JPH09184041A - Chromium-iron single crystal alloy and gas turbine member using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a chromium-iron alloy excellent in mechanical properties at high temp., particularly creep rupture characteristic, high temp. oxidation resistance, etc., and suitable for gas turbine member, etc., by regulating chromium content to a high value in a specific range in a chromium-iron binary alloy and forming a single crystal free from grain boundaries. SOLUTION: This alloy is a chromium-iron single crystal alloy having a composition consisting of, by weight, 60-95% chromium and the balance essentially iron. As to chromium content, creep rupture characteristic at high temp. becomes insufficient and a region embrittled by the presence of Σ-phase is brought about when it is below 60%, and on the other hand, hardness is deteriorated when it exceeds 95%. Because of the absence of grain boundaries in this chromium-iron single crystal alloy, intergranular fracture does not occur and this alloy becomes excellent in high temp. oxidation resistance as well as in mechanical properties at high temp. in particular. By using a gas turbine member composed of this alloy, a high-powered and high-efficiency gas turbine can be obtained. Further, it is preferable to regulate the contents of the elements other than chromium and iron to <=0.1wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromium-iron single crystal alloy and a gas turbine member using the same, and more specifically, it has excellent mechanical properties at high temperatures, particularly excellent creep rupture properties and oxidation resistance. For example, the present invention relates to a chromium-iron single crystal alloy mainly containing chromium, which is preferably used for a gas turbine member such as a blade or a nozzle of a gas turbine, and a gas turbine member made of this alloy.

[0002]

2. Description of the Related Art In recent years, it has become essential to increase the air / fuel ratio in order to increase the combustion efficiency of heat engines such as gas turbines. As a result, the combustion temperature rises, and blade materials such as blades (moving blades) and nozzles (stating blades) of gas turbines have excellent mechanical properties at high temperatures near 1000 ° C., especially creep rupture characteristics, and corrosion resistance, Materials with excellent oxidation resistance are required. Conventionally, polycrystalline ordinary casting alloys have been used as materials for gas turbine blades and nozzles, but with increasing combustion temperature, unidirectional columnar solidified alloys that do not have grain boundaries in the stress load direction. Has been used, and more recently, single crystal alloys having no grain boundaries have been used. However, these conventional alloys, which are mainly nickel-based alloys, have not been sufficiently satisfactory to meet the demands for high output and high efficiency of gas turbine engines, which are undergoing remarkable development in recent years.

On the other hand, stainless steel is known as an iron-chromium alloy. This stainless steel is called stainless steel and is a steel containing chromium as a main alloying element, and is austenitic (Cr: 16 to 20% by weight, Ni: 8 to 14% by weight),
Ferrite type (Cr: 11.5 to 18% by weight), austenite / ferrite type (Cr: 23 to 28% by weight, N
i: 3 to 6% by weight, Mo: 1 to 3% by weight), martensite system (Cr: 11.5 to 13.5% by weight) and precipitation hardening system (Cr: 15 to 17.5% by weight, Ni: 3-5% by weight, C
u: 3 to 5% by weight, Nb: 0.15 to 0.45% by weight). These stainless steels contain chromium in the range of 1 to 28% by weight, and are all polycrystalline alloys. Further, as iron-chromium alloys, there are multi-component heat resistant steels and super heat resistant alloys, which are also polycrystalline alloys.

By the way, regarding iron-chromium binary polycrystal alloys, according to the studies so far, (1) Brinell hardness increases as the chromium content increases in the standard state, and the chromium content is about 75. It peaks at the atomic% and decreases rapidly with increasing chromium content (F.
Adcock: J. Iron Steel Inst., Volume 124, (1931), 99.
(2) When the chromium content is in the range of 0 to 60% by weight, the tensile strength and the Rockwell hardness increase with the increase of the chromium content in the standard state, but the elongation and the drawing decrease with the chromium state in the standard state. About 10% by weight
It becomes the highest at 0, and it begins to decrease when the chromium content increases further, and becomes 0 when the chromium content is about 60% by weight (WO Bin
der: Trans. ASM, Volume 43, (1951), pages 759-777), and (3) Izod impact value increases with increasing chromium content in the standard state, reaching a maximum at about 25% by weight. When the chromium content is further increased, it rapidly decreases, and becomes 0 when the chromium content is about 50% by weight (WO B
inder: Trans. ASM, Vol. 43, (1951), pp. 759-777). In the case of a polycrystalline body, it is well known that softening starts from grain boundaries in a high temperature corrosive environment.

On the other hand, Japanese Examined Patent Publication No. 60-57432 discloses a chromium-iron binary polycrystalline alloy containing chromium as a main component, and this chromium-iron binary polycrystalline alloy contains chromium. It is described that when the amount is about 60% by weight or more, the pulverizability is remarkably improved, and particularly when the amount is about 70% by weight or more, the pulverizability is extremely good.

[0006]

Under such circumstances, the present invention is excellent in mechanical properties at high temperatures, particularly creep rupture properties and oxidation resistance at high temperatures. For example, gas such as gas turbine blades and nozzles It is an object of the present invention to provide a chromium-iron alloy that is preferably used for a turbine member and the like, and a gas turbine member including the same.

[0007]

The inventors of the present invention have conducted extensive studies in order to achieve the above object, and in the chromium-iron binary polycrystal alloy, the content of chromium is about 30 based on the results of conventional studies. When the content is more than 10% by weight, the crystal grains are coarse, so that breakage easily occurs at the crystal grain boundaries. On the other hand, Japanese Patent Publication No. 60-574.
From Japanese Patent No. 32, it was inferred that an extremely strong alloy was obtained when examining each particle after fracture. As a result of further research with these things in mind, the present inventor obtained a single crystal of chromium-iron binary alloy having a chromium content of 30% by weight or more with no grain boundary at all. For example, it has come to be predicted that this material will have extremely excellent mechanical properties, and under such prediction or attention, a chromium-iron single crystal alloy containing chromium in a specific ratio is provided. As a result of the preparation, it was found that this alloy is excellent in mechanical properties and oxidation resistance at high temperatures, can be suitably used for gas turbine members, and can achieve its purpose. By the way, chromium content is 30-60
The chromium-iron binary alloy of wt% is a region where the embrittlement phenomenon due to intragranular heterocrystal precipitation occurs due to the formation of the σ phase.
Therefore, it has been found that the region having a chromium content of 30 to 60% by weight is not preferable. The present invention has been completed based on such findings. That is, the present invention provides a chromium-iron single crystal alloy containing 60 to 95% by weight of chromium and the balance substantially iron, and a gas turbine member formed of the chromium-iron single crystal alloy. Is.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the chromium-iron single crystal alloy of the present invention, the chromium content is selected in the range of 60 to 95% by weight. If this content is less than 60% by weight, the creep rupture property at high temperature is insufficient, and the region in which the σ phase exists (region where the chromium content is about 43 to 50% by weight and the temperature is about 800 ° C or less). , And it becomes particularly brittle in this region. On the other hand, if it exceeds 95% by weight, the hardness decreases. From the viewpoint of creep rupture properties and hardness, the particularly preferable chromium content is in the range of 70 to 85% by weight. Further, in the single crystal alloy of the present invention, the component other than chromium is substantially iron. In the present specification, “substantially” means that an impurity element that is inevitably mixed in from the raw material at the time of alloy production may be contained in a proportion of usually 0.1% by weight or less. That is, the total content of chromium and iron in the single crystal alloy of the present invention is usually 99.9% by weight or more.

Since the chromium-iron single crystal alloy of the present invention has no grain boundaries, it does not cause grain boundary fracture.
Particularly in the case of a chromium-iron single crystal alloy having excellent mechanical properties at a high temperature, for example, a chromium content of 80% by weight and the balance being substantially iron, a temperature of 1040 ° C. and a load of 19 kgf
In the creep rupture test at / mm ² , the life is about 1000 hours. Furthermore, the single crystal alloy of the present invention is also excellent in oxidation resistance at high temperatures. As described above, the chromium-iron single crystal alloy of the present invention has excellent mechanical properties at high temperatures, particularly excellent creep rupture properties, and also excellent oxidation resistance at high temperatures, and thus has high creep rupture strength at high temperatures. It is preferably used as a member used in a severe environment where excellent oxidation resistance is required, for example, a gas turbine member, especially a material for a blade and a nozzle of a gas turbine.

The method for producing the chromium-iron single crystal alloy of the present invention is not particularly limited, and a conventionally known method for producing a single crystal alloy, for example, a nickel-based single crystal alloy (Japanese Patent Laid-Open No. 5-5)
143, JP 7-11365, JP 7
-70678 gazette) and the like, which are used in the production, can be applied. This unidirectional solidification method is a method in which the molten metal is grown in one direction through a narrow portion when the crystal is grown by cooling. Next, an example of a preferred method for producing a chromium-iron single crystal alloy of the present invention will be described. First, an arc type high temperature atmosphere melting apparatus,
Using a resistance heating type high temperature atmosphere melting apparatus, an atmosphere melting apparatus such as a high frequency induction atmosphere melting apparatus, a purity of 9
A mixture of chromium of 9.9% or more and iron of 99.9% or more in purity is preferably melted in an atmosphere of an inert gas such as argon to form an alloy melt, and the melt is cooled and solidified to obtain a desired alloy. A master ingot having the composition of is prepared. Next, this master ingot is single-crystallized by a unidirectional solidification apparatus. FIG. 1 is a schematic explanatory view of an example of a unidirectional solidification apparatus, in which a solidification tank 1 having a solidification initiation portion 5 through a narrowed portion 4 at the bottom is fixed on a cooling board 2 and installed in a heater 3. ing. The above master ingot is melted by high-frequency heating or the like, and the obtained molten metal is poured into the coagulation tank 1 heated to a temperature higher than the melting point of the alloy (hatched portion in the figure), and then the coagulation tank 1 is gradually heated from the heater 3. One-way solidification is sequentially carried out from the drawing and solidification starting section 5. Although a number of columnar crystals grow in the solidification starting portion 5, only one crystal of the columnar crystal further grows through the narrow portion 4, and the portion above the narrow portion 4 becomes a single crystal alloy. The heater 3 is maintained at a temperature equal to or higher than the melting point of the alloy until the solidification tank 1 is completely drawn out and the molten metal is completely solidified. This unidirectional solidification treatment is advantageously performed in an atmosphere of an inert gas such as argon or under reduced pressure. Thus, the chromium-iron single crystal alloy of the present invention can be easily manufactured.

The present invention also provides a gas turbine member made of this chromium-iron single crystal alloy, particularly a blade and nozzle of a gas turbine. In order to manufacture a gas turbine member made of the chromium-iron single crystal alloy of the present invention, in the above-mentioned method for manufacturing the chromium-iron single crystal alloy, the solidification tank has a solidification start part through a narrowed part at the bottom. A mold having a desired shape may be used. After completely solidifying, the single crystal casting is taken out from the mold, and the solidification starting portion and the narrowing portion are cut to obtain a desired gas turbine member. In the case of producing a gas turbine blade, the crystal is set in the blade longitudinal direction, that is, <001>.
It is desirable to grow so that the direction is the direction in which centrifugal force is applied. On the other hand, in the case of producing a gas turbine nozzle, the crystal is oriented in the lateral direction of the blade,
It is desirable to grow so that the 001> direction is the direction in which the thermal stress generated from the thermal cycle accompanying the start / stop of the gas turbine is applied.

[0012]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The creep rupture characteristics and oxidation resistance of the alloy were evaluated according to the following procedures. (1) Creep rupture property The alloy was processed into a test piece with a diameter of 6.35 mm in the parallel part and a distance between the scores of 25.4 mm, and a load of 19 kgf / mm ² was applied at a temperature of 1040 ° C based on the ASTM method, and the creep rupture time. I asked for the growth at that time. (2) Oxidation resistance A disc-shaped test piece having a diameter of 7 mm and a thickness of 4 mm was processed, and the test piece was heated in a crucible at 1100 ° C. for 16 hours,
The oxidation weight loss value was obtained after repeating the air-cooling thermal cycle 10 times.

Example 1 (1) Preparation of chromium-iron-based polycrystalline alloy ingot Chromium and iron having a purity of 99.9% or more were blended so that the chromium content in the alloy would be 80% by weight. Using an arc type high-temperature atmosphere melting device, under an argon gas atmosphere 17
After heating and melting at 80 ° C., the molten alloy was poured into a mold and naturally cooled to room temperature to produce a chromium-iron-based polycrystalline alloy ingot. (2) Preparation of chromium-iron single crystal alloy The ingot obtained in (1) above was single crystallized by the unidirectional solidification apparatus shown in FIG. That is, a mold (solidification tank) in which the ingot is melted by high-frequency heating, and the molten metal is heated by a heater 3 to a temperature of 1750 ° C. which is higher than the melting point of the alloy.
After pouring into the mold 1, the mold 1 was gradually drawn out from the heater 3 and was sequentially unidirectionally solidified from the solidification starting portion 5 in contact with the water-cooled cooling board 2. After 3 hours, the mold 1 was completely withdrawn from the heater 3, the molten metal was completely solidified, and the portion above the narrowed portion 4 became a single crystal alloy. This solidification treatment was performed in an argon atmosphere, and the heater 3 was kept at a temperature not lower than the melting point of the alloy until the mold 1 was completely drawn out. The alloy was taken out of the mold, and the alloy at the narrowing portion and the solidification starting portion was cut to obtain a chromium-iron single crystal alloy having a chromium content of 80% by weight. Table 1 shows the evaluation results of creep rupture properties and oxidation resistance of this single crystal alloy. An X-ray diffraction chart is shown in FIG.

Comparative Example 1 With respect to the chromium-iron-based polycrystalline alloy ingot having a chromium content of 80% by weight obtained in Example 1 (1), creep rupture characteristics and oxidation resistance were evaluated. Table 1 shows the results. Comparative Example 2 In the same manner as in Example 1, a chromium-iron based single crystal alloy having a chromium content of 50% by weight was prepared, and the creep rupture characteristics and the oxidation resistance were evaluated. Table 1 shows the results.

[0015]

[Table 1]

Note) * 1: Measured under conditions of 137 MPa and 1000 hours * 2: Measured at 650 ° C. * 3: Indicates the increase in oxidation measured under conditions of 1200 ° C. and 5 hours As can be seen from Table 1, the chromium-iron single crystal alloy of the present invention is superior to the alloys of Comparative Examples in yield strength, service temperature and oxidation resistance.

[0017]

The chromium-iron single crystal alloy of the present invention has excellent mechanical properties at high temperature, particularly excellent creep rupture properties,
And because it is also excellent in oxidation resistance at high temperatures,
It is preferably used for members used in a severe environment where high creep rupture strength at high temperature and excellent oxidation resistance are required, for example, gas turbine members such as gas turbine blades and nozzles. Further, by using the gas turbine blade or the gas turbine nozzle made of the single crystal alloy of the present invention, a gas turbine with high output and high efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an example of a unidirectional solidification apparatus for producing a chromium-iron based single crystal alloy of the present invention.

FIG. 2 is an X-ray diffraction chart of an example of a chromium-iron based single crystal alloy.

[Explanation of symbols]

 1: Solidification tank (mold) 2: Cooling plate 3: Heating heater 4: Narrow part 5: Solidification start part

Claims (5)

[Claims] 1. A chromium-iron single crystal alloy containing 60 to 95% by weight of chromium and the balance substantially consisting of iron. 2. The content of elements other than chromium and iron is 0.1.
The chromium-iron single crystal alloy according to claim 1, which is not more than wt%. 3. A gas turbine member made of the chromium-iron single crystal alloy according to claim 1. 4. The gas turbine member according to claim 3, which is a gas turbine plate. 5. The gas turbine member according to claim 3, which is a gas turbine nozzle.