Vacuum Smelting Research Articles

Anodic leaching plus chronopotentiometric aging of Ni2Fe ingot for sustainable oxygen evolution and urea oxidation reactions

A Ni–Fe binary alloy ingot, prepared by conventional vacuum smelting, was adopted as substrate in this work to fabricate the anode for water splitting. To improve the surface roughness of anode surface, the electrode was firstly subjected to anodic leaching in a simple KSCN solution. The as-leached electrode was subsequently activated through linear sweep voltammetry in 1 M KOH solution with or without 0.33 M urea addition to finish the final step for electrode preparation. The as-prepared anode delivers the 10 mA cm−2 current density at an overpotential of 284 mV for oxygen evolution reaction (OER) and at 1.361 V (RHE) for urea oxidation reaction (UOR), respectively. No apparent change of OER and UOR performance was observed after chronopotentiometric aging. The more complex UOR behavior was analyzed to elucidate the synergy among all constituents functioning through direct or indirect mechanisms for the half-reaction on this binder-free, self-supporting and substrate-rejuvenating anode.

Enhancing the SCC Resistance of the Anchor Steel with Microalloying in a Simulated Mine Environment.

This work explored a new idea for enhancing the resistance to stress corrosion cracking (SCC) of mining anchor steel through microalloying. Microalloyed anchor steels with Nb, Cu, Ni, Sb, and C were prepared through vacuum smelting and hot rolling. Electrochemical measurements, slow strain rate tensile (SSRT) tests, and fracture morphology observations were used to study the electrochemical and SCC behavior in the simulated mine environment. The results proved that the microstructure of microalloyed steels varies slightly. Adding Ni, Cu, and Sb can improve the mechanical properties of the anchor steel, while reducing C content decreases tensile strength as a result of loss of the solution-strengthening effect. The addition of Sb, Cu, Ni, and reducing the content of C enhances the resistance to corrosion and SCC by mitigating anodic dissolution (AD), while adding Nb improves SCC resistance by inhibiting hydrogen embrittlement (HE). The combined addition of 1% Ni, 0.5% Cu, 0.05% Nb, 0.1% Sb, and 0.5% C presented the highest SCC resistance, which is a promising prospect for the development of high-performance, low-alloy anchor steels. The combined addition of 1% Ni, 0.5% Cu, 0.05% Nb, and 0.1% Sb resulted in the inhibition of electrochemical reactions and corrosion. As a result of the synergistic effect of the microalloy, both AD and HE mechanisms were simultaneously inhibited, which greatly enhanced SCC resistance.

Precipitation behaviors and property variations of Cu-3.0 wt% Ti fabricated by a novel short-processing non-vacuum heating-cooling combined mold continuous casting

A Cu-3.0 wt% Ti alloy is fabricated by a novel non-vacuum short-process based on heating-cooling combined mold (HCCM) continuous casting in this study. Similar properties including tensile strength, hardness and electrical conductivity are obtained by this newly developed process, compared to its counterpart alloy prepared by conventional vacuum smelting. The tensile strength, total elongation and conductivity of the HCCM prepared Cu-3 wt% Ti alloy were 895 MPa, 13% and 13.00% IACS, respectively, after 95% deformation and aging treatment at 450 °C for 1 h. The cast materials fabricated by HCCM method can be directly cold rolled and aged after solution treatment without hot deformation such as hot forging. Through the HCCM continuous casting method, not only the Cu-Ti alloy can be fabricated under non-vacuum conditions, but also the fabrication process can apparently shortened by shortening the solid solution treatment time. Similar precipitation process is also found in the Cu-3.0 wt% Ti alloy prepared by this method. The precipitation of the ordered, metastable and coherent β'-Cu4Ti phase with body-centered tetragonal (bct) structure are formed in the early stage of aging treatment, which is transformed into stable β-Cu3Ti with an orthogonal structure in the over-aging stage. The precipitation hardening of β'-Cu4Ti phase, i.e., Orowan strengthening effect, is believed to be the leading strengthening mechanism in this alloy.

Effects of Heat Treatment on Fatigue Properties of Double Vacuum Smelting High‐Carbon Chromium‐Bearing Steel

Herein, the tensile and fatigue properties of double vacuum smelting GCr15‐bearing steel under different heat treatments are studied. With the increase in ultimate tensile strength, the fatigue strength of double vacuum smelting GCr15‐bearing steel first increases and then reduces, and the origin of fatigue failure changes from specimen surface to internal inclusion. For the specimen with fatigue cracks initiated from the surface, the fatigue strength would increase as the tensile strength enhances, while for the specimen with fatigue cracks initiated from the internal inclusion, the fatigue strength reduces with the increment in tensile strength. It should be an effective method to obtain both excellent fatigue strength and enough tensile strength by heat treatment in the temperature range below temper brittleness and reducing tensile strength. These findings may be helpful for the antifatigue design of GCr15‐bearing steel through heat treatment control in the future.

Induction vacuum smelting of Co-Al-W superalloys - optimizing the feedstock based on the alloy's chemical composition, elemental segregation, and slag formation

In this study, the manufacturing of Co-Al-W alloys by smelting in a vacuum induction furnace was discussed taking into account the optimizing of the feedstock material morphology. Herein, the influence of various feedstock conditions and the order of introducing the alloying elements into a liquid alloy were analyzed and described. The investigation revealed that it was possible to obtain the desired chemical composition of Co-Al-W alloys using fragmented tungsten pellets introduced from a vacuum feeder into the liquid Co-Al alloy heated above the liquidus temperature to maximum of 40-50?C. This technical variant required accurate temperature control of the molten alloy, which did not ensure complete reproducibility. The disadvantage of this process was a relatively high slag formation. The optimal technical solution involved obtaining the liquid Co-W solution and introducing Al at the end of the smelting process; in this variant, the slagging effect was relatively low. Additionally, melting of the alloy in an argon atmosphere reduced the loss of aluminum due to evaporation, as compared to melting in a vacuum. The smelting process could be carried out either in Al2O3 solid crucibles or in compacted crucibles made of MgO-based refractory mass.

Recycling high-purity silicon from diamond-wire saw kerf slurry waste by vacuum refining process

Approximately 35%–40% crystalline silicon becomes silicon powder waste (SPW) when producing silicon wafers. Substantial amount of SPW will be produced as the demand for wafers increases. Recycling Si from SPW for preparing silicon has been a significant issue. Considering the current recovery ratio of SPW is low, it is urgent to investigate an effective method to recycle SPW. In this paper, SPW was re-melted into high-purity silicon ingots by vacuum refining process and the recycling process involved two stages. In the first stage, SPW was pelletized by a double-roll type presser. In the second stage, the pellets were melted into high-purity silicon ingots by vacuum refining. The effects of the smelting time and atmosphere condition on the silicon recovery ratio, and the influence of the smelting time on impurities removal ratio were investigated. The maximum silicon recovery ratio could be increased from 56.5% by atmosphere smelting to 68.65% by vacuum smelting. Si ingots with a purity of 99.65%, B 0.21 ppmw and P 3.03 ppmw were prepared. The melting mechanism of the silicon powder and economical evaluation were also discussed in this paper. The recovery of SPW by vacuum refining can not only realize resource reutilization but also bring about economic benefits ($0.406/kg) at laboratory-scale.

Volatilization Behavior of Manganese from Molten Steel with Different Alloying Methods in Vacuum

The volatilization loss of manganese during the vacuum smelting process is one of the key factors that determines the manufacturing cost and quality of manganese steel. In this study, the laboratory experiments and thermodynamic calculations were performed to investigate volatilization behavior of manganese from molten steels with different alloying methods in vacuum process. Based on the thermodynamic analysis, with the increase of manganese content, the partial vapor pressure of the manganese component increased, resulting in manganese being easily volatilized from molten steel. The carbon content in the steel shows an evident influence on partial vapor pressure of manganese component, and a higher carbon content in steel leads to a lower partial vapor pressure of manganese, but it not influenced by the silicon content. Compared with the alloying method of high carbon ferromanganese, the volatilization loss of manganese in the alloying method of silicon manganese presents faster decay, agreeing well with the thermodynamic analysis. Besides, the volatile fraction generated in the alloying method of high-carbon ferromanganese is composed of a large amount of MnO nanorods with a lateral length approximately 500 nm and a small number of Mn3O4/Mn nanoparticles with a diameter less than 500 nm. Additionally, the volatile fraction generated in the alloying method of silicon manganese shows Mn3O4 nanoparticles as the main phase. It can be inferred that the existence of the manganese oxide phase is attributed to the high chemical activity of nanoscale particles within air.

Effect of vacuum smelting method on the quality of pipe steel of northern application

Pipe metal of Northern application must meet increased requirements of strength properties, low-temperature ductility, cold resistance and weldability. Cracks, skins, flaws, roll-ins and other defect are not allowed on the surface of pipes. The fulfillment of the requirements substantially can be provided by the process of steel smelting by a vacuum remelting method. Study of the effect of 03ХГ grade pipe steel smelting in vacuum and without vacuum on its contamination by nonmetallic inclusions and resistance against hydrogen cracking was accomplished. The smelting of ingots of adjusted chemical composition was carried out in a vacuum induction furnace ZG-0.06L. To imitate the process of hot roughing rolling, hydraulic press П6334 of 250 t force was used. Finishing rolling was carried out at reversible hot rolling mill 500 duo, combined with a controlled cooling facility. It was determined, that the samples, smelted in vacuum, had insignificant number of nonmetallic inclusions and withstand the test of resistance against hydrogen cracking; cracks were not detected on them. After testing on resistance against hydrogen cracking of the samples smelted without vacuum, cracks were discovered, located on both the surface and central layers amounting to 600 mm and 1700 mm length correspondently. It was shown, that steel smelting in vacuum allows to reach a high degree of the steel purity, results in increased crack growth resistance and in decreased number of nonmetallic inclusions in the pipe steel of Northern application.

Enhancing Pb Removal and Synthesizing Glass–Ceramics from Waste CRTs Funnel Glass by Red Mud

In this paper, a novel and effective process for removing lead and synthesizing glass–ceramics from the hazardous waste CRTs funnel glass and red mud was developed. Glass–ceramics was produced through an appropriate sintering treatment of the residual glass after lead from funnel glass was removed. Vacuum smelting results showed that the addition of red mud had contributed to enhance Pb removal from funnel glass as compared to the same process without red mud. When the red mud mass was added 60 wt%, more than 99.93% of Pb was successfully removed and the Pb content was reduced to 0.0093 wt%. Metallic lead with 99% purity was recycled. The sintering process showed that the CaO–Al2O3–SiO2 type glass–ceramics were synthesized with different microstructure crystallinity and morphology. Overall, the results demonstrated that red mud can not only enhance PbO removal from waste CRT funnel glass, but also fabricate glass–ceramics combining residual glass. Route of removing Pb and synthesizing glass–ceramics from waste CRTs funnel glass by red mud.

Experimental preparation and property analysis of rare earth modified impact resistant steel

To further improve the comprehensive performance of existing impact-resistant steel, rare-earth-modified steel samples were experimentally prepared and their performance was analyzed. Different amounts of mixed rare earths were added into the 30MnCrNiMo impact-resistant steel, followed by vacuum smelting, forging, and rolling to prepare the steel plate. The effects of rare earths on the phase transformation critical points, high-temperature deformation behavior, microstructure, and mechanical properties were studied. The results show that rare earths can play a purifying role in the test steel. The Ac1-Ac3 phase transition temperatures were increased, and those of the Bs-Bf phase transition were decreased significantly. When compressed at 1000 °C, the deformation resistance of the test steel with rare earth became higher. Thus, the added rare earths improve the microstructural morphology and inclusions in the steel, as well as the comprehensive mechanical properties.

Different Effects of Annealing on Microstructure Evolution and SERS Performance for Cu-Cr Alloy Film and Bulk Alloy.

Copper–chromium alloy film and Cu–Cr bulk alloy were obtained using magnetron sputtering and vacuum smelting. Experimental results indicated that Cu–Cr bulk alloy and alloy films having different residual stress and atomic diffusion exhibit a significant difference in microstructure evolution behaviors after annealing. Numerous polyhedral Cu particles and dendritic Cr particles precipitated on the surface of annealed Cu–Cr alloy film and as–cast Cu–Cr bulk alloy, respectively. Cu particles were formed under the driving of energy and residual stress in the film. The effect of annealing temperature and Cr content on the size and quantity of Cu particles is discussed. Cr particles precipitated on the bulk alloy due to the low solid solubility of Cr in Cu, and the crystallinity of Cu grains promoted the diffusion of Cr atoms. The surface–enhanced Raman scattering (SERS) intensity of the Cu–14.6%Cr alloy film was obviously higher than that of the Cu–14.2%Cr bulk alloy. The particles/film composite structure possessed the appropriate particle number, surface roughness, and interstitial gap, as opposed to the bulk material, to effectively improve SERS enhancement.

Discrepancies in the Microstructures of Annealed Cu-Zr Bulk Alloy and Cu-Zr Alloy Films.

Copper–zirconium bulk alloy and Cu–Zr alloy films are prepared by vacuum smelting and magnetron sputtering, respectively, and subsequently annealing is conducted. Results show that Cu–Zr bulk alloy and alloy films exhibit significantly different microstructure evolution behaviors after annealing due to different microstructures and residual stress states. CuxZr alloy compounds disperse at the grain boundary of Cu grains in as-cast and annealed Cu–Zr bulk alloys. However, unlike bulk alloys, a large number of polyhedral Cu particles are formed on the Cu–Zr thin films’ surface upon thermal annealing. Kinetically, the residual compressive stress in the Cu–Zr films promotes the formation of Cu particles. The influencing factors and the path for mass transport in the formation of the particles are discussed. The large-specific surface area particles/film composite structure has potential applications in Surface-Enhanced Raman Scattering, catalysis, and other fields.

Remanufacturing of silicon powder waste cut by a diamond-wire saw through high temperature non-transfer arc assisted vacuum smelting.

Non-transfer arc assisted vacuum smelting technology is presented for the first time to recycle harmful silicon powder waste derived from diamond-wire cutting. The final yield and filling rate of silicon could reach 93.9% and 73%, respectively. The oxidation characteristics of silicon powder waste, formation mechanism of a hollow silicon block and removal efficiency of impurities were analyzed in detail to offer profound insights into a non-transfer arc granulation method. The critical conditions for continuous and efficient preparation of a solid silicon block were further confirmed through orthogonal experiments with 7.5 kW welder output power, 3 mm vertical scanning height, and 5 mm/s scanning speed. The yield of the silicon block was more than 96%. Meanwhile, the granulating process demonstrated a favorable effect on removing most impurities, such as C, Al, and Na, without introducing any other impurities. The residual impurities could be further removed by vacuum directional smelting. Given the extremely low equipment cost and huge room for improvement, this work is crucial for large-scale recovery of silicon powder waste.

Recycling of silicon powder waste cut by a diamond-wire saw through laser-assisted vacuum smelting

This paper proposes laser granulating technology for recycling harmful silicon powder waste cut by a diamond-wire saw. The silicon block produced by laser was easily melted in a traditional vacuum smelting furnace to form a silicon ingot with a high yield and filling rate, which could reach up to 94.7% and 65.7%, respectively. The removal efficiency of the carbon contamination was 74.2% during laser melting process and reached 86% after 30 min of vacuum smelting. In addition, laser melting process promoted the removal of most metal impurities, such as Al, Na, Ca, Mg, and so on, in the silicon powder waste without introducing any other impurities. The residual impurities could be further removed by vacuum smelting. The experiment revealed that the out capacity of the silicon block melted by a single laser gun was 1.91 kg/h, the energy consumption of laser melting was 2.63 kWh/kg, and the yield of the silicon block exceeded 97% at a laser power of 2000 W, a laser scanning interval of 5 mm, and a scanning speed of 6 mm/s. Therefore, the proposed approach is one of the most simple and efficient silicon powder waste pretreatment methods.

Thermodynamic and experimental study of C-S system and C-S-Mo system

In order to better utilize the low-grade molybdenite concentrates and obtain high quality products, thermodynamic analysis and experimental study of vacuum smelting process of molybdenite concentrates were carried out in detail. The possible reactions of the C-S system were analyzed, and the indirect reduction reactions and direct reduction reactions of MoS2 were discussed. To clarify the reaction mechanism under vacuum condition, the Mo-S-C system was also studied by thermodynamic and experimental methods. The results indicated that vacuum decomposition reactions and equilibrium reactions of Mo-S-C system were carried out simultaneously in the vacuum smelting process. Temperature and pressure are the main factors affecting the vacuum smelting process. There is reaction equilibrium of C, CS, CS2 and S2 in the vacuum smelting process and molybdenum sulfides can be easily reduced to Mo, Mo2C, Mo3C2 and MoC. The contents of carbon and sulfur in the product have relationship with the reaction equilibrium of Mo-S-C system. The CS generated in carbon sulfidation reaction(C + CS2→2CS) may accelerate the reaction rates in the vacuum smelting process. When the grade of molybdenite concentrates is 48%, the optimum content of carbon added in the molybdenite concentrates is about 4%, and the content of Mo in the metal molybdenum products can reach 92%, and the content of sulfur and residual carbon are all low.

Investigation on Composition, Mechanical Properties, and Corrosion Resistance of Mg-0.5Ca-X(Sr, Zr, Sn) Biological Alloy.

Four nontoxic biological alloys, Mg-0.5Ca-1Sr-4Zr (Alloy 1), Mg-0.5Ca-1Sr-1.5Zr (Alloy 2), Mg-0.5Ca-3Sr-1.5Zr (Alloy 3), and Mg-0.5Ca-1Sr-0.5Sn (Alloy 4), were prepared by vacuum smelting, gravity casting, and hot rolling. The composition and microstructure of the alloys were investigated by optical microscope, X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion spectroscopy (EDS). The mechanical properties and corrosion behaviors of the alloys in Hank's solution were studied. Results showed that a large amount of fine and uniformly distributed second-phase particles (Zr, Mg17Sr2, and CaMgSn) was observed in four alloys obtained after rolling and alloying. The segregation of Zr in alloys was observed in EDS image, and chemical analysis showed that there was macrosegregation of the elements in the alloys. Furthermore, Mg17Sr2 phases in the Mg-0.5Ca-1Sr-0.5Sn alloy homogenized the distribution of CaMgZn phases. The comprehensive mechanical properties of four newly designed rolled alloys were much higher than those of pure Mg, and the compressive strength of the alloys was more than twice as high as that of pure magnesium. The Mg-0.5Ca-1Sr-0.5Sn alloy released the least hydrogen in Hank's solution, which was lower than that of pure magnesium. Electrochemical test results in Hank's solution further showed that the Mg-0.5Ca-1Sr-0.5Sn alloy had delayed corrosion and lowest Icorr which was 25% of that of pure magnesium. Biological experiments results showed that the Mg-0.5Ca-1Sr-0.5Sn alloy had better biocompatibility and optimal potential for bone substitute material.

Microstructure and Plastic Properties of Mg-Li Alloys Smelted in Vacuum Induction Furnaces after Hot Working

AbstractThe paper analyses the characteristics of plasticity and microstructure of magnesium alloys with lithium meant for hot plastic working with different lithium content. The alloys were prepared in conditions of vacuum smelting. Achieved ingots were subject to hot extrusion. Tests on Gleeble simulator were conducted to assess the susceptibility of tested alloys to plastic forming in conditions of hot plastic working. For tested alloy the activation energy was marked for hot plastic deformation and plasticity characteristics in function of Zener-Hollomon parameter. After the analysis of the influence of temperature on the deformability of tested alloys it was stated that the alloy containing 8%Li (LAZ831) has better susceptibility to plastic treatment than alloy containing 4%Li (LAZ431), but higher than in case of classic magnesium alloys - AZ31.

Behavior of Element Vaporization and Composition Control of Fe-Ga Alloy during Vacuum Smelting

Saturated vapor pressure, critical evaporation temperature and evaporation loss rate of Fe-Ga alloy were calculated under different conditions of Ga and Fe contents with activity coefficients. The relationship between the change of Ga content and melting time was determined. The results demonstrated that saturated vapor pressure of Ga was higher than that of Fe under the same conditions. The difference value of critical evaporation temperature of Ga with and without Ar was nearly 800 K. The critical evaporation temperature of Fe was higher than that of Ga under vacuum, indicating that Ga was more volatile than Fe. At 1 800 K, the evaporation rate of Ga was 84 times higher than that of Fe in the melt of Fe81Ga19 alloy. Under this condition, the change of Ga content and smelting time kept a linear relationship. The higher the temperature was, the faster the Ga content decreased, which was consistent with theoretical calculations.

A comparative research on TiAlN coatings reactively sputtered from powder and from smelting TiAl targets at various nitrogen flow rates

Abstract The aim of this work is to illuminate the influence of two widely applied target types, i.e. powder TiAl target produced by powder metallurgy technique and smelting TiAl target produced by vacuum smelting technique, on the structure and properties of the TiAlN coatings. The characteristics, such as deposition rate, microstructure, surface morphology and mechanical properties, of TiAlN coatings prepared by the two targets at various nitrogen flow rates were analyzed in detail. The deposition rate achieved with the powder targets was ∼30% higher than that obtained from the smelting targets. TiAlN coatings deposited by two types of targets have totally different surface morphology. The surface roughness of the coating with powder target was 20% lower than with smelting target. The number of metallic macro-particles in the coating prepared by powder target was fewer than that by smelting target as a function of the nitrogen flow rates. The phase of coatings is related to the nitrogen flow rate. When the nitrogen flow rate is 20 sccm, both coatings have a phase c-TiN. When the nitrogen flow rate is >20 sccm, both coatings exhibits a stable phase Ti2AlN. The formation of Ti2AlN was attributed to the nitrogen concentration in the coatings and the elevated deposition temperature. The coatings grown from powder targets showed superiority in adhesion strength but less well-behaved in hardness, which is in contrast to those synthesized from the smelting targets.

Preparation of High-Grade Titania Slag from Ilmenite-Bearing High Ca and Mg by Vacuum Smelting Method

Ilmenite produced from the Panxi area in China has high impurities such as Ca and Mg. High-grade titanium (Ti) slag can be obtained by the electric arc furnace process, a traditional method of treating ilmenite. Thus, Ti slag prepared from the Panxi ilmenite contains high CaO and MgO, exceeding 5 pct of the slag content. This high CaO and MgO content confers considerable difficulty in producing titania (TiO2) white using fluidizing chlorination. In this study, a new process named vacuum separation was found to produce high-grade TiO2 materials. The effects of separation temperature and time on the TiO2 grade were studied. The high-grade TiO2 slag, which has 93 pct TiO2, <0.1 pct MgO, <1.2 pct SiO2, and <0.5 pct CaO, can be produced at 1823 K (1550 °C) in 45 minutes through the proposed method.