JPS6059289B2 - High-strength Co-based heat-resistant alloy for gas turbines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention exhibits excellent strength and oxidation resistance in a high-temperature oxidizing atmosphere of 100 O°C or higher, and is particularly suitable for use as a structural material for gas turbines that require these properties. The present invention relates to a suitable Co-based heat-resistant alloy.

Conventionally, various Co-based heat-resistant alloys with excellent high-temperature oxidation resistance have been used to manufacture structural members such as turbine nozzles and vanes of gas turbines that are exposed to high-temperature oxidizing atmospheres.

On the other hand, in recent years, as the performance of gas turbines has improved, the inlet temperature of gas turbines has continued to rise, and the temperature has reached 1
The temperature has reached over 300 degrees Celsius.

However, when the above-mentioned conventional β0-base heat-resistant alloy gas turbine member is exposed to the above-mentioned high-temperature oxidizing atmosphere of 1300°C or higher, its own temperature will decrease to 1
The temperature rose to over 1,000°C, and due to insufficient high-temperature strength, the service life was reached in a relatively short period of time. Therefore, from the above-mentioned viewpoint, the present inventors conducted research to develop a material that has not only high-temperature oxidation resistance but also particularly high-temperature strength. , further containing either or both of the following as necessary, and the remainder being CO and unavoidable impurities. When this CO-based heat resistant alloy is used in the manufacture of gas turbine components requiring these properties, the resulting gas turbine component exhibits exceptional strength and excellent high temperature oxidation resistance. They have found that even under the harsh conditions mentioned above, it exhibits excellent performance over an extremely long period of time.

This invention was made based on the above knowledge, and the reason why the component composition range was limited as described above will be explained below.

(a) C The C component includes Cr, W, and H, in addition to solid solution in the base material.
It combines with f to form carbides, which strengthens the inside of grains and grain boundaries, improves high-temperature strength, and further improves weldability and castability, but if the content is 0. If the content is less than 0.05%, the desired effect cannot be obtained, while if the content exceeds 0.6%, the toughness will deteriorate, so the content should be reduced to 0.05 to 0.6%.
It was determined that

(b) In addition to having a deoxidizing effect, the SiSl component also has the effect of improving the fluidity of the molten metal and further improving the high-temperature oxidation resistance, but if its content is less than 0.1%, the desired effect is not achieved. On the other hand, if the content exceeds 2%, no effect can be obtained.
Since toughness and weldability deteriorate, the content was set at 0.1 to 2%.

(c) Cr The Cr component is an essential austenite component for ensuring excellent high-temperature oxidation resistance.
If the content is less than 8%, the desired high-temperature oxidation resistance cannot be ensured, while if the content exceeds 25%, the high-temperature strength and toughness will decrease rapidly. It was set at 25%.

(d) W The W component combines with C to form MC type carbide, which is a high melting point carbide, while suppressing the formation of low melting point carbides of M7C3 type and M3C6 type, thereby improving high temperature strength. , which has the effect of solid solution in the austenite matrix and strengthens it, but if its content is less than 10%, the desired effect cannot be obtained. Not only will the hardness deteriorate rapidly, but also intermetallic compounds such as σ phase, which cause deterioration of toughness, will be formed.
It was set as 0%.

(e)Nl The Ni component has the effect of improving high-temperature strength when coexisting with Cr, further forming an austenitic matrix, stabilizing it well, and improving workability, but when its content is 25 If the content is less than 35%, the desired effect cannot be obtained, while if the content exceeds 35%, the high temperature oxidation resistance will deteriorate, so the content should be reduced to 25 to 35%.
It was determined that

(f) HfHf component contains high melting point carbide without forming MC type or M7C3 type eutectic carbide.
Formation of C-type primary carbides has the effect of improving high-temperature oxidation resistance and high-temperature strength, as well as improving toughness, but if the content is less than 0.5%, the desired effect is not achieved. On the other hand, even if the content exceeds 5%, the effect of improving the saw layer cannot be obtained due to the above-mentioned action, so the content was determined to be 0.5 to 5% in consideration of economic efficiency.

(g) Mn In addition to having a strong deoxidizing effect, the Mn component has the effect of solid solution in the austenite matrix, stabilizing it, and improving toughness, so it is necessary when these properties are required. However, if the content is less than 0.1%, the desired effect cannot be obtained, while if the content exceeds 2%, the high temperature oxidation resistance tends to deteriorate. Therefore, its content was determined to be 0.1 to 2%.

(h) Rare earth elements These elements have the effect of significantly improving high-temperature oxidation resistance, especially when coexisting with Hf, so they may be used as necessary when particularly excellent high-temperature oxidation resistance is required. Contains, but the content is 0.005%
The desired effect can be obtained with less than 0.1
If the content exceeds 0.0%, the castability and workability tend to deteriorate.
It was set at 0.05 to 0.1%.

Note that among the inevitable impurities in the CO-based heat-resistant alloy of the present invention, particularly regarding Fe, the alloy properties are not impaired in any way even if it is contained up to 3%. It may be actively included. Next, the CO-based heat-resistant alloy of the present invention will be specifically explained with reference to Examples.

Examples CO-based heat-resistant alloys 1 to 23 of the present invention and comparative CO alloys having the compositions shown in Table 1 were prepared by a conventional melting method.
The base heat-resistant alloys 1 to 7 were melted, and using the wax precision casting method, parallel part outer diameter: 7WfSφ x parallel part length: 50
A test piece material having the following dimensions: rfn x outer diameter of chuck part: 25mm x total length: 9- was cast.

Next, a creep lap tear test piece was cut out from this test piece material for the purpose of evaluating high temperature strength, and using this test piece, atmosphere: air, heating temperature: 1100°C, added load: 3.5k9/? A creep rapture test was conducted under the conditions of 2 to measure the life at break and the area of area at break. Also,
A test piece with dimensions of diameter: 10 mφ x height: 1'' was cut out from the chuck part of the test piece after the above creep lap tear test, and after holding the test piece at a temperature of 1100°C in the atmosphere for 1 hour using this test piece, A high temperature oxidation resistance test was conducted to measure the oxidation loss after 10 cycles of descaling.

Claims (1)

[Claims] 1 C: 0.05-0.6%, Si: 0.1-2%, Cr: 18-25%, W: 10-20%, Ni: 25-35%, Hf: 1. A high-strength Co-based heat-resistant alloy for gas turbines, characterized in that it has a composition (the above weight %) consisting of: 0.5 to 5%, the remainder being Co and unavoidable impurities. 2C: 0.05-0.6%, Si: 0.1-2%, Cr: 18-25%, W: 10-20%, Ni: 25-35%, Hf: 0.5-5% , Mn: 0.1 to 2%, Co and unavoidable impurities: remainder, A high-strength Co-based heat-resistant alloy for gas turbines, characterized in that it has a composition (the above weight %) consisting of: 3C: 0.05-0.6%, Si: 0.1-2%, Cr: 18-25%, W: 10-20%, Ni: 25-35%, Hf: 0.5-5% , rare earth elements: 0.005 to 0.1%, Co and unavoidable impurities: the remainder, A high-strength Co-based heat-resistant alloy for gas turbines, characterized in that it has a composition (the above weight %) consisting of the following. 4C: 0.05-0.6%, Si: 0.1-2%, Cr: 18-25%, W: 10-20%, Ni: 25-35%, Hf: 0.5-5% , Mn: 0.1 to 2%, rare earth elements: 0.005 to 0.1%, Co and unavoidable impurities: remainder, High strength Co for gas turbines characterized by having the following composition (the above weight %) Base heat-resistant alloy.