JP2018150594A - Cast steel, nozzle plate, method for producing nozzle plate, and stationary blade row - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cast steel that has high production efficiency and can easily achieve cost reduction.SOLUTION: A cast steel according to an embodiment contains, in mass%, C: 0.11-0.15%, Si: 0.20-0.50%, Mn: 0.3-1.0%, Ni: 0.3-0.8%, Cr: 9.0-11.0%, Mo: 0.9-1.1%, V: 0.15-0.25%, W: 0.9-1.1%, Nb: 0.05-0.10%, N: 0.015-0.03% with the balance being Fe and inevitable impurities. The inevitable impurities are Al: less than 0.005%.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to cast steel, a nozzle plate, a nozzle plate manufacturing method, and a stationary blade cascade.

  In a steam turbine, a stationary blade cascade is constituted by, for example, a nozzle diaphragm in which a plurality of nozzle plates (stationary blades) are arranged between a diaphragm outer ring and a diaphragm inner ring. In the nozzle diaphragm, the nozzle plate is fixed to each of the diaphragm outer ring and the diaphragm inner ring by means other than welding or welding.

Patent No. 4040922 Patent No. 3106130 JP 2010-242221 A Japanese Unexamined Patent Publication No. 2000-297606

  In general, the nozzle plate is formed by cutting a square bar formed by forging or rolling. For this reason, when producing a nozzle plate as mentioned above, much time is required. Further, since the difference between the weight of the square material as the raw material and the weight of the nozzle plate as the final product is large, the yield is low. Under such circumstances, the production of the nozzle plate is low in manufacturing efficiency, and cost reduction is not easy. In other words, it is not reasonable from the viewpoint of economy.

  Therefore, the problem to be solved by the present invention is to provide a cast steel, a nozzle plate, a method for manufacturing a nozzle plate, and a stationary blade cascade, which have high manufacturing efficiency and can easily realize cost reduction.

  The cast steel of the embodiment is mass%, C: 0.11 to 0.15%, Si: 0.20 to 0.50%, Mn: 0.3 to 1.0%, Ni: 0.3 to 0 0.8%, Cr: 9.0 to 11.0%, Mo: 0.9 to 1.1%, V: 0.15 to 0.25%, W: 0.9 to 1.1%, Nb: 0.05 to 0.10%, N: 0.015 to 0.03%, with the balance being Fe and unavoidable impurities. Inevitable impurities are Al: less than 0.005%.

FIG. 1 schematically shows a steam turbine including a stationary blade cascade composed of nozzle plates (static blades) of the present embodiment.

  First, the cast steel (M1), (M2), and (M3) of the embodiment will be described. The cast steels (M1), (M2), and (M3) of the embodiment are in the ranges shown below for each component.

  Cast steel (M1) is mass%, C: 0.11 to 0.15%, Si: 0.20 to 0.50%, Mn: 0.3 to 1.0%, Ni: 0.3 to 0 0.8%, Cr: 9.0 to 11.0%, Mo: 0.9 to 1.1%, V: 0.15 to 0.25%, W: 0.9 to 1.1%, Nb: 0.05 to 0.10%, N: 0.015 to 0.03%, and the balance consists of Fe and inevitable impurities. In the cast steel (M1), the inevitable impurities are Al: less than 0.005% (value after being cast in the atmosphere).

  The composition of the cast steel (M2) is mass%, C: 0.11 to 0.15%, Si: 0.20 to 0.50%, Mn: 0.3 to 1.0%, Ni: 0.3 -0.8%, Cr: 9.0-11.0%, Mo: 0.9-1.1%, V: 0.15-0.25%, Nb: 0.05-0.20%, N: 0.015 to 0.03%, with the balance being Fe and inevitable impurities. In the cast steel (M2), the inevitable impurities are Al: less than 0.005% (value after being cast in the atmosphere). That is, the cast steel (M2) is obtained by removing the W component from the components of the cast steel (M1) described above, and the content ratio of the Nb component is changed to the above range.

  Cast steel (M3) is mass%, C: 0.11 to 0.15%, Si: 0.20 to 0.50%, Mn: 0.3 to 1.0%, Cr: 12.0 to 14 0.0%, N: 0.015 to 0.03%, the balance being Fe and inevitable impurities. In the cast steel (M3), the inevitable impurities are Al: less than 0.005% (value after being cast in the atmosphere). That is, the cast steel (M3) is obtained by removing the Ni component, the Mo component, the V component, the W component, and the Nb component from the components of the cast steel (M1) described above, and the content ratio of the Cr component is as described above. The range has been changed.

  The cast steels (M1), (M2), and (M3) of the embodiment have almost no anisotropy, have uniform mechanical properties, and are excellent in economic efficiency. In the above, “C: 0.11 to 0.15%” or the like indicates that the C element content is 0.11% by mass or more and 0.15% by mass or less (the same applies hereinafter). ).

  The reason why the ratio (content ratio) contained in each component in the cast steel (M1), (M2), (M3) of the embodiment is set in the above range will be described.

C (carbon) [(M1), (M2), (M3) ... 0.11 to 0.15%]
C is a component necessary for ensuring hardenability and hot water flow during casting, and is an indispensable component as a constituent element constituting the carbide contributing to precipitation strengthening. In the cast steels (M1), (M2), and (M3) of the embodiment, when the C content is less than the lower limit of the above range, the above-described functions and effects are reduced. When the C content exceeds the upper limit of the above range, the agglomeration of the carbide is promoted and the segregation tendency at the time of casting is increased, so that weldability including repair is lowered. For this reason, in the cast steel (M1), (M2), (M3) of the embodiment, the C content is set in the above range.

Si (silicon) [(M1), (M2), (M3) ... 0.20 to 0.50%]
Si is a component that is useful as a deoxidizer and improves the flow of molten metal. In the cast steels (M1), (M2), and (M3) of the embodiment, when the Si content is less than the lower limit of the above range, the above-described functions and effects are reduced. When the Si content exceeds the upper limit of the above range, toughness reduction and embrittlement are significantly promoted. For this reason, in the cast steel (M1), (M2), (M3) of the embodiment, the Si content is set in the above range.

Mn (manganese) [(M1), (M2), (M3) ... 0.3-1.0%]
Mn is a component useful as a desulfurization agent. In the cast steels (M1), (M2), and (M3) of the embodiment, when the Mn content is less than the lower limit of the above range, the desulfurization effect is not sufficiently exhibited. When the Mn content exceeds the upper limit of the above range, the creep strength decreases. For this reason, in the cast steel (M1), (M2), (M3) of the embodiment, the Mn content is set in the above range.

Ni (nickel) [(M1), (M2) ... 0.3-0.8%, (M3) ... 0.0%]
Ni is a component that improves hardenability and toughness and has an effect of suppressing the formation of ferrite. In the cast steels (M1) and (M2) of the embodiment, when the Ni content is less than the lower limit of the above range, the above effects are not sufficiently exhibited. When the Ni content exceeds the upper limit of the above range, the creep strength decreases. For this reason, in the cast steel (M1) and (M2) of the embodiment, the Ni content is set in the above range.

-Cr (chromium) [(M1), (M2) ... 9.0-11.0%, (M3) ... 12.0-14.0 %%]
Cr is an effective component for improving oxidation resistance and corrosion resistance, and is an indispensable component as a constituent element of carbonitride contributing to precipitation strengthening. In the cast steels (M1) and (M2) of the embodiment, when the Cr content is less than the lower limit of the above range, there are few precipitates (carbonitrides) that precipitate with Cr as a constituent element in the refining heat treatment. Therefore, sufficient high temperature stability may not be ensured. When the Cr content exceeds the upper limit of the above range, the tendency for ferrite to be generated increases. For this reason, in the cast steel (M1) and (M2) of the embodiment, the Cr content is set in the above range. On the other hand, since the cast steel (M3) of the embodiment does not contain a ferrite forming element (Mo, W, Nb, V, etc.), it is difficult to generate ferrite. For this reason, in the cast steel (M3) of embodiment, it can be made the said range with the content rate of Cr higher than the case of cast steel (M1) and (M2).

Mo (molybdenum) [(M1), (M2) ... 0.9 to 1.1%, (M3) ... 0.0%]
Mo is a component that contributes to solid solution strengthening, and is a constituent element of carbonitride and a component that contributes to precipitation strengthening. Mo becomes a constituent element of precipitates when long-time heat treatment is performed in a high-temperature environment. However, in the cast steels (M1) and (M2) of the embodiment, when the Mo content is less than the lower limit of the above range, it is difficult to keep the amount of Mo contributing to solid solution strengthening high for a long time. Become. When the Mo content exceeds the upper limit of the above range, toughness is reduced and the formation of ferrite is promoted. For this reason, in the cast steel (M1) and (M2) of the embodiment, the Mo content is within the above range.

V (Vanadium) [(M1), (M2) ... 0.15-0.25%, (M3) ... 0.00%]
V is a component contributing to solid solution strengthening and a component contributing to the formation of fine carbonitrides. In the cast steels (M1) and (M2) of the embodiment, when the V content is less than the lower limit of the above range, the above-described functions and effects are not sufficient. When the V content exceeds the upper limit of the above range, toughness is reduced. For this reason, the content rate of V was made into the said range in cast steel (M1) of the embodiment (M2).

W (tungsten) [(M1) ... 0.9 to 1.1%, (M2), (M3) ... 0.0%]
W is a component that contributes to solid solution strengthening and is a constituent element of carbonitride and a component that contributes to precipitation strengthening. W can remarkably enhance the high-temperature stability of the precipitate, particularly when added in combination with Mo. W becomes a constituent element of precipitates when long-time heat treatment is performed in a high-temperature environment. However, in the cast steel (M1) of the embodiment, when the W content is less than the lower limit of the above range, it is difficult to keep the amount of W contributing to solid solution strengthening high for a long time. When the W content exceeds the upper limit of the above range, toughness decreases and the formation of ferrite is promoted. For this reason, the content rate of W was made into the said range in the cast steel (M1) of embodiment.

Nb (niobium) [(M1) ... 0.05-0.10%, (M2) ... 0.05-0.20%, (M3) ... 0.00%]
Nb is a component that contributes to solid solution strengthening and contributes to the formation of fine carbonitrides.
In the cast steels (M1) and (M2) of the embodiment, when the Nb content is less than the lower limit of the above range, the above-described functions and effects are not sufficient. When the Nb content exceeds the upper limit of the above range, the amount of coarse Nb carbonitrides generated increases. For this reason, in the cast steel (M1) and (M2) of the embodiment, the Nb content is set to the above range. In addition, in cast steel (M2), since W is not added, the precipitation strengthening effect | action by Nb carbonitride is heightened by making the upper limit about the content rate of Nb component larger than cast steel (M1).

N (nitrogen) [(M1), (M2), (M3) ... 0.015 to 0.05%]
N is a component that contributes to precipitation strengthening by forming nitrides or carbonitrides. Further, N remaining in the matrix contributes to solid solution strengthening. N is dissolved and absorbed in cast steel when casting is performed in the atmosphere. In the cast steels (M1), (M2), and (M3) of the embodiment, when the N content is less than the lower limit of the above range, the amount of carbonitride produced by the heat treatment is reduced. , Not enough. When the N content exceeds the upper limit of the above range, the coarsening of the nitride is promoted and the precipitation strengthening action is reduced. Therefore, it is necessary to reduce the N content by adjusting the components. For this reason, in the cast steel (M1), (M2), and (M3) of the embodiment, the N content is within the above range.

・ Al (aluminum) [(M1), (M2), (M3) ... less than 0.005%]
Al is a component useful as a deoxidizer. However, in the steel containing N, Al nitride is easily generated. For this reason, it is preferable that the Al content is as low as possible. Therefore, in the cast steels (M1), (M2), and (M3) of the embodiment, the upper limit of the content of Al that is an inevitable impurity is set to the above value.

  Hereinafter, in the embodiment, the nozzle plate formed of the cast steel will be described.

  In the present embodiment, the nozzle plate is manufactured by casting. Here, for example, the nozzle plate is manufactured by casting in the atmosphere by a precision casting method.

  Specifically, a prototype is formed in the shape of a nozzle plate with wax. Next, the periphery of the original mold is covered with cast sand and hardened, and then the wax is dissolved and removed to produce a sand mold. Next, after pouring a molten metal in which each component constituting the cast steel is poured into a sand mold, the nozzle plate which is a casting (cast steel) is formed by cooling. Then, temper heat treatment is performed on the nozzle plate. Here, annealing, normalizing, quenching (cooling), and tempering are sequentially performed as the tempering heat treatment. Finally, the nozzle plate is completed by finishing. In the present embodiment, the nozzle plate formed of the above cast steel is strengthened by precipitation of carbonitrides together with solid solution strengthening of the matrix phase in the initial state.

  The production period can be shortened by producing the nozzle plate formed of the above cast steel by a precision casting method. For example, when a nozzle plate is manufactured by cutting a square bar formed by forging or rolling, a manufacturing period of 7 to 9 months is required. On the other hand, when the nozzle plate formed of the cast steel is manufactured by a precision casting method, the manufacturing period is 2 to 3 months, and the manufacturing period can be effectively shortened.

The nozzle plate of the present embodiment is composed of a martensite single-phase structure and includes precipitates. The precipitate is a carbonitride intentionally deposited by tempering heat treatment. By performing the tempering heat treatment, each element existing in the matrix phase precipitates as M ₂ C type, MC type, and M ₂₃ C ₆ type precipitates, thereby contributing to improvement in strength and maintenance of strength. . In the M ₂ C type, MC type, and M ₂₃ C ₆ type, M represents a metal element. In the M ₂ C type and the M ₂₃ C ₆ type, M is mainly Cr and Fe, and may be Mo and W (for example, (Cr, Fe, Mo, W) ₂₃ ( C, N) ₆ )). In the MC type, M is mainly V and Nb.

  In the nozzle plate (N1) formed of cast steel (M1), the ratio of each component constituting the precipitate is mass%, Fe: 0.5-0.8%, Cr: 1.0-1.5% , Mo: 0.3 to 0.5%, W: 0.3 to 0.5%, V: 0.05 to 0.10%, Nb: 0.02 to 0.10% are preferable.

  In the nozzle plate (N2) formed of cast steel (M2), the ratio of each component constituting the precipitate is mass%, Fe: 0.5 to 0.8%, Cr: 1.0 to 1.5% , Mo: 0.3 to 0.5%, V: 0.05 to 0.10%, Nb: 0.04 to 0.12% are preferable.

The measurement and identification of the precipitate can be performed by the following method. First, the weight X1 (before dissolution) of the sample is measured. Then, a sample is put in a mixed solution (methanol, acetylacetone, tetramethylammonium chloride), and the parent phase of the sample is dissolved in the mixed solution by electrolysis. Thereby, the residue of the sample is isolated as a precipitate in the mixed solution. And the deposit (residue) of the sample is wash | cleaned, and the weight X2 is measured about the deposit of the sample. Further, by performing analysis such as an X-ray analysis method on the sample precipitate, the components constituting the sample precipitate are identified and quantified. Thereby, the ratio Rm (%) of each component constituting the sample (precipitate) after dissolution is obtained. And the weight X1 of the sample (matrix and precipitate) before dissolution, the weight X1 of the sample (precipitate) after dissolution, and the ratio R1 (%) of each component constituting the sample (precipitate) after dissolution The ratio R2 of each component constituting the precipitate in the cast steel (nozzle plate) (the ratio when the total weight of the cast steel (nozzle plate) is 100% by mass) can be calculated (the following) (See formula (A)).
R2 = (X2 / X1) · R1 Formula (A)

  The reason why the ratio of each component constituting the precipitate in the nozzle plates (N1) and (N2) formed of the cast steel (M1) and (M2) of the embodiment is set in the above range will be described.

Fe [(N1), (N2) ... 0.5 to 0.8%]
In the precipitate, Fe is a constituent element that mainly constitutes the M ₂₃ C ₆ type precipitate and is a component that contributes to the stabilization of the precipitate. In the nozzle plates (N1) and (N2), when the Fe content constituting the precipitate is less than the lower limit of the above range, the precipitate is not sufficiently precipitated and the stability is lowered. That is, the effect of precipitation strengthening does not work sufficiently. On the other hand, when the Fe content exceeds the upper limit of the above range, the precipitates are coarsened, so that the high temperature characteristics cannot be sufficiently exhibited. For this reason, in the nozzle plates (N1) and (N2) of the embodiment, the content of Fe constituting the precipitate is set in the above range.

・ Cr [(N1), (N2) ... 1.0-1.5%]
In the precipitate, Cr is mainly a constituent element constituting the M ₂₃ C ₆ type precipitate and the M ₂ C type precipitate. Cr is a component that contributes to precipitation strengthening and increases the high-temperature stability of the precipitate. In the nozzle plates (N1) and (N2), when the content of Cr constituting the precipitate is less than the lower limit of the above range, the precipitate is not sufficiently precipitated. That is, the precipitation strengthening effect does not work sufficiently. On the other hand, when the Cr content exceeds the upper limit of the above range, the transformation and coarsening of fine M ₂ C type precipitates are induced, so that the precipitation strengthening action does not work sufficiently. For this reason, in the nozzle plates (N1) and (N2) of the embodiment, the content of Cr constituting the precipitate is set in the above range.

Mo [(N1), (N2) ... 0.3-0.5%]
In the precipitate, Mo is a constituent element that is mainly substituted by a part of the M ₂₃ C ₆ type precipitate and the M ₂ C type precipitate. Mo is a component that enhances the high-temperature stability of the precipitate. In the nozzle plates (N1) and (N2), when the Mo content constituting the precipitate is less than the lower limit of the above range, the stability of the precipitate is lowered. On the other hand, when the Mo content exceeds the upper limit of the above range, the solid solution amount of Mo in the matrix phase decreases, so that the solid solution strengthening action at high temperatures becomes insufficient. For this reason, in the nozzle plates (N1) and (N2) of the embodiment, the content of Mo constituting the precipitate is set in the above range.

W [(N1) ... 0.3-0.5%, (N2) ... 0.0%]
In the precipitate, W is a constituent element that is mainly substituted with part of the M ₂₃ C ₆ type precipitate and the M ₂ C type precipitate. W is a component that enhances the high-temperature stability of the precipitate. When the content of W constituting the precipitate in the nozzle plate (N1) is less than the lower limit of the above range, the stability of the precipitate is lowered. On the other hand, when the W content exceeds the upper limit of the above range, the amount of solid solution in which the solid phase is dissolved in the mother phase is reduced, so that the solid solution strengthening action at high temperatures becomes insufficient. For this reason, in the nozzle plate (N1) of the embodiment, the content of W constituting the precipitate is set in the above range.

・ V [(N1), (N2) ... 0.05-0.10%]
In the precipitate, V is a constituent element that is mainly substituted for part of the MC-type precipitate and the M ₂ C-type precipitate. V is a component that enhances the high-temperature stability of the precipitate. When the content of V constituting the precipitate in the nozzle plate is less than the lower limit of the above range, the stability of the precipitate is lowered. On the other hand, when the content of V exceeds the upper limit of the above range, the M ₂ C type precipitate is coarsened, so that the high temperature characteristics cannot be sufficiently exhibited. For this reason, in the nozzle plates (N1) and (N2) of the embodiment, the content of V constituting the precipitate is set in the above range.

Nb [(N1) ... 0.02-0.10%, (N2) ... 0.04-0.12%]
In the precipitate, Nb is mainly a constituent element that is substituted for a part of the MC type precipitate.
Nb is a component that enhances the high-temperature stability of the precipitate. When the content of Nb constituting the precipitate in the nozzle plate (N1) is less than the lower limit of the above range, the stability of the precipitate is lowered. On the other hand, when the Nb content exceeds the upper limit of the above range, the MC-type precipitates are coarsened, so that the high temperature characteristics cannot be sufficiently exhibited. On the other hand, the nozzle plate (N2) does not include W unlike the nozzle plate (N1). For this reason, in the case of a nozzle plate (N2), the content rate of Nb which comprises a precipitate can be made larger than a nozzle plate (N1). Therefore, in the nozzle plates (N1) and (N2) of the embodiment, the content of Nb constituting the precipitate is set in the above range.

  Hereinafter, in the present embodiment, a steam turbine including a stationary blade cascade composed of the nozzle plate (static blade) will be described with reference to FIG. FIG. 1 shows a cross section along a vertical plane (yz plane).

  As shown in FIG. 1, the steam turbine 1 is a rotating machine, and is configured such that a turbine rotor 22 rotates when steam is supplied as a working fluid. Here, the steam turbine 1 is an axial turbine, and the steam flows with the horizontal direction y along the rotation axis AX of the turbine rotor 22 as the flow direction. The steam turbine 1 is a multistage type, in which turbine stages composed of moving blades 21 and stationary blades 25 are arranged in a plurality of stages in the axial direction along the rotation axis AX, and the steam is in each of the plurality of turbine stages. Do the job. As a result, the turbine rotor 22 rotates in the steam turbine 1. Below, the detail of each part which comprises the steam turbine 1 is demonstrated.

  The casing 20 accommodates the turbine rotor 22 therein. One end of the turbine rotor 22 is connected to a generator (not shown), and the generator (not shown) is driven by the rotation of the turbine rotor 22 to generate power. The turbine rotor 22 is provided with a plurality of rotor disks 221 on the outer peripheral surface. A rotor blade 21 is installed on the outer peripheral surface of a rotor disk 221 provided in the turbine rotor 22. A plurality of moving blades 21 are arranged in the circumferential direction R (rotational direction) of the turbine rotor 22 so as to surround the outer peripheral surface of the turbine rotor 22, and constitute a moving blade cascade. The moving blade cascade has a plurality of stages, and each of the plurality of moving blade cascades is arranged along the rotation axis AX of the turbine rotor 22.

  A nozzle diaphragm 10 is installed inside the casing 20. The nozzle diaphragm 10 includes a diaphragm outer ring 23, a diaphragm inner ring 24, and a stationary blade 25. In the nozzle diaphragm 10, the diaphragm outer ring 23 is installed on the inner peripheral surface of the casing 20. The diaphragm inner ring 24 is installed inside the diaphragm outer ring 23 and spaced from the diaphragm outer ring 23. A plurality of stationary blades 25 are installed between the diaphragm outer ring 23 and the diaphragm inner ring 24.

  Here, the plurality of stationary blades 25 are arranged at intervals in the circumferential direction R so as to surround the outer peripheral surface of the turbine rotor 22, and constitute a stationary blade cascade. Like the moving blade cascade, the stationary blade cascade is provided in a plurality of stages, and the multiple stages of stationary blade cascades are arranged along the rotation axis AX of the turbine rotor 22.

  In the steam turbine 1, a steam inlet pipe 28 passes through the inlet of the casing 20, and steam is introduced into the casing 20 as a working fluid via the steam inlet pipe 28.

  In the present embodiment, the stationary blade 25 is the nozzle plate described above and is formed using cast steel corresponding to the operating temperature.

  In addition to arranging a nozzle plate as the stationary blade 25 between the diaphragm outer ring 23 and the diaphragm inner ring 24, a plurality of nozzle plates may be arranged in the circumferential direction R as the stationary blade 25 in the casing 20 (turbine casing). Good.

  Hereinafter, examples and comparative examples of the cast steel (nozzle plate) described above will be described with reference to Table 1.

  In Table 1, P1 to P9 are examples, and C1 to C5 are comparative examples. Here, for cast steel (M1) containing W element, the examples are P1 to P3, and the comparative examples are C1 and C2 (the cast steel (M1) is C, Si, Mn, Ni, Cr, Mo. , V, W, Nb, N, Fe, and inevitable impurities (Al). For cast steel (M2) that does not contain W element, the examples are P4 to P6 and the comparative examples are C3 and C4 (cast steel (M2) is C, Si, Mn, Ni, Cr, Mo, V , Nb, N, Fe, and inevitable impurities (Al). For cast steel (M3) containing no ferrite forming element other than Cr element, the examples are P7 to P9 and the comparative example is C5 (cast steel (M3) is C, Si, Mn, Cr, N, Fe and inevitable impurities (Al)).

  First, the cast steel of each example was prepared so that each component had the values shown in Table 1.

  Specifically, first, the materials of each component constituting the cast steel of each example were mixed at a ratio shown in Table 1 and melted at a temperature higher than the melting point. Here, a total of about 50 kg of material was melted. Next, casting was performed in the atmosphere using the melted material, thereby producing a nozzle plate-shaped casting. Next, a tempering heat treatment was performed on the nozzle plate-shaped casting. Here, the sample cast steel of each example was produced by performing annealing, normalization, quenching, and tempering sequentially as the tempering heat treatment.

  Annealing, normalizing, quenching, and tempering were performed under the conditions shown in Table 2. The test cast steel of each example was produced so that the tensile strength at room temperature was about 700 MPa.

  Table 3 shows the results of tests performed on the cast steels in each example.

  As shown in Table 3, the tensile strength at 500 ° C. (JIS Z 2241) and the 100,000-hour creep rupture strength at 550 ° C. (JIS Z 2271) were determined for each of the cast steels. Here, a tensile test was performed at 500 ° C. using a JIS No. 4 test piece. Thus, the tensile strength at 500 ° C. was measured, and “100,000 hours creep rupture strength at 550 ° C.” was calculated from the measurement result of the creep rupture strength.

[Welding construction]
As shown in Table 3, the “welding” test was performed on the cast steel of each example. The “welding” test was performed according to the following procedure. The tempered cast steel was processed into a flat plate having a thickness of 10 mm. Then, after preheating the flat plate to 250 ° C., a weld bead was applied to the flat plate using a 9% Cr welding rod in a gas shield environment in which Ar gas and CO 2 gas were mixed. And the presence or absence of generation | occurrence | production of a crack was confirmed about the vicinity of the welding part among the flat plates. In Table 3, a case where no crack is generated in the welded part during welding is indicated by “◯”, and a case where a crack is generated in the welded part during welding is indicated by “x”.

  In addition to the above, a “repetitive tensile test” was performed in which tensile stress was repeatedly applied to the cast steel of each example. The “repeated tensile test” is a test that simulates a state in which tensile stress is applied when welding is performed in a state where both ends of the nozzle plate are constrained. Here, first, in the first test, after applying a load that generates a strain amount of 1% to the nozzle plate, it is confirmed whether or not a defect has occurred on the surface of the nozzle plate by the penetration test. It was. When no defect was generated, a load for generating a strain amount of 2% was applied to the nozzle plate, and it was confirmed whether or not a defect was generated on the surface of the nozzle plate in the same manner as described above. This test was repeated until the amount of strain increased at a constant rate until a defect occurred. In Table 3, when the “repetitive tensile test” is performed, a case where there is no defect on the cast steel surface is indicated as “none”, and a case where a defect occurs on the cast steel surface is indicated as “present”.

  Moreover, in Table 3, when the defect generate | occur | produced on the surface of the cast steel in the "repetitive tensile test", the ratio which the cast steel extended from the initial state (before test) is shown as "elongation value (%)".

  When the test results are compared between P1 to P3 and C1 and C2, the “tensile strength at 500 ° C.” is equivalent between the two. However, “100,000 hour creep rupture strength” is higher in P1 to P3 than in C1. In “welding”, P1 to P3 had no cracks in the welded portion, but C1 had cracks in the welded portion. C2 is equivalent to the case where “100,000 hours creep rupture strength” is P1 to P3, but cracks occurred in the welded part in “welding operation”. In the “repetitive tensile test”, the number of tests in which defects are generated is greater in P1 to P3 than in C1 and C2, and defects are less likely to occur. Further, the “elongation value” is larger in P1 to P3 than in C1 and C2. Unlike the case of C1 and C2, the content rate of each component which comprises P1-P3 is in the range of the content rate of each component which comprises the above-mentioned cast steel (M1). For this reason, P1-P3 is equipped with the outstanding mechanical characteristic as mentioned above.

  When test results are compared between P4 to P6 and C3 and C4, “tensile strength at 500 ° C.” is higher in P4 to P6 than in C3 and C4. Similarly, “100,000 hours creep rupture strength” is higher for P4 to P6 than for C3 and C4. In “welding construction”, cracks occurred in the welded part in P4 to P6, but cracked in the welded part in C3. In the “repeated tensile test”, P4 to P6 have a larger number of tests in which defects occur than C3 and C4, and defects are less likely to occur. Further, the “elongation value” is larger for C4 to P6 than for C3 and C5. Unlike the case of C3 and C4, the content rate of each component which comprises P4-P6 is in the range of the content rate of each component which comprises the above-mentioned cast steel (M2). Therefore, P4 to P6 have excellent mechanical properties as described above.

  When the test results are compared between P7 to P9 and C5, “tensile strength at 500 ° C.” is higher in P7 to P9 than in C5. Similarly, “100,000 hours creep rupture strength” is higher for P4 to P6 than for C5. In “welding construction”, P7 to P9 are not cracked in the welded portion. In the “repetitive tensile test”, P7 to P9 have the same or higher number of tests in which defects are generated as in P1 to P6, and are less likely to generate defects. Moreover, also about "elongation value", P7-P9 is equal to or more than the case of P1-P6. Unlike the case of C5, the content rate of each component which comprises P7-P9 is in the range of the content rate of each component which comprises the above-mentioned cast steel (M3). For this reason, P7-P9 is equipped with the outstanding mechanical characteristic as mentioned above.

  From the above results, it can be seen that the cast steels (M1), (M2), and (M3) have excellent mechanical properties. That is, in the cast steels (M1), (M2), and (M3), “tensile strength at 500 ° C.” and “100,000 hours creep rupture strength” are sufficiently high and the welded portion is cracked in “welding”. It turns out that does not occur. In addition, in the cast steels (M1), (M2), and (M3), it can be seen that defects are unlikely to occur even when tensile stress is repeatedly applied during welding.

  Table 4 shows the results when the tempering temperature is changed for the examples of P1, P2, P5, C1, and C3 (other conditions are the same as above). In Table 4, when the tempering temperature is 700 ° C., the conditions are the same as those shown in Table 2. Table 4 further shows the case where the tempering temperature is 660 ° C. and the case where the tempering temperature is 740 ° C. Table 4 shows the ratio of each component constituting the precipitate in the nozzle plates (N1) and (N2) formed of cast steel (M1) and (M2). Furthermore, in Table 4, it shows about the result of "100,000 hours creep rupture strength" and "welding construction".

  When the tempering temperature for P1 and P2 is 700 ° C., the ratio of each component constituting the precipitate in the nozzle plate (N1) formed of cast steel (M1) is included in the specific range described above. For this reason, “100,000 hours creep rupture strength” is sufficiently high, and no cracks are generated in the welded part in “welding operation”. On the other hand, when the temperature of tempering is 660 ° C., the proportion of each component constituting the precipitate in the nozzle plate (N1) is out of the specific range described above with respect to some components. In this case, the “100,000 hour creep rupture strength” is further increased, but cracking occurs in the welded part in “welding operation”. Similarly, when the temperature of tempering is 740 degreeC, the ratio of each component which comprises a precipitate in a nozzle plate (N1) remove | deviates from the specific range mentioned above regarding a part of component. In this case, cracking does not occur in the welded part in “welding”, but “100,000 hour creep rupture strength” is low.

  When the tempering temperature for P5 is 700 ° C., the ratio of each component constituting the precipitate in the nozzle plate (N2) formed of cast steel (M2) is included in the specific range described above. For this reason, “100,000 hours creep rupture strength” is sufficiently high, and no cracks are generated in the welded part in “welding operation”. On the other hand, when the temperature of tempering is 660 ° C., the proportion of each component constituting the precipitate in the nozzle plate (N2) is out of the specific range described above with respect to some components. In this case, the “100,000 hour creep rupture strength” is further increased, but cracking occurs in the welded part in “welding operation”. Similarly, when the temperature of tempering is 740 degreeC, the ratio of each component which comprises a precipitate in a nozzle plate (N2) remove | deviates from the specific range mentioned above regarding a part of component. In this case, cracking does not occur in the welded part in “welding”, but “100,000 hour creep rupture strength” is low.

  When C1 has a tempering temperature of 700 ° C., the “100,000 hour creep rupture strength” is lower than that of P1 and P2. When the tempering temperature is 660 ° C., the “100,000 hour creep rupture strength” is slightly higher, but cracking occurs in the welded part in “welding operation”. When the tempering temperature is 740 ° C., cracks do not occur in the welded part in “welding operation”, but “100,000 hour creep rupture strength” is further reduced.

  When the tempering temperature for C3 is 700 ° C., the “100,000 hour creep rupture strength” is lower than that of P5, and cracks occur in the welded part in “welding operation”. When the tempering temperature is 660 ° C., the “100,000 hour creep rupture strength” is slightly higher, but cracking occurs in the welded part in “welding operation”. When the tempering temperature is 740 ° C., cracking occurs in the welded part in “welding operation” and “100,000 hours creep rupture strength” is further reduced.

  From the above results, the ratio of each component constituting the precipitate in the nozzle plates (N1) and (N2) formed of cast steel (M1) and (M2) is high by being included in the specific range described above. It can be seen that "creep rupture strength" can be secured. Moreover, it turns out that it can prevent effectively that a crack arises in a welding part in "welding construction".

<Others>
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.

DESCRIPTION OF SYMBOLS 1 ... Steam turbine, 10 ... Nozzle diaphragm, 20 ... Casing, 21 ... Moving blade, 22 ... Turbine rotor, 23 ... Diaphragm outer ring, 24 ... Diaphragm inner ring, 25 ... Stator blade (nozzle plate), 28 ... Steam inlet pipe, AX …Axis of rotation

Claims (8)

  In mass%, C: 0.11 to 0.15%, Si: 0.20 to 0.50%, Mn: 0.3 to 1.0%, Ni: 0.3 to 0.8%, Cr: 9.0-11.0%, Mo: 0.9-1.1%, V: 0.15-0.25%, W: 0.9-1.1%, Nb: 0.05-0. Cast steel containing 10%, N: 0.015 to 0.03%, the balance consisting of Fe and inevitable impurities, the inevitable impurities being Al: less than 0.005%.   In mass%, C: 0.11 to 0.15%, Si: 0.20 to 0.50%, Mn: 0.3 to 1.0%, Ni: 0.3 to 0.8%, Cr: 9.0-11.0%, Mo: 0.9-1.1%, V: 0.15-0.25%, Nb: 0.05-0.20%, N: 0.015-0. Cast steel containing 03%, the balance consisting of Fe and inevitable impurities, the inevitable impurities being Al: less than 0.005%.   In mass%, C: 0.11 to 0.15%, Si: 0.20 to 0.50%, Mn: 0.3 to 1.0%, Cr: 12.0 to 14.0%, N: Cast steel containing 0.015 to 0.03%, with the balance being Fe and inevitable impurities, the inevitable impurities being Al: less than 0.005%. A nozzle plate formed of the cast steel of claim 1,
The nozzle plate is composed of a martensite single-phase structure containing precipitates,
The ratio of each component constituting the precipitate in the nozzle plate is mass%, Fe: 0.5-0.8%, Cr: 1.0-1.5%, Mo: 0.3-0. Nozzle plate having 5%, W: 0.3-0.5%, V: 0.05-0.10%, Nb: 0.02-0.10%. A nozzle plate formed of the cast steel of claim 2,
The nozzle plate is composed of a martensite single-phase structure containing precipitates,
The ratio of each component constituting the precipitate in the nozzle plate is mass%, Fe: 0.5-0.8%, Cr: 1.0-1.5%, Mo: 0.3-0. Nozzle plate having 5%, V: 0.05 to 0.10%, and Nb: 0.04 to 0.12%.   A nozzle plate formed of the cast steel of claim 3. The nozzle plate according to any one of claims 4 to 6 is manufactured by a precision casting method.
Manufacturing method of nozzle plate. A stator blade cascade comprising the nozzle plate according to any one of claims 4 to 6.

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