the steel cleanliness. The results can support the example steel plant to optimize the mixing process concerning productivity and cleanliness quality of the liquid steel.

Life Cycle Assessment Comparison of Two Refractory Brick Product Systems for Ladle Lining in Secondary Steelmaking

This paper aims to compare the environmental performance of two types of refractory bricks for the internal lining of ladles in secondary steelmaking, where the dissolved inclusions coming from the refractory material require fine control to obtain the target steel quality. In this context, magnesia-carbon-based refractories are largely utilized, thanks to the adequate durability of the ladle lining in terms of number of heats before re-lining, but the utilization of organic binders in the mixture (pitch, resins) arises ecological and human health concerns. Concurrently, research efforts in refractory material science look at improving the quality of steel by reducing the content of dissolved carbon due to the release from the bricks, thus focusing on different refractory materials and specifically on alumina-based materials. The European Commission funded the research project “LeanStory”, aiming to promote such new lines of refractories through the cooperation between industrial partners and scholars where different recipes are considered. In the present paper, two representative systems of the refractory types considered, magnesia-carbon and magnesia-alumina, are compared with a preliminary Life Cycle Assessment (LCA). Suppliers and transports for the two product systems have been taken into account, referring to one tonne of refractory material as the functional unit for comparison. Preliminary impact results (adopting the ReCiPe Midpoint–Hierarchist perspective methodology for calculating the impact indicators) show that the new solution performs largely better almost for each indicator. Further investigations are required in order to assess the ecological performance of the two systems, considering the effective consumption of bricks for the production of steel.