RU2680321C1 - Method of obtaining semi-finished product from alloy on basis of niobium - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to the field of metallurgy and can be used to obtain semi-finished products from niobium alloys. Method involves the preparation of a mixture of oxides of niobium, molybdenum and tungsten in quantities, determined by the grade of the alloy, and aluminum, taken with an excess of 1–15 % of the stoichiometric amount. Aluminothermic reduction is carried out, the obtained ligature is crushed, electron-beam remelting is performed on a plant with a horizontal mold with an ingot, the ingot is first melted on the one hand, cooled, turned over and melted from the other side thereof, then cooled and transferred to the subsequent double or triple electron-beam remelting of the ingot on a plant with a vertically located crystallizer. Then, vacuum-arc remelting of the ingot is carried out on the installation with a consumable electrode with simultaneous introduction of zirconium and carbon into the alloy. Semi-finished product from the ingot is produced by hot and cold pressure treatment with a total deformation of at least 20 % and intermediate annealing.EFFECT: invention allows to obtain a niobium alloy with high temperature properties.1 cl, 1 ex

Description

The invention relates to ferrous metallurgy, and specifically to methods for producing niobium alloys.

The prior art method for producing a niobium alloy, including the preparation of a charge and a double electric arc remelting in a vacuum furnace with a step crystallizer, the first remelting is carried out in a mold of a smaller diameter, and the obtained ingot is remelted a second time in a mold of a larger diameter (G.V. Zakharova and Niobium and its alloys, Metallurgizdat, Moscow, 1961, p. 67).

This method does not provide a high degree of uniformity in the distribution of alloying and, as a consequence, a high level of alloy properties.

A known method of producing niobium-tantalum alloys by aluminothermic reduction of niobium-tantalum-containing materials (columbite, tantalite, pyrochlore or mixtures thereof) in the presence of potassium chlorate. (R. Durrer, G. Volkert, "Metallurgy of Ferroalloys", M., Metallurgy, 1976, pp. 389-391)

The disadvantage of this method is the insufficient level of alloy properties, as well as the insufficiently homogeneous alloy structure.

A known method of producing a heat-resistant alloy based on niobium, including the preparation of a mixture containing silicon, aluminum, titanium, niobium and at least one element selected from chromium, molybdenum and tungsten and loading the mixture into a ceramic crucible. Smelting is carried out at 1800-2100 ° C in a vacuum induction furnace in a vacuum or inert gas medium, the melt is poured into a heated inert form. At least 10-15 minutes before casting, at least one active element selected from zirconium, hafnium and yttrium is introduced into the melt. (patent RU 2618038 C2, C22C1 / 02, C22B9 / 22, C22C27 / 02, 02/02/2017).

The obtained ingots have equiaxial structure and homogeneous chemical composition over the entire volume of the ingot, however, the level of homogeneity is insufficient to obtain a high level of alloy properties.

The prior art method for producing a niobium alloy (CN, selected as a prototype), including the preparation of a mixture and the formation of strips of niobium-tungsten-molybdenum, laying a plurality of niobium-tungsten-molybdenum metal strips and a first layer of pure zirconium in the middle of folded metal strips and welding to form then the semi-finished product is obtained in the form of an ingot, twice performing vacuum electron beam melting of the melting electrode. To the outer surface of the said semi-finished product is tight strips of pure zirconium are attached in order to obtain a consumable electrode for electric arc melting and double vacuum-arc remelting is carried out to obtain a niobium-tungsten-molybdenum-zirconium alloy ingot.

The disadvantage of this method is the insufficiently uniform distribution of alloying in a niobium base, which does not allow to achieve the required level of high temperature properties.

The present invention is to develop a method for producing a niobium alloy, which will allow to obtain an alloy having high properties at high temperatures.

The stated technical problem is achieved by the fact that in the method for producing a semi-finished product from a niobium-based alloy, including the preparation of a charge, electron beam melting and vacuum arc melting, the mixture is prepared from niobium, molybdenum and tungsten oxides in quantities determined by the alloy grade and aluminum, taken with an excess of 1-15% of the stoichiometric amount, aluminothermic reduction is carried out, the resulting ligature is crushed, electron beam remelting of the crushed ligature into an ingot is carried out on a plant with horizontally a molten mold and subsequent double or triple electron-beam remelting of the obtained ingot in a unit with a vertically arranged mold, after which a vacuum-arc remelting of a round ingot is carried out in a unit with a consumable electrode with the simultaneous introduction of zirconium and carbon and subsequent hot and cold pressure treatment with a total deformation not less than 20% and intermediate annealing.

The technical result is to improve the uniform distribution of tungsten and molybdenum in a niobium base, increase the thermal stability of the alloy at high temperatures, reduce the creep rate at temperatures above 1000 ° C, increase ductility without loss of strength.

The introduction of aluminum in an excess of a relatively stoichiometric amount provides deep refining of the material during subsequent remelting, which leads to an increase in ductility without loss of strength.

The introduction of refractory alloying tungsten and molybdenum in the form of oxides at the stage of aluminothermic reduction, and zirconium and carbon at the stage of vacuum-arc remelting ensures uniform distribution of them in a niobium base. In this case, the introduction of zirconium and carbon at the first stage worsens their distribution in the material, coarse (tens to hundreds of microns in size) second phases (carbides and intermetallic compounds) are formed, which in this form cease to work as hardeners. The dimensions of the formed second phases should be less than 1 μm, which occurs when zirconium and carbon “pull” W and Mo onto themselves from an already formed solid solution.

All of the above leads to the formation of a uniform Nb-W-Mo solid solution at the nanoscale (none of the physical methods sees tungsten and molybdenum separately), which helps to increase the thermal stability of the alloy and reduce the creep rate by 30%.

Carrying out double or triple vacuum-arc remelting provides purification of the alloy from impurities, while the number of stages of remelting depends on the rate of their removal.

Pressure treatment with intermediate annealing is carried out to relieve stresses and form a fine-grained structure of a niobium alloy, since an alloy with a fine-grained structure will have the highest elongation and impact strength. It should be said that the degree of deformation of the material less than 20% will not allow to form a homogeneous fine-grained structure and, therefore, to obtain the final product with high ductility.

An example embodiment of the invention

To obtain a semi-finished product from a niobium alloy Nb5V2MTs, a mixture is prepared containing:

niobium oxide Nb ₂ O ₅ - 120-122 kg,

MoO ₃ molybdenum oxide - 3.1-3.3 kg,

tungsten oxide WO ₃ - 5.2-5.4 kg,

ALF aluminum powder - 54-56 kg.

Mixing is carried out in a mixer with an eccentric axis of rotation of 250 dm ³ for 40-60 minutes, in addition to a charge, 10-15 kg of cylinders with a diameter of 10-15 and a height of 10-15 mm made of niobium or niobium alloy are loaded into the mixer.

Aluminothermic reduction is carried out in a steel or cast iron reactor with a copper crystallizer. 180-185 kg of the charge are rammed into the reactor, then the reactor is installed in a water-cooled airtight chamber, 20-30 g of an ignition mixture of aluminum powder and potassium permanganate are placed in the upper part of the charge and the ignition is in the form of a spiral of aluminum wire. After equipping, the chamber is pumped to 0.02-0.05 bar forvacuum and the charge is ignited by supplying a voltage of 12 V. The charge burning reaction occurs within 7-12 minutes, while the pressure in the chamber rises to 0.5-0.8 bar. After the reaction, the chamber is cooled for 3-4 hours and the reactor is removed from the chamber. After extraction, the reactor is disassembled, the ingot and slag are recovered. The ingot is first crushed into pieces 100-200 mm in size manually, then on a jaw crusher to a fraction of 10-20 mm, which is transferred to the 1st electron-beam remelting (EBL).

The first CRP of crushed ligature in the ingot is carried out in a plant with a horizontally located mold. Pieces of the ligature are poured into a 20-30 mm thick layer in a copper water-cooled crystallizer with internal dimensions of 1200x200x30 mm and melted for 2-2.5 hours by a scanning electron beam with parameters of 18-20 kV / 3.5-4 A and slot focusing. The ingot is first melted on one side, then cooled for 2-3 hours, turned over and melted on the other side, then cooled again and transferred to the 2nd and subsequent EBLs.

The second and subsequent EBP of the ingots is carried out in a plant with a vertically located mold. The ingots are connected with 3 pcs niobium wire, mounted on a loading unit and fed under an electron beam with parameters of 22-24 kV / 8.5-10A with cylindrical focusing. The melt flows into a 120-160mm water-cooled copper crystallizer, part of the beam energy maintains a melt level of 15-20 mm in the mold, while the solidified part of the ingot is continuously pulled down. In the process of remelting, the contents of oxygen, silicon and iron are controlled, remelting is completed when the content of 0.005-0.008% for each of the mentioned impurities is reached.

The vacuum-arc remelting (VDP) of the ingot of the last ELP is carried out on a unit with a sacrificial electrode in a water-cooled copper mold of 120-160 mm. 0.5-0.7 kg of tape with a cross section of 2x10 mm from iodide zirconium and 50-70 g of graphite fiber fabric are tied to an ingot with an average weight of 65-70 kg. Melting is carried out at 25-28 V / 11-13 kA, the melting time of an ingot weighing 70 kg is 40-55 minutes. After melting, the ingot is cooled in the mold for 2-3 hours.

To obtain a semi-finished product from an ingot, hot pressing is carried out from a temperature of 1450-1500С, heating in air for 40-50 minutes, a pressing speed of 28-32 mm / s on a round or flat bar with a degree of deformation of 70-75%. After that, cold rolling of the hot-pressed rod / suture with a deformation of 15-20% per pass and intermediate vacuum annealing at 1200-1300C for 1-1.5 hours every 3-5 passes is carried out. The final vacuum annealing is carried out at 1350-1400C for 1.5-2 hours.

Mechanical properties of the obtained material (grade Nb5V2MTs, sheet 5 mm thick):

- at 20 ° C: tensile strength σ _in = 450-490 MPa, yield strength σ _0.2 = 350-380 MPa, elongation δs = 30-45%;

- at 1200 ° C: σ _in = 120-140 MPa, σ _0.2 = 110-120 MPa, δs = 55-65%;

- at 1500 ° C: σ _in = 50-70 MPa, σ _0.2 = 45-50 MPa, δs = 100-110%

- at 1700 ° С: σ _в = 35-40 MPa, σ _0.2 = 30-35 MPa, δs = 130-150%

- long-term strength: at 1200 ° С σ ₁₀₀ = 50-60 MPa, at 1500 ° С - 15-20 MPa.

Claims (2)

A method of producing a semi-finished product from an alloy based on niobium, including the preparation of a charge, electron beam melting and vacuum arc melting, characterized in that the mixture is prepared from oxides of niobium, molybdenum and tungsten in quantities determined by the alloy grade and aluminum taken in excess of 1 -15% of the stoichiometric amount, aluminothermic reduction is carried out, the resulting ligature is crushed, electron beam remelting is carried out in a plant with a horizontally located crystallizer to obtain an ingot, while the current is first melted on one side, cooled, turned over and melted on the other side, after which it is cooled and the ingot is transferred to the subsequent double or triple electron-beam remelting in a unit with a vertically arranged crystallizer, then a vacuum-arc remelting of the ingot in a unit with a consumable electrode is carried out with the simultaneous introduction of zirconium and carbon into the alloy, after which hot and cold pressure treatment with a total deformation of at least 20% and intermediate annealing is carried out.