Refractory Wear Research Articles

The Wear of Tundish Stopper Refractories by Inclusion Slags

Liquid inclusions in the steel may play an important role in the wear of the stopper tip refractories in tundish operations. In the present study, the attack and wear of the tundish stopper refractories by inclusion slagsin OneSteel Whyalla billet product have been investigated. Three stopper tip refractories, Al 2 O 3 -C, ZrO 2 -C and MgO-C, have been tested with inclusion slags (SiO 2 -Al 2 O 3 -CaO-MnO-FeO) under argon at 1 570-1 610°C for 1-4 h using an in-situ gravimetric technique. The in-situ gravimetric data, combined with autopsy of the samples after the tests, provide valuable insights into the dynamic processes of the slag-refractory interactions and the mechanisms for refractory wear. It was found that the performance of the three refractories differed considerably and was determined predominantly by the resistance to the chemical attack by the liquid inclusions and the extent of internal carbon-oxide reactions. The FeO in the inclusion had a detrimental effect on the oxidation of carbon in the refractory, causing vigorous reaction and severe wear. The MnO in the slag also reacted with carbon, but to a much lesser extent, while severe wear only occurred when slag attacked the refractory grains. The weight loss, due to internal carbon-oxide reactions, appeared to be an important issue. Of the refractories tested, the MgO-C performed the worst, suffering from severe inclusion attack on both the carbon and the periclase grains, and considerable weight loss due to internal carbon reaction. The ZrO 2 -C showed a reasonable resistance to the chemical attack from the inclusion, with MnO up to 33wt%; but showed extensive weight loss due to internal carbon reaction. The Al 2 O 3 -C was the best performer in terms of resistance to both the inclusion attack and internal carbon reaction. The results were found to be in broad agreement with plant experience and observations.

PENETRATION AND DISSOLUTION OF MAGNETITE COATINGS BY COPPER CONVERTER MELTS

Copper converters are often protected against refractory wear by the application of a magnetite coating, but under some operating conditions, this coating is not stable. Under these conditions, if a magnetite coating is applied it will be easily dissolved and the refractory lining will suffer severe wear. Since the dissolution conditions of a magnetite coating are not well defined, an attempt has been made to understand the effect of changes in temperature and oxygen potential on the dissolution of magnetite coatings and the subsequent ability to withstand penetration when in contact with copper melts. In the present work magnetite coatings were applied to two different refractories: a magnesite chrome and a chrome-free brick. Behaviour of the products was assessed using techniques such as X-ray diffraction (XRD), differential thermal analyzer (DTA), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and energy dispersive spectroscopy (EDS). The results show that dissolution of the magnetite coating is a complex process that involves diffusion, copper penetration and incremental changes in temperature and oxygen potential. It is postulated that of these, the increased temperatures at the tuyere zone due to the use of oxygen enriched air is the primary cause of the dissolution.Les convertisseurs de cuivre sont souvent protégés contre l’usure des réfractaires par application d’un revêtement de magnétite, mais sous certaines conditions de fonctionnement, ce revêtement n’est pas stable. Sous ces conditions, si l’on applique un revêtement de magnétite, celui-ci sera facilement dissous et la paroi réfractaire souffrira d’une usure importante. Puisque les conditions de dissolution du revêtement de magnétite ne sont pas bien définies, on a tenté de comprendre l’effet de changements de température et de potentiel d’oxygène sur la dissolution des revêtements de magnétite et sur l’habileté subséquente à résister à la pénétration lorsqu’en contact avec des bains de cuivre. Dans le présent travail, on a appliqué des revêtements de magnétite à deux réfractaires différents: une brique de chrome-magnésie et une brique sans chrome. On a évalué le comportement des produits en utilisant des techniques comme la diffraction des rayons x (XRD), l’analyseur thermique différentiel (DTA), la microscopie électronique à balayage (SEM), l’analyse par microsonde électronique (EPMA) et la spectroscopie par dispersion d’énergie (EDS). Les résultats montrent que la dissolution du revêtement de magnétite est un procédé complexe qui implique la diffusion, la pénétration de cuivre et des changements graduels de température et de potentiel d’oxygène. On postule que, parmi ces facteurs, la cause principale de la dissolution est l’augmentation de la température dans la zone de la tuyère en raison de l’utilisation d’air enrichi en oxygène.

Heat Transfer Analysis and Estimation of Refractory Wear in an Iron Blast Furnace Hearth Using Finite Element Method

The wear of hearth refractory by hot metal penetration and mechanical erosion is the limiting factor in the life of a blast furnace and their control and minimisation result in a direct benefit in an extended campaign. At the same time, it is difficult to directly measure the amount and location of hearth erosion during any campaign. Heat transfer mathematical model is an appropriate tool to quantify the amount of erosion based on the prediction of temperature profile particularly 1150°C freeze line isotherm in the hearth.In the present investigation, an axisymmetric conductive heat transfer model based on finite element method has been formulated and computer software is developed. Using the model and the computer code, temperature profile is predicted in the hearth zone of two different designs of industrial blast furnaces and maximum (worst) hearth wear has been estimated. The erosion pattern is calculated on the basis of worst-case location of 1150°C isotherm that can occur during the furnace campaign. Effects of hot metal temperature, cooling conditions and coke-bed states (floating and sitting) on temperature profile and refractory wear are also investigated.

Wear of Direct-Bonded Magnesia-Chrome Ore Refractories in the RH-TOB Process

In order to elucidate the wear mechanism of direct-bonded magnesia-chrome ore refractories in RH-TOB (RH-Top Oxygen Blowing), crucibles were made from the MgO-Cr2O3 refractory, which are used as a side wall refractory material for the RH-TOB lower vessels. The crucibles were charged with melting stock to carry out the oxygen blowing experimental at 1650°C. Experiment was discriminated the wear by FeO permeation and the wear by Fe fume. The chromite in the MgO-Cr2O3 refractory creates a complex spinel of a high melting point with FeO, therefore chromite is stable and shows a high corrosion resistance on FeO. On the other hand, FeO that has a very low melting point permeates magnesia that are composed of fine particles combined by silicate bonds. Consequently, an eutectic reaction causes the bond melts and separating the particles. The wear during the RH-TOB process results from the oxidation heat that is produced when the Fe fumes react with oxygen and impact the refractory dissolve away both magnesia and chromite.

Wear of Basic Refractories in the Lining of Waelz Kilns in the Production of Zinc

Operating conditions of the refractory lining for Waeltz kilns in the production of zinc are considered. Results of an examination of post-service periclase-spinellide refractories for the Waelz kiln lining are given and major factors involved in the wear and failure of refractory materials are discussed.

Stresses in Refractory Lined Circular Vessels and Pipes

The determination of stresses with refractory lined vessels etc. must take into account the interrelatedness of both components, the shell and the lining. The necessary equations, displayed elsewhere, are clearly represented step by step. Tension stresses within the refractory are imaginary and can be traced only by calculation. They may be attributed to the shell, if only the equilibrium of forces is preserved. The effect of joint gaps within the refractory can also be calculated by introducing imaginary temperature reductions. To conclude, this report presents an example accompanying all comments and dealing with refractory wear as well.

Updating the Circulating Vacuum Degassing Technology at the Magnitogorsk Iron and Steel Works Joint-Stock Co.

Updating of a unit for outside-the-furnace vacuum degassing intended for the preparation of a low-carbon (≤ 0.004% C) IF-steel is described. The updating involved replacement of the electric heater for the work space with a gas-oxygen burner. Changes in the refractory lining wear rate associated with this replacement are discussed. Routes towards further improvement of the vacuum degassing technology are outlined.

From viscosity and surface tension to marangoni flow in melts

This article covers some of our recent work on slag viscosity, the surface tension of liquid Cu-O alloys, and the relative role of Marangoni and bulk flow on refractory wear in iron-silicate slags. A viscosity model developed for slags containing SiO2, Al2O3, Fe2O3, CaO, MgO, MnO, FeO, PbO, NiO, Cu2O, ZnO, CoO, and TiO2 is capable of representing the effects of temperature, silica, and network-modifier cations within a wide range of temperatures and compositions. It forms a useful part of a computational package for multiphase-equilibrium (MPE) calculations and for predicting slag viscosities. The models are well applicable to a range of industrial slags (blast furnace, new iron making, base-metal and Platinum Group Metals (PGM) smelting, and coal-ash slags). The package has also some capability of predicting the viscosity of slags containing suspended solids. The surface tension of liquid copper-oxygen alloys has also been analyzed. The adsorption behavior of oxygen in liquid copper is well represented by the combined Langmuir-Gibbs isotherm. According to the rate data for silica-rod dissolution in liquid iron-silicate slags at 1573 K, the preferential attack at the slag line diminishes as the linear velocity of flow at the surface of the rotating silica rod reaches 9 to 16 cm/s. A tentative analysis gives the critical condition, that relates the critical Reynolds (Re) and Marangoni (Ma) number by the equation Re*2=0.13 Ma*.

Oscillatory flow in the steelmaking vessel

Physical modelling of the basic oxygen furnace (BOF) was undertaken with the object of developing an overall flow pattern within the vessel as a function of fluid‐flow dynamics/vessel geometry interaction. The study was initiated as the result of localised refractory wear occurring in the knuckle region of a BOF vessel. The occurrence of the wear coincided with a change in lance tip design. This preferential wear limited the campaign life of the vessel. Modelling the fluid dynamics of the system was to examine any possible relationship between fluid‐flow patterns and this refractory wear pattern. The 4‐fold symmetry of the newer lance tip allowed the application of a quadrant sector model of the bath. This simplified the flow to the effect of an individual nozzle. A scale of 1/6th was chosen on the basis of the bath depth and flow rates required. Results from this work indicate that waves may have a role in this localised wear.The multiphase system of the BOF involving supersonic gas jets, molten iron and slag, and the interaction between these, ensure that there is no single model, in which all facets of similarity may be satisfied simultaneously. This is the major problem in modelling the BOF.

State of the Art in Evaluation and Control of Steel Cleanliness.

This paper first reviews the current “state-of-the-art” in the evaluation of steel cleanliness, discussing over 20 different methods. The demand for cleaner steels requires lowering non-metallic oxide inclusions and also controlling their morphology, composition and size distribution. Because no single method can measure all of these aspects accurately, it is best to combine several methods together to quantify steel cleanliness in a given operation. Owing to the cost, time requirements, and sampling difficulties, steel cleanliness is widely inferred using total oxygen, nitrogen pick-up, and other indirect methods. Recent cleanliness values using these indicators are summarized for LCAK at many steel plants around the world. Secondly, this paper reviews operating practices to improve steel cleanliness at the ladle, tundish and continuous caster, emphasizing findings quantified with plant measurements. Inclusions come from many sources, including deoxidation, reoxidation, slag entrapment, refractory wear, and chemical reactions. They generate many defects such as cracks and slivers in the steel product. Steel cleanliness is controlled by attention to a wide range of important operating conditions throughout the steelmaking and casting processes. For ladle operations, FeO and MnO in the slag, ladle treatments, and inclusion modification are discussed. For tundish operations, tundish depth and capacity, casting transitions, refractory lining, tundish flux; gas stirring, and flow controls are discussed. Important transfer operations from ladle to tundish and from tundish to mold, such as argon protection, sealing issues, and SEN clogging are summarized. Caster operations reviewed include the effect of casting speed, fluid flow pattern control, surface level control, and caster curvature.

Effect of Marangoni‐induced flow on the rate of refractory dissolution in molten slags

Dissolution rate of silica rods in iron‐saturated silicate slags containing 15–30% SiO2 was measured using the rotating cylinder technique at 1300°C, under a controlled atmosphere of deoxidized Ar‐gas. These measurements were aimed at quantifying the magnitude of Marangoni‐induced flow near the slag–refractory region. The Marangoni effect was found to be significant under stagnant conditions, but gradually became dominated by bulk flow when the linear velocity of the flowing melt was increased, and reached values in the range of 0.09–0.16 m/s. This implies that, in highly agitated vessels, the Marangoni effect is unlikely to play a dominant role in refractory wear at the slag line. Also, the silica dissolution rate and mass transfer coefficient were examined, and it was found that with increasing silica content of the slag, the dissolution rate and mass transfer coefficient decreased. Furthermore, the relationship between Marangoni number and Reynolds number was calculated, and boundary flow conditions determined using the experimental critical velocity.

Flow Characteristics of a Blast Furnace Taphole Stream and Its Effects on Trough Refractory Wear.

An investigation consisting of plant trials and water modelling studies has been carried out with the aim of gaining a better understanding of flow characteristics of a blast furnace taphole stream and its effect on the trough refractory wear. It has been found that the entrainment of the blast gas into the taphole is the most likely root cause for splashy taphole stream, which is believed to greatly contributes to refractory wear on the trough in the region above the liquid level and on the trough cover. Based on the findings from the present studies, changes were made to furnace operation and casting practices at BHP Steel's Flat Products Division No. 6 Blast Furnace (BF6) to minimise splashy taphole streams. As a result, the refractory wear on the trough and its cover has been significantly reduced. The trough cover life of BF6 has been improved, from 60 000 to 300 000 tonnes of hot metal.

Flow Characteristics in a Blast Furnace Trough.

The aim of this study was to better understand flow characteristics in the taphole stream impingement region of a blast furnace trough, and its effect on localized trough refractory wear. A 1/5th scale perspex model was used, and oil and water were adopted to simulate the molten iron and slag, respectively. Velocities and turbulence intensities in the region adjacent to the trough wall were measured by means of laser doppler velocimetry (LDV). This study highlighted the entrainment of bubbles by the impinging taphole stream, resulting in a buoyancy-driven flow pattern within the trough. The identified buoyancy-driven flow resulted in high velocities and turbulence intensities in the region where maximum refractory wear occurred. Methods for minimizing the influence of the buoyancy-driven flow, and resultant high velocities and turbulence intensities are proposed in this paper.

Sloshing of Melts in a Bath Smelting Process Having an Elliptic Cross Section.

Recently, the use of the elliptic cross section cylinder for bath smelting operations was adopted by the Ausiron process. The high gas flow rates used have been found to generate wave motion in the bath that can enhance refractory wear. The standing wave modes were found for the bath. Two distinct sets of eigenvalues were obtained, one in the major axis and the other in the minor axis. The two sets converged when the ellipticity of the cylinder is zero, which is the shape of a circle. The calculated wave frequency was found to agree well with experimental data. A complete set of eigenvalues have been calculated for elliptic cylinders and fitted to Chebyshev polynomials, enabling quick estimation of the standing wave frequencies. The study showed that the ellipticity of the vessel for the Auslron process needs to be carefully chosen as the standing wave modes that can be generated may result in beat frequencies that can interact with the natural frequencies of the vessel support and auxilliary equipment.

In-Situ Gravimetric Studies of Wetting, Penetration and Wear of Refractories by Molten Slags

Article In-Situ Gravimetric Studies of Wetting, Penetration and Wear of Refractories by Molten Slags was published on October 1, 2001 in the journal High Temperature Materials and Processes (volume 20, issue 3-4).

Preferential refractory wear in top blown basic oxygen furnace

Physical modelling of the basic oxygen furnace (BOF) was undertaken with the object of developing an overall flow pattern within the vessel as a function of fluid flow dynamics–vessel geometry interaction. The study was initiated as the result of localised refractory wear occurring in the knuckle region of a BOF vessel. The occurrence of the wear coincided with a change in lance tip design. This preferential wear limited the campaign life of the vessel. Modelling the fluid dynamics of the system was carried out to examine any possible relationship between fluid fow patterns and this refractory wear pattern. The fourfold symmetry of the newer lance tip allowed the application of a quadrant sector model of the bath. This simplified the flow to the effect of an individual nozzle. A scale of one-sixth was chosen on the basis of the bath depth and flowrates required. Results from this work indicate that waves may have a role in this localised wear. The multiphase system of the BOF involving supersonic gas jets, molten iron, and slag, and the interaction between these, ensure that there is no single model in which all facets of similarity may be satisfied simultaneously. This is the major problem in modelling the BOF.

Design and implementation of slag practices for reduction in refractory consumption at BHP steelmaking centres

BHP Steel produces about 8 million tpa of steel for the local and overseas markets. The costs associated with refractory materials are considerable and thus strategies have been developed to reduce the refractory wear in steelmaking operations. The approaches developed take into account some of the key fundamental factors influencing the metallurgical performance of the process and the rate of chemical attack of refractories by molten slags. Thermodynamic models have been used for analysis of plant data and design/tuning of suitable practices to prolong the refractory life via in‐situ coating of refractories with solid phases with high resistance to slag attack. Examples of the results obtained from implementation of such practices are presented.

Effect of electric arc vitrification of bottom ash on the mobility and fate of metals.

Increasing amounts of municipal solid waste incineration (MSWI) residues are treated prior to landfilling or reuse. In Japan, electric arc melting is used for bottom ash vitrification that generates a glasslike slag. The objective of this paper was to assess this pretreatment technique with respect to its effect on metal mobility and metal content. Both bottom ash and slag were sampled and analyzed on total solids (TS), fixed solids (FS), particle density (pp), specific BET surface area, particle size distribution, and total element content. A six-step wet sequential extraction procedure was used for assessing metal mobility. The results were qualitatively verified by scanning electron microscopy. The major conclusion was that the availability of various metals was affected differently by electric arc vitrification. Metals were solidified, stabilized, and/or separated from the slag. The mobility of Cr, Cu, Zn, Pb, and Ca was reduced. In slag, majorfractions of these elements were found in moderately reducible phases or in the residual slag lattice. The approximately three-fourths of Pb [174 +/- 7 mg (kg of FS)-1] and half of Zn content [676 +/- 352 mg (kg of FS)-1] were most likely removed from bottom ash through evaporation. The total content increases of Al, Cr, Ni, and Cd (51 +/- 3, 621 +/- 27, 138 +/- 19, and 99 +/- 32%, respectively) were probably caused by the wear of furnace refractories.

Degradation mechanisms of magnesia-chromite refractories in vacumm-oxygen decarburisation ladles during production of stainless steel

Magnesia–chromite bricks are used as refractories for the refining of stainless steel in vacuum–oxygen decarburisation (VOD) ladles. Refractory wear is not uniform. In the present work, worn bricks from different zones in the ladle have been analysed, and a set of interdependent degradation mechanisms is proposed. Refractory wear as a function of position in the ladle is discussed. Slag infiltration and MgO dissolution from the refractory were observed in all samples, whereas FeOx decomposition was seen at two levels in the high wear samples. First, partial decomposition of primary chromite crystals ( (Mg) [Fe3+, Cr, Al]2 O4 ) occurred at the hot face of the brick. Three layers were distinguished in the reacted chromite crystals and a reaction mechanism is presented. Second, a decrease in the FeOx content of the magnesia phase occurred at the hot face of the brick. The negative effect of the presence of FeOx in magnesia–chromite refractories is discussed and the influence of the ferrostatic pressure is demonstrated. Finally, the consequences of the following phenomena are discussed: increase in brick porosity, slag infiltration, corrosion, erosion of the partially liquid bonded refractory system, and spalling and cracking.

Study of Refractory Wear in the Tuyere Region of a Peirce-Smith Nickel Convertor

Profiles of the composition variation with distance from the hot face were mapped out by SEM analysis of chrome-magnesite tuyere refractory bricks from a Peirce-Smith nickel converter. The presence of magnesium sulphate was confirmed by XRD, SEM and wet analysis. The work showed that periclase was highly susceptible to attack by sulphur dioxide and formed magnesium sulphate in the cooler regions of the refractory brick where the reaction was favourable. Thermal cycling caused the periclase to alternate between the sulphate and the oxide leading to increased pore formation and decreased brick strength. This combined with tuyere punching contributed to the enhanced loss of refractory at the tuyere line. The accretion layer had a high nickel ferrite content which agreed with the high oxygen potential expected at the tuyere region. An interface region between the accretion layer and the refractory showed that counterdiffusion of iron and magnesium assisted in removing periclase from the refractory. Nickel and nickel compounds were limited to the first two mm of the hot face and no infiltration was found. The chrome-spinel is more resistant to attack than the periclase. The pore structure in the refractory brick was identified as the key variable in resisting sulphate formation. An ability to close or fill the pores will reduce the possibility of sulphur dioxide diffusion into the cooler regions for magnesium sulphate formation. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.RésuméOn a tracé, par analyse SEM, des profils de la variation de la composition en fonction de la distance, à partir de la face chaude de briques réfractaires en chromite-magnésie de la tuyére d'un convertisseur Peirce-Smith pour le nickel. On a confirmé la présence de sulfate de magnésium par XRD, SEM et analyse par voie humide. Le travail a montré que la périclase était extremement susceptible à l'attaque par le bioxyde de soufre et formait du sulfate de magnésium dans les zones les plus froides de la brique réfractaire, la ou la réaction était favorable. Les cycles thermiques ont fait en sorte que la périclase alternait entre le sulfate et l'oxyde, conduisant a une augmentation de la formation de pore et à la diminution de la résistance de la brique. Ceci, en combinaison avec la perforation de la tuyére, a contribue à une augmentation de la perte de réfractaire a la ligne de tuyére. La couche d'accretion avait un contenu élevé en ferrite-nickel, en accord avec le haut potentiel en oxygene de la zone de la tuyére. Une region interfaciale entre la couche d'accretion et le réfractaire a montré que la contre-diffusion du fer et du magnésium a contribue à I'enlevement de la periclase du réfractaire. Le nickel et les composes de nickel etaient limites aux premiers deux mm de la face chaude et l'on a trouvé aucune infiltration. Le chrome-spinelle est plus résistant à I'attaque que la periclase. On a identifie la structure de pore de la brique refractaire comme etant la variable-cle dans la resistance à la formation de sulfate. Une habilite à fermer ou remplir les pores reduira la possibilité de diffusion de bioxyde de soufre vers les regions les plus froides pour la formation de sulfate de magnésium. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.