JPH06287666A - Heat resistant cast co-base alloy - Google Patents

Abstract

PURPOSE:To produce a heat resistant cast Co-base alloy suitably used for gas turbine-stationary blade material and excellent in high temp. strength and fatigue strength. CONSTITUTION:This heat resistant cast Co-base alloy has a composition consisting of, by weight ratio, 0.05-0.45% C, 5-15% Ni, 15-30% Cr, 3-10% W, 1-5% Re, 0.01-1% Ti, 0.01-1% Nb, <=1% Si, <=1% Mn, <=1.5% Fe, and the balance essentially Co with inevitable impurities. The alloy can further contain prescribed amounts of Ta, Hf, B, and Al.

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 fatigue strength and is particularly suitable for use as a stationary blade material of a gas turbine which requires these characteristics.

[0002]

2. Description of the Related Art Combined cycle power plants combining a gas turbine and a steam turbine are mainly used as peak load power because they have particularly excellent starting characteristics as compared with steam turbine power plants. But,
When it is used for peak load, the start and stop of the plant becomes frequent, so the thermal stress generated in various parts of the gas turbine due to start and stop also becomes frequent, and the environment is extremely harsh for the constituent materials of each part. Becomes

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.

[0004]

However, under the present circumstances 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 also important. It is becoming a characteristic. In particular, gas turbine stationary blades, which are generally constrained in shape, are prone to fatigue cracks in stress concentration areas.Therefore, in addition to the high temperature strength conventionally required for stationary blade materials, sufficient fatigue Strength is also required.

The present invention has been made from the above viewpoint, and an object of the present invention is to provide a heat-resistant cast Co-based alloy excellent in high temperature strength and fatigue strength, which is suitable for use as a stationary blade material of a gas turbine. .

[0006]

Therefore, the inventors of the present invention have conducted research to develop a material excellent not only in high temperature strength but also in fatigue strength which meets the above-mentioned object, and as a result, It was the invention.

That is, in the present invention, the weight ratio of C: 0.05-
0.45%, Ni: 5-15%, Cr: 15-30%, W: 3-10
%, Re: 1 to 5%, Ti: 0.01 to 1%, Nb: 0.01 to
1%, Si: 1% or less, Mn: 1% or less, Fe: 1.5%
Including the following, if necessary, Ta: 1-5%, H
f: 0.5 to 5%, B: 0.1% or less, Al: 0.05 to 0.5%
The present invention provides a heat-resistant cast Co-based alloy characterized by containing any one or more of the above and the balance substantially consisting of Co and inevitable impurities.

[0008]

The heat-resistant cast Co-based alloy of the present invention exhibits not only excellent high-temperature strength but also excellent fatigue strength, and this heat-resistant cast Co-based alloy is required to have these characteristics. As a result, it has been found that even in a severe gas turbine environment where frequent start and stop are performed, excellent performance is exhibited for a remarkably long time.

[0009]

EXAMPLES Examples of the present invention will be described below. First, the reason for limiting the composition range in the heat-resistant cast Co-based alloy of the present invention 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 is not obtained, while if it exceeds 0.45%, the fatigue strength is reduced, so the content was made 0.05 to 0.45%. (B) Ni Ni improves the high-temperature strength in the coexistence with Cr and further stabilizes the austenite matrix, but if the content is less than 5%, the desired effect cannot be obtained, while 15%
If it is contained in excess of 10%, the high temperature strength and corrosion / oxidation resistance will be reduced, 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 deteriorated, so the content was made 1 to 5%. (F) Ti, Nb Ti and Nb both combine with C to form MC type carbides, which are uniformly dispersed and precipitated at grain boundaries and within grains to contribute to improvement of high temperature strength and fatigue strength. This effect is particularly great when added in combination, but the addition amounts of Ti and Nb are
If it is less than 0.01%, the desired effect cannot be obtained, while on the other hand 1
%, The carbides excessively precipitate at the grain boundaries and conversely decrease the fatigue strength.
It was set to 0.01 to 1%. (G) 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. Further, when performing vacuum melting or vacuum casting, it is not necessary to add it, so the content is set to 1%. (H) Mn Mn is added as a deoxidizing agent like Si, but if its content exceeds 1%, the high temperature oxidation resistance decreases. 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. (I) Ta, Hf Ta and Hf 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 Ta is less than 1% and Hf is less than 0.5%, the effect of improving the high temperature strength cannot be obtained. On the other hand, if each of them exceeds 5%, the weldability and the fatigue strength are extremely reduced. ~ 5%, 0.5-5%
And (J) BB B strengthens the crystal grain boundary and contributes to improvement of high temperature strength and ductility, and therefore, when more excellent properties are required, they can be added as necessary. However, if the content exceeds 0.1%, the weldability deteriorates, so the content was made 0.1% or less. (K) Al Al forms a film of Al ₂ O _{3 on} the surface of the core during casting, suppresses the reaction between 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.

Using a master alloy having the composition shown in Table 1 and having been 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 materials of 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.

[0012]

[Table 1]

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.

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 with excellent fatigue strength, although its high-temperature strength is not so severe, while sample material 14 is an alloy with excellent high-temperature strength but never high fatigue strength.

[0015]

[Table 2]

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.

In other words, the alloy of the present invention is superior to the Co-based alloy used in the conventional vane of a gas turbine,
This alloy has creep rupture strength equal to or higher than that, but fatigue strength is greatly improved.

[0018]

According to the present invention, as compared with the Co-based alloy used for the conventional vane of a gas turbine, it has a high temperature strength equal to or higher than that, but the fatigue strength is significantly improved. Given alloy. For this reason,
If used as a vane material for a gas turbine, it will have excellent industrial performance, such as excellent performance over a long period of time and improved reliability of a combined cycle power plant even in a severe gas turbine that is frequently started and stopped. Be brought.

Claims (4)

[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
%, Ti: 0.01 to 1%, Nb: 0.01 to 1%, Si: 1%
Hereinafter, a heat-resistant cast Co-based alloy characterized by containing Mn: 1% or less and Fe: 1.5% or less, and the balance substantially consisting of Co and inevitable impurities. 2. By weight ratio, Ta: 1 to 5%, Hf: 0.5
The heat-resistant cast Co-based alloy according to claim 1, containing at least one of 5% to 5%. 3. The heat-resistant casting Co according to claim 1 or 2, wherein B: 0.1% or less by weight is contained.
Base alloy. 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.