JP2017214835A - MANUFACTURING METHOD FOR HIGH Cr STEEL COMPONENT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a high Cr steel component in which individual characteristics having an antinomic relationship can be easily added to a required portion in the high Cr steel component.SOLUTION: A manufacturing method for a high Cr steel component according to one embodiment includes a metal layer forming step of forming a metal layer containing nitrogen by melting metal powder by irradiating the metal powder of high Cr steel containing the nitrogen as its composition with an energy beam, and manufactures the high Cr steel component containing a gradient composition in which the nitrogen is inclined by repeatedly executing the metal layer forming step and laminating the metal layer based on three-dimensional design data. In this case, the gradient composition is formed by adjusting a heat gain by which heat is input to the metal powder by the energy beam in the metal layer forming step.SELECTED DRAWING: Figure 2B

Description

  Embodiments of the present invention relate to a method for manufacturing a high Cr steel part.

  In the thermal power generation system, the temperature of steam supplied as a working fluid to the steam turbine tends to increase in order to further increase the power generation efficiency. As a result, steam turbine components that constitute the steam turbine are required to have improved high-temperature characteristics. In particular, as a high-temperature characteristic, the requirement for creep strength has become strict.

  The steam turbine component is formed using, for example, high Cr steel (alloy steel having a chromium (Cr) content of 9% by mass or more) in order to ensure heat resistance. However, as the temperature of the working fluid vapor rises, it has become difficult to obtain sufficient creep strength.

JP 2012-24670 A

  High Cr steel parts such as steam turbine parts have parts that require characteristics other than creep strength in addition to parts that require high creep strength. For example, in a turbine rotor, which is a steam turbine component, the central portion of the shaft on which the moving blades are installed is exposed to a high-temperature working fluid, and thus high creep strength is required. On the other hand, in the turbine rotor, the shaft end portion supported by the bearing is not exposed to a high-temperature working fluid, so that the strength in a relatively low temperature state is high without requiring high creep strength. I need. Both the creep strength and the strength at a low temperature are in a trade-off relationship. In the conventional manufacturing method of high Cr steel parts, it is not easy to add each of the above-mentioned characteristics in a trade-off relationship to necessary portions in the high Cr steel parts. That is, in high Cr steel parts, it is difficult to achieve both conflicting characteristics.

  Therefore, the problem to be solved by the present invention is to provide a method for manufacturing a high Cr steel part, which can easily add each of the characteristics in a trade-off relationship to a necessary part in the high Cr steel part. It is.

  The manufacturing method of the high Cr steel part which concerns on embodiment is the metal which forms the metal layer containing nitrogen by melting metal powder by irradiating an energy beam to the metal powder of the high Cr steel which contains nitrogen in a composition A high Cr steel part including a gradient composition in which nitrogen is inclined is manufactured by repeatedly performing the metal layer formation process based on the three-dimensional design data and laminating the metal layers. Here, the gradient composition is formed by adjusting the amount of heat input to the metal powder by the energy beam in the metal layer forming step.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the high Cr steel component which can add each of the characteristic in a trade-off relationship to a required part in a high Cr steel component easily can be provided.

FIG. 1 is a cross-sectional view schematically showing the high Cr steel part of the embodiment. FIG. 2A is a cross-sectional view schematically showing a production method for producing the high Cr steel part of the embodiment. FIG. 2B is a cross-sectional view schematically showing a manufacturing method for manufacturing the high Cr steel part of the embodiment. FIG. 3A is a cross-sectional view schematically showing a manufacturing method for manufacturing the high Cr steel part of the embodiment. FIG. 3B is a cross-sectional view schematically showing a manufacturing method for manufacturing the high Cr steel part of the embodiment. FIG. 4 is a cross-sectional view schematically showing a manufacturing method for manufacturing the high Cr steel part of the embodiment.

  The configuration of the high Cr steel part according to the embodiment will be described.

  FIG. 1 is a cross-sectional view schematically showing the high Cr steel part of the embodiment. Here, the turbine rotor 10 which is a steam turbine part is illustrated as a high Cr steel part. The turbine rotor 10 is a rod-shaped body, and is installed in a turbine casing (not shown) so that the rotation axis AX extends along the horizontal direction.

  In the turbine rotor 10, a moving blade (not shown) is installed at the shaft center portion 11 located at the center in the axial direction along the rotation axis AX. In the shaft center portion 11, the moving blade is provided with a plurality of stages along the axial direction. In the shaft central portion 11, when the steam turbine is operated, high-temperature steam supplied as a working fluid into the turbine casing flows along the axial direction sequentially through the plurality of stages of moving blades. For example, when the steam turbine is a double-flow exhaust type, high-temperature steam flows from the center to the side in the shaft central portion 11 and is exhausted to the outside. Since the shaft center portion 11 is exposed to high-temperature steam during operation of the steam turbine, the temperature becomes high.

  In the turbine rotor 10, shaft end portions 12 located on both sides in the axial direction include portions supported by bearings (not shown). Unlike the shaft center portion 11, the shaft end portion 12 is not exposed to high-temperature steam when the steam turbine is operated, so that the temperature does not become higher than that of the shaft center portion 11.

  In the present embodiment, the turbine rotor 10 is a functionally graded material formed so as to include a gradient composition in which nitrogen is inclined. Specifically, in the turbine rotor 10, the nitrogen content contained in the high Cr steel composition is smaller at the shaft end portion 12 than at the shaft center portion 11. That is, in the turbine rotor 10, the shaft center portion 11 is a portion having a first nitrogen content, and the shaft end portion 12 is a portion having a second nitrogen content higher than the first nitrogen content. In the axial direction, the nitrogen content changes stepwise.

  Thereby, in this embodiment, the creep strength is higher in the shaft center portion 11 than in the shaft end portion 12. On the other hand, the strength of the shaft end portion 12 is higher than that of the shaft center portion 11 in a state where the temperature is lower than the measurement temperature of the creep strength.

  A manufacturing method for manufacturing the turbine rotor 10 as a high Cr steel part will be described.

  FIG. 2A, FIG. 2B, FIG. 3A, FIG. 3B, and FIG. 4 are sectional views schematically showing a manufacturing method for manufacturing the high Cr steel part of the embodiment.

  In this embodiment, the turbine rotor 10 including a gradient composition in which nitrogen is inclined is manufactured using a three-dimensional additive manufacturing technique. Here, a case where the turbine rotor 10 is manufactured using a “powder bed type” three-dimensional additive manufacturing apparatus 30 (3D printer) including a nozzle 31 and a stage 32 is illustrated.

  When manufacturing the turbine rotor 10, first, as shown in FIG. 2A, the metal powder layer 41 is provided on the upper surface of the stage 32. Here, the metal powder 310 is supplied from the nozzle 31 and filled in the powder storage space (not shown) in which the stage 32 is accommodated in the three-dimensional additive manufacturing apparatus 30. Thereafter, the upper surface of the metal powder 310 is leveled and flattened using a plate (not shown) such as a squeegee. Thereby, the metal powder layer 41 is formed with a uniform thickness.

  As the metal powder 310, high Cr steel containing a nitrogen component in its composition is used. For example, as high Cr steel, 9 to 11.5 mass% chromium (Cr), 0.15 to 0.30 mass% vanadium (V), 0.01 to 0.03 mass% nitrogen (N) , A heat resistant steel containing 0.005 to 0.015% by mass of boron (B) in the composition is used. By using this heat-resistant steel as a raw material, it is possible to ensure sufficient creep strength in the turbine rotor 10.

  As the metal powder 310, one having a particle diameter (JIS Z8815-1994 “General Rules for Screening Test Method”) of, for example, 15 to 150 μm can be suitably used.

  Next, as shown in FIG. 2B, the metal layers 411 and 412 are formed by irradiating the metal powder layer 41 with energy beams EB1 and EB2. Here, an electron beam or a laser beam is irradiated as the energy beams EB1 and EB2. As a result, sintered bodies solidified after the metal powder 310 constituting the metal powder layer 41 is melted are formed as the metal layers 411 and 412.

  The irradiation of the energy beams EB1 and EB2 is executed by the control device (not shown) of the three-dimensional additive manufacturing apparatus 30 adjusting the irradiation position based on the three-dimensional design data (three-dimensional CAD data) of the turbine rotor 10. To do.

  At this time, in this embodiment, the ratio of nitrogen contained in the metal layers 411 and 412 is adjusted by the control device of the three-dimensional additive manufacturing apparatus 30 by adjusting the amount of heat input to the metal powder 310 by the energy beams EB1 and EB2. To control.

  Specifically, the energy beam EB1 is applied to the portion of the metal powder layer 41 that forms the shaft center portion 11 so that the first heat input amount of heat is input. Thereby, the metal layer 411 which comprises a part of axial center part 11 which is 1st nitrogen content is formed.

  On the other hand, the energy beam EB2 is applied to the portion of the metal powder layer 41 that forms the shaft end portion 12 so that heat having a second heat input amount smaller than the first heat input amount is input. Irradiate. Thereby, the metal layer 412 which comprises a part of axial end part 12 which is 2nd nitrogen content larger than 1st nitrogen content is formed.

  In the metal powder layer 41, heat is applied by the energy beams EB1 and EB2, whereby the metal powder 310 is melted, and the nitrogen component contained in the composition of the metal powder 310 is released as nitrogen gas. The amount separated as nitrogen gas increases as the amount of heat input by the energy beams EB1 and EB2 increases. For this reason, in this embodiment, as described above, the nitrogen content of the metal layer 412 constituting a part of the shaft end portion 12 is higher than that of the metal layer 411 constituting a part of the shaft center portion 11. Less. Thereby, regarding the creep strength, the metal layer 411 in the shaft center portion 11 is higher than the metal layer 412 in the shaft end portion 12. The metal layer 412 at the shaft end portion 12 is higher than the metal layer 411 at the shaft center portion 11 with respect to the strength when the temperature is relatively lower than the measured temperature of the creep strength.

  As shown in FIG. 3A, the metal powder layer 41 is formed in the same manner as described above (see FIG. 2A). Then, as shown to FIG. 3B, irradiation of energy beam EB1 and EB2 is performed similarly to the above (refer FIG. 2B). That is, the metal layer forming process for forming the metal layers 411 and 412 is repeatedly executed based on the three-dimensional design data, and the metal layers 411 and 412 are sequentially stacked.

  Thereby, as shown in FIG. 4, a laminated body of the metal layers 411 and 412 is formed as the turbine rotor 10. And the turbine rotor 10 is completed by removing the metal powder 310 of the unmelted part which remained around the turbine rotor 10 (refer FIG. 1).

  As described above, in the present embodiment, when manufacturing using the three-dimensional additive manufacturing technique, the nitrogen content is controlled by adjusting the amount of heat input to the metal powder 310 by the energy beams EB1 and EB2. . Therefore, in the present embodiment, each of the characteristics that are in a trade-off relationship, such as the creep strength and the strength in a state where the temperature is relatively lower than the measured temperature of the creep strength, is a necessary part of the turbine rotor 10. Can be easily added to.

  Specifically, it is possible to form a gradient composition by changing the blending ratio of a plurality of metal powders having different compositions, but in this embodiment, the energy beams EB1 and EB2 are used without using a special mechanism. A gradient composition can be easily formed by adjusting the amount of heat input. Further, in the present embodiment, a fine and complicated gradient composition can be easily formed, compared to the case where the gradient composition is formed by changing the heat treatment conditions.

  In the above embodiment, the turbine rotor 10 is illustrated as a high Cr steel part having a gradient composition in which nitrogen is inclined. However, the present invention is not limited to this. In addition to the turbine rotor 10, steam turbine components such as moving blades and stationary blades may be configured to have a gradient composition as in the above embodiment. For example, the moving blade or the like may be formed so as to have a gradient composition in the radial direction.

  In the above embodiment, the high Cr steel part having a gradient composition in which the nitrogen content changes stepwise is exemplified, but the present invention is not limited to this. High Cr steel parts may be configured to have a graded composition with a continuously changing nitrogen content.

  The three-dimensional additive manufacturing apparatus 30 used in the production of the high Cr steel part in the above embodiment is a “powder bed method”, but is not limited thereto. The three-dimensional additive manufacturing apparatus may be a “deposition method”. In other words, the metal powder injected from the nozzle onto the upper surface of the stage is irradiated with an energy beam and the metal powder is sintered to repeatedly form a metal layer based on the three-dimensional design data of the high Cr steel part. Thus, a high Cr steel part may be manufactured by laminating metal layers.

  Examples of the above embodiment will be described below.

  In this example, 10 mass% chromium (Cr), 0.2 mass% vanadium (V), 0.08 mass% niobium (Nb), 2 mass% tungsten (W), 0.03 mass%. A high Cr steel metal powder containing nitrogen (N) and 0.01% by mass of boron (B) in the composition was prepared. Here, a metal powder having a particle size range of 45 to 95 μm was prepared.

  And the rectangular parallelepiped shaped modeling thing was produced as a high Cr steel component using said metal powder. In the production of the modeled object, a “powder bed type” three-dimensional layered modeling apparatus that irradiates an electron beam as an energy beam was used.

  Specifically, the first layer was fabricated under the condition that the current value of the electron beam is 10 mA. Thereafter, the second layer was laminated on the first layer under the condition that the current value of the electron beam was 25 mA. Each of the first layer and the second layer was formed so that the vertical dimension was 70 mm, the horizontal dimension was 15 mm, and the thickness was 15 mm.

And after taking a creep test piece from each of the 1st layer and the 2nd layer which constitute the above-mentioned modeling thing, the creep test was done about the creep test piece. The creep test was performed under test conditions where the temperature was 650 ° C. and the pressure was 16 kgf / mm ² . In addition, a tensile test was performed on each test piece in order to measure “strength at a low temperature”.

  The creep test piece of the first layer produced under the condition that the current value of the electron beam is 10 mA has a creep rupture life of 1616 hours. Further, the creep test piece of the first layer had a nitrogen content of 210 ppm. And as a result of performing the tensile test about the test piece of this 1st layer, tensile strength was 950 MPa.

  In contrast, the creep test piece of the second layer produced under the condition that the current value of the electron beam is 25 mA has a creep rupture life of 2525 hours. Further, this second layer creep test piece had a nitrogen content of 140 ppm. And as a result of performing a tensile test about the test piece with a small nitrogen content, the tensile strength was 900 MPa.

  Thus, it was confirmed that the nitrogen content in the composition and the creep characteristics can be changed by changing the amount of heat input by the electron beam.

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

DESCRIPTION OF SYMBOLS 10 ... Turbine rotor, 11 ... Shaft center part, 12 ... Shaft end part, 30 ... Three-dimensional additive manufacturing apparatus, 31 ... Nozzle, 32 ... Stage, 41 ... Metal powder layer, 310 ... Metal powder, 411 ... Metal layer, 412 ... Metal layer, AX ... Rotating shaft, EB1, EB2 ... Energy beam

Claims (4)

A metal layer forming step of forming a metal layer containing nitrogen by melting the metal powder by irradiating an energy beam to a metal powder of high Cr steel containing nitrogen in the composition, the metal layer forming step Is a method of manufacturing a high Cr steel part, which repeatedly executes the process based on the three-dimensional design data and stacks the metal layer to manufacture a high Cr steel part including a gradient composition in which nitrogen is inclined,
Forming the gradient composition by adjusting the amount of heat input to the metal powder by the energy beam in the metal layer forming step;
Manufacturing method for high Cr steel parts. In the metal layer forming step,
By irradiating the metal powder with an energy beam so as to put heat of the first heat input into the metal powder, a portion of the first nitrogen content in the gradient composition is formed,
By irradiating the metal powder with an energy beam so as to put a heat having a second heat input amount smaller than the first heat input amount into the metal powder, a second second content higher than the first nitrogen content in the gradient composition. Forming part of the nitrogen content,
The manufacturing method of the high Cr steel component of Claim 1. The high Cr steel part is a steam turbine part,
The manufacturing method of the high Cr steel component of Claim 1 or 2. The steam turbine component is a turbine rotor;
The manufacturing method of the high Cr steel component of Claim 3.

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