In this study, an improved water-cooled copper probe was used to obtain solidified films of a mold flux used to cast peritectic steel. Different bulk temperatures of molten mold flux and different probe immersion times were used. The results reveal that the surface roughness of the slag film (in contact with the copper probe) has no direct relationship with solidification crystallization or devitrification in the slag film. Higher bulk temperatures (of molten flux) gave rougher surface slag-probe interfaces. Pores contribute to the surface roughness.

Unweathered ilmenite, weathered ilmenite, and a rutile-rich (zircon-containing) concentrate were reduced with 39 pct H2-6 pct CH4 (balance Ar) reduction gas at 1473 K (1200 °C). Despite differences in initial iron content, phase composition, and thermal stability of the phases, the main steps of the reaction sequence for the three materials were the same. The metallic iron product could be removed by leaching. In all cases, the product after leaching was a carbon-rich titanium oxycarbide.

•Fatigue properties of additively manufactured (AM) AlSi10Mg are similar to castings.•Oxide-driven porosity is the most common internal defect in the AM parts.•Pores and oxide particle size at the part surface control fatigue life.It is well-known that the fatigue behavior of cast aluminum alloy parts is largely determined by internal defects, particularly pores and inclusions. In this work, it is shown that such imperfections are also present in AlSi10Mg parts produced by selective laser melting, and serve as sites to initiate fatigue cracks. The effect of hatch spacing and building orientation on tensile and fatigue properties was tested. Oxide-driven pores dominate the fatigue resistance of the samples in this work. The larger oxide particles which are associated with crack initiation likely form by oxidation of metal vapor during part manufacture.Download high-res image (221KB)Download full-size image

This work investigated the use of FactSage macros to simulate steel–slag and steel–inclusion reaction kinetics in silicon-manganese killed steels, and predict oxide inclusion composition changes during ladle treatment. These changes were assessed experimentally using an induction furnace to simulate deoxidation and slag addition. The average steel mass transfer coefficient for the experimental setup was calculated from the analyzed aluminum pick-up by steel. Average oxide inclusion composition was measured using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Confocal laser scanning microscopy was used to assess the physical state (solid or liquid) of oxide inclusions in selected samples. The changes in the chemical compositions of the oxide inclusions and the steel agreed with the FactSage macro simulations.

AlSi10Mg cylinders produced by laser powder-bed fusion have somewhat different yield behavior for cylinders with XY orientation and Z orientation. Earlier yielding for Z-oriented samples is likely related to micro-residual stress, resulting from the difference in thermal expansion of the aluminum matrix and cellular silicon. Smaller tensile reduction in area of Z-oriented samples is related to tearing along the softer region at the boundaries of melt pools, where the silicon cell spacing is larger. Indentation measurements confirmed the lower hardness at the edges of melt pools.

Iron ore pellets, reduced with hydrogen, were isothermally carburized in CH4-H2-N2 at 823 K, 923 K, and 1023 K (550 °C, 650 °C, and 750 °C). Temperature strongly affected the total carbon concentration after carburization; significant unbound carbon deposited at the highest temperature. For the range of sizes tested (10 to 12 mm), pellet size did not affect carburization. The variability between pellets was much smaller than for industrial pellets; inhomogeneous gas distribution likely affects carburization under large-scale industrial conditions.

The free energy of mixing in the Ti(O,C) shows negative deviation from ideality. A recent paper in Journal of Materials Chemistry A erroneously shows a large positive deviation from ideality.

The nature of MgO and Al2O3 dissolution in metallurgical slags may affect production cost, efficiency, and product quality. However, the rate-limiting dissolution mechanism, chemical reaction or boundary layer diffusion, is not well understood. In the present report, the dissolution mechanism of MgO and Al2O3 in metallurgical slag was evaluated based on available literature data. The mass balance between the dissolving particle and the flux equation through the boundary layer was applied to predict the dissolution curve. The influence of fluid flow was taken into account to calculate the mass transfer rate at the oxide/slag interface. It was found that the rate-limiting step of MgO and Al2O3 dissolution is the same: mass transfer through the boundary layer. Depending on the slag composition and experimental temperature, the effective diffusion coefficient for MgO and Al2O3 dissolution falls in the range of 10−12 to 10−9 m2/s.

The purpose of the study presented here is to determine to what extent chemical reactions between carbon-based refractory and slag or metal in the tap-hole of a SiMn furnace can contribute to wear of tap-hole refractory. The results of the study are reported in two parts. In Part I, thermodynamic calculations suggested that reaction between silicomanganese slag and carbon-based tap-hole refractory is possible, and experiments with nominally pure materials support this. However, practical refractory materials are by no means pure materials and contain secondary phases and porosity which can be expected to affect reaction with slag. In Part II, such reactions are examined experimentally, in cup and wettability tests, using commercially available carbon block and cold-ramming paste refractory materials and mainly industrial SiMn slag. Clear evidence was found of chemical reaction at approximately 1870 K (approximately 1600 °C), forming SiC and, it appears, metal droplets. Both carbon block and ramming paste refractory reacted with slag, with preferential attack on and penetration into the binder phase rather than aggregate particles. The two types of carbon-based refractory materials showed similar extents of chemical reaction observed as wetting and penetration in the laboratory tests. The differences in refractory life observed practically in industrial furnaces should therefore be attributed to wear mechanisms other than pure chemical wear as studied in this work.

Silicomanganese (SiMn) as an alloy supplies silicon and manganese to the steelmaking industry. It is produced through carbothermic reduction in a submerged arc furnace. The slag and metal are typically tapped through a single-level tap hole at 50 K (50 °C) below the process temperature of 1873 K to 1923 K (1600 °C to 1650 °C). In one tapblock refractory design configuration, the tap hole is installed as a carbon tapblock and rebuilt during the life of the lining using carbon-based cold ramming paste. The carbon tapblock lasts for a number of years and ramming paste only for months. The purpose of the study presented here was to determine to what extent chemical reactions between carbon-based refractory and slag or metal in the tap hole of a SiMn furnace can contribute to wear of tap-hole refractory. The results of the study are reported in two parts. In Part I, the results of thermodynamic calculations of the potential for chemical reaction between carbon-based refractory material and slag or metal are reported. The results were tested experimentally using pure graphite and synthetic SiMn slag (produced from pure oxides). The paper also reports the composition, microstructure, and phases of industrial SiMn slag, and commercially available carbon block and cold ramming paste refractory materials. These compositions were used in predicted equilibria of refractory–slag reactions. Thermodynamic calculations suggest that reaction between SiMn slag and carbon-based tap-hole refractory is possible, and experiments with nominally pure materials support this. However, practical refractory materials are by no means pure materials, and contain secondary phases and porosity which can be expected to affect reaction with slag. Such reactions are examined in Part II.

It is suggested that oxygen enrichment in the gas atmosphere, during continuous heating of magnetite pellets, can cause pellets to be oxidized throughout their volumes, eliminating unoxidized cores. The peculiarities of the oxidation kinetics of magnetite concentrate imply that such oxygen enrichment might be particularly effective at lower temperatures. This suggestion was tested by developing and testing a mixed-control model for pellet oxidation (to allow the sizes of unreacted cores to be predicted), and by experimentally testing the effects of oxygen enrichment at relatively low temperatures (“early oxygen enrichment”). The results confirmed that the extents (depth) of oxidation and pellet strength were both improved significantly by applying oxygen enrichment up to 873 K (600 °C), as part of a heating cycle up to 1073 K (800 °C).

Oxidation of magnetite pellets is commonly performed to prepare strong pellets for ironmaking. This article presents a contribution to quantitative understanding of fundamental pellet oxidation kinetics, based on measured oxidation kinetics of magnetite particles and pellets. The commonly observed “plateau” oxidation behavior is confirmed to be consistent with the effect of very large differences in magnetite particle sizes in the concentrate from which pellets are produced. The magnetite particles range in size from less than a micron to several tens of a microns; changing the size distribution by inert sintering of pellets decreases both the plateau level of oxidation and the specific surface area, in ways that are compatible with an assumed Rosin-Rammler magnetite particle size distribution.

Recent observations suggest that increased silicon levels improve ladle desulfurization of aluminum-killed steel. A kinetic model was developed and presented in part I of this paper, demonstrating that increased silicon levels in steel suppress the consumption of aluminum by parasitic reactions like silica reduction and FeO/MnO reduction, thus making more aluminum available at the interface for desulfurization. The results are increases in the rate and the extent of desulfurization. Predictions were compared with laboratory induction furnace melts using 1 kg of steel and 0.1 kg slag. The experimental results demonstrate the beneficial effect of silicon on the desulfurization reaction and that alumina can be reduced out of the slag and aluminum picked up by the steel, if the silicon content in the steel is high enough. The experimental results are in close agreement with the model predictions. Plant trials also show that with increased silicon content, both the rate and extent of desulfurization increase; incorporating silicon early into the ladle desulfurization process leads to considerable savings in aluminum consumption.

Based on equilibrium considerations, copper sulfide is not expected to form in manganese-containing steel, yet previous workers reported finding copper sulfide in transmission electron microscope samples which had been prepared by electropolishing. It is proposed that copper sulfide can form during electrolytic dissolution because of the much greater stability of copper sulfide relative to manganese sulfide in contact with an electrolyte containing copper and manganese cations. This mechanism has been demonstrated with aluminum-killed steel samples.

Recent observations suggest that increased silicon levels improve ladle desulfurization of aluminum-killed steel. While the overall desulfurization reaction of Al-killed steels does not show a direct role of silicon in desulfurization, model calculations are presented which test the idea that silicon suppresses the reduction of silica which can consume aluminum at the slag/metal interface. Consumption of aluminum would increase the oxygen potential at the slag/metal interface and decrease the sulfur partition coefficient between slag and metal. The model considers the coupled reactions of the reduction of silica, iron oxide, and manganese oxide in the slag and desulfurization of the steel by aluminum. The results show that silicon can indeed suppress consumption of aluminum at the slag/metal interface by side reactions other than desulfurization, with silicon affecting both the kinetics and the equilibrium of desulfurization.

Sulphur control is an essential part of steel production. This paper summarises two aspects of sulphur in secondary metallurgy. First, it is shown that silicon can contribute to ladle desulphurisation if the ladle slag is low in silica; the effect of silicon is primarily on the equilibrium sulphur level, rather than a specific kinetic effect. Second, sulphur is shown to capture calcium (as calcium sulphide) upon calcium injection to modify inclusions. In steels with less than approximately 100 ppm sulphur, the calcium sulphide subsequently back-reacts with alumina inclusions, to modify the oxide inclusions to calcium aluminates.

Calcium treatment is a well-established way to modify solid alumina inclusions to liquid or partially liquid calcium aluminates. Spinels (Al2O3·xMgO) can also form in liquid steel after aluminum deoxidation. Like alumina, the spinels can be modified readily to liquid inclusions by a calcium treatment. The modification of spinels was studied by observing the transient evolution of inclusions, in laboratory and industrial heats. Spinel modification involves the preferential reduction of MgO from the spinel, with Mg dissolving in the steel, and it proceeds through transient calcium sulfide formation, just like in the case of alumina inclusions. Because magnesium dissolves in steel after the calcium treatment of spinels, the reoxidation of the melt will produce new spinels.

The free energy of mixing in the Ti(O,C) shows negative deviation from ideality. A recent paper in Journal of Materials Chemistry A erroneously shows a large positive deviation from ideality.