Vacuum Arc Furnace Research Articles

EFFECT OF ZIRCONIUM ADDITION ON MICROSTRUCTURE AND MECHANICAL PROPERTY OF TiC/Ti6A14V COMPOSITES

TiC/Ti6A14V composites with different Zr additions were prepared successfully in a consumable vacuum arc furnace equipped with a water-cooled copper crucible and the effect of the Zr content on the microstructure and mechanical property of 15 vol.% TiC/Ti6A14V composites was investigated by XRD, SEM and hardness testing. The results show that when the level of Zr addition is less than 4 wt.%, the morphology of the primary TiC in the composites is dendrite, and the petal-shape, piece-shape or palpus-shape eutectic TiC separates out around the primary TiC . The average size of the primary TiC decreases and the amount of eutectic TiC increases gradually with increasing Zr content. The effects of Zr on morphology of the primary TiC weaken with further addition of Zr . And the hardness (HRC) of composites was obviously increased in the whole range of Zr addition. The refinement mechanism of Zr was attributed to the combined effects of increase in nucleation rate at the constitutionally supercooled zone ahead of the solidification front and reduction in growth rate.

Thermophysical processes in vacuum plasma electric furnaces for heating powdered materials

Vacuum hollow-cathode plasmatrons permit heating, melting, and refining of fine powders in plasma during the flight of particles from the introduction zone to a receiver. A powder in plasma is heated through its interaction with electrons and ions. Such a plasmatron exhibits the following performance characteristics: the total heat flow per particle is 10 6 ‐10 7 W/m 2 , the operation pressure range is 0.1‐100 Pa, the current is 7.5‐10 kA, the voltage is 80‐100 V, and the working gas is argon. As a result of the electrodynamic interaction of every powder particle with the magnetic field of the plasma column, the powder concentrates at the plasma-column axis and moves only within the plasma column. All of the charged powder is treated. The initial content of impurities in the powder can reach 3% [1]. As the probe measurements of the column structure established, the plasma density decreases when going from the cathode cut toward the anode [2]. In this case, the plasma density is maximal in the active zone in the cathode hollow. To intensify the heat flow to a powder particle, we developed a special ring cathode, in which the inner cylinder is shorter than the external cylinder by (0.5‐1) the inner cylinder diameter. The external cylinder has a diaphragm and serves as a guard ring, and it prevents the plasma from sharp decomposition. As a result, the zone of the interaction of the powder with the dense plasma increases. Figure 1 presents a photograph of the ring hollow cathode providing effective heating of powder materials in a plasma column. The new cathode unit design allowed us to increase the temperature of the treated powdered material to 3500 ° C. When producing a compacted tantalum ingot from a powder of sodium-thermic reduction in a commercial plant, we achieved a decrease in the metallicimpurity content by a factor of 10‐40 and in the gaseousimpurity content by a factor of 5‐50. The quality of the ingots fabricated using the vacuum plasmatron is significantly higher than that of similar ingots produced in vacuum arc furnaces and is close to the quality of the metal produced by electron-beam remelting [1].

Investigation of Structural and Chemical Uniformity of Zr2.5% Nb and E635 Alloy by Radioactive Indicators

Abstract The performance and structure of final nuclear zirconium alloy components is formed at all processing steps, from ingot melting and subsequent forging, quenching, pilgering, and heat treatment. The subject of this investigation was the structure of zirconium alloy ingots made by double melting in a vacuum arc furnace, and investigated by the use of radioactive indicators (RAIs). The isotopes that were used were W185 and C14, which were added in very small quantities to the charge before melting the ingot. The RAI isotopes decorate the ingot structure, and provide an opportunity to investigate the behavior of impurity levels during solidification of the molten pool, and the structure in the various types of solidification zones within the ingot. The forged material and other products were investigated using the C14 isotope. Carbon distribution data were obtained for both Zr2.5Nb and for E635 structures on both macroscopic and microscopic levels. The structures and phases in which the carbon isotope was concentrated were discovered.

Preparation of the preform of pure carbon reaction bonded silicon carbide byin-situ consolidation molding method

A new kind of in-situ ceramic consolidation molding process was investigated on the basis of the characteristics of starch swelling in water and gelatinizing when heated. The SiC ceramic suspension containing about 50vol% solids loading and about 3wt% starch can be cast and molded into various complex-shape SiC ceramic parts in a water-thermostat. The dry shrinkage of the green body was less than 1.0% when the solid volume fraction of SiC suspension was up to 52.5%. The density and pore size were homogeneously distributed inside the biscuits. Soaked with melt silicon in a vacuum arc furnace, the biscuits were turn into SiC ceramic materials with homogeneous structure and high performances.

Effect of Alloy Addition(Ta, Nb) on Oxidation Behavior of cp-Ti for Biomaterials

The oxidation behaviors of Ti-10Ta-10Nb alloy and Ti-6Al-4V alloy were studied in dry air atmosphere. Specimens were melted in consumable vacuum arc furnace and homogenized at <TEX>$1050^{\circ}C$</TEX> for 24 h. Hot rolling was performed at <TEX>$1000^{\circ}C$</TEX>. Specimens of the alloys were oxidized as the temperature range <TEX>$400~650^{\circ}C$</TEX> for 30 min. The oxidation behavior of the alloys was analysed by optical microscope, SEM/EDX, XRD, XPS and TGA. Immersion test was performed in 1% Lactic acid. In the microscope observation, oxide layer of Ti-10Ta-10Nb alloy was denser and thinner than Ti-6Al-4V's. The weight gains during the oxidation rapidly increased at the temperature above <TEX>$600^{\circ}C$</TEX> in Ti-6Al-4V's alloy and<TEX>$ 700^{\circ}C$</TEX> in Ti-10Ta-10Nb alloy. According to XRD results, oxide layers were composed of mostly <TEX>$TiO_2$</TEX>(rutile) phase. It was analysed that the passive film of the Ti alloys consisted of <TEX>$TiO_2$</TEX> through X-ray photoelectron spectroscopy(XPS) analysis.

Effects of Nb Addition on Corrosion Resistance and Cytotoxicity Behavior of Ti Alloys

The corrosion resistance and cytotoxicity behavior of Ti alloys were studied as a function of Nb contents(3wt.%Nb, 20wt.%Nb, 40wt.%Nb). Ti-Nb alloys were melted by vacuum arc furnace and then rolled to 50% reduction ratio after homogenized at 105 for 24hrs. The corrosion resistance of Ti-Nb alloys were investigated by potentiodynamic polarization test in the 0.9% NaCl and 5% HCI solution. Biocompatibility of Ti-Nb alloys was evaluated by cytotoxicity test. The results can be summarized as follows 1) The microstructure change from equiaxial to acicular and the increased phase in Ti-Nb alloys were obtained as the Nb content increased. 2) For the corrosion test in the solution of 0.9% NaCl and 5% HCI, the corrosion behavior of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 3) For the cytotoxicity test, Ti-Nb alloys showed excellent biocompatibility compared to ASTM grade 2 CP Ti, 316L STS and Co-Cr alloys.

Production of bimetallic ingots in vacuum arc furnaces

Production of bimetallic ingots in vacuum arc furnaces

Manufacture of semifinished items of alloys V4Ti4Cr and V10Ti5Cr for use as a structural material in fusion applications

Vanadium—titanium—chromium alloys are considered as structural materials with the most appropriate properties for fusion applications. However, the final ratio VTiCr in an alloy is not yet determined. On the one hand, it is offered to optimize structure on the basis of an alloy V4Ti4Cr. On the other hand, it is proposed that the optimum of total Ti and Cr content should be near 15%, and the Ti to Cr ratio should be 2:1. Melting, casting and processing by pressure of ingots of vanadium alloys V4Ti4Cr and V10Ti5Cr weighing as much as 50 kg are considered in the report. The ingots in diameters up to 130 mm were obtained by melting in vacuum-arc furnaces. Results on chemical uniformity and structure of the ingots are presented. A basic scheme of semifinished items manufacture is submitted. Rod and tube hot extrusion conditions are presented. A new technology for protection of ingot and billet surface from gases during hot processing is used to discard application of protective stainless steel and to lower temperature of processing. Sheet and tube products were made from extruded billets by cold rolling with intermediate heat treatment. The list of obtained products, including sheets 0.5–5 mm thick, rods 10–18 mm in diameter and tubes from 50 mm up to 6.0 mm in diameter is presented. The availability of large-scale ingots processing with weight above 300 kg is discussed.

Molten Streams of Ti Alloys by a Single-Melt System

The U.S. Bureau of Mines has developed a single-melt system to purify pressedralloy-sponge electrodes and produce molten titanium alloy streams. Melting was done in a vacuum arc furnace under an inert gas atmosphere using a single, funnel-shaped, water-cooled copper anode. Melt parameters were varied to increase the superheat and produce a stream of molten titanium alloy metal that could ultimately be fed to rotary atomizing equipment. Increasing the power to the arc from 36 to 150 kW produced a molten stream of titanium alloy metal, while a constant flow of helium gas removed volatile impurities. Both the chlorine and magnesium concentrations in the product were below 25 ppm, and aluminum and vanadium homogeneity matched that of commercial titanium alloy powder.

ばね鋼の曲げ疲れ強さに及ぼす超清浄化の影響

There is a recent tendency to develop a motorcars suspension coil spring that can be used under higher-stressed condition and to develop a valve spring having a higher-level of strength therefore creating better engine performance. Since there is a difference between the required fatigue strength level of suspension coil spring and valve spring steel, improvement of fatigue property is a common destination. In order to achieve this purpose, ultra clean steel is considered to be one of the effective methods.The degassing process for producing ultra clean steel satisfies the needs for low cost and mass production. Ultra clean steel is examined and tested as to the properties required for valve spring and suspension coil spring steel. The following results are obtained.(1) Ultra-Low-Oxygen steel (ULO steel) with oxygen content less than 15ppm is confirmed one of the effective means to realize a suspension coil spring satisfying 200kgf/mm2 high stress level.(2) ULO+UL·TiN steel produced by ultra low oxygen and ultra low TiN process exhibits almost the same endurance limit as the Vacuum Arc-furnace Remelted steel. Therefore, this steel is found to be applicable to high strength valve spring.

4435818 Method and apparatus for monitoring the melting process in vacuum arc furnaces : Otto Stenzel, Pierre Flecker, Grundau, Federal Republic Of Germany assigned to Leybold-Heraeus GmbH

4435818 Method and apparatus for monitoring the melting process in vacuum arc furnaces : Otto Stenzel, Pierre Flecker, Grundau, Federal Republic Of Germany assigned to Leybold-Heraeus GmbH

Comprehensive introduction of not (scientific organization of labor) in a vacuum-arc furnace section

Recommendations to improve the organization of labor in this area have been developed by the All-Union Scientific-Research Institute for the Organization of Production and Labor in Ferrous Metallurgy (VNIIOchermet) and the Chelyabinsk Metallurgical Plant based on an analysis of production processes at existing plants. The recommendations permit more efficient use of working space (Fig. I), expand the service area, create safe and more pleasant working conditions, reduce idle time, increase efficiency, and improve the quality of the product.

Melting square- and rectangular-cross-section ingots in vacuum arc furnaces

Melting square- and rectangular-cross-section ingots in vacuum arc furnaces

Electrical and magnetic interactions in vacuum-arc remelting and their effect on the metallurgical quality of specialty steels

The principal interactions between melting current, self-generated magnetic fields, and structural parts of the vacuum arc furnace, and the effect of unsymmetrical stray fields on arc characteristics, pool behavior, and metallurgical quality are briefly reviewed. Various macrosegregation defects are caused by unbalanced electromagnetic interactions affecting pool rotation and the solidification process. The procedure for measuring magnetic-flux density is described, and the results obtained on a large vacuum arc furnace with different bus-bar arrangements are presented. These results, along with extensive operational observations, strongly pointed out the importance of properly located current connections and coaxial current flow on furnace operation and ingot quality. Corrective actions and modifications of the current transmission system to eliminate nonuniform magnetic stray fields from the arc and melting zone are outlined. A coaxial, electromagnetically “clean” configuration of the entire current circuit to and within the furnace is a most important requirement for consistent consumable-electrode melting operation and reliable avoidance of macrosegregations in specialty steels and alloys. A discussion of controlling electromagnetic interactions by careful engineering of the current supply layout and incorporation of these concepts into an advanced furnace design concludes the paper.

Anode Phenomena in Vacuum and Atmospheric Pressure Arcs

This paper summarizes recent experimental data related to anode phenomena in both vacuum and atmospheric pressure arcs. Currents in the range 10A to 3OkA are discussed, and particular emphasis is placed on the effect of plasma flow from the cathode. For vacuum arcs this plasma flow is the directed motion of metal ions from the cathode spots. These ions reduce the anode voltage drop, and maintain a diffuse anode termination. At atmospheric pressure the ion flow is impeded by gas-atom collisions. However, a plasma flow towards the anode can result from magnetic pinch forces at the constricted cathode termination. In the absence of plasma flow, the anode termination constricts to a vigorously evaporating anode spot. For a typical non-refractory electrode such as copper, the spot operates at a temperature close to the boiling point irrespective of the gas pressure. The spot temperature is dictated by the balance between electrical input power and evaporative losses. These anode phenomena are discussed in relation to vacuum switchgear, arc welding and arc furnaces.

Use of high currents for remelting stainless steels in vacuum arc furnaces

Use of high currents for remelting stainless steels in vacuum arc furnaces

Superconducting alloys of the Nb?Al?Ge system

1. Melting Nb−Al−Ge alloys with 60–85 at. % Nb (88. 5–95 wt. %) in a vacuum arc furnace, with a nonconsumable electrode ensures fairly precise composition and good quality of the ingots. 2. On the diagram of composition vs superconducting transition temperature for alloys of the Nb−Ge−Al system there is a region of alloys with Tc>16°K. This region is bounded by alloys with 75–76 at. % (89. 6–91. 6 wt. %) Nb, 3–5 at. % (2.8–4.5 wt. %) Ge, and the rest aluminum. To obtain high values of Tc it is necessary that the ratio of niobium to the total concentration of aluminum+germanium be strictly controlled —75–76:24–25.

1018. The effect of alloying elements on oxygen and nitrogen contents of steel after vacuum-arc furnace remelting: H Zak,Prace Inst Hutn, 18, 1966, 55–61 ( in Polish)

1018. The effect of alloying elements on oxygen and nitrogen contents of steel after vacuum-arc furnace remelting: H Zak,Prace Inst Hutn, 18, 1966, 55–61 ( in Polish)

1864. Losses of certain elements on melting selected steels in the vacuum arc furnace: Z Eminger and Z Kletecka, Hutnicka Conf. VSBV Ostrave, Sbornik Referatu Ocelarske, 1965, 155–171 (in Czech)

1864. Losses of certain elements on melting selected steels in the vacuum arc furnace: Z Eminger and Z Kletecka, Hutnicka Conf. VSBV Ostrave, Sbornik Referatu Ocelarske, 1965, 155–171 (in Czech)

732. A laboratory lined vacuum arc furnace: A M Khromov et al, Electroetermiya Nauk Tekn, 42, 1965, 30–32, (in Russian)

732. A laboratory lined vacuum arc furnace: A M Khromov et al, Electroetermiya Nauk Tekn, 42, 1965, 30–32, (in Russian)