Steel Melt Research Articles

In situ layer formation on MgO–C refractories with different MgO grade by static and dynamic contact with liquid steel

Modern, high-quality steelmaking requires a comprehensive understanding of the behavior of refractories in service. Therefore, MgO–C refractories with different MgO grade were immersed once and twice into a steel melt at 1600 °C and 1680 °C, respectively, in a near-industrial steel casting simulator. The same materials were tested in static crucible melting tests. A coherent MgO layer containing low-melting phases and MgAl2O4 crystal-like structures formed on the specimens’ surface. The morphology and frequency of these structures were strongly related to the MgO grade of the specimens and the immersion procedure. A lower MgO grade caused an increased formation of low-melting phases, which contributed to a denser layer formed on the specimens’ surface, hampering gas diffusion and the formation of MgAl2O4 crystal-like structures. An increased steel melt temperature and the double immersion had a similar effect. Conversely, an excessive formation of MgO and/or MgAl2O4 was observed when the formed layer contained less low-melting phases.

Combined steel melt filtration through reactive and active filters

A combined filtration system was investigated for the first time in the present work. A reactive filter was immersed in a steel melt containing artificially generated endogenous inclusions. After extracting the filter, the melt was poured through a second filter and into a crucible where it cooled down. The second filter had a pure aluminum oxide flame-sprayed coating, in order to prevent reactions and only remove pre-existing inclusions. It was observed that the immersion of a reactive, coated filter generally resulted in larger inclusions. When no casting was performed, or when the second filter was omitted, smaller remaining inclusions were found. Calcium aluminate based coatings resulted in the creation of new multiphase inclusions (and less alumina). Although these results cannot be directly compared with state-of-the-art industrial filtration procedures, active filtration seems so far the most promising approach to produce steel of improved quality. In addition, filters with a calcium aluminate-based coating might be interesting in the production of steel with tailored inclusions for special applications.

Effect of La Content on Inclusion Morphology in Automobile Sulfur‐Containing Gear Steel SCr420H

The inclusion morphology of sulfur‐containing gear steel with different La addition (0, 0.08, 0.5, and 1%) is investigated in laboratory experiments. The La and S concentrations in steel melt significantly decrease with the holding time after La addition increases, leading to different types of inclusions with specific shapes. Inclusion transformation routes with the holding time increased under different La addition are summarized as follows: 1) 0%La addition: cluster‐like Al2O3 + cluster‐like MnS → irregular block‐like MgAl2O4 + cluster‐like MnS; 2) 0.08%La addition: cluster‐like LaAlO3 + spherical‐like La‐Al‐O‐S‐(MnS) → spherical‐like La‐Al‐O‐S‐(MnS) + spherical‐like La‐Al‐O‐S‐(MgO)‐(MnS) + cluster‐like MnS; 3) 0.5%La addition: flower‐like La‐O + spherical‐like La‐O‐S → spherical‐like La‐O‐S; and 4) 1%La addition: flower‐like La‐O + spherical‐like La‐O‐S → spherical‐like La‐O‐S + cubic‐like La‐O‐S‐N‐As. The results of hot compression suggest that La‐containing inclusions are less prone to the shape change than MnS; moreover, microcracks are formed at the surface of La‐containing inclusions. The nanoindentation test demonstrates that the hardness of La‐O‐S is higher than MnS. The high La addition has a remarkable effect on refractory degradation. For 0.5% and 1% La, dissolved La reacts with the MgAl2O4 phase in the MgO‐MgAl2O4 dual‐phase refractory and changes into LaAlO3.

Effect of ferrochromium (FeCr) and ferroniobium (FeNb) alloys on inclusion and precipitate characteristics in austenitic stainless steels

Lab-scale alloying experiments were carried out by first adding commercial low-carbon ferrochrome (LCFeCr) alloys and then adding ferroniobium (FeNb) alloys in 316-grade austenitic stainless steel in this study. The inclusion and precipitation characteristics in LCFeCr and FeNb were evaluated as well as in a 316 austenitic stainless steel after the alloy additions by using two- and three-dimensional characterization methods in combination with thermodynamic calculations. The results showed that MnCr2O4 spinels and pure Al2O3 were the main types of inclusions in LCFeCr alloys, while pure TiOx, Al2O3 inclusions and complex TiOx-Al2O3 aggregates were mainly found in FeNb alloys. After the addition of LCFeCr alloy to the steel, the SiO2 contents in liquid inclusions decreased to some extent, while more inclusions containing higher MnO contents were observed. Some MnCr2O4 spinel inclusions can be reduced by Si in steel and form liquid inclusions. Some MnCr2O4 spinel and Al2O3 inclusions from LCFeCr alloy can remain in the steel melt, which decreased the steel cleanliness. After the addition of FeNb alloy, pure TiOx inclusions present in this alloy can hardly be found in the steel melt. The inclusion types in steel were not changed so much but high Nb-containing phases were found around the inclusions and coarse Laves phases were formed in the matrix. Overall, this work aims to understand the impurity particle behavior during the alloying process when using ferroalloys to produce high-performance stainless steels.

On transition to hydrogen metallurgy

The article shows that climate change is not only warming, but also extraordinary natural phenomena (droughts, floods, storms, tornadoes etc), which lead to significant economic damage. Climate warming is caused by increasing concentrations of greenhouse gases in the earth's atmosphere. The main task is to reduce carbon dioxide emissions. An analysis has been carried out of international documents such as the Kyoto Protocol, the Paris Climate Agreement, aimed at reducing greenhouse gas emissions into the atmosphere. It is shown that a significant amount of CO2 enters the atmosphere during the production of pig iron and steel, the data on the amount of carbon dioxide emissions from steel smelting in Ukraine and at «Azovsteel» iron and steel works have been provided. The article contains a critical analysis of the existing steel production technology, which is highly efficient but requires significant capital investment, fuel and energy resources, the source of which is the product of heat treatment of hard coal – coke, its carbon in the form of CO2 entering the atmosphere. Numerous proposed methods of steel production without the use of this coke are considered. One of the directions was the production of sponge iron without melting, another direction of coke-free metallurgy was high-temperature processes of obtaining liquid metal, that are carried out in one stage. The theoretically required amount of reducing agent at of iron with carbon monoxide and hydrogen has been determined. Methods of producing renewable gas by conversion of natural gas and gasification of coal are considered. The plans of the Metinvest Group management to develop a long-term technological strategy for metallurgical production taking into account environmental requirements are presented

Correlation and Prediction of Molten Steel Temperature in Steel Melting Shop Using Reliable Machine Learning (RML) Approach

Correlation and Prediction of Molten Steel Temperature in Steel Melting Shop Using Reliable Machine Learning (RML) Approach

Low-carbon technological innovation of coal production and utilization impetus carbon neutrality in China.

European energy crisis, triggered by the conflict between Russia and Ukraine, has again drawn attention to the decarbonization of fossil energy sources. However, few studies have objectively considered coal from an integrated life cycle and its position in the energy system. In the present study, we used the integrated life cycle analysis and fixed-effect panel threshold model to reveal that (1) power generation and heating and iron and steel smelting are the highest CO2 emission sectors. In addition, the coal chemical industry and power generation and heating are the two sectors with the highest contribution rate of CO2 emissions. (2) Based on these, underground coal gasification (UCG) and underground coal gasification-integrated gasification combined cycle (UCG-IGCC) technologies were introduced to innovate the coal life cycle (the process cycle of coal production and utilization). The panel threshold model has proved that when the energy intensity falls in the interval 0.363-2.599, UCG-IGCC technology could be the complement in mitigating CO2 emissions. (3) Finally, for the same amount of emission mitigations, the social cost of innovating coal production and utilization processes using UCG-IGCC technology will be lower than phasing out coal-fired power plants using carbon prices. For China, UCG-IGCC and renewable energy should be developed simultaneously.

Interfacial reaction mechanism and high temperature stability of heat-resistant steel and SiC under a vacuum environment

The physical and chemical stabilities of SiC and heat-resistant steel were assessed by the diffusion couple method under vacuum at 1200 °C, which is a commonly used condition in magnesium metallurgy. High-temperature visualization instruments were used and Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic analyses were performed to verify the relevant mechanism. The reaction between SiC and heat-resistant steel can be divided into two stages: solid–solid and solid–liquid reactions. The solid–solid interfacial reaction produces graphite, which hinders the interfacial reaction. The interfacial reaction simultaneously generates silicides (NiSi, Ni2Si, and Ni3Si) with low melting points and transforms the reaction interface into a solid–liquid interface. The formation of the liquid phase promotes the dissolution and diffusion of carbon, leading to the accelerated corrosion of SiC and low-temperature melting of steel. Supersaturated carbon precipitates in the melt in the form of nanowires or nanotubes are catalyzed by Fe/Ni. Herein, a general model describing the direct interfacial reaction mechanism of SiC and heat-resistant steel is proposed to explain the reaction process under vacuum.

Characterization and Health Risk of Heavy Metals in PM2.5 from Road Fugitive Dust in Five Cities of Yunnan Province

In order to study the contents, sources, and health risk of PM2.5 in road fugitive dust in Yunnan, road fugitive dust samples were collected from five typical cities including Kunming, Baoshan, Wenshan, Zhaotong, and Yuxi. Particulate matter resuspension technology was used to levitate the dust samples and collect PM2.5. Eight heavy metals including chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), selenium (As), cadmium (Cd), and lead (Pb) in PM2.5 were detected using ICP-MS. The results showed that the contents of Cr, Ni, Cu, Zn, and Pb in road fugitive dust seriously exceeded the background values of Yunnan soil. The enrichment factors showed that most of the heavy metals in PM2.5 of road fugitive dust in the five cities of Yunnan were moderately enriched and strongly enriched, which were greatly influenced by human activities. The results of correlation analysis and principal component analysis showed that the heavy metals in PM2.5 of road fugitive dust in Yunnan were all affected by soil and traffic sources. The other sources varied greatly in different cities:Kunming was affected by iron and steel melting sources, Baoshan and Yuxi were affected by non-ferrous metal smelting sources, and Zhaotong was affected by coal sources. Health risk analysis showed that Cr, Pb, and As in road fugitive dust PM2.5 had non-carcinogenic risk in children in Kunming, Yuxi, and Zhaotong, respectively, and Cr in Kunming also had a lifetime carcinogenic risk.

Cobalt and Manganese Extraction from Ocean Nodules by Co-Processing with Steel Metallurgical Slag

Polymetallic nodules, also called manganese nodules (due to their high content of this element), contain various valuable metals such as Cu, Ni and Co. These seabed minerals are a good alternative source of Co and Mn due to the decrease in the grade of mineral deposits on the earth’s surface. For the treatment of manganese nodules, acid-reducing leaching is apparently the most attractive, due to its low cost compared to other processes, short operational times, and it is more friendly to the environment. In this investigation, the extraction of Mn and Co from manganese nodules from two different locations was studied in acid media and by reusing a steel slag obtained from a steel smelting process. An ANOVA analysis was performed to determine the most appropriate Manganese Nodule/Fe(res) ratio and time to dissolve Co and Mn from the nodules. Effect of temperature on the process was evaluated, and then a residue analysis was carried out. Finally, it was discovered that the best results were obtained when working at 60 °C in a time of 15 min, obtaining extractions of approximately 98% Mn and 55% Co. Additionally, the formation of polluting elements was not observed, nor the precipitation of Mn and Co species in the studied residues.

CFD Predictions for Mixing Times in an Elliptical Ladle Using Single- and Dual-Plug Configurations

Argon bottom stirring is commonly practiced in secondary steelmaking processes due to its positive effects on achieving uniform temperatures and chemical compositions throughout a steel melt. It can also be used to facilitate slag metal refining reactions. The inter-mixing phenomena associated with argon gas injection through porous plugs set in the bottom and its stirring efficiency can be summarized by evaluations of 95% mixing times. This study focuses on investigating the impact of different plug positions and ratios of argon flow rates from two plugs on mixing behavior within a 110-tonne, elliptical-shaped industrial ladle. A quasi-single-phase modeling technique was employed for this purpose. The CFD findings revealed that the optimal position of the second plug is to be placed diametrically opposite the existing one at an equal mid-radius distance (R/2). An equal distribution of argon flow rates yielded the best results in terms of refractory erosion. A comparative study was conducted between single- and dual-plug-configured ladles based on flow behavior and wall shear stresses using this method. Furthermore, a transient multiphase model was developed to examine the formation of slag open eyes (SOE) for both single- and dual-plug configurations using a volume of fluid (VOF) model. The results indicated that the dual-plug configuration outperformed the current single-plug configuration.

Flame-sprayed alumina molten metal filters for dead-mould casting application

Ceramic foam filters are applied to remove non-metallic inclusions during steel melt filtration. The flame-spray technology can contribute to improving such filters by increasing the deposition capability of inclusions and decreasing the impairment of the filter substrate by the steel melt. This makes them suitable for application to the continuous steel casting process and foundry casting. The ball-on-three-balls test was utilized at elevated temperatures to determine the high-temperature behaviour of thermally sprayed alumina. Additionally, the flame-spray technology was used to produce carbon-free filters composed of flame-sprayed alumina by coating and burning out the Al2O3–C filter substrate during a sintering step. The B3B revealed a ductile behaviour with increasing temperature and a bending strength of 23.28 MPa at 1400 °C. After sintering at 1400 °C, the filters showed a sufficient CCS of 0.16 MPa, which allows the performance of casting tests (immersion and pouring) with molten steel at 1580 °C.

A Computational Fluid Dynamics Study on Physical Refining of Steel Melts by Filtration

In this paper, a previous experimental investigation on physical refining of steel melts by filtration was numerically studied. To be specific, the filtration of non-metallic alumina inclusions, in the size range of 1–100 µm, was stimulated from steel melt using a square-celled monolithic alumina filter. Computational fluid dynamics (CFD) studies, including simulations of both fluid flow and particle tracing using the one-way coupling method, were conducted. The CFD predicted results for particles in the size range of ≤5 µm were compared to the published experimental data. The modeled filtration setup could capture 100% of the particles larger than 50 µm. The percentage of the filtered particles decreased from 98% to 0% in the particle size range from 50 µm to 1 µm.

CO2 sequestration and CaCO3 recovery with steel slag by a novel two-step leaching and carbonation method

The steel smelting process produces extensive CO2 and Ca-containing steel slag (SS). Meanwhile, the low value utilization of steel slag results in the loss of Ca resources. CO2 sequestration utilizing SS can reduce carbon emissions while achieving Ca circulation. However, conventional SS carbon sequestration methods suffer from slow reaction rates, finite Ca usage efficiency, and difficulty separating the CaCO3 product from SS. Herein, an innovative two-step leaching (TSL) and carbonation method was presented based on the variations in leaching efficiency of activated Ca under different conditions, aiming at efficient leaching, carbon sequestration, and high-value reuse of SS. This method employed two NH4Cl solutions in sequence for two leaching operations on SS, allowing the Ca leaching rate to be effectively increased. According to the findings, TSL could increase the activated Ca leaching rate by 26.9 % and achieve 223.15 kg CO2/t SS sequestration compared to the conventional one-step leaching (CSL) method. If part of the CaCO3 is recovered as a slagging agent, about 34.1 % of the exogenous Ca introduction could be saved. In addition, the CO2 sequestration of TSL did not significantly decrease after 8 cycles. This work proposes a strategy that has the potential for recycling SS and reducing carbon emissions.

Ranking of Injection Biochar for Slag Foaming Applications in Steelmaking

The electric arc furnace (EAF) has the potential to significantly contribute to the decarbonization of the iron and steel industry. However, during EAF steelmaking, carbon still needs to be injected into the molten slag to initiate slag foaming, which is beneficial to the energy efficiency and protection of the furnace. To move away from fossil carbon, biocarbon has gained attention as an injection carbon agent. In this study, two biochar candidates were added to the molten slag layer of an induction furnace for steel melting, to simulate EAF steelmaking conditions. The resultant slag foaming height was measured, and a ranking in comparison to two fossil carbon candidates was developed. The results indicate that the injection biochar sample, in the form of a bio-briquette, has a considerable degree of slag foaming capacity. More work is ongoing to develop a standardized testing methodology of ranking various injection biochar candidates for their suitability and qualification for use on a larger scale.

Improving the properties of nickel/graphene oxide coated copper plate by changing the electroplating process conditions

One of the attractive ways to improve the mechanical properties and prevent damage to the surface of the copper plate is to create a nickel/graphene coating on it. In this work, the effect of bath type and process conditions on mechanical and wettability properties of nickel/graphene oxide coated copper plate via electroplating, has been investigated. Ultrasonic stirring of the bath with a power of 200 W increased the hardness of the coating to 747 Vickers and the wetting angle with molten steel to 125° by uniformly distributing the graphene oxide layers among the nickel grains and preventing the growth of the grains. By using a chloride bath instead of a Watts bath, due to the adhesion and delamination mechanism, a slight weight loss occurred in the pin-on-disk wear test. The coating obtained by electroplating in a chloride bath containing 20 cc of colloidal graphene oxide had a structure with a thickness of 12–15 μm consisting of large and compact masses of cauliflower with a uniform distribution of graphene layers. This sample shown a contact angle of 130° with the surface tension of 25 × 10−6 N/m to the aluminum melt drop and a 135° and 120 × 10−6 N/m to the steel melt drop.

Characteristics and provenances of rare earth elements and Nd isotopes in surface sediments of mangrove wetlands in the Jiulong River Estuary, China.

Rare earth elements (REEs) and Nd isotopes are frequently employed to determine provenance, although their characteristics and provenances in the surface sediments of mangrove wetlands are rarely analyzed. In this study, a thorough analysis of the characteristics and provenances of REEs and Nd isotopes in the surface sediments of mangrove wetland in the Jiulong River Estuary was carried out. According to the results, the mean concentration of REEs in the surface sediments was 290.9mg·kg-1, which was greater than the background value. Unpolluted to moderately polluted for La and Ce, as well as a moderate ecological risk for Lu, were indicated by the geoaccumulation index (Igeo) and potential ecological risk of individual factors ([Formula: see text]), respectively. The surface sediments showed substantial negative Eu anomalies but no significant Ce anomalies. The enrichments in LREE and flat HREE patterns are visible in the chondrite-normalized REE patterns. REEs in the surface sediments might be attributed to both natural sources (granite and magmatic rocks) and anthropogenic activities, including coal combustion, vehicle exhaust, steel smelting, and fertilizer, based on the (La/Yb)N-∑REE and ternary (La/Yb)N-(La/Sm)N-(Gd/Yb)N plots. The three-dimensional ∑LREE/∑HREE-Eu/Eu*-εNd(0) plot, when combined with the Nd isotope, further demonstrated that the REEs in the surface sediments appeared to have come from additional nonlocal potential sources.

Laser surface melting of 304L SS: increase in resistance to transpassive dissolution and pitting corrosion

ABSTRACT In the present study, laser surface melting (LSM) of 304L stainless steel (SS) was performed using 250 W pulse Nd: YAG laser which resulted in a 250 µm thick melted layer with refined microstructure on the surface. Potentiostatic polarisations at various potentials in the transpassive regime in 6 M HNO3 solution at 95°C were used to quantify the IGC rate. The transpassive dissolution rate was significantly reduced after LSM. The pitting corrosion susceptibility was assessed by potentiodynamic polarisation in 3.5 wt-% NaCl solution. LSM resulted in an increase in pitting potential. Following electrochemical tests, sample surfaces were examined using optical and scanning electron microscopes besides a 3-D optical profilometer. The depths of IGC attack and pit were significantly reduced after LSM. The improvement in resistance to pitting corrosion and transpassive dissolution was attributed to the elimination of inclusions and impurity segregation at the grain boundaries brought about by LSM.

The Behavior of Direct Reduced Iron in the Electric Arc Furnace Hotspot

Hydrogen-based direct reduction is a promising technology for CO2 lean steelmaking. The electric arc furnace is the most relevant aggregate for processing direct reduced iron (DRI). As DRI is usually added into the arc, the behavior in this area is of great interest. A laboratory-scale hydrogen plasma smelting reduction (HPSR) reactor was used to analyze that under inert conditions. Four cases were compared: carbon-free and carbon-containing DRI from DR-grade pellets as well as fines from a fluidized bed reactor were melted batch-wise. A slag layer’s influence was investigated using DRI from the BF-grade pellets and the continuous addition of slag-forming oxides. While carbon-free materials show a porous structure with gangue entrapments, the carburized DRI forms a dense regulus with the oxides collected on top. The test with slag-forming oxides demonstrates the mixing effect of the arc’s electromagnetic forces. The cross-section shows a steel melt framed by a slag layer. These experiments match the past work in that carburized DRI is preferable, and material feed to the hotspot is critical for the EAF operation.

Non-metallic inclusion (NMI) deposition in a slide-gate submerged entry nozzle (SEN)

Clogging of the submerged entry nozzle (SEN) is a common and persistent issue in the continuous casting process for steel alloys. The dominant clogging mechanism has been attributed to the deposition and accumulation of non-metallic inclusions (NMI) in the steel melt. Prior studies of NMI deposition assume that every collision between an inclusion and the nozzle wall results in adhesion, which is unrealistic. In this study, a macroscopic transport model for fluid and NMI motion is combined with a microscale model for NMI adhesion and applied to a slide-gate nozzle. Eight NMI sticking probabilities (S) and three slide-gate linear opening positions are explored. Simulation results indicated that the more closed the slide-gate, the greater the total deposition of NMI. When the slide-gate was partially open, the particle area number density was highest above, within and just below the slide-gate. But when the slide-gate was fully opened the deposition was concentrated in the upper tundish nozzle. Deposition behaviour fell into two regimes based on S. When S ≤ 0.05, the particle deposition was low and increased rapidly with sticking probability. When S ≥ 0.05, the particle deposition was high but changed very little with sticking probability. Changes to sticking probability did not significantly affect the deposition locations or relative distribution of particles within the nozzle.