JPH03215644A - Heat-resistant cast alloy for gas turbine blade - Google Patents

Abstract

PURPOSE:To improve the high temp. strength, corrosion resistance and oxidation resistance of a heat-resistant cast alloy by increasing the amt. of C in a Co base alloy and adding specified amounts of Ta, Ti and W thereto as well as Cr as a carbide forming element. CONSTITUTION:The compsn. of this Co base cast alloy used for a turbine stationary blade of a gas turbine jet engine is formed of, by weight, 25 to 32% Cr, 6 to 12% Ni, 6 to 8% W, 2 to 5% Ta, 0.1 to 0.3% Ti, 0.45 to 0.6% C, one or 2 kinds of 0.02 to 0.2% La and 0.01 to 0.2% Al and the balance Co with inevitable impurities. Besides the strengthening of solid soln. by W, the C content is increased and the amt. of carbides to be precipitated is increased by the addition of Ta, Ti and W to attain precipitation hardening, by which its high temp. strength can be improved. Furthermore, by the increase of Cr and by the addition of La and Al, its corrosion resistance and oxidation resistance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat-resistant cast alloy for gas turbine blades, and more particularly for high-temperature parts of gas turbines and jet engines.
This invention relates to a Co-based heat-resistant cast alloy that is applied to turbine stator blades.

[Prior art] Turbine stationary blades of gas turbines and jet engines contain C.
Precision castings made of O-based heat-resistant alloys are used. In order to improve the performance of gas turbines and jet engines, it is necessary to increase the inlet gas temperature, and for this reason, efforts have been made to develop stator vanes from both the cooling structure and the high-temperature strength improvement of the alloys used.

Conventionally, alloys shown in Table 1 have been used as cast alloys for stator blades.

x-40 and This is an alloy with improved high-temperature strength by adding Ti.

As mentioned above, as the inlet gas temperature increases, even existing alloys with these improvements cannot meet the requirements in terms of high-temperature strength or corrosion and oxidation resistance. Alloys with excellent properties on both sides are required.

[Problem to be solved by the invention]

As mentioned above, precision castings made of CO-based heat-resistant casting alloys are used for turbine stationary blades of gas turbines and jet engines. However, with existing alloys, as the gas temperature at the gas turbine inlet increases, high Cr, which has improved properties,
Co-based heat-resistant cast alloys also lack high-temperature strength, and high C
．． Ta and Ti-added Co-based heat-resistant cast alloys have a low Cr content, so they lack corrosion and oxidation resistance and have a short lifespan.

In view of the above-mentioned state of the art, the present invention aims to provide a Co-based heat-resistant cast alloy that has high high-temperature strength and excellent corrosion resistance and oxidation resistance.

[Means to solve the problem]

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

(1) The strength was improved by increasing the carbon content within a range that does not impair weldability and increasing the amount of carbide precipitation. In addition to Cr, Ta, Ti, and W were added as carbide-forming elements to aim at precipitation hardening by carbides of these elements.

(2) In addition to precipitation hardening of carbides, solid solution strengthening with W was aimed at improving high-temperature strength.

(3) Corrosion resistance and oxidation resistance were improved by adding Cr, but from the viewpoint of structural stability, the amount of Cr added was within the allowable range. Furthermore, La was added to further improve the oxidation resistance.

(4) Ni was added to stabilize the substrate FC.

(5) Furthermore, by adding a small amount of A1, the oxidation resistance was further improved.

That is, in the present invention, Cr: 25-32%, N
l: 6-12%, W: 6-8%, Ta: 2-5%: T
i: 0. 1-0.3%, C: 0.45-0.6%
and La: 0. 0 2 ~ 0. 2%, A1:0
．． This is a heat-resistant casting alloy for gas turbine blades consisting of one or two types of 0.01 to 0.2%, the balance being CO and inevitable impurities.

[For production]

The composition of the Co-based heat-resistant casting alloy that is the object of the present invention is within the chemical composition range shown in Table 2, and the reason for limiting the composition range will be described below.

Cr: This is a necessary element from the viewpoint of corrosion resistance and oxidation resistance. It is also a carbide-forming element, and is an element necessary to form carbides and obtain high-temperature strength. In particular, when used in land gas turbine stationary blades, corrosion resistance at high temperatures is required to be higher than that of aircraft engine stationary blades due to the diversity of fuels. Note that, since accessory parts such as inserts for cooling are welded to the stator blade, weldability is also a characteristic required of the alloy for the stator blade. From these points, Cr is required to be 25% or more. On the other hand, if the amount is too high, the structure will lack stability due to long-term use at high temperatures, and weldability will decrease, so 32%
The following was made.

Nl: Substrate austenite (FCC) stabilizing element, and also an element that improves processability. From this point 6
% or more is required. If the amount is too large, the thermal fatigue resistance and sulfidation resistance, which are the characteristics of Co-based heat-resistant alloys, will deteriorate;
It was set to 2% or less.

W: A solid solution strengthening element, which is absolutely necessary in order to ensure the high-temperature strength of the Co-based heat-resistant alloy. In addition, some of them form carbides and contribute to improving strength. If too much is added, the structure will lack stability due to long-term use at high temperatures, and ductility will be impaired, so the content was set at 6 to 8%.

Ta; is a solid solution strengthening element and a carbide forming element. In a high C-added Co-based heat-resistant alloy, if only carbide formation by Cr and W is effective for corrosion and oxidation resistance, m<Cr or W, which is effective for solid solution strengthening, will decrease. It was added to ensure its effectiveness. Adding too much will impair ductility, so add 2 to 5%.
And so.

T1: A carbide-forming element that forms fine carbides and is an element effective in improving high-temperature strength. By adding Ta in combination, the aim is to further improve high-temperature strength. Adding too much will impair ductility and will not change the high-temperature strength much, so it was set at 0.1 to 0.3%.

La: The oxide of La is dense and forms a scale with high oxidation resistance. Therefore, although the oxidation resistance can be significantly improved by adding a small amount, 0.02% or more is required for this purpose. However, since La is an expensive element, it was limited to 0.2% or less.

C: A carbide-forming element that forms carbides and contributes to strength. To ensure excellent high temperature strength, 0.45%
The above is necessary. However, if it is too large, ductility will drop significantly and weldability will deteriorate, so the content is set at 0.6% or less.

A1: A1 may be added in small amounts (approximately 0.5% or less) as it forms a dense distillation film and contributes to improving oxidation resistance, but since it is added with a You don't have to. 0.01-0.2% when La is not added
is necessary.

Further, if both La and A1 are added, further effects will be exhibited.

2r, B; 2r is added in a small amount (0.5% or less) because it strengthens the grain boundary dentrite boundary and contributes to improving high temperature strength.
A small amount (0.02% or less) of B may be added.

The remainder is Co, but it is desirable that industrially unavoidable impurity elements such as Fe, Si, MnSP, Ag, etc. be as low as possible.

〔Example〕

Test material with chemical components shown in Table 1 (φ25×200
βmm) was melted in a high frequency melting furnace.

Test materials ■～■ are alloys of the present invention, and test materials ■(FSX
414 equivalent material) and sample material (2) (Mar M509 equivalent material) are comparative materials. All test materials except sample (■) were subjected to the test as they were after melting. On the other hand, the sample material ■ was heated to 1150℃ x 4
The sample was held for a period of time, then cooled in a furnace to 927°C, held at this temperature for 10 hours, and then cooled in air, and then subjected to a heat treatment.

Next, tensile test pieces (
Parallel part diameter d = 6 mmφ) Creep rupture test piece (parallel part diameter d = 6 mmφ), corrosion test piece (1
5 x 30 x 2 tmm) and oxidation test piece (
15 x 30 x 2 tmm) was processed.

The following tests were conducted using the above-mentioned test pieces.

The tensile test was conducted at 850°C. The results are shown in Table 4.

As shown in Table 4, the tensile properties of test materials ■ to ■ are slightly higher than those of test materials ■ to ■, which are comparative materials, and the 0.2% strength and tensile strength are slightly higher than that of test materials ■. It tends to be slightly lower than sample material ■. On the other hand, there is no significant difference in elongation and reduction of area between the sample materials.

Creep rupture test was carried out at a temperature of 980℃ and a stress of 11.3kg/
The test was carried out under the condition of mm2. The results are also shown in Table 4. As shown in Table 4, the rupture time of test materials ■ to ■ (alloys of the present invention) was 54 to 75 hours, while that of test material ■, which was a comparative material, was significantly weaker at 1.7 hours. The test material (■) was strong for 80 hours. On the other hand, elongation
Regarding the reduction of area, there was no significant difference between the sample materials (■) to (2) and (2), and the sample material (2) had a high value and was an alloy with high ductility.

This difference in creep rupture properties is thought to be due to chemical components. In other words, it is considered that sample material (2) had no TaSTi added and the amount of C added was small, so the contribution of carbide precipitation hardening and solid solution strengthening was small, resulting in a weak strength. On the other hand, it has high ductility. In addition, sample materials ■～■ have lower Cs Ta, T+ than sample material ■.
It is presumed that the strength was low because the

Next, a corrosion test was conducted with V20S: NazSO4=8
Using corrosive ash (5% = 15%), it was applied to the entire surface at a rate of 20 cm/cm and heated in an electric furnace at 850°C for 20 hours to cause corrosion. After the test, descaling was performed and the amount of corrosion was measured. As a result, the corrosion weight loss of the sample material■》Sample material■
- Sample material ■> Sample material ■ - Sample material ■ were smaller in order. As a result, the amount of corrosion of sample material (2) with a small amount of Cr was significantly greater than that of the other sample materials. Although there was no major difference between the sample materials ■ to ■ and ■, the above-mentioned tendency in the order was observed.

Finally, an oxidation test was performed. 1000 in an atmospheric electric furnace
It was oxidized by heating at °C for 100 hours.

After the test, the weight was measured to determine the weight change. All sample materials increased in weight. The amount of weight increase was smaller in the order of sample material ■> sample material ■> sample material ■ ~ sample material ■ ~ sample material ■. Sample material (1) and sample material (2) have a small weight increase and are excellent in oxidation resistance. This is considered to be the effect of La or A1.

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

〔Effect of the invention〕

As described above, the Co-based heat-resistant cast alloys having the chemical composition range shown in Table 2 have high high temperature strength as shown in Table 4, and are excellent in corrosion resistance and oxidation resistance.

In other words, the improvement of high temperature strength is achieved by not only solid solution strengthening of W but also by high C
By adding Ta, Ti, and W to increase the precipitation of carbides and achieve precipitation hardening, on the other hand, corrosion resistance and
The oxidation resistance was improved by adding high Cr, La, and AI.

Claims (1)

[Claims] In weight%, Cr: 25-32%, Ni: 6-12%, W
: 6-8%, Ta: 2-5%: Ti: 0.1-0.3%
, C: 0.45-0.6% and La: 0.02-0.
2%, Al: 0.01 to 0.2% of one or two types, and the remainder Co and inevitable impurities.