DE102009012877A1 - Nickel-based alloy for a turbine rotor of a steam turbine and turbine rotor of a steam turbine - Google Patents

Abstract

A Ni-base alloy for a turbine rotor of a steam turbine contains in wt% C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22, Mo: 8 to 12, Al: 0.8 to less than 1.5, Ti: 0.1 to 0.6, B: 0.001 to 0.006, Re: 0.1 to 2.5, and balance Ni and unavoidable impurities.

Description

REFERENCE TO RELATED APPLICATIONS:

This application is based on and claims the priority of the previous ones Japanese Patent Application 2008-092782 , filed on March 31, 2008; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION:

1. Field of the invention:

The The present invention relates to a material comprising a turbine rotor forms a steam turbine, in the high-temperature steam as the working fluid (Fluid) flows, and in particular an alloy Ni-based for a turbine rotor of a steam turbine, relating to high-temperature strength and the like excels, and a turbine rotor of a steam turbine, the made of the Ni-base alloy.

2. State of the art:

A Technology for suppressing the emission of carbon dioxide for a thermal power plant, which is a steam turbine will be of interest in view of global environmental protection pursued, and the requirements for highly efficient Energy production increase.

Around to increase the energy production efficiency of a steam turbine, it is effective, the turbine steam temperature to a high degree increase, and in modern thermal power plants with a steam turbine, the steam temperature to 600 ° C. or more. There is a tendency that in the future the Steam temperature to 650 ° C, and further to 700 ° C, will be increased.

One Turbine rotor, used in the blades, by high-temperature steam rotates, points through the circulation of high-temperature steam a high temperature and exercises by the rotation one high load off. Therefore, the turbine rotor has high temperatures and withstand high loads, and it's for a material that forms the turbine rotor requires that it has excellent strength / hardness, Ductility and toughness in the range of room temperature up to a high temperature.

In particular, when the steam temperature exceeds 700 ° C, a conventional iron-based material is insufficient in high-temperature strength, so that e.g. In JP-A-7-150277 (Kokai, OS), the use of a Ni-based alloy is considered.

A Ni-based alloy is widely used as material for jet or jet engines and gas turbines has been used because of its high temperature strength and the corrosion resistance is excellent. As typical Examples of these are Inconel 617 alloy (manufactured by Special Metals Corporation) and Inconel 706 alloy (manufactured by Special Metals Corporation).

As a mechanism for improving the high-temperature strength of the Ni-based alloy, Al and Ti are added to ensure the high-temperature strength by a precipitation phase serving as a gamma prime phase (Ni ₃ (Al, Ti)) or as a gamma double prime phase or both of them are precipitated within the base phase material of the Ni-based alloy. For example, there is the Inconel 706 alloy, which ensures high temperature strength by eliminating both the gamma prime phase and the gamma double prime phase.

Meanwhile, the high temperature strength of the Inconel 617 alloy is ensured by strengthening the base phase of the Ni group (solid solution hardening) by adding Co and Mo. For example, disclose JP-A-2002-88455 (OS) and JP-A-2001-247942 (OS) A Ni-based alloy having high-temperature strength properties which are improved by adjusting the added elemental components based on the components of the Inconel alloy. The Ni-based alloy of JP-A-2002-88455 (OS) is provided with improved sulfidation corrosion at a high temperature. JP-A-2001-247942 (OS) describes a rotor shaft using a Ni-base alloy which suppresses the formation of a fragile intermetallic compound which forms over a long period of use.

There the conventional Ni-based alloys described above concerning productivity are bad They only for relatively small high temperature parts and the like used. Therefore, when the conventional Ni-based alloy for z. B. jet engine or gas turbine parts is used, the parts in which the Ni-based alloy is used on small blades with a length of less than 1 m, a disc material with a gross weight of less than 1 ton or so.

BRIEF SUMMARY OF THE INVENTION:

Corresponding The present invention provides a Ni-based alloy for a turbine rotor of a steam turbine whose processability, such as B. forgeability, is outstanding and with a large format Forged product, a turbine rotor, can be produced and it provides a turbine rotor of a steam turbine.

Corresponding An aspect of the invention is a Ni-based alloy for provided a turbine rotor of a steam turbine, which in wt.% contains: C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22, Mo: 8 to 12, Al: 0.8 to less than 1.5, Ti: 0.1 to 0.6, B: 0.001 to 0.006, Re: 0.1 to 2.5 and balance Ni and unavoidable impurities.

Corresponding In one aspect of the invention, there is also provided a turbine rotor, which is arranged within a steam turbine, in the high-temperature steam is introduced, wherein at least a predetermined part from the Ni-base alloy described above for a turbine rotor of a steam turbine is formed.

DETAILED DESCRIPTION OF THE INVENTION:

below Embodiments of the invention will be described.

In An embodiment of the invention is an alloy Ni-based for a turbine rotor of a steam turbine from the areas of the composition components shown below together. In the following description, the percentages, which designate the composition components, on the weight unless otherwise stated.

(M1) Ni-based alloy containing C: 0.05 to 0.15%, Cr: 22 to 28%, Co: 10 to 22%, Mo: 8 to 12%, Al: 0.8 to less than 1.5%, Ti: 0.1 to 0.6%, B: 0.001 to 0.006%, Re: 0.1 to 2.5%, and balance Ni and unavoidable impurities.

The unavoidable impurities in the Ni-based alloy according to The above (M1) are preferably kept so low that at least the content of Si is 1% or less and the content of Mn is 1% or less.

The Ni-based alloy having the above-described ranges the composition component is suitable as a material with which a turbine rotor of a steam turbine is built up during Operating at a temperature in the range of 680 to 750 ° C. having. It can all parts of the turbine rotor of the steam turbine can be made of the Ni-based alloy, and it can some parts of the turbine rotor of the steam turbine, which is a special high temperature, made of this Ni-based alloy become. Some parts of the turbine rotor of the steam turbine, the one high temperature, are specifically all areas of a high-pressure steam turbine section or areas extending from the high pressure steam turbine section to some parts of a medium pressure steam turbine section extend.

The Ni-based alloys having the above-described ranges the composition components can increase the processability, such as As the forgeability, improve. In other words For example, the Ni-based alloy is used to form the turbine rotor build a steam turbine, so that the workability, such as z. As the forgeability, the turbine rotor can be improved and a turbine rotor made with high reliability can be, without cracks or the like in the production form.

below Be the reasons why the areas of the individual Composition components of the inventive alloy be limited to Ni-based described.

(1) C (carbon):

C is useful as a component element of a M ₂₃ C ₆ -type carbide which is a solidifying (hardening) phase, and more particularly, the creep strength of the alloy is eliminated by precipitating the M ₂₃ C ₆ -type carbide during the Maintaining the steam turbine in a high temperature environment of 650 ° C or higher. It also has an effect of ensuring the fluidity (flowability) of a molten metal at the time of casting. When the C content is less than 0.05%, a sufficient precipitation amount of carbide can not be secured to lower the mechanical strength, and the fluidity of the molten metal decreases considerably at the time of casting. Meanwhile, when the C content exceeds 0.15%, the tendency of the components to separate at the time of producing a large ingot increases, the formation of M ₆ C-type carbide which is an embrittlement phase is promoted, and the mechanical deterioration Strength is improved, but the forgeability deteriorates. Therefore, the C content is determined to be 0.05 to 0.15%.

(2) Cr (chromium):

Cr is an indispensable element for improving the oxidation resistance, corrosion resistance and mechanical strength of the Ni-based alloy. Moreover, as a component element of the M ₂₃ C ₆ -type carbide, it is indispensable, and in particular, the creep rupture strength of the alloy is eliminated by precipitating the M ₂₃ C ₆ -type carbide during operation of the steam turbine in a high-temperature environment of 650 ° C or higher. And Cr improves the oxidation resistance in a high temperature steam environment. When the Cr content is less than 22%, the oxidation resistance decreases. Meanwhile, when the Cr content exceeds 28%, the precipitation of the M ₂₃ C ₆ -type carbide is considerably accelerated, resulting in an increase in tendency for coarsening. Therefore, the Cr content is determined to be 22 to 28%.

(3) Co (cobalt):

In In the Ni-based alloy, Co improves the mechanical strength a basic phase by forming a solid solution in the basic phase. However, if the Co content exceeds 22%, a phase of an intermetallic compound is formed, the reduces mechanical strength and deteriorates forgeability yourself. However, if the Co content is less than 10%, the processability and the mechanical strength deteriorate is reduced. Therefore, the Co content is determined to be 10 to 22%.

(4) Mo (molybdenum):

Mo provides an effect of forming a mixed crystal in a Ni base phase to increase the mechanical strength of the base phase, and its partial substitution in M ₂₃ C ₆ -type carbides increases the stability of the carbide. If the Mo content is less than 8%, the above effect is not exerted, and if the Mo content exceeds 12%, the tendency of segregation of the components when producing a large ingot and the formation of a carbide from the M ₆ C-type is accelerated, which is an embrittlement phase. Therefore, the Mo content is determined to be 8 to 12%.

Not a word has in common with the above Co the property that they have a Effect of improving the mechanical strength of the base phase exhibit. To effectively the common property and their others To exhibit properties, it is when z. As the Mo content 8 to is less than 10%, it is desirable that the Co-content greater than 15% and not greater than 22% is. If the Mo content z. B. is 10 to 12%, is it is desirable that the Co content is 10 to 15%.

(5) Al (aluminum):

Al forms a γ'-phase (gamma-prime phase: Ni ₃ Al) with Ni and improves the mechanical strength of the Ni-based alloy based on the precipitation. If the Al content is less than 0.8%, the mechanical strength is not improved as compared with conventional steel, and if the Al content is 1.5% or more, the mechanical strength is improved, but the deteriorates Malleability. Therefore, the Al content is determined to be 0.8 to less than 1.5%.

(6) Ti (titanium):

Similar to Al, Ti forms a γ'-phase (gamma-prime phase: Ni ₃ Ti) with Ni and improves the mechanical strength of the Ni-based alloy. When the Ti content is less than 0.1%, the above effect is not exerted, and when the Ti content exceeds 0.6%, the hot workability is deteriorated and the notch sensitivity becomes large. Therefore, the Ti content is determined to be 0.1 to 0.6%.

(7) B (boron):

B Separates in the grain boundary to the high temperature properties to influence. In addition, B has an effect for improvement the mechanical strength of a Ni base phase by precipitation in the basic phase. If the B content is less than 0.001%, then the effect of improving the mechanical strength of the base phase not exercised, and if the B content exceeds 0.006%, there is a possibility that the grain boundary becomes brittle becomes. Therefore, the B content is determined to be 0.001 to 0.006%.

(8) Re (rhenium):

re has an effect of improving mechanical strength a Ni base phase by forming mixed crystals in the ground phase. If the Re content is less than 0.1%, the effect becomes improvement the mechanical strength of the basic phase is not exercised, and if the Re content exceeds 2.5%, becomes a fragile Phase formed. Therefore, the Re content is determined to be 0.1 to 2.5%.

Similar For Re, Co and Mo have an effect of improving the mechanical properties Strength of Ni base phase by mixed crystal formation in the ground phase. However, if the content is the same, Re is relative the best way to improve mechanical strength increase the mechanical strength without the chemical Large component composition of a base metal change.

(9) Si (silicon), Mn (manganese), Cu (copper), Fe (iron) and S (sulfur):

In the Ni-based alloy according to the invention are Si, Mn, Cu, Fe and S are classified as unavoidable impurities. The residual content of unavoidable impurities should go so far be reduced to 0% as possible. It is desirable that at least the content of Si and Mn in the unavoidable impurities reduced to 1% or less.

Si is added to conventional steel to improve corrosion resistance to support. However, since the Ni-based alloy has a has high Cr content to provide adequate corrosion resistance to ensure the residual content of Si in the inventive Ni-based alloy is determined to be 1% or smaller, and it is desirable that the residual content is reduced as far as possible to 0%.

In conventional steel, Mn avoids brittleness, which results from S (sulfur), in the form of MnS. However, since in the Ni-based alloy, the S content is very small, it is not necessary to add Mn. Therefore, the residual content of Mn in the inventive Ni-based alloy to 1% or smaller determined, and it is desired that the residual content as low as possible to 0%.

The above-described inventive alloy Ni base is made by adding the composition components, building the Ni-based alloy in a vacuum induction melting furnace are melted, the obtained ingot (ingot) of a holding treatment (soaking treatment), it is forged and one Treatment for the formation of mixed crystals carried out becomes.

It is preferable that the holding treatment is conducted at a temperature in the range of 1050 to 1250 ° C for 5 to 72 hours, and the treatment for forming mixed crystals is carried out at a temperature in the range of 1100 to 1200 ° C for 4 to 5 hours. Here, the temperature of the treatment for forming mixed crystals is determined so as to form a homogeneous solid solution of the γ'-phase precipitates, and when the temperature is lower than 1100 ° C, a solid solution (solid solution) is not adequately formed. When the temperature exceeds 1,200 ° C, the crystal grains are coarsened and the strength decreases. Also, forging is at a temperature in the range of 950 to 1150 ° C carried out.

If the inventive alloy described above Ni-base for building a turbine rotor of a steam turbine is used, for. B. with a method (double melt; double melt), the starting material of a vacuum induction melting (VIM) and an electroslag remelting (electro-slag remelting; ESR) and then poured into a predetermined shape. Then be a forging / forging and a heat treatment performed to make the turbine rotor. In one Another method (double melt) is the starting material one Vacuum Induction Melting (VIM) and Vacuum Ground Remelting (Vacuum arc remelting) and then poured into a predetermined shape. Subsequently, a forging / impact pressing and a heat treatment performed to make the turbine rotor. In one Another method (triple melting, triele melt) is the starting material a vacuum induction melting (VIM), an electroslag remelting (ESR) and Vacuum Arc Remelting (VAR) and then poured into a predetermined shape. Subsequently become a forging treatment and a heat treatment performed to make the turbine rotor. With Turbine rotors produced by the above method checked by ultrasound examination or the like.

below It is described that the inventive alloy Ni-base outstanding in forgeability is.

Evaluation of forgeability:

below It is described that the Ni-based alloy with the inventive Areas of chemical composition excellent forgeability having. Table 1 shows the chemical compositions of sample 1 to 5, which were used to evaluate forgeability. Also, Sample 1 to Sample 4 are Ni-base alloys having the ranges the chemical composition of the present invention, and the Sample 5 is a Ni-based alloy having a composition not within the ranges of the chemical composition of the present invention and that as a comparative example is used. The sample 5 has a chemical composition, which corresponds to the conventional steel Inconel 617. The alloy Ni-based with the inventive areas of the chemical Composition contains Fe (iron), Cu (copper) and S (sulfur) as unavoidable impurities, in addition to Si and Mn.

to Evaluation of forgeability were based on Ni-based alloys from Sample 1 to Sample 5 with the chemical shown in Table 1 Compositions, each 10 kg, in a vacuum induction melting furnace melted, and there were test pieces of cylindrical Crude blocks with a diameter of 87 mm and a length made of 140 mm. Subsequently, the ingots were a holding treatment at 1050 ° C for 5 hours subjected. It was a blacksmith treatment (impact press treatment) with a 500 kgf hammer forging machine at a temperature in the Range from 950 to 1150 ° C (reheat to 1,100 ° C) performed. For the forgeability was the above-described forging treatment (impact pressing treatment) performed until the test pieces have a diameter of 30 mm. The rating was based on the forging ratio (Impact compression ratio) of the above treatment and the Presence or absence of a Schmiederisses (Schlagpressrisses) too performed this time.

The forging ratio is defined by the pitch of the length of the test piece, which is a forged object stretched by the forging treatment, by the length of the test piece that is the forged object before the forging treatment. According to the forging treatment, if the temperature of the test piece decreases, namely, when the test piece hardens, the forging treatment is repeated by reheating to a reheating temperature of 1100 ° C. In addition, the test pieces subjected to the forging treatment are visually inspected for the presence or absence of a putty. If there is no crack, it will be displayed as "none" and the Forgeability is rated "O" to indicate that forgeability is outstanding.

If on the other hand there is a crack, this is called "yes", and the forgeability is rated as "x", to indicate that the forgeability is bad.

Table 2 shows the results obtained by evaluating the forgeability of the respective samples. TABLE 2 forging ratio Crack malleability example Sample 1 6.6 none O Sample 2 6.3 none O Sample 3 6.7 none O Sample 4 6.4 none O Comparative example Sample 5 5.4 Yes x

As shown in Table 2, it was found that Sample 1 through Sample 4 have excellent forgeability as compared to Sample 5.

Even though the invention above with reference to the inventive Embodiments has been described is the invention not to the embodiments described above limited. It is obvious that modifications and variations the embodiments can be carried out without departing from the spirit and scope of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 2008-092782 [0001]
• - JP 7-150277 A [0006]
• - JP 2002-88455 A [0009, 0009]
• - JP 2001-247942 A [0009, 0009]

Claims (4)

Ni-based alloy for a turbine rotor a steam turbine, wherein the Ni-based alloy in wt.% Contains: C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22, Mo: 8 to 12, Al: 0.8 to less than 1.5, Ti: 0.1 to 0.6, B: 0.001 to 0.006, Re: 0.1 to 2.5 and balance Ni and unavoidable impurities. Ni-based alloy for a turbine rotor A steam turbine according to claim 1, wherein the content in unavoidable impurities in% by weight on Si: 1 or lower and Mn: 1 or lower are suppressed. Turbine rotor, configured to pass through a steam turbine to extend into which high-temperature steam is introduced, wherein at least a predetermined portion of the Ni-based alloy for a turbine rotor of a steam turbine according to Claim 1 is formed. Turbine rotor, configured to pass through a steam turbine to extend into which high-temperature steam is introduced, wherein at least a predetermined portion of the Ni-based alloy for a turbine rotor of a steam turbine according to Claim 2 is formed.