JP5395516B2 - Nickel-based alloy for steam turbine turbine rotor and steam turbine turbine rotor - Google Patents

Description

  The present invention relates to a nickel-base alloy for a turbine rotor of a steam turbine and a turbine rotor of a steam turbine.

The proportion of thermal power generation in Japan's total power generation today is approximately 60%, and the dependence on fossil fuels is still high. Among them, coal is widely distributed all over the world and has an advantage in terms of supply stability. For this reason, the development of a coal-fired power generation system as a base power source is being promoted together with nuclear power in Japan. However, the CO ₂ emission per unit power of coal is higher than that of other fossil fuels. Is an important issue.

  In order to improve the power generation efficiency of the steam turbine, it is effective to raise the turbine steam temperature. For this reason, in the recent steam turbine thermal power plant, the steam temperature is raised to 600 ° C. or higher. In the future, the steam temperature in a steam turbine thermal power plant has become a global trend of 650 ° C., more preferably 700 ° C. or higher.

  In the turbine rotor that supports the rotating blades that receive the high-temperature steam, the high-temperature steam circulates also around the turbine rotor, so that the temperature becomes high and high stress is generated by the rotation. Therefore, the turbine rotor needs to withstand high temperature and high stress, and a material having excellent strength, ductility, and toughness in a range from room temperature to high temperature is required as a material for the turbine rotor.

  When the steam temperature exceeds 700 ° C., the conventional iron-based material lacks high temperature strength. Conventionally, nickel-based alloys have been known as materials having excellent high-temperature strength (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). For this reason, it has been studied to apply a nickel base alloy to a turbine rotor or the like.

Nickel-based alloys are roughly classified into a precipitation strengthening type and a solid solution strengthening type. The former precipitates a precipitation phase called gamma prime phase (γ 'phase) (Ni ₃ (Al, Ti)) or gamma double prime phase (Ni ₃ Nb) by adding Al, Ti, Ta, Nb to nickel. By doing so, the strength at high temperature is improved. A typical precipitation strengthened nickel alloy is Inconel 706 alloy (manufactured by Special Metal). The latter reinforces the nickel matrix itself by adding Co, Mo or the like to nickel, and corresponds to Inconel 617 alloy (made by Special Metal).

Japanese Unexamined Patent Publication No. 7-150277 Japanese Patent No. 2862487 US Patent Application Publication No. 2005/0244296

  As described above, in a steam turbine in which the steam temperature exceeds 700 ° C., application of a nickel-base alloy is being studied because the high-temperature strength of iron-based materials is insufficient. For this reason, while maintaining the workability such as forgeability, the high temperature strength is satisfied, and even when exposed to a high temperature for a long period of time, the soundness and structure stability of the material can be maintained over a long period of time. There is a need to develop a nickel-based alloy that can be used.

  The present invention has been made in response to the above-described conventional circumstances, has high high-temperature strength while maintaining workability such as forgeability, and also has soundness and structure stability over a long period of time even in a high-temperature environment. It is an object of the present invention to provide a nickel-base alloy for a turbine rotor of a steam turbine and a turbine rotor of a steam turbine capable of maintaining the above.

The nickel-base alloy for the turbine rotor of the steam turbine according to one aspect of the present invention is, in mass%, C: 0.01 to 0.15, Cr: 22.98 to 28, Co: 10 to 15, Mo: 4 to 7 Al: 0.3 to 2.0, Ti: 0.3 to 3.0, B: 0.001 to 0.035, and the balance is made of Ni and inevitable impurities.

  According to the present invention, a nickel-base alloy and steam that maintain high workability such as forgeability, have high high-temperature strength, and can maintain soundness and structural stability over a long period of time even in a high-temperature environment. A turbine rotor for a turbine may be provided.

The graph which shows the relationship between Mo density | concentration in Inconel 617, and the mole fraction of each phase. (A) And (b) is an electron micrograph which shows the structure | tissue of the nickel base alloy for turbine rotors of the steam turbine which concerns on embodiment of this invention, and the structure | tissue of Inconel 617 alloy. The graph which shows a greeble test result. The electron micrograph which shows the structure | tissue of the conventional nickel base alloy.

  Embodiments of the present invention will be described below with reference to the drawings. The nickel-base alloy for the turbine rotor of the steam turbine according to the present embodiment is improved in mechanical strength at high temperatures while maintaining the workability such as forgeability of the conventional nickel-base alloy by finely adjusting the composition component range. And maintaining the soundness of the material over a long period of time. As a result, as a turbine rotor material for a steam turbine into which high-temperature steam is introduced, high reliability can be maintained over a long period of tens of thousands of hours in a high-temperature environment. Realization is possible.

  As described above, nickel bases such as Inconel 706 and Inconel 617 are extremely useful materials as a turbine rotor material. However, in order to further improve the efficiency of steam turbine power generation equipment, processing such as forgeability of a nickel base alloy is required. Therefore, there has been a need for an improved composition that can ensure long-term reliability while satisfying the properties and high-temperature strength.

  For example, Inconel 617 is an alloy that improves the high-temperature strength by solid solution strengthening of the Ni-based matrix by adding Co and Mo, and by γ ′ phase precipitation by adding Al, Ti, Ta, and Nb. It is possible to further increase the high temperature strength. However, excessive addition of added components may cause a decrease in strength due to precipitation of a phase that causes weakening, which is called a harmful phase. The nickel-base alloy for the turbine rotor of the steam turbine according to the present embodiment is intended to suppress precipitation of harmful phases that cause weakening while utilizing solid solution strengthening and γ ′ phase precipitation strengthening.

  Details will be described below. Addition of Al and Ti to conventional Inconel 617 increases the amount of precipitated γ 'phase and improves the creep strength. However, as shown in FIG. Precipitation of σ phase is promoted. In addition, the alloy shown in FIG. 4 is C: 0.1 mass%, Cr: 23 mass%, Co: 12 mass%, Mo: 10 mass%, Al: 3.0 mass%, Ti: 0.3 mass%. The balance consists of Ni and inevitable impurities.

  Precipitation of such a hard and brittle σ phase TCP (Topological Closed Packed) phase is said to cause a decrease in mechanical properties such as impact value, creep properties, and low cycle fatigue life. This is thought to be due to the fact that cracks are likely to propagate along such plate-like or needle-like precipitates, and that the strengthening elements contained in the parent phase are consumed by the formation of such precipitates. It has been.

  According to the equilibrium calculation result of Inconel 617 shown in FIG. 1 with the vertical axis representing the mole fraction of each phase and the horizontal axis representing the Mo concentration (mass%), the amount of precipitation of the σ phase greatly depends on the amount of Mo, and the σ phase precipitation In order to suppress this, the Mo concentration needs to be about 7% by mass or less. Therefore, in the present embodiment, the Mo amount is 4 to 7% by mass, and Ta and Nb are further added as necessary to stably precipitate the γ ′ phase and improve the stability of the γ ′ phase itself. As a result, high strength of the nickel-base alloy was achieved.

  The nickel-base alloy for the turbine rotor of the steam turbine according to the present embodiment is configured in the composition range shown below. In the following description, “%” representing an alloy composition component is “% by mass” unless otherwise specified.

(Alloy 1)
C: 0.01-0.15 mass%, Cr: 22.98-28 mass%, Co: 10-15 mass%, Mo: 4-7 mass%, Al: 0.3-2.0 mass%, A nickel-base alloy for a turbine rotor of a steam turbine comprising Ti: 0.3 to 3.0% by mass, B: 0.001 to 0.035% by mass, the balance being Ni and inevitable impurities.

(Alloy 2)
C: 0.01-0.15 mass%, Cr: 22.98-28 mass%, Co: 10-15 mass%, Mo: 4-7 mass%, Al: 0.3-2.0 mass%, Ti: 0.3-3.0% by mass, B: 0.001-0.035% by mass, Ta: 0.1-0.7% by mass, the balance of the steam turbine made of Ni and inevitable impurities Nickel base alloy for turbine rotor.

(Alloy 3)
C: 0.01-0.15 mass%, Cr: 22.98-28 mass%, Co: 10-15 mass%, Mo: 4-7 mass%, Al: 0.3-2.0 mass%, Ti: 0.3-3.0% by mass, B: 0.001-0.035% by mass, Nb: 0.1-0.4% by mass, the balance of the steam turbine made of Ni and inevitable impurities Nickel base alloy for turbine rotor.

(Alloy 4)
C: 0.01-0.15 mass%, Cr: 22.98-28 mass%, Co: 10-15 mass%, Mo: 4-7 mass%, Al: 0.3-2.0 mass%, Ti: 0.3-3.0% by mass, B: 0.001-0.035% by mass, Ta: 0.1-0.7% by mass, Nb: 0.1-0.4% by mass, The balance is a nickel-based alloy for a turbine rotor of a steam turbine composed of Ni and inevitable impurities.

(Alloy 5)
C: 0.01-0.15 mass%, Cr: 22.98-28 mass%, Co: 10-15 mass%, Mo: 4-7 mass%, Al: 0.3-2.0 mass%, Ti: 0.3-3.0% by mass, B: 0.001-0.035% by mass, Ta + 2Nb = 0.1-0.7% by mass, with the balance being a steam turbine made of Ni and inevitable impurities Nickel base alloy for turbine rotor.

  Here, in the inevitable impurities in the nickel base alloy for the turbine rotor of the steam turbine of the above (Alloy 1) to (Alloy 5), among the inevitable impurities, at least the Si content is 0.1% or less, and the Mn content is Is preferably reduced to 0.1% or less. Inevitable impurities include Fe and Cu.

  According to the nickel-base alloy for the turbine rotor of these steam turbines, the mechanical strength at high temperature and the workability such as forgeability of the conventional nickel-base alloy are maintained by being configured in the above-described composition component range. The soundness of the material over a long time is improved. In addition, at least a predetermined portion of the turbine rotor penetrating the steam turbine into which the high-temperature steam is introduced can be constituted by any one of the above-described nickel-base alloys for the turbine rotor of the steam turbine. According to this turbine rotor, the high-temperature strength can be improved, and it has high reliability even in a high-temperature environment.

  Next, the reason for limitation of each composition component range in the nickel base alloy for turbine rotors of the steam turbine according to the above-described embodiment will be described.

C (carbon)
C is useful as a constituent element of M ₂₃ C ₆ type carbide, which is a strengthening phase. Particularly in a high temperature environment of 650 ° C. or higher, precipitation of M ₂₃ C ₆ type carbide during turbine operation causes creep of the alloy. This is one of the factors that maintain strength. It also has the effect of ensuring the fluidity of the molten metal during casting. When the C content is less than 0.01%, a sufficient precipitation amount of carbide cannot be secured, so that the strength is lowered and the fluidity of the molten metal during casting is significantly lowered. On the other hand, if the C content exceeds 0.15%, the tendency of component segregation during the production of large ingots increases and the formation of M ₆ C type carbides, which are embrittled phases, is promoted and the strength is improved. Sex declines. For this reason, the C content is determined to be 0.01 to 0.15%.

Cr (chrome)
Cr is an essential element for enhancing the oxidation resistance, corrosion resistance, and strength of the nickel-based alloy. Further, it is indispensable as a constituent element of M ₂₃ C ₆ type carbide, and particularly in a high temperature environment of 650 ° C. or higher, the creep strength of the alloy is maintained by precipitating M ₂₃ C ₆ type carbide during turbine operation. . Moreover, Cr improves the oxidation resistance in a high temperature steam environment. When the Cr content is less than 22.98 %, the oxidation resistance is lowered, and when the Cr content exceeds 28%, the precipitation of M ₂₃ C ₆ type carbides is remarkably promoted to increase the coarsening tendency. Therefore, the Cr content is determined to be 22.98 to 28%.

Co (Cobalt)
Co is a solid solution in the parent phase in the nickel-based alloy and has a strengthening action on the parent phase. If the Co content is less than 10%, the strength decreases, and if the Co content exceeds 15%, a harmful intermetallic compound phase is generated, and the forgeability decreases. For this reason, the Co content is determined to be 10 to 15%.

Mo (molybdenum)
Mo has an effect of increasing the strength of the matrix phase by dissolving in the nickel matrix phase, and also increasing the stability of the carbide by partially replacing the M ₂₃ C ₆ type carbide. However, as described above, when the Mo content exceeds 7%, precipitation of the σ phase, which is a harmful phase, is promoted together with the above strengthening, and as a result, mechanical properties such as impact value, creep characteristics, and low cycle fatigue life are reduced. cause. When the Mo content is less than 4%, precipitation of the σ phase is suppressed, but the strengthening effect cannot be obtained. For this reason, the Mo content is determined to be 4 to 7%.

Al (aluminum)
Al forms a γ ′ phase (Ni ₃ (Al, Ti)) together with nickel, and strengthens the nickel-base alloy by precipitation. If the Al content is less than 0.3%, the strength decreases. When the Al content exceeds 3.0, σ phase precipitation is caused regardless of the concentration of other additive components. Therefore, the Al content is determined to be 0.3 to 3.0%.

Ti (titanium)
Ti, like aluminum, produces a γ ′ phase (Ni ₃ (Al, Ti)) together with nickel and strengthens the nickel-based alloy. When the Ti content is less than 0.3%, the strength is the same as that of the conventional material. When the Ti content exceeds 3%, the hot workability is lowered, the forgeability is lowered, and σ phase precipitation is caused. Or For this reason, the Ti content is determined to be 0.3 to 3.0%.

B (boron)
B segregates at the grain boundaries and improves the high temperature characteristics. This effect is manifested when the B content is 0.001% or more. Therefore, the B content needs to be 0.001% or more. However, if the B content is excessive and the B content exceeds 0.035%, grain boundary embrittlement may occur. Therefore, the B content is determined to be 0.001 to 0.035%.

Ta (tantalum)
Ta dissolves in the γ 'phase and has the effect of stabilizing the precipitation strengthening phase, so it is contained as necessary. When the Ta content is less than 0.1%, the above effects are not exhibited. When the Ta content exceeds 0.7%, the strength is improved, but the forgeability is lowered. For this reason, the content rate of Ta was made into 0.1 to 0.7%.

Nb (Niobium)
Nb, like Ta, has the effect of forming a solid solution in the γ ′ phase, increasing the strength, and stabilizing the precipitation strengthening phase. When the Nb content is less than 0.1%, the above-described effects are not exhibited. When the Nb content exceeds 0.4%, the strength is improved but the forgeability is lowered. For this reason, the Nb content is determined to be 0.1 to 0.4%.

Mn (manganese)
In the case of plain steel, brittleness is prevented by adding Mn to S (sulfur) resulting from brittleness. However, the nickel content of the nickel-based alloy is extremely small, and it is not necessary to add Mn. For this reason, it is preferable to remove Mn as much as possible, and the Mn content is set to 0.1% or less.

Si (silicon)
In the case of ordinary steel, Si is added to supplement the corrosion resistance. However, in the case of a nickel-base alloy, the Cr content is high and sufficient corrosion resistance can be secured. For this reason, it is preferable to remove Si as much as possible, and the Si content is set to 0.1% or less.

  FIG. 2A shows an electron micrograph of a conventional Inconel 617, and FIG. 2B shows an electron micrograph of a nickel-based alloy for a turbine rotor of a steam turbine according to this embodiment. As shown in FIG. 2 (b), in the nickel-base alloy for the turbine rotor of the steam turbine according to the present embodiment, by setting the alloy composition range as described above, the γ phase is finely suppressed while suppressing the precipitation of the σ phase. It was possible to stably precipitate the γ ′ phase, and even when compared with Inconel 617, it was possible to obtain a better structure state.

  Next, the preferable manufacturing method of the nickel base alloy for turbine rotors of the steam turbine which concerns on this embodiment is demonstrated. First, the alloy whose components are adjusted as described above is melted and cast by a conventional method. Thereafter, the steel ingot is subjected to stabilization treatment, normal hot forging, and solution treatment. In the solution treatment after hot forging, it is desirable that the temperature be higher than the melting temperature of the γ ′ phase and lower than the local melting start temperature.

  The conditions for the stabilization treatment and the solution treatment differ depending on the alloy composition and the size of the processed material. In the case of the stabilization treatment, for example, the treatment can be performed by heating at 1000 ° C. to 1250 ° C. for 3 to 72 hours. In the case of a process, it can carry out by 1000 to 1200 degreeC, the heating for 3 to 24 hours, and subsequent rapid cooling, for example. These processes may be performed in multiple stages. Furthermore, early precipitation of the γ ′ phase can be achieved by performing an aging treatment at 700 ° C. to 800 ° C. for 3 to 24 hours as necessary. These processes may be performed in multiple stages.

  The results of investigating the alloy composition, high temperature strength characteristics and workability of the nickel base alloy for the turbine rotor of the steam turbine of the example of the present invention and the nickel base alloy of the comparative example will be described. Table 1 shows the alloy compositions of the nickel-base alloy for the turbine rotor of the steam turbine of these examples and the nickel-base alloy of the comparative example.

  20 kg of nickel-base alloy having chemical components shown in Table 1 was melted in a vacuum induction melting furnace, and forgings were obtained from 38 types of ingots. 18 types of comparative examples 1-18 adjust the content rate out of the range in order to evaluate the content range of each element in the examples. Comparative Example 1 has a chemical component equivalent to Inconel 617, which is a conventional material. In Comparative Examples 2 and 3, the C content is outside the scope of the present invention. In Comparative Examples 4 and 5, the Cr content is outside the scope of the present invention. In Comparative Examples 6 and 7, the Co content is outside the scope of the present invention. In Comparative Examples 8 and 9, the Mo content is outside the scope of the present invention. In Comparative Examples 10 and 11, the Al content is outside the scope of the present invention. In Comparative Examples 12 and 13, the Ti content is outside the scope of the present invention. In Comparative Example 14, the B content is outside the scope of the present invention. In Comparative Examples 15 and 16, the Ta content is outside the scope of the present invention. In Comparative Examples 17 and 18, the Nb content is outside the scope of the present invention.

  Of the remaining 20 types of Examples 1 to 20, Examples 1 to 4 correspond to the alloy 1 described above, and Examples 5 to 8 correspond to the alloy 2 described above. Examples 9 to 12 correspond to the alloy 3 described above, Examples 13 to 16 correspond to the alloy 4 described above, and Examples 17 to 20 correspond to the alloy 5 described above. It is. In Table 1, Fe and Cu are inevitably mixed.

  The 38 kinds of forged materials were obtained by cutting and removing the black skin structure of a solid cylindrical ingot having a diameter of about 125 mm and a length of about 210 mm. The forged material after removal of the black skin was about 120 mm in diameter and about 200 mm in length. These forgings were subjected to stabilization treatment at 1180 ° C. for 6 hours, and immediately thereafter hot forging was performed. Hot forging was carried out until the forging ratio reached 3, but at that time the temperature of the forging material was measured, and once the forging material temperature dropped to 1000 ° C, the forging operation was interrupted and reheating was performed at 1180 ° C. did. When the forging ratio reached 3, that is, when the total length of the forged product reached 600 mm, the forging was finished and allowed to cool. At this time, the diameter of the forged product was about 63 mm. After cooling, the surface of the forged product was observed to check for forging cracks.

  Next, each of the forged products was heated at 1170 ° C. for 4 hours and then subjected to a solution treatment for forced air cooling. The forged product after the solution treatment was subjected to an aging treatment at 750 ° C. for 10 hours. Test pieces were appropriately collected from the forged product after the aging treatment and used for various tests.

  Table 2 shows the 700 ° C./100,000 hour creep rupture strength (MPa) obtained from the creep test results and the forging status of Comparative Examples 1 to 18 and Examples 1 to 20 after solution treatment and aging treatment. The creep test was performed according to JIS Z 2271.

  As shown in Table 2, the creep rupture strength of 700 ° C. and 100,000 hours of Comparative Example 1 having a chemical component equivalent to Inconel 617, which is a conventional material, was 112 (MPa), whereas Example 1 The creep rupture strength of ˜20 at 700 ° C. and 100,000 hours was 190 to 214 (MPa), and it was found that the high temperature strength was improved by precipitation / solid solution strengthening. Moreover, in Examples 1-20, it turned out that it has the forgeability equivalent to the comparative example 1 (conventional material: Inconel 617 equivalent) without the forging crack by the reheat frequency 10 (forging ratio = 3). In Comparative Examples 3, 7, 16, and 18, the creep rupture strength at 700 ° C./100,000 hours was about the same as in each example, but the number of reheats increased, forging cracks occurred, and the forgeability was increased. A decrease was seen.

  Table 3 shows the results of a greeble test in which the hot workability was evaluated for five types of Comparative Example 1 (conventional material: equivalent to Inconel 617) and Examples 1, 5, 9, 13, and 17. The greeble test was conducted at 900 ° C., 1000 ° C., 1100 ° C., 1200 ° C. and 1300 ° C. with a tensile rate of 10% strain / second. FIG. 3 is a graph showing the above greeble test results, where the vertical axis represents the cross-sectional reduction rate (drawing value) (%), and the horizontal axis represents the test temperature (° C.).

  As shown in Table 3 and FIG. 3, as a result of the greeble test, Examples 1, 5, 9, 13, and 17 ensure a drawing value of 50% or more at 900 to 1200 ° C. that is a forging temperature range. It turned out that it has the hot workability equivalent to the comparative example 1 (conventional material: Inconel 617 equivalency). Therefore, there are no manufacturing problems.

  As described above, the nickel-base alloy for the turbine rotor of the steam turbine according to the above embodiment has high high-temperature strength while maintaining workability such as forgeability, and is sound for a long time even in a high-temperature environment. And maintain tissue stability. Therefore, the high temperature strength of the turbine rotor is increased by configuring all or at least a predetermined portion of the turbine rotor penetrating the steam turbine into which the steam is introduced with any one of the nickel-based alloys according to the above embodiment. In addition, it is possible to maintain soundness and tissue stability over a long period of time even in a high temperature environment, and a steam turbine having a steam temperature of 700 ° C. or higher can be realized.

Claims (6)

In mass%, C: 0.01 to 0.15, Cr: 22.98 to 28, Co: 10 to 15, Mo: 4 to 7, Al: 0.3 to 2.0, Ti: 0.3 to 3.0, B: A nickel-base alloy for a turbine rotor of a steam turbine, including 0.001 to 0.035, the balance being made of Ni and inevitable impurities. In mass%, C: 0.01 to 0.15, Cr: 22.98 to 28, Co: 10 to 15, Mo: 4 to 7, Al: 0.3 to 2.0, Ti: 0.3 to A nickel-base alloy for a turbine rotor of a steam turbine, comprising 3.0, B: 0.001 to 0.035, Ta: 0.1 to 0.7, the balance being made of Ni and inevitable impurities. In mass%, C: 0.01 to 0.15, Cr: 22.98 to 28, Co: 10 to 15, Mo: 4 to 7, Al: 0.3 to 2.0, Ti: 0.3 to A nickel-base alloy for a turbine rotor of a steam turbine, comprising 3.0, B: 0.001 to 0.035, Nb: 0.1 to 0.4, the balance being made of Ni and inevitable impurities. In mass%, C: 0.01 to 0.15, Cr: 22.98 to 28, Co: 10 to 15, Mo: 4 to 7, Al: 0.3 to 2.0, Ti: 0.3 to 3.0, B: 0.001 to 0.035, Ta: 0.1 to 0.7, Nb: 0.1 to 0.4, with the remainder consisting of Ni and inevitable impurities Nickel-based alloy for turbine rotors of turbines. In mass%, C: 0.01 to 0.15, Cr: 22.98 to 28, Co: 10 to 15, Mo: 4 to 7, Al: 0.3 to 2.0, Ti: 0.3 to 3.0, B: 0.001 to 0.035, Ta + 2Nb = 0.1 to 0.7, the balance being made of Ni and unavoidable impurities, a nickel-base alloy for a turbine rotor of a steam turbine,   A turbine rotor penetrating a steam turbine into which steam is introduced, wherein at least a predetermined portion is made of a nickel-based alloy for a turbine rotor of a steam turbine according to any one of claims 1 to 5. Turbine rotor of a steam turbine.