JPS59232247A - Nozzle having weldable structure for gas turbine - Google Patents

Abstract

PURPOSE:To obtain a nozzle having a weldable structure and showing superior creep rupture strength for a gas turbine by using an alloy consisting of specified percentages of C, Si, Mn, Ni, Cr, W, B, Nb, Ti, Zr, Y and Co and having a specified total content of Y and Zr. CONSTITUTION:An alloy consisting of, by weight, 0.15-1% C, <=1% Si, <=1% Mn, 5-15% Ni, 18-35% Cr, 3-15% W, 0.003-0.1% B, 0.01-0.8% Nb, 0.01- 0.8% Ti, 0.01-0.8% Zr, 0.1-0.7% Y and the balance Co with inevitable impurities and satisfying Y+Zr=0.1-0.8% is prepd., and a nozzle having a weldable structure for a gas turbine is made of the alloy. The resulting weldable nozzle shows superior creep rupture strength, thermal fatigue resistance and corrosion resitance at about 850-900 deg.C.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a welded structure nozzle for a gas turbine.

[Background of the invention]

Gas turbine nozzles are exposed to corrosive gases at 900-100 OC. However, conventionally, there is no heat-resistant alloy that can withstand such high temperatures, so as shown in Figure 1, the nozzle is made hollow and the inside is cooled with air, reducing the nozzle surface temperature to 850%.
I am using it below C. In that case, simply flowing cooling air will result in poor cooling efficiency, so it is necessary to flow a large amount of air. However, when a large amount of air is passed through, the gas temperature drops to 9.
, which is undesirable because it lowers the efficiency of the gas turbine.

Therefore, the core 5 shown in FIG. 1 is inserted into the nozzle to make the nozzle a double structure. The core 5 is sealed at one end and has a large number of pores, and air from inside the core passes through the pores and is ejected onto the inner wall surface of the nozzle, thereby intensely cooling the nozzle.

Instead, it efficiently lowers the nozzle temperature even with a small amount of air. Therefore, during use, the nozzle suffers from creep damage due to thermal stress due to temperature differences between inside and outside, and thermal fatigue cracking due to repeated activation.

The nozzle is precision cast, the core is manufactured by machining, and finally the two are welded together. Therefore, no matter how good the alloy applied to the nozzle is in thermal fatigue resistance, creep rupture strength, and high temperature corrosion resistance, it cannot be used if it has poor weldability.

Conventionally, welded gas turbine nozzles have been manufactured using Co-based alloy F S X 414 (Table I
AI) is used. However, thermal fatigue cracking due to heating embrittlement occurs in a short period of time, and the reliability of the gas turbine is significantly reduced. Therefore, the inventor first conducted C
We proposed an alloy with improved thermal fatigue resistance by adding N'ri%Nb and Zr to the
5).

Incidentally, in recent years, in order to improve the efficiency of gas turbines, it has become necessary to design gas turbine nozzles so that they can withstand temperatures of 800 to 950C.

This is because even if the gas temperature is raised to improve efficiency, if the nozzle alloy can only be used at temperatures below 850C, a large amount of cooling air will be required, and as a result, the gas temperature will drop, causing the gas temperature to drop. This is because the efficiency of the turbine decreases. Therefore, it has become necessary to develop a Co-based alloy with well-balanced properties in the range of 850C to 950C. However, the above proposal (Japanese Patent Application No. 53-14)
The Co-based alloy of 9135) has good thermal fatigue resistance and creep rupture properties, but the high temperature corrosion resistance rapidly decreases at 8500 or higher. On the other hand, a Co-based alloy to which Y is added (Japanese Patent Application No. 457123130) has excellent high-temperature corrosion resistance at temperatures above 8500, but has the disadvantage that it cannot be welded.

The present inventor has found that 1) high temperature corrosion resistance is significantly improved when Yo is 1 wt% or more, and 2) when Y is 0.1 to Q, 7 wt
% or less, weldability is improved; 3) weldability is significantly affected by Zr; if Zr o, s V/t% or more, welding becomes impossible; 4) However, when Y and 7. It has been found that when r coexists, Y + Z r-0.1 to 0.8 w 1% can be fully welded.

[Purpose of the invention]

The purpose of the first invention and the second invention according to the present application is to
It is an object of the present invention to provide a welded structure nozzle for a gas turbine that has excellent creep rupture strength, thermal fatigue resistance, and corrosion resistance at 900C, and can be welded.

[Summary of the invention]

The first invention according to the present application is C0,15~l w i%,
511 wt% or less, M'rl I W t% or less, Ni
5-15wt%, Cr18-35wt%, W3-15w
t%, J30.003~0.1 W 1%, Nb01o
1~o, sw %, TiO, 01~o, s w 1%
, Zr0.01-0.8wt%, Y O,1-0.7
Consisting of W 1%, balance Co and unavoidable impurities, Y
This is a welded structure nozzle for a gas turbine made of an alloy in which +zr=o, t~o, s w 1%.

The second invention is C0,15~Q, 6W 1%, 5itW
j% or less, Mn1wt% or less, Nl) 5-1.5w
t%, crts ~35wt%, W3~1-5wt%,
BO, 003~0. IW 1%, NbO, 01~
0.8 w t%, 'ri o, o i ~o, sw
t%, Z r 0.01-0.8Wi%, Yo, 1-0
．． 7wt%, Fe 10wt% or less, balance Co and unavoidable impurities, Y+zr=o, t~0.8wt%
This is a welded structure nozzle for gas turbines made of an alloy.

Next, the reason for limiting the composition of each element in the first invention will be described.

Below, % represents wt%.

C0.15~1% C is essential for increasing the strength and strength of the alloy. However, if it is less than 0.15%, the desired strength cannot be obtained. Moreover, if it exceeds 1%, coarse dendrite-like carbides will crystallize, resulting in a decrease in thermal fatigue resistance, and when heated at high temperatures for a long time, carbides will agglomerate, resulting in a decrease in ductility. In particular, 0.2 to 0.4% is Tt, Nb, which will be described below.
, is preferable in combination with the amount of zr.

Si 1% or less Si is generally added as a deoxidizing agent, but in the present invention it is also important from the viewpoint of weldability, and furthermore, it improves oxidation resistance. In order to obtain a sufficient effect, the content is preferably 0.3% or more. However, if it exceeds 1%, it causes inclusions to remain during casting, resulting in a decrease in weldability, so it is set at 1% or less. In particular, 0
．． 5 to 1% is preferred.

W 3-15% W is added in an amount of 3% or more for the purpose of improving high-temperature strength, but on the other hand, if it exceeds 15%, high-temperature ductility and surface 1 oxidation property as well as weldability deteriorate, so W is added in an amount of 3-15%.

Among these, 6 to 8% is preferable.

Bo, 0.003~0.1% B is added to improve high temperature strength and high section ductility, but it has no effect if it is less than 0.003%, and 0.1%
If it exceeds 0.003 to 0.003, problems will occur in weldability.
It was set at 1%. Among these, 0. O (15 to 0.015% is preferred.

7. r O, 01-0.8% Ti 0.01-0.8% Nb 0.01-0.8% Ti, Nb, and zr show even greater effects by adding a combination of them. It is something. These elements exhibit an optimal relationship particularly in the above and below-mentioned C content, W content, B content, Cr content, and Ni content.

Generally, zr, Ti, and Nb are used as carbide precipitation strengthening elements in heat-resistant alloys for the purpose of strengthening by carbide precipitation. We found that zr, Tf and Nb
It was found that high strength and high toughness can be obtained by the combined addition of . If the content of any of these elements is less than 0.01%, the target high temperature strength and high temperature ductility cannot be obtained. In other words, the addition of trace amounts of these elements has the effect of splitting eutectic carbides and grain boundary carbides, suppressing coarsening of secondary carbides,
Furthermore, deoxidizing and denitrifying effects can be obtained, and creep rupture strength, elongation at break, and reduction of area are significantly improved.

However, if the content of any of these elements exceeds 0.8%, it causes increased formation of inclusions, agglomeration of carbides, and embrittlement. In addition, when zr is 0.8% or more, Ni as well as Y
, and co to form a low melting point eutectic to accelerate weld cracking. Furthermore, if Nb exceeds 0.8%, the oxidation resistance will be significantly deteriorated. Therefore, these elements were set at 0.01 to 0.8%.

Among these, Ti 0.05-0.5%, N b O,1
~0.6% and Zr 0.05-0.25% are preferred.

Especially Tio, t~0.2%, NbO, 2~0.3
% and 0.1 to 0.2% of Zr is the best combination.

The amount of Y added is very important from the viewpoint of high temperature corrosion resistance and weldability. From the viewpoint of high-temperature corrosion resistance, at least 0.1% is necessary, and the larger the amount, the greater the effect.

However, if it exceeds 0.7%, the effect is small. Further, from the viewpoint of weldability, the content is preferably 0.1 to 0.7%. Considering both characteristics, 0.15 to 0.5% is particularly preferable.

Mn 1% or lessMn is added as a deoxidizing agent like Si, but it is preferably 0.3% or more to obtain a sufficient effect.However, if it exceeds 1%, oxidation resistance deteriorates.Especially 0.3% or more. It is preferably 4 to 0.6%.In addition, it may be 0.3% or less in vacuum melting.

Ni 5-15% Ni is contained in an amount of 5% or more in order to improve high-temperature strength, but even if it is increased, no improvement in strength is expected considering the amount added, so it is set at 5-15%. Among these, 9.5 to 11.5%
is preferred.

Cr 18-35% Cr should be selected in a range so as not to undergo cold shot and internal oxidation of carbides in relation to Ti. Cr
is required to be 18% or more in order to improve oxidation resistance. However, if it exceeds 35%, cold shots will occur,
The internal oxidation of carbides that occurs during use causes a decrease in high-temperature ductility, which further causes embrittlement during long-term use at high temperatures.

Among these, 28 to 31% is preferable.

Y+Zr 0.1-0.8% Welding is possible if Y+Zr=0.1-0.8% is satisfied. Weld cracking is proportional to the amount of S, but when a small amount of Y is added, Y fixes S, so weldability is improved. However, when Y + Zr = 0.8% or more, (Ni, Co) - (
It is thought that the low melting point co-content of Y, Zr) crystallizes in many cases and causes high temperature cracking during welding. Therefore, Y
It is important to satisfy +Zr=0.1 to 0.8% in order to simultaneously satisfy high temperature corrosion resistance and weldability. Among these, Y+Z r = 0.15 to 15% is particularly preferred.

The second invention differs from the first invention in the following points and is otherwise the same.

C0.15-0.6% C is essential to increase the strength of the alloy, but since high temperature strength is maintained by adding Fe, the upper limit of the amount of C added can be lower than in the first invention.

Fe　10% or less pe is C, Si, Mn, w, Nb, 'J'i, Zr.

When adding B and the like, adding it as a master alloy is effective in increasing the yield of these additions. However, if it exceeds 10%, the high temperature strength will be lowered. In particular, the content is preferably 4% or less in order to maintain high high temperature strength.

[Embodiments of the invention]

Example 1 100+nmX 2.00mm using 0 stwax method
A material of ×15+nm was fabricated. Melting was carried out by high frequency vacuum melting, and casting was carried out in an Ar atmosphere. Heat treatment is 1230C
After being maintained for 4 hours, it was air cooled to room temperature. A high-temperature corrosion test piece (5 mm x 10 m x 15 m) and a palestrain welding test piece (6 mm x 6'Omm x 200 m) were collected from this material.
Tested. The chemical composition of each sample is shown in the attached table. A1.
A2 is a conventional alloy, and A4 to A8 are alloys according to examples of the present invention. A9. A10 is a comparative example.

High-temperature corrosion resistance was evaluated by corrosion weight loss after holding at 850C, 1900C, and 100OC for 500 hours using a Na2SO425%NaCt coating method.

Weldability was tested using a Palestrain welding tester. The heat input was 7'920 J/catSt flow 110AX', the pressure was 12V, the welding speed IQCrn/miq, and the strain was 1% (plate thickness 6mm, bending radius 300mm). The welding rod is C
011%, Cr2O, 5%, W15%, Ni10.5%
, Fe2.5%, NbO, 15%, Tio, t5
%, Z r 0.05%, Yo, 15%, sio, s%
, Mn1.1%, Ba1. It has a composition of co.

Welding was performed on the 60×200 m+n surface of the test piece.

Figure 3 shows the results of the high temperature corrosion test. yo, i%(
Boiled 5) has about twice the corrosion resistance of the conventional example (&2). Moreover, when Yo is 6% (8th) or more, corrosion hardly occurs.

Figures 4 to 6 show the results of the welding tests.

FIG. 4 shows the relationship between weldability and Y.

If Y exceeds 0.7%, weldability will drop sharply.

Note that welding to the nozzle is possible when the weld crack length is 3 m or less. This is because the weld crack length of FSX414 (aai) is 3M as shown in FIGS. 4 and 6, and conventionally there has been no problem with welding FSX414 to the nozzle.

FIG. 5 shows the relationship between weldability and Zr content.

It can be seen that the weldability significantly decreases in proportion to the increase in the Zr content, and welding becomes difficult when the Zr content exceeds 0.8%.

FIG. 6 shows the relationship between weldability and Y+Zr content. The ``hunting area'' in Figure 6, in other words, Y+Zr=
It can be seen that welding is possible at 0.1 to 0.8%.

Example 2 The nozzle segment main body 4 shown in FIG. 1 was precision cast in an argon gas atmosphere by the lost wax method. The components of the nozzle are Co26%, Cr29.5%, W7.2%,
Ni1O, 2%, Fe1.2%, Zr0115%, Ti
o, xs%, NbO, 25%, YO25%, SiO, 8
5%, Mn0.5%, Ba1. It is Co.

This casting product is inspected visually and with a Zygro, etc., and found casting defects such as shell bites, plowholes, and other Zygro defects are removed using a grinder, etc., and the removed parts are repaired by overlay welding, etc. I did it.

The welding rod is 1.6φ and the composition is co, i%, cr20
．． 5%, W15%, Ni10.5%, Fe 2.5%
, Nb0.15%, T i 0.1 s%, zro, o
s%, YO315%, sio, s%, Mn1.1%, B
al6C.

It is. Welding is edge arc welding with a welding current of 80 to 9.
0A1 welding voltage 10~11V, welding speed 200cm/m
I went with m.

In addition, before welding repair of casting defects, 1230tl'X4h
, gas cooling heat treatment was performed.

Next, under the same welding conditions, the nozzle segment main body 4, the core 5 of 8US304, and the blind plate 6 are welded at the welded portion 7.
and 8 welded. That is, for example, as shown in FIG.
was welded around the base of the nozzle segment main body 4 (so-called inner shroud part). Both sections are particularly prone to weld cracking in closed coffin castings.

The welded gas turbine nozzle according to the example of the present invention thus obtained had no weld cracks and was excellent in thermal fatigue resistance, corrosion resistance, and creep resistance at high temperatures.

〔Effect of the invention〕

According to the first invention of the present application, a welded structure nozzle for a gas turbine which is excellent in creep rupture strength at 850 to 900C, thermal fatigue resistance, and corrosion resistance and can be welded is obtained. Further, the second invention according to the present application can also achieve the same effects as the first invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional configuration diagram of a gas turbine nozzle, and FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. Figure 3 shows high temperature corrosion test.
Figures 4, 5, and 6 show the relationship between corrosion loss and Y amount in the Palestrain welding test, and the relationship between the length of the crack in the Palestrain welding test,
FIG. 3 is a diagram showing the relationship between Y amount, Zr amount, and Y+Zr&, respectively. 1... Retainer ring, 2... Cooling air flow, 3...
・High temperature combustion gas flow, 4... Nozzle segment body, 5
... Core, 6 ... Blank plate, 7, 8 ... Welded part. Agent Patent Attorney Tatsuno Kaya Unuma l Mouth/ Kaya 20 $3 Mouth 276- $4. Eye γ (×) Chi 5 solid lr ('/-9 4th solid γ↑zr (wt :l)

Claims (1)

[Claims] 1°Co15~Iwt%, 511wt% or less, Mn1w
t% or less, Ni5-15wt%, Cr18-35wt%
, W3~15wt%, Bo, 003~0.1 w 1%
, Nb0.01~o, s w 1%, Tio, oi
~o, swt%, Z r 0.01~0.8W 1%,
Yo, 1~0.7 W 1%, balance from CO and unavoidable impurities'), y+z r ==0.1~0.8w
A welded structure nozzle for gas turbines made of a 1% alloy. The welded structure nozzle for a gas turbine according to claim 1, wherein: =0.01 to 0.17. 'I' i (at%) + Nb (at%) + Zr (at
%)3, -XZ r (w
The welded structure nozzle for a gas turbine according to claim 2, wherein C(at%) = 0.03 to 0.08. 4, C0,15~0.6 W 1%, 511 wt% or less, Mn 1 wt% or less, Ni 5~15 wt%, Cr18~
35wt%, W3-15wt%, Bo, 003-0.
IW 1%, NbO, 01-0.8 W 1%, Ti
O, 01-0.8 w 1%, Z r 0.01-0.
8w 1%, Y 0.1~0.7 w 1%, 'pel
A welded structure nozzle for a gas turbine made of an alloy consisting of Qwt% or less, the balance being Co and unavoidable impurities, and Y+Zr=061 to o, swt%. The welded structure nozzle for a gas turbine according to claim 4, wherein W = 0.01 to 0.17 W 1%. The welded structure nozzle for a gas turbine according to claim 5, wherein: =0.03 to Q, 93wt%.