RU2847892C1 - Method for producing nickel-scandium or nickel-ytrium ligatures - Google Patents

Abstract

FIELD: special metallurgy.

SUBSTANCE: invention relates to methods for producing nickel-scandium or nickel-yttrium master alloys. The method for producing nickel-scandium or nickel-yttrium master alloys includes preparing charge materials in the form of nickel and a rare earth metal, melting, induction stirring of the resulting melt, casting it, and cooling the resulting master alloy ingot. When preparing the charge materials, the charge is formed by layering nickel carbonyl grade DNK-0 granules in a crucible in an amount equal to 90% of the charge weight, the calculated amount of rare earth metal scandium metal or yttrium metal and the remaining amount of DNK-0 nickel carbonyl granules. After complete melting in an argon atmosphere, the charge materials are held at a temperature of 1530-1550°C for 2-4 minutes, after which the melt is stirred by induction and poured into a prepared horizontal cast iron mould, followed by cooling in a furnace.

EFFECT: obtaining nickel-scandium or nickel-yttrium alloys with a calculated content of scandium or yttrium with insignificant liquidation along the cross-section of the casting and with a low content of sulphur and non-ferrous metal impurities in the form of lead, bismuth, antimony, tin, zinc and cadmium.

7 cl, 2 dwg, 3 tbl, 2 ex

Description

1. Field of technology

The invention relates to the field of special metallurgy, namely to a method for producing nickel-scandium or nickel-yttrium ligatures, and can be used in refining cast and wrought heat-resistant nickel-based alloys.

2. Prior art

A known method is "Method for Manufacturing Master Alloys in a Vacuum Arc Furnace with a Non-Consumable Electrode" (RU Patent No. 2734220, Class C22C 35/00, C22B 9/20, published October 13, 2020). This method involves loading charge materials into a water-cooled copper crystallizer located in the melting chamber of a vacuum arc furnace with a non-consumable tungsten electrode, closing the furnace melting chamber, evacuating air and introducing inert gas into the furnace melting chamber, initially melting the charge materials with an electric arc, inverting the resulting ingot, and remelting it. A disadvantage is that it is not economically feasible due to increased burn-off and high energy consumption.

A "Method for Obtaining an Aluminum-Scandium Master Alloy (Variants)" (RU Patent No. 2213795, Class C22C 1/00, C22C 21/00, C22C 35/00, published on October 10, 2003) is known, which includes the aluminothermic reduction of scandium from its compounds in a medium of molten metal halides. The main disadvantages of this method are as follows. When using it, it is not possible to significantly increase the relative content of the scandium-containing reagent in the batch (due to its rheological properties), which leads to excessive consumption and an increase in the volume of reagents (potassium chloride, sodium fluoride), which are subsequently used for additional scandium extraction. This same circumstance reduces the technological efficiency of the process of introducing scandium-containing charge into liquid aluminum, leading to undesirable processes, including the formation of difficult-to-recover scandium oxyfluorides.

A "Method for producing an aluminum-scandium master alloy" is known (RU patent No. 2507291, class C22C 21/00, C22C 1/03, C22C 35/00, published on 20.02.2014), which includes melting aluminum, aluminothermic reduction of scandium from the initial charge containing scandium fluoride, potassium chloride and sodium fluoride under a covering flux, and subsequent holding of the resulting melt. The disadvantages of the method are the low density and scandium content of approximately 2% in the resulting aluminum-scandium master alloy and the high probability of scandium segregation in a single batch of 0.4 to 2.0%, which complicates its use in alloy smelting as a deep deoxidizer and in full due to limitations on the aluminum content in the alloys.

Also known is the technical solution “Method for producing nickel-rare earth metal ligature” (patent RU No. 2556176, cl. C22C 1/02, C22C 19/03, C22C 35/00, published 10.07.2015), accepted by the authors as the closest analogue. The method involves melting nickel, holding the resulting melt and mixing it with a rare earth metal, inductively mixing the melt, pouring it and cooling it, while melting the nickel in a vacuum in an inert crucible of an induction furnace, heating the resulting melt to a temperature of 1500-1700°C and holding it until it degasses in a melting chamber under vacuum, after which the temperature of the nickel melt is reduced to 1400-1550°C and the rare earth metal is added to it in portions in a vacuum or inert gas atmosphere.

This method does not produce a nickel-scandium master alloy. However, this method still results in high losses of rare earth metals, as they are added to the melt, and the development of liquation along the ingot's height. Furthermore, the method is low-productivity due to the lengthy cooling time of the ingot in a vacuum induction furnace (approximately 6 hours), and high labor costs associated with purchasing a separate crucible for each melt, as well as a separate electric furnace for drying the nickel.

3. The essence of the invention

3.1. Statement of the technical problem

The objective of the invention is to develop a method for producing nickel-scandium or nickel-yttrium ligatures with minimal production costs and a low labor intensity coefficient, which makes it possible to obtain scandium or yttrium content in the ligature at the level of calculated values with insignificant liquation across the cross-section of the casting, with low contents of sulfur impurities and non-ferrous metals (lead, bismuth, antimony, tin, zinc, cadmium).

The result of solving a technical problem

The technical result to which the present invention is directed is achieved by means of sequential layer-by-layer horizontal charging of highly pure charge materials (with a low content of gases and non-ferrous metal impurities): nickel → scandium or yttrium → nickel, smelting nickel-scandium or nickel-yttrium ligatures in a vacuum induction furnace by melting, holding in an argon atmosphere and mixing the melt - nickel-scandium or nickel-yttrium, pouring it into a prepared horizontal cast iron mold and cooling.

3.2. Distinguishing features

Unlike the known technical solution for producing a nickel-rare earth metal master alloy by melting nickel, holding the resulting melt and mixing it with a rare earth metal in a vacuum induction furnace, followed by casting and cooling, in the claimed technical solution, at the stage of charge formation, the charge materials are sequentially placed layer by layer in a crucible, then, after complete melting of the charge in an argon atmosphere at a temperature of 1530-1550°C, a holding period of 2-4 minutes is carried out, after which induction mixing of the melt is performed and casting is performed into a prepared horizontal cast iron mold, followed by cooling in the furnace.

When preparing the charge materials, the charge is formed by layer-by-layer placement of DNA-0 grade nickel carbonyl shot into a crucible in an amount of 90% of the charge weight, the calculated amount of metallic scandium or metallic yttrium, and the remaining amount of DNA-0 grade nickel carbonyl shot.

For the smelting of both nickel-scandium and nickel-yttrium ligatures in a vacuum induction furnace, a universal refractory corundum oxide zirconium silicate crucible is used.

When a vacuum of at least 5x10 ^-2 mm Hg is reached, high-purity argon is introduced into the furnace to a pressure of 300 to 380 mm Hg.

Induction mixing of the melt is achieved by switching the furnace power from one stage to another.

The nickel-scandium ligature is poured at a temperature of 1490-1510°C, and the nickel-yttrium ligature at 1520-1550°C.

The resulting ligature is cooled in a closed vacuum induction furnace until complete crystallization for at least 20 minutes.

4. Description of the invention

Traditional deoxidation of steels and alloys with aluminum, silicon, and manganese results in contamination of the metal with inclusions of alumina, silicates, aluminosilicates, and ductile ferromanganese sulfides. Hard, acute-angled alumina inclusions reduce the quality of the metal, as they can lead to crack initiation during service. Ferromanganese sulfides, which stretch in the direction of deformation, significantly increase anisotropy, ductility, and toughness. Sulfur, a harmful impurity, has a particularly significant impact on the process ductility of heat-resistant alloys, significantly impairing their deformability even in negligible concentrations (thousandths of a percent).

The problem of metal contamination is solved by deoxidizing and modifying steels and alloys with rare earth metals (REMs) (e.g., cerium, lanthanum, scandium, yttrium), which have a high affinity for harmful impurities such as oxygen, sulfur, and non-ferrous metals. Adding rare earth metals to the molten metal results in effective deoxidation due to the formation of an REM-containing oxysulfide phase at high temperatures and its intensive removal from the melt during stirring.

The proposed technical solution enables the production of nickel alloys with rare earth metals. The method involves sequentially loading the calculated amount of scandium or yttrium and nickel directly into an inert crucible using scandium or yttrium (Sc or Y), whose melting points (1541°C and 1522°C, respectively) are close to that of nickel (1453°C). The charge is prepared by layering DNA-0 nickel carbonyl shot into the crucible, amounting to 90% of the charge weight, the calculated amount of metallic scandium or metallic yttrium, and the remaining amount of DNA-0 nickel carbonyl shot.

To implement the proposed technical solution, nickel carbonyl shot (grade DNA-0) with low gas and impurity content and one of the components are used:

– metallic scandium;

- yttrium metal.

Table 1 shows the melting temperatures and densities of the charge materials.

Table 1. Melting temperatures and density of charge materials.

Material Melting point, °C Density, g/ ^cm3 Nickel 1453 8.92 DNA-0 1455 8.9 Yttrium 1522 5.5 Scandium 1541 2,985

The use of highly pure carbonyl nickel in the form of shot enables dense charging for stable smelting and eliminates the need for additional high-temperature holding of the molten nickel for degassing. It also reduces labor costs associated with cutting nickel plates and pre-drying them in a resistance furnace when using metallic nickel for smelting.

To calculate the optimal contents of scandium or yttrium in a nickel-based ligature and to determine the temperature regime for melting (melt temperature, drain temperature), binary nickel-REM phase diagrams are used (Fig. 1-2).

When smelting nickel-scandium or nickel-yttrium master alloys, a universal refractory corundum-oxide-zirconium-silicate crucible is used. The crucible material was chosen based on the fact that during the master alloy smelting, the interaction of scandium or yttrium with the crucible material results in a small amount of skull formation on the crucible walls from melt to melt. This allows for up to 20 melts of master alloys of different compositions to be smelted without clogging the crucible.

When preparing the charge materials, the charge is formed by layer-by-layer placement of DNA-0 grade nickel carbonyl shot into a crucible in an amount of 90% of the charge weight, the calculated amount of metallic scandium or metallic yttrium, and the remaining amount of DNA-0 grade nickel carbonyl shot.

Nickel (DNA-0) is loaded into the crucible without the need for additional pre-drying, for example, in a resistance furnace at a temperature of 200°C to 300°C for two hours. After loading, the melting chamber is sealed, evacuated with vacuum pumps, and the charge is simultaneously heated, which is an alternative to pre-drying nickel (DNA-0 grade).

Since scandium or yttrium, which are part of the nickel master alloy, have high vapor pressure and are prone to intense evaporation, in the proposed method, once a vacuum of at least 5×10 ^-2 mmHg is achieved, high-purity argon is introduced into the furnace to a pressure of 300 to 380 mmHg. The melting and casting processes of the master alloy occur in a protective argon atmosphere.

Then, after the complete melting of the charge materials in an argon atmosphere at a temperature of 1530-1550°C, they are held for 2-4 minutes. High-temperature (1600-1700°C) holding of the melt in a vacuum is not performed, since charge materials with low contents of gases and harmful impurities are used for smelting.

Throughout the entire process of smelting nickel-scandium or nickel-yttrium alloys, there is no interaction between the melt and the atmosphere. Short-term melt holding times and low pressure in the melting chamber ensure degassing of the melt from oxygen.₂And N₂and removal of harmful impurities of non-ferrous metals (lead, bismuth, antimony, tin, zinc, cadmium).

After the rare earth metals have been absorbed, the melt is inductively mixed by switching the furnace power from one stage to the next. This operation ensures uniform distribution of the components and equalization of temperature throughout the melt.

To prevent REE segregation along the casting's height and cross-section, nickel-scandium or nickel-yttrium master alloys are poured into a prepared horizontal cast iron mold. A heat-resistant ceramic composite (HRC) is applied to the mold's working surface before use to achieve a high-quality casting surface and protect the casting stock from cracks and voids. This prevents contamination of the metal with the HRC's main components (such as silicon, aluminum, zirconium, titanium, and magnesium oxides).

The nickel-scandium ligature is poured at a temperature of 1490-1510°C, and the nickel-yttrium ligature at 1520-1550°C.

Cooling of the resulting ligature is carried out in a closed vacuum induction furnace until complete crystallization for at least 20 minutes, which is guaranteed by a horizontal cast iron mold.

The use of the claimed technical solution ensures the production of nickel-scandium or nickel-yttrium ligature with scandium or yttrium content at the level of the calculated values without the liquation of rare earth metals along the height and cross-section of the casting, with low contents of sulfur and non-ferrous metal impurities (lead, bismuth, antimony, tin, zinc, cadmium).

This technical solution is guaranteed to reduce production costs by eliminating the drying of charge materials, including the availability of the equipment required for this technological operation, minimizing the waste of expensive and scarce materials (scandium and yttrium), reducing the time for crystallization of the molten casting of the master alloy, and the use of a universal refractory crucible of corundum oxide zirconium silicate allows for the melting of up to 20 melts of master alloys of different compositions without clogging the crucible.

5. Example of specific implementation

Example 1. Smelting of nickel-scandium ligature.

Two batches of nickel-scandium alloy were smelted in a vacuum induction furnace. The charge materials used were DNA-0 grade nickel carbonyl shot and scandium metal.

Nickel and scandium were loaded into the furnace crucible layer by layer. First, up to 90% of the nickel in the charge was loaded onto the bottom of the furnace crucible. Then, scandium was evenly distributed, and the remaining nickel was placed on top of the charge. After sealing the furnace, the melting chamber was pre-evacuated with forevacuum pumps while the charge was simultaneously heated. After filling with high-purity argon to a pressure of 350 mmHg, the charge was melted. After melting the charge materials at 1540°C, the metal was held for three minutes. Next, at a melt temperature of 1510°C, the master alloy was inductively mixed and poured into a horizontal cast iron mold, the surface of which had been coated with TCC before use. The master alloy was then cooled in a closed furnace until complete crystallization, over a period of 20 minutes.

The chemical composition of the molten master alloy after cooling was determined from samples taken from the casting using the edge-center-edge system. The master alloy's chemical composition was analyzed using an IRIS Intrepid atomic emission analyzer. The content of harmful non-ferrous metal impurities (lead, zinc, bismuth, tin, antimony, arsenic, copper, and cadmium) was determined using a PGS-2 mass spectrometer with a MaES. Carbon and sulfur contents were determined using Leco gas analyzers. Table 2 presents the chemical analysis results for the nickel-scandium master alloy.

Table 2. Result of chemical analysis of nickel-scandium ligature.

Melt No. Sampling location Sc C S Fe Cu Pb 1 edge 1 22.1 0.01 0.001 0.3 0.01 0.0003 middle 22.1 0.01 0.001 0.3 0.01 0.0003 edge 2 22.2 0.01 0.001 0.3 0.01 0.0003 2 edge 1 21.7 0.02 0.001 0.3 0.01 0.0003 middle 21.8 0.02 0.001 0.3 0.01 0.0003 edge 2 21.8 0.02 0.001 0.3 0.01 0.0003

Continuation of Table 2

Melt No. Sampling location Sn As Sb Bi Zn CD 1 edge 1 0.0005 0.001 0.001 0.0001 0.001 0.00005 middle 0.0005 0.001 0.001 0.0001 0.001 0.00005 edge 2 0.0005 0.001 0.001 0.0001 0.001 0.00005 2 edge 1 0.0005 0.001 0.001 0.0001 0.001 0.00005 middle 0.0005 0.001 0.001 0.0001 0.001 0.00005 edge 2 0.0005 0.001 0.001 0.0001 0.001 0.00005

Based on the results of chemical composition determinations (edge-middle-edge), a conclusion was made about the absence of liquation of elements along the height and cross-section of the casting and the selection of one sample from the “middle” of the casting is sufficient to determine the chemical composition of the ligature.

Example 2. Melting of nickel-yttrium alloy.

Three batches of nickel-yttrium alloy were smelted in a vacuum induction furnace. The charge materials used were DNA-0 grade nickel carbonyl shot and yttrium metal.

Nickel and scandium were loaded into the furnace crucible layer by layer. First, up to 90% of the nickel charge's weight was loaded into the bottom of the furnace crucible. Then, yttrium was evenly distributed, and the remaining nickel was placed on top of the charge. After sealing the furnace, the melting chamber was pre-evacuated with forevacuum pumps while the charge was simultaneously heated. After filling with high-purity argon to a pressure of 350 mmHg, the charge was melted. After melting the charge materials at 1540°C, the metal was held for three minutes. Next, at a melt temperature of 1540°C, the master alloy was inductively mixed and poured into a horizontal cast iron mold, the surface of which had been coated with TCC before use. The master alloy was then cooled in a closed furnace until complete crystallization, over a period of 20 minutes.

The chemical composition of the molten master alloy after cooling was determined from samples taken from the casting using the edge-middle-edge system. The master alloy's chemical composition was analyzed using an IRIS Intrepid atomic emission analyzer. The content of harmful non-ferrous metal impurities (lead, zinc, bismuth, tin, antimony, arsenic, copper, and cadmium) was determined using a PGS-2 mass spectrometer with a MaES. Carbon and sulfur contents were determined using Leco gas analyzers. Table 3 presents the chemical analysis results for the nickel-yttrium master alloy.

Table 3. Result of chemical analysis of nickel-yttrium ligature.

Melt No. Sampling location Y C S Fe Cu Pb 1 edge 1 25.14 0.015 0.001 0.01 0.01 0.0001 middle 25.16 0.015 0.001 0.01 0.01 0.0001 edge 2 25.16 0.015 0.001 0.01 0.01 0.0001 2 edge 1 25.08 0.012 0.001 0.01 0.01 0.0001 middle 25.09 0.012 0.001 0.01 0.01 0.0001 edge 2 25.10 0.012 0.001 0.01 0.01 0.0001

Continuation of Table 3

Melt No. Sampling location Sn As Sb Bi Zn CD 1 edge 1 0.0005 0.001 0.001 0.0001 0.001 0.00005 middle 0.0005 0.001 0.001 0.0001 0.001 0.00005 edge 2 0.0005 0.001 0.001 0.0001 0.001 0.00005 2 edge 1 0.0005 0.001 0.001 0.0001 0.001 0.00005 middle 0.0005 0.001 0.001 0.0001 0.001 0.00005 edge 2 0.0005 0.001 0.001 0.0001 0.001 0.00005

Based on the results of determining the chemical composition (edge-middle-edge), a conclusion was made about the absence of liquation of elements along the height and cross-section of the casting and the selection of one sample from the “middle” of the casting is sufficient to determine the chemical composition of the ligature.

Thus, the use of the claimed technical solution ensures the production of nickel-scandium or nickel-yttrium ligature with scandium or yttrium content at the level of the calculated values without liquation across the casting cross-section and with low contents of sulfur and non-ferrous metal impurities (lead, bismuth, antimony, tin, zinc, cadmium).

Claims (7)

1. A method for producing nickel-scandium or nickel-yttrium master alloys, including the preparation of charge materials in the form of nickel and a rare earth metal, melting, induction mixing of the resulting melt, pouring it and cooling the resulting ingot of the master alloy, characterized in that during the preparation of the charge materials, the charge is formed by layer-by-layer laying in a crucible of DNA-0 nickel carbonyl shot in an amount of 90% of the charge weight, the calculated amount of the rare earth metal scandium metal or yttrium metal and the remaining amount of DNA-0 nickel carbonyl shot, after complete melting in an argon atmosphere of the charge materials at a temperature of 1530-1550 °C, holding is carried out for 2-4 minutes, after which induction mixing of the melt is performed and it is poured into a prepared horizontal cast iron mold with subsequent cooling in ovens. 2. The method according to paragraph 1, characterized in that a refractory corundum oxide zirconium silicate crucible is used to smelt the nickel-scandium or nickel-yttrium ligature. 3. The method according to paragraph 1, characterized in that before smelting, when a vacuum of no worse than 5×10 ^-2 mm Hg is reached in the furnace, high-purity argon is introduced into it to a pressure of 300 to 380 mm Hg. 4. The method according to paragraph 1, characterized in that induction mixing is carried out by switching the furnace power from one stage to another. 5. The method according to paragraph 1, characterized in that the pouring of the nickel-scandium ligature is carried out at a temperature of 1490-1510°C, and the pouring of the nickel-yttrium ligature is carried out at a temperature of 1520-1550°C. 6. The method according to paragraph 1, characterized in that before pouring the melt, a horizontal cast iron mold is prepared by applying a heat-resistant ceramic composite to its working surface. 7. The method according to paragraph 1, characterized in that the cooling of the ligature is carried out in a closed vacuum induction furnace until complete crystallization for at least 20 minutes.