JP2009242902A - Ni based alloy for turbine rotor of steam turbine, and turbine rotor of steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Ni-based alloy for a turbine rotor of a steam turbine which is excellent in workability such as forgeability, and enables production of a turbine rotor, i.e. a large-sized forging, and a turbine rotor of a steam turbine. <P>SOLUTION: The Ni-based alloy for the turbine rotor of the steam turbine contains, by weight %, 0.05 to 0.15 C, 22 to 28 Cr, 10 to 22 Co, 8 to 12 Mo, 0.8 to <1.5 Al, 0.1 to 0.6 Ti, 0.001 to 0.006 B, 0.1 to 2.5 Re, and consists of the balance Ni and inevitable impurities. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a material constituting a turbine rotor of a steam turbine into which high-temperature steam flows as a working fluid, and particularly comprises a Ni-based alloy for a turbine rotor of a steam turbine excellent in high-temperature strength and the like, and this Ni-based alloy. The present invention relates to a turbine rotor of a steam turbine.

  In a thermal power plant including a steam turbine, carbon dioxide emission suppression technology has attracted attention from the viewpoint of protecting the global environment, and there is a growing need for higher efficiency in power generation.

  In order to increase the power generation efficiency of the steam turbine, it is effective to increase the turbine steam temperature. In a thermal power plant equipped with a steam turbine in recent years, the steam temperature has increased to 600 ° C. or higher. In the future, there is a tendency to increase to 650 ° C. and further to 700 ° C.

  In a turbine rotor in which moving blades that are rotated by high-temperature steam are implanted, high-temperature steam circulates in the surroundings and becomes high temperature, and high stress is generated by rotation. Therefore, it is necessary for the turbine rotor to withstand high temperatures and high stresses, and materials having excellent strength, ductility, and toughness in a range from room temperature to high temperature are required as materials constituting the turbine rotor.

  In particular, when the steam temperature exceeds 700 ° C., the conventional iron-based material lacks high-temperature strength, and therefore application of a Ni-based alloy has been studied (for example, see Patent Document 1).

  Ni-base alloys have been widely applied mainly as jet engine and gas turbine materials because of their excellent high-temperature strength and corrosion resistance. Typical examples thereof include Inconel 617 alloy (made by Special Metal) and Inconel 706 alloy (made by Special Metal).

As a mechanism to strengthen the high-temperature strength of Ni-base alloys, precipitation is called gamma prime phase (Ni ₃ (Al, Ti)) or gamma double-prime phase in the matrix material of Ni-base alloys by adding Al or Ti. There are phases that precipitate both phases to ensure high temperature strength. As an example of depositing the gamma prime phase or the gamma double prime phase to ensure high temperature strength, Inconel 706 alloy can be cited.

On the other hand, as in Inconel 617 alloy, there is one in which high temperature strength is ensured by strengthening (solid solution strengthening) the Ni-based matrix by adding Co and Mo. Further, a nickel-base alloy is disclosed in which high temperature strength characteristics are improved by adjusting additive element components based on the components of this Inconel alloy (see, for example, Patent Document 2-3). The nickel-base alloy in Patent Document 2 has improved sulfide corrosion resistance at high temperatures. Patent Document 3 describes a rotor shaft that uses a nickel-based alloy that suppresses fragile intermetallic compounds that are formed after long-term use.
Japanese Unexamined Patent Publication No. 7-150277 JP 2002-88455 A JP 2001-247842 A

  The above-described conventional nickel-based alloys have been used only for relatively small high-temperature parts and the like because of their poor productivity. Therefore, when a conventional nickel-based alloy is applied to, for example, a jet engine or a gas turbine member, a small blade having a length of less than 1 m or a total weight of less than 1 ton is used as a part where the nickel-based alloy is used. It was limited to disk materials.

  Therefore, the present invention has been made to solve the above-mentioned problems, and is excellent in workability such as forgeability, Ni-based alloy for a turbine rotor of a steam turbine capable of manufacturing a turbine rotor that is a large forged product, and It aims at providing the turbine rotor of a steam turbine.

  In order to achieve the above object, the Ni-based alloy for the turbine rotor of the steam turbine of the present invention is C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22, Mo. : 8 to 12, Al: less than 0.8 to 1.5, Ti: 0.1 to 0.6, B: 0.001 to 0.006, Re: 0.1 to 2.5, the balance Consists of Ni and inevitable impurities.

  According to the Ni-based alloy for the turbine rotor of the steam turbine, workability such as forgeability is improved by being configured in the above-described composition component range.

  Further, at least a predetermined portion of the turbine rotor penetrating the steam turbine into which the high-temperature steam is introduced may be constituted by any one of the Ni-based alloys described above. By using this Ni-based alloy having excellent workability such as forgeability, a turbine rotor having high reliability can be provided without causing cracks during production.

  According to the present invention, it is possible to provide a Ni-based alloy for a turbine rotor of a steam turbine and a turbine rotor of a steam turbine that are excellent in workability such as forgeability and can manufacture a turbine rotor that is a large forged product.

  Hereinafter, an embodiment of the present invention will be described.

  An Ni-based alloy for a turbine rotor of a steam turbine in an embodiment according to the present invention is configured with a composition component range shown below. In the following description, “%” representing a composition component is “% by weight” unless otherwise specified.

  (M1) C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22, Mo: 8 to 12, Al: less than 0.8 to 1.5, Ti: 0.1 to 0. 6, Ni: Alloy containing B: 0.001 to 0.006, Re: 0.1 to 2.5, the balance being Ni and inevitable impurities.

  Here, in the inevitable impurities in the Ni-based alloy (M1), it is preferable that at least Si is suppressed to 1 or less and Mn is suppressed to 1 or less among the inevitable impurities.

  The Ni-based alloy having the composition range described above is suitable as a material constituting a turbine rotor of a steam turbine in which the temperature during operation is 680 to 750 ° C. Here, all the parts of the turbine rotor of the steam turbine may be made of this Ni-based alloy, or some parts of the turbine rotor of the steam turbine that is particularly hot may be made of this Ni-based alloy. . Here, as a part of the turbine rotor of the steam turbine that becomes high temperature, specifically, the entire region of the high-pressure steam turbine unit or the region from the high-pressure steam turbine unit to a part of the intermediate-pressure steam turbine unit may be mentioned. .

  Moreover, the Ni-based alloy having the above compositional component range can improve workability such as forgeability. That is, by using this Ni-based alloy to configure the turbine rotor of a steam turbine, the workability such as forgeability of the turbine rotor can be improved, and high reliability can be achieved without causing cracks during production. A turbine rotor having

  Next, the reasons for limiting the respective composition component ranges in the Ni-based alloy according to the present invention will be described.

(1) C (carbon)
C is useful as a constituent element of M ₂₃ C ₆ type carbide, which is a strengthening phase. In particular, in a high temperature environment of 650 ° C. or higher, it is possible to precipitate M ₂₃ C ₆ type carbide during operation of a steam turbine. This is one of the factors that maintain the creep strength. It also has the effect of ensuring the fluidity of the molten metal during casting. When the C content is less than 0.05%, a sufficient amount of carbides cannot be ensured, so that the mechanical 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 generation of M ₆ C type carbides, which are embrittled phases, is promoted, and the mechanical strength is improved. However, forgeability is reduced. Therefore, the C content is determined to be 0.05 to 0.15%.

(2) Cr (chromium)
Cr is an essential element for increasing the oxidation resistance, corrosion resistance and mechanical strength of the Ni-based alloy. Furthermore, it is indispensable as a constituent element of M ₂₃ C ₆ type carbide, and especially 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 the operation of the steam turbine. The Moreover, Cr improves the oxidation resistance in a high temperature steam environment. When the Cr content is less than 22%, the oxidation resistance decreases. On the other hand, when the content of Cr exceeds 28%, increasing the tendency of coarsening significantly promotes the precipitation of the M ₂₃ C ₆ type carbide. Therefore, the Cr content is determined to be 22 to 28%.

(3) Co (cobalt)
Co is a solid solution in the parent phase in the Ni-based alloy and improves the mechanical strength of the parent phase. However, if the Co content exceeds 22%, an intermetallic compound phase that lowers the mechanical strength is generated, and forgeability is reduced. On the other hand, if the Co content is less than 10%, the workability decreases. Further, the mechanical strength is lowered. Therefore, the Co content is determined to be 10 to 22%.

(4) Mo (molybdenum)
Mo has the effect of improving the mechanical strength of the parent phase by solid solution in the Ni parent phase, and increases the stability of the carbide by partially replacing the M ₂₃ C ₆ type carbide. When the Mo content is less than 8%, the above-mentioned effects are not exhibited. When the Mo content exceeds 12%, the tendency of component segregation during the production of a large ingot increases and the embrittlement phase Promotes the formation of certain M ₆ C type carbides. Therefore, the Mo content is determined to be 8 to 12%.

  Here, Mo is common in that it has the effect of improving the mechanical strength of the parent phase with Co described above. And in order to exhibit this common feature and each other feature effectively, for example, when the Mo content is less than 8 to 10%, the Co content is set to more than 15% and 22% or less. It is preferable. For example, when the Mo content is 10 to 12%, the Co content is preferably 10 to 15%.

(5) Al (aluminum)
Al forms a γ ′ (gamma prime: Ni ₃ Al) phase together with Ni, and improves the mechanical strength of the Ni-based alloy by precipitation. When the Al content is less than 0.8%, the mechanical strength is not improved as compared with the conventional steel. When the Al content is 1.5% or more, the mechanical strength is improved, but the forgeability is improved. Decreases. Therefore, the Al content is set to 0.8 to less than 1.5%.

(6) Ti (titanium)
Ti, like Al, produces a γ ′ (gamma prime: Ni ₃ Al) phase together with Ni and improves the mechanical strength of the Ni-based alloy. When the Ti content is less than 0.1%, the above-described effects are not exhibited. When the Ti content exceeds 0.6%, the hot workability and forgeability are reduced. The lack sensitivity increases. Therefore, the Ti content is determined to be 0.1 to 0.6%.

(7) B (boron)
B segregates at the grain boundaries and affects the high temperature characteristics. Further, B has an effect of being precipitated in the Ni matrix and improving the mechanical strength of the matrix. When the B content is less than 0.001%, the effect of improving the mechanical strength of the matrix is not exhibited, and when the B content exceeds 0.006%, grain boundary embrittlement may occur. There is. Therefore, the B content is determined to be 0.001 to 0.006%.

(8) Re (Rhenium)
Re has the effect of improving the mechanical strength of the parent phase by dissolving in the Ni parent phase. When the Re content is less than 0.1%, the effect of improving the mechanical strength of the parent phase is not exhibited, and when the Re content exceeds 2.5%, a fragile phase is formed. Therefore, the Re content is determined to be 0.1 to 2.5%.

  Here, Co and Mo also have the effect of improving the mechanical strength of the parent phase by dissolving in the Ni parent phase in the same way as Re, but Re has the highest mechanical strength improvement at the same content. The mechanical strength can be improved without greatly changing the chemical composition of the base metal.

(9) Si (silicon) and Mn (manganese)
Si and Mn are classified as inevitable impurities in the Ni-based alloy according to the present invention. Here, among the inevitable impurities, in particular, the residual content of Si and Mn is limited. It is desirable that such inevitable impurities have a residual content as close to 0% as possible.

  In the case of plain steel, Si is added to supplement the corrosion resistance. However, since the Ni-based alloy has a large Cr content and can sufficiently secure corrosion resistance, the Ni-based alloy according to the present invention has a residual content of Si of 1% or less and a residual content of 0% as much as possible. It is desirable to be close to

  In the case of ordinary steel, Mn prevents brittleness by using S (sulfur) due to brittleness as MnS. However, the content of S in the Ni-based alloy is extremely small, and it is not necessary to add Mn. Therefore, in the Ni-based alloy according to the present invention, it is desirable that the residual content of Mn is 1% or less and that the residual content is as close to 0% as possible.

  The above-described Ni-based alloy according to the present invention is produced by soaking, forging, and solution-treating an ingot obtained by melting composition components constituting the Ni-based alloy in a vacuum induction melting furnace. Is done.

  In the soaking process, it is preferably maintained in a temperature range of 1050 to 1075 ° C. for 5 to 6 hours, and in the solution treatment, it is preferably maintained in a temperature range of 1100 to 1180 ° C. for 4 to 5 hours. Here, the solution treatment temperature is carried out in order to form a solid solution of the γ ′ phase precipitate. When the temperature is lower than 1100 ° C., the solution is not sufficiently dissolved, and when the temperature is higher than 1180 ° C., the crystal grains are coarse. As a result, the strength decreases. Forging is performed in a temperature range of 950 to 1100 ° C. (reheating temperature 1100 ° C.).

  Further, when the turbine rotor of the steam turbine is configured in the above-described Ni-based alloy according to the present invention, for example, as one method (double melt), the raw material is subjected to vacuum induction melting (VIM) and electroslag remelting ( ESR) and pour into a predetermined mold. Subsequently, a forging process and a heat treatment are performed to produce a turbine rotor. As another method (double melt), the raw material is subjected to vacuum induction melting (VIM), vacuum arc remelting (VAR), and poured into a predetermined mold. Subsequently, a forging process and a heat treatment are performed to produce a turbine rotor. Further, as another method (triple melt), the raw material is subjected to vacuum induction melting (VIM), electroslag remelting (ESR), vacuum arc remelting (VAR), and poured into a predetermined mold. Subsequently, a forging process and a heat treatment are performed to produce a turbine rotor. In addition, ultrasonic inspection etc. are performed for the turbine rotor produced by the said method.

  The following explains that the Ni-based alloy according to the present invention is excellent in mechanical strength and forgeability.

(Evaluation of forgeability)
Here, it is explained that the Ni-based alloy in the chemical composition range of the present invention has excellent forgeability. Table 1 shows the chemical compositions of Sample 1 to Sample 5 used for evaluation of forgeability. Samples 1 to 4 are Ni-based alloys in the chemical composition range of the present invention, and Sample 5 is a Ni-based alloy whose composition is not in the chemical composition range of the present invention, and is a comparative example. Sample 5 has a chemical composition equivalent to Inconel 617, which is a conventional steel. The Ni-based alloy in the chemical composition range of the present invention used here contains Fe (iron) and Cu (copper) S (sulfur) in addition to Si and Mn as unavoidable impurities.

  In the evaluation of forgeability, 10 kg of the Ni-based alloys of Samples 1 to 5 having the chemical compositions shown in Table 1 were melted in a vacuum induction melting furnace, respectively, and a cylindrical ingot having a diameter of 87 mm and a length of 140 mm A test piece was prepared. Subsequently, the ingot was subjected to a soaking process at 1050 ° C. for 5 hours. Thereafter, forging treatment was performed with a 500 kgf hammer forging machine in a temperature range of 950 to 1100 ° C. (reheating was 1100 ° C.). Here, the forgeability was evaluated by performing the forging process described above until the diameter of the test piece reached 30 mm, and the forging ratio at that time and the presence or absence of forging cracks.

  Here, the forging ratio is obtained by dividing the length of a test piece that is an elongated forged object after the forging process by the length of the test piece that is a forged object before performing the forging process. It is what. Further, in the forging process, when the temperature of the test piece is lowered, that is, when the test piece is cured, the forging process is repeated by heating again to the above-described reheating temperature of 1100 ° C. In addition, the presence or absence of forging cracks, by visually observing the test piece after the forging process, when there is no crack, indicates "No", and further indicates that the forgeability is excellent, the evaluation of forgeability is " “○”. On the other hand, when there is a crack, it is indicated as “present”, and further, the forgeability is indicated by “x” in order to indicate that the forgeability is inferior.

  Table 2 shows the results of evaluation of forgeability in each sample.

  As shown in Table 2, it was revealed that Sample 1 to Sample 4 were superior in forgeability compared to Sample 5.

Claims (3)

  By weight, C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22, Mo: 8 to 12, Al: less than 0.8 to 1.5, Ti: 0.1 to 0 .6, B: 0.001 to 0.006, Re: 0.1 to 2.5, the balance being Ni and inevitable impurities, Ni-based alloy for steam turbine turbine rotors .   2. The Ni-based alloy for a turbine rotor of a steam turbine according to claim 1, wherein among the inevitable impurities, by weight percent, Si is 1 or less and Mn is 1 or less. A turbine rotor penetrating a steam turbine into which high-temperature steam is introduced,
A turbine rotor for a steam turbine, wherein at least a predetermined portion is made of a Ni-based alloy for a turbine rotor of a steam turbine according to claim 1 or 2.