Steam turbine rotor blade, method for manufacturing a steam turbine rotor blade, and steam turbine

Abstract

Steam turbine rotor blade (49) for forming a turbine rotor cascade (47) of a steam turbine (3), wherein the steam turbine rotor blade (49) has: a rotor blade body (50) comprising: a blade section (51); a blade base section (53) provided at one end of the blade section (51); a first connecting section (55) provided at another end of the blade section (51) having first facing surfaces (59); and a second connecting section (57) provided in a central section of the blade section (51) having second facing surfaces (63), wherein the first facing surfaces (59) are each configured to face one of the first facing surfaces (59) of an adjacent rotor blade body (50) in the turbine rotor cascade (47), and the second facing surfaces (63) are each configured to face one of the second facing surfaces (63) of the adjacent rotor blade body (50) in the turbine rotor cascade (47); and a cover layer (65) consisting of a co-based alloy, having a single composition and formed by high-speed flame spraying on a surface of at least one of the first facing surface (59) and the second facing surface (63), such that a diffusion layer with a thickness of 10 µm or less is formed between the cover layer (65) and the surface (59, 63), wherein the rotor blade main body (50) is made of precipitation-hardened stainless steel.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a steam turbine rotor blade, a method of manufacturing a steam turbine rotor blade, and a steam turbine. BACKGROUND

[0002] Axial steam turbines are used, for example, for power generation and the like and comprise a plurality of turbine stator cascades and turbine rotor cascades. The turbine stator cascades each comprise a plurality of turbine stator blades, and the turbine rotor cascades each comprise a plurality of turbine rotor blades.

[0003] An integrated faired blade for a turbine rotor blade was disclosed in Japanese Laid-Open Patent Application JP H04-5402 A and has an integrated fairing at a distal end thereof. The blade is configured to deform due to centrifugal force so as to be in a detorsion state when a turbine is operating, causing adjacent integral fairings to come into contact with each other.

[0004] In some cases, the turbine rotor blade of this type has a center section equipped with an integrated stub, as described in Japanese Patent Application Laid-Open No. JP H04-5402 A, to achieve higher structural damping as a measure primarily related to the increase in stresses due to the increase in length of steam turbine blades. The integrated faired blade disclosed in Japanese Patent Application Laid-Open No. JP H04-5402 A is equipped with the integrated fairing on the distal end section and also with integrated stubs provided as triangular protrusions on both surfaces on the center section of the blade. When the blade is reversed by centrifugal force, adjacent integrated stubs come into contact with each other, thereby achieving higher structural damping.

[0005] Japanese Patent JP 4 058 906 B2 and Japanese Laid-Open Patent Application JP 2011-137 424 A each also disclose a turbine rotor blade having a distal end portion provided with an integral fairing and a middle portion provided with an integral stub.

[0006] In the rotor blade of a steam turbine disclosed in Japanese Patent JP 4 058 906 B2, a distance between end surfaces of the integral coating (first connecting members) opposite to each other is set to be shorter than a distance between end surfaces of the integral stubs (second connecting members) opposite to each other. Thus, the integral coatings first come into contact with each other, and subsequently, the integral stubs come into contact with each other as the rotation speed of the rotor increases. Thus, additional stress is prevented at a connecting portion between connecting members and the blade portion. The steam turbine with this configuration is regarded as a steam turbine having rotor blades having improved reliability in terms of hardness and vibration in an operating state from start-up to operation of the turbine.

[0007] In Japanese Patent Application Laid-Open No. 2011-137424 A, an intermediate connecting portion provided on rotor blades as a long blade serves to improve vibration characteristics by acting as a resistance in a path of steam flowing between the rotor blades, thus impairing aerodynamic performance. Thus, the turbine rotor cascade disclosed in Japanese Patent Application Laid-Open No. 2011-137424 A optimizes the spatial relationship between the rotor blades, the intermediate connecting portions, and the cross-sectional shape of the intermediate connecting portions to reduce aerodynamic losses between the rotor blades.

[0008] The steam in the steam turbine is used for expansion work in each turbine stage to reduce energy. Thus, in a stage further downstream, the steam temperature is low, resulting in a steam path section being a wet area. A turbine rotor blade rotating in a wet area may have a leading edge portion at the distal end of the blade, which involves a high peripheral speed, that is eroded due to corrosion by dripping in the steam. In this regard, Japanese Patent Application Laid-Open No. 2004-270023 A discloses a method for treating equipment subject to corrosion with fluids and an anti-erosion coating.

[0009] The method for treating devices subject to corrosion disclosed in Japanese Patent Application Laid-Open No. JP 2004-270023 A involves applying a cobalt-based alloy having a predetermined composition by laser coating to the blade of the steam turbine as a device subject to erosion by liquids.

[0010] Japanese Patent Application Laid-Open No. 2014-163371 A discloses a technique for forming a coating on a fastener contact surface of a turbine rotor blade made of a titanium alloy by high-velocity oxyfuel (HVOF) spraying, in which chromium carbide (CrC) is sprayed with NiCr as a binder. Thus, high-velocity oxyfuel (HVOF) spraying, in which a mixture is sprayed, is disclosed in Japanese Patent Application Laid-Open No. 2014-163371 A. German Publication DE 38 73 436 T2 discloses a thermal spray coating method for thermally spraying a multilayer coating onto a substrate, with the aim of improving the adhesion of the coating to the substrate and achieving improved low residual stress in the coating.US patent application US 2004 / 0124231 A1 discloses a method for coating a substrate and comprises providing a substrate, attaching a preform to the substrate, the preform comprising a solder alloy and wear-resistant particles, and bonding the preform to the substrate to form a wear-resistant coating. EP 1 403 397 B1 describes cobalt-based alloys for coating components exposed to liquid erosion, as well as coating by laser deposition processes. SUMMARYTechnical problem

[0011] A recent trend toward higher power outputs from steam turbines has resulted in a turbine operating condition that is harsh for a turbine rotor blade, and in particular, for a final-stage turbine rotor blade. The inventors recognized that there are several issues beyond leading-edge erosion (erosion due to droplet collision) that are specific to each turbine rotor blade and that should be preferentially improved to achieve greater durability of the steam turbine under harsh conditions.

[0012] In particular, the inventors have recognized that it is preferable to prevent damage due to fretting in a contact portion, such as a shroud and an integral stub of the turbine rotor blade, between the turbine rotor blades. More specifically, fretting wear and fatigue can occur due to repeated slipping and repeated load cycling on the contact surface.

[0013] The inventors have found that even a turbine rotor blade made of stainless steel, which has a lower coefficient of friction than a titanium alloy and thus should have almost no risk of damage due to fretting, is preferentially protected from fretting damage due to an increase in a stress peak at the contact portion as a result of increased output power.

[0014] Against this background, it is an object of at least one embodiment of the present invention to provide a steam turbine rotor blade, a method for manufacturing a steam turbine rotor blade, and a steam turbine in which the damage due to fretting wear and fatigue contact portion between adjacent turbine rotor blades is prevented. Solution to the problem

[0015] The present invention is defined by the independent claims. Preferred embodiments are set out in the dependent claims. (1) A steam turbine rotor blade for forming a turbine rotor cascade of a steam turbine, the steam turbine rotor blade comprising: a rotor blade main body comprising: a blade portion; a blade base portion provided at one end side of the blade portion; a first connecting portion provided at another end side of the blade portion and having first facing surfaces; and a second connecting portion provided in a central portion of the blade portion and having second facing surfaces, wherein the first facing surfaces are each configured to face one of the first facing surfaces of an adjacent rotor blade main body in the turbine runner cascade, and the second facing surfaces are each configured to face one of the second facing surfaces of the adjacent rotor blade main body in the turbine runner cascade; and a covering layer made of a Co-base alloy and having a single composition, formed by high-velocity flame spraying on a surface of at least one of the first facing surface and the second facing surface, with a diffusion layer having a thickness of 10 µm or less provided between the covering layer and the surface.

[0016] The covering layer is formed of the Co-based alloy with a single composition on at least one of the first facing surfaces and the second facing surface. Adjacent surfaces of the turbine rotor blades have the covering layers made of the Co-based alloy with a single composition in contact with each other. The covering layers made of the Co-based alloy with a single composition have high fretting resistance performance. In the configuration (1) described above, at least one of the first connecting portion and the second connecting portion with the covering layer is free from damage due to fretting wear and fatigue.

[0017] The coating layer is formed on the first facing surface and / or the second facing surface by high-velocity flame spraying, and the thickness of the diffusion layer is 10 μm or less. Thus, a crack may occur due to fretting, but will not reach the coated layer (the base material). Thus, damage due to fretting may occur, but does not require replacing the entire sheet, but simply requires repair with the Co-base alloy coating, which is again provided by high-velocity flame spraying.

[0018] (2) In some embodiments of the configuration (1) described above, the covering layer is formed at least on the surface of the second facing surface. The second connecting portion is provided to achieve higher structural damping, and the peak load acting on the second facing surface of the second connecting portion is not so large. However, the trend toward higher power outputs of the steam turbine and longer steam turbine rotor blades has led to an increase in the load stress acting on the second facing surface of the second connecting portion. Thus, it has been found that the risk of the second connecting portion being damaged by fretting has increased.

[0019] In view of this, in configuration (2) as described above, the coating layer is formed on the second facing surface of the second connecting portion. Thus, the second connecting portion can be prevented from damage due to fretting.

[0020] (3) In some embodiments of the configuration (1) or (2) described above, the first connecting portion has first inclined surfaces that continue inclined to side edges of the first facing surfaces so that a distance between adjacent first connecting portions in the turbine rotor cascade increases, and the second connecting portion has second inclined surfaces which continue inclined to side edges of the second facing surfaces, so that a distance between adjacent second connecting portions in the turbine rotor cascade increases.

[0021] In configuration (3) as described above, the first inclined surfaces are provided, which extend to both side edges of the first facing surface of the first connecting portion. This prevents uneven contact between the first facing surfaces, thereby reducing stress peaks acting on the first facing surface. Thus, the first connecting portion can be more effectively protected from damage due to fretting.

[0022] When the first inclined surfaces are provided, the area of ​​the first facing surface is significantly reduced, and thus the average surface pressure on the first facing surface increases. Nevertheless, with the covering layer formed on the surface of the first facing surface, fretting wear and fatigue due to the increase in average pressure can be prevented.

[0023] In configuration (3) as described above, the second inclined surfaces are provided up to the side edges of the second facing surface of the second connecting portion. This prevents uneven contact between the second facing surfaces, thereby reducing stress peaks acting on the second facing surface. Thus, the second connecting portion can be more effectively prevented from sustaining damage due to fretting.

[0024] When the second inclined surface is provided, the area of ​​the second facing surface is significantly reduced, and thus the average surface pressure on the second facing surface increases. Nevertheless, with the coating layer formed on the surface of the second facing surface, fretting wear and fatigue due to the increase in average surface pressure can be prevented.

[0025] (4) In some embodiments according to any one of the configurations (1) to (3), the first connecting portion has first curved surfaces that continue to distal end edges of the first facing surfaces so that a distance between adjacent first connecting portions in the turbine rotor cascade increases, and the second connecting portion has a second curved surface which continues to distal end edges of the second facing surfaces, so that a distance between adjacent second connecting portions in the turbine rotor cascade increases.

[0026] In the configuration (4) described above, the first curved surfaces are provided up to the distal end edges of the first facing surface of the first connecting portion. This prevents uneven contact between the first facing surfaces, thereby reducing a stress spike acting on the first facing surface. Thus, the first connecting portion can be more effectively prevented from sustaining damage due to fretting.

[0027] When the first curved surfaces are provided, the area of ​​the first facing surface is significantly reduced, and thus the average surface pressure on the first facing surface increases. Nevertheless, with the covering layer formed on the surface of the first facing surface, fretting wear and fatigue due to the increase in the average surface pressure can be prevented.

[0028] In the configuration (4) described above, the second curved surfaces are provided, which continue to the distal end edges of the second facing surfaces of the second connecting portion. Thus, uneven contact is provided between the second facing surfaces, which can reduce stress peaks acting on the second facing surfaces. Thus, the second connecting portion can be effectively prevented from sustaining damage due to fretting.

[0029] When the second curved surfaces are provided, the area of ​​the second facing surface is significantly reduced, and thus the average surface pressure on the second facing surface increases. Nevertheless, with the coating layer formed on the surface of the second facing surface, fretting wear and fatigue due to the increase in average surface pressure can be prevented.

[0030] (5) In some embodiments of the configurations (1) to (3), the first connecting portion has third inclined surfaces continuing to distal end edges of the first facing surfaces so that a distance between adjacent first connecting portions in the turbine rotor cascade increases, and the second connecting portion has fourth inclined surfaces which continue to distal end edges of the second facing surfaces, so that a distance between adjacent second connecting portions in the turbine rotor cascade increases.

[0031] In the configuration (5) as described above, the third inclined surface and the fourth inclined surface are provided, so that the first connecting portion and the second connecting portion are more effectively prevented from being damaged by fretting as in the configuration (4) described above.

[0032] The local stress acting on the distal end is greater than that on the side edges of the first facing surface and the second facing surface. Therefore, as described in configuration (4) above, the inclined surface continues to the side edges, with the curved surface continuing to the distal end edge. The curved surface is thus designed to continue to the distal end edge, which has a higher local stress, thus ensuring the prevention of uneven contact, thereby more effectively preventing fretting wear and fretting fatigue.

[0033] (6) In some embodiments of the configuration (2) as described above, the second connecting portion comprises: second inclined surfaces which continue inclined to side edges of the second facing surfaces so that a distance between adjacent second connecting portions in the turbine rotor cascade increases; and second curved surfaces continuing to distal end edges of the second facing surfaces so that the distance between adjacent second connecting portions in the turbine rotor cascade increases.

[0034] In the configuration (6) described above, the second inclined surface is continued to the side edges of the second facing surface, and the second curved surfaces are provided, which continue to the distal end edges of the second facing surface. Thus, the second connecting portion can be more effectively prevented from sustaining damage due to fretting.

[0035] (7) A steam turbine rotor blade for forming a turbine rotor cascade of a steam turbine according to one of the preceding embodiments comprises: a rotor blade main body comprising: a blade portion; a blade base portion provided at one end side of the blade portion; a first connecting portion provided at another end side of the blade portion and having first facing surfaces; and a second connecting portion provided in a central portion of the blade portion and having second facing surfaces, wherein the first facing surfaces are each configured to face one of the first facing surfaces of an adjacent rotor blade main body in the turbine runner cascade, and the second facing surfaces are each configured to face one of the second facing surfaces of the adjacent rotor blade main body in the turbine runner cascade; and a cover layer made of a fretting wear-resistant material and formed on a surface of each of the second facing surfaces, wherein in a cross section of the rotor blade main body in a position in which the second connecting portion is provided, an acute angle is formed between the second facing surface and a line connecting a leading edge and a trailing edge of the blade portion, and a perpendicular line to the second facing surface crosses the blade portion, and the second connecting portion has a second inclined surface which continues obliquely to side edges of the second facing surface, so that a distance between adjacent second connecting portions in the turbine rotor cascade increases.

[0036] In a case where the second connecting portion is provided up to the blade portion such that, in a cross-sectional area of ​​the rotor blade main body, at a position where the second connecting portion is provided, an acute angle is formed between the second facing surface and a line connecting a leading edge and a trailing edge of the blade portion, and a perpendicular line to the second facing surface crossing the blade portion, when machining the surface up to the side edges of the second facing surface, a manual operation is necessary because a machine tool would come into contact with the blade portion at the base end of the second connecting portion. However, by forming the surface up to the side edge as a simple inclined surface, the manual operation can be simple and stable.

[0037] (8) According to the present invention, the rotor blade main body is made of precipitation hardening stainless steel.

[0038] If the rotor blade main body is made of precipitation hardening stainless steel, the manufactured rotor blade main body is subjected to heat treatment, for example, solution heat treatment and age hardening, performed in this sequence, so that the hardness of the stainless steel can be adjusted to an appropriate value. If the rotor blade main body is heated after heat treatment, the heat treatment must be performed again to adjust the hardness. If any treatment is to be performed on the rotor blade main body after heat treatment, the temperature of the rotor blade main body must be maintained so that it does not exceed the heat treatment temperature.

[0039] In this regard, as described in configuration (8) above, high-velocity oxygen spraying requires almost no heat input to the rotor blade main body. Thus, high-velocity oxygen spraying does not change the hardness of the rotor blade main body. Therefore, the topcoat layer can be easily formed without the need for special temperature management for the rotor blade main body.

[0040] Precipitation-hardening stainless steel has a lower coefficient of friction than titanium alloy. Thus, rotor blades made of precipitation-hardening stainless steel are virtually free from fretting wear and fatigue. However, due to the recent trend toward higher power steam turbines and longer rotor blades, there has been an increase in stress peaks acting on the first facing surface and the second facing surface. Thus, the risk of damage to the first and second connecting sections due to fretting has been found to have increased.

[0041] In view of this, in the configuration (8) as described above, the coating layer is formed on the surface of at least one of the first facing surface and the second facing surface in the rotor blade main body made of precipitation hardening stainless steel, whereby the damage due to fretting can be prevented.

[0042] In the steam turbine, the final-stage rotor blade is designed to be long to provide a larger annular area, making it easier to reduce the exhaust air losses. In this context, the turbine rotor blade according to the configurations (1) to (8) can be designed to be long without promoting damage to the contact portions between the adjacent turbine rotor blades, and is thus feasible as a final-stage rotor blade in the steam turbine.

[0043] (9) A steam turbine provided according to at least one embodiment of the present invention includes a steam turbine rotor blade having one of the configurations (1) to (8) as described above.

[0044] (10) A method for manufacturing a steam turbine rotor blade for forming a turbine rotor cascade of a steam turbine according to one of the embodiments of the present invention comprises: a step of providing a rotor blade main body comprising: a rotor blade main body comprising: a blade portion; a blade base portion provided at one end side of the blade portion; a first connecting portion provided at another end side of the blade portion and having first facing surfaces; and a second connecting portion provided in a central portion of the blade portion and having second facing surfaces, wherein the first facing surfaces are each configured to face one of the first facing surfaces of an adjacent rotor blade main body in the turbine runner cascade, and the second facing surfaces are each configured to face one of the second facing surfaces of the adjacent rotor blade main body in the turbine runner cascade; and a high-speed flame spraying step of performing high-speed flame spraying to form, on a surface of at least one of the first facing surface and the second facing surface, a covering layer consisting of a Co-based alloy and having a single composition, wherein in the high velocity flame spraying step, powder of the Co-base alloy is sprayed onto a surface to be covered, which is one of the first facing surface and the second facing surface, at an angle equal to or greater than 0° and equal to or less than 60° relative to the normal line of the surface.

[0045] When the spray direction is inclined relative to the normal line to the facing surface by an angle in the range between 0° and 60° inclusive, the top layer can have low porosity and thus high fretting resistance performance. Beneficial effects

[0046] According to at least one embodiment of the present invention, a steam turbine rotor blade, a method for manufacturing steam turbine rotor blades, and a steam turbine in which damage due to fretting is prevented in a contact portion between adjacent turbine rotor blades are provided. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram schematically illustrating a configuration of a power generation system according to one of the embodiments of the present invention. Fig. 2 is a vertical cross-sectional view showing a schematic configuration of a steam turbine. Fig. Figure 3 is a plan view schematically illustrating a final stage turbine rotor cascade. Fig. 4 is a perspective view schematically illustrating a rotor in a final stage turbine rotor cascade. Fig. 5 is a diagram schematically illustrating a first connecting portion and a part of the blade portion. Fig. 6 is a development diagram schematically illustrating a plurality of the first connecting portions, with an enlarged view in a compass schematically illustrating a cross section taken along a line orthogonal to the radial direction. Fig. 7 is a diagram schematically illustrating a second connecting portion and a part of the blade portion. Fig. 8 is a development diagram schematically illustrating a plurality of second connecting portions, with an enlarged view in a compass schematically illustrating a cross section taken along the line orthogonal to the radial direction. Fig. 9 is a flowchart schematically illustrating a method for manufacturing a final stage rotor blade. Fig. 10 is a diagram illustrating a result of photographing a cross section of a cover layer formed on a second facing surface of a second joint portion with an optical microscope after a fretting fatigue test. Fig. 11 is a schematic cross-sectional view taken along a line XI-XI in Fig. 8. Fig. 12 is a development diagram schematically illustrating a first connecting portion according to another embodiment. Fig. 13 is a development diagram schematically illustrating a second connection portion according to the other embodiment. Fig. Figure 14 shows a cross-section of a metal structure on a cover layer, corresponding, for example, to that obtained by high velocity oxygen spraying using Stellite (registered trademark) #6. Fig. 15 shows a cross-section of a metal structure of a covering layer according to a comparable example, obtained by high-velocity flame spraying using mixed powder of Cr3C2 and NiCr (Cr3C2-25NiCr), as well as a result of a microhardness test. DETAILED DESCRIPTION

[0047] The following describes some embodiments of the present invention with reference to the accompanying drawings. It should be understood that the sizes, materials, shapes, relative arrangements, and the like of the components described or illustrated in the drawings as embodiments are exemplary and are not intended to limit the scope of the present invention.

[0048] For example, as used herein, terms representing relative or absolute arrangements, including "in a direction," "along a direction," "parallel with," "orthogonal to," "center," "concentric," and "coaxial," not only represent exactly what they mean, but imply conditions with relative displacement by a tolerance or by an angle or distance small enough to maintain the same level of functionality.

[0049] For example, as used here, expressions that mean things are in identical states, such as "the same," "identical," and "homogeneous," among others, mean not only that they are in exactly identical states, but also that they are in states with a tolerance or difference small enough to maintain the same level of functionality.

[0050] For example, as used herein, terms representing shapes such as quadrilaterals and cylinders do not only mean geometrically exact quadrilaterals and cylinders, or the like, but also include shapes that have some irregularities, as long as the same level of functionality is maintained.

[0051] Furthermore, the terms “including,” “having,” “provided therein,” and “having” do not exclude other components.

[0052] Fig. 1 is a block diagram schematically illustrating a configuration of a power generation system according to an embodiment of the present invention. The power generation system is a combined cycle power generation system including a gas turbine 1, a steam turbine 3, a waste heat recovery boiler 5, and generators 7 and 9.

[0053] In some embodiments, the power generation system is a conventional power generation system including: a boiler provided in place of the waste heat recovery boiler 5, in which fuel is burned to generate steam; and the steam turbine 3. In some embodiments, the power generation system is for household use, and in some embodiments, the power generation system is for commercial use.

[0054] The gas turbine 1 includes a compressor 11, a combustion chamber 13, and a turbine 15. The compressor 11 compresses air using an outlet of the turbine 15. The compressed air is supplied to the combustion chamber 13. In the combustion chamber 13, the compressed air and fuel are provided, and the fuel is burned. Combustion gases generated by the fuel combustion are supplied to the turbine 15 to be used by the turbine 15 as torque.

[0055] The turbine 15 is connected to the generator 7, which uses part of the power of the turbine 15 to generate power.

[0056] After working in the turbine 15, the combustion gas (hereinafter also referred to as exhaust gas) is supplied to the waste heat recovery boiler 5. The waste heat recovery boiler 5 uses heat (outlet heat) from the combustion gas to generate steam.

[0057] The waste heat recovery boiler 5 includes, for example, a preheater 17, a receiver 19, an evaporator 21, a superheater 23, a reheater 25, and a denitrifier 27. Water is heated by the preheater 17, the evaporator 21, and the superheater 23, thereby obtaining superheated steam. The superheated steam is supplied to the steam turbine 3. The steam supplied to the steam turbine 3 temporarily returns to the waste heat recovery boiler 5 and is then supplied to the reheater 25. The reheater 25 heats the steam, and the heated steam is supplied to the steam turbine 3.

[0058] The denitrifier 27 functions to remove NOx in the exhaust gas. The exhaust gas discharged from the waste heat recovery boiler 5 is discharged, for example, through a chimney 29.

[0059] Steam turbine 3 is connected to generator 9. Steam turbine 3 uses steam to generate torque. Generator 9 uses this torque to generate power. Steam turbine 3 includes, for example, a high-pressure turbine 31, a medium-pressure turbine 33, and a low-pressure turbine 35, all of which use steam to generate torque.

[0060] A condenser 37 is connected to the steam turbine 3. The steam discharged from the low-pressure turbine 35 of the steam turbine 3 condenses at the condenser 37 to become water. The condenser 37 is connected to the waste heat recovery boiler 5 via a condensation pump 39. The condensation pump 39 supplies the water recovered by the condenser 37 to the waste heat recovery boiler 5.

[0061] Fig. 2 is a vertical cross-sectional view showing a schematic configuration of the steam turbine 3.

[0062] The steam turbine 3 as shown in Fig. 2 is a single-chamber steam turbine in which the high-pressure turbine 31, the intermediate-pressure turbine 33, and the low-pressure turbine 35 are integrally formed. In some embodiments, a combined-chamber steam turbine may be used in which a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine are formed separately from each other. The combined-chamber steam turbine may have a tandem structure or a cross structure.

[0063] The steam turbine 3 as shown in Fig. 2 comprises: a housing 41 defining a chamber; a rotor 43; turbine stator cascades attached to the housing 41; and a plurality of turbine rotor cascades attached to the rotor 43. The rotor 43 is rotatably supported by radial bearings 44 and 45 and extends at least partially within the housing 41. The generator 9 is connected to one end of the rotor 43.

[0064] A tubular inner flow path 46 is formed between the casing 41 and the 43. The turbine stator cascades and the turbine runner cascades are arranged in the inner flow path 46. The turbine stator cascades and the turbine runner cascades belong to the high-pressure turbine 31, the medium-pressure turbine 33, and the low-pressure turbine 35, respectively. Each turbine stator cascade includes a plurality of stator blades arranged in a circumferential direction of the rotor 43 and fixed to the casing 41. Each turbine runner cascade has a plurality of rotor blades arranged in the circumferential direction of the rotor 43 and fixed to the rotor 43. In each turbine stator cascade, the steam flow is accelerated, and in each turbine runner cascade, steam energy is converted into rotational energy of the rotor 43.

[0065] A turbine runner cascade (hereinafter referred to as final-stage turbine runner cascade) 47, which is arranged on a most downstream side in a steam flow direction and which corresponds to the low-pressure turbine 35, corresponds to the largest proportion of the power of the steam turbine 3. Thus, the final-stage turbine runner cascade 47 is designed to have the largest possible size to achieve higher efficiency of the steam turbine 3 with a reduced exhaust air loss.

[0066] Fig. 3 is a plan view schematically illustrating the final stage turbine rotor cascade 47. Fig. 4 is a perspective view schematically illustrating a rotor blade (hereinafter referred to as final stage rotor blade) 49 in the final stage turbine rotor cascade 47.

[0067] The rotor blade 49 includes a rotor blade main body 50 having a blade portion 51, a blade base portion 53, a first connecting portion 55, and a second connecting portion 57.

[0068] The blade portion 51 includes a high-pressure surface (front side) 51a and a low-pressure surface (rear side) 51b oriented in opposite directions. A flow path of the steam is formed between the high-pressure surface 51a and the low-pressure surface 51b of the blade portions 51, which are adjacent to each other. The blade portion 51 receives energy from the steam flowing along the flow path. The high-pressure surface 51a and the low-pressure surface 51b of the blade portion 51 each have a predetermined width and extend in a radial direction of the rotor 43. The blade portion 51 has a predetermined shape in a cross-section formed along a line orthogonal to the radial direction. The peripheral speed of the blade portion 51 is different between the inner and outer sides in the radial direction.Thus, the high-pressure surface 51a and the low-pressure surface 51b of the blade portion 51 each have a shape that is progressively twisted from the inner side to the outer side in the radial direction of the rotor 43.

[0069] The blade base portion 53 is integrally formed with one end side (base end side) of the blade portion 51 in the radial direction of the rotor 43. The rotor 43 has a connecting portion to enable it to be connected to the blade base portion 53. Thus, the final stage rotor blade 49 is firmly connected to the rotor 43 via the blade base portion 53.

[0070] In some embodiments, the blade base portion 53 has a Christmas tree shape in a cross-section arranged along a line orthogonal to an axial direction of the rotor 43. In this case, a groove extending in the axial direction of the connecting portion is formed in the rotor 43, and the blade base portion 53 is fitted into the groove of the rotor 43 in the axial direction.

[0071] The first connecting portion 55 is formed integrally with the other end side (distal end side) of the blade portion 51 in the radial direction of the rotor 43. Fig. 5 schematically illustrates the first connecting portion 55 and a part of the blade portion 51. Fig. 6 is a development diagram schematically illustrating the plurality of first connecting portions 55.

[0072] The first connecting portion 55 is also referred to as an integral coating and is provided to achieve a small vibration amplitude and a small mode number of the final-stage turbine rotor cascade 47, which has a large size. Specifically, the small vibration amplitude and the small mode number of the final-stage turbine rotor cascade 47 are achieved by the final-stage rotor blades 49 being connected to each other via the first connecting portion 55 on an outer side in the radial direction of the rotor 43.

[0073] More specifically, the first connecting portion 55 has first facing surfaces 59 on both sides in the circumferential direction of the rotor 43. The first facing surfaces 59 of adjacent final-stage rotor blades 49 are arranged opposite each other. The first facing surfaces 59, which are opposite each other, are formed in such a way as to be parallel to each other when deformation of the blade portions 51 is achieved by centrifugal force when the steam turbine 3 is operating.

[0074] For example, the first connecting portion 55 has protrusions 61 having a triangular pole shape on both sides in the circumferential direction of the rotor 43, and the protrusion 61 has a side surface forming the first facing surface 59.

[0075] The second connecting portion 57 is integrally provided on each of the high-pressure surfaces 51a and a low-pressure surface 51b of the blade portion 51 and a center portion in the radial direction of the rotor 43. Fig. 7 schematically illustrates the second connecting portion 57 and a part of the blade portion 51. Fig. 8 is a development diagram schematically illustrating the plurality of second connecting portions 57.

[0076] The second connecting portion 57 is also referred to as an integral stub and is primarily intended to achieve higher structural damping of the final-stage turbine rotor cascade 47 with a larger size. More specifically, the higher structural damping of the final-stage turbine rotor cascade 47 is achieved with adjacent final-stage rotor blades 49 connected to each other at center portions in the radial direction of the rotor 43 via the second connecting portion 57.

[0077] Furthermore, the second connecting portion 57 has a second facing surface 63. The second facing surfaces 63 of the adjacent final stage rotor blades 49 are arranged opposite one another. The second facing surfaces 63, which are opposite one another, are further configured to be parallel to one another when the deformation of the blade portions 51 is achieved by centrifugal force when the steam turbine 3 is in operation.

[0078] The second connecting portion 57 has, for example, a triangular pole shape, and has a side surface forming the second facing surface 63.

[0079] For example, as shown in Fig. 8, in a cross section of the rotor blade main body 50, at a position where the second connecting portion 57 is provided, an acute angle θa is formed between the second facing surface 63 and a line Lc connecting a leading edge and a trailing edge of the blade portion 51, and a perpendicular line Lr to the second facing surface 63 crossing the blade portion 51.

[0080] A cover layer 65 made of a Co-based alloy with a single composition is formed on a surface of at least one of the first facing surface 59 and the second facing surface 63 by high-velocity flame spraying. A diffusion layer with a thickness of 10 μm or less is provided between the cover layer 65 and the coating layer.

[0081] The Co-based alloy is a fretting wear-resistant material with high fretting wear resistance. Examples of Co-based alloys include a stellite compound and a tribaloy alloy. The fretting wear-resistant material can be a Co-based alloy or a Cu-based alloy such as CuNiIn, CuAl, or CuTi.

[0082] In the present embodiment, as schematically shown in an enlarged view in a circle in Fig. 6 and Fig. As shown in Figure 8, the cover layer 65 is formed on the first facing surface 59 and on the second facing surface 63. In this configuration, of the final stage rotor blades 49 that are adjacent to each other, the cover layers 65 on the first facing surfaces 59 that are opposite each other come into contact with each other, and the cover layers 65 on the second facing surfaces 63 that are opposite each other come into contact with each other.

[0083] For example, the cover layers 65 are formed entirely on a surface on which the first facing surfaces 59, which are opposite, come into contact with each other, and on the surface on which the second facing surfaces 63, which are opposite, come into contact with each other.

[0084] A method of manufacturing the final stage rotor blade 49 as described above will now be described.

[0085] Fig. 9 is a flow chart schematically illustrating a method for manufacturing the final stage rotor blade 49. As shown in Fig. 9, the rotor blade main body 50 is first formed, for example, by forging (S10). The rotor blade main body 50 thus formed is then subjected to a heat treatment to adjust its strength and hardness (S12). The heat treatment includes, for example, a quenching process (solution heat treatment) and a tempering process (hardening process).

[0086] For example, the solution annealing temperature is in a range between 1020°C and 1060°C, and the age hardening temperature is in a range between 470°C and 660°C.

[0087] For example, the surface hardness of the rotor blade main body 50 after heat treatment is 500HV0.5 or higher according to the Vickers hardness test as defined by JIS Z2244 2008.

[0088] The rotor blade main body 50 after the heat treatment is subjected to the oxide film removal process, which is performed by polishing. Thus, an oxide film on the surface is removed (S14).

[0089] After removing the oxide film, the rotor blade main body 50 is subjected to a roughening treatment performed on the first facing surface 59 and the second facing surface 63 (S16). The roughening treatment in S16 is performed by increasing the surface roughness of the first facing surface 59 and the second facing surface 63, for example, by blasting. In some embodiments, the roughening treatment in S16 is performed by sandblasting with sharp particles.

[0090] The first facing surface 59 and the second facing surface 63 after the roughening treatment have, for example, an arithmetic mean roughness Ra, which is defined as surface roughness by JIS B0601 2013, in a range between 6.0 µm and 7.0 µm inclusive.

[0091] When the roughening treatment is performed in S16, an area other than the first facing surface 59 and the second facing surface 63 is covered to prevent this surface from being roughened.

[0092] After the roughening treatment on the rotor blade main body 50, the covering layer 65 is formed on the first facing surface 59 and the second facing surface 63 by high-velocity flame spraying (S18).

[0093] HVOF (High Velocity Oxygen-Fed) Flame Spraying or HVAF (High Velocity Air-Fed) Flame Spraying is performed as high-velocity flame spraying in S18. In the high-velocity flame spraying in S18, a powder material is sprayed onto a coating target with a high-velocity combustion gas generated by the combustion of fuel and oxygen or air, so that the coating layer 65 can be formed.

[0094] In the present embodiment, HVOF flame spraying is used.

[0095] The powder material for forming the cover layer 65 includes a Co-based alloy having the same composition as the cover layer 65.

[0096] For example, the powder material has an arithmetic particle diameter as defined by JIS Z8819-2 2001 as a particle diameter in a range between 10 µm and 70 µm inclusive.

[0097] The powder material is sprayed, for example, in an inclined direction relative to the normal line on the first facing surface 59 or the second facing surface 63 as the coating target, with an entrance angle θi in a range between 0° and 60° inclusive, as shown in Fig. 8. When the spray direction is inclined at an angle in the range of 0° to 60°, the top layer 65 can have low porosity and thus high fretting resistance. For example, the porosity of the top layer 65 is 5% or less.

[0098] In the steam turbine 3 according to at least one embodiment of the present invention as described above, the covering layer 65 is made of the Co-based alloy having a single composition and is formed on at least one of the first facing surface 59 and the second facing surface 63. In adjacent final-stage rotor blades 49, the covering layers 65 made of the Co-based alloy having a single composition are in contact with each other. The covering layers 65 made of the Co-based alloy having a single composition have high fretting resistance performance. Thus, the first connecting portion 55 and the second connecting portion 57 provided with the covering layer 65 remain free from damage due to fretting.

[0099] The coating layer 65 is formed on the surface of the first facing surface 59 or the second facing surface 63 by high-velocity flame spraying, and no thermal diffusion treatment is performed after the high-velocity flame spraying. Thus, the diffusion layer is provided between the coating layer 65 and the surface of the coated layer and has a thickness of 10 μm or less. Thus, a crack in the coating layer 65 can propagate due to fretting fatigue, but will not reach the first connecting portion 55 or the second connecting portion 57, which is not coated. Thus, damage due to fretting can occur, but does not require replacement of the entire sheet, but requires simple repair with the Co-based alloy coating, which can be reapplied by high-velocity flame spraying.If this is taken into account, lower repair costs and a shorter repair time can be achieved, which allows a higher operating share of the steam turbine to be achieved.

[0100] When the steam turbine 3 is operating, a vicinity of the first connecting portion 55, which is arranged in an outer peripheral portion of the final-stage turbine rotor cascade 47, is in a wet region. Nevertheless, the first facing surfaces 59 are arranged opposite each other. Thus, it is extremely unlikely that wear will occur on the first facing surfaces 59. The vicinity of the second connecting portion 57, which is arranged at a middle blade portion of the final-stage turbine rotor cascade 47, is not in the wet region. Furthermore, the second facing surfaces 63 are arranged opposite each other. Thus, it is extremely unlikely that wear will occur on the second facing surfaces 63 as in the case of the first facing surfaces 59. Thus, no protective coating for preventing wear is necessary.

[0101] However, due to the trend toward longer final-stage rotor blades and higher turbine power, even the second connecting portion, which has higher structural damping and whose peak stress acting on its facing surface was not considered to be so large, has an increased peak stress at its contact portion. Therefore, the inventors found that a measure to prevent damage due to fretting, such as forming a covering layer with higher fretting resistance on the facing surface, is preferable.

[0102] In some embodiments, the cover layer 65 is formed directly on the first facing surface 59 or the second facing surface 63.

[0103] Fig. 10 shows the result of monitoring the cover layer 65 formed on the second facing surface 63 of the second connecting portion 57 with an optical microscope after a fretting fatigue test. As in Fig. 10, when the covering layer 65 is formed by high-speed flame spraying, the thickness of the diffusion layer is 10 µm or less, and thus substantially nonexistent. As shown in Fig. 10, the crack formed on the coating layer 65 reaches an interface with the coated surface (base material) and then propagates transversely along the interface and does not reach the coating layer.

[0104] In some embodiments, the Co-based alloy material of the top layer is 65 Stellite (registered trademark) No. 6, having a composition (64Co-28Cr-4W-1C-3Fe) exemplified in Table 1. [Table 1] Element Konzentration (Massenprozent) Co Bal. Cr 28 W 4 C 1 Fe 3

[0105] The thickness of the cover layer 65 is in some embodiments in a range between 0.1 mm and 0.6 mm inclusive, and in some embodiments in a range between 0.3 mm and 0.5 mm inclusive.

[0106] In some embodiments, the cover layer 65 is formed at least on the second facing surface 63.

[0107] In this configuration, the cover layer 65 is formed on the surface of the second facing surface 63 of the second connecting portion 57. Thus, the second connecting portion 57 can be prevented from being damaged by fretting.

[0108] In some embodiments, the final stage rotor blade 49 may have a blade height of 40 inches or more.

[0109] Fig. 11 is a schematic cross-sectional view taken along a line XI-XI in Fig. 8. In some embodiments, as shown in Fig. 7 and Fig. 11, the second connecting portion 57 has a second inclined surface 69 configured to provide a larger distance between adjacent second connecting portions 57 in the final-stage turbine rotor cascade 47. More specifically, the second inclined surface 69 continues obliquely to both side edges of the second facing surface 63.

[0110] Both side edges of the second connecting portion 57 are separated from each other in the radial direction of the rotor 43, that is, in a height direction of the final stage rotor blade 49 and the second inclined surface 69 are inclined with respect to the height direction of the final stage rotor blade 49.

[0111] In this configuration, the second inclined surface 69 is provided, which extends both side edges of the second facing surface 63 of the second connecting portion 57. Thus, uneven contact, i.e., local contact between the second facing surfaces 63, is prevented, thereby reducing stress peaks acting on the second facing surface 63. In summary, the second connecting portion 57 is prevented from sustaining damage due to fretting.

[0112] When the second inclined surfaces 69 are provided, the area of ​​the second facing surface 63 is substantially reduced, and thus the average surface pressure on the second facing surface 63 increases. Nevertheless, with the cover layer 65 formed on the surface of the second facing surface 63, fretting wear and fatigue due to the increase in the average surface pressure can be prevented.

[0113] In some embodiments, the cover layer 65 is also formed on the second inclined surface 69.

[0114] In some embodiments, as shown in a schematic enlarged view in the circle in Fig. 5, the first connecting portion 55 includes a first inclined surface 67 configured to achieve a greater distance between adjacent first connecting portions 55 in the final stage turbine rotor cascade 47. More specifically, the first inclined surface 67 continues obliquely to both side edges of the first facing surface 59.

[0115] Both side edges of the first connecting portion 55 are separated from each other in the radial direction of the rotor 43, that is, in the height direction of the final stage rotor blade 49, the first inclined surface 67 is inclined with respect to the height direction of the final stage rotor blade 49.

[0116] In this configuration, the first inclined surface 67 is provided, extending to both side edges of the first facing surface 59 of the first connecting portion 55. This prevents uneven contact between the first facing surfaces 59, thereby reducing stress peaks acting on the first facing surface 59. Overall, the first connecting portion 55 can be more effectively prevented from sustaining damage due to fretting.

[0117] When the first inclined surface 67 is provided, the area of ​​the first facing surface 59 is significantly reduced, and thus the average surface pressure on the first facing surface 59 increases. Nevertheless, with the covering layer 65 formed on the surface of the first facing surface 59, fretting wear and fatigue can be prevented due to the increase in the average surface pressure.

[0118] In some embodiments, the cover layer 65 is also formed on the first inclined surface 67.

[0119] In some embodiments, as shown in Fig. 5 and Fig. 6, the first connecting portion 55 includes a first curved surface 71 configured to achieve a greater distance between adjacent first connecting portions 55 in the final stage turbine rotor cascade 47. The first curved surface 71 continues to distal end edges of the first facing surface 59.

[0120] In this configuration, the first curved surface 71 is provided, which extends to the distal end edges of the first facing surface 59 of the first connecting portion 55. Thus, uneven contact between the first facing surfaces 59 is prevented, thereby reducing stress peaks acting on the first facing surface 59. Overall, the first connecting portion 55 can be more effectively prevented from sustaining damage due to fretting wear and fatigue.

[0121] When the first curved surfaces 71 are provided, the area of ​​the first facing surface 59 is significantly reduced, and thus the average surface pressure on the first facing surface 59 increases. Nevertheless, with the cover layer 65 formed on the surface of the first facing surface 59, fretting wear and fatigue due to the increase in the average surface pressure can be prevented.

[0122] In some embodiments, the cover layer 65 is also formed on the first curved surfaces 71.

[0123] In some embodiments, as shown in Fig. 7 and Fig. 8, the second connecting portion 57 includes a second curved surface 73 configured to achieve a greater spacing between adjacent second connecting portions 57 in the final stage turbine rotor cascade 47. The second curved surface 73 continues to distal end edges of the second facing surface 63.

[0124] In this configuration, a second curved surface 73 is provided, which continues to distal end edges of the second facing surface 63 of the second connecting portion 57. Thus, uneven contact between the second facing surfaces 63 is prevented, thereby reducing a stress spike acting on the second facing surface 63. Thus, the second connecting portion 57 can be more effectively prevented from sustaining damage due to fretting wear and fatigue.

[0125] When the second curved surfaces 73 are provided, the surface area of ​​the second facing surface 63 is significantly reduced, and thus the average surface pressure on the second facing surface 63 increases. Nevertheless, with the cover layer 65 formed on the surface of the first facing surface 59, fretting wear and fatigue due to the increase in the average surface pressure can be prevented.

[0126] In some embodiments, the cover layer 65 is also formed on the second curved surfaces 73.

[0127] In some embodiments, as shown in Fig. 12 and Fig. 13, the first connecting portion 55 includes a third inclined surface 75 instead of the first curved surface 71, and the second connecting portion 57 includes a fourth inclined surface 77 instead of the second curved surface 73.

[0128] The third inclined surface 75 is configured to achieve a greater distance between adjacent first connecting sections 55 in a turbine rotor cascade. The third inclined surface 75 continues to distal end edges of the first facing surface 59.

[0129] The fourth inclined surface 77 is configured to achieve a greater distance between adjacent second connecting sections 57 in a turbine rotor cascade. The fourth inclined surface 77 continues to distal end edges of the second facing surface 63.

[0130] In this configuration, the third inclined surface 75 and the fourth inclined surface 77 are provided, so that the first connecting portion 55 and the second connecting portion 57 can be more effectively prevented from being damaged by fretting than in the configuration with the first curved surface 71 and the second curved surface 73.

[0131] The local stress acting on the distal end edge is greater than that on the side edge in the first facing surface 59 and the second facing surface 63. Therefore, in the configurations as shown in Fig. 5 and Fig. 7, the first inclined surface 67 or the second inclined surface 69 extends to the side edges, while the first curved surface 71 or the second curved surface 73 extends to the distal end edges. With the first curved surface 71 or the second curved surface 73 provided in such a way as to extend to the distal end edge, this means higher local stress, preventing uneven contact is guaranteed, and thus effectively preventing fretting wear and fretting fatigue.

[0132] In some embodiments, the rotor blade main body 50 is made of precipitation hardening stainless steel.

[0133] The rotor blade main body 50, made of precipitation-hardening stainless steel, undergoes heat treatment after forming to adjust the hardness of the stainless steel to an appropriate value. An example of the heat treatment includes solution heat treatment and age hardening, which are performed in this order. If the rotor blade main body 50 is heated after the heat treatment, the heat treatment must be performed again to adjust the hardness. If any treatment is performed on the rotor blade main body 50 after the heat treatment, the temperature of the rotor blade main body 50 must not exceed the heat treatment temperature.

[0134] In this regard, the high-velocity flame spraying used to form the covering layer 65 involves almost no heating of the rotor blade main body 50. Thus, the high-velocity flame spraying does not change the hardness of the rotor blade main body 50, even if the rotor blade main body 50 is made of precipitation-hardening stainless steel. Thus, the covering layer 65 can be easily formed without providing any special temperature management for the rotor blade main body 50.

[0135] Precipitation-hardening stainless steel has a lower coefficient of friction than a titanium alloy. Thus, a rotor blade made of precipitation-hardening stainless steel has virtually no risk of fretting wear and fatigue. However, the recent trend toward higher steam turbine power and longer rotor blades has led to an increase in the stress peaks acting on the first facing surface 59 and the second facing surface 63. Thus, it has been recognized that the risk of damage to the first connecting section 55 and the second connecting section 57 due to fretting has increased.

[0136] Therefore, in some embodiments, the cover layer 65 is provided on at least one of the first facing surface 59 and the second facing surface 63 in the rotor blade main body 50, which is made of precipitation hardening stainless steel, whereby the damage due to fretting wear and fatigue can be prevented.

[0137] In some embodiments, the age hardenable stainless steel is 17-4PH (SUS630) having the composition exemplified in Table 2. When the coating layer is made of precipitation-hardening stainless steel and the cover layer 65 is made of a Co-based alloy, the thickness of the cover layer 65 can be easily measured with an electromagnetic thickness gauge. Thus, the separation and fatigue of the cover layer 65 can be easily detected, allowing the cover layer 65 to be easily repaired if necessary. High-velocity flame spraying is performed, so temperature management is not required for the rotor blade main body 50, and thus the cover layer 65 can be easily repaired. [Table 2] Element Konzentration (Massenprozent) C ≤0.07 Si ≤1.00 Mn ≤1.00 P ≤0.040 S ≤0.030 Ni 3.00 bis 5.00 Cr 15.50 bis 17.50 Cu 3.00 bis 5.00 Nb+Ta 0.15 bis 0.45 Fe Bal.

[0138] Fig. 14 shows a metal structure in a cross-section of the cover layer, corresponding, for example, to that achieved by high-velocity oxygen spraying using Stellite (registered trademark) #6. It can be Fig. 14 that the cover layer according to this example has a substantially uniform metal structure and no uneven structure. A microhardness test (Hv0.002) conducted on a plurality of sections on the cover layer according to the example revealed that the microhardness is approximately 800 to 1200 over the entire surface of the cover layer. Thus, the metal structure of the cover layer according to the example is substantially uniform.

[0139] Fig. 15 shows a cross section of a metal structure of a covering layer according to the comparative example obtained by high-velocity flame spraying with mixed powder of Cr3C2 and NiCr (Cr3C2-25NiCr), as well as as a result of the microhardness test.

[0140] The appearance and result of the microhardness test as shown in Fig. 15 indicates that the uneven structure, which shows a large difference in hardness in surfaces, is formed due to the coating layer of this sample with the mixture of Cr3C2 and NiCr. More specifically, as shown in Fig. 15, the top layer according to this example includes a white area 1, a white area 2, and a gray area with a large difference in microhardness.

[0141] A coating layer (spray coating film) formed by high-velocity flame spraying in which chromium carbide (Cr3C2) is sprayed with NiCr as a binder can be achieved for a contact portion with a large area and a small surface pressure distribution. More specifically, the invention disclosed in Japanese Patent Application JP 2014-163371 A shows a coating layer formed by high-velocity flame spraying in which chromium carbide (Cr3C2) is sprayed with NiCr as a binder for achieving better slip performance of a Ti material. It is considered that the invention disclosed in Japanese Patent Application JP 2014-163371 A shows high-velocity flame spraying in which CrC is sprayed with NiCr as a binder to enable a state in which both the cladding and the stub contact surface show "full contact" in a sheet.

[0142] Nevertheless, the inventors have discovered the following for a configuration such as a steam turbine blade with local contact. The covering layer 65 formed by high-velocity flame spraying in which the Co-based alloy having a single composition is sprayed, as in the embodiment according to the present invention, can achieve smaller unevenness in the hardness of the structure, achieve higher wear resistance, and the like, compared with the covering layer formed by high-velocity flame spraying in which a mixture is sprayed. Thus, in the embodiment of the present invention, the covering layer 65 is formed by high-velocity flame spraying in which the Co-based alloy having a single composition, preferably Stellite (registered trademark) #6, is sprayed.Thus, the cover layer 65 has a uniform structure and the hardness distribution can be formed to suit the local surface contact.

[0143] The rotor blade used for the final stage rotor blade 49 can be used for the steam turbine rotor blade in a stage other than the final stage, but is particularly suitable for use for the final stage of the low-pressure steam turbine used under the most severe conditions.

[0144] This is because the physical properties of the coating layer do not change due to the covering layer 65 formed by high-velocity flame spraying, with only a small influence of the coating layer. Thus, for example, stress corrosion cracking can be prevented from forming in the rotor blade main body 50 under wet steam, even when the covering layer 65 is formed. List of reference symbols 1 gas turbine 3 steam turbines 5 waste heat recovery boilers 7, 9 Generator 11 Compressor 13 Combustion chamber 15 turbines 17 preheaters 19 collectors 21 evaporators 23 superheaters 25 reheaters 27 denitrifiers 29 Chimney 31 High-pressure turbine 33 medium-pressure turbine 35 Low-pressure turbine 37 condensers 39 Condensation pump 41 Housing (chamber) 43 Rotor 44, 45 Radial bearings 46 Inner River Trail 47 Final stage turbine rotor cascade 49 Power stage rotor blade 50 rotor blade main body 51 sheet section 51a High pressure surface 51b Low pressure surface 53 Leaf base section 55 First connecting section 57 Second connecting section 59 First facing surface 61 lead 63 Second facing surface 65 Top layer 67 First inclined surface 69 Second inclined surface 71 First curved surface 73 Second curved surface 75 Third inclined surface 77 Fourth inclined surface

Claims

[1] Steam turbine rotor blade (49) for forming a turbine rotor cascade (47) of a steam turbine (3), wherein the steam turbine rotor blade (49) comprises: a rotor blade main body (50) comprising: a blade portion (51); a blade base portion (53) provided at one end side of the blade portion (51); a first connecting portion (55) provided at another end side of the blade portion (51) and having first facing surfaces (59); and a second connecting portion (57) provided in a central portion of the blade portion (51) and having second facing surfaces (63), wherein the first facing surfaces (59) are each configured to face one of the first facing surfaces (59) of an adjacent rotor blade main body (50) in the turbine rotor cascade (47), and the second facing surfaces (63) are each configured to face one of the second facing surfaces (63) of the adjacent rotor blade main body (50) in the turbine rotor cascade (47); and a cover layer (65) made of a Co-based alloy and having a single composition, which is formed by high-speed flame spraying on a surface of at least one of the first facing surface (59) and the second facing surface (63), so that a diffusion layer with a thickness of 10 µm or less is formed between the cover layer (65) and the surface (59, 63), wherein the rotor blade main body (50) is made of precipitation hardening stainless steel. [2] Steam turbine rotor blade according to claim 1, wherein the cover layer (65) is formed at least on the surface of the second facing surface (63). [3] Steam turbine rotor blade according to claim 1 or 2, wherein the first connecting portion (55) has first inclined surfaces (67) which continue inclined to side edges of the first facing surfaces (59) so that a distance between adjacent first connecting portions (57) in the turbine rotor cascade (47) increases, and the second connecting portion (57) has second inclined surfaces (69) which continue inclined to side edges of the second facing surfaces so that a distance between adjacent second connecting portions (57) in the turbine rotor cascade increases. [4] Steam turbine rotor blade according to one of claims 1 to 3, wherein the first connecting portion (55) has first curved surfaces (71) which continue to distal end edges of the first facing surfaces (59) so that a distance between adjacent first connecting portions (55) in the turbine rotor cascade (47) increases, and the second connecting portion (57) has second curved surfaces (73) which continue to distal end edges of the second facing surfaces (63) so that a distance between adjacent second connecting portions (57) in the turbine rotor cascade increases. [5] Steam turbine rotor blade according to one of claims 1 to 3, wherein the first connecting portion (55) has third inclined surfaces (75) which continue to distal end edges of the first facing surfaces (59) so that a distance between adjacent first connecting portions (55) in the turbine rotor cascade (47) increases, and the second connecting portion (57) has fourth inclined surfaces (77) which continue to distal end edges of the second facing surfaces (63) so that a distance between adjacent second connecting portions (63) in the turbine rotor cascade (47) increases. [6] Steam turbine rotor blade according to claim 2, wherein the second connecting portion (57) comprises: second inclined surfaces (69) which continue inclined to side edges of the second facing surfaces (63) so that a distance between adjacent second connecting sections (57) in the turbine rotor cascade (47) increases; and second curved surfaces (73) continuing to distal end edges of the second facing surfaces (63) so that the distance between adjacent second connecting portions (57) in the turbine rotor cascade increases. [7] Steam turbine rotor blade for forming a turbine rotor cascade (47) of a steam turbine (3), the steam turbine rotor blade comprising: a rotor blade main body (50) comprising: a blade portion (51); a blade base portion (53) provided at one end side of the blade portion (51); a first connecting portion (55) provided at another end side of the blade portion (51) and having first facing surfaces (59); and a second connecting portion (57) provided in a central portion of the blade portion (51) and having second facing surfaces (63), wherein the first facing surfaces (59) are each configured to face one of the first facing surfaces (59) of an adjacent rotor blade main body (50) in the turbine rotor cascade (47), and the second facing surfaces (63) are each configured to face one of the second facing surfaces (63) of the adjacent rotor blade main body (50) in the turbine rotor cascade (47); and a cover layer (63) made of a fretting wear-resistant material and formed on a surface of each of the second facing surfaces (63), wherein in a cross section of the rotor blade main body (50) in a position in which the second connecting portion (57) is provided, an acute angle is formed between the second facing surface (63) and a line connecting a leading edge and a trailing edge of the blade portion (51), and a perpendicular line to the second facing surface (63) crosses the blade portion, and the second connecting portion (57) has second inclined surfaces (59) which continue obliquely to side edges of the second facing surface (63), so that a distance between adjacent second connecting portions (57) in the turbine rotor cascade (47) increases. [8] Steam turbine (3) comprising the turbine rotor blade (49) according to one of claims 1 to 7. [9] Method for producing steam turbine rotor blades (49) for forming a turbine rotor cascade (47) of a steam turbine (3), the method comprising: a step of providing a rotor blade main body (50) made of precipitation hardening stainless steel, comprising: a blade portion (51); a blade base portion (53) provided at one end side of the blade portion (51); a first connecting portion (55) provided at another end side of the blade portion (51) and having first facing surfaces (59);and a second connecting portion (57) provided in a central portion of the blade portion (51) and having second facing surfaces (63), wherein the first facing surfaces (59) are each configured to face one of the first facing surfaces (59) of an adjacent rotor blade main body (50) in the turbine runner cascade (47), and the second facing surfaces (63) are each configured to face one of the second facing surfaces (63) of the adjacent rotor blade main body (50) in the turbine runner cascade (47); and; a high-speed flame spraying step of performing high-speed flame spraying to form, on a surface of at least one of the first facing surface (59) and the second facing surface (63), a covering layer (65) consisting of a Co-based alloy and having a single composition, wherein in the high-speed flame spraying step, powder of the Co-based alloy is sprayed onto a facing surface to be covered, which is one of the first facing surface (59) and the second facing surface (63), at an angle equal to or greater than 0° and equal to or less than 60° relative to the normal line of the facing surface, so that a diffusion layer with a thickness of 10 µm or less is provided between the cover layer and the facing surface.

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