Melting. Melt Treatment
Afanasyev V.K., Popova M.V., Maslyayev M.V., Tolstoguzov V.N., Chibryakov M.V., Korneva O.V. A New Material - Build-up Electrodes Made from Blast-Furnace Iron without Graphite Precipitations
The article addresses the problem of producing high-quality build-up materials for increasing the service life of machine-building products. The build-up materials used in industry contain high amounts of chromium (13…30%), and also nickel, cobalt, tungsten.
There is proposed a new material for build-up electrodes - Ä×ÁÂÃ blast-furnace iron whose structure is absolutely free of graphite precipitations. Its chemical composition is given. The material is economically alloyed, as the total content of alloying elements is ≤ 2%.
Effect of crystallization conditions on the Ä×ÁÂÃ iron's microstructure, its hardness and the volume fraction of cementite Vc in it has been investigated. It has been shown that Ä×ÁÂÃ iron for bars has a sufficiently high hardness (52…54 HRC) due to a high Vc = 69…74%. Besides cementite, there are pearlite areas in the microstructure of iron bars. There are no graphite precipitations.
In mastering the build-up technology they used cast Ä×ÁÂÃ iron bars and, for comparison, build-up electrodes of the grades T-590, stalinite, ÝÍ-60Ì and sormite No. 1. Building-up was carried out by the electric arc method with direct current of reverse polarity, current strength was selected based on 40 A/mm of electrode section. Quality of obtained built-up layers was compared by several criteria: presence of a pronounced transition zone, absence of cracks in the fusion zone, and general condition of structure.
Optimal build-up conditions using iron electrodes have been determined, which ensure the presence of a transition zone of considerable extension from the base metal to built-up metal. That transition zone (bonding zone) is the main determining factor for the quality of the built-up joint. In analyzing the joints obtained by using sormite, ÝÍ-60Ì, stalinite, T-590 it was found that there was no such zone. Moreover, after building-up with sormite electrodes, the transition zone has graphitization areas that, being ready cracks, would cause spalling of the built-up layer even under low loads. Absence of a transition zone and, consequently, sharp degradation of built-up joints, is related to the alloying degree of the built-up metal.
Application of Ä×ÁÂÃ iron electrodes ensuring a quality bonding zone and having the lowest price as compared to build-up electrodes of well known grades, can produce a high economic effect.
Shumikhin V.S., Shcheretsky A.A. Caste Composites with Amorphous Matrix
A complex of investigations has been carried out, regimes of heat-and-time treatment of zirconium-based melts have been worked out, and process parameters of producing amorphous Zr-Cu-Ni-Al-Ti system based alloys at low cooling rates allowing using casting technologies have been determined.
Special features of interphase interaction between ceramic materials and zirconium-based melts have been studied. It has been found that zirconium-based alloys can be melted in yttrium oxide crucibles, and quartz can be used as a material for a short-time contact with the melt, in particular, for metal ducts.
Kinetic and thermodynamic features of Zr-Cu-Ni-Al-Ti system alloys' changing to nanocrystalline and crystalline state have been studied. Effect of heating rate, holding time and alloying on the processes of amorphous alloys crystallization has been investigated. It has been found that, by adjusting the composition and conditions of heat treatment, a range of materials with different phase compositions and properties and structures from amorphous to nanocrystalline and microcrystalline can be obtained.
Optimal process conditions for obtaining composite materials with an amorphous matrix based on zirconium-based alloys by the method of heat treatment of amorphous alloys have been worked out. It has been shown that the change from amorphous to crystalline state for Zr62,9Cu17,7Ni9,7Al7,5Ti2,2 alloy is of a diffusion nature, which allows regulating the process depending on the temperature-and-time regimes and obtaining composite materials with different sizes of intermetallic inclusions.
Structure and mechanical properties of the obtained materials have been studied. It has been found that the mechanical characteristics increase virtually in a linear manner with increasing of the crystalline phase fraction and decrease with increasing of the size of intermetallic phases.
Zadrutsky S.P., Korolev S.P., Sheshko A.G. High-Performance Complex Preparations for Making Quality Castings
The branch research laboratory of Advanced Melting Processes and High-Strength Cast Iron at the Byelorussian National Technical University, together with ODO Evtektika (Minsk), has developed a modular principle of creating a new generation of preparations for making Al alloy castings. Materials for deep degassing and refining treatment of melt, its inoculation, metallurgical remelting, correction of chemical composition, cleaning of furnace and ladle walls, process coatings for metal molds, dies, iron and steel crucibles, melting-and-pouring tools and others have been created.
The action of the new smokeless tableted preparations for treating silumin is based not only on the thermal dissociation of components to form a refining gas, but also on the melting of salt compositions to subsequently clean metal with surfacing droplets of the refining liquid. The preparations can be used at foundry shops with insufficient ventilation. System approach to casting quality allowed stabilizing the processes at many foundries in Russia, Belarus and Ukraine using the available equipment and the preparations produced by ODO Evtektika.
Malinovsky V.S., Malinovsky V.D., Vlasova I.B. All-Purpose DC Arc Furnaces of the New Generation for Metallurgy and Machine-Building Industry
The article discusses special features of operation and results of commercialization of a new type of melting and holding furnaces designed by NTF EKTA, which are successfully operated at many foundries in Russia and abroad.
The all-purpose DC arc furnaces of the new generation (DCAF-NG) with a capacity of 0.5 to 100 tons and DC arc holding furnaces (DCAHF-NG) with a capacity of up to 150 tons are designed for the production of high-quality castings and recycling scrap of common and high-alloy steel and iron grades, Al-, Cu-, Ni-, Co-, Pb-based alloys and other metals, and foundry alloys based, ferroalloys, deoxidizers and other materials. The new technical solutions allowed to considerably expand the performance capabilities of arc heating and to eliminate the main disadvantages of arc furnaces.
The melting and holding furnaces are versatile and designed for melting various metals. They do not differ by design and refractories used, which allows to produce a wide range of alloys. DCAF-NGs can remelt any kinds of charge, including chips, without special preparation.
The furnaces are supplied in a standard package and modular configuration (DCAF-MC) with two melting vessels. The DCAF-NGs have created conditions for a highly profitable replacement of AC furnaces, induction furnaces and other melting furnaces. The DCAF-NG can also be created by changing AC furnaces to direct current. The payback period for the replacement of the existing melting equipment with DCAF-NG is less than 1 year.
The concept of creating DCAF-NG worked out by NTF EKTA's specialists includes special energy technologies that allowed, for example, in steel making, not to use alternative energy sources, natural gas, oxygen, coal powder and others; and to run the production of, e. g., aluminum, without using chlorine- and fluorine-containing fluxes and other harmful substances usually used for refining aluminum.
The DCAF-NG s fundamentally differ from other firms' arc furnace developments - by versatile energy technologies including, inter alia, organization of the metal melting process and new efficient controlled magnetohydrodynamic (MHD) agitation of melt. The energy technologies used in DCAF-NG s allow to maximally reduce dust and gas emissions from the furnaces during melting.
The controlled MHD agitation in the DCAF-NGs provides a developed effective surface of interaction between slag and melt, an ideal homogeneity of the melt's temperature and chemical composition, rapid dissolving and high assimilation of alloying elements, intensive rate of running the processes: desulfurization, dephosphorization, carburization, decarburization of the melt, removal of nonmetallic inclusions, degassing of the melt; minimal specific power consumption. It allows to considerably, to 0.5-1.5%, reduce charge loss, guarantee a high quality of metals being made.
The developments and equipment by NTF EKTA Ltd. are protected with RF patents.
Nekhamin S.M., Stomakhin A.Y., Chernyak A.I., Filippov A.K. Improvement of Performance Characteristics of Low-Tonnage Steel Melting Electric Arc Furnaces for the Foundry Industry
Efficiency of operation of a low-tonnage steel-melting complex is to a considerable extent determined by the right choice of a DC or an AC electric ark furnace (DCEAF or ACEAF).
DCEAFs and ACEAFs have similarly made basic design elements, charging and metal casting patterns, use the same refractories, allow using the same melting and metal finishing processes. However, the electromagnetic effects with the alternating and direct current running through the metal bath are fundamentally different, as a result of which, with the direct current, in addition to the creation of a reducing atmosphere, it is more economical to consume ferroalloys.
A significant savings item is the reduction of consumption of graphitized electrodes.
Unlike ACEAFs, DCEAFs have a single vertical crown electrode fastened in the body of the electrode holder and, through an aperture in the center of the crown, introduced to the melting space of the furnace. This allows making DCEAFs more gasproof than ACEAFs, and also provides more uniform heating of the charge and lining along the perimeter of the bath. DCEAF are powered from a specialized DC source whose negative pole is connected to the crown electrode, and the positive pole is connected to an electrical pathway structure leading to the metal being melted (anode). The source is a set of equipment including a power transformer, a converter, smoothing reactors, a heat exchanger.
Thanks to the hearth-level electrode's ability to self-restore during melting and the possibility of hot inter-heat repairs of the bottom, their continuous service life is 2…3 thousand heats, after which the hearth-level electrode undergoes maintenance work and is mounted to the furnace for repeated operation. The electric regime of DCEAF provides lowering of the level of arc voltage fluctuations during melting, which is achieved by keeping the crown electrode above the charge level without deepening it into the "well".
The arc voltage lowers in the course of melting, at the same time the power source accordingly increases the current thereby maintaining the power unchanged. Due to the high stability of the DC arc regime and the possibility of good sealing of the furnace there is no air inflow to the melting chamber resulting in a lower, as compared to ACEAF, loss of charge during melting (≤ 3…5%), lower dust and gas emissions, a significantly lower noise level (by 10…15 dBA).
Although the price of the rectifier for a DCEAF is 10-35% of the price of the unit, because of the necessity of using more powerful gas cleaning and filter-compensation devices in the electrical circuit in the ACEAF, the capital cost for both variants is about the same. But if the power supply net of arc furnaces is sufficiently weak, a DCEAF has a clear advantage over an ACEAF. It is also preferable for melting high-quality steels and remelting its waste, because the loss of alloying elements in the latter case is 20% lower.
In the production of common steel of the 20ÃË type the overall economic effect of using a 15-ton DCEAF instead of an ACEAF is about 170,000 Euros a year. The price of a thyristor rectifier being 300,000 Euros, its cost is repaid in less than two years.
21st Century Technologies
Kabaldin Y. G., Muravyov S.N. Information Model of Self-Directed Synthesis of Nanomaterials - the Basics of Intelligent Nanotechnologies
The quantum mechanism of formation of nanostructures and the problem of their structural stability have been investigated. It has been shown that the electronic structure, size and shape of atomic nucleus are conditioned by the quantum character of the microworld's development, its evolution. The process of atoms' uniting to a molecule or a cluster is of an exchange character and determined by the quantum state of individual atoms and accompanied by collectivization of "weakly bonded" valence electrons with a decrease of the total energy in the system. Collectivization of valence electrons, formation of molecules or a cluster should be regarded as a result of the system's self-organization, formation and decay of quantum states, the system's change to a new stable quantum state with formation of dissipative structures having fractal properties.
The quantum character of molecule or cluster formation is a manifestation of collective effects during self-assembly of atoms, which are inherent to synergetic systems. Therefore, self-similarity and stability of clusters (nanosystems) can be expressed with a quantitative characteristic - fractal dimensionality. The atom in the electron shell and nucleus stores information on the evolution that occurred before, i. e. possesses memory. In this connection, the fractal dimensionality carries information on the quantum state of a molecule or a cluster during exchange of information of isolated atoms. Dependence DF of the fractal dimensionality on the d dimension of cluster at uniting of atoms of the same kind (identical atoms), is of a monotonous, smoothed character, increasing with the increase of its size, which indicates the formation of a united quantum state. When atoms of different kinds, and, consequently, with different quantum states, unite, for example, iron - cobalt, dependence DF on the size of nanostructure is of a periodical character, and the system's stability is low. When isolated atoms with identical quantum states, and, consequently, with the same fractal dimensionality, unite, for example, titanium - aluminum, dependence DF on the size of nanostructure is smoothed, i. e. just like in uniting of atoms of the same kind. In this connection, the ability of isolated atoms to self-assemble to a stable molecule or cluster will be determined, first of all, by the quantum state of individual atoms, information on which is carried by the fractal dimensionality. As the dimensions of nanostructure increase, the fractal dimensionality approaches three. Therefore, the increase of the number of degrees of freedom with the increase of the nanosystem's size (> 100 nm) contributes to its change to a chaotic state, and the nanostructure's stability lowers. A neural network has been developed that allows performing self-assembly of isolated atoms, proceeding from their electronic structure, with evaluating the fractal dimensionality of the nanostructure with its different dimensions under the conditions of self-directed synthesis with plotting the dependence DF on d (nanostructure's size).
Marukovich E.I., Stetsenko V.Y., Ki-Young Choi Continuous Casting îf Aluminium Alloys Without Application îf Modifiers
By now, fining of microstructure of ingots at continuous casting of Al-alloys was performed with application of doped modifiers of I and II type (modifiers). They have the following drawbacks: lack of universality of modification of all phases, environmental aggressiveness, relatively short lifetime, their effectiveness depends on the temperature of teeming. This brings in certain difficulties into the technology continuous of casting of ingots with homogeneous disperse structure. Considering, that continuous horizontal casting (CHC) of Al-alloys is quite a long process, these difficulties become insuperable, which decreases the quality of obtained billets.
Application of modifiers is caused by insufficient cooling capability of standard slot crystallizers. To increase the effectiveness of modification during continuous casting of Al-alloys, a crystallizer with jet cooling system (jet crystallizer) has been designed. Its design includes: jacket 1, body 2 with upper 3 and lower 4 flanges, shield 5, baffle 6, inlet 7 and outlet 8 branches (fig. 1). Shield 5, above baffle 6, has holes of specified diameter with set step along the height and perimeter. At that, shield 5 is installed at the distance of not less than 7 mm from jacket 1. To originate overpressure in upper manifold 10, shield 5 is joined with upper flange 3. There is an annular slot between lower flange 4 and shield 5, which, together with annular channel, allows regulating cooling intensity of the lower part of the crystallizer's jacket (fig. 1). Cooling of jacket 1 is performed in the following way. Cooler (water) from inlet branch 7 is delivered to the upper manifold 10 and pressed through holes in shield 5 as submerged jets. They hit the outer surface of the jacket, which significantly increases stream turbulence near the cooling surface. At that, one can observe decrease of thickness of hydrodynamic and thermal boundary level, through which heat transfer from the jacket to the main stream of the cooler is performed. Near the cooling surface, hydrodynamic pressure of water is also increased, which is especially important for preventing origination of steam jacket. All these factors increase cooling ability of the crystallizer.
Let us perform a comparative analysis of work effectiveness of jet and standard slot crystallizers.
Jet crystallizer was used for CHC of silumin ingots with diameter 50 mm. Casting scheme is shown in fig. 2. Ingots of AK12 and AK18 were produced. AK12 bars and alloying agent Al+40%Si were used as charge material. Modifying fluxes and alloying agents were not used. Temperature of teeming of AK12 alloy made 840…860°C, silumin AK18 - 880…920°C. Cross-section samples were cut out of the ingots. After grinding, polishing and etching with water solution of acids (2% HCl + 3% HNO3 + 1% HF), by the method of metallographic analysis, middle areas of the samples were analyzed with optical microscope "Axiotech-100". Results of microstructure analysis of pilot samples were compared with standard billets, produced with application of sodium-bearing fluxes and fluorine-bearing alloying agents. As a result of performed research, it is discovered, that intensity of jet cooling of the jacket of the crystallizer seriously influences the size of phase components of silumin ingots. Thus, at consumption of water and pressure in the crystallizer 50 m3/h è 0,4 MPa in AK12 pilot samples dispersion of silicon crystals made 1.0…2.0 μm, α-phase grain - 30…40 μm (fig. 3, à). In analogous serial ingots, the size of silicon crystals made 4…8 μm, α-phase - 60…80 μm (fig. 3, â). In AK18 pilot billets eutectic silicon was fined up to 2…3 μm and primary silicon - 20…30 μm (fig. 3, á). In analogous serial ingots, the size of eutectic silicon made 4…8 μm, α-phase - 60…80 μm (fig. 3, â). In analogous serial ingots, the size of eutectic silicon crystals made and primary silicon 40…60 μm (fig. 3, ã). Thus, ÑÐÑ of silumins into jet crystallizer without application of allows increasing dispersion of phase components of ingots with ∅50 mm by 2…4 times as compared to casting into standard slot crystallizer.
High productivity of CHC into jet crystallizer allows recycling waste of Al-alloys into ingots with more disperse structure. Being added into the chage, they increase structure heredity of castings. This improves physical-mechanical properties of Al-alloy billets. Such method, in particular, can solve the problem of production of pistons out of hypereutectic silumins AK18, 21. This requires producing billets with highly-dispersed structure out of these alloys by CHC into jet crystallizer. Than add into the charge in the quantity not less than 30% of total load of the furnace and teem liquid metal on piston billets chill casting machine. It is stated that after such heredity modification, both eutectic and primary silicon are fined and lifetime of the process is not less than 2.5 hours.
Improvement of structure heredity - is the universal modifier of increase of dispersion of all phase components of alloys and reserve of increase of mechanical properties of billets. Structure heredity of Al-Si-alloys will be determined by concentration of silicon crystals in the charge. These are crystallographic identical (isomorphic) natural nuclei. Thus, the higher is the concentration of silicon crystals in the charge, the higher is their dispersion in produced billet. This is the essence of hereditary modification. This requires high-dispersion charge materials. CHC into jet crystallizer - is the most productive process of obtaining such materials. Hereditary modification will allow not only to increase dispersion of phase components of silumin billets at chill casting, but also to reduce gas-shrinkage porosity in castings at pressure die casting. It is noticed, that the smaller is the structure of the obtained billets, the less defects of this kind show up. Hereditary modification is applicable for all Al-alloys, if charge with fine-crystalline structure is used. CHC into jet crystallizer allows obtaining low-melt high-dispersion deoxidizing agents Al-based modifiers. They increase effectiveness of structure modification of produced billets at any method of casting.
Thus, CHC into jet crystallizer allows:
- obtaining silumin ingots with highly dispersed microstructure without application of modifiers;
- provide highly productive recycling of waste of Al-alloys into ingots with highly dispersed structure;
- increase effectiveness of hereditary modification of Al-alloy billets;
- obtain highly dispersed and relatively light modifiers;
- significantly improve environment in the foundry.
Borisov G.P. Some aspects concerning the positive role of gas porosity in controlling the processes of aluminium castings formations