JPS6187841A - Nozzle for gas turbine - Google Patents

Abstract

PURPOSE:To obtain the titled nozzle having superior corrosion resistance and ductility at high temp. and satisfactory weldability by using an alloy having a specified composition consisting of C, Cr, W, Mo. Ta, Hf, Zr, B and Ni and a cast structure contg. dispersed carbides contg. Cr. CONSTITUTION:A nozzle for a gas turbine is made of a heat resistant Ni superalloy consisting of, by weight, >0.3-1% C, 20-40% Cr, 5-20% W and/or Mo, 0.2-1% at least one among Ta, Hf and Za, 0.005-0.1% B and the balance essentially Ni or further contg. 5-15% Co and/or 0.05-1% Y and/or Al and having a cast structure contg. dispersed carbides contg. Cr. The nozzle has superior corrosion and oxidation resistances at high temp. and is easily welded and repaired. The nozzle can be manufactured by melting and casting in the air.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a novel nozzle for a gas turbine, and particularly to a Ni-based heat-resistant superalloy having excellent high-temperature corrosion resistance and high-temperature ductility.

[Background of the invention]

Gas turbine nozzles are manufactured by precision casting, and the materials used therein include Go-based heat-resistant superalloys and Ni-based heat-resistant superalloys. Go-based heat-resistant superalloys have excellent high-temperature corrosion resistance at temperatures below 1000°C, but are inferior in high-temperature corrosion resistance above 1000°C. In addition, it has low high-temperature ductility and becomes brittle, especially during use, and cracks occur under the action of external forces such as thermal stress. Furthermore, when applying a diffusion coating of Al, embrittlement occurs due to the σ phase of co-AΩ.

Weldability is also poor. Also, CO is very expensive. On the other hand, conventional Ni-based alloys have excellent high-temperature oxidation resistance at temperatures above 1000°C, but because they contain Ti and Al and are strengthened with a γ' phase, they have high high-temperature strength but have lower ductility than Go-based alloys. Therefore, it is unsuitable for parts such as nozzles that are subject to repeated thermal stress. On the other hand, there is also a Ni-based alloy represented by N1-C,r which does not contain γ', but in this case the strength is low and it is unsuitable as a high-temperature groove forming member. Also γ′
Ni-based alloys precipitated require vacuum melting and vacuum casting techniques and have poor weldability, making repair welding difficult8.
Furthermore, since γ' is included, the Cr content is as low as 10 to 15%, and the high temperature corrosion resistance at temperatures below 1000°C is extremely poor.

[Purpose of the invention]

An object of the present invention is to provide a Ni-based heat-resistant superalloy for gas turbine nozzle materials that has excellent high-temperature corrosion resistance and high-temperature oxidation resistance, is easy to repair by welding, and can be manufactured by atmospheric melting and atmospheric casting.

[Summary of the invention]

The present invention is based on weight of more than 0.3% of CO and less than 1% of Cr20.
~40%, 5 to 20% of at least one of W and Mo,
0.2 to 1% of at least one of Ta, Hf and Zr;
Contains Bo, 0.005 to 0.1%, and the remainder is substantially N.
A nozzle for a gas turbine is characterized in that it has a cast structure in which carbide containing Cr is dispersed.

Further, in the present invention, the aforementioned alloy contains 5 to 15% Co and 0.05 to 1% of at least one of Y and Al, or both.

Go-based cast superalloys are generally used for gas turbine nozzles, but when used at high temperatures for long periods of time, they become brittle and crack due to thermal fatigue. Furthermore, when used at temperatures above 1000°C, oxidation resistance is poor. On the other hand, although Ni-base superalloy is rarely used, it is a strong precipitation-strengthened alloy in which Ni-base superalloy γ', which is used for gas turbines, is precipitated. Most Ni-based superalloys are used as blades, but they may also be used as nozzles. However, since γ' is precipitated, although it has excellent high-temperature strength, it has poor high-temperature ductility and is difficult to weld, and is used after being vacuum melted or vacuum cast. The alloy of the present invention is a Ni-based superalloy for nozzles that does not contain γ' and therefore has a very high Cr content, can be manufactured by atmospheric melting, has high ductility, and has excellent weldability. In addition, high-temperature strength is achieved by increasing C and mainly by solid solution strengthening, so Mo, W
including.

Furthermore, since Go is very expensive, it is an inexpensive nozzle material because it is based on Ni. This is a Ni-based heat-resistant superalloy with excellent thermal fatigue and high-temperature corrosion resistance, which are most required for nozzles.

Next, the reason for limiting the components will be explained. 6CTC is an essential element for improving high temperature strength, and also plays a very important role in the material of the present invention. Conventional Ni-based superalloys for gas turbines have a low C content because they precipitate γ'. γ
' is N1x(Al.

T i ) and contains a large amount of Ti. If there is a lot of C, TiC
precipitates and becomes γ' mainly composed of N1aAl.

Undesirable. Moreover, Or carbide with high Cr precipitates excessively, and during long-term use at high temperatures, it grows and becomes coarser, resulting in embrittlement and a decrease in strength. Therefore, there is a relationship with Cr, and C
It is not preferable to make the content more than 1%, and if it is less than 0.3%, σ phase tends to appear due to the relationship with high CrJt, and sufficient high temperature strength cannot be obtained. Most preferably, C is 0.3 to 0.6%.

Cr: Cr cannot be increased because the precipitation of the conventional Ni-based superalloy σ phase, which precipitates γ', is discouraged.

Furthermore, since the alloy is mainly designed for high-temperature strength, the amount of γ' is large, and therefore the amount of Al+Ti is large.

On the other hand, since there is a limit to the remaining amount of Ni groups, C
r is kept low. Furthermore, when CO is included and the amount of Cr is increased, the solid solution temperature of γ' is lowered, making it difficult for γ' to precipitate. For this reason, the Cr content is lowered for strength reasons, with the expectation that high-temperature corrosivity will be lowered. This is because Ni-based superalloys have been developed as blade materials with severe stress. The nozzle is not required to have as much stress as the blade, but rather requires high-temperature ductility to improve thermal fatigue resistance.1 Since the alloy of the present invention does not contain γ', it is possible to select a sufficiently high Cr content. A content of 20% or more is necessary from the viewpoint of high temperature corrosion and oxidation resistance, and a content of 40% or more is inappropriate from the viewpoint of excessive precipitation of carbides and embrittlement, so it is limited to 20 to 40%. Among these, 25 to 30
% is most suitable.

W, Mo; W, Mo are the second most important after C and Cr.6 Unlike general Ni-based superalloys used for gas turbines, the alloy of the present invention has low high-temperature strength because γ' does not precipitate. . W and Mo are added for the purpose of solid solution strengthening of the base. Of course, it is a strong carbide-forming element, so it is a type in which C is combined with (Cr, Mi, W) that replaces a part of Cr in Cr carbide, but these are not so important, mW and Mo are also small. W does not play the role of solid solution strengthening (if it is too large, it will cause the precipitation of preferable phases such as σ phase, thereby lowering the high temperature.

Although MO alone exhibits a sufficient effect, the effect is greater when added in combination. Therefore, each content is preferably 5 to 20%, and 7 to 13% is most suitable.

Zr, Hf, Ta; Unlike W and Mo, these elements are added because they are expected to cause carbide precipitation.
These elements form MC-type carbides, whereas r replaces part of the Cr in carbides. This M does not contain CP, and when it is Zr alone, it is Z r C + When it is added in combination with Hf t Ta (Zr.

Each element is contained in M of <MC, such as Hf, Ta)C. Precipitation of MC type carbides lowers the amount of C in the matrix, suppressing the precipitation of Cr carbides. Cr carbides appear finely near grain boundaries and continuously at grain boundaries, so it is important to appropriately suppress the precipitation of Cr carbides.
It is an element that forms MC type carbides such as f and Ta. If the content of these elements is small, the effect will be small, and if the content is large, the high temperature strength will decrease. Most preferably, the atomic ratio of M/C (M is the sum of elements forming the MC type carbide) is 0.2 to 0.3.

T a T Z r + Hf are each 0.2 to 1%
Each of them has a great effect singly or in combination, but Ta, Zr, and Z
The effect is greater when r and Hf are combined.

Co: Co is added for the purpose of solid solution strengthening to strengthen the base, but if it is too large, the effect is small considering the high price, so 5 to 15% is appropriate.

Y, Al: Y and Al are added to improve oxidation resistance and high-temperature corrosion resistance, and are not added for the purpose of improving strength. In particular, Al is added to γ′, which is found in conventional Ni-based superalloys.
Not for precipitation. If the amount is too low, the effect is ineffective, and when the amount is too high, weldability worsens and undesirable phases that cause embrittlement are precipitated. Therefore, Y was limited to O and OS to 1%, and Al was limited to 0.05 to 1%.

BIB is added in hopes of improving both high-temperature strength and high-temperature ductility. If it is too little, there will be no effect, and if it is too much, weldability will deteriorate, so the content should be o, oos ~ 0.1%.

The chemical components (% by weight) of the test materials are shown in the Examples table. Nα1°2 is a conventional material for comparison, and &3 to 7 are alloys of the present invention. H
a All sample materials 1 to 7 were cast at 100 r by precision casting.
A plate-shaped material of rn x 200 rye x 15 rn t was used. Nu 2 is 10-'Torr vacuum melting,
Vacuum casting was used, but everything else was done by atmospheric melting and atmospheric casting.

Each test piece was taken from the above-mentioned board. The creep rupture test piece was 982”C with a parallel part of 60+w+φ and 30mmρ.
, 3,0 kg/no'' and compared the rupture time and rupture area.The results are shown in Figure 1.
The one containing γ' is the best because it is precipitation strengthened, but on the other hand, the reduction area at break is 0%, making it strong and brittle. In addition, &1 has low strength and ductility, C is increased to 0.4, solid solution strengthened with W and Mo, and further Ti.

Inventive materials No. 3 to 7 strengthened with Nb and Zre Ta are not as strong as Nα2, but all alloys are stronger than Nα1 and particularly ductile. The high-temperature properties required for gas turbine nozzles require an alloy that has both strength and ductility. Regarding points &3 to 7, any alloy is suitable as a nozzle material. In particular, -4 and &6 are excellent.

On the other hand, regarding thermal shock resistance, cracks in the vertical cross section of a test piece of 10 wmφXIO side Ω were examined after repeating 200 cycles between 982° C. and water for 6 minutes per cycle. The length and number of cracks are shown in FIG. Nα1 has poor high temperature strength and ductility, and Nα has high strength but extremely poor ductility.
2 has poor thermal shock resistance, and there is almost no difference between the alloys of the present invention with Nα3 to 7, but they are overall superior to Nα1 and 2.Among them, h4, which has a large creep rupture area, is the best, and the others have a large creep rupture area. There is a correlation.

Regarding high temperature corrosion, the same 10 as used in the thermal shock test was used.
A test piece with a surface φX 10 lff1Q was examined by a coating method. The coating agent is 75% NazSOt and 25% Na.
After corrosion at 750° C. for 500 hours with Cf1, the corrosion weight loss was evaluated. The results are shown in Figure 3.The Na2 alloy contains only 15% Cr and therefore has extremely poor high-temperature corrosion resistance.The alloy of the present invention contains Na5 containing Y and Al.
is the best.

There is almost no difference from NQ 1 in other respects.

Since Nα1 is an alloy currently widely used as a nozzle material and rarely causes problems with high-temperature corrosion, the alloy of the present invention is considered to be suitable for use as a nozzle material also from the viewpoint of wet corrosion resistance.

On the other hand, the weldability test was 100mm x 100mm x 51ffI
It was evaluated by the Palestrene test method, in which a 1.5 liter plate was used as a test piece and a 2% strain was applied without a filler rod.

As a result, Nα2 was the worst, followed by Nα1, and all of the alloys of the present invention were superior to Nα1 except for Nα6. Since Nα6 contains Y and A, it has poor weldability.

The alloy of the present invention, which replaces the Go-based superalloy and the γ' precipitation type Ni supersuperalloy, has both high-temperature strength and ductility. ■
Since it does not contain γ', it can contain 20 to 40% Cr. Therefore, it has excellent high temperature corrosion resistance. ■Excellent weldability. ■Can be dissolved in the atmosphere.

■Inexpensive as it does not contain CO.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the results of the creep rupture test, FIG. 2 is a diagram showing the results of the thermal shock test, and FIG. 3 is a diagram showing the results of the high temperature corrosion test.

Claims (1)

[Claims] 1. More than 0.3% C and less than 1% by weight, 20 to 4 Cr
0%, at least one of W and Mo 5 to 20%, Ta
, 0.2 to 1% of at least one of Hf and Zr, B0
．． 1. A nozzle for a gas turbine, characterized in that the cast structure includes 0.005 to 0.1%, the remainder substantially consists of Ni, and carbides containing Cr are dispersed therein. 2. By weight, more than 0.3% C and less than 1%, Cr20-4
0%, at least one of Mo and W 5-20%, Ta
, 0.2 to 1% of at least one of Hf and Zr, B0
．． 001~0.1%, Co5~15%, and Y and A
1. A nozzle for a gas turbine, characterized in that the cast structure contains 0.05 to 1% of at least one type of l, the remainder being substantially Ni, and a cast structure in which carbides containing Cr are dispersed.