JP6411084B2 - Manufacturing method of rotor for steam turbine - Google Patents

Description

  Embodiments described herein relate generally to a method for manufacturing a steam turbine rotor.

  Some steam turbines are used for geothermal power generation. In geothermal power generation, underground steam or the like is guided to a steam turbine provided on the ground surface, and the rotor of the steam turbine is rotated by the force of the steam. The temperature of natural steam introduced into such a steam turbine for geothermal power generation is lower than the temperature of steam introduced into a general steam turbine for thermal power generation, for example, about 200 ° C. . In addition, natural steam introduced into a steam turbine in geothermal power generation may contain corrosive gas that corrodes metals such as hydrogen sulfide.

  Such a rotor of a steam turbine for geothermal power generation may be cracked by hydrogen embrittlement (hereinafter simply referred to as “hydrogen cracking”). In addition to mechanical properties such as tensile strength, proof strength, toughness, and corrosion resistance, the materials that make up the rotor of steam turbines (hereinafter referred to as rotor materials) are capable of preventing cracking due to hydrogen embrittlement ( Hereinafter, the resistance to hydrogen cracking is required.

Japanese Patent No. 4713796

  In order to ensure the above-mentioned hydrogen cracking resistance and corrosion resistance, the rotor material of the steam turbine for geothermal power generation is based on 1% CrMoV steel, which has been used as a rotor material for steam turbines for thermal power generation. In many cases, a 1-2% Cr-based material strengthened with bismuth is used.

  By the way, among the rotors of a steam turbine for geothermal power generation, a part that is first exposed to natural steam may be used in an environment that is more corrosive than other parts. Such a part has a problem that hydrogen cracking particularly occurs and the hydrogen cracking easily progresses as compared with other parts, and there is a demand for improving the hydrogen cracking resistance.

  Therefore, the problem to be solved by the present invention is to provide a technology for manufacturing a steam turbine rotor capable of improving the hydrogen cracking resistance for a predetermined target portion of the steam turbine rotor. .

A method for manufacturing a rotor for a steam turbine according to an embodiment of the present invention is a method for manufacturing a rotor constituting a steam turbine, and reduces a residual stress in a predetermined target portion of the rotor as compared with other portions. Tempering step, which is a step of tempering the rotor at least once by setting the tempering temperature, which is the heating temperature thereof, to a higher temperature than the other parts. The portion has a step of refining crystal grains compared to other portions, and the step of refining the crystal grains is performed before the tempering step, and the target portion is A quenching process, which is a process of quenching the rotor by setting the quenching austenitizing temperature, which is a heating temperature, to a lower temperature than other parts, and the quenching process An annealing step before tempering, which is a step of performing the rotor annealing by setting the pre-tempering annealing temperature, which is the heating temperature, to 1050 to 1300 ° C., and the rotor is made of carbon. 0.15-0.33%, silicon 0.03-0.20%, manganese 0.5-2.0%, nickel 0.1-1.3%, chromium 0.9-3. 5%, Molybdenum 0.1-1.5%, Vanadium 0.15-0.35%, Tungsten as an optional component is contained in 1.0% or less by mass%, the balance is iron and inevitable It is made of ferritic alloy steel, which is a typical impurity .

  According to the embodiment of the present invention, hydrogen cracking resistance can be improved for a predetermined target portion of the steam turbine rotor.

It is a schematic diagram which shows an example of the rotor for steam turbines of 1st and 2nd embodiment, and its periphery structure. It is explanatory drawing explaining an example of the rotor material for steam turbines of 1st and 2nd embodiment. It is a figure which shows the heat processing conditions of the manufacturing method of 1st and 2nd embodiment. It is a figure which shows the determination result of the crystal grain size (G.S.No.), the residual stress (maximum tensile stress), and hydrogen cracking resistance of the test material subjected to the heat treatment of the manufacturing method of the first and second embodiments. It is a figure which shows the heat processing conditions of a comparative example. It is a figure which shows the determination result of the crystal grain size (G.S.No.), residual stress (maximum tensile stress), and hydrogen cracking resistance of the test material which was heat-treated in the comparative example.

  Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment]
An example of a steam turbine rotor to which the manufacturing method of the first embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic diagram showing a steam turbine rotor according to the present embodiment and its peripheral configuration. In FIG. 1, the lower side of the moving blade, the stationary blade, and the casing is omitted for easy understanding.

  As shown in FIG. 1, the steam turbine 1 is an axial-flow turbo fluid machine, and includes a casing 5 in which a stationary blade 3 is coupled to an inner side, and a rotation center shaft (indicated by a one-dot chain line A in the figure). And a rotor for a steam turbine (hereinafter simply referred to as “rotor”) 10 that rotates around the center. The rotor 10 has a substantially cylindrical shape and extends in the axial direction. A plurality of rotor blades 12 are arranged in the circumferential direction of the rotor 10. In the axial direction of the rotor 10 (direction indicated by the alternate long and short dash line A), the moving blades 12 are arranged to face the stationary blades 3 and constitute a plurality of turbine stages together with the stationary blades 3.

  In the steam turbine 1, as indicated by an arrow F in the figure, steam is introduced from one side (hereinafter referred to as an upstream side) in the axial direction of the rotor 10. The steam turbine 1 of this embodiment is used for geothermal power generation, and natural steam is introduced. Natural vapor contains corrosive gases that corrode metals, such as hydrogen sulfide. Thus, the rotor 10 is exposed to natural steam containing corrosive gas.

  In particular, the vicinity of the turbine stage constituting the upstream side of the steam turbine 1 is a portion where natural steam flows as shown in FIG. 1 and is exposed to the above-described corrosive gas. Sex is required. For example, in the rotor 10, coupling portions 20 a, 21 a, to which the rotor blades 12 constituting the first turbine stage to the fourth turbine stage on the upstream side are coupled (hereinafter referred to as blade implantation parts and indicated by broken lines in the drawing) In 22a and 23a, the corrosive component contained in natural steam may be deposited and deposited in the gap with the moving blade 12. Therefore, portions of the rotor 10 that have a substantially cylindrical shape including the blade implantation portions 20a, 21a, 22a, and 23a (hereinafter referred to as paragraph portions and indicated by two-dot chain lines in the drawing) 20, 21, 22, In 23, hydrogen cracking is likely to occur compared to other parts.

  On the other hand, on the downstream side (not shown) of the steam turbine 1, natural steam works and condenses and drains (liquefies) in the turbine stage. For this reason, the corrosive component in the steam is discharged to the outside of the turbine together with the condensed drain without accumulating in the blade implantation part. For this reason, hydrogen cracking hardly occurs in a portion of the rotor 10 on the downstream side of the steam turbine 1.

  In the rotor 10 of the present embodiment, the stage portions 20, 21, 22, and 23 including the blade implantation portions 20a, 21a, 22a, and 23a of the turbine stage on the upstream side of the steam turbine into which geothermal steam flows are provided with hydrogen resistance. This is a site that requires particularly improved crackability, and is referred to as a “target site” in the following description. In the present embodiment, parts of the rotor 10 other than the predetermined target parts (paragraphs) 20, 21, 22, 23 are referred to as “other parts” in the following description.

  Next, the rotor material used in the steam turbine rotor manufacturing method of the present embodiment will be described with reference to FIG. FIG. 2 is an explanatory view illustrating an example of the steam turbine rotor material of the present embodiment. FIG. 2 shows, as an example, components of a rotor material used for evaluation (hereinafter referred to as “test material”) and components of the rotor material shown in the claims. The results of performing the heat treatment of the present embodiment on the specimens A, B, C, D, E, F, and G will be described later.

  As shown in FIG. 2, the steam turbine rotor is made of so-called ferritic alloy steel, the main part of which is made of iron (element symbol: Fe). The ferritic alloy steel is in mass% as an alloy element, carbon (element symbol: C) is 0.15 to 0.33%, silicon (element symbol: Si) is 0.03 to 0.20%, manganese ( Element symbol: Mn) is 0.5-2.0%, nickel (element symbol: Ni) is 0.1-1.3%, chromium (element symbol: Cr) is 0.9-3.5%, molybdenum (Element symbol: Mo) is 0.1 to 1.5%, vanadium (element symbol: V) is 0.15 to 0.35%, tungsten (element symbol: W) is 1.0% or less as an optional component, Contained. Note that the ferritic alloy steel of this embodiment does not contain tungsten.

  In addition, the ferritic alloy steel contains nitrogen (element symbol: N) in an amount of 0.005 to 0.015% by mass, as required in production. Nitrogen improves the hardenability and suppresses the formation of ferrite in the central portion of a large steel ingot, and is therefore effective in increasing the diameter of the rotor material. Nitrogen is effective in increasing the strength of the rotor 10 by being dissolved in the matrix (main metal) and precipitated as Nb (C, N) carbonitride. In addition to the elements described above, impurities that cannot be avoided in manufacturing (hereinafter referred to as inevitable impurities) may be included.

  Next, the manufacturing method (heat treatment method) of this embodiment will be described with reference to FIGS. FIG. 3 is a diagram showing the heat treatment conditions of the manufacturing method of the present embodiment. FIG. 4 is a diagram showing the determination results of the crystal grain size, residual stress (maximum tensile stress), and hydrogen cracking resistance of the test material subjected to the heat treatment of the manufacturing method of the present embodiment.

  The rotor material of the present embodiment described above can be obtained by melting by a general method, and the obtained high temperature alloy steel is subjected to hot working such as forging. After such hot working, various heat treatments of this embodiment are performed. The heat treatment includes, for example, quality heat treatment. The tempering is a heat treatment that is tempered at a relatively high temperature after hardening by quenching in order to stabilize the material, and is simply referred to as “tempering treatment” in the following description.

(1) Pre-annealing annealing step In the manufacturing method of the present embodiment, annealing is performed before the above-described tempering treatment step. This will be described below with reference to FIGS. In this step, the steam turbine rotor is heated to a predetermined temperature, held at that temperature, and then gradually cooled. Thereby, a rotor material can be softened and the distortion which exists inside can be removed. Before performing the tempering treatment, the step of annealing is referred to as “pre-tempering annealing step” in the following description. The pre-tempering annealing process described below is performed on the entire steam turbine rotor including the above-described target part and other parts.

  In the pre-annealing annealing process of the present embodiment, the heating temperature for annealing (hereinafter simply referred to as “annealing temperature”) is set to 1050 to 1300 ° C. As an example, as shown in the figure, the annealing temperature is set to 1150 ° C or 1050 ° C. In the pre-annealing annealing step, the rotor material is heated until it reaches an annealing temperature set at 1050 to 1300 ° C., and the annealing temperature is maintained for a predetermined time (hereinafter referred to as holding time), and then cooled in the furnace. Or gradually cool at a sufficiently slow cooling rate such as air cooling. And refinement | miniaturization of a crystal grain is aimed at about the object part in the hardening process of subsequent tempering processing. The holding time for the annealing temperature is set to 5 hours.

  The lower limit of the annealing temperature is set to 1050 ° C. in order to remove strain generated in a hot working process such as forging, and a coarse carbide or carbonitride is used as a matrix (main metal, This is because an annealing temperature of 1050 ° C. or higher is required to form a homogeneous structure in the base material). If it is less than 1050 ° C., the quality and material characteristics required for the rotor material cannot be obtained in the tempering process performed after the process.

  Further, the upper limit of the annealing temperature is set to 1300 ° C. because if it exceeds 1300 ° C., the life of the annealing furnace is remarkably shortened, which is inappropriate in actual production. For this reason, annealing temperature is set to the range of 1050 to 1300 degreeC. For the same reason, it is more preferable to set the lower limit value to 1100 ° C. and the upper limit value to 1250 ° C. for the same reason.

  By performing the pre-annealing annealing process at such a temperature, it is possible to remove distortion inside the rotor material and to generate a pearlite structure at a relatively high rate. The higher the proportion of the pearlite structure generated in the pre-annealing annealing step, the finer the crystal grains after the refining treatment described below. That is, the step of atomizing crystal grains includes the pre-annealing step described above.

(2) Refining process (2-1) Quenching process In the refining process of this embodiment, quenching is first performed to austenite the structure of the rotor material. In this step, the rotor material is heated and maintained at a predetermined heating temperature (hereinafter referred to as quenching austenitizing temperature), and then the rotor material is rapidly cooled. Thereby, the structure | tissue of a rotor material is austenitized. The process of austenitizing the structure by this quenching is simply referred to as “quenching process” in the following description.

  In the quenching process of the present embodiment, the quenching austenitizing temperature is set to a lower temperature than the other parts for the target part of the rotor that particularly requires hydrogen cracking resistance. The quenching austenitizing temperature of other parts is set to 910-950 ° C. On the other hand, the quenching austenitizing temperature of the target part is set to 880 to 910 ° C., which is a lower temperature than other parts. By performing quenching at such an austenitizing temperature, the quenching process of the present embodiment can make crystal grains finer for the target portion of the rotor as compared with other portions. That is, the step of atomizing crystal grains includes the quenching step.

  As shown in FIG. 3, the quenching austenitizing temperature is set to 920 ° C. for the other parts, and the target part is set to 900 ° C., which is a lower temperature than the other parts. . In the quenching step, the rotor material is heated until reaching the quenching austenitizing temperature described above, and after maintaining the quenching austenitizing temperature for a predetermined holding time, by spraying water on the rotor in the form of a mist. Cool quickly. In the present embodiment, the holding time of the quenching austenitizing temperature is set to 5 hours.

  Compared to the case where the target part is not refined, the life of cracks generated by hydrogen cracking is the same, but the crack growth rate (hereinafter referred to as crack growth). (Denoted as speed). By suppressing the “crack growth rate”, the hydrogen cracking resistance of the target portion is improved.

  Even if the quenching austenitizing temperature is less than 880 ° C., it is possible to obtain the effect of refining the crystal grains, but since the carbonitride is not sufficiently dissolved, the strength required after tempering, which will be described later, Toughness cannot be obtained. In addition, the residual stress (tensile) can be relatively large. On the other hand, if the quenching austenitizing temperature exceeds 910 ° C., it becomes the same as the quenching austenitizing temperature applied to other parts, and sufficient hydrogen cracking resistance required for the target part cannot be ensured. For this reason, the quenching austenitizing temperature is set in a range of 880 to 910 ° C. for a target portion that is particularly required to improve hydrogen cracking resistance. For the same reason, it is more preferable that the quenching austenitizing temperature of the target site is set to a lower limit value of 890 ° C. and an upper limit value of 905 ° C.

  In addition, after hold | maintaining the quenching austenitization temperature mentioned above for the predetermined holding time, the rotor is rapidly cooled by the water spray which injects water, and the said hardening process is completed.

(2-2) Tempering step Tempering is performed in the tempering process of this embodiment. In this process, after performing the above-described quenching process, the rotor material is again heated to a predetermined heating temperature (hereinafter referred to as tempering temperature) set to a temperature lower than the quenching austenitizing temperature, and then cooled. To do. Thereby, the rotor material can obtain required properties such as toughness. This step of tempering is referred to as “tempering step” in the following description. The tempering step is referred to as “first stage tempering” in FIG.

  In the tempering step of the present embodiment, the tempering temperature is set to a higher temperature than the other parts for the target part of the rotor that particularly requires hydrogen cracking resistance. The tempering temperature of other parts is set to 600 to 660 ° C. On the other hand, the tempering temperature of the target part is set to 660 to 700 ° C., which is a higher temperature than other parts. By performing tempering at such a tempering temperature, the tempering step of the present embodiment can reduce the residual stress (tensile) generated after tempering of the target portion of the rotor as compared with other portions. That is, for the target part, the tempering process (2-2) is included in the process of reducing the residual stress compared to the other parts.

  As shown in “First-stage tempering” in FIG. 3, in the present embodiment, the tempering temperature of the target part is set to 670 ° C., and the tempering temperatures of the other parts are set to 630 ° C. In the tempering step, the rotor material is heated until reaching the tempering temperature described above, and the tempering temperature is maintained for a predetermined holding time, and then cooled. The holding time for the tempering temperature is set to 20 hours.

  The stress acting on the rotor material includes external stress (external force) and internal stress (residual stress). For target parts that require particularly improved hydrogen cracking resistance, the residual stress (tensile) is reduced by tempering at a temperature of 660 to 700 ° C., which is higher than that of other parts. The acting stress is reduced. Thereby, progress of the hydrogen crack in the object part of a rotor can be controlled.

  In the above-described ferritic alloy steel, the effect of reducing the residual stress (tensile) can be obtained at 660 ° C. or higher, but when it exceeds 700 ° C., the strength of the rotor decreases. For this reason, the tempering temperature is set to 660 to 700 ° C. for the target portion where the improvement of hydrogen cracking resistance is particularly required. For the same reason, it is more preferable to set the lower limit value of the tempering temperature to 665 ° C. and the upper limit value to 685 ° C. for the target part.

  In the steam turbine rotor, a high-frequency induction heating method can be used as a method of setting the tempering temperature of the target part to be higher than the tempering temperature of other parts. By heating only the target part that is particularly required to have hydrogen cracking resistance in the rotor by the high frequency induction heating method, the tempering temperature of the target part can be made higher than the tempering temperature of the other part.

[Rotor material and heat treatment conditions]
The resistance to hydrogen cracking when the steam turbine rotor manufacturing method (heat treatment method) of this embodiment is applied to various rotor materials will be described with reference to FIGS.

  FIG. 2 is an explanatory diagram for explaining an example of a steam turbine rotor material according to the present embodiment, and shows components of a rotor material (hereinafter referred to as a test material) used for evaluation. The specimens shown in FIG. 2 were three 50 kg test ingots A, B, C, D, E, F, and G that were melted and forged by a vacuum induction melting furnace (VIM).

  FIG. 3 is a diagram showing the heat treatment conditions of the manufacturing method of the present embodiment. FIG. 4 is a diagram showing the determination results of the crystal grain size (G.S.No.), residual stress (maximum tensile stress), and hydrogen cracking resistance of the specimen subjected to the heat treatment of the manufacturing method of the present embodiment. FIG. 5 is a diagram showing the heat treatment conditions of the comparative example. FIG. 6 is a diagram showing the determination results of the crystal grain size (G.S.No.), residual stress (maximum tensile stress), and hydrogen cracking resistance of the test material subjected to the heat treatment of the comparative example.

  The crystal grain size (G.S.No.) was determined by comparing the prior austenite grain size defined by JIS with the grain size standard diagram. G.S.No. represents that the crystal grain size decreases as the numerical value increases.

  The residual stress (maximum tensile stress) was determined using the following formula (1) and the X-ray stress measurement method.

nλ = 2dsinθ (1)
In equation (1),
n: diffraction order λ: wavelength of X-ray d: crystal lattice spacing of material θ: diffraction angle.

  According to Bragg's law in X-ray diffraction shown in Equation (1), if θ (diffraction angle) is known, d (crystal lattice spacing of the material) can be obtained, strain is obtained from the difference from the standard crystal lattice spacing, and Young's Residual stress can be calculated from the rate and Poisson's ratio.

  Hydrogen cracking resistance is the pressure of hydrogen gas generated by molecularization of hydrogen generated by corrosion of materials entering and diffusing into the material and gathering at the interface between non-metallic inclusions and the matrix (main metal, base material). Resistance to cracking caused by

  The hydrogen cracking test was performed according to NACE standards (TM0284, Evaluation of Pipeline and Pressure Vessel Steels for Resistance to Hydrogen-Induced Cracking). After dipping in a 5% NaCl + 0.5% acetic acid solution at pH 4 at a test temperature of 24 ± 2.8 ° C. for 96 hours, the cross section was cut and evaluated to confirm the presence or absence of cracks. The test piece size is 50 mm x 30 mm x 10 mm. Three test pieces were used for each specimen, and "Hydrogen cracking resistance: ◯" only when no cracks were observed in any of the test pieces. Was "hydrogen cracking resistance: x".

  When the pre-annealing, quenching, and tempering (first stage tempering and second stage tempering) are performed within the range of the heat treatment conditions of this embodiment as in the example shown in FIGS. 3 and 4, at least hydrogen cracking resistance For all the target parts that require the above, the hydrogen cracking resistance was “◯”.

  However, as in the comparative example shown in FIGS. 5 and 6, any of the conditions before annealing, quenching, and tempering (first stage tempering and second stage tempering) is the heat treatment condition of this embodiment. When it implemented without satisfy | filling the range, all the target site | parts which require hydrogen cracking resistance were "x".

  That is, it has been clarified that the method for manufacturing a rotor for a steam turbine according to the present embodiment provides good hydrogen cracking resistance at a target site that particularly requires hydrogen cracking resistance.

  As described above, the method for manufacturing a rotor for a steam turbine according to the present embodiment includes the step (2-2) of reducing the residual stress in the target portion of the rotor as compared with other portions. did. As for the target portion of the rotor, the residual stress generated after tempering is reduced as compared with other portions, so that the progress of hydrogen cracking can be suppressed and the hydrogen cracking resistance can be improved.

In the present embodiment, the step of reducing the residual stress includes a tempering step (2-2) that is a step of tempering the rotor after quenching the rotor. In the tempering step, as shown by configuration examples 4, 5, 7-9, 12, 13, 15, 16, 18, 19, 21, 23, 25, 27-31, 34-40, 42 in FIG. About the object site | part of the rotor for steam turbines, the tempering temperature (1st stage tempering) which is the heating temperature is set to high temperature compared with another site | part. By setting the tempering temperature in this way, the residual stress can be reduced for the target part compared to other parts.
In the present specification, the “configuration example” (see FIG. 3) is not an embodiment of the invention according to the claims of the present application. Of the structural examples 1 to 42, examples of the invention according to claim 1 of the present application are 19 to 21, 26 to 31, 34 to 37, 42. Other examples 1 to 18, 22 to 25, 32, 33, and 38 to 41 are examples that are useful for understanding the effects of residual stress reduction and crystal grain refinement.

  In the present embodiment, the target portion of the steam turbine rotor is heated to a tempering temperature set higher than other portions by heating by a high frequency induction heating method. By the high frequency induction heating method, it is possible to increase the tempering temperature of only the target portion that is particularly required to have resistance to hydrogen cracking in the rotor as compared with other portions.

  Moreover, in this embodiment, about the object site | part, it shall have further the process (2-1) which refines | miniaturizes a crystal grain compared with another site | part. By making the crystal grains finer for the target portion, it is possible to improve the strength and toughness and to make the progress of hydrogen cracking slower.

  In the present embodiment, the step of “refining crystal grains” includes a quenching step (2-1) that is a step of quenching the rotor before the tempering step (2-2). In the quenching step (2-1), as shown by configuration examples 2, 3, 19-21, 26-37, 41, 42 in FIG. 3, for the target portion, the austenitizing temperature, which is the heating temperature, It was assumed that the temperature was set lower than that of other parts. By setting the austenitizing temperature in this manner, the crystal grains can be made finer in the target part than in other parts.

  In this embodiment, the steam turbine rotor is composed of 0.15 to 0.33% carbon and silicon as shown by test materials A, B, C, D, E, F, and G in FIG. 0.03-0.20%, manganese 0.5-2.0%, nickel 0.1-1.3%, chromium 0.9-3.5%, molybdenum 0.1-1. 5%, 0.15 to 0.35% vanadium, 0.005 to 0.015% nitrogen, 1.0% or less tungsten as an optional component, and composed of ferritic alloy steel containing by mass%. It was supposed to be. By constructing a rotor with such ferritic alloy steel, hydrogen cracking is unlikely to occur even when exposed to highly corrosive gases such as hydrogen sulfide, and even if hydrogen cracking occurs, the crack progresses. It is possible to realize a rotor that is difficult to perform.

  Further, as shown in FIG. 3 as configuration examples 4, 5, 7 to 9, 12, 13, 15, 16, 18, 19, 21, 23, 25, 27 to 31, 34 to 40, 42, for steam turbines For the target portion of the rotor, the heating temperature in the tempering step, that is, the tempering temperature was set to 660 to 700 ° C. In the ferritic alloy steel described above, the effect of reducing the residual stress can be obtained if the tempering temperature is 660 ° C. or higher. However, when the tempering temperature exceeds 700 ° C., the strength of the rotor decreases. For this reason, with respect to the target portion where improvement in hydrogen cracking resistance is particularly required, by setting the tempering temperature to 660 to 700 ° C., it is possible to reduce the residual stress while suppressing a decrease in strength. .

  In the tempering step (2-2) of the above-described embodiment, the tempering temperature of the target part is set to 670 ° C., and the other parts are set to 630 ° C., but according to the present invention. The tempering temperature is not limited to this. For example, as shown in the figure, the target part can be set to 630 ° C., which is the same tempering temperature as the other parts.

  Moreover, as shown by structural examples 2, 3, 19 to 21, 26 to 37, 41, and 42 in FIG. 3, in the quenching step (2-1), the austenitizing temperature is 880 to 910 ° C. for the target portion. It was assumed that it was set to. If the austenitizing temperature is less than 880 ° C., the carbonitride is not sufficiently dissolved, so that necessary strength and toughness cannot be obtained after tempering, which will be described later, and the residual stress may become relatively large. On the other hand, if the quenching austenitizing temperature exceeds 910 ° C., it is difficult to ensure sufficient hydrogen cracking resistance required for the target part. For this reason, for target parts that need to improve the hydrogen cracking resistance, the quenching austenitizing temperature is set to 880 to 910 ° C., while ensuring the necessary strength and toughness, and finer crystal grains. It can be made.

  Further, in the present embodiment, the above-described “refining crystal grains” step includes a pre-annealing annealing step (1) that is a step of annealing before the quenching step (2-1), In the pre-annealing step (1), the pre-annealing annealing temperature, which is the heating temperature, is set to 1050 to 1300 ° C. By performing the pre-tempering step at such a temperature, a pearlite structure can be generated at a relatively high rate. By performing the quenching step (2-1) described above on the rotor material having a high percentage of the pearlite structure, the crystal grains can be further refined.

  In the refining process of the present embodiment described above, tempering is performed only once. However, the aspect of the refining process according to the present invention is not limited to this. For example, it is also preferable to perform the tempering process twice in the tempering process, and an example of another tempering process will be described below.

[Second Embodiment]
The tempering process of this embodiment will be described. In the present embodiment, the entire steam turbine rotor is tempered in two stages. In addition, the quenching austenitizing temperature in the quenching process of the tempering treatment is different from that of the first embodiment, and the details will be described below. Note that a description of a configuration substantially common to the first embodiment is omitted.

(2-1B) Quenching Step In the quenching step of the present embodiment, the quenching austenitizing temperature is the same temperature in the target portion where hydrogen cracking resistance is particularly required in the steam turbine rotor and in other portions. Is set. That is, the entire rotor including the target part and other parts is quenched at a uniform quenching austenitizing temperature. The quenching austenitizing temperature is set to 910-950 ° C. Note that, as in the first embodiment, the quenching austenitizing temperature may be set to a lower temperature than the other parts for the target part.

(2-2B) Two-stage tempering step In the tempering process of this embodiment, two-stage tempering is performed. That is, the tempering step of the tempering treatment of the present embodiment includes a first tempering step (2-2B1) and a second tempering step (2-2B2). In the following description, the tempering temperature in the first stage tempering process is referred to as “first stage tempering temperature”, and the tempering temperature in the second stage tempering process is referred to as “second stage tempering temperature”.

(2-2B1) First-stage tempering process In the first-stage tempering process, the first-stage tempering temperature, which is the heating temperature of both the target part and other parts of the steam turbine rotor, is , 600 to 700 ° C. In addition, the 1st step tempering temperature of an object site | part and the 1st step tempering temperature of another site | part can be set to the same temperature. Hereinafter, a description will be given with reference to FIGS. 3 and 5.

  As shown in each figure, the first stage tempering temperature is set to 670 ° C. for the target part and 630 ° C. for the other parts. In the first stage tempering step, the rotor material is heated until it reaches the first stage tempering temperature, the first stage tempering temperature is maintained for a predetermined holding time, and then cooled. The holding time for the first stage tempering temperature is set to 20 hours.

  Note that the first stage tempering temperature of the target part may be set to 630 ° C., which is the same as other parts, as shown in each drawing. Moreover, about an object site | part, it is good also as what heats only the surface layer so that it may be 670 degreeC which is 1st step tempering temperature.

  In the first stage tempering process, the first stage tempering temperature is set to 670 ° C. at the highest point for the target part, and the first stage tempering temperature decreases from the target part toward the other parts. It is also preferable to perform so-called gradient heating. In the first-stage tempering step, the first-stage tempering temperature of other parts is set to 630 ° C. By performing the inclined heating, it is not necessary to perform heat treatment or the like for increasing the strength of the “predetermined position” of the rotor. After performing the first-stage tempering step (2-2B1) described above, the second-stage tempering step (2-2B2) is performed.

(2-2B2) Second-stage tempering step In the second-stage tempering step, the second-stage tempering temperature, which is the heating temperature of both the target part and other parts of the steam turbine rotor, is , 600 to 700 ° C. In the second stage tempering step, the rotor material is heated until it reaches the second stage tempering temperature, and the second stage tempering temperature is maintained for a predetermined holding time, and then cooled. The holding time of the second stage tempering temperature is set to 20 hours. In addition, the 2nd step tempering temperature of an object site | part and the 2nd step tempering temperature of another site | part can be set to the same temperature. For example, as shown in FIG. 3, the second stage tempering temperature can be set to 630 ° C.

  It is also preferable to set the second stage tempering temperature of the target part to a higher temperature than the second stage tempering temperature of other parts. For example, as shown in the figure, for the target part, the second stage tempering temperature is set to 670 ° C. at the highest point and heated so that the second stage tempering temperature decreases from the target part toward the other part. It is also preferable to perform gradient heating.

  When performing gradient heating in the second stage tempering step, the target part is heated to the second stage tempering temperature in the furnace. At this time, the other parts do not require second-stage tempering, and thus are left out of the furnace. Thereby, the gradient heating which heats so that a 2nd step tempering temperature may become low as it goes to another part from an object part by this is realized.

  As shown by configuration examples 6-8, 10-27, 32-37, 39-42 in FIG. 3, in this embodiment, the tempering step (2-2B) is the first stage set at 600-700 ° C. The first tempering step (2-2B1), which is a tempering step by heating to the tempering temperature, and the first tempering step (2-2B1), and is set to 600 to 700 ° C. And a second tempering step (2-2B2), which is a step of tempering by heating to the second tempering temperature.

  In the quenching step (2-1B), most of the rotor material has a quenched bainite structure. However, when the retained austenite structure remains, in the next tempering stage, not all of the rotor material becomes a tempered bainite structure, but partly quenched. A bainite structure remains. For this reason, the rotor material has a mixed structure of a tempered bainite structure with a balance between strength and toughness and a quenched bainite structure with high strength and low toughness. Strain is accumulated between the two structures, resulting in residual stress. To increase.

  Therefore, the residual stress can be reduced by performing two-step tempering treatments (2-2B1) and (2-2B2) to completely change the quenched bainite structure to the tempered bainite structure. This effect is obtained when the first stage tempering temperature and the second stage tempering temperature exceed 600 ° C., but when the temperature exceeds 700 ° C., the strength required for the rotor material is not satisfied. For this reason, especially in the target part where it is necessary to improve the hydrogen cracking resistance, both the first stage tempering temperature and the second stage tempering temperature are limited to the range of 600 to 700 ° C., and two-stage tempering is performed. Thus, the residual stress can be reduced. Thereby, generation | occurrence | production of the hydrogen crack in the object site | part of a rotor and progress of a hydrogen crack can be suppressed.

  Moreover, as shown in structural examples 4, 5, 7-9, 12-31, 34-40, and 42 in FIG. 3, at least one of the first-stage tempering temperature and the second-stage tempering temperature for the target part. The temperature is set to be higher than that of other parts, and the temperature is set to 660 to 700 ° C. In the ferritic alloy steel, the effect of reducing the residual stress can be obtained at a tempering temperature of 660 ° C. or higher. On the other hand, when the tempering temperature exceeds 700 ° C., the strength of the rotor decreases. For this reason, in the target part where the improvement of hydrogen cracking resistance is particularly required, in at least one of the first stage tempering process (2-2B1) and the second stage tempering process (2-2B2). By setting the tempering temperature to 660 to 700 ° C., it is possible to reduce the residual stress while suppressing a decrease in strength.

  Moreover, as shown in structural examples 13 to 27 in FIG. 3, in at least one of the first stage tempering process (2-2B1) and the second stage tempering process (2-2B2), Inclined heating was performed so that the tempering temperature was lowered toward the part. There is no need to perform heat treatment or the like for increasing the strength of the “predetermined position” of the rotor.

  In addition, as shown by configuration examples 22 to 27 in FIG. 3, in the second-stage tempering step described above, when performing gradient heating, the target part is heated to the second-stage tempering temperature in the furnace, About the site | part, tempering shall be performed in the state put out of the furnace. In the second tempering step, tempering is not required for “other parts” other than the target part. For this reason, “other parts” can be cooled in a state of being taken out of the furnace.

  As shown by configuration examples 6, 10, 11, 32, 33, and 41 in FIG. 3, the target part and other parts are set to the same first stage tempering temperature, and the first stage tempering is performed. The temperature is set to 600 to 660 ° C., the target part and the other part are set to the same second stage tempering temperature, and the second stage tempering temperature is set to 600 to 660 ° C. It can also be assumed. Also in this method, as shown in FIG. 4, it is possible to ensure the hydrogen cracking resistance of the target part.

[Other Embodiments]
In the quenching step of each of the embodiments described above, the quenching austenitizing temperature is assumed to be a lower temperature than other parts for the target part where hydrogen cracking resistance is particularly required. The quenching austenitizing temperature according to the invention is not limited to this. For example, as shown in the figure, the same quenching austenitizing temperature may be set in the target portion and other portions.

  Further, in the present embodiment, the target portion for particularly improving the hydrogen cracking resistance is a paragraph portion of the rotor including the blade implantation portions 20a, 21a, 22a, and 23a on the upstream side of the steam turbine 1, as shown in FIG. Although it was set as 20, 21, 22, and 23, the object site | part which concerns on this invention is not limited to this aspect. Any part of the rotor can be used as the target part as long as the corrosive components in the vapor are easily deposited and the hydrogen cracking resistance needs to be improved.

  Although several embodiments of the present invention have been described, these embodiments have been 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 spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Steam turbine 3 Stator blade 5 Casing 10 Rotor 12 Rotor blade 20, 21, 22, 23 Paragraph part (target part) of rotor
20a, 21a, 22a, 23a Blade implantation part

Claims (8)

A method of manufacturing a rotor constituting a steam turbine,
The predetermined target part of the rotor is a step of reducing the residual stress compared to other parts, and the tempering temperature that is the heating temperature of the target part is higher than that of the other parts. A tempering step that is a step of setting the rotor to tempering the rotor at least once;
For the target part, compared to other parts, the step of making the crystal grains finer,
Have
The step of refining the crystal grains is as follows:
A quenching step, which is performed before the tempering step, is a step of quenching the rotor by setting the quenching austenitizing temperature, which is the heating temperature thereof, to a lower temperature than other portions, for the target portion. ,
A pre-annealing annealing step that is performed before the quenching step and is a step of performing the rotor annealing by setting the pre-annealing annealing temperature that is the heating temperature to 1050 to 1300 ° C .;
Including
The rotor has 0.15-0.33% carbon, 0.03-0.20% silicon, 0.5-2.0% manganese, 0.1-1.3% nickel, 0.1% chromium 0.9 to 3.5%, molybdenum is 0.1 to 1.5%, vanadium is 0.15 to 0.35%, tungsten is contained as an optional component in 1.0% or less and mass%, The method for manufacturing a rotor for a steam turbine , wherein the balance is made of iron and ferritic alloy steel which is an inevitable impurity . The method of manufacturing a rotor for a steam turbine according to claim 1 , wherein the tempering temperature is set to 660 to 700C for the target portion . The method for manufacturing a rotor for a steam turbine according to claim 1 , wherein a quenching austenitizing temperature of the target part is set to 880 to 910C . The tempering step includes
A first stage tempering step which is a step of heating and tempering to a first stage tempering temperature set to 600 to 700 ° C;
A second tempering step which is performed after the first tempering step and is tempered by heating to a second tempering temperature set to 600 to 700 ° C .;
The method for manufacturing a rotor for a steam turbine according to claim 1 , comprising : For the target part, at least one of the first stage tempering temperature and the second stage tempering temperature is set to a higher temperature than the other parts, and the temperature is set to 660 to 700 ° C. The method for manufacturing a rotor for a steam turbine according to claim 4 , wherein the rotor is used. In at least one of the first-stage tempering process and the second-stage tempering process, gradient heating is performed in which heating is performed such that the tempering temperature decreases from the target part toward the other part. The manufacturing method of the rotor for steam turbines of Claim 5 . When gradient heating is performed in the second stage tempering step, the target part is heated to the second stage tempering temperature in the furnace, and the other parts are tempered in the state of being out of the furnace <br / The method for manufacturing a rotor for a steam turbine according to claim 6 . The steam turbine according to any one of claims 1 to 7, wherein the steam turbine is used for geothermal power generation, and the rotor is exposed to steam containing a corrosive gas . The manufacturing method of the rotor for steam turbines as described in 1 item | term .

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