JP2012036485A - Ni-BASED ALLOY FOR FORGED PART IN STEAM-TURBINE AND FORGED PART IN STEAM-TURBINE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Ni-based alloy for forged parts in a steam-turbine excellent in high-temperature strength and castability and to provide the forged parts in the steam-turbine produced using the Ni-based alloy for forged parts of the steam turbine.SOLUTION: The Ni-based alloy for forged parts in the steam-turbine is composed, by mass, of 0.01-0.15% C, 14-20% Cr, 10-15% Co, 8-12% Mo, 0.5-4% Al, 0.5-4% Ti, 0.001-0.006% B, 0.1-0.7% Ta, 0.1-0.4% Nb, and the balance Ni with inevitable impurities. A relationship of 9.5 mass%≤0.45Cr+Al+Ti≤13 mass% is satisfied.

Description

  Embodiments of the present invention relate to a Ni-based alloy for forged parts of a steam turbine and a forged part of a steam turbine that are excellent in forgeability and the like.

As a means for reducing CO ₂ emitted from coal-fired power generation equipment, it is effective to improve the efficiency of the coal-fired power generation system. For example, the power generation efficiency of the steam turbine provided in the coal-fired power generation equipment is improved. It can be realized by improving. To improve the power generation efficiency of the steam turbine, it is most effective to raise the turbine steam temperature. In recent thermal power plants, the steam temperature has risen to 600 ° C. or higher, and currently, thermal power generation systems having a steam temperature of 700 ° C. or higher are being developed worldwide.

  Forged parts such as turbine rotors, moving blades and stationary blades provided in steam turbines exposed to high-temperature steam, and forged parts such as bolted members and pipes used in steam turbines become high temperature. At the same time, high stress is generated. Therefore, materials having excellent strength, ductility, and toughness are demanded from the room temperature to a high temperature range as materials constituting them.

  The material currently used for the components constituting the steam turbine is an Fe-based alloy containing Fe as a main component and added with elements such as Cr and Mo in order to improve high-temperature strength. However, when the temperature of the steam is 700 ° C. or higher, the heat resistance temperature of the Fe-based alloy is exceeded, so application of a Ni-based alloy having a higher heat resistance temperature is being studied.

Typical examples of Ni-based alloys include Inconel 718 alloy (made by Special Metal) and Inconel 617 alloy (made by Special Metal). The strengthening mechanism of the Ni-based alloy is roughly divided into a precipitation strengthening type and a solid solution strengthening type. In a precipitation strengthened Ni-base alloy, by adding Al, Ti, Ta, Nb to Ni, a γ ′ (gamma prime: Ni ₃ (Al, Ti)) phase or γ ″ (gamma double prime: Ni ₃ Nb) The strength at high temperature is improved by precipitating a precipitation phase called “phase.” As a typical precipitation strengthened Ni-based alloy, the above-mentioned Inconel 718 alloy can be cited, while solid solution strengthened Ni-based alloy. Then, the matrix phase itself is strengthened by adding Co, Mo, etc. to Ni. A typical solid solution strengthened Ni-based alloy includes the above-mentioned Inconel 617 alloy.

Japanese Unexamined Patent Publication No. 7-150277

  As described above, application of a Ni-based alloy has been studied as a material for components of steam turbines used in a steam environment exceeding 700 ° C. The material of the components of the steam turbine is required to have a sufficiently high temperature strength in a steam environment exceeding 700 ° C. Further, since it is exposed to a high temperature for a long time, the soundness of the material for a long time is required.

  Moreover, when the component of a steam turbine is provided with connection parts, such as joining, fastening, or fitting, in this connection part, the thermal stress resulting from the thermal expansion difference of the material which comprises a connection part generate | occur | produces.

  Accordingly, the present invention provides a Ni-based alloy for steam turbine forged parts excellent in high-temperature strength characteristics and forgeability, and a steam turbine forged part manufactured using the Ni-based alloy for steam turbine forged parts. With the goal.

  The Ni-based alloy for forged parts of steam turbines according to an embodiment of the present invention is in mass%, C: 0.01 to 0.15, Cr: 14 to 20, Co: 10 to 15, Mo: 8 to 12, Al : 0.5-4, Ti: 0.5-4, B: 0.001-0.006, Ta: 0.1-0.7, Nb: 0.1-0.4, the balance is Ni and inevitable And 9.5% by mass ≦ 0.45Cr + Al + Ti ≦ 13% by mass.

It is a figure which shows the precipitation area | region of the (sigma) phase in 700 degreeC obtained by the thermodynamic calculation.

  Embodiments according to the present invention will be described below.

For example, in Inconel 617 alloy, Al, Ti, Ta, and Nb are added and high temperature strength is improved by strengthening (solid solution strengthening) the Ni-based matrix by adding Co and Mo. By precipitating a γ ′ (Ni ₃ (Al, Ti)) phase that is a stable intermetallic compound, the high-temperature strength can be further improved. However, excessive addition of strengthening elements promotes the precipitation of a TCP (Topologically Close-Packed) phase that deteriorates the stability of the structure and causes deterioration of mechanical properties.
In the embodiment according to the present invention, focusing on Cr, which is a main component of the σ phase that is one of the TCP phases, Al and Ti that contribute to the precipitation of the γ ′ phase while suppressing the precipitation of the harmful phase causing the weakening. The high temperature strength is improved by the addition of.

Details will be described below.
For example, when Al and Ti are added in combination to conventional Inconel 617, the amount of precipitated γ ′ phase is increased and the creep strength is improved. Precipitation of acicular σ phase is promoted and mechanical properties are deteriorated.

  FIG. 1 is a diagram showing the precipitation region of the σ phase at 700 ° C. obtained by thermodynamic calculation. In FIG. 1, the horizontal axis represents the Cr content (mass%), and the vertical axis represents the total content of Al (mass%) and Ti (mass%) (hereinafter, Al and Ti content). Further, the region above the line L shown in FIG. 1 is a region where the σ phase is precipitated, and the region below the line L is a region where the σ phase is not precipitated. In the Ni-based alloy shown in FIG. 1, the composition components other than Cr, Al, and Ti are mass%, C is 0.05, Co is 12.5, Mo is 9, B is 0.003, Ta 0.1, Nb 0.3, the balance being Ni and inevitable impurities.

  As shown in FIG. 1, as the Cr content increases, the range of the Al and Ti content in the region where the σ phase does not precipitate becomes narrower. Based on such results, the Cr content and the Al and Ti contents are adjusted, and the γ ′ phase is precipitated to the maximum in the region on or near the line L shown in FIG. By doing so, it is possible to improve the tissue stability and the high temperature strength.

  In consideration of the relationship between the contents of lines L and Cr and the contents of Al and Ti obtained by thermodynamic calculation, the Ni-based alloy for forged parts of a steam turbine in the embodiment according to the present invention is used. Invented.

  The Ni-based alloy for forged parts of a steam turbine in the embodiment according to the present invention is composed of the following composition component ranges. In the following description, “%” representing a composition component is “% by mass” unless otherwise specified.

  Ni-based alloys for forged parts of steam turbines according to embodiments of the present invention are: C: 0.01 to 0.15, Cr: 14 to 20, Co: 10 to 15, Mo: 8 to 12, Al: 0.00. 5-4, Ti: 0.5-4, B: 0.001-0.006, Ta: 0.1-0.7, Nb: 0.1-0.4, the balance from Ni and inevitable impurities And a Ni-based alloy satisfying the relationship of 9.5% by mass ≦ 0.45Cr + Al + Ti ≦ 13% by mass.

  In the inevitable impurities described above, it is preferable that at least Si is suppressed to 0.1% or less and Mn is suppressed to 0.1% or less among the inevitable impurities. In addition, as an unavoidable impurity, Cu, Fe, S etc. are mentioned other than Si and Mn mentioned above, for example.

  The above-described Ni-based alloy according to the embodiment of the present invention is suitable as a material constituting a forged part of a steam turbine having a temperature during operation of 680 to 750 ° C. Examples of the forged parts of the steam turbine include a turbine rotor of the steam turbine, a moving blade of the steam turbine, a stationary blade of the steam turbine, a screwed member for the steam turbine, and a pipe for the steam turbine. All of these steam turbine forged parts are installed in a high-temperature and high-pressure environment.

  Here, as the screwing member for the steam turbine, for example, a bolt or a nut for fixing various components inside the turbine casing or the turbine can be exemplified. Further, examples of the steam turbine piping include piping installed in a steam turbine plant and the like for supplying high-temperature and high-pressure steam to the steam turbine, piping inside the steam turbine, and the like. Specific examples of steam turbine piping include, for example, a main steam pipe that guides steam from a boiler to a high-pressure turbine, and a high-temperature reheat steam pipe that guides steam from a boiler reheater to an intermediate-pressure turbine. Can do. Furthermore, examples of the steam turbine pipe include a main steam introduction pipe that guides high-temperature and high-pressure steam introduced into the steam turbine to the nozzle box. Note that the steam turbine piping is not limited to these, and includes, for example, piping through which steam having a temperature of 680 to 750 ° C. flows.

  Even if all the parts of the forged parts of the steam turbine described above are composed of the Ni-based alloy described above, some parts of the forged parts of the steam turbine that are particularly hot are composed of the Ni-based alloy described above. May be. Here, as the region where the forged part of the steam turbine becomes high temperature, specifically, for example, 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, etc. . Furthermore, examples of the region where the forged parts of the steam turbine are heated include piping sections such as a main steam pipe and a high-temperature reheat steam pipe that guide the above-described high-temperature and high-pressure steam to various steam turbines. In addition, the part from which the forge components of a steam turbine become high temperature is not restricted to these, For example, if it is a part from which temperature becomes about 680-750 degreeC, it will be contained in this.

  In addition, in the forged parts of the steam turbine described above, when the connecting parts for joining, fastening, or fitting the forged parts are provided, at least the connecting parts of the respective forged parts should be composed of the Ni-based alloy according to the embodiment of the present invention. Thus, it is possible to reduce the thermal stress due to the difference in thermal expansion as compared with the case of a combination of different alloys. Specific examples of such combinations of forged parts of the steam turbine include a moving blade and a turbine rotor in which the moving blade is implanted.

  In addition, the Ni-based alloy according to the embodiment of the present invention described above is superior in high-temperature strength characteristics and superior in forgeability than conventional Ni-based alloys. That is, using this Ni-based alloy, forging parts of a steam turbine such as a turbine rotor of a steam turbine, a moving blade of a steam turbine, a stationary blade of a steam turbine, a threaded member for a steam turbine, and a pipe for a steam turbine are configured. Therefore, forging parts such as a turbine rotor of a steam turbine, a moving blade of a steam turbine, a stationary blade of a steam turbine, a threaded member for a steam turbine, and a pipe for a steam turbine having high reliability even in a high temperature environment. Can do.

  Next, the reason for limitation of each composition component range in the Ni-based alloy according to the embodiment of the present invention described above will be described.

(1) C (carbon)
C is useful as a constituent element of the carbide that is the strengthening phase, and also has a function of suppressing the coarsening of the crystal grains at a high temperature by the pinning effect of the carbide that prevents the movement of the crystal grain boundary. When the C content is less than 0.01, strengthening with carbides is not sufficient, and a sufficient amount of precipitation of carbides cannot be secured, which may cause coarsening of crystal grains. On the other hand, if the C content exceeds 0.15%, the forgeability decreases. Therefore, the C content is determined to be 0.01 to 0.15%.

(2) Cr (chromium)
Cr is an essential element for enhancing the oxidation resistance, corrosion resistance and high temperature strength characteristics of the Ni-based alloy. When the Cr content is less than 14%, the oxidation resistance and the corrosion resistance decrease. On the other hand, if the Cr content exceeds 20%, precipitation of the σ phase is induced, and mechanical properties such as impact value, creep properties, and low cycle fatigue life are deteriorated. Therefore, the Cr content is determined to be 14 to 20%.

(3) Co (cobalt)
Co dissolves in the matrix phase in a Ni-based alloy, and improves the creep strength and tensile strength. If the Co content is less than 10%, sufficient mechanical strength cannot be obtained. On the other hand, if the Co content exceeds 15%, the forgeability decreases. Therefore, the Co content is determined to be 10 to 15%.

(4) Mo (molybdenum)
Mo dissolves in the Ni matrix and has the effect of improving the creep strength and tensile strength, and also increases the stability of the carbide by partially replacing the M ₂₃ C ₆ type carbide. When the Mo content exceeds 12%, the mechanical strength is significantly lowered due to precipitation of the σ phase. On the other hand, when the Mo content is less than 8%, the mechanical strength cannot be improved. Therefore, the Mo content is determined to be 8 to 12%.

(5) Al (aluminum)
Al forms a γ ′ (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 0.5%, the effect of precipitation of the γ ′ phase is not exhibited because it is completely dissolved in the Ni matrix. On the other hand, when the Al content exceeds 4%, precipitation of the σ phase is promoted, the mechanical properties are lowered, and the solid solution temperature of the γ ′ phase is raised, so that the hot workability is significantly lowered. Therefore, the Al content is determined to be 0.5 to 4%.

(6) Ti (titanium)
Ti, like Al, produces a γ ′ (Ni ₃ Ti) phase together with Ni, and improves the mechanical strength of the Ni-based alloy. When the Ti content is less than 0.5%, the effect of precipitation of the γ ′ phase is not exhibited. On the other hand, if the Ti content exceeds 4%, precipitation of the σ phase is promoted, the mechanical properties are lowered, and the solid solution temperature of the γ ′ phase is raised, so that the hot workability is remarkably lowered. Therefore, the Ti content is determined to be 0.5 to 4%.

(7) B (boron)
B segregates at the grain boundaries and improves the high temperature strength characteristics. When the B content is less than 0.001%, the effect of improving the high temperature strength characteristics is not exhibited. On the other hand, if the B content exceeds 0.006%, grain boundary embrittlement is caused. Therefore, the B content is determined to be 0.001 to 0.006%.

(8) Ta (tantalum)
Ta dissolves in the γ ′ (Ni ₃ (Al, Ti)) phase and stabilizes the precipitation strength of the γ ′ phase. When the Ta content is less than 0.1%, the above effect is not improved as compared with the conventional steel. When the Ta content exceeds 0.7%, the forgeability decreases. Therefore, the Ta content is determined to be 0.1 to 0.7%.

(9) Nb (Niobium)
Nb, like Ta, dissolves in the γ ′ (Ni ₃ (Al, Ti)) phase and stabilizes the precipitation strength of the γ ′ phase. When the Nb content is less than 0.1%, the above effects are not improved as compared with the conventional steel. When the Nb content exceeds 0.4%, segregation occurs during melting and casting. Invite. Therefore, the Nb content is determined to be 0.1 to 0.4%.

(10) Si (silicon), Mn (manganese), Cu (copper), Fe (iron) and S (sulfur)
Si, Mn, Cu, Fe and S are classified as inevitable impurities in the Ni-based alloy according to the embodiment of the present invention. It is desirable that the residual content of these inevitable impurities is as close to 0% as possible. Of these inevitable impurities, at least Si and Mn are preferably suppressed to 0.1% or less.

  In the case of plain steel, Si is added to supplement the corrosion resistance. However, since the Ni-based alloy has a high Cr content and can sufficiently secure corrosion resistance, the Ni-based alloy of the embodiment according to the present invention has a residual content of Si of 0.1% or less, and the residual content is as much as possible. It is desirable to bring the content closer to 0%.

  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 of the embodiment according to the present invention, it is desirable that the residual content of Mn is 0.1% or less and that the residual content is as close to 0% as possible.

(11) 0.45Cr + Al + Ti
In FIG. 1 described above, the line L, which is the boundary line between the region where the σ phase precipitates and the region where the σ phase does not precipitate, is the Cr content (mass%) and the Al and Ti contents (mass%). (0.45Cr + Al + Ti = 10.5% by mass). When the value of 0.45Cr + Al + Ti is 10.5 or less, the precipitation of the σ phase can be completely prevented, but when the value of 0.45Cr + Al + Ti is less than 9.5, sufficient precipitation of the γ ′ phase is obtained. In other words, the effect of improving the mechanical characteristics is reduced.

  On the other hand, even in the region above the line L where the σ phase precipitates, when the value of 0.45Cr + Al + Ti is 13 or less, the mechanical characteristics are degraded even if the σ phase is precipitated. There is nothing. On the other hand, when the value of 0.45Cr + Al + Ti exceeds 13, the amount of precipitation of the σ phase increases, and the mechanical properties are significantly deteriorated. Therefore, 0.45Cr + Al + Ti was made into the range of 9.5-13 mass%.

  Here, a Ni-based alloy for a forged part of a steam turbine according to an embodiment of the present invention and a method for manufacturing a forged part of a steam turbine manufactured using the Ni-based alloy for a forged part will be described.

  The above-described Ni-based alloy for forged parts of a steam turbine according to an embodiment of the present invention includes, for example, vacuum induction melting (VIM) of composition components constituting the Ni-based alloy and injecting the molten metal into a predetermined mold. An ingot is formed, the ingot is soaked, forged by rolling or the like, and subjected to a solution treatment, an aging treatment, or the like.

  Moreover, the turbine rotor of the steam turbine which is a forged part of embodiment which concerns on this invention is produced as follows, for example.

  For example, as one method (double melt), vacuum induction melting (VIM) and electroslag remelting (ESR) are performed on the composition components constituting the Ni-based alloy for forged parts of the steam turbine according to the embodiment of the present invention, Pour into a predetermined mold. Subsequently, a soaking process, a forging process, a solution treatment, an aging process, and the like are performed to produce a turbine rotor.

  As another method (double melt), the composition components constituting the Ni-based alloy for forged parts of the steam turbine according to the embodiment of the present invention are vacuum induction melted (VIM), vacuum arc remelted (VAR), predetermined Pour into the mold. Subsequently, a soaking process, a forging process, a solution treatment, an aging process, and the like are performed to produce a turbine rotor.

  Furthermore, as another method (triple melt), the composition components constituting the Ni-based alloy for forged parts of the steam turbine according to the embodiment of the present invention are vacuum induction melted (VIM), electroslag remelted (ESR), Vacuum arc remelting (VAR) and pouring into a predetermined mold. Subsequently, a soaking process, a forging process, a solution treatment, an aging process, and the like are performed to produce a turbine rotor. In addition, ultrasonic inspection etc. are performed for the turbine rotor produced by the said method.

  At least a predetermined portion of the turbine rotor is manufactured by the above-described method for manufacturing a turbine rotor of a steam turbine. Examples of the predetermined portion include a portion of the turbine rotor that is exposed to a high temperature of 700 ° C. or higher. In this case, the part exposed to a temperature of, for example, about 600 ° C. in the turbine rotor is manufactured by a conventional heat-resistant alloy. And the component which consists of Ni base alloy of embodiment which concerns on this invention manufactured by the above-mentioned manufacturing method, and the component which consists of conventional heat-resistant alloys are joined by welding, for example, and a turbine rotor is comprised.

  In addition, the joining method of the component which consists of Ni base alloy of embodiment which concerns on this invention, and the component which consists of the conventional heat-resistant alloy is not restricted to welding, For example, you may fasten with a volt | bolt and a nut. In this way, by selecting materials based on the temperature conditions to be used and dividing and manufacturing the components that make up the turbine rotor, even in Ni-based alloys of small steel ingots in a high temperature environment of 700 ° C. or higher A usable turbine rotor can be produced. Depending on the temperature conditions used, all of the turbine rotor may be manufactured by the above-described method for manufacturing a turbine rotor of a steam turbine.

  Moreover, the moving blade of the steam turbine, the stationary blade of the steam turbine, and the screwing member for the steam turbine, which are the forged parts according to the embodiment of the present invention, are manufactured as follows, for example.

  First, the composition components constituting the Ni-based alloy for forged parts of a steam turbine according to an embodiment of the present invention are vacuum induction melted (VIM), remelted by electroslag (ESR), and poured into a predetermined mold in a reduced-pressure atmosphere. A lump is made and soaked. The ingot is placed in a mold corresponding to the shape of the forged part and subjected to a forging process such as rolling, a solution treatment, an aging process, etc., so that a moving blade of a steam turbine, a stationary blade of a steam turbine, a steam turbine A screwing member is produced. That is, the moving blade of the steam turbine, the stationary blade of the steam turbine, and the screwed member for the steam turbine are produced by die forging.

  In addition, the moving blade of the steam turbine, the stationary blade of the steam turbine, and the screwed member for the steam turbine, for example, vacuum induction melting (for example, the composition component constituting the Ni-based alloy for forged parts of the steam turbine of the embodiment according to the present invention) VIM), vacuum arc remelting (VAR), pouring into a predetermined mold in a reduced pressure atmosphere to produce an ingot, soaking treatment, forging treatment, solution treatment, aging treatment, etc. Good.

  Furthermore, the moving blade of the steam turbine, the stationary blade of the steam turbine, and the screwed member for the steam turbine are, for example, vacuum induction melting (for example) the composition components constituting the Ni-based alloy for forged parts of the steam turbine according to the embodiment of the present invention ( VIM), electroslag remelting (ESR), vacuum arc remelting (VAR), casting into a predetermined mold in a reduced pressure atmosphere, producing an ingot, soaking treatment, forging treatment, solution treatment, aging treatment It may be produced by a method of applying the above.

  Moreover, the piping for steam turbines which is a forged part of embodiment which concerns on this invention is produced as follows, for example.

  First, the composition components constituting the Ni-based alloy for forged parts of a steam turbine according to an embodiment of the present invention are melted in an electric furnace (EF), subjected to argon-oxygen decarburization (AOD) to produce an ingot, and soaked Apply processing. This ingot is perforated with a vertical press to produce a cup-shaped tube, and processing with a mandrel and a die and reheating are repeated with a horizontal press, and then molded into the shape of a steam turbine piping to produce a steam turbine piping. Is done. This processing method is the Erhard-push bench pipe manufacturing method. And a solution treatment, an aging treatment, etc. are given.

  Here, the soaking process, the solution treatment, and the aging process in manufacturing the Ni-based alloy for the forged part of the steam turbine and the forged part of the steam turbine are performed as follows. In addition, the temperature and time in each process are set in the following ranges according to the forged parts to be processed.

  In the soaking process, it is necessary to heat a metal or alloy at a high temperature for a sufficient time in order to reduce segregation of chemical components by thermal diffusion. Therefore, it is preferable to maintain in the temperature range of 1000 to 1250 ° C. for 3 to 72 hours. Moreover, since it is necessary to perform forging in the range from the temperature which can obtain sufficient deformability of material to zero ductility temperature, it is preferable to be performed in the temperature range of 950-1100 degreeC.

  In the solution treatment, it is preferably maintained in a temperature range of 1000 to 1200 ° C. for 3 to 24 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 below 1000 ° C., the solution is not sufficiently dissolved, and at a temperature above 1200 ° C., the crystal grains are coarse. As a result, the strength decreases. These heat treatments may be performed under several set conditions in stages within the above temperature range. Cooling after the solution treatment is performed by water cooling or forced air cooling.

  In the aging treatment, it is preferable to maintain for 3 to 30 hours in a temperature range of 700 to 1050 ° C., which is a precipitation temperature range of carbide, γ ′ phase and the like. By performing this aging treatment, it is possible to achieve morphology control and early precipitation of precipitates. This aging treatment may be performed in multiple stages.

  The above-described method for producing the steam turbine turbine rotor, the steam turbine rotor blade, the steam turbine stationary blade, the steam turbine screw member, and the steam turbine pipe is not limited to the above method. .

  Below, it demonstrates that the Ni base alloy for forge components of the steam turbine of embodiment which concerns on this invention is excellent in a high temperature strength characteristic and forgeability.

(Evaluation of high temperature strength characteristics and forgeability)
Table 1 shows the chemical compositions of Sample 1 to Sample 25 used for the evaluation of the high temperature strength characteristics and forgeability, and Table 2 shows the chemistry of Sample 26 to Sample 48 used for the evaluation of the high temperature strength characteristics and forgeability. The composition is shown. Note that Sample 1 to Sample 25 shown in Table 1 are Ni-based alloys in the chemical composition range of the embodiment according to the present invention, and Sample 26 to Sample 48 shown in Table 2 have the same composition. It is a Ni-based alloy that is not within the chemical composition range of the embodiment according to the invention, and is a comparative example. The Ni-based alloy in the chemical composition range of the embodiment according to the present invention used here contains Fe, Cu, and S in addition to Si and Mn as unavoidable impurities.

  High temperature strength properties were evaluated by creep rupture test. In the creep rupture test, 20 kg of the Ni-based alloys of Samples 1 to 48 having the chemical compositions shown in Table 1 and Table 2 were respectively melted in a vacuum induction melting furnace to produce an ingot.

  Subsequently, the ingot was subjected to a soaking process at 1050 ° C. for 5 hours. Then, it forged with a 500 kgf hammer forging machine in the temperature range of 950-1100 degreeC (reheating temperature is 1100 degreeC). After forging, it was heated at 1180 ° C. for 4 hours, and then cooled by forced air cooling to give a solution treatment. After solution treatment, aging treatment was performed by heating at 750 ° C. for 30 hours to obtain forged steel. And the test piece of the predetermined size was produced from this forged steel.

  Then, the creep rupture strength at a temperature of 700 ° C. and 100,000 hours was measured for the test piece of each sample. The creep rupture test was performed according to the standard of JIS Z 2271.

  Here, 700 ° C., which is a temperature condition in the creep rupture test, was set in consideration of a temperature condition during normal operation of the steam turbine and a temperature in consideration of the safety factor. Table 2 shows the measurement results of the creep rupture test.

  Moreover, forgeability was evaluated with respect to each sample. Evaluation of forgeability forged the sample after the above-mentioned soaking treatment with a 500 kgf hammer forging machine to produce a cylindrical test piece having a diameter of 63 mm and a length of 500 to 570 mm. Further, the forging process was performed until the forging ratio (forging ratio based on JIS G 0701 (how to express the forging forming ratio of steel forging work)) was 3. Note that the forging process is performed in the range of 950 to 1100 ° C., and when the temperature of the test piece that is the forging object decreases, that is, when the forging object has hardened, it is heated again to the reheating temperature of 1100 ° C. The forging process was repeated. Evaluation of forgeability was performed by visually observing the presence or absence of forging cracks after cooling a cylindrical sample.

  Here, the forging ratio refers to the cross-sectional area of the forged object perpendicular to the direction in which the forged object is elongated before the forging process, and the direction in which the forged object is elongated after the forging process. Is divided by the cross-sectional area of the forging object perpendicular to.

  The evaluation results of forgeability are shown in Table 3. The number of reheats shown in Table 3 is the number of times that the forging object is reheated until the forging ratio is set to 3 in the forging process. Here, in Table 3, when there is no forging crack, it is indicated as “none”, and further, the forging property is indicated by “◯” in order to indicate that the forgeability is excellent. On the other hand, when there is a forging crack, it is indicated as “present”, and further, the forgeability is indicated by “x” in order to indicate that the forgeability is inferior.

  As shown in Table 3, it was found that Sample 1 to Sample 25 had higher creep rupture strength than Sample 26 to Sample 48. Furthermore, it was found that Sample 1 to Sample 25 were excellent in forgeability. It is considered that the reason why the creep rupture strength was high in Samples 1 to 25 was that precipitation strengthening and solid solution strengthening were achieved.

  On the other hand, in the sample of the comparative example, for example, the samples according to the comparative example of the sample 32, the sample 42, and the sample 44 showed high creep rupture strength, but it was found that the forgeability was inferior. Moreover, although the sample which concerns on the comparative example of the sample 46 showed high creep rupture strength, since the temperature range which can be forged was narrow, the frequency | count of reheating increased. Such materials are not only likely to require reheating during the forging process, but are also more likely to experience fatal cracking during forging. Thus, in the sample according to the comparative example, results excellent in both high temperature strength characteristics and forgeability were not obtained.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  L ... Line.

Claims (3)

  In mass%, C: 0.01 to 0.15, Cr: 14 to 20, Co: 10 to 15, Mo: 8 to 12, Al: 0.5 to 4, Ti: 0.5 to 4, B: 0.001 to 0.006, Ta: 0.1 to 0.7, Nb: 0.1 to 0.4, the balance is made of Ni and inevitable impurities, and 9.5% by mass ≦ 0.45Cr + Al + Ti ≦ 13 A Ni-based alloy for steam turbine forged parts, characterized by satisfying a mass% relationship.   The Ni-based alloy for steam turbine forged parts according to claim 1, wherein among the inevitable impurities, at least Si is suppressed to 0.1 mass% or less and Mn is controlled to 0.1 mass% or less.   A forged component of a steam turbine, wherein at least a predetermined portion is made by forging using the Ni-based alloy for forged components of a steam turbine according to claim 1 or 2.

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