JPH06287667A - Heat resistant cast co-base alloy - Google Patents

Abstract

PURPOSE:To produce a heat resistant cast Co-base alloy used for gas turbine stationary blade material having high temp. strength, excellent in high temp. strength and long-time stability, and further fatique strength. CONSTITUTION:This heat resistant cast Co-base alloy has a composition consisting of, by weight, 0.05-0.8% C, 5-15% Ni, 15-30% Cr, 3-10% W, 1-5% Re, <=1% Si, <=1% Mn, <=1.5% Fe, and the balance essentially Co with inevitable impurities. The alloy can further contain prescribed amounts of Ti, Ta, B, and Al, if necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant cast Co-based alloy which is excellent in high temperature strength and is particularly suitable for use as a stationary blade material of a gas turbine which requires these properties.

[0002]

2. Description of the Related Art Combined cycle power plants that combine gas turbines and steam turbines are considered to be the main power plant of the future because they have higher efficiency and excellent starting characteristics than steam turbine power plants. Recently, development has been promoted in the direction of increasing the inlet gas temperature of the gas turbine in order to further increase the plant efficiency. However, if the temperature of the inlet gas is increased, the temperatures of various members of the gas turbine are also increased, and thus the environment becomes more severe for the structural material of each member. For such temperature rise, it is necessary to adopt measures such as strengthening the cooling of members or applying materials with higher high temperature strength, but strengthening the cooling leads to a decrease in efficiency,
The application of a material having high high temperature strength becomes a more effective means.

Further, the combined cycle power generation plant is mainly used as electric power for peak load because it has particularly excellent starting characteristics as compared with the steam turbine power generation plant. However, when used for peak load,
Since the start and stop of the plant becomes frequent, the thermal stress repeatedly generated in various members of the gas turbine due to the start and stop also becomes frequent, resulting in a very harsh environment for the constituent materials of each member.

Generally, various heat-resistant cast Co-based alloys excellent in high-temperature strength, formability and weldability are used for stationary members such as turbine vanes of a gas turbine exposed to a high temperature atmosphere. Conventionally, these heat-resistant cast Co-based alloys have been developed mainly for the purpose of improving high temperature strength, especially creep rupture strength.

[0005]

However, when the gas turbine is driven toward higher temperature and higher efficiency, C which is currently used is increased.
In the o-based alloy, creep deformation of the stationary blade due to insufficient high temperature strength becomes a problem. Further, Co-based alloys have the property that when exposed to a high temperature environment, carbides precipitate and ductility and toughness deteriorate. When the temperature of the gas turbine rises, this characteristic deterioration becomes more significant than it is at present, and the resistance to flying objects and the resistance to thermal fatigue become a problem.
Greater long-term stability than now is needed.

In addition, in the present situation where the gas turbine for power generation is mainly used for peak load, resistance to fatigue crack generation due to thermal stress generated by frequent start and stop is becoming an important characteristic. . In particular, in a turbine blade of a gas turbine that has a generally large constraint, fatigue cracks are likely to occur in the stress concentration area,
In addition to the high temperature strength conventionally required for stationary vanes,
Sufficient fatigue strength is also required.

The present invention has been made from the above-mentioned viewpoint, and is heat-resistant casting excellent in high-temperature strength, high-temperature strength and long-term stability, and high-temperature strength and fatigue strength suitable for use as a stationary blade material of a gas turbine. The purpose is to provide a Co-based alloy.

[0008]

The heat-resistant cast Co-based alloy of the present invention has a weight ratio of C: 0.05-
0.8%, Ni: 5-15%, Cr: 15-30%, W: 3-10
%, Re: 1 to 5%, Si: 1% or less, Mn: 1% or less, Fe: 1.5% or less, and the balance is substantially composed of Co and inevitable impurities.

Further, in order to obtain a heat-resistant cast Co-based alloy having both high temperature strength and long-term stability, the weight ratio is
C: more than 0.45% and 0.8% or less, Ni: 5 to 15%, Cr:
15-30%, W: 3-10%, Re: 1-5%, Si: 1%
Hereinafter, Mn: 1% or less, Fe: 1.5% or less, and further, Ti: 0.01 to 1%, Ta: 1 to 5%, B:
0.1% or less, Al: Any one or more of 0.05 to 0.5%, and the balance is composed essentially of Co and unavoidable impurities.

On the other hand, in order to obtain a heat-resistant cast Co-based alloy excellent in high temperature strength and fatigue strength, the weight ratio of C: 0.05-
0.45%, Ni: 5-15%, Cr: 15-30%, W: 3-
10%, Re: 1 to 5%, Si: 1% or less, Mn: 1% or less, Fe: 1.5% or less, and if necessary, T
i: 0.01 to 1%, Ta: 1 to 5%, B: 0.1% or more, A
l: 0.05 to 0.5% of any one kind or more, and the balance is substantially composed of Co and inevitable impurities.

[0011]

The heat-resistant cast Co-based alloy of the present invention exhibits not only excellent high-temperature strength but also excellent long-term stability. When used as a blade material, it exhibits excellent performance for a remarkably long time even in a severe gas turbine environment where the temperature is raised.

On the other hand, the heat-resistant cast Co-based alloy of the present invention exhibits not only excellent high-temperature strength but also excellent fatigue strength. When used as a wing material, it exhibits excellent performance over a long period of time even in a harsh gas turbine environment where frequent start and stop are performed.

[0013]

EXAMPLE An example of the present invention will be described below. Prior to that, the reason why the composition range of the heat-resistant cast Co-based alloy of the present invention is limited as described above will be described. In the following description, “%” representing a composition is a weight ratio unless otherwise specified. (A) CC In addition to being solid-solved in the matrix, C has the action of forming carbides by combining with Cr, W, Ti and Ta, strengthening the insides of crystal grains and the grain boundaries, and improving the high temperature strength. Its content is 0.
If it is less than 05%, the desired effect cannot be obtained, while if it exceeds 0.8%, the weldability deteriorates.
It was set to 0.05 to 0.8% or less.

Here, when the C content is 0.05 to 0.45% or less, the effect of long-term stability is slightly inferior, while when the content of C exceeds 0.45%, the fatigue strength is slightly lowered, so high temperature strength and long time In order to obtain a heat-resistant cast Co alloy with excellent stability, the C content should exceed 0.45% and 0.8% or less,
To obtain a heat-resistant cast Co alloy excellent in high temperature strength and fatigue strength, the C content is set to 0.05 to 0.45%. (B) Ni When Ni and Cr coexist, they have the effects of improving high-temperature strength and stabilizing the austenite matrix, but if the content is less than 5%, the desired effect cannot be obtained.
%, The high temperature strength and corrosion / oxidation resistance are deteriorated, so the content was made 5 to 15%. (C) Cr Cr is an essential component to combine with C to form a carbide, improve the high temperature strength as a main strengthening phase, and ensure excellent high temperature corrosion resistance and oxidation resistance. If less than 15%, the desired effect cannot be obtained, while if more than 30% is contained, a σ phase is formed with Co to weaken the alloy, so the content was made 15 to 30%. (D) WW has an action of forming MC type carbides by combining with C to improve high temperature strength and to form a solid solution in the austenite matrix to strengthen it, but if the content is less than 3%, it is desirable. Effect is not obtained, on the other hand, if the content exceeds 10%, σ
Since an intermetallic compound such as a phase is formed to weaken the alloy, its content is set to 3 to 10%. (E) Re Re has the action of forming a solid solution in the austenite matrix to strengthen it and further delay the diffusion of the elements contained in the alloy in a high temperature environment to improve the stability of the alloy in service. If the content is less than 1%, the desired effect cannot be obtained, while if it exceeds 5%, the fatigue properties are degraded, so the content was made 1 to 5%. (F) Si Si is generally added as a deoxidizer, but its content is 1%.
If it exceeds, it will cause the formation of inclusions during casting. In addition, when performing vacuum melting or vacuum casting, there is no need to add it in particular, so the content was made 1% or less. (G) Mn Mn is added as a deoxidizing agent like Si, but if its content exceeds 1%, the high temperature oxidation resistance is lowered. In addition, when performing vacuum melting or vacuum casting, there is no need to add it in particular, so the content was made 1% or less. (H) Ti, Ta Ti and Ta both combine with C to form MC type carbides, mainly strengthening the inside of the grains and contributing to the improvement of high temperature strength.
If higher high temperature strength is needed, it can be added as needed. If Ti is less than 0.1 and Ta is less than 1%, the effect of improving the high temperature strength cannot be obtained, while 1% and 5 respectively.
%, The weldability and fatigue strength are extremely reduced, so the contents are 0.01 to 1% and 1 to
It was set to 5%. (I) BB Since B strengthens the crystal grain boundary and contributes to the improvement of high temperature strength and ductility, it can be added if necessary when these excellent properties are required. However, if the content exceeds 0.1%, the weldability deteriorates, so the content was made 0.1% or less. (J) Al Al forms a film of Al ₂ O _{3 on} the surface of the core during casting, suppresses the reaction between the SiO ₂ contained in the core and the molten metal, and improves the surface condition. When precision casting is performed using a complicated core, it is preferable to contain it. 0.05
If the content is less than 0.5%, the desired effect cannot be obtained. On the other hand, if the content exceeds 0.5%, the castability deteriorates and the alloy becomes brittle, so the content was made 0.05 to 0.5%.

It is desirable that the impurities contained incidentally when the above-mentioned components and Co as the main component are added are as small as possible. The heat-resistant cast Co-based alloy of the present invention can be obtained as an ingot by melting and refining each material metal under vacuum or atmospheric pressure and casting the melted metal. When applied to a vane of a gas turbine, the obtained ingot is remelted and precision cast into the shape of the vane. Next, Table 1 shows examples for obtaining a heat-resistant cast Co alloy excellent in high temperature strength and fatigue strength.

[0016]

[Table 1]

Using a master alloy having the composition shown in Table 1 and preliminarily refined in a vacuum induction furnace of 150 kg, it was remelted in a vacuum high frequency melting furnace and cast in a mold made by the lost wax method to obtain φ14 × 150 l The test material was obtained. Specimens 1 to 12 are heat-resistant cast Co-based alloys of the present invention, and specimens 13 and 14 are comparative materials, which are named FSX414 and Mar-M509, respectively, and are used for the stationary blades of current gas turbines. C
It is an o-based alloy. Except for the test material 13, the samples were used as they were after casting. On the other hand, the test material 13 was subjected to solution treatment at 1149 ° C. for 4 hours and then aging treatment (furnace cooling) at 982 ° C. for 4 hours after casting.

Next, a creep rupture test piece (parallel part diameter d = 6 mmφ) and a fatigue test piece (parallel part diameter d = 8 mmφ) were processed from these test materials, and a creep rupture test at 816 ° C. and 700 ° C. and 900 An axial strain control fatigue test was performed at ℃. The results are shown in Table 2.

[0019]

[Table 2]

First, sample materials 13 and 14 which are comparative alloys will be compared. It can be seen that the rupture time of the creep rupture test is much longer for the test material 14, and the high temperature strength is significantly better for the test material 14. On the other hand, in the fatigue test, although the number of repeated ruptures was about the same at 900 ° C, at 700 ° C the test material 13
It can be seen that the sample No. 13 has a larger number of repeated ruptures, and the sample material 13 is superior in fatigue strength especially at the low temperature side. That is, the test material
No. 13 is an alloy having a high fatigue strength but not so high in high temperature strength. On the other hand, the test material 14 is an alloy having an excellent high temperature strength but never a high fatigue strength.

Next, the alloy of the present invention will be compared with the comparative alloy.
Specimen 1 which is the alloy of the present invention in the creep rupture test
〜12 is longer than the test material 13 in the breaking time, and some of them are higher than the test material 14 which is a high-strength comparative alloy. Alloy material 1
It can be seen that it has a sufficient creep rupture strength equal to or higher than that of Nos. 3 and 14. On the other hand, in the fatigue test, each of the test materials 1 to 12 which is the alloy of the present invention has a much higher fracture repetition number than the test materials 13 and 14 which are the comparative alloys, and the fatigue strength is Certain test materials 13, 14
It can be seen that it is significantly improved compared to.

That is, the alloy of the present invention has a creep rupture strength equal to or higher than that of the Co-based alloy used for the conventional vane of a gas turbine,
Moreover, it is an alloy with significantly improved fatigue strength.

Next, Table 3 shows examples of obtaining a heat-resistant cast Co alloy excellent in high temperature strength and long-term stability. As in the case of the composition shown in Table 3, as in the case of the composition shown in Table 1, a master alloy preliminarily refined in a 150 kg vacuum induction furnace was used, remelted in a vacuum high-frequency melting furnace, and made by the lost wax method. Cast in a mold and dia. 14 x 150 l
The test materials of The test materials 21 to 32 are heat-resistant cast Co of the present invention.
It is a base alloy, and the test materials 33 and 34 are comparative materials, and FS
X414 and Mar-M509 are Co-based alloys used in the vanes of current gas turbines. Except for the test material 33, they were subjected to the tests as they were after casting. On the other hand, the test material
33 is 1149 ℃ × 4 hours after solution treatment after casting, 982 ℃ ×
A heat treatment of aging treatment (furnace cooling) was performed for 4 hours.

Next, tensile test pieces and creep rupture test pieces (diameter of parallel portion d = 6 mmφ) were processed from these test materials,
Tensile tests at room temperature and 850 ° C and creep rupture tests at 980 ° C were conducted. The results are shown in Table 4.

[0025]

[Table 3]

[0026]

[Table 4] First, the test materials 33 and 34, which are comparative alloys, are compared. At room temperature, there is not much difference in tensile strength between the two, but the 0.2% proof stress is higher in the test material 34. Further, at 850 ° C, the tensile strength and 0.2% proof stress of the test material 34 are higher. On the other hand, regarding the tensile elongation at break, the test material 33 is higher at any temperature. The rupture time of the creep rupture test is much longer for the test material 34, but the creep rupture elongation is smaller. That is, the test material 33 is an alloy having excellent ductility, although the high temperature strength is not so high, while the test material 34 is an alloy having excellent high temperature strength but not high ductility.

Next, the alloy of the present invention will be compared with the comparative alloy.
In the tensile test at room temperature and 850 ° C., the test materials 21 to 32, which are the alloys of the present invention, exceed the test material 33, which is a comparative alloy having low tensile strength and 0.2% proof stress, and are high strength comparative alloys. It shows a value equal to or higher than a certain test material 34.
The tensile elongation at break is higher than that of the test material 34 which is a low-ductility comparative alloy, and is almost the same as that of the test material 33 which is a high-ductility comparative alloy. On the other hand, in the creep rupture test, each of the test materials 21 to 32 which is the alloy of the present invention has a rupture time longer than that of the test material 34 which is a high strength comparative alloy. Also,
The creep rupture elongation is almost equal to that of the test material 33, which is a comparative alloy with high ductility. From these results, the test materials 21 to 32, which are the alloys of the present invention, have excellent high-temperature strength as compared to the test material 34, which is a high-strength comparative alloy, and are also high-ductility comparative alloys. It can be seen that it has the same ductility as the test material 33.

In addition to the above-mentioned tensile test and creep rupture test, a heat aging test of the test material was carried out. 850 sample materials
After aged at 1000C for 1000 hours, a tensile test piece and an impact test piece (2 mm V notch Charpy test piece) were processed, and a tensile test and an impact test were carried out at room temperature. The results are shown in Table 5 together with the characteristics of the test material in the initial state.

[0029]

[Table 5]

First, the test materials 33 and 34, which are comparative alloys, are compared. In Specimen 33, the tensile strength, 0.2% proof stress and absorbed energy are decreased by aging, and the tensile breaking elongation is increased, but the changes are small. On the other hand, in the case of the test material 34, the tensile strength and the 0.2% proof stress are increased by aging, and the tensile breaking elongation and the absorbed energy are greatly decreased. That is, the test material 33 is an alloy excellent in long-term stability, and conversely, the test material is an alloy poor in long-term stability.

Next, the alloy of the present invention will be compared with the comparative alloy.
All of the test materials 21 to 32, which are the alloys of the present invention, increase in tensile strength and 0.2% proof stress due to aging. On the other hand, although tensile elongation at break and absorbed energy tend to decrease,
The change is small and has the same long-term stability as the test material 33 which is a comparative alloy excellent in long-term stability.

That is, the alloy of the present invention has a significantly improved creep rupture strength as compared with the Co-based alloy used in the conventional vane of a gas turbine, and is excellent in long-term stability. It is an alloy.

[0033]

As described above, according to the present invention, as compared with the Co-based alloy used in the conventional vane of a gas turbine, it has the same or higher high temperature strength and fatigue An alloy is provided which has significantly improved strength. Therefore, if it is used as a vane material for a gas turbine, even in a harsh gas turbine that frequently starts and stops,
It has excellent performance over an extremely long period of time, and has industrially beneficial effects such as improved reliability of a combined cycle power plant.

Further, as compared with the Co-based alloy used for the conventional vane of a gas turbine, an alloy having a much improved high temperature strength and excellent long-term stability is given. To be Therefore, if it is used as a vane material for a gas turbine, it will exhibit outstanding performance over a long period of time even in a severe gas turbine with high temperature and high efficiency.
Industrially beneficial effects such as improved reliability of combined cycle power plants will be brought about.

Claims (9)

[Claims] 1. A weight ratio of C: 0.05 to 0.45% and Ni: 5
-15%, Cr: 15-30%, W: 3-10%, Re: 1-5
%, Si: 1% or less, Mn: 1% or less, Fe: 1.5% or less, and the balance substantially consisting of Co and unavoidable impurities. 2. By weight ratio, Ti: 0.01 to 1%, Ta: 1
The heat-resistant cast Co-based alloy according to claim 1, containing at least one of 5% to 5%. 3. The heat-resistant cast Co-based alloy according to claim 1 or 2, wherein B: 0.1% or less by weight is contained. 4. The heat-resistant cast Co-based alloy according to claim 1, 2 or 3, wherein Al: 0.05 to 0.5% is included in a weight ratio. 5. By weight ratio, C: more than 0.45% and 0.8% or less, Ni: 5-15%, Cr: 15-30%, W: 3-10%,
Re: 1 to 5%, Si: 1% or less, Mn: 1% or less, F
e: A heat-resistant cast Co-based alloy, characterized by containing 1.5% or less, and the balance substantially consisting of Co and inevitable impurities. 6. A weight ratio of Ti: 0.01 to 1% and Ta: 1
The heat-resistant cast Co-based alloy according to claim 5, wherein the heat-resistant cast Co-based alloy contains at least one of 5% to 5%. 7. The heat-resistant casting Co according to claim 5 or 6, wherein B: 0.1% or less by weight is contained.
Base alloy. 8. The heat-resistant cast Co-based alloy according to claim 5, 6, or 7, which contains Al: 0.05 to 0.5% by weight. 9. A weight ratio of C: 0.05 to 0.8% and Ni: 5
-15%, Cr: 15-30%, W: 3-10%, Re: 1-5
%, Si: 1% or less, Mn: 1% or less, Fe: 1.5% or less, and the balance substantially consisting of Co and unavoidable impurities.