 Subjects -> METALLURGY (Total: 58 journals)
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- A New Approach in Numerical Modeling of Inoculation of Primary Silicon in
a Hypereutectic Al-Si Alloy- Abstract: Abstract The applicability of classical heterogeneous nucleation theory for an inoculated Al-18.6Si (wt pct) alloy was investigated. Nucleation model proposed by Perepezko was used to study heterogenous nucleation of primary silicon in phosphorus-inoculated alloys. For this system, the nucleation temperature was found to be the most crucial variable in the model. If a spherical cap model is assumed for heterogenous nucleation, then the contact angle changes only by the interfacial energy. However, the data applied to Perepezko’s model showed it changed by undercooling. Therefore, it is suggested that the Perepezko’s nucleation model is not applicable for analyzing data in inoculated hypereutectic Al-Si alloy. Instead, for the first time, the free growth model developed by Greer to study the inoculation of Aluminum by Al-Ti-B was used for the Al-18.6Si (wt pct) alloy inoculated with Al-Fe-P. The results of modeling compared with the experimental data showed that the free growth model gives a closer approximation when predicting the size of the primary silicon in the investigated alloy. Mechanical properties of the as-cast hypereutectic alloys are influenced by size and shape of the primary silicon and eutectic silicon, type, size, and frequency of entrainment defects and residual stresses. Finer silicon particles lead to higher tensile strength in the cast components. Being able to predict the size of primary silicon particles will facilitate control of the inoculation process, to enhance mechanical properties such as tensile strength. Developed model here provides a basis to predict the size of primary silicon in hypereutectic Al-Si alloys treated with phosphorous-containing inoculants.
PubDate: 2021-01-11
- An Integrated Multi-scale Model for Graphite Growth Mechanism in
Industrial Cast Iron- Abstract: Abstract The prediction of precipitated graphite nodules size and distribution in a large industrial casting is critical to understand the mechanical behavior of cast iron components used in heavy vehicles. An accurate prediction of the graphite nodules requires a validated and integrated macro-micro modeling framework, which forms the motivation behind the present study. Classical theories in the literature (Lesoult et al. in Acta Mater 46:983–995, 1998) proposed two stages of graphite growth: in (i) liquid stage, after encapsulation by the austenite grain, and in (ii) solid stage, surrounded by only austenite phase. In this work, a new stage of graphite growth was proposed, where a graphite nodule was in direct contact with the liquid metal, existing in the presence of an austenite grain separated from the nodule. The resulting three-stage graphite growth in a microscopic control volume was formulated using a volume-averaged micro-model. This was made to evolve with the help of a macroscopic temperature field obtained from finite-element-based numerical simulation and thus creating a comprehensive modeling framework. Further, for the first time, a diffusion-based deforming-grid micro-model was developed to obtain the exact nature of a single graphite nodule growth based on the position of individual phases in the microscopic control volume. The model predictions were validated with experimental results from the step-casting experiments in the present study, as well as with the observations of single nodule growth from in situ synchrotron X-ray tomography (Bjerre et al. in Model Simul Mater Sci Eng 26:085012, 2018; Azeem et al. in Acta Mater 155:393–401, 2018). The proposed models captured, faithfully, the experimental patterns of graphite growth evolution, number density of the nodules, and the size distribution as a function of cooling rate. This integrated multi-scale modeling approach is envisaged to be effective for determining exact graphite growth behavior of a single nodule and volume-averaged graphite growth in a large casting.
PubDate: 2021-01-11
- Function Mechanism of Sodium Sulfate Additive on Iron Carbide Preparation
with Low-Grade Siderite- Abstract: Abstract The carburization roasting treatment followed by the magnetic separation is an effective way to utilize low-grade siderite, in which the sodium sulfate additive plays an important role. In order to investigate the role of sodium sulfate additive, the present study fixes its particular attention on the function mechanism of sodium sulfate additive during the preheating treatment, carburization, and separation process. The results show that sodium sulfate additive can enhance the oxidation, reduction, and carburization reactions of siderite pellet, which dramatically increases the carburization rate and degree of siderite pellet. Besides, sodium sulfate additive can significantly improve the growth of iron carbide particle, transform the dense gangue into loose gangue, and produce the cracks inside pellet, which greatly promotes the separation of iron carbide and gangue. In the whole process, preheating treatment at high temperature is a necessary process to intensify and maintain the additive’s effects.
PubDate: 2021-01-08
- Density of Liquid Manganese Measured Using the Maximum Bubble Pressure
Method- Abstract: Abstract Manganese is an important metal for steelmaking. Data on the density of the metal are scarce and show considerable scatter. Present work reports the density of the liquid manganese in the range of 1535 K to 1836 K estimated for the first time with the use of the maximum bubble pressure technique. The obtained density of the manganese is marginally higher than previously reported in the literature.
PubDate: 2021-01-08
- Surface Laser Treatment on Ferritic Ductile Iron: Effect of Linear Energy
on Microstructure, Chemical Composition, and Hardness- Abstract: Abstract Surface transformation treatments like laser surface melting and laser surface hardening have been mostly developed in austempered ductile iron and gray cast iron. In this work, we explore the effects of the linear laser energy of the treatment on the microstructure, chemical composition, and hardness of ferritic nodular cast iron, using a fiber delivery diode laser. We found changes in the microstructure above 120 J/mm, characterized by the presence of graphite nodules surrounded by martensitic/dendritic shells. Above 316 J/mm, Fe3C and γ-Fe2O3 phases arise, together with a saturation of the microhardness around 1000 HV0.3 within the first 200 μm of depth, and of the surface hardness around 90 HR15N. Changes in microstructure and composition due to the laser treatment directly affect the thermal diffusion between the surface-modified zones and the nodular cast iron bulk. Our work highlights the importance of the linear energy in the design and planning of laser treatments.
PubDate: 2021-01-07
- Numerical Study of Evaporation Behavior of Molten Manganese Metal During
Electroslag Recycling Process- Abstract: Abstract Electroslag remelting (ESR) technology has been adopted to recycle the rejected electrolytic manganese metal scrap. In this study, a transient 3D coupled numerical model accounting for the electromagnetism, multiphase flow, heat transfer, and solidification was elaborated and used to simulate the evaporation behavior of the molten manganese metal (MM) during the ESR process. The volume of fluid approach was employed to capture the interfaces between the gaseous manganese, molten slag, and molten MM. The evaporation rate of the molten MM was defined by applying the Lee model, while the enthalpy-porosity formulation described the solidification. An industrial experiment via a commercial-scale ESR furnace was conducted for the model validation. The research findings indicate that the molten MM’s evaporation occurs during the droplet falling and in the metal pool. Then, gaseous manganese bubbles ascend to the molten slag-free surface, thus promoting the melt movement, especially the slag-metal pool interface fluctuation. The evaporation rate of the molten MM is promoted by the increased applied current and the reduced ambient gauge pressure. The recycling ratio drops from 81.75 to 71.79 pct with the applied current increase from 3000 to 4000 A and drops from 78.19 to 73.71 pct with the ambient gauge pressure reduction from 0 to − 1000 Pa.
PubDate: 2021-01-06
- Evolution Mechanism of Microporosity of Nickel-Based Single-Crystal
Superalloy During Solution Heat Treatment Under an Alternating Magnetic
Field
- Evolution of Non-metallic Inclusions in Si-Killed Stainless Steelmaking
- Abstract: Abstract The evolution of non-metallic inclusions (> 10 μm) for the Si-killed stainless steelmaking process is studied. The effects of the slag basicity in the AOD (argon oxygen decarburization) process, Ca treatment, refractory in the casting ladle, impurities (Ti, Al) in scraps and tapping temperature in the AOD process on the evolution of the non-metallic inclusions are investigated using the thermo-chemical program (FactSageTM) and SEM analysis of the non-metallic inclusions at each process (AOD—ladle treatment—tundish—continuous casting). A new phase stability diagram of the non-metallic inclusion was developed from the analysis results, and we discuss the mechanism of the formation of spinel Mg[Al,Cr]2O4 in the inclusion with the aid of the diagram.
PubDate: 2021-01-06
- Effects of Interphase Forces on Multiphase Flow and Bubble Distribution in
Continuous Casting Strands- Abstract: Abstract A three-dimensional computational model, combining the large eddy simulation (LES) turbulent model, VOF multiphase model for air phase, and discrete phase model (DPM) for injected bubbles, was established to evaluate the effects of drag force, lift force, pressure gradient force, virtual mass force, and wall lubrication force on the fluid flow and spatial distribution of bubbles in a continuous casting (CC) strand. The effect of lift force and wall lubrication force on the fluid flow was achieved via a user defined subroutine (UDF). The contribution of interphase forces was quantitatively evaluated using UDF. The appropriate interphase force model was determined by comparing the predicted fluid flow and bubble distribution in the CC strand with the measured results one using particle image velocimetry (PIV). The interphase force had a significant effect on the spatial distribution of bubbles and the flow field near the meniscus. The drag force and buoyancy force were the dominant ones at low turbulent kinetic locations. Moreover, the magnitude of the lift force, pressure gradient force, and virtual mass force was increased sharply at high turbulent kinetic locations, approximately one to two orders greater than that of the buoyancy force.
PubDate: 2021-01-06
- Experimental Study of Magnesium (Mg) Production by an Integrated
Calcination and Silicothermic Reduction Short Process- Abstract: Abstract To promote the innovation of raw magnesium production technology, an integrated calcination and silicothermic reduction short process for magnesium production was experimentally studied on the laboratory scale in this article. The influences of the thermal decomposition temperature, silicothermic reduction temperature, pelletizing pressures and silicon ratio on the characteristics of producing the magnesium by the short process was studied. The crosslinking effect, including reactions between CO2 decomposed from dolomite and metal elements in ferrosilicon, microstructure change at thermal decomposition and silicothermic reduction stages, was analyzed and discussed. In addition, comparison of the magnesium reduction rate and production efficiency between the new short process and the traditional Pidgeon process was made. The results indicated that the decomposition and reduction temperatures have a more significant influence on the magnesium reduction process than the pelletizing pressure and silicon ratio. A decomposition temperature < 1000 °C and reduction temperature > 1100 °C was proven to be favorable for improving the magnesium reduction rate and production efficiency of the new short process. It was also found that the integrated short process for magnesium production can reach the same total reduction rate and has lower efficiency compared to the traditional process. The decrease of magnesium production efficiency in the new short process was expected to result from reduction of the contact area and hindering of diffusion between CaO·MgO molecules and Si(Fe) atoms because of the microstructure change and ferrosilicon consumption by the reactions between CO2 and metal elements in ferrosilicon. Preparing briquettes with additives of binder or ultrafine particles of raw materials was proposed and considered for further study to improve the production efficiency.
PubDate: 2021-01-06
- Behavior of Al 4 C 3 Particles During Flotation and Sedimentation in
Aluminum Melts- Abstract: Abstract Al4C3 particles form during the primary production of aluminum via molten salt electrolysis due to the carbon solubility and direct contact between bath, metal, and carbon anodes. Additional Al4C3 may form during melt processing through direct contact between the melt and carbonaceous materials. As a result of their small size and similar density to aluminum, removal of aluminum carbide particles can be challenging. If not removed, carbides can produce inclusion defects or poor surface condition in aluminum products. The current work studies the removal and behavior of Al4C3 particles during flotation with different gas mixtures, as well as sedimentation. The interaction between carbide particles and Al2O3 films during the melt treatment processes was also studied and reported. Factsage thermochemical software was used to model the interactions at the interface of inclusions and bubbles covered by films. The highest degree of carbide removal was obtained after flotation with an H2O-containing argon gas mixture, where the carbide concentration dropped below the measured solubility limit of carbon at the corresponding temperature. Strong interaction between Al4C3 particles and Al2O3 films was observed during sedimentation which worked as an efficient removal method for the particles. Oxidation of carbides and formation of oxycarbides were suggested as the mechanisms promoting the attachment of carbides on oxide films.
PubDate: 2021-01-06
- A Mineralogical Investigation on Volatilization of Impurity Elements from
Cu-Rich Polymetallic Concentrates During Roasting in Inert Atmosphere- Abstract: Abstract Four different Cu-rich polymetallic concentrates are tested for volatilization of Sb and As during laboratory-scale roasting. The experiments are performed between 200 °C and 700 °C, at intervals of 100 °C and in an inert atmosphere. Sb volatilization is much less (maximum approximately 45 pct) than As volatilization (maximum approximately 95 pct) in these conditions at 700 °C. As volatilization is however limited from the concentrate having As mainly in a tetrahedrite solid solution ((Cu,Ag,Fe,Zn)12(Sb,As)4S13). Sb and As retained in the roasted calcine are found in the low-melting liquid phase, formed at approximately 500 °C. This melt phase gets enlarged and enriched in Sb with an increase in temperature. However, there is noticeable As volatilization from this melt phase with the temperature approaching 700 °C. Furthermore, there is an early and relatively high Sb volatilization from the concentrate having Sb substantially as gudmundite. Micron-scale elemental redistribution in gudmundite in the 350 °C roasted calcine confirms its transformation at this temperature. Other Sb minerals did not undergo any detectable transformation at this temperature, suggesting that the significant Sb volatilization starting between 300 °C and 400 °C was primarily from gudmundite. This benign attribute of gudmundite featured in this work in the context of roasting should also be relevant from the geometallurgical perspective during concentrate production, where concentrates bearing Sb are considered substandard for further Cu extraction irrespective of the Sb mineralogy.
PubDate: 2021-01-06
- Mechanism of Enhancing Phosphorus Removal from Metallurgical Grade Silicon
by Si-Fe-Ti Phase Reconstruction- Abstract: Abstract Metallurgical grade silicon (MG-Si) contains iron (Fe) as its main impurity, where phosphorus (P) is occasionally enriched in the FeSi2Ti phase. Based on this phenomenon, the precipitation superiority of P in the silicon-iron-titanium (Si-Fe-Ti) phase was verified by Si-5Fe and Si-3Fe-2Ti (wt pct) alloy refining for MG-Si. Microscopic characterization showed that P enrichment in the Si-Fe-Ti phase was more than in the Si-Fe phase. Thermodynamically, FeTiP phase is more stable than Fe3P. Dynamically, Fe and Ti will increase the solubility of each other in the melt because the activity interaction coefficient of Fe and Ti is 5.7027. Therefore, during the solidification of the Si-Fe-Ti melt, the enhanced precipitation of Fe and Ti promotes the formation and co-precipitation of the Si-Fe-Ti and FeTiP phases. With acid leaching, the phosphorus removal efficiencies from MG-Si, the Si-Fe alloy, and Si-Fe-Ti alloy were 12.33, 39.15, and 71.20 pct, respectively, which again verify the distribution characteristics of P in different samples and its mechanistic analysis.
PubDate: 2021-01-06
- Carbothermic Reduction of Zinc Containing Industrial Wastes: A Kinetic
Model- Abstract: Abstract Effective recycling of zinc-containing industrial wastes, most importantly electric arc furnace dust, is of tremendous importance for the circular economy of the steel and zinc industry. Herein, we propose a comprehensive kinetic model of the combined carbothermic and metallothermic reduction of zinc oxide in a metal bath process. Pyro-metallurgical, large-scale lab experiments of a carbon-saturated iron melt as reduction agent for a molten zinc oxide slag were performed to determine reaction constants and accurately predict mass transfer coefficients of the proposed kinetic model. An experimentally determined kinetic model demonstrates that various reactions run simultaneously during the reduction of zinc oxide and iron oxide. For the investigated slag composition, the temperature-dependent contribution of the metallothermic zinc oxide reduction was between 25 and 50 pct of the overall reaction mechanism. The mass transfer coefficient of the zinc oxide reduction quadrupled from 1400 °C to 1500 °C. The zinc recovery rate was > 99.9 pct in all experiments.
PubDate: 2021-01-06
- Transient Simulations and Experiments on Compound Roll Produced by
Electroslag Remelting Cladding- Abstract: Abstract In this study, a comprehensive transient numerical model of electroslag remelting cladding process with dynamic mesh technology is simulated to study the effect of the applied power on the uniformity of melting layer depth along the height of the as-prepared compound roll. The multi-physics fields are solved by the ANSYS Parametric Design Language and Fluent simulation software. The simulation results show that the mandrel absorbs heat (Qmsi) from the slag pool and the melting layer is formed on the mandrel surface. A sufficient metallurgical bonding quality between the mandrel and the clad is confirmed by the close contact of the melting layer with the molten bath of the clad. In addition, the use of high and low power during the early and later stages, respectively, improves the uniformity of the melting layer depth along the height. When high power (235 kW) is applied during the early stage, the height of the compound roll without metallurgical bonding decreases to 52 mm. After the melting layer depth increases to 6 mm along the height, the power decreases to 187 kW. The slag temperature and Qmsi decreases rapidly, and consequently, the melting layer depth initially decreases and then slightly increases along the height. The melting layer depth is acceptable within height of 52 to 260 mm. The change tendency of the melting layer depth along the height of the compound roll obtained by the semi-industrial experiment is in agreement with the simulation results, proving the reliability of the process. Moreover, the results of tensile and Charpy impact tests indicate good metallurgical bonding quality. The process investigated in this paper is expected to be efficient for industrial production of the compound rolls with a uniform melting layer depth.
PubDate: 2021-01-06
- The Influence of Powder Reuse on the Properties of Nickel Super Alloy ATI
718™ in Laser Powder Bed Fusion Additive Manufacturing- Abstract: Abstract Gas-atomized nickel alloy ATI 718™ powders with a nominal particle distribution of 15 to 45 µm were used in a laser powder bed fusion (LPBF) additive manufacturing (AM) process for ten sequential builds without refreshing with new powder. The repeated feedstock use caused the particle size distribution, particle morphology, and oxygen content to change in comparison to virgin powder. Unusual particle morphologies were observed in the powder with repeated use when compared to virgin gas-atomized feedstock. Particles after use were found to contain surface features such as films and spots, which consisted of aluminum oxides and likely contributed to increasing the oxygen content in the recycled feedstock powder.
PubDate: 2021-01-06
- Study on the Activity Interaction Coefficients of V in Fe-C-V Melts at
1873 K- Abstract: Abstract The first- and second-order interaction coefficients of V in Fe-C-V melts were accurately measured using the chemical equilibrium technique, by equilibrating CaO-MgO-Al2O3-VOx slags with Fe-C melts under controlled oxygen potential for 24 hours at 1873 K (1600 °C). The argon was employed as the protective gas and a purification device was used to control the oxygen potential in the atmosphere. The values of the interaction coefficients were determined as follows: $$ e_{\text{V}}^{\text{C}} = - 0.468,\quad r_{\text{V}}^{\text{C}} = 0.286,\quad r_{\text{V}}^{\text{V,C}} = - 0.213 $$
PubDate: 2021-01-05
- Investigation of the Thermodynamic Stability of C(A, F) 3 Solid Solution
in the FeO-Fe 2 O 3 -CaO-Al 2 O 3 System and SFCA Phase in the FeO-Fe 2 O
3 -CaO-SiO 2 -Al 2 O 3 System- Abstract: Abstract Silico-ferrite of calcium and aluminum (SFCA) is the major bonding phase in iron ore sintering process and is critical to enhancing the sinter properties, such as reducibility and mechanical strength in subsequent blast furnace operations. The phase relations foundations of the alumina-free silico-ferrite of calcium (SFC) have been previously experimentally investigated in air by the authors (Chen et al. ISIJ Int 59:795–804, 2019, Cheng et al. Metall Mater Trans B 51:1587–1602, 2020) and in 1 atm CO2 (Chen et al. ISIJ Int, 59:805–809, 2019). Present investigation using equilibration and quenching followed by electron probe X-ray microanalysis (EPMA) technique, follows those previous works on the SFC, with the focus on the effects of: (i) Al2O3 (in the “Fe2O3”-CaO-Al2O3 and the “Fe2O3”-CaO-SiO2-Al2O3 system in air), and (ii) the effect of \( p_{{{\text{O}}_{2} }} \) (the “Fe2O3”-CaO-Al2O3 in 1 atm CO2 atmosphere), to investigate the thermodynamic stability of the C(A, F)3 [Ca(Al, Fe)6O10] solid solution in the “Fe2O3”-CaO-Al2O3 system in both air and pure CO2 atmospheres between 1150 °C and 1250 °C; and the silico-ferrite of calcium and aluminum (SFCA) solid solution with 1, 2 and 4 wt pct of Al2O3 in bulk compositions in the “Fe2O3”-CaO-SiO2-Al2O3 system at temperatures in the range between 1255 °C and 1340 °C. Present study shows that C(A, F)3 is stable over a wide range of Al2O3 concentration (8.8 to 26.7 wt pct Al2O3, or 12.5 to 34.8 mol pct AlO1.5). It also becomes less stable in terms of both the temperature and the compositional stability range as the oxygen partial pressure is reduced. The SFCA phase in the “Fe2O3”-CaO-SiO2-Al2O3 system is found to be present in the range of 1 to 4 wt pct Al2O3 bulk compositions selected in air. The relative stability of this phase increases with increased Al2O3 in the bulk material. Tie-lines joining the SFCA and the corresponding liquid and hematite phases are constructed over the range of composition investigated at sub-liquidus temperatures. The new experimental measurements show that the CaO/SiO2 ratio in the SFCA phase is almost identical to that in the liquid. The distribution ratio of Al2O3 between SFCA and liquid is in the range 2/1 to 3/1.
PubDate: 2021-01-05
- Modification of Double Oxide Film Defects with the Addition of Mo to An
Al-Si-Mg Alloy- Abstract: Abstract In this work, Mo was added into Al melt to reduce the detrimental effect of double-oxide film defect. An air bubble was trapped in a liquid metal (2L99), served as an analogy for double-oxide film defect in aluminum alloy castings. It was found that the addition of Mo significantly accelerated the consumption of the entrapped bubble by 60 pct after holding for 1 hour. 2 sets of testbar molds were then cast, with 2L99 and 2L99+Mo alloy, with a badly designed running system, intended to deliberately introduce double oxide film defects into the liquid metal. Tensile testing showed that, with the addition of Mo, the Weibull modulus of the Ultimate Tensile Strength and pct Elongation was increased by a factor of 2.5 (from 9 to 23) and 2 (from 2.5 to 4.5), respectively. The fracture surface of 2L99+Mo alloy testbars revealed areas of nitrides contained within bi-film defects. Cross-sections through those defects by Focused Ion Beam milling suggested that the surface layer were permeable, which could be as thick as 30 μm, compared to around 500 nm for the typical oxide film thickness. Transmission Electron Microscopy analysis suggested that the nitride-containing layer consisted of nitride particles as well as spinel phase of various form. The hypothesis was raised that the permeability of the nitride layers promote the reaction between the entrapped atmosphere in the defect and the surrounding liquid metal, reducing the defect size and decreasing their impact on mechanical properties.
PubDate: 2021-01-05
- Oxidation Mechanism of Vanadium Slag with High MgO Content at High
Temperature- Abstract: Abstract Based on two considerations of making full use of the residual heat of vanadium slag and exploring a novel green vanadium extraction process, this article employs vanadium slag with high MgO content as raw material, blowing oxygen into the molten vanadium slag and using the residual heat of the vanadium slag to carry out high-temperature roasting experiments. XRD and SEM/EDS were used to characterize the phase evolution and morphology of vanadium slag with high MgO content during oxidation. The results show that at a high temperature of 1723 K, the trivalent vanadium in vanadium slag can be partly transformed into acid-soluble pentavalent vanadium. Titanium-bearing spinel was oxidized into a large amount of strip pseudobrookite Fe2TiO5. After oxidation, vanadium existed in the form of the solid solution of magnesium pyrovanadate (Mg, Mn, Ca)2V2O7. The leaching rate of roasted vanadium slag with high MgO content is significantly higher than that of industrial vanadium slag. With the increase of oxygen blowing time from 10 to 30 minutes, the leaching rate of roasted vanadium slag with high MgO content increases from 23.19 to 53.69 pct.
PubDate: 2021-01-04
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