RU2691790C1 - Cast nickel alloy - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy, namely to nickel-based alloys, and can be used in gas transfer, power and offshore gas turbine plants (GTP) with long operating time, in particular for casting of cooled working and nozzle blades with equiaxial structure. Cast nickel alloy for casting of cooled working and nozzle blades with equiaxial structure of gas-turbine plants contains, wt. %: C 0.08–0.18; Cr 10.0–16.0; Co 10.0–16.0; W 2.0–10.0; Ti 2.0–5.5; Al 2.0–5.5; Re 1.2–3.6; Ta 4.0–9.0; Hf 0.05–2.0; B 0.005–0.5; Zr 0.005–0.05; Ce 0.005–0.5; La 0.005–0.5; Y 0.01–0.5; Mg 0.005–0.3; Mn 0.05–0.5; Si 0.05–0.5; Ca 0.02–0.2; Ni – rest.EFFECT: alloy is characterized by high values of resistance to sea salt corrosion, heat resistance, as well as high manufacturability and output of suitable products, significantly lower labour input in production and cost.1 cl, 1 dwg, 2 tbl

Description

The invention relates to the field of metallurgy and can be used in gas pumping, power and marine gas turbine installations (GTU) with a long operating time, in particular for casting cooled workers and nozzle blades with equiaxial structure, the production of which is significantly less labor-intensive, and therefore costs 6-8 times cheaper compared to alloys having a single crystal structure.

The essence of the problem lies in the fact that currently used for GTU heat-resistant nickel alloys with equiaxial structure, capable of working under conditions of active influence of sulfide-oxide corrosion (for example, alloy CHS-70, CS-88, CS-104, etc.) have insufficient level of heat resistance, which dramatically reduces the resource of their work and increases the number of expensive repairs, especially in adverse conditions of the North, Siberia and other low-habitat areas, increases downtime for the repair of marine equipment, etc.

In this regard, the task of creating a heat-resistant alloy with:

- high resistance to sulfide oxide corrosion, able to work effectively under the active influence of such combustion products of liquid and gaseous fuels like Na ₂ SO ₄ (the results of the interaction of the NaCl salts and hydrogen sulfide present in the fuel), calcium, magnesium, silicon salts, sulfidization from compounds containing the nitriding medium and carburizing the surface, the negative influence of vanadium, lead compounds and other harmful elements in the fuel;

, равной (320-340) МПа,- high heat resistance level

equal to (320-340) MPa,

close to heat resistance of the best alloys with high resistance to sulfide-oxide (marine) corrosion;

- equiaxial structure, which reduces the labor intensity of production and, as a result, the cost price is 6–8 times the number of working and nozzle vanes compared to single crystal;

- differing by more economical (at the most expensive and scarce rhenium element) by doping.

Thus, the task is reduced to the creation of an alloy with high resistance to "marine" corrosion, while simultaneously providing increased efficiency and much cheaper production of the nodal parts of GTU with a noticeable decrease in the cost of the material of the turbine blades.

As the closest analogue (prototype) selected cast nickel alloy containing, by weight. %: Cr 9-18, Co 7-20, W 1-8, Mo 0.2-4.0, Al 1.5-5.0, Ti 1.5-5.0, Ta 2.4-7 , 5, Nb 0.05-2.0, B 0.005-0.5, La 0.005-0.5, Y 0.01-0.5, Ce 0.02-0.5, Re 0.5-6 , 0, Hf 0.05-1.5, Mn 0.05-1.0, Si 0.05-1.0, Mg 0.01-0.5, C 0.003-0.03, Sc 0.0002 -0.01, Pr 0.0002-0.01, Gd 0.0002-0.01, Nd 0.0002-0.01, Ni the rest (see Patent RU 2623940).

≈ 350 МПа),The alloy possesses the highest among all domestic and foreign nickel heat-resistant materials with increased resistance to sulfide-oxide corrosion

≈ 350 MPa),

at the same time, unlike a number of alloys currently in use, it is not prone to the formation of embrittling topologically close-packed (TPU) phases during operation.

High structural stability provides him with the ability to maintain performance over a very long resource.

Quite so typical for this alloy is a number of disadvantages:

- first, this alloy has a single crystal structure, and, as is known, the laboriousness of production, a large number of defects, and hence the cost of blades with a single crystal structure, is significantly higher than blades with equiaxial structure;

- secondly, it contains up to 9% rhenium, which makes it very expensive.

Therefore, it is not by chance that leading foreign and domestic firms and enterprises are currently actively working to create nickel-based superalloys that are economically doped for rhenium. The production of gas turbines for power generation is much more widespread compared to the manufacture of gas turbine engines for aviation.

Here, the issues of the maximum possible reduction in the cost of installations, while ensuring their high performance and reliability, becomes especially acute.

These circumstances make the task of creating a high-temperature-resistant nickel alloy with an equiaxial structure, which is highly resistant to sulfide-oxide corrosion and heat resistance, but at the same time economically doped with rhenium, is highly relevant.

The technical result, the achievement of which the invention is directed, is the development of a new nickel-based alloy with an equiaxial structure, which simultaneously has high resistance to marine salt corrosion, heat resistance, processability and usable products, significantly lower labor input and cost.

This technical result is achieved by the fact that the foundry Nickel alloy containing C, Cr, Co, W, Ti, Al, Re, Ta, Hf, B, Ce, La, Y, Mg, Mn, Si, according to the present invention, for casting cooled working and nozzle blades with equiaxial structure of gas turbine installations, it additionally contains Zr with Ca in the following ratio of components, wt. %: C 0.08-0.18, Cr 10.0-16.0, Co 10.0-16.0, W 2.0-10.0, Ti 2.0-5.5, Al 2, 0-5.5, Re 1.2-3.6, Ta 4.0-9.0, Hf 0.05-2.0, B 0.005-0.5, Zr 0.005-0.05, Ce 0.005- 0.5, La 0.005-0.5, Y 0.01-0.5, Mg 0.005-0.3, Mn 0.05-0.5, Si 0.05-0.5, Ca 0.02- 0,2, Ni else.

The solution of this task is carried out in the following areas:

- since it was necessary to develop an alloy having an equiaxial structure, which, as is well known, is characterized by the presence of grain boundaries located in the transverse direction to the existing force and being the weakest point at high temperature loading, a significant amount was introduced into the alloy compared to the prototype carbon (0.08 -0.18) wt. % Carbon forms carbides, which, being located along the grain boundaries, strengthen them.

Since carbon combining with Ti and Hf creates carbides of the type (Ti, Hf) C that strengthen the grain boundaries and a part of Ti and Hf goes to the formation of carbides, the maximum Ti content in the alloy is increased to 5.5 wt. % because it is necessary that the amount of Ti forming the hardening γ'-phase does not change: Ti, which is part of the hardening γ'-phase, has a positive effect on heat resistance. Hafnium, being a part of carbides, changes their morphology from “Chinese characters” (which is not very favorable) to small rounded inclusions, which more effectively control the grain boundaries and do not reduce the plasticity of the material. Therefore, the maximum content in the new alloy Hf is also increased to 2.0 wt. %

- one of the main tasks in the development of the alloy was to reduce its cost by reducing the concentration of extremely scarce and extremely expensive rhenium. Its maximum amount in the claimed alloy is reduced to 3.6 wt. % (almost 2 times). However (since Re effectively increases the heat resistance of nickel alloys) it was necessary to reduce the negative effect on high-temperature long-term strength caused by a decrease in Re concentration in the alloy. This is achieved by the exception of Mo, which strengthens the alloy almost 2 times less efficiently than W, and by simultaneously increasing the maximum content in the alloy W from 8.0 wt. % to 10.0 wt. % In addition, Mo, being present in the alloy, contributes to its internal oxidation, which is undesirable primarily for alloys intended for operation in an oxidizing environment.

In order to realize additional possibilities of increasing the heat resistance, the following has been accomplished. It is known that Nb is an element that rather well increases the heat resistance at medium temperatures, but at high temperatures (800-1000 ° C), at which GTU blades mainly work, its positive effect on long-term strength weakens and noticeably inferior in magnitude to its effect. on the heat resistance of W and Ta. Therefore, Nb is excluded from the composition of the alloy, and the average content of Ta and W is increased to (4.0-9.0) wt. % and (2,0-10,0) wt. % respectively.

In addition, to use another opportunity to improve the heat resistance by reducing the content in the claimed alloy of oxygen, the composition of the material additionally introduced Zr in an amount of (0.005-0.05) wt. % and Ca (0.02-0.2) wt. % These elements, on the one hand, having a high affinity for oxygen, form compounds with it, thus effectively reducing its concentration in the alloy, on the other hand, they markedly reduce the oxidation rate along the grain boundaries, which is extremely important for alloys with equiaxial structure. (It is known that the oxidation of alloys effectively develops precisely along the grain boundaries).

The content of increasing the resistance of the alloy to the oxidation of Si and Mn, as well as the micro-alloying elements B, Zr, Mg, Y and OZM (La, Ce) remained at the same level.

Thus, compared to the prototype, in the composition of the proposed alloy, Mo and Nb are excluded, the amount of Re is almost halved, the average carbon content is significantly (more than 9 times), the concentration of Ti, Ta, Hf and W is increased.

Since the concentration of γ'-forming elements Ti, Ta and Hf is simultaneously increased in this alloy, it is important that during its operation the γ'-phase does not decompose with the formation of lamellar embrittling compounds such as Ni ₃ Ti and Ni ₃ Ta. Therefore, we have introduced another additional condition:

where C _A1 C _Ti , C _Ta , C _Hf are the concentrations of the corresponding elements, at. %

Our numerous experimental studies of the corrosion-resistant alloy of the prototype have shown that with the ratio C _A1 / (C _Ti + C _Ta + C _Hf ) ≤1.1 at. % / at. %, the phases of Ni ₃ Ti, Ni ₃ Ta, Ni ₃ Hf and their mixtures begin to precipitate from the γ'-phase, which significantly reduces the heat resistance of the alloy as a whole and its resistance to brittle fracture.

The essence of the claimed invention is illustrated by the following tables: - Table 1 presents the results of short-term and long-term tests of samples of four heats in comparison with the results of the prototype, shown in the RF patent №2623940.

It should be noted that for testing samples of 4 compositions, an alloy was produced with an average (optimal) content of all alloying components, which was then doped with various amounts of Cr, W and Re - the content of these elements primarily determines the possibility of embrittling TPU-phases , as well as the level of heat resistance and resistance to sulfide corrosion.

A comparative assessment of the corrosion resistance of the samples to sulfide-oxide effects was carried out in the combustion products of diesel fuel containing 1% S, with an excess air ratio of 30: 1 and an injection of 200 particles / min of sea salt at 950 ° C for 100 hours. The values of the depth of penetration of the oxidized layer of 4 samples of the prototype are shown in Table 2.

FIG. 1 shows the dependence of the long-term strength of the new alloy on the Larsen-Miller parameter (dashed curve) in comparison with a similar dependence for the alloy according to the patent of Russian Federation №2623940, which has a single crystal structure, where O and are experimental points and the averaging curve of the new alloy; x and - experimental data and a synthesis curve of the alloy according to the patent of Russian Federation №2623940.

From tables 1 and 2, as well as figure 1 clearly shows that the prototypes in terms of long-term strength and resistance to sulfide-oxide corrosion is not inferior to the alloy - the prototype.

Thus, we have created an alloy for casting cooled work and nozzle blades with an equiaxial structure of gas turbines, corresponding to the level of long-term strength and resistance to sulfide-oxide corrosion to the known alloy, selected as a prototype.

Claims (2)

1. Foundry nickel alloy for casting of cooled workers and nozzle blades with equiaxial structure of gas turbine installations, containing C, Cr, Co, W, Ti, Al, Re, Ta, Hf, B, Ce, La, Y, Mg, Mn, Si , characterized in that it additionally contains Zr and Ca in the following ratio of components, wt. %: C 0.08-0.18, Cr 10.0-16.0, Co 10.0-16.0, W 2.0-10.0, Ti 2.0-5.5, Al 2, 0-5.5, Re 1.2-3.6, Ta 4.0-9.0, Hf 0.05-2.0, B 0.005-0.5, Zr 0.005-0.05, Ce 0.005- 0.5, La 0.005-0.5, Y 0.01-0.5, Mg 0.005-0.3, Mn 0.05-0.5, Si 0.05-0.5, Ca 0.02- 0,2, Ni else. 2. The alloy according to claim 1, characterized in that C _A1 / (C _Ti + C _Ta + C _Hf )> 1.1 at.% / At.%, Where C _A1 , C _Ti , C _Ta , C _Hf - concentration of the corresponding elements, at.%.

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