Slag Layer Research Articles

Effect of Al Content in Steel on Interfacial Interaction between Molten Steel and MgO Substrate

The apparent contact angles between the molten steel with different [Al] contents (w[Al]) from 0.002% to 0.831% (mass fraction) and the microporous MgO (MM) substrates are measured at 1823 K using the sessile drop method. In particular, the contact angles of No. 1 (w[Al] = 0.002%) and No. 5 (w[Al] = 0.831%) molten steels gradually increase with time at the initial stage. As w[Al] increases from 0.002% to 0.831%, the transformation route of interfacial products between molten steel and the MM substrate is MgO–FeO → MgO·Al2O3 → CaO·2Al2O3 + MgO·Al2O3. The w[Al] of No. 1 molten steel is small, and the dissolution of CaO·ZrO2(s) in the substrate is mainly affected by FeO. As w[Al] increases gradually, [Al] consumes the (MgO) contained in CaO·MgO·SiO2 (CMS), and turns the CMS into (CaO·SiO2) slag layer, which promotes the CaO·ZrO2(s) dissolving and thus increasing the interaction area percentage. When w[Al] is 0.831%, [Al] can react with (CaO·SiO2) slag layer or CaO·ZrO2(s) to form CaO·2Al2O3(s).

Heat Exchange in High-Power Arc Steel-Making Furnaces. Part III. Interconnection of Heat Exchange, Height of the Slag Layer, Efficiency of Arcs, and Specific Electricity Consumption

Heat Exchange in High-Power Arc Steel-Making Furnaces. Part III. Interconnection of Heat Exchange, Height of the Slag Layer, Efficiency of Arcs, and Specific Electricity Consumption

Heat Conduction through Different Slag Layers in Mold. Thermal Conductivity Measurement of Commercial Mold Fluxes

The thermal conductivity of two commercial mold fluxes has been investigated using the transient hot-wire method in the temperature range of 298 K to 1573 K. Experiments were conducted on granules, sintered granules, molten fluxes and glassy samples under ambient atmosphere. Characteristic temperatures of the mold fluxes were investigated using a hot stage microscope. Results are discussed in the context of the characteristic temperatures, the particle size of granules, the bulk density and the structure of the mold fluxes. The temperature dependence of the thermal conductivity for granules of mold fluxes is positive in the temperature range of 298 to 873 K (λ = 0.058 + 1.245 × 10−4 T). The further temperature increase causes the rapid increase of the thermal conductivity above the temperature, at which the granules start to sinter Tdeformation. The thermal conductivity of the glassy sample is around two times lower than the thermal conductivity of the devitrified sample. The effect of the glass transition temperature on the thermal conductivity was shown. The thermal conductivity rapidly increases above the glass transition temperature in the glass transition region as the temperature rises and decreases above the softening temperature Tsoftening. The further temperature increase caused the crystallization of the sample. The crystallization of the sample was observed at T ≈ Tg + 100 K. Moreover, results show the dependence of the thermal conductivity of molten mold fluxes on the basicity (CaO/SiO2) at 1573 K.

Investigating the origins of metals used in the Early Shang capital of Zhengzhou

Lead isotope analysis of crucibles and a metal droplet has revealed new information about the provenance of the lead and copper resources used at Zhengzhou Shang City during the Upper Erligang period. The crucibles were found to be divided into three types and associated with copper smelting/refining, leaded tin bronze alloying, and bronze pouring. The copper smelting/refining crucible contains common lead (206Pb/204Pb = 18.12) and low Pb content in its slag layer. In contrast, the bronze processing crucibles mostly contained highly radiogenic lead (206Pb/204Pb ≥ 19). One bronze pouring crucible was found to have an exceptionally low 206Pb/204Pb ratio (≤17.2), indicating that it was made with recycled bronze from an earlier period. This research is the first to reveal the lead isotope characteristics of the copper material used during the Upper Erligang period, which is strikingly different from the dominant highly radiogenic lead reported in previous research. The Middle Yangtze River Valley is tentatively proposed as the geological source. This result also shows that the Upper Erligang Shang people had a complex metal supply network, including at least southern copper, highly radiogenic lead, and recycled early bronze.

Enhanced Productivity of Bottom-Blowing Copper-Smelting Process Using Plume Eye

Bottom-blowing copper smelting is a bath smelting technology recently developed in China. It has the advantages of good adaptability of raw materials, high oxygen utilization and thermal efficiency, and flexible production capacity. Plume eye is a unique phenomenon observed in the bottom-blowing copper-smelting furnace where the slag on the surface of the bath is pushed away by the high-pressure gas injected from the bottom. The existence of plume eye was first confirmed by analyzing the quenched industrial samples collected above the gas injection area and then investigated by laboratory water model experiments. Combining the plant operating data and the smelting mechanism of the copper concentrate, the role of the plume eye in bottom-blowing-enhanced smelting is analyzed. It reveals that the direct dissolution of copper concentrate as a low-grade matte into the molten matte can significantly accelerate the reactions between the concentrate and oxygen. The productivity of the bottom-blowing furnace is therefore increased as a result. The effects of the gas flow rate and thickness of the matte and of the slag layer on the diameter of the plume eye were studied using water-model experiments. It was found that increasing the gas flow and the thickness of the matte and reducing the thickness of the slag can increase the diameter of the plume eye. This work is of great significance for further understanding the copper bottom-blowing smelting technology and optimizing industrial operations.

Mathematical modelling of novel combined stirring method during the final stage of ladle refining

ABSTRACT A novel horizontal stirring has been introduced to investigate the effect of such a stirring on the ladle profile during the combined stirring process at the refining stage. The multiphaseInterFoam solver has been updated to consider the induction forces imposed on the liquid bath by the magnetic stirrer.During the combined stirring stage, the gas plume is affected by the rotational movement. The gas plume seems to be intact in the lower one-third of the domain, then breaks into clusters in the upper section while the rotational movement of clusters dissipates a large portion of upward momentum of the bubbles. This prevents large openings in the slag layer and respectively, prevents the exposure of steel. It also disperses the bubbles to various sections of the ladle. Hence, such a novel stirring strategy seems to have the potential of improving the cleanness of the liquid steel during the ladle refining process.

Multiscale and Adaptive Modeling of Bubbling Flow and Slag Layer Behavior in Gas-Stirring Vessels

Multiscale and Adaptive Modeling of Bubbling Flow and Slag Layer Behavior in Gas-Stirring Vessels

Laser Directed Energy Deposition-Based Additive Manufacturing of Fe20Cr5.5AlY from Single Tracks to Bulk Structures: Statistical Analysis, Process Optimization, and Characterization

Laser directed energy deposition (LDED) can be deployed for depositing high-performance materials for various engineering applications. Alumina-forming steel is a high-performance material that possesses excellent corrosion and oxidation resistance, finding application in the power generation sector. In the present work, LDED using powder feeding (LDED-PF) was used to deposit Fe20Cr5.5AlY alloy using single-track, multi-track, and multi-layer deposition on SS 316L substrate. Response surface methodology (RSM)-based optimization was used to optimize the single-track deposition. The relationship between the track geometry parameters and the build rate with the LDED-PF processing parameters was studied. Further, the nonlinear relationship among the major process parameters was developed and an analysis of variance (ANOVA) was utilized to find significant parameters. The multi-track deposition yielded densely clad layers with a columnar grain structure. The presence of complex oxide slag of Y, Al, and Zr on the clad layer was detected. A micro-hardness of 240–285 HV was observed in the clad layer, with a hardness of 1088–1276 HV at the slag layer. The multi-layered structures showed a relative density of 99.7% with columnar growth and an average microhardness of 242 HV. The study paves the way for the deposition of dense alumina-forming steel structures for building components for power generation applications.

Numerical simulation on inclusion removal behaviours in refining processes of spring steel

ABSTRACT Aiming at the unsatisfactory removal rate of various inclusions in refining process of spring steel in a steel plant, this study proposes a unequal flow bottom blowing method with an inlet flow ratio of 2:1, and its effectiveness is verified by numerical simulation and actual production. The numerical simulation results show that under the 2:1 bottom blowing method, the molten steel has greater axial flow strength, which is conducive to the inclusion floating to the slag layer. The removal rate of inclusions under the 2:1 bottom blowing method is about 8% higher than that of the equal flow. The production results are consistent with the numerical simulation, when the inlet flow is 100 NL/min, the inclusion removal rate under 2:1 bottom blowing method is about 18% higher than that of equal flow, meanwhile, the total number of inclusions and large size inclusions are lower than that of equal flow.

Slagging Characteristics of a Steam Boiler Furnace with Flare Combustion of Solid Fuel When Switching to Composite Slurry Fuel

Two interconnected mathematical models have been developed to describe slagging of a steam boiler furnace at the macro and micro levels. The macro-level model is implemented in Ansys Fluent. Using the fuel characteristics and temperature in the furnace, this model can predict the characteristics of ash formation on heat exchanger tubes when the melting temperature of the mineral part of solid fossil fuel is exceeded. The obtained values of slagging rates are used as initial data in the software implementation of the original Matlab microlevel model. Under conditions of dynamic change in the thickness of the slag layer, this model can evaluate the heat transfer characteristics in the hot gas/slag layer/tube wall/water coolant system. The results showed that switching a coal-fired boiler from a solid fossil fuel to a fuel slurry will improve stability and uninterrupted boiler operation due to a lower slagging rate. The combustion of coal water slurries with petrochemicals compared with coal–water fuel is characterized by higher maximum temperatures in the furnace (13–38% higher) and a lower average growth rate of slag deposits (5% lower), which reduces losses during heat transfer from flue gases to water coolant by 2%.

Extending powder lifetime in additive manufacturing: Chemical etching of stainless steel spatter

• Chemical etching can eliminate most oxides from 316 L spatter. • A reduction in oxide coverage from 7–0.7% was possible. • Removal is thought to occur via initial dissolution of oxide-surrounding metal. • Etched spatter powder performed better in LPBF. • Reduced slag layer, and better wetting was seen for LPBF etched spatter. In laser powder bed fusion, unconsolidated metal powder on the build plate tends to comprise a proportion of oxidised powder after repeated use. This is generally caused by the generation of oxidised spatter particles during processing which can contaminate the powder bed, and be incorporated into future builds, ultimately undermining part integrity. Oxidised metal powder often results in porosity, poor layer-layer bonding and detrimental oxides in the printed part. This work uses a new chemical etching approach to remove oxides from the surface of oxidised stainless steel spatter powder. It was shown that a ten-fold reduction in oxide area coverage on spatter powder was possible through submersion in a solution of heated Ralph's etchant for one hour. Oxide removal is thought to occur mostly via dissolution of the metal surrounding and underneath oxide islands on the powder, allowing more aggressive oxide removal. LPBF processing was performed using spatter, etched and virgin powder sieved to an identical powder size range. Etched spatter showed a reduced oxide slag layer on track surfaces compared to spatter. In addition, incorporation of powder into tracks appeared improved after chemical etching of the powder. This work demonstrates that chemical etching has the potential to be used to increase the re-usability and lifetime of spatter or heavily used powder from widely used and corrosion resistant stainless steel powder.

Effect of Oxide Flux Particle Size on Weld Bead Morphology of Hastelloy C-22

Activated tungsten inert gas welding (ATIG) welding is a new approach to Tungsten Inert Gas (TIG) welding that has the potential to improve weld penetration. This paper investigates the effect of micro and nanoparticle size oxide flux during TIG welding of Hastelloy C-22. The effect of SiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> oxide fluxes in terms of particle size and thermal stability on surface appearance, bead geometry, and microhardness of the fusion zone of hastelloy C-22 is investigated. The surface appearance of ATIG weld has a better appearance using nanoparticle size oxide flux when compared with the same micro size oxide flux. A slag layer produced by nano flux decomposition during TIG welding is very less compared to micro oxide fluxes. Nanoparticle SiO<sub>2</sub> flux has the potential to improve weld penetration and depth to width (D/W) ratio in the generated weldment when compared to microparticle SiO<sub>2</sub> flux during TIG welding Process. When nanoparticle Al<sub>2</sub>O<sub>3</sub> is used in TIG welding, weld penetration or the D/W ratio do not increase significantly. Due to the high voltage produced at the same arc length, TIG welding with nanoparticle SiO<sub>2</sub> flux produces a high heat input. Furthermore, higher arc temperatures produce by nanoparticle fluxes at the arc column, resulting in increased penetration depth.

Experimental Study on Bubble Entrainment by a Free Fall Jet in an Argon‐Filled Continuous Casting Tundish

Inert gas entrainment by the impact of free fall jet can avoid the bubble grow‐up on nonwetting interface between liquid steel and refractory gas nozzle, which produces bubbles as small as 0.37 mm for deep cleaning the liquid steel in an argon‐filled tundish. The time‐dependent vibration of free fall jet is described by a high‐speed camera combined with image postprocessing software. The effect of liquid flow rate and free fall length on jet vibration is investigated. The equivalent surface roughness is proposed to characterize the surface wave of free fall jet without fixed amplitude and frequency. The entrained gas flow rate shows a good correlation with the equivalent surface roughness. Gas entrainment cannot happen with a free fall jet shorter than 2 mm, as the jet vibration is insufficient to make the bubbles separate from the gas sheath. The surface fluctuation caused by the impact of free fall jet can be well isolated within a submerged shield that remains a stable slag layer outside of the shield. Besides, the strong mixing flow caused by free fall jet is beneficial to dissipate the turbulence kinetic energy of the entry flow, which improves the tundish flow field.

A post‐mortem analysis of the used gel‐bonded Al2O3–MgAl2O4 castables in an industrial steelmaking ladle

AbstractIn this work, a cement‐free alumina‐spinel (Al2O3–MgAl2O4) castables with a new aluminum–magnesium gel binder were developed to line the Ruhrstahl Heraeus refining ladle, chemical attacks, and degradation mechanisms of the used alumina‐spinel castables after industrial trials were investigated. The results indicated that a reaction product layer of (Mg, Fe)Al2O4 was observed between the slag layer and penetration layer (PL), which was mainly derived from the reaction between MgAl2O4 spinel in the refractory matrix and FeOt from slag or an oxidation of steel, and thereby prevented the further penetration of FeOt. Meanwhile, the in situ spinel could also entrap slight CaO, SiO2, and FeOt from the infiltrated slag to form composite spinel in the PL. Moreover, chemical corrosion/penetration and structural spalling dominated the degradation process of the refractory lining in this case. Cracks formed between the deteriorated layer and original layer because of mechanical and thermal stress, which caused spalling from the refractory's hot face.

Diverse strategies for copper production in Chalcolithic Iberia

Our understanding of early copper metallurgy in the Iberian Peninsula is mostly based on analysis from well-studied regions in the Southeast and Southwest. This paper focuses on two recently recovered Chalcolithic metallurgical assemblages outside these traditional research foci: two slagged crucibles from Lugar Viejo III (Zaragoza) and two large slag cakes from Cueva del Cañaveralejo (Córdoba). Analysis of the compositions and microstructures of the artifacts using optical microscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) suggests they are related to primary copper production, namely smelting in crucible-furnaces under relatively oxidizing conditions, as is standard for this period. The slag layers on crucibles from Lugar Viejo indicate the production of copper with minor amounts of arsenic, also typical for this period. Of special note is the use of organic temper in the crucibles from Lugar Viejo, a practice found at the nearby site of Moncín but rare at other sites in Iberia. However, the slags from Cueva del Cañaveralejo are atypical in their large size (approx. 125 g each), fayalitic composition, unusual efficiency as demonstrated by a low copper content, and lack of arsenic; furthermore, the high sulfur content raises the possibility of the use of sulfidic ores. Results from both sites are compared against published data from well-known sites such as Los Millares, Las Pilas, Almizaraque, and Bauma del Serrat del Pont. The new data from Lugar Viejo and Cueva del Cañaveralejo reinforce the interpretation of metallurgy in the Iberian Peninsula as a low-skilled, conservative technology but also indicate the need for more research into regional variations. (See Supplementary Data 1 for a summary in Spanish).

Optimization of Process Parameters for ESR Waspaloy Superalloy by Numerical Simulation.

A transient numerical simulation method is used to investigate the temperature field, velocity field, and solidified field of large-size Waspaloy superalloy during the electroslag remelting (ESR) process. The effects of melting rate, filling rate, and thickness of the slag layer on the molten pool shape and dendrite arm spacing evolution have been discussed. The temperature in the slag pool is high and relatively uniformly distributed, the temperature range is 1690-1830 K. The highest temperature of the melt pool appears in the center of the slag-metal interface, 1686 K. There are two pairs of circulating vortices in the slag pool, the side vortices are caused by the density difference caused by the buoyancy of the slag, the center vortices are the result of the combined action of electromagnetic force and the momentum of the falling metal droplets. The molten pool depth and dendrite arm spacing increase with the increase of melting rate, but the slag layer thickness and electrode filling rate have little effect on the molten pool morphology and dendrite arm spacing if the droplet effect is not taken into account. Considering the morphology and depth of the molten pool as well as the size and distribution uniformity of the dendrite arm spacing, it is appropriate to maintain the melting rate at 5.8 kg/min for the industrial scale ESR process with the ingot diameter of 580 mm.

Formation and control of longitudinal cracks in hypoperitectic steel slabs

ABSTRACT Hot delivery and charging techniques can significantly reduce energy consumption, carbon emissions, and the production cycle of products. The defect-free slab is the precondition of this techniques. Herein, the morphological characteristics of the longitudinal cracks were described in detail. The actual phase transition process and solidification shrinkage behavior were analyzed considering the effect of alloy elements. Due to the unreasonable submerged entry nozzle (SEN) structure, the vertical heat transfer is not optimal around the meniscus. When the gap cannot be filled with sufficient liquid slag, an air gap is easily formed between the solidified shell and the mould plates. The effect of uneven solidification and stress concentration on the crack formation will be enlarged by the air gap. A novel SEN with a reasonable structure can significantly improve the thickness of the liquid slag layer and solidification uniformity, and decrease the crack sensitivity of the steel.

Multi-physics coupling model–based numerical analysis of the effect of the electric current path on electroslag remelting

A multi-physics coupling model is developed to study the effect of the electric current path on the electroslag remelting (ESR) process. The electromagnetic field is calculated in the whole system including the molten slag, solidified slag, ingot and mold by the finite element method (FEM), while the two-phase flow, heat transfer, and solidification/melting are simultaneously solved using the finite volume method (FVM). The electrode melting rate is evaluated considering the actual heat flux from the slag to the electrode. Three electric current paths on an industrial scale ESR process are predicted after the experimental verification. When the current conductive mold (CCM) is used, approximately 73.7% of the total current entering the mold directly from the slag layer, wihle the skin effect disappers. The total Joule heat is 12.55 kW lower than that in the typical ESR system, causing a reduction of 7.4% in metal pool depth. When the slag skin is assumed to perfectly insulate the slag and ingot from the mold, the total Joule heating, electrode melting rate, and metal pool depth are overestimated. The insulation hypothesis must be used with great caution. Additionally, the effects of the fill ratio and slag height on the heat balance and metal pool profile in the ESR-CCM system are analyzed. The development of the model and the findings can help understand the industrial ESR processes with CCM and optimise the process design and operational parameters.

A novel approach to predict the inclusion removal in a billet caster mold with the use of electromagnetic stirrer

Use of in-mold electromagnetic stirrer (M-EMS) in continuous casting (CC) mold has been an effective means to get clean steel. However, at times their application results in slag entrainment and inclusion particles from the meniscus due to improper positioning of the stirrer along the length of the mold. More importantly, the inclusion particles coming through the tundish outlet pose a great challenge as they are likely to get trapped in the swirl flow developed due to the stirrer and finally move towards the mold outlet. In this study, a multiphase model involving solidification, slag-metal interface and inclusion transport is developed in the billet continuous casting process. The multiphase study involves the study of slag metal interface as well as the inclusion transport in the billet caster mold. For inclusion removal at the interface, a new realistic approach based on volume fraction criterion is adopted and incorporated using user defined function. The numerical results reveal that both intensity and size of the recirculation loop decrease on shifting the EMS away from meniscus. Tangential velocity increases significantly in the presence of EMS. Stirring generated due to EMS decreases the temperature and increases the uniformity in liquid fraction in the region above the stir. This region becomes wider as EMS moves downwards. Stirring pulls down most of the interface originated 2 μm and a few 100 μm in the mold, which is otherwise trapped back in slag layer when EMS is off. Moreover, this effect diminishes with shifting the EMS down.

Element migration and phase distribution characteristics during crystallization of rare earth phase in rare earth slag

The crystallization experiment of molten rare earth (RE) slag under different cooling rates was carried out. The characteristics of element migration and phase distribution during RE phase crystallization were studied by using different equipment. The experimental results show that there are two RE phases in the RE slag, namely (Ca, Ce, La)5(SiO4)6F and (Ca,Ce,La,Mg)3(Ti,Al,Nb)2O7. During the cooling crystallization process of molten RE slag, Ca and P elements in the RE phase of (Ca,Ce,La)5(SiO4)6F migrate from inside to outside, and finally gather at the outer edge of the phase to form phase Ca3(PO4)2. The RE phase (Ca,Ce,La)5(SiO4)6F is distributed inside the furnace-cooled slag, and the RE phase (Ca,Ce,La,Mg)3(Ti,Al,Nb)2O7 is distributed in the surface layer of the furnace-cooled slag. And based on the phase distribution characteristics, the central hollowing method is proposed to realize the preliminary enrichment of valuable elements Ti, Nb and RE in RE slag.