Method for manufacturing steam turbine blades

Abstract

To provide a method of manufacturing a steam turbine blade having both erosion resistance and stress corrosion cracking resistance.SOLUTION: A method of manufacturing a steam turbine blade includes a heat treatment step of applying a laser beam with an irradiation area of 400 mm2 or more, so that a surface temperature of a leading edge portion 10 of a precipitation hardening stainless steel base material 1 that has been processed into the shape of a steam turbine blade becomes 1150°C and 1300°C, and a post-heat treatment step of performing a post-heat treatment at the leading edge portion surface temperature of 400°C to 600°C and the holding time of 1 to 10 hours. There is also provided a steam turbine blade manufactured by the method.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a steam turbine blade and a steam turbine blade. In particular, the present invention relates to a method for manufacturing a steam turbine blade using a precipitation hardening stainless steel as a base material, which has both erosion resistance and stress corrosion cracking resistance, and a steam turbine blade. [Background technology]

[0002] In general, in a steam turbine, condensed steam collides with the steam turbine blades rotating at high speed, causing erosion wear at the leading edge (inlet side) of the steam turbine blades, significantly shortening the lifespan of the steam turbine blades.In addition, steam turbine blades used in geothermal power generation contain a large amount of corrosive elements such as sulfur and chlorine in the steam, which causes stress corrosion cracking (hereinafter referred to as SCC), which also significantly shortens the lifespan of the steam turbine blades.

[0003] As a measure to suppress such a decrease in life, a method is known in which the leading edge of a steam turbine blade is subjected to a surface treatment (hardening treatment) by flame quenching to suppress the occurrence of erosive wear (see, for example, Patent Document 1). However, there is a problem in that it is difficult to control the temperature of the quenched part. This causes problems such as: (1) if the temperature control is insufficient, the hardness of the quenched part does not satisfy the target value; (2) the hardness and metal structure of the quenched part become nonuniform, making it difficult to achieve stable quality; and (3) the erosion life is short because the quenching depth is shallow (≦2 mm), so the steam turbine blade must be replaced at least every 10 years.

[0004] As a method for improving the problems of Patent Document 1, a method of performing laser hardening has been proposed (see, for example, Patent Document 2). This method is said to realize stable quality through precise heat input control, form a high-hardness layer, and achieve a deep hardening depth.

[0005] In order to achieve both deep penetration and high corrosion resistance, it is known that irradiating the leading edge surface of a steam turbine blade with a laser beam at 1050°C to 1100°C, and then performing subsequent heat treatment at a temperature of 240°C to 260°C for a holding time of 10 to 100 hours, makes it possible to achieve both high strength and high corrosion resistance (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-225828 [Patent Document 2] JP 2013-209912 A [Patent Document 3] JP 2017-222912 A Summary of the Invention [Problem to be solved by the invention]

[0007] The method disclosed in Patent Document 3 is extremely useful from the viewpoint of imparting high strength and high corrosion resistance to a given stainless steel base material. However, this method cannot be applied to precipitation hardening stainless steel, and there is a problem in that steam turbine blades using precipitation hardening stainless steel base materials cannot achieve both high strength and high corrosion resistance. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have come up with a heat treatment method capable of imparting high strength and high corrosion resistance to precipitation hardened stainless steel, and have completed the present invention. That is, according to one embodiment, the present invention relates to a method for performing a 400mm heat treatment at a surface temperature of 1150°C to 1300°C on the leading edge of a precipitation hardened stainless steel base material processed into a steam turbine blade shape. 2 The present invention relates to a method for manufacturing a steam turbine blade, the method including: a heat treatment step of irradiating laser light over the above irradiation area; and a post-heat treatment step of, after the heat treatment step, performing post-heat treatment at a surface temperature of the leading edge portion of 400°C to 600°C for a holding time of 1 to 10 hours.

[0009] In the manufacturing method of the steam turbine blade, it is preferable that the heat treatment process includes a process of detecting the surface temperature of the leading edge of the laser irradiated portion based on thermal radiation light from the laser irradiated portion, and a process of feedback controlling laser output so that the surface temperature of the leading edge of the laser irradiated portion is 1150°C to 1300°C.

[0010] In the method for manufacturing the steam turbine blade, the post-heat treatment step is preferably performed by heating the entire base material or by locally heating a laser irradiated portion.

[0011] In the method for producing the steam turbine blade, it is preferable that, after the post-heat treatment step, a high-hardness layer having a hardness of 430 Hv or more and a hardening depth of 2 mm or more is formed on the leading edge surface.

[0012] In the method for manufacturing the steam turbine blade, it is preferable that after the post-heat treatment step, an amount of precipitation of δ-ferrite on the leading edge surface is 5% or less.

[0013] According to another embodiment, the present invention relates to a steam turbine blade manufactured by any of the manufacturing methods described above.

[0014] According to another embodiment, the present invention relates to a steam turbine blade, in which a high-hardness layer having a hardness of 430 Hv or more and a hardening depth of 2 mm or more is formed at the leading edge of a precipitation-hardened stainless steel base material, and the amount of precipitation of δ-ferrite on the surface of the high-hardness layer is 5% or less. Effect of the Invention

[0015] According to the manufacturing method of the present invention, it is possible to form an erosion-resistant hardened layer on the leading edge of a steam turbine blade made of a precipitation hardened stainless steel base material, thereby making it possible to suppress the occurrence of erosion and SCC in the steam turbine blade. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of a heat treatment process by laser irradiation of a steam turbine blade according to the present invention. [Diagram 2] FIG. 2 is a diagram showing locations of a steam turbine blade where corrosion is likely to occur. [Diagram 3] FIG. 3 is a graph showing the relationship between laser spot size to achieve a required hardening depth and leading edge thickness. [Figure 4] FIG. 4 is a scanning electron microscope photograph of the surface of a steam turbine blade according to the embodiment. [Diagram 5] FIG. 5 is a scanning electron microscope photograph of the surface of a steam turbine blade of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiment described below. Also, the drawings are illustrative schematic diagrams for explaining the present invention, and the dimensions and relative positional relationships of each member in the drawings do not limit the present invention.

[0018] According to one embodiment, the present invention provides a method for manufacturing a steam turbine blade, comprising the following steps. (1) The leading edge of a precipitation hardened stainless steel base material processed into the shape of a steam turbine blade is subjected to a 400 mm 2 A heat treatment process in which laser light is irradiated over the above irradiation area. (2) a post-heat treatment step in which, after the heat treatment step, a post-heat treatment is performed at a surface temperature of the front edge portion of 400°C to 600°C for a holding time of 1 to 10 hours.

[0019] The first step is a heat treatment step by laser irradiation. FIG. 1 is a conceptual diagram showing an example of a turbine blade hardening treatment device 2 used to perform the first step. The laser irradiation step will be described below with reference to FIG. 1. The hardening treatment device 2 includes a laser generator 21, a laser irradiation head 22, an irradiation head position detector 23, a laser light scanning mechanism 24, a control device 25, and a radiation light detector 26. In FIG. 1, a device that irradiates only one surface of the base material with a laser is used, and the other surface is not irradiated with a laser. However, the heat treatment step by laser irradiation is not limited to the device that uses this device, and can be performed using any device that can perform a similar process.

[0020] The heat treatment process by laser irradiation can be performed on the precipitation hardened stainless steel base material processed into the shape of a steam turbine blade. Any type of precipitation hardened stainless steel base material can be heat treated, for example, martensitic precipitation hardened stainless steel, semi-austenitic precipitation hardened stainless steel, austenitic precipitation hardened stainless steel, etc., and erosion resistance and SCC resistance can be imparted. The predetermined precipitation hardened stainless steel material can be formed into a predetermined blade shape to be used as the base material in this embodiment. Before the laser irradiation, the laser irradiated part of the base material may be subjected to physical surface treatment such as polishing with abrasive paper or other surface treatment that does not affect the properties such as the strength of the base material, as necessary. This is to suppress the variation in the laser absorption rate.

[0021] The laser irradiated portion is a portion where corrosion is likely to occur when used as a steam turbine blade, and may be, for example, a portion near the blade tip where the peripheral speed is high or a peripheral portion where the thickness is thin, and is typically the surface of the blade leading edge. FIG. 2 is a diagram showing a typical steam turbine blade. In FIG. 2, the blade leading edge 10 of the steam turbine blade 1 shown by the dotted line is a portion where corrosion is likely to occur. Typically, this portion is irradiated with a laser spot S, and heat treatment (hardening) by laser irradiation can be performed.

[0022] For the laser irradiation, a laser generator 21 and a laser irradiation head 22 can be used. As the laser generator 21 (laser light source), it is preferable to use a semiconductor laser. The laser irradiation head 22 has a focusing lens (not shown) that focuses the laser light L generated by the laser generator 21, and the laser light L that has passed through this focusing lens is irradiated onto the surface of the blade leading edge portion 10 of the steam turbine blade 1. The laser irradiation conditions are an irradiation area (laser spot area) of 400 mm 2 By increasing the irradiation area, the hardening volume increases, and it becomes possible to increase the hardening depth. 2 If the hardening depth is less than this, the hardening depth will be insufficient and will fall short of the required hardening depth of 2 mm. In this specification, the hardening depth refers to the depth of the portion where the Vickers hardness of the cross section of the laser irradiated portion is measured and has a hardness of 430 Hv or more. Hardening depth is sometimes also called hardening depth. In this specification, Vickers hardness is used as an example for explanation, but the hardness can be specified by measuring using other hardness tests such as Rockwell, Brinell, and Knoop hardness, and converting the measurement into a Vickers hardness value. When the irradiation area is 400 mm 2 By changing the irradiation area according to the thickness of the leading edge of the steam turbine blade within the above range, the required hardening depth can be achieved. The shape of the laser spot is not particularly limited, and may be a square, a rectangle, a circle, or an ellipse. In addition, when the laser spot shape is a rectangle, the length of the side in the width direction may be longer than the length of the side in the scanning direction of the laser light, or vice versa. The same applies to the case of an ellipse.

[0023] The laser irradiation head 22 is disposed in such a manner that the laser light L reflected on the base material surface of the laser irradiation portion can be prevented from entering the laser device. Specifically, it is preferable to dispose the laser light L so that the base material surface is irradiated with the laser light L at an angle of, for example, 45°, but the irradiation angle is not limited to a specific angle.

[0024] In the heat treatment process by laser irradiation, the laser light is irradiated at a temperature in the range of 1150°C to 1300°C. Here, the temperature in the range of 1150°C to 1300°C refers to the surface temperature of the laser irradiated part. This temperature is also called the solution temperature. If the solution temperature is less than 1150°C, the hardening depth is significantly reduced and falls below the required hardening depth of 2 mm. If the solution temperature is higher than 1300°C, the SCC resistance is significantly reduced due to the formation of δ ferrite and the coarsening of grain boundaries. In the hardening treatment device 2 shown in FIG. 1, the surface temperature of the laser irradiated part can be controlled to a constant value by a temperature control system composed of the control device 25 and the radiation detector 26. Therefore, in the heat treatment process by laser irradiation, the laser irradiated part can be precisely heat treated at a temperature at which the base material surface does not melt.

[0025] Control of the surface temperature of the irradiated portion can be performed by feedback control, and includes, for example, a process of detecting the temperature of the laser irradiated portion based on the thermal radiation light from the laser irradiated portion, and a process of feedback controlling the laser output using the laser irradiated portion temperature as an index so that the temperature of the leading edge surface is a value within the temperature range of 1150°C to 1300°C.

[0026] In the heat treatment process by laser irradiation, the laser beam is scanned in the X and Y directions, so that the hardening treatment can be performed on the entire laser irradiation portion corresponding to the leading edge portion of the turbine blade under the above-mentioned irradiation area and temperature conditions. The scanning speed of the laser beam can be, for example, 1 to 5 mm / sec, but is not limited to a specific value. The scanning of the laser beam can be performed by a laser beam scanning mechanism 24. The laser beam scanning mechanism 24 drives the laser irradiation head 22 to scan the laser beam L in two-dimensional directions. The laser beam scanning mechanism 24 can be composed of, for example, an X-direction driving mechanism section that drives the laser irradiation head 22 in the X direction (left and right direction in FIG. 1) and a Y-direction driving mechanism section that drives the laser irradiation head 22 in the Y direction (direction perpendicular to the paper surface in FIG. 1) (neither is shown). The irradiation head position detector 23 detects the position of the laser irradiation head 22, and may be attached to the laser beam scanning mechanism 24. Since the base material is usually processed into a three-dimensional shape, the three-dimensional shape of the base material is stored in advance using a touch sensor or the like.Then, the laser irradiation head 22 is positioned by the irradiation head position detector 23, and scanning is performed by the laser light scanning mechanism 24.

[0027] An example of feedback control in a heat treatment process by laser irradiation using the device shown in Fig. 1 will be described in more detail. A laser beam L is irradiated from a laser irradiation head 22 onto a front edge portion 10 of a base material. Next, when the laser beam L is scanned in two dimensions by a laser beam scanning mechanism 24, a control device 25 takes in an output of an irradiation head position detector 23 and judges whether or not the laser irradiation head 22 has reached an irradiation completion position of the laser beam L. Here, if the laser irradiation head 22 has reached the laser irradiation completion position, the output of the laser generator 21 is reduced to zero, and then the heat treatment process by laser irradiation is terminated.

[0028] When the laser irradiation head 22 has not reached the laser irradiation completion position, the control device 25 takes in the output of the thermal radiation detector 26, converts the temperature based on the intensity of the thermal radiation light M, which is the output, and judges whether it is 1300°C or less. When the converted temperature is above 1300°C, the control device 25 controls the laser output of the laser generator 21 so that the intensity of the thermal radiation light M corresponds to a temperature of 1300°C or less. Specifically, the control device 25 controls the laser output of the laser generator 21 according to a function whose variable is the deviation between the detected intensity of the thermal radiation light M and the intensity corresponding to the upper limit temperature. Then, the process returns to the step of taking in the output of the irradiation head position detector 23.

[0029] On the other hand, when the intensity of the thermal radiation light M detected by the thermal radiation light detector 26 is equal to or lower than the intensity corresponding to the upper limit temperature of 1300°C, the control device 25 judges whether or not the intensity of the thermal radiation light M detected by the thermal radiation light detector 26 is equal to or higher than the lower limit intensity corresponding to the lower limit temperature of 1150°C. Here, when the intensity is equal to or higher than the lower limit intensity, the process returns to the step of taking in the output of the irradiation head position detector 23. When the intensity of the thermal radiation light M detected by the thermal radiation light detector 26 is lower than the lower limit intensity, the control device 25 controls the output of the laser generator 21 so that the output of the laser generator 21 is equal to or higher than the lower limit intensity corresponding to the lower limit temperature of 1150°C. Specifically, the control device 25 controls the output of the laser generator 21 so that the output of the laser generator 21 is equal to, for example, 40 W added to the current output. Then, the process returns to the step of taking in the output of the irradiation head position detector 23.

[0030] In this manner, the feedback control is repeatedly performed from the start to the end of the laser irradiation, thereby enabling the heat treatment process to be performed by laser irradiation with an accurate temperature control.

[0031] At the time when the heat treatment step by laser irradiation is completed, the treated portion has a martensite structure with minute amounts of inclusions such as Cr carbides precipitated.

[0032] After the heat treatment process by laser irradiation, preferably after the temperature of the base material has dropped to about room temperature, a post-heat treatment process is performed. At this time, a heat removal process such as gas blowing may be performed to remove heat from the base material. It is preferable to perform the post-heat treatment process, for example, one hour to one day after the temperature of the base material has dropped to about room temperature. This is to prevent quench cracks during the post-heat treatment process.

[0033] The post-heat treatment step is a step of performing post-heat treatment at a temperature at which the front edge surface is 400°C to 600°C, for a holding time of 1 to 10 hours. The treatment temperature in the post-heat treatment step can also be called a precipitation strengthening temperature. By performing post-heat treatment at the precipitation strengthening temperature, precipitates whose main component is Cu or the like are formed in the base material, and the hardness of the front edge portion can be improved. In addition, the post-heat treatment step can promote the diffusion of Cr and reduce the sensitization of the metal structure that may occur in the laser irradiation step. The post-heat treatment step is preferably performed by heating the entire base material. This is because the post-heat treatment step takes about 10 hours at the longest, and the productivity is poor when the post-heat treatment step is performed locally. However, if the time is not a problem in terms of productivity, the post-heat treatment step may be performed locally.

[0034] For example, the base material is heated in an atmosphere by putting the base material into a heating furnace and holding it at a temperature in the range of 400°C to 600°C for 1 to 10 hours. If the precipitation strengthening temperature is lower than 400°C, the amount of precipitates becomes insufficient, and if it is higher than 600°C, the precipitates become coarse, and sufficient hardness cannot be obtained. The precipitation strengthening temperature refers to the surface temperature of the base material, not the temperature inside the furnace, and refers to a value measured, for example, by a thermocouple or the like attached to the surface of the base material. If the holding time is lower than 1 hour, the amount of precipitates formed becomes insufficient. The upper limit of the holding time is preferably within 10 hours. This is because if heated for a long time, the precipitates become coarse and the hardness decreases. It is preferable to determine the holding time depending on the temperature. For example, in the case of a holding temperature of 400°C to 500°C, the holding time can be 7 to 10 hours, and in the case of a holding temperature of 500°C to 600°C, the holding time can be 1 to 7 hours.

[0035] More preferably, the base material is placed in a furnace at room temperature, and the temperature is increased, for example, at a rate of 50 to 150°C / h. After being held at a constant temperature within a range of 400°C to 500°C for the above-mentioned specified time, it is slowly cooled in the furnace and taken out after returning to room temperature.

[0036] The local heating can be performed, for example, by irradiating the front edge portion, which has been previously heat-treated by laser irradiation, with a laser at a precipitation strengthening temperature again. In this case, the adjustment of the base material surface temperature can be performed by feedback control, as in the previous heat treatment process.

[0037] The steam turbine blade obtained through the above process has a high-hardness layer with a hardness of 430Hv or more and a hardening depth of 2mm or more, preferably 6mm or more. The state of the structure at this point is that fine precipitates (main component Cu, etc.) are formed in the martensite structure. The amount of δ-ferrite formed in the laser irradiated area is 5% or less. The amount of δ-ferrite formed here can be calculated by taking multiple images of the surface of the laser irradiated area and calculating the area of ​​δ-ferrite structure per observation area.

[0038] The steam turbine blade obtained through the above process has a rupture life of 3000 hours or more. - A sample is immersed in an aqueous solution containing 30,000 ppm of carbon black at 80°C and a stress of 600 MPa is applied to it, and a tensile test is performed. The life span is defined as the life until breakage occurs.

[0039] The method for manufacturing a steam turbine blade according to the present embodiment can be applied to the manufacture of any steam turbine blade using a precipitation hardened stainless steel base material, and is particularly suitable for the manufacture of steam turbine blades for thermal power generation. The obtained steam turbine blade has both erosion resistance and SCC resistance. EXAMPLES

[0040] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[0041] In the following examples and comparative examples, austenitic precipitation hardening stainless steel was used as the base material, which was processed into the shape of a steam turbine blade. In order to suppress the variation in laser absorption rate, the front edge surface of the base material processed into the shape of a steam turbine blade was polished in advance with abrasive paper with a roughness of about #60 to #120. A semiconductor laser (manufactured by Laserline) was used for the heat treatment process by laser irradiation.

[0042] (1) Laser spot size and base material thickness A heat treatment process was carried out with different laser spot sizes on steam turbine blade base materials with different leading edge thicknesses. The heat treatment temperature was controlled so that the leading edge surface temperature was 1250°C, and the laser scanning speed was 1mm / s. Figure 3 is a graph showing the relationship between the laser spot size that achieves the required hardening depth of 2mm or more and the thickness of the leading edge. The hardening depth was measured by measuring the Vickers hardness of the cross section of the laser irradiated area, and the depth of the area with a hardness of 430Hv or more was taken as the hardening depth. As can be seen from Figure 3, there is a proportional relationship between the thickness of the leading edge and the laser spot size that achieves the required hardening depth, and although no numerical values ​​are shown in the graph, when the laser spot size was set to 400mm 2 It has been confirmed that the required hardening depth can be obtained for typical steam turbine blades by following the above method.

[0043] (2) Heat treatment temperature, δ-ferrite formation, and corrosion resistance The steam turbine blades of the example and the comparative example were manufactured by changing the heat treatment process temperature. 2A heat treatment step was performed by laser irradiation at a surface temperature of 1150°C, followed by a post-heat treatment step of heating in a furnace at 425°C for 8 hours. The steam turbine blade of the comparative example was obtained in the same manner, except that the surface temperature in the heat treatment step by laser irradiation was set to over 1300°C. Scanning electron microscope photographs of the surface of the steam turbine blade at the location of laser irradiation of the example and comparative example after the post-heat treatment step were taken.

[0044] A photograph of the surface of the steam turbine blade of the example is shown in Fig. 4, and a photograph of the surface of the steam turbine blade of the comparative example is shown in Fig. 5. No δ ferrite formation was observed in the sample of Fig. 4, and similarly, no δ ferrite formation was observed in other fields of view, or even if it was present, the amount of formation was 5% or less. In Fig. 5, the formation of δ ferrite structure 3 was visible, and the amount of formation was more than 5%.

[0045] A corrosion resistance test was carried out on the steam turbines of the examples and the comparative examples. The test conditions were as follows: - A tensile test was performed by immersing a sample loaded with a stress of 600 MPa in an aqueous solution of 30,000 ppm sodium chloride and 80° C. to measure the life until fracture. As a result, the fracture life of the steam turbine of the embodiment was 3,000 hours or more, and the fracture life of the steam turbine of the comparative example was 900 hours.

[0046] (3) Solution temperature, precipitation strengthening temperature and hardness A heat treatment process by laser irradiation and a post-heat treatment process were performed on a plate-shaped austenitic precipitation hardening stainless steel base material at different temperatures, and the Vickers hardness of the surface of the laser irradiated area was measured. The laser spot size during laser irradiation was 1600 mm 2 The post-heat treatment process was carried out for 8 hours. The results are shown in Table 1.

[0047] [Table 1]

[0048] From Table 1, it was confirmed that the surface hardness was 430Hv or more by performing a heat treatment process by laser irradiation in a specific solution temperature range and a post-heat treatment process in a precipitation strengthening temperature range. Although data is not shown in Table 1, samples that were subjected to a heat treatment process by laser irradiation in the range of 1150 to 1300°C and then a post-heat treatment process in the range of 400 to 500°C achieved a hardening depth of 2mm or more, particularly a hardening depth of about 7 to 9mm. Note that, referring to Table 1, there were samples that were able to achieve a surface hardness of 430Hv or more even when heated at 1100°C, but the hardening depth did not reach 2mm. [Industrial Applicability]

[0049] The steam turbine blade manufactured by the method of the present invention is preferably used for power generation, for example, as a steam turbine blade for thermal power generation, and is particularly preferably used as a turbine blade subjected to high stress. [Explanation of symbols]

[0050] 1 Precipitation hardening stainless steel base material, 10 Leading edge 2 hardening treatment device, 21 laser generator, 22 laser irradiation head 23 irradiation head position detector, 24 laser light scanning mechanism 25 control device, 26 radiation detector

Claims

1. The precipitation hardening stainless steel base material processed into the shape of a steam turbine blade is subjected to a 400 mm ２ a heat treatment step of irradiating the laser beam with the irradiation area described above; a post-heat treatment step in which, after the heat treatment step, a post-heat treatment is performed at a surface temperature of the leading edge portion of 400° C. to 600° C. for a holding time of 1 to 10 hours; Including, The heat treatment step comprises: detecting a surface temperature of the front edge portion of the laser irradiation portion based on thermal radiation light from the laser irradiation portion; feedback-controlling the laser output so that the surface temperature of the front edge of the laser irradiation portion is 1150° C. to 1300° C.; Including, a high-hardness layer having a hardness of 430 Hv or more and a hardening depth of 2 mm or more is formed on the leading edge surface after the post-heat treatment step.

2. 2. The method for manufacturing a steam turbine blade according to claim 1, wherein the post-heat treatment step is performed by heating the entire base material or by locally heating a laser irradiated portion.

3. 3. The method for manufacturing a steam turbine blade according to claim 1, wherein after the post-heat treatment step, an amount of precipitation of δ-ferrite calculated from an area of ​​δ-ferrite structure per observation area on the surface of the leading edge of the steam turbine blade is 5% or less.

4. A steam turbine blade in which a high-hardness layer having a hardness of 430 Hv or more and a hardening depth of 2 mm or more is formed at the leading edge of a precipitation-hardened stainless steel base material, and the amount of precipitation of δ-ferrite calculated from the area of ​​δ-ferrite structure per observation area on the surface of the high-hardness layer is 5% or less.

Images