RU2678352C1 - Heat-resistant alloy based on nickel for casting of working blades for gas turbines - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy, in particular to foundry heat-resistant corrosion-resistant alloys based on nickel, and can be used for the manufacture of casting parts of the hot path of gas turbines, for example gas turbine blades with equiaxial or single-crystal structure operating in corrosive environments at operating temperatures of 750–900 °C. Heat-resistant alloy based on Nickel for casting rotor blades of gas turbines contains, by wt. %: carbon 0.05–0.10; chromium 11.8–12.6; cobalt 8.4–9.2; tungsten 4.2–4.8; molybdenum 1.0–1.5; aluminum 3.0–3.4; titanium 3.7–4.15; tantalum 4.0–4.5; zirconium 0.01–0.025; boron 0.005–0.02; hafnium 0.06–0.15; iron 0.08–0.3; copper ≤0.05; sulfur ≤0.005; nitrogen ≤30 ppm; oxygen ≤20 ppm; niobium 0.05–0.15; cerium 0.002–0.012; silicon 0.002–0.012; manganese 0.002–0.012; phosphorus ≤0.005; nickel else. Total content of niobium and hafnium is ≤0.20 wt. %, cerium, silicon and manganese are contained in equal amounts, and the total content of aluminum and titanium is 7.0–7.5 wt. % at the ratio of the titanium content to the aluminum content ≥1.2.EFFECT: alloy is characterized by high values of long-term strength, resistance to oxidation and corrosion effects, as well as increased structural stability of the resource.1 cl, 2 tbl

Description

The invention relates to metallurgy, in particular, to casting heat-resistant corrosion-resistant alloys based on nickel with chromium, tungsten, tantalum and cobalt, and can be used for casting parts of the hot path of gas turbine plants, for example, working blades of a gas turbine with an equiaxed or single-crystal structure, working in aggressive environments at operating temperatures of 750-900 ° C.

High strength characteristics of such alloys are achieved due to a significant amount (50-60 vol.%) Of the hardening γ'-phase (Ni ₃ Al) doped with niobium, titanium, tantalum, etc., as well as hardening of the solid solution (γ-phase ) cobalt, chromium, molybdenum and tungsten. Increased corrosion resistance is provided by a high chromium content (10-15% wt.%) With a ratio of titanium to aluminum Ti / Al≥1.0; as well as the introduction of rare earths. Oxidation resistance at elevated temperatures is provided by an increased content of aluminum, tantalum and, above all, a decrease in the content of molybdenum, as well as the introduction of rare earth elements.

Known heat-resistant alloy based on Nickel (IN792-5A) for casting blades of gas turbine units with equiaxial structure, containing carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, tantalum, zirconium, boron, niobium, silicon, sulfur, phosphorus and nickel in the following ratio of components, wt. %: carbon 0.08; chrome 12.5; cobalt 8.91; tungsten 4.01; molybdenum 1.9; aluminum 3.42; titanium 4.01; tantalum 4.0; zirconium 0.020; boron 0.018; niobium 0.03; silicon ≤0.02; iron 0.22; sulfur ≤0.001; phosphorus ≤0.005 and nickel - the rest.

(Jiri Zyka, Karel Hrbacek, Vaclav Sklenicka, Analysis of creep tests of the IN792 alloy, Hradec nad Moravici, May 19-21, 2009, Metal 2009)

The known alloy has satisfactory heat resistance and corrosion resistance, as well as a significant volume (~ 5 vol.%) Of the nonequilibrium eutectic phase, which, when casting the working blades of a gas turbine, leads to increased porosity of the casting and a decrease in the service characteristics of the product. During eutectic precipitations and on a needle-shaped σ-phase during the operation of the products, cracks arise that propagate along the grain boundaries, reducing the level of short-term and long-term strength by 15-20%.

The closest is a heat-resistant nickel-based alloy for the manufacture of gas turbine blades with equiaxed and directional structure. The known alloy includes carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, tantalum, zirconium, boron, hafnium, iron, copper, sulfur, nitrogen, oxygen and nickel in the following ratio of components, mass. %: 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; tantalum 2.3-2.7; zirconium ≤0.020; boron 0.010-0.020; hafnium ≤0.05; iron ≤0.15; copper ≤0.10; sulfur ≤0.0012; nitrogen ≤0.020; oxygen ≤0.010; nickel rest.

(RU2443792, C22C 19/05, published 02.27.2012)

However, this known alloy with high corrosion resistance tends to soften at operating temperatures above 800 ° C. Moreover, products from a known alloy have up to 7 vol. % eutectic discharge. In addition, up to 5 vol. % embrittling σ-phase, which reduces the service characteristics of the product.

The aim of the invention and its technical result is to increase the long-term strength of the heat-resistant alloy for cast gas turbine blades with equiaxial or single-crystal structure in combination with high oxidation resistance and corrosion, as well as increased structural stability on the resource.

The technical result is achieved in that the heat-resistant nickel-based alloy for casting rotor blades of gas turbine plants includes carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, tantalum, zirconium, boron, hafnium, iron, copper, sulfur, nitrogen, oxygen , niobium, cerium, silicon, manganese and phosphorus and nickel, in the following ratio of components, wt. %: carbon 0.05-0.10; chrome 11.8-12.6; cobalt 8.4-9.2; tungsten 4.2-4.8; molybdenum 1.0-1.5; aluminum 3.0-3.4; titanium 3.7-4.15; tantalum 4.0-4.5; zirconium 0.01-0.025; boron 0.005-0.02; hafnium 0.06-0.15; iron 0.08-0.3; copper ≤0.05; sulfur ≤0.005; nitrogen ≤30 ppm; oxygen, 20 ppm; niobium 0.05-0.15; cerium 0.002-0.012; silicon 0.002-0.012; manganese 0.002-0.012; phosphorus ≤0.005; the rest is nickel, while the total content of niobium and hafnium is ≤0.20 wt. %, cerium, silicon and manganese are contained in equal amounts, and the total content of aluminum and titanium is 7.0-7.5 wt. % with the ratio of titanium to aluminum content ≥1.2.

The optimal tungsten content of 4.2-4.8 wt. % and tantalum 4.0-4.5 wt. % gives increased heat resistance of the cast alloy, however, a further increase in their total content causes a significant increase in the dissolution temperature of the γ'-phase, which can be compensated by an increase in the cobalt content, but this increases the cost of the alloy.

Hafnium in an amount of 0.06-0.15 wt. % in combination with niobium at a concentration of 0.05-0.15 wt. % and zirconium 0.01-0.025 wt. % with a carbon content of 0.05-0.10 wt. % provide stabilization of carbides and sufficient ductility of the cast alloy for a long life, both in single-crystal and in equiaxial conditions.

The achieved level of heat resistance was also ensured by reaching the volume of the strengthening γ'-phase of 52.8-54.4 at. % the introduction of 3.0-3.4 wt. % aluminum and 3.7-4.5 wt. % titanium with a total content of 7.0-7.5 wt. % with the ratio of titanium to aluminum content ≥1.2.

Selected limited concentration of chromium 11.8-12.6 wt. %, cobalt 8.4-9.2 wt. %, molybdenum 1.0-1.5 wt. %, forming embrittling σ-phase, allowed to eliminate its precipitation during operation, despite the fact that:

- a high ratio of titanium to aluminum content ≥1.2 in combination with chromium and a limitation of the content of molybdenum, the presence of rare earth metals, manganese (0.002-0.12 wt.%) and silicon (0.002-0.12 wt.%) contribute to increased corrosion resistance of the proposed alloy;

- the optimal content of aluminum and tantalum with a reduced content of molybdenum of 1.0-1.5 wt. % together with rare earth elements allowed to provide increased oxidation resistance;

- moderate cobalt content of 8.4-9.2 wt. % and the indicated contents of tungsten and tantalum ensured a low temperature for the complete dissolution of the γ'-phase (1180–1190 ° C), which makes the alloy quite technologically advanced during heat treatment.

The selected optimal concentrations of titanium, aluminum and niobium (0.05-0.15 wt.%) Allowed us to significantly limit the volume of eutectic phases to 1.5 vol. %

The niobium content of 0.05-0.15 wt. %, hafnium 0.06-0.15 wt. % and zirconium 0.01-0.025 wt. % made it possible to achieve structural stability of carbides at grain boundaries, increased long-term ductility of the new alloy per resource and high resistance to grain-boundary corrosion, which is also facilitated by cerium, silicon and manganese introduced in equal concentrations (0.002-0.012 wt.%) and limited sulfur content (not more than 0.005 wt.%), Phosphorus (not more than 0.005 wt.%) And copper (not more than 0.05 wt.%).

The content of boron is 0.005-0.02 wt. %, iron 0.08-0.3 wt. % and the stated ratios of components in the alloy exclude the occurrence of embrittling phases during the operating time and limit the release of the nonequilibrium eutectic phase to 1.5%, which provides a 25% reduction in gas shrink porosity compared to the prototype and increases the resistance of the product to cracking. It also contributes to the limitation of the content of nitrogen in the metal ≤30 ppm and oxygen ≤20 ppm.

The achievement of the required technical result can be illustrated by the data from Tables 1 and 2.

Structural stability per resource (eliminating the formation of embrittleing phases) and limiting the formation during crystallization of nonequilibrium eutectic phases, in the place of which pores and cracks will nucleate after their decomposition during heat treatment, were evaluated using the well-known FACOMP method. In addition, the characteristics of long-term strength, critical points of the alloy and its other physical and mechanical properties were evaluated by known methods.

(H. Harada et al., Sat. Superalloys, 1998, pp. 733-742, Sat. Superalloys, 2000, pp. 729-736)

From the presented data it follows that the alloy according to the invention, due to the selected concentrations of carbon and boron, provides blades with an equiaxial structure, a whole with a single crystal structure or with a single crystal structure of a profile part and a shank, and with an equiaxed structure of lightly loaded retaining shelves. At the same time, the service characteristics of the metal shelves with equiaxial structure will be no worse than, for example, the well-known prototype alloy.

At the same time, the advantage of working blades with the equiaxed structure of the retaining shelves will allow to increase the yield and reduce the cost of cast billets of working blades.

In addition, the alloy according to the invention with equiaxial structure in terms of corrosion resistance is equal to the prototype, but surpasses it in long-term strength by 15-20%.

The use of alloy in products with a single-crystal structure gives an increase in heat resistance by 15-20% compared with the equiaxed structure of the products and increases the resource by 30-50%.

* - values for metal with equiaxial structure

** - values for a metal with a single crystal structure

Claims (1)

A heat-resistant nickel-based alloy for casting rotor blades of gas turbine plants containing carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, tantalum, zirconium, boron, hafnium, iron, copper, sulfur, nitrogen, oxygen and nickel, characterized in that it additionally contains niobium, cerium, silicon, manganese and phosphorus, in the following ratio of components, wt. %: carbon 0.05-0.10; chrome 11.8-12.6; cobalt 8.4-9.2; tungsten 4.2-4.8; molybdenum 1.0-1.5; aluminum 3.0-3.4; titanium 3.7-4.15; tantalum 4.0-4.5; zirconium 0.01-0.025; boron 0.005-0.02; hafnium 0.06-0.15; iron 0.08-0.3; copper ≤0.05; sulfur ≤0.005; nitrogen ≤30 ppm; oxygen ≤20 ppm; niobium 0.05-0.15; cerium 0.002-0.012; silicon 0.002-0.012; manganese 0.002-0.012; phosphorus ≤0.005; the rest is nickel, while the total content of niobium and hafnium is ≤0.20 wt. %, cerium, silicon and manganese are contained in equal amounts, and the total content of aluminum and titanium is 7.0-7.5 wt. % with the ratio of titanium to aluminum content ≥1.2.