JP2721723B2 - Heat-resistant cast alloy for gas turbine blades - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-resistant cast alloy for gas turbine blades, and more particularly to a Co-based heat-resistant cast applied to high-temperature components (turbine stationary blades) of gas turbines and jet engines. Alloys.

[Conventional technology]

Gas turbine and jet engine turbine vanes
Precision castings made of Co-based heat-resistant alloy are used. In order to improve the performance of gas turbines and jet engines, it is necessary to increase the inlet gas temperature. For this reason, there have been keen developments on the stationary blade in terms of both the cooling structure and the improvement of the high-temperature strength of the alloy used.

Conventionally, alloys shown in Table 1 have been used as casting alloys for stationary blades.

X-40 and X-45 are alloys that have been used for a long time, FSX-414 is an alloy having a high Cr content to improve corrosion resistance and oxidation resistance, and MarM509 adds a large amount of C and has a high Ta content. This is an alloy with improved high-temperature strength by adding Ti.

As described above, as the inlet gas temperature increases, even existing alloys that have improved these properties have high temperature strength or corrosion resistance.
Since the requirements cannot be satisfied in terms of oxidation resistance, an alloy having excellent characteristics in both high-temperature strength and corrosion / oxidation resistance is required.

[Problems to be solved by the invention]

As described above, gas turbines and jet engine turbine stationary blades use precision castings made of a Co-based heat-resistant cast alloy. However, as the gas temperature at the gas turbine inlet rises with existing alloys, even high Cr, Co-based heat-resistant cast alloys with improved properties have insufficient high-temperature strength, and high C, Ta, Ti
Since the added Co-based heat-resistant cast alloy has a low Cr content, the corrosion resistance and oxidation resistance are insufficient and the life is short.

The present invention has been made in view of the above technical level, and aims to provide a Co-based heat-resistant cast alloy having high high-temperature strength and excellent corrosion resistance and oxidation resistance.

[Means for solving the problem]

The present invention employs the following means in order to obtain a Co-based heat-resistant cast alloy having high high-temperature strength and excellent corrosion and oxidation resistance.

(1) High C was set within a range that does not impair the weldability, and the precipitation amount of carbide was increased to improve the strength. In addition to Cr as a carbide forming element, Ta, Ti, and W were added to aim at precipitation hardening of these elements by carbide.

(2) In addition to precipitation hardening of carbides, solid solution strengthening by W was aimed at and high temperature strength was improved.

(3) The corrosion resistance and oxidation resistance were improved by adding Cr, but a large amount was added within an allowable range from the viewpoint of structural stability. Further, La was added to further improve oxidation resistance.

(4) Ni was added for austenite (FCC) stabilization of the substrate.

(5) The oxidation resistance was further improved by adding a small amount of Al.

That is, in the present invention, by weight%, Cr: 25-32%, Ni: 6-1
2%, W: 6 to 8%, Ta: 2 to 5%: Ti: 0.1 to 0.3%, C: 0.45 to
This is a heat-resistant cast alloy for gas turbine blades comprising one or two of 0.6%, La: 0.02 to 0.2%, and Al: 0.01 to 0.2%, the balance being Co and inevitable impurities.

[Action]

The composition of the Co-based heat-resistant cast alloy which is the object of the present invention is in the chemical composition range shown in Table 2, and the reasons for limiting the composition range are described below.

Cr: an essential element from the viewpoint of corrosion resistance and oxidation resistance. It is also a carbide-forming element and is necessary for forming carbides and obtaining high-temperature strength. In particular, when used for land gas turbine stationary blades, corrosion resistance at high temperatures is required more than that of aircraft engine stationary blades from the viewpoint of fuel diversity. Since an accessory such as an insert for cooling is welded to the stationary blade, weldability is also a characteristic required for the stationary blade alloy. From these points, Cr needs to be 25% or more. On the other hand, if the amount is too large, the structure stability due to long-time use at high temperature is lacking, and the weldability is reduced.

Ni; austenitic (FCC) stabilizing element of the substrate,
Also, it is an element that improves workability. From this point, 6% or more is required. If the content is too large, the heat-resistant fatigue characteristics and the sulfidation resistance, which are the characteristics of the Co-based heat-resistant alloy, are reduced.

W is a solid solution strengthening element, and is an indispensable element for securing the high-temperature strength of the Co-based heat-resistant alloy. Some also form carbides and contribute to strength improvement. If too much is added, tissue stability due to long-term use at high temperature is lacking, and ductility is impaired.

Ta is a solid solution strengthening element and a carbide forming element. In a high C-added Co-based heat-resistant alloy, Cr that effectively acts on corrosion and oxidation resistance or W that effectively acts on solid solution becomes less if only carbide is formed by Cr and W.
W was added so that the original effect could be exhibited. If too much is added, the ductility is impaired.

Ti; a carbide-forming element that forms fine carbides and is effective for improving high-temperature strength. The aim is to further improve high-temperature strength by adding Ta and composite. If too much is added, the ductility is impaired, and the high temperature strength is not significantly changed.

La; La oxide is dense and forms a scale with high oxidation resistance. Therefore, oxidation resistance is remarkably improved by adding a small amount, but 0.02% or more is required for this purpose. However, since La is an expensive element, the content is set to 0.2% or less.

C; a carbide-forming element that forms carbide and contributes to strength. To ensure excellent high-temperature strength, 0.45% or more is required. However, if the content is too large, the ductility is significantly reduced and the weldability is deteriorated.

Al: A small amount of Al (approximately 0.5% or less) may be added because it forms a dense oxide film and contributes to the improvement of oxidation resistance.
Since Al is added, it is not necessary to add Al. La
If not added, 0.01 to 02% is required. Note that La and
A further effect is exhibited by adding both of Al.

Zr, B: Since the grain boundary dentrite boundary is strengthened and contributes to the improvement of high-temperature strength, a small amount of Zr (0.5% or less) and a small amount of B (0.0%
2% or less).

The balance is Co, but it is desirable that the impurity elements unavoidable in the industry, such as Fe, Si, Mn, P, and Ag, be as low as possible.

〔Example〕

Test material having the chemical components shown in Table 1 (φ25 × 200lm
m) was melted in a high-frequency melting furnace. The test materials are alloys of the present invention, and the test material (FSX414 equivalent material) and the test material (Mar M509 equivalent material) are comparative materials. Except for the test material, it was subjected to the test as it was after melting. On the other hand, the test material was melted, held at 1150 ° C. × 4 hours, then cooled in a furnace to 927 ° C., kept at this temperature for 10 hours, subjected to a heat treatment of air cooling, and subjected to a test.

Then, Mom material or tensile from the heat-treated test piece of melting (parallel portion diameter d = diameter: 6 mm), the creep rupture test specimen (parallel part diameter d = diameter: 6 mm), corrosion test pieces ^{(15 × 30 × 2 t mm} ) and An oxidized test piece (15 × 30 × 2 ^t mm) was processed.

 The following tests were performed using the test pieces described above.

The tensile test was performed at 850 ° C. Table 4 shows the results.

As shown in Table 4, the tensile properties of the specimens were 0.2% proof stress and tensile strength slightly higher than those of the comparative specimens, and tended to be slightly lower than those of the specimens. is there. On the other hand, there is no great difference between the test materials in elongation and drawing.

The creep rupture test was performed at a temperature of 980 ° C. and a stress of 11.3 kg / mm ² . The results are also shown in Table 4. As shown in Table 4, the rupture time of the test material (the alloy of the present invention) was 54 to 75 hours, whereas that of the comparative material was 1.7 hours, which was significantly weaker. 80
It was time and strong. On the other hand, there was no significant difference between the test material and the elongation and drawing, and the test material was a high value and highly ductile alloy.

Such a difference in creep rupture properties is considered to be due to a chemical component. That is, it is considered that the test material did not contain Ta and Ti, and the addition amount of C was small, so that the contribution of precipitation hardening and solid solution strengthening of the carbide was small and the strength was weakened. On the other hand, ductility is high. In addition, it is presumed that the test materials were lower in strength because C, Ta, and Ti were slightly lower than the test materials.

Next, a corrosion test was performed using a corrosive ash of V ₂ O ₅ : Na ₂ SO ₄ = 85%: 15% at a rate of 20 mg / cm ² and heated at 850 ° C. × 20 hours in an atmospheric electric furnace. Corroded. After the test, descaling was performed and the amount of corrosion was measured. As a result, the corrosion weight loss was smaller in the order of test material / test material / test material / test material. As a result, the amount of corrosion of the test material having a small Cr content was significantly higher than that of the other test materials. Although there is no significant difference between the test materials and, the above-mentioned tendency was observed.

Finally, an oxidation test was performed. 1000 ℃ in atmospheric electric furnace
It was oxidized by heating for 100 hours. After the test, the weight was measured to determine the change in weight. The weight of all test materials increased. The amount of weight increase was smaller in the order of test material> test material≫test material test material. The test material and the test material have a small weight increase and are excellent in oxidation resistance. This is considered to be the effect of La or Al.

As described above, the alloy of the present invention has the advantages of existing alloys,
This is a Co-based heat-resistant cast alloy that has excellent high-temperature strength that compensates for the disadvantages and has both corrosion resistance and oxidation resistance.

〔The invention's effect〕

As described above, the Co-base heat-resistant cast alloy having the chemical composition range shown in Table 2 has a high high-temperature strength as shown in Table 4 and has excellent corrosion resistance and oxidation resistance.

That is, the improvement of the high-temperature strength is achieved by increasing the carbon content, adding Ta, Ti, and W, increasing the precipitation amount of carbides, and achieving precipitation hardening in addition to strengthening the solid solution of W. On the other hand, corrosion resistance and acid resistance are improved. The improvement of the chemical properties is due to the fact that the addition of high Cr, La and Al has been attempted.

Claims (1)

(57) [Claims] 1. Cr: 25-32%, Ni: 6-12%, W: 6-% by weight%
8%, Ta: 2 to 5%: Ti: 0.1 to 0.3%, C: 0.45 to 0.6%, La: 0.02 to 0.2%, Al: 0.01 to 0.2%, one or two kinds, balance Co and inevitable impurities Heat-resistant cast alloy for gas turbine blades.