RU2593807C2 - Method for production of hafnium by vacuum arc remelting - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to obtaining hafnium ingots. Pressed briquettes of charge hafnium material with density of briquette not less than ρ_br = 7.2 g/cm³. Consumable electrode is formed by electron beam welding of briquettes. First vacuum arc remelting of obtained consumable electrode with ARC current force I = K₁×Ding is made, where the coefficient of proportionality K₁ = 70-220 a/cm, Ding -melted ingot diameter, cm, and then the second vacuum arc remelting in two-stage mode is made, wherein the arc current intensity of the first stage I₁ = K₂×Ding, where the coefficient of proportionality is K₂ = 220-350 A/cm, and the arc current intensity of the second stage I₂ = K₃×I₁, where the coefficient of proportionality is K₃ = 0.25-0.5. As a charge hafnium material the electrolytic hafnium powder and additionally milled recycled and/or iodide hafnium can be used.

EFFECT: higher quality of produced hafnium ingots due to reduced casting defects.

3 cl, 1 tbl, 7 ex

Description

The invention relates to the field of metallurgy, in particular to the production of hafnium ingots.

There is a method of smelting hafnium ingots in an electron beam furnace (RF patent No. 2443789 IPC С22В 9/22, С22В 34/14 publ. February 27, 2012), which includes loading the charge and melting the metal with an electron beam with electromagnetic stirring of the melt, while melting carried out in a crucible with a skull in a three-stage mode.

This method is not intended to produce ingots from refractory metal powders. In addition, the disadvantage of this method is the duration of the melting process, the small size of the obtained ingot, limited by the size of the crucible.

The closest analogue is the method for producing hafnium ingots by double vacuum-arc remelting of hafnium iodide rods (“Hafnium Metallurgy” edited by Thomas DE and Hayes ET, 1967, p. 141-142). The formation of a consumable electrode in the described method is carried out by spot welding of iodide rods, previously corrected by cold deformation, and then annealing is performed to relieve residual stress, after which an ingot is made by a double vacuum-arc remelting.

The disadvantages of the described method are:

- the impossibility of manufacturing electrodes from electrolytic powder;

- the optimal values of the current strength of the arc of the vacuum arc melting are not determined depending on the diameter of the smelted ingot, including the mode of withdrawal of the shrink shell, which leads to the appearance of casting defects in the ingot (for example, non-melts on the side surface, shrinkage defects in the upper part), as a result, the yield is reduced.

The objective of the invention is to develop a method that allows to produce hafnium ingots by forming a mechanically strong electrode, stabilizing the melting process by selecting the arc current strength depending on the diameter of the mold (ingot) and using the two-stage mode of the second vacuum-arc remelting.

The technical result is the production of hafnium ingots of high quality by reducing casting defects (on the side surface and in the upper part of the ingot) and increase yield.

The technical result in the claimed method for producing hafnium ingots is achieved by pressing briquettes from charge materials, while the density of the briquette is not less than ρ _bР = 7.2 g / cm ³ ; forming a consumable electrode by electron beam welding of briquettes with a power determined by the formula P = k × m _el , where the proportionality coefficient k = 28-70 W / kg, and the electrode moving speed during welding is not more than 5 mm / s, and the minimum number seams N are determined by the formula N = 2 + n × D _bP , where D _bp is the briquette diameter, cm, the proportionality coefficient n = 0.1 cm ^-1 , while the first vacuum-arc remelting of the resulting consumable electrode with the arc current I = K ₁ × D _SL , where the proportionality coefficient K ₁ = 70-220 A / cm, D _sl is the diameter of the smelted ingot, cm, and the second vacuum-arc remelting is carried out in a two-stage mode: first-stage arc current I ₁ = K ₂ × D _sl , where the proportionality coefficient K ₂ = 220-350 A / cm, second arc current steps I ₂ = K ₃ × I ₁ , where the proportionality coefficient K ₃ = 0.25-0.5. As charge materials, hafnium electrolytic powder is used and, in addition, ground iodide rods and / or turns are used.

Pressing briquettes with a density of less than 7.2 g / cm ³ led to an increased formation of scree from the surface of the briquettes during their turning and transportation. The maximum possible density of briquettes is 13.1 g / cm ³ , which corresponds to the theoretical density of hafnium. The power obtained by using the values of the coefficient k> 70 W / kg leads to excessive energy consumption, increased gas release from the briquettes, as well as the flow of the melt from the side surface of the briquettes due to the increase in the volume of molten metal.

When welding briquettes with the power obtained when using the coefficient values k <28 W / kg, and when the electrode travels more than 5 mm / s, the weld becomes insufficiently strong, and the mechanical strength of the electrode decreases. The application of the number of welds N less than determined by the stated ratio leads to a similar result.

The minimum value of the proportionality coefficient K ₁ for the arc current of the first vacuum-arc remelting is determined by the stability of the arc burning, the maximum - by the maximum allowable gas evolution from unsintered briquettes.

The minimum value of the proportionality coefficient K ₂ for the arc current of the second vacuum-arc remelting is determined by the melt of the peripheral zones, the maximum is determined by the increase in the number of casting defects in the ingot in the form of pores.

When the arc current I ₂ <(0.25 × I ₁ ) in the second stage of the second vacuum-arc remelting, the arc burning process becomes unstable, and when I ₂ > (0.5 × I ₁ ) the volume of the metal liquid bath remains sufficient great. In both cases, a zone is formed in the ingot with an increased number of casting defects that reduce the yield.

The method was carried out as follows: briquettes with a diameter of 200 mm of various densities were pressed from batch hafnium materials on a P-814 and HPM 1500E press. The briquettes were welded in the electron-beam welding systems ASTK-30 / 6-10 and Luch-1. The electrodes were melted in the DKV-3.2 and VDP-300 vacuum arc furnaces: the first remelting was made into a mold with a diameter of 280 mm, the second remelting was made into a mold with a diameter of 320 mm.

For comparison, a double vacuum-arc remelting of an electrode from hafnium iodide rods was carried out (prototype). The mass of the first remelting electrode was 420 kg. The second remelting electrode consisted of two ingots of the first remelting. The first vacuum-arc remelting was carried out into a mold with a diameter of 280 mm (corresponds to the diameter of the ingot) with an arc current of 7 kA, the second remelting into a mold with a diameter of 320 mm with an arc current of 9 kA.

Example 1

A portion of PGE-1 grade hafnium electrolytic powder weighing 20 kg was poured into the press mold and briquettes with a density of 9.1 g / cm ^{3 were made} . To form the electrode of the first remelting, the compressed briquettes were laid in columns and welded with four longitudinal seams along the lateral surface over the entire length of the electrode. Welding mode: power 25.7 kW (coefficient value k = 61.2 W / kg), electrode movement speed 3.3 mm / s.

The first remelting was carried out in a mold with a diameter of 280 mm (corresponds to the diameter of the ingot) with an arc current of 6.2 kA (K ₁ = 220 A / cm). The second remelting electrode consisted of two ingots of the first remelting. The second remelting was carried out in a mold with a diameter of 320 mm: the arc current of the first stage was 11.2 kA (K ₂ = 350 A / cm), the arc current of the second stage was 4 kA (K ₃ = 0.36).

Examples 2-4

They differ from example 1 in the mass and density of briquettes, the mass of electrodes, electron beam welding modes and current loads of vacuum-arc melts, example 4 - in the number of seams.

Example 5-7

They differ from example 1 in the composition of the mixture using electrolytic powder, ground iodide rods (grade GFI-1) and revolutions (chemical composition corresponds to grade GFE-1), as well as the current strength of vacuum-arc melts.

The results are shown in the table. The increase in yield compared to the prototype ranged from 2.6 to 5.3%.

Thus, a new method has been developed for producing hafnium ingots by pressing briquettes from charge materials with a given density, manufacturing a mechanically durable electrode with set welding mode parameters and the number of welds, conducting a double vacuum-arc remelting with selected values of the arc current depending on the diameter of the ingot and the use of the two-stage regime of the second vacuum-arc remelting, which allowed to increase the yield by reducing casting defects of the ingot (improvement roplav of the lateral surface and localization of the shrinkage shell).

Claims (3)

1. A method of producing hafnium ingots, including a vacuum-arc remelting of a consumable electrode, characterized in that the briquettes are pressed from a charge hafnium material with a briquette density of at least ρ _br = 7.2 g / cm ³ , and a consumable electrode is formed by electron beam welding briquettes with a power determined by the formula P = k × m _e, where the proportionality factor k = 28-70 W / kg, and the rate of movement of the welding electrode is not more than 5 mm / sec, and the minimum number of seams defined by the formula N N = 2 + n × D _{br br} where D - diameter of the preform cm proportionality factor n = 0,1 cm ^-1 is carried out first vacuum arc remelting the consumable electrode obtained with the arc current strength I = K ₁ × D _slab, where the proportionality coefficient Κ ₁ = 70-220 A / cm, D _SL is the diameter of the smelted ingot, cm, and then the second vacuum-arc remelting is carried out in a two-stage mode, and the arc current of the first stage is I ₁ = K ₂ × D _SL , where the proportionality coefficient K ₂ = 220-350 A / cm, the arc current of the second stage I ₂ = K ₃ × I ₁ , where the proportionality coefficient K ₃ = 0.25-0.5. 2. The method according to p. 1, characterized in that as the charge of hafnium material using an electrolytic powder of hafnium. 3. The method according to p. 2, characterized in that the charge hafnium material additionally contains ground comminuted and / or iodide hafnium.