RU2539643C1 - Heat-resistant alloy based on nickel for manufacture of blades of gas-turbine units and method of its heat treatment - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to corrosion-resistant heat-resistant alloys based on nickel and can be used for manufacture of parts of a hot path of gas-turbine units operating in corrosive media. Heat-resistant alloy based on nickel contains the following, wt %: carbon 0.05-0.09; chrome 15.4-15.8; cobalt 10.0-10.4; tungsten 5.0-5.3; molybdenum 1.6-1.8; titanium 4.3-4.5; aluminium 3.0-3.2; boron 0.06-0.09; zirconium <0.015; hafnium 0.2-0.3; silicone <0.1; iron <0.1; copper <0.05; sulphur <0.005; nitrogen <20 ppm; oxygen <15 ppm, cerium <0.015; niobium 0.1-0.2; yttrium <0.03; manganese <0.1; phosphorus <0.005 and nickel is the rest. A manufacturing method of blades of gas-turbine units from heat-resistant alloy based on nickel is characterised by the fact that heat treatment is performed by homogenising annealing and ageing. Homogenising annealing is performed in inert atmosphere at heating rate of 5-10°C/min to the temperature of 1060±10°C, with exposure during 3-4 hours and cooling to the rate of 30-50°C/min to the temperature of 600-700°C and further to room temperature. Ageing is performed at the temperature of 850±10°C during 16 hours with further cooling in the air to room temperature.

EFFECT: increasing strength, ductility and corrosive resistance of an alloy with an equiaxial structure in combination with high structural stability for operating life and reduced level of gas shrinkage porosity.

2 cl, 2 tbl

Description

The invention relates to metallurgy, in particular to casting corrosion-resistant heat-resistant alloys based on nickel with chromium, cobalt, tungsten, molybdenum, and can be used for casting parts of the hot tract of gas turbine units (GTU) operating in aggressive natural gas environments at temperatures 600-900 ° C, for example vanes with equiaxial structure.

High strength characteristics such alloys are achieved by a significant amount (35-55 at.%) Of the strengthening γ'-phase (Ni ₃ Al), niobium alloy, tantalum and other elements, and solid solution hardening (γ-phase) cobalt, chromium , molybdenum, tungsten. Increased corrosion resistance is provided by a chromium content of 13-17 wt.% With a ratio of titanium to aluminum content of ≥1.0, as well as the introduction of rare earth elements. Oxidation resistance at elevated temperatures is provided by a high content of aluminum and titanium, a limitation of the molybdenum content in combination with the introduction of rare earth elements. The service characteristics of the blades of heat-resistant nickel-based alloys depend on the heat treatment method, which ensures the optimal metal structure and the distribution of hardening compounds in the alloy.

Service characteristics of alloys, including structural stability per resource (eliminating the formation of embrittlement phases), and the tendency to form non-equilibrium eutectic phases in the molded state, at the site of which pores and cracks form during heat treatment, can be evaluated using the well-known FACOMP method. The long-term strength characteristics, critical points of the alloy and its other physical and mechanical properties can also be evaluated by known methods (N. Harada, Sat. Alloys Design for Nickel-base Superalloys, 1982, pp721-735; H. Harada et al., Sat. Superalloys, 1988; pp733-742; Sat. Superalloys, 2000; pp729-736).

Known corrosion-resistant heat-resistant alloy based on Nickel for the manufacture of cast rotor blades of gas turbine units (GTU) with equiaxed structure. Known alloys include carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, niobium, tantalum, boron, zirconium and nickel in the following ratio, wt.%: Carbon 0.015; chrome 16.0; cobalt 8.75; tungsten 2.7; molybdenum 1.75; aluminum 3.6; titanium 3.7; niobium 1.0; tantalum 1.8; boron 0.1; zirconium 0.01; nickel rest. The known alloy is used for the manufacture of gas turbine blades with reduced gas-shrinkage porosity due to the increased boron content (up to 0.10 wt.%) And low carbon content (up to 0.02 wt.%). The decrease in gas-shrinkage porosity is achieved as a result of more complete impregnation of the dendritic regions during crystallization by liquid melt, since boride eutectics have a lower dissolution temperature T _SOL ≈ 1150-1170 ° С in comparison with the dissolution temperature of carboloride eutectics TSol ~ 1200-1235 ° С of traditionally alloyed alloys . Such alloys are called BC alloys (GLR Durber, Sat. "High Temperature Alloys for Gas Turbines", 1978, pp459-465).

However, well-known alloys of this type, for example, B1981, which is used for the manufacture of large-sized GTU rotor blades, with sufficient structural stability for the service life and high corrosion resistance, have low heat resistance, despite the content of about 1.6 wt.% Tantalum.

Known heat-resistant alloy based on Nickel, including carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, boron, cerium, niobium, calcium, zirconium, silicon, manganese, sulfur, phosphorus and nickel in the following ratios of components, wt.%: carbon 0.07-0.15; chrome 12.5-14.0; cobalt 4.0-6.0; tungsten 4.0-6.0; molybdenum 1.5-2.5; aluminum 2.8-3.2; titanium 4.5-5.5; boron 0.01-0.05; cerium 0.02-0.05; niobium 0.05-1.0; calcium 0.005-0.01; zirconium 0.005-0.01; silicon 0.4; manganese 0.4; sulfur not more than 0.015, phosphorus not more than 0.015; nickel - the rest (description SU 1072497, С22С 19/05, published 07.07.1993).

The known alloy is characterized by a sufficiently high heat resistance and structural stability for a resource, but has moderate corrosion resistance, as well as insufficient short-term and long-term ductility. Moreover, with a sufficiently high boron content (up to 0.05 wt.%), The known alloy has a volume of gas-shrink porosity that is almost equal to the porosity of alloys with traditional alloying.

The closest in technical essence and the achieved result is a heat-resistant nickel-based alloy for the manufacture of a working or nozzle blade with an equiaxed structure for a gas turbine and a method for its heat treatment (RU 2443792, С22С 19/05, published 02.27.2012).

The known alloy contains carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, boron, tantalum, zirconium, hafnium, silicon, iron, copper, sulfur, nitrogen, oxygen and nickel in the following ratios of components, wt.%: Carbon 0, 04-0.12; chrome 11.5-12.5; cobalt 11.5-12.5; tungsten 3.3-3.7; molybdenum 1.7-2.1; aluminum 3.35-3.65; titanium 4.85-5.15; boron 0.01-0.02; tantalum 2.3-2.7; zirconium 0.0-20 ppm; hafnium 0.0-0.05; silicon less than 0.05; iron 0.0-0.15; copper 0.0-0.10; sulfur 0.0-0.0012, nitrogen 0.0-25 ppm; oxygen is 0.0-10 ppm and nickel is the rest.

The heat treatment method of the known alloy includes heating to a temperature of 2050 ± 25 ° F (1120 ± 4 ° C) and holding for 2 hours ± 15 minutes, quenching in a gas stream (argon, helium) to a temperature of 1100 ° F (593 ° C) or lower, reheating to a temperature of 1975 ± 25 ° F (1080 ± 4 ° C), and holding for 4 hours ± 15 minutes, re-quenching in a gas stream to a temperature of 1100 ° F (593 ° C) or lower, heating alloy to a temperature of 1550 ° F ± 25 ° F (843 ± 4 ° C) and aging (aging) for 24 hours ± 30 minutes, and cooling the alloy to a temperature of 1100 ° F (593 ° C) or lower.

Due to the significant volume of the strengthening γ′-phase (≈56 at.%), The known alloy is characterized by increased heat resistance, however, it contains up to 6% eutectic, which cannot be dissolved with the heat treatment method used for this alloy (its T _SOL > 1200 ° C) does not participate in hardening and leads to an increase in gas-shrinkage porosity. In addition, the well-known alloy does not possess sufficient corrosion resistance and, during operation, it is predicted that ≈ 2% embrittlement of the σ phase will drop out.

The objective and technical result of the invention is to increase the strength, ductility and corrosion resistance of metal blades with equiaxial structure in combination with increased structural stability on the resource and a lower level of gas shrink porosity.

The technical result is achieved in that the heat-resistant nickel-based alloy for the manufacture of gas turbine blades contains carbon, chromium, cobalt, tungsten, molybdenum, titanium, aluminum, boron, zirconium, hafnium, silicon, iron, copper, sulfur, nitrogen, oxygen, cerium , niobium, yttrium, manganese, phosphorus and nickel in the following ratio of components, wt.%: carbon 0.05-0.09; chrome 15.4-15.8; cobalt 10.0-10.4; tungsten 5.0-5.3; molybdenum 1.6-1.8; titanium 4.3-4.5; aluminum 3.0-3.2; boron 0.06-0.09; zirconium <0.015; hafnium 0.2-0.3; silicon <0.1; iron <0.1; copper <0.05 sulfur <0.005; nitrogen <20 ppm; oxygen <15 ppm, cerium <0.015; niobium 0.1-0.2; yttrium <0.03; manganese <0.1; phosphorus <0.005 and nickel else.

The technical result is also achieved by the fact that the method of heat treatment of the alloy according to claim 1 includes homogenizing annealing with heating, aging and cooling, as well as aging at a temperature of 850 ± 10 ° C, and homogenizing annealing is carried out with heating at a speed of 5-10 ° C / min to a temperature of 1060 ± 10 ° C, holding for 3-4 hours in an inert environment, and cooling - at a speed of 30-50 ° C / min to a temperature of 600-700 ° C and then at an arbitrary speed to room temperature, and aging lead for 16 hours, followed by cooling in air to room temperature temperature first.

It is impossible to heat a known alloy to temperatures close to 1150 ° C and above, since fusion of a boride eutectic is possible, which will lead to a decrease in the service characteristics of the blade.

The achievement of the technical result can be illustrated by an example of the method and the data in tables 1-2, which show the compositions of the known alloys and alloy according to the invention, as well as their performance characteristics, evaluated by known methods, including those used in the description of patent RU 2443792.

It was taken into account that the known alloy according to the patent RU 2443792 was subjected to heat treatment, including heating to a temperature of 1120 ± 4 ° C, holding for 2 hours ± 15 minutes, cooling by quenching in an argon gas stream to a temperature of 590 ° C, reheating to a temperature 1080 ± 4 ° C and holding for 4 hours ± 15 minutes, re-cooling by quenching in an argon stream to a temperature of 590 ° C, heating the alloy to a temperature of 843 ± 4 ° C and holding for 24 hours ± 30 minutes, as well as subsequent cooling to room temperature.

It was also taken into account that the alloy according to the invention was subjected to homogenizing annealing, including heating at a speed of 5-10 ° C / min to a temperature of 1060 ± 10 ° C, holding for 3-4 hours in an inert medium, followed by cooling at a speed of 30-40 ° C / min to a temperature of 650 ± 25 ° C and further at an arbitrary rate to room temperature, and re-heating for aging at a temperature of 850 ± 10 ° C was carried out with exposure for 16 hours, followed by cooling in air to room temperature.

The increased boron content (0.06-0.09 wt.%), The additional presence of cerium, niobium, yttrium, manganese with a limited phosphorus content will allow the formation of an alloy structure that provides a more complete impregnation of the dendritic regions with a liquid melt, increase heat resistance, ductility and corrosion resistance metal blades with equiaxial structure.

The implementation of homogenizing annealing with the given heating and cooling rates, holding in an inert medium at a temperature below the lower threshold of boride eutectic dissolution T _SOL = 1150 ° C, as well as the proposed regime of aging and subsequent cooling, will allow us to obtain the optimal volume and size of the strengthening γ′-phase as inside grains and at grain boundaries. The composition of the alloy and its heat treatment mode provide a high level of structural stability per resource (indicators M _{dy crit} ≤0.928 N _v ≤2.36 less than critical values).

The data in table 2 show that the alloy according to the invention has the optimal combination of service characteristics, has increased stability on the resource (there is no loss of the σ-phase), higher rates (4 times) in corrosion resistance and lower (1.5-1, 7 times) gas-shrink porosity.

Table 1 The chemical composition of the alloys for casting blades Content Famous alloys Alloy according to the invention components B1981 According to patent According to patent wt.% SU 1072497 RU 2443792 carbon 0.015 0.07-0.15 0.04-0.12 0.05-0.09 chromium 16,0 12.5-14.0 11.5-12.5 15.4-15.8 cobalt 8.75 4.0-6.0 11.5-12.5 10.0-10.4 tungsten 2.7 4.0-6.0 3.3-3.7 5.0-5.3 molybdenum 1.75 1.5-2.5 1.7-2.1 1.6-1.8 titanium 3,7 4,5-5,5 4.85-5.15 4.3-4.5 aluminum 3.6 2.8-3.2 3.35-3.65 3.0-3.2 boron od 0.01-0.05 0.01-0.02 0.06-0.09 tantalum 1.8 - 2.3-2.7 - zirconium 0.01 0.005-0.01 0.0-20 ppm ≤0.015 hafnium - - 0,0-005 0.2-0.3 silicon - 0.4 ≤0.05 ≤0.1 iron - - 0,0-0,15 ≤0.1 copper - - 0,0-0,1 ≤0.05 sulfur - ≤0.15 0,0-0,0012 ≤0.005 nitrogen - - 0.0-25 ppm ≤20 ppm oxygen - - 0.0-10 ppm ≤15 ppm cerium - 0.02-0.05 - ≤0.015 niobium 1,0 0.05-1.0 - 0.1-0.2 yttrium - - - ≤0.03 manganese - 0.4 ≤0.08 ≤0.1 phosphorus - ≤0.015 ≤0.005 ≤0.005 calcium - 0.005-0.01 - - nickel rest rest rest rest

table 2 Heat resistant alloys with equiaxed blade structure Alloy characteristics Famous alloys Alloy according to the invention B1981 According to patent SU 1072497 According to patent RU 2443792 1. The strengthening γ′-phase 1.1. The volume of the γ′-phase, at.% 47.9 49.2 55.7 45.1 1.2. The total content of titanium and aluminum, wt.% 7.3 8.0 8.5 7.5 1.3. Solvus Тγ ′, ° C averaged 1167 1231 1198 1194 1.4. Degree of legality of the γ′-phase 1,088 1,059 1,081 1,078 1.5. Ti / Al 1,03 1,66 1.43 1.42 1.6. Mismach at 850 ° C +0.001 -0.003 -0.006 -0.005 1.7. The amount of non-equilibrium eutectic γ′-phase, inter-molten,% 5-6 1-2 5-6 1-2 2. The energy of stacking faults in the γ phase 1,911 2,212 1,156 1,422 3. The density of t / m ³ 8.13 8.22 8.22 8.18 4. Structural stability of FACOMP, 4.1. M _{dy crit} ≤0.928 averaged with TO 0.927 0.920 0.932 0.925 σ≈2% 4.2. Cast without MOT: interax 0.915 0.899 0.914 0.913 5. Long-term strength, MPa

°Cone) $${\sigma }_{{10}^3}^{760}$$

° C 472 493 498 473 2) $${\sigma }_{{10}^3}^{850}$$

° C 244 277 283 261 3) $${\sigma }_{{10}^3}^{900}$$

° C 162 184 182 176 four) $${\sigma }_{{10}^2}^{982}$$

° C 124 150 148 138 6. Comparative corrosion resistance -1.375 -1,156 -0.369 -1,482 lg Metall loss (JN792 = -0.26) lg corros Rate (JN792 = 0.1) 0.224 0.195 0.010 0.116 7. The price of the charge (conditional), $ / t 15690 10780 17800 11600

Claims (2)

1. A heat-resistant nickel-based alloy for the manufacture of gas turbine blades containing carbon, chromium, cobalt, tungsten, molybdenum, titanium, aluminum, boron, zirconium, hafnium, silicon, iron, copper, sulfur, nitrogen, oxygen and nickel, characterized in that it additionally contains cerium, niobium, yttrium, manganese and phosphorus in the following ratio of components, wt.%: carbon 0.05-0.09; chrome 15.4-15.8; cobalt 10.0-10.4; tungsten 5.0-5.3; molybdenum 1.6-1.8; titanium 4.3-4.5; aluminum 3.0-3.2; boron 0.06-0.09; zirconium <0.015; hafnium 0.2-0.3; silicon <0.1; iron <0.1; copper <0.05; sulfur <0.005; nitrogen <20 ppm; oxygen <15 ppm, cerium <0.015; niobium 0.1-0.2; yttrium <0.03; manganese <0.1; phosphorus <0.005 and nickel - the rest. 2. A method of manufacturing the blades of gas turbine plants from a heat-resistant nickel-based alloy according to claim 1, characterized in that the heat treatment is carried out by homogenizing annealing with heating, aging and cooling and aging, while homogenizing annealing is carried out in an inert atmosphere with heating at a speed of 5 -10 ° C / min to a temperature of 1060 ± 10 ° C, holding for 3-4 hours and cooling at a speed of 30-50 ° C / min to a temperature of 600-700 ° C and then to room temperature, and aging is carried out at a temperature 850 ± 10 ° C for 16 hours afterwards cooling in air to room temperature.