JP5626920B2 - Nickel-base alloy castings, gas turbine blades and gas turbines - Google Patents

Description

  The present invention relates to a nickel-base alloy having excellent strength, corrosion resistance and oxidation resistance at high temperatures, a cast product using the nickel-base alloy, and a blade for a gas turbine.

  In recent years, in a power engine such as a jet engine or a gas turbine, it is indispensable to increase the turbine inlet temperature in order to improve the performance and efficiency. Turbine blade materials that can withstand such high temperatures are required to have excellent creep rupture strength and toughness that can withstand centrifugal force at high temperatures, and excellent oxidation resistance and corrosion resistance to high-temperature combustion gas atmospheres. In order to satisfy this required characteristic, nickel-based alloys are currently used. Ni-based alloys include normal cast alloys made of equiaxed crystals, unidirectionally solidified alloys made of columnar crystals, and single crystal alloys made of one crystal.

  High-Cr ordinary cast nickel base alloy is used for land gas turbines (fuel gas turbines fixed to the ground and used for power generation) that use fuel with a lot of impurities in consideration of corrosion resistance and cost. . For example, Japanese Patent Laid-Open No. 51-34819 (Patent Document 1), Japanese Patent Application Laid-Open No. 2004-197131 (Patent Document 2), US Pat. There is a common casting alloy disclosed in Japanese Patent No. 084166 (Patent Document 4). Moreover, even with a normal casting alloy for a round gas turbine, the corrosion resistance is similar to the alloys disclosed in Japanese Patent Publication No. 46-27144 (Patent Document 5) and Japanese Patent Laid-Open No. 6-57359 (Patent Document 6). Some alloys have increased strength at the expense of.

JP 51-34819 A Japanese Patent Laid-Open No. 2004-197131 U.S. Pat. No. 3,449,545 JP 2010-084166 A Japanese Patent Publication No.46-27144 JP-A-6-57359

  Since a normal casting alloy for a gas turbine has a lower strength than a unidirectionally solidified alloy and a single crystal alloy, further improvement in strength characteristics is required. In addition, since the blades for gas turbines are larger in shape than the moving and stationary blades of a jet engine, there are problems such as the solidification rate in casting becomes slow, and the coarsening of crystal grains and the coarsening of carbides are likely to occur. there were.

  Further, unidirectionally solidified alloys and single crystal alloys are mainly used for the moving and stationary blades of jet engines. In such a moving vane for a jet engine, the Cr content is reduced with emphasis on strength, and a large amount of W or Ta having a high degree of solid solution strengthening is added to increase the creep rupture strength. As a result, although the creep rupture strength is high, the corrosion resistance at high temperatures is not sufficient, so that it is unsuitable for a land gas turbine using a fuel with many impurities.

  On the other hand, a moving blade for a gas turbine also needs to be used by unidirectional solidification casting from the viewpoint of improving the strength, and a normal casting alloy is used by unidirectional solidification casting. For this reason, the solidification rate is further slowed down and coarse carbides are generated, which causes workability and cracks.

  Accordingly, an object of the present invention is to provide a Ni-based alloy having excellent cast structure stability, corrosion resistance, oxidation resistance, and high strength, and suitable for ordinary casting and unidirectional solidification casting.

  The nickel-base alloy is a nickel-base alloy containing Cr, Co, Al, Ti, Ta, W, Mo, Nb, C, B and unavoidable impurities and the balance being Ni, and Cr: 12.1 to 15. 0% by mass, Co: 1.0 to 6.8% by mass, Al: 3.4 to 4.6% by mass, Ti: 2.8 to 3.9% by mass, Ta: 1.5 to 3.0% by mass %, W: 4.55-8.0 mass%, Mo: 0.5-2.5 mass%, Nb: 0.4 mass% or less, C: 0.01-0.20 mass%, B: 0 The alloy composition is 0.005 to 0.03 mass%.

  According to the above configuration, it is possible to provide a balanced Ni-based alloy in which coarsening of carbides during casting is suppressed, corrosion resistance at high temperatures, oxidation resistance, and creep rupture strength are high. Further, by applying the Ni-based alloy to the blades of the gas turbine, it is possible to provide a highly durable product such as a gas turbine using a fuel with a large amount of impurities.

It is a graph which shows the creep rupture time with respect to an alloy test piece. It is a graph which shows the oxidation weight loss in the high temperature oxidation test with respect to an alloy test piece. It is a graph which shows the corrosion weight loss in the molten salt immersion corrosion test with respect to an alloy test piece. It is a figure which shows an example of the moving blade shape of a gas turbine.

  The feature of the present invention that solves the above problems is that the high-temperature corrosion resistance is improved by increasing the amounts of Cr and Ti. Further, when Ti is increased, the oxidation resistance is remarkably lowered. Therefore, the amount of Al, which is highly effective in improving the oxidation resistance, is increased to the limit at which no foreign phase is precipitated, and further, the amount of Mo that lowers the oxidation resistance is reduced. In this way, the oxidation resistance is improved. On the other hand, since the creep strength at high temperature decreases when the amount of Mo is reduced, the amount of Co is reduced, and by adding W and Ta correspondingly, the creep strength at high temperature is maintained. Further, the amount of Nb is reduced in order to prevent generation of coarse carbides.

  Specifically, Cr: 12.1 to 15.0 mass%, Co: 1.0 to 6.8 mass%, Al: 3.4 to 4.6 mass%, Ti: 2.8 to 3.9 % By mass, Ta: 1.5 to 3.0% by mass, W: 4.55 to 8.0% by mass, Mo: 0.5 to 2.5% by mass, Nb: 0.4% by mass or less, C: A nickel-base alloy containing 0.01 to 0.20% by mass, B: 0.005 to 0.03% by mass, the balance being Ni and other inevitable impurities.

  By adjusting the components as described above, the cast structure stability is excellent. An alloy having high strength and excellent corrosion resistance and oxidation resistance can be provided, and is suitable as a material for members used at high temperatures such as gas turbine blades.

  Further, the nickel-base alloy having excellent strength and corrosion / oxidation resistance according to the present invention is Cr: 13.1 to 15.0 mass%, Co: 1.0 to 6.8 mass%, Al: 3.4. To 4.6% by mass, Ti: 3.05 to 3.9% by mass, Ta: 1.5 to 3.0% by mass, W: 4.55 to 8.0% by mass, Mo: 0.5 to 2 0.5% by mass, Nb: 0.4% by mass or less, C: 0.01 to 0.20% by mass, B: 0.005 to 0.03% by mass and the balance Ni and other inevitable impurities.

  Further, preferred nickel-base alloys having excellent strength and corrosion / oxidation resistance according to the present invention are Cr: 13.1 to 15.0 mass%, Co: 1.0 to 6.8 mass%, Al: 3. 4 to 4.6% by mass, Ti: 3.05 to 3.9% by mass, Ta: 1.5 to 2.9% by mass, W: 4.55 to 8.0% by mass, Mo: 1.5 to 2.0% by mass, Nb: 0.4% by mass or less, C: 0.01 to 0.20% by mass, B: 0.005 to 0.03% by mass, the balance Ni and other inevitable impurities. .

  Further, a nickel-based alloy excellent in strength, corrosion resistance and oxidation resistance according to the present invention is preferably Cr: 13.1 to 14.5% by mass, Co: 5.0 to 6.8% by mass, Al: 3 0.6 to 4.4 mass%, Ti: 3.05 to 3.6 mass%, Ta: 1.5 to 2.9 mass%, W: 4.55 to 7.0 mass%, Mo: 0.5 ~ 2.5 mass%, Nb: less than 0.1 mass%, C: 0.05-0.12 mass%, B: 0.01-0.02 mass%, the balance Ni and other inevitable impurities is there.

  By setting it in such a range, the cast structure is excellent, stable characteristics such as the tensile strength, creep strength, corrosion resistance and oxidation resistance of the material can be obtained, and the variation of the product is reduced. As a result, the reliability of the product is improved. Moreover, since the variation range can be estimated small, for example, a design with a high allowable stress can be performed, and the performance of the product is improved.

  Hf, Re, Zr may be added to the above alloy composition. In this case, the addition amounts are Hf: 0 to 2.0 mass%, Re: 0 to 0.5 mass%, and Zr: 0 to 0.05 mass%. Further, as impurities, O and N may be increased beyond the unavoidable amount. In this case, the increase amounts are O: 0 to 0.005% by mass and N: 0 to 0.005% by mass. When an additive is added, the component amount of the alloy is adjusted by the composition of Ni and inevitable impurities.

  The above Ni-based alloy can be applied to cast products, particularly high-temperature components for gas turbines such as moving blades, stationary blades, and shrouds. Gas turbine blades or stationary blades are particularly excellent in strength, corrosion resistance, and oxidation resistance at high temperatures. Therefore, a gas turbine excellent in durability can be provided, and is particularly suitable for a land gas turbine using a fuel containing impurities.

  Hereinafter, description will be given with reference to the drawings.

  FIG. 4A shows an example of a moving blade shape of an aircraft gas turbine, and FIG. 4B shows an example of a moving blade shape of a land power generation gas turbine. Land wings and aircraft wings differ in shape and size. The land is composed of a wing part, a shank part, and a root part (dovetil part), and the size is about 10 to 100 cm and the weight is about 1 to 10 kg. On the other hand, for aircraft, it consists of a wing part and a root part (dovetil part), and the size is about 3 to 20 cm and the weight is about 0.1 to 1 kg. . Various characteristics are required for the moving and stationary blade material of the gas turbine, and the importance varies depending on the use environment. In particular, basic material properties include room temperature tensile strength, high temperature tensile strength, creep strength, corrosion resistance, and oxidation resistance. Development of a cast alloy composition having a balanced characteristic without significantly inferior to these characteristics is regarded as important. The inventors of the present application have reached the present invention as a result of studying an alloy that is a normal cast alloy and can simultaneously improve the corrosion resistance and oxidation resistance while maintaining the creep strength.

  Conventionally, as a means for improving strength, there is a technique of using a unidirectionally solidified alloy or a single crystal alloy. Unidirectionally solidified alloys and single crystal alloys are mainly used for the moving and stationary blades of small and lightweight jet engines (aviation gas turbines). By reducing the Cr content and sacrificing corrosion resistance at high temperatures, a large amount of W or Ta having a high degree of solid solution strengthening is added to increase the creep rupture strength. For this reason, the corrosion resistance and oxidation resistance characteristics at high temperatures are not sufficient, and it is an unsuitable material for a land gas turbine using a fuel with many impurities.

  Furthermore, since the wing using a unidirectionally solidified alloy or a single crystal alloy has a complicated casting process, the casting yield when the wing is cast deteriorates. In particular, the blades of land gas turbines have a large shape and a complicated shape, so that the casting yield is very low, resulting in a very expensive product.

  Although it is not so important for a land gas turbine to be lightweight, cost and reliability are required. Jet engines are inspected and overhauled in a short period of time, while gas turbines for power generation are used continuously for at least a few years.

  Therefore, conventional conventional nickel-base alloys have a conflicting characteristic that the strength at high temperatures is insufficient because corrosion resistance is important, and that the corrosion resistance and oxidation resistance characteristics are not sufficient in alloys that emphasize strength. It was. The present invention has been made in view of the above-described conventional circumstances, and improves the corrosion resistance at high temperatures without sacrificing the creep rupture strength and oxidation resistance of nickel-based ordinary cast alloys at high temperatures. I am letting.

  Although the alloy composition of this invention is as above-mentioned, below, the function of each component of a nickel base alloy and a preferable composition range are demonstrated.

Cr: 12.1 to 15.0 mass%
Cr is an element effective for improving the corrosion resistance of the alloy at a high temperature. In particular, in order to improve the corrosion resistance against molten salt corrosion, the effect increases as the Cr content is further increased. And the effect appears more remarkably from 13.1% by mass or more. However, in the alloy of the present invention, since Ti, W, Ta, etc. are added in a large amount, if the amount of Cr is excessively large, the TCP phase which is an embrittlement phase is precipitated, so that the high temperature strength and the high temperature corrosion resistance are remarkably impaired. Therefore, it is necessary to balance with other alloy elements and to set the upper limit to 15.0 mass%. In this composition range, when considering the balance between strength and corrosion resistance, it is preferably in the range of 13.1 to 14.5% by mass.

Co: 1.0 to 6.8% by mass
Co lowers the solid solution temperature of the γ 'phase (Ni ₃ Al intermetallic compound of Ni and Al) to facilitate solution treatment, and also has the effect of strengthening the γ phase by solid solution strengthening and improving high-temperature corrosion resistance. Have. Such an effect appears when the Co content is 1.0 mass% or more. On the other hand, since Ti, W, Ta, etc. are added to the alloy of the present invention, if the Co content exceeds 6.8% by mass, the balance with other alloy elements is lost, and the precipitation of the γ ′ phase occurs. Is suppressed and the high-temperature strength is lowered, so that it is necessary to make it 6.8% by mass or less. In the composition range of the present invention, when considering the balance between the ease of solution heat treatment and the strength, it is preferably in the range of 5.0 to 6.5% by mass.

W: 4.55-8.0 mass%
W is an element effective for increasing the creep strength by solid solution strengthening by forming a solid solution in the matrix γ phase and the precipitation γ ′ phase. And in order to acquire such an effect sufficiently, content of 4.55 mass% or more is required. However, W has a large specific gravity and not only increases the mass of the alloy, but also reduces the corrosion resistance of the alloy at high temperatures. Further, in the case of an alloy having a large amount of Ti and Cr such as the alloy of the present invention, when it exceeds 8.0% by mass, acicular α-W precipitates, and the creep strength, high temperature corrosion resistance and toughness are lowered. It is necessary to make it 8.0 mass%.

  In the composition range of the present invention, when considering the balance of strength at high temperature, corrosion resistance, and structure stability at high temperature, it is preferably in the range of 4.55 to 7.0% by mass.

Ta: 1.5-3.0 mass%
Ta forms a solid solution in the form of [Ni ₃ (Al, Ta)] in the γ ′ phase and strengthens the solution. This improves the creep strength. In order to sufficiently obtain this effect, a content of 1.0% by mass or more is necessary. When the content is 3.0% by mass or more, supersaturation occurs and acicular δ phase [Ni, Ta] precipitates, Reduce creep strength. Therefore, the upper limit needs to be 3.0 mass%. In this composition range, when considering the balance between strength and structure stability at high temperature, the range is preferably 2.0 to 2.9% by mass.

  W is solid-solved in the matrix γ phase and the precipitated γ ′ phase, and the creep strength is increased by solid solution strengthening, while Ta is dissolved in the precipitated γ ′ phase and solid solution strengthened. Increases the creep strength. Therefore, the effect of increasing the creep strength is greater as a synergistic effect when the two elements are added simultaneously than when they are added individually. Therefore, for Ta and W, it is effective to define the composition range in the total amount of (Ta + W). In order to sufficiently obtain this synergistic effect, a content of (Ta + W) of 6.0% by mass or more is necessary. However, when the added amount of (Ta + W) is 10.0% by mass or more, supersaturation occurs, and acicular α-W precipitates, and the creep strength is lowered. Therefore, the upper limit needs to be 10.0 mass%. In this composition range, when considering the balance between strength and structure stability at high temperatures, it is preferably in the range of 7.0 to 9.0% by mass, more preferably in the range of 7.5 to 8.5% by mass. It is.

Mo: 0.5 to 2.5% by mass
Since Mo has the same effect as W, it can be replaced with a part of W if necessary. Moreover, since the solid solution temperature of the γ ′ phase is increased, the creep strength is improved although not as high as W. And in order to acquire such an effect, content of 0.5 mass% or more is required. Moreover, since Mo has a smaller specific gravity than W, the weight of the alloy can be reduced. On the other hand, Mo decreases the oxidation resistance and corrosion resistance of the alloy, so even if it is added, the upper limit thereof needs to be 2.5% by mass. In this composition range, when considering the balance of strength at high temperature, corrosion resistance and oxidation resistance at high temperature, the range is preferably 1.5 to 2.5% by mass, more preferably 1.58 to 2%. The range is 0.0 mass%.

Ti: 2.8 to 3.9% by mass
Ti, like Ta, strengthens the γ ′ phase in the form of [Ni ₃ (Al, Ta, Ti)], but is not as effective as Ta. Rather, Ti has the effect of significantly improving the corrosion resistance of the alloy at high temperatures. In particular, in order to have an effect on the corrosion resistance against molten salt corrosion, a content of 2.8% by mass or more is necessary. However, if added over 3.9% by mass, the oxidation resistance is remarkably deteriorated, and the embrittled η phase is precipitated, so the upper limit must be 3.9% by mass. In an alloy containing 13.1 to 16.0% by mass of Cr as in the case of the present invention alloy, it is preferably 3.05 to 3.9% by mass in consideration of the balance between strength, corrosion resistance and oxidation resistance at high temperatures. More preferably, it is the range of 3.05-3.6 mass%.

Al: 3.4 to 4.6% by mass
Al is a main constituent element of the γ ′ phase [Ni ₃ Al] which is a precipitation strengthening phase, and thereby the creep strength is improved. It also greatly contributes to the improvement of oxidation resistance. In order to sufficiently obtain these effects, a content of 3.4% by mass or more is necessary. Since the alloy of the present invention has a high content of Cr, Ti, and Ta, when it exceeds 4.6% by mass, the γ ′ phase [Ni ₃ (Al, Ta, Ti)] is excessively precipitated, on the contrary, the strength is increased. In addition to lowering, forming a complex oxide with chromium and lowering the corrosion resistance, it is necessary to set the range of 3.4 to 4.6% by mass. In this composition range, when considering the balance between strength at high temperature, oxidation resistance, and corrosion resistance, the range is preferably 3.6 to 4.4% by mass.

Nb: 0 to 0.4% by mass
Nb, like Ti, is solid solution strengthened in the form of [Ni ₃ (Al, Nb, Ti)] in the γ ′ phase, and solid solution strengthening is more effective than Ti. Moreover, although there is no remarkable effect like Ti, there exists an effect which improves the corrosion resistance in high temperature. However, in the moving and stationary blades of the gas turbine for power generation where the solidification rate is slow, Nb carbides combined with C are coarsened, and characteristics such as castability and workability are deteriorated. In order to improve castability, workability, etc., it is necessary to suppress the precipitation of coarse Nb carbides, so the upper limit of the alloy of the present invention needs to be 0.4% by mass. In the alloy of the present invention, when used in unidirectional solidification casting, the content is preferably less than 0.01% by mass, and is substantially not added.

  Accordingly, the above components (Cr: 12.1 to 15.0% by mass, Co: 1.0 to 6.8% by mass, Al: 3.4 to 4.6% by mass, Ti: 2.8 to 3) 9.9% by mass, Ta: 1.5 to 3.0% by mass, W: 4.55 to 8.0% by mass, Mo: 0.2 to 2.5% by mass, Nb: 0.4% by mass or less, C: 0.05 to 0.20% by mass, B: 0.005 to 0.03% by mass), and Ni-based alloy composed of inevitable impurities and the balance Ni is a cast structure, high temperature strength, oxidation resistance, corrosion resistance. Excellent. This Ni-based alloy has characteristics that are balanced in corrosion resistance at high temperature, oxidation resistance, and creep rupture strength. Therefore, in a power engine such as a gas turbine using a fuel with a large amount of impurities, it can sufficiently cope with the use environment thereof, and an effect excellent in corrosion resistance and oxidation resistance is brought about. Further, in a land gas turbine using a fuel with a large amount of impurities, it is possible to achieve an improvement in thermal efficiency by increasing the combustion gas temperature.

  Further, the Ni-based alloy containing the components in the above composition range may contain Hf, Re, C, B, Zr, and O as appropriate. In addition to the above-described components, the preferred range is that Hf: 0 to 2.0 mass%, Re: 0 to 0.5 mass%, Zr: 0 to 0.05 mass%, O: It is an alloy comprising Ni and other inevitable impurities with the balance being within the limits of 0 to 0.005 mass% or less, N: 0 to 0.005 mass% or less.

Hf: 0 to 2.0% by mass
Although Hf hardly contributes to the improvement of strength, it improves corrosion resistance and oxidation resistance at high temperatures by improving the adhesion of a protective film (for example, Cr ₂ O ₃ , Al ₂ O ₃ ) formed on the alloy surface. When the amount of Hf added is increased, the adhesion of the protective film is improved. However, in the alloy of the present invention, if the amount of Hf added exceeds 2.0% by mass, a large amount of [Ni ₃ (Hf, Ti)] eutectic is formed, and the melting point of the nickel-base alloy is remarkably lowered. In order to make the heat treatment difficult, it is necessary to set the upper limit to 2.0 mass%. In the alloy of the present invention, it is preferably 0.1% by mass or less, and is not substantially added.

Re: 0 to 0.5% by mass
Re can be replaced with part of W if necessary, and is an element effective for improving the corrosion resistance of the alloy while increasing the creep strength by solid solution strengthening in the γ phase as a matrix. It is. However, Re is expensive and has a large specific gravity and increases the specific gravity of the alloy. In addition, in an alloy containing 12.1 to 16.0% by mass of Cr, such as an alloy of the present invention, if it exceeds 0.5% by mass, it promotes precipitation of acicular α-W or α-Re (Mo), In order to reduce the creep strength and toughness, the upper limit needs to be 0.5 mass%. In the alloy of the present invention, the content is preferably 0.1% by mass or less, and more preferably substantially not added.

C: 0.01-0.2 mass%
C segregates at the crystal grain boundaries to improve the strength of the crystal grain boundaries, and partly forms carbides (TiC, TaC, etc.) and precipitates in a lump shape. In order to segregate at the grain boundaries and increase the grain boundary strength, addition of 0.01% by mass or more is necessary, but if added over 0.2% by mass, excessive carbides are formed and creep at a high temperature. Since the strength and ductility are lowered and the corrosion resistance is also lowered, the upper limit needs to be 0.2% by mass. In this composition range, considering the balance of strength, ductility and corrosion resistance, the range is preferably 0.05 to 0.12% by mass.

B: 0.005 to 0.03 mass%
B segregates at the grain boundaries to improve the strength of the grain boundaries and partly forms boride [(Cr, Ni, Ti, Mo) ₃ B ₂ ] and precipitates at the grain boundaries of the alloy. In order to increase the grain boundary strength by segregating at the grain boundaries, addition of 0.005% by mass or more is necessary. However, since this boride has a lower melting point than the melting point of the alloy, the melting temperature of the alloy is significantly reduced. Therefore, the upper limit is set to 0.03 mass%. In this composition range, considering the balance between strength and solution heat treatment property, the range is preferably 0.01 to 0.02 mass%.

Zr: 0 to 0.05% by mass
Zr segregates at the grain boundaries and has the effect of improving the strength of the grain boundaries, but most of them form nickel and an intermetallic compound [Ni ₃ Zr], which are the main components of the alloy, at the grain boundaries. Since this intermetallic compound lowers the ductility of the alloy and has a remarkably low melting point, it has many harmful effects such as lowering the melting temperature of the alloy and making the solution treatment temperature difficult. It is necessary to make it 05% by mass or less. In the alloy of the present invention, it is preferably 0.03% by mass or less, more preferably 0.01% by mass or less and substantially not added.

O: 0 to 0.005 mass% or less, N: 0 to 0.005 mass% or less These elements are impurities, all of which are often brought from the alloy raw material, and O also enters from the crucible, Exists in a lump as an oxide (Al ₂ O ₃ ) or a nitride (TiN or AlN). If these are present in the casting, it becomes the starting point of cracks during creep deformation, which lowers the creep rupture life or decreases the fatigue life as the starting point of fatigue crack generation. In particular, O appears as an oxide on the surface of the casting, thereby causing a surface defect of the casting and causing a reduction in the yield of the casting. Accordingly, the lower the content of these elements, the better. However, since it cannot be reduced to 0 when an actual ingot is made, the upper limit of both elements is set to 0.005% by mass as a range in which the characteristics are not greatly deteriorated. .

  Table 1 shows the chemical compositions of the inventive alloys (A1 to A12), and Table 2 shows the chemical compositions of the comparative alloys (H1 to H8) and the existing alloys (C1 to C5). The existing alloy C1 is disclosed in JP-A-2004-197131, C2 is disclosed in JP-B-46-27144, C3 is disclosed in JP-A-2010-084166, and C4 is disclosed in JP-A-51-34819. Is an alloy disclosed in JP-A-6-57359.

  Each alloy was melted using a vacuum induction furnace using a refractory crucible having a capacity of 12 kg, and each alloy was formed into an ingot having a diameter of 80 mm and a length of 300 mm. Next, the melted ingot was vacuum melted with an alumina crucible and cast into a ceramic mold heated to 1000 ° C. to cast a test piece having a diameter of 20 mm and a length of 150 mm. After casting, the test piece was subjected to solution heat treatment and aging heat treatment shown in Table 3.

  The heat-treated test piece is machined to produce a creep test piece having a parallel part diameter of 6.0 mm and a parallel part length of 30 mm, a high-temperature oxidation test piece having a length of 25 mm, a width of 10 mm, and a thickness of 1.5 mm, and 15 mm × 15 mm × 15 mm. A high temperature corrosion test piece having a cubic shape was cut out and the microstructure was examined with a scanning electron microscope to evaluate the structural stability of the alloy.

Table 4 shows the characteristic evaluation test conditions performed on the alloy specimens of the present invention. The creep rupture test was performed under the condition of 1255K-138 MPa. In the high-temperature oxidation test, the oxidation test held for 1423 K-20 hours was repeated 10 times, and the change in mass was measured for each. Further, the high temperature corrosion test, 850 ° C. molten salt _{(composition, Na 2 SO 4: 75%} , NaCl: 25%) 3 times a test of immersing for 20 hours in a (total 60 hours) was measured conducted mass change .

  Table 5, FIG. 1, FIG. 2, and FIG. 3 show the property evaluation test results of the alloys shown in this example. Table 5 lists the results. FIG. 1 is a graph showing the creep rupture time at 1255 K-138 MPa, FIG. 2 is a bar graph of the oxidation weight loss in the high temperature oxidation test, and FIG. 3 is the corrosion weight loss in the molten salt immersion corrosion test.

As is apparent from the results shown in Table 5, the inventive alloys A1 to A12 have slightly inferior oxidation resistance, but the creep rupture time has a slightly superior creep rupture strength than that of the existing alloy C1, and the corrosion weight loss. Is greatly reduced and the corrosion resistance is greatly improved. The feature of the alloy of the present invention is that the Nb amount is reduced with respect to C1 of the prior application, thereby improving the castability and workability, and further increasing the amount W by which Nb is reduced, at a high temperature. Increases creep strength. Moreover, the corrosion resistance and the oxidation resistance are enhanced by balancing the Ti amount and the Al amount.
Compared with another existing alloy C2, the alloy examples A1 to A12 of the present invention have improved creep strength and oxidation resistance while maintaining substantially the same corrosion resistance. In particular, the improvement in oxidation resistance is remarkable. In the alloy of the present invention, the oxidation resistance is greatly improved by significantly reducing the amount of Mo and further reducing the amount of Ti with respect to C2. On the other hand, since the creep strength at high temperature is remarkably lowered by reducing the amount of Mo, the amount of addition of W and Ta is increased, and the amount of Co is further reduced to increase the creep strength at high temperature.

  Moreover, compared with the existing alloy C3, although the alloy of the present invention is slightly inferior in corrosion resistance, the creep strength and oxidation resistance are improved, and the creep rupture time is also greatly improved. In the alloy of the present invention, the creep strength at high temperature is increased by decreasing the Ti amount and Nb amount relative to C3 and increasing the amount of Mo added accordingly. When the amount of Mo is increased, the oxidation resistance is deteriorated. However, in the alloy of the present invention, the oxidation resistance is improved by increasing the Al content to the limit.

  In addition, compared with the existing alloy C4, the alloy according to the present invention has almost the same corrosion resistance but improved creep strength and oxidation resistance, and in particular, the creep rupture time is more than doubled. In the alloy of the present invention, the oxidation resistance is improved by reducing the Ti content and increasing the Al content relative to C4. Furthermore, the creep strength at high temperature is increased by reducing the amount of Co and increasing the amount of W added accordingly.

  Moreover, when compared with another existing alloy C5, it can be seen that the creep rupture time is substantially the same and the oxidation resistance is substantially the same, but the corrosion resistance to the molten salt is remarkably improved. In the alloy of the present invention, for C5, the amount of Ti was increased and the corrosion resistance against the molten salt was improved. If the Ti amount is simply increased in a C5 alloy, the balance of the alloy is greatly lost, and the heterogeneous phase is significantly precipitated. Therefore, the amount of Ta and Co was reduced to balance the entire alloy.

  In other words, the alloy according to the present invention has significantly improved the corrosion resistance and oxidation resistance to molten salt at high temperature without sacrificing the high temperature creep rupture life, and the balance of creep strength, oxidation resistance and corrosion resistance is balanced. It was found to be an alloy.

  On the other hand, Comparative Alloys H1 to H8 have almost the same composition as the alloys of the present invention, but do not satisfy the component range, and therefore are inferior in creep rupture strength, oxidation resistance characteristics, or corrosion resistance characteristics. And do not satisfy all the characteristics.

  From the above, it is clear that the alloy of the present invention is balanced in all the points of creep rupture strength, oxidation resistance, and corrosion resistance, and is more practical than existing alloys. A moving blade of a gas turbine is used in a high-temperature gas of 1300 ° C. or higher while the inside is cooled with air.

  Therefore, the moving blades must have excellent creep strength, corrosion resistance, and oxidation resistance. Since the moving blade receives a centrifugal force due to rotation, it needs a creep strength that can withstand it. However, as the creep strength is higher, the amount of internal cooling air can be reduced and the thermal efficiency can be improved.

  On the other hand, the blade life (use period) is hardly determined by the creep strength, and is often determined by local damage due to oxidation or corrosion. The average metal temperature of the rotor blade is suppressed to 800 to 900 ° C. from the viewpoint of creep strength, but the temperature rises locally at the poorly cooled part, for example, the tip part of the blade or the blade surface, and due to oxidation Since the blade life is significantly shortened due to damage, excellent oxidation resistance is required to use the blade until its design life. Further, the dovetail portion of the moving blade is embedded in the disk, but the temperature of the dovetail portion is generally 500 ° C. or less. Therefore, the temperature of the blade decreases toward the dovetail portion, and the blade surface at a temperature (850 to 900 ° C.) at which molten salt corrosion occurs appears. In this case, a gas turbine using a clean fuel such as LNG hardly causes molten salt corrosion. However, a gas turbine using a fuel with a large amount of impurities suffers corrosion damage and significantly shortens the blade life. End up. In extreme cases, there may occur an accident in which the blade is damaged starting from the part that has been damaged by corrosion. In order to use the blade until its design life, excellent corrosion resistance is required.

  On the other hand, a major feature of gas turbines is that they can be operated in response to a wide range of fuels from gas to liquid. For example, the gas fuel includes LNG and off-gas. In a gas turbine using LNG, an alloy excellent in oxidation resistance is suitable. However, in a gas turbine using off-gas having many impurities, it is necessary to have excellent oxidation resistance and corrosion resistance. On the other hand, liquid fuel includes light oil and heavy oil, and these contain corrosive components such as S and Na. Therefore, gas turbines using these fuels have excellent oxidation resistance and corrosion resistance. is necessary. In addition, since gas turbines have different installation locations, operating conditions, and fuels for each unit, the moving and stationary blade materials are excellent in both corrosion resistance and oxidation resistance characteristics in order to cope with them. Things are necessary. As described above, the alloy of the present invention is excellent in all of the creep strength, corrosion resistance, and oxidation resistance characteristics from the characteristics required for the moving and stationary blades of the gas turbine, and can be operated corresponding to a wide range of fuels from gas to liquid. It is a material suitable for gas turbines.

  In the examples, the effect as a normal cast material has been described, but it is also very effective to use it as a unidirectionally solidified blade obtained by unidirectionally solidifying the alloy of the present invention. In particular, the alloy of the present invention has a composition in which carbides do not coarsen even when unidirectionally solidified, and thus, by unidirectionally solidifying, the creep rupture strength can be significantly improved while maintaining corrosion resistance and oxidation resistance characteristics. . Furthermore, the alloy of the present invention contains C and B which are effective for strengthening grain boundaries, and it is possible to add Hf which is effective for suppressing grain boundary cracking during casting, if necessary. Therefore, the alloy composition is suitable for use as a unidirectional solidified material.

Claims (8)

It is a normal casting made of equiaxed crystals using a nickel-based alloy,
The nickel-base alloy is Cr: 12.1 to 15.0 mass%, Co: 1.0 to 6.8 mass%, Al: 3.4 to 4.6 mass%, Ti: 2.8 to 3. 9% by mass, Ta: 1.5 to 3.0% by mass, W: 4.55 to 8.0% by mass, Mo: 0.5 to 2.5% by mass, Nb: 0.4% by mass or less, C 0.01 to 0.20 mass%, B: 0.005 to 0.03 include mass% and unavoidable impurities, Ri balance Ni der, the total content of Ta and W 6.0-10. A nickel-base alloy normal casting characterized by 0% by mass . 2. A nickel-base alloy ordinary cast product according to claim 1, wherein Cr: 13.1 to 15.0 mass% and Ti: 3.05 to 3.9 mass%. In Claim 1, Cr: 13.1-15.0 mass%, Ti: 3.05-3.9 mass%, Ta: 1.5-2.9 mass%, Mo: 1.5-2.0. A nickel-base alloy normal casting characterized by a mass%. In Claim 1, Cr: 13.1-14.5 mass%, Co: 5.0-6.8 mass%, Al: 3.6-4.4 mass%, Ti: 3.05-3.6 % By mass, Ta: 1.5 to 2.9% by mass, W: 4.55 to 7.0% by mass, Nb: less than 0.1% by mass, C: 0.05 to 0.12% by mass, B: A nickel-base alloy ordinary cast product characterized by being 0.01 to 0.02 mass%. 5. The method according to claim 1, further comprising: Hf: 0 to 0.1 mass% or less, Re: 0 to 0.1 mass% or less, Zr: 0 to 0.03 mass% or less, O: 0 to 0 A nickel-base alloy ordinary cast product characterized by containing 0.005 mass% or less and N: 0 to 0.005 mass% or less. A gas turbine blade comprising a nickel-base alloy ordinary cast product according to any one of claims 1 to 5. A gas turbine comprising the gas turbine blade according to claim 6 . 8. The gas turbine according to claim 7 , wherein the fuel of the gas turbine is light oil, heavy oil, or off-gas containing a corrosive component.