JP6244179B2 - Heat treatment method for turbine rotor - Google Patents

Description

The present invention relates to a heat treatment how the turbine rotor, to a heat treatment method to improve SCC (Stress Corrosion Cracking) resistance of the low-pressure turbine rotor material for use particularly in power generation facilities.

  In thermal power plants and nuclear power plants, energy is given to fluid by burning fuel, and water is vaporized along with this, and the generated steam energy is converted into rotational motion of the turbine rotor via turbine blades. Electricity is generated by rotating a generator connected to the rotor. After passing through the turbine, the steam is guided to the condenser, and returned to the water by being cooled by the condenser.

  Generally, a steam turbine is designed with a plurality of configurations of a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine depending on steam conditions and the like. In particular, in a nuclear power plant, a low-pressure turbine is often composed of a plurality of shafts, such as being used with three low-pressure turbines with respect to one shaft of a high-pressure turbine. Each turbine has several stages in the axial direction in which a plurality of turbine blades are planted in the circumferential direction according to steam conditions. On the low-pressure turbine inlet side, the length of the turbine blade is small because the energy of the steam is large, and the length of the turbine blade is large because the energy of the steam is small as it approaches the steam outlet. The steam led to the low-pressure turbine gradually decreases in pressure and temperature each time the steam passes through each stage, and the steam property changes to moist steam. Stress corrosion cracking (hereinafter referred to as “SCC”) may occur in a low-pressure turbine stage in such a wet steam environment. In particular, a large stress acts on the attachment portion between the turbine blade and the turbine rotor in a humid steam environment, and it is considered that SCC is likely to occur because the impurities are likely to be concentrated.

  In general, SCC is known to occur when three factors of stress, usage environment (temperature, wetness, type of fluid with which the turbine contacts, etc.) and material are superimposed. Therefore, it is estimated that the occurrence of SCC can be suppressed by improving any one or more factors. Low alloy steels such as 3.5NiCrMoV steel and 2.5NiCrMoV steel are used for the turbine rotor. In low-pressure turbines, improving the SCC property from the viewpoint of the material that is one of the causes of SCC generation, This is thought to be useful for improving turbine reliability.

  Conventionally, the following methods have been proposed as a method for improving the SCC property from the viewpoint of materials.

  In Patent Document 1, only the final stage portion where high strength is required is individually heat-treated, and tempering is performed at a lower temperature than other parts to increase the strength, while the final stage where SCC resistance is required. A method for manufacturing a rotor shaft is disclosed in which SCC is prevented from occurring by lowering the strength of parts other than the part, and high reliability is ensured.

  Patent Documents 2 and 3 disclose a surface treatment method for coating the surface of a material constituting the turbine as a method for improving the SCC resistance of the turbine rotor. Patent Document 2 coats platinum (Pt) -based elements as a catalyst layer to form a catalytic site on the surface to reduce oxygen in the environment and make the corrosion potential of the alloy less than the corrosion potential that minimizes SCC. Is. In Patent Document 3, the surface of the turbine rotor constituent member is shielded from the environment where SCC occurs by applying gold plating to the surface of the turbine rotor constituent member.

Non-Patent Document 1 discloses a technique for improving the SCC resistance of a turbine rotor material by setting an upper limit value for the yield stress of the turbine rotor material. Non-Patent Document 1 reports that, as a result of the SCC susceptibility test, a tendency for the SCC susceptibility to increase as the yield stress of the turbine rotor material increases was observed. As a cause of this, a carbide mainly composed of Fe is precipitated in the metal grain boundary, and this kind of carbide tends to increase as the yield stress increases. Therefore, Fe _{2 having} low SCC resistance is observed. It is presumed that the SCC cracks are likely to propagate due to the precipitation of this kind of carbide that produces only an O ₃ film. Based on the results of this study, it has been reported that the yield stress at which carbides mainly composed of Fe are not recognized at the grain boundaries of the material is a target value for improving the SCC resistance of the turbine rotor material.

JP 2002-349206 A JP 2005-9491 JP 2013-15123 A

Satoshi Ito, “Strength Dependence of Intergranular Stress Corrosion Cracking Susceptibility of 3.5% NiCrMoV Steel in 403K Water”, Materials (J. Soc. Mat. Sci., Japan), May 2002, Vol. 51, no. 5, p. 549-554

  The above Patent Documents 1 to 3 all focus on improving the SCC resistance of the turbine rotor. However, Patent Document 1 requires a plurality of heat treatments, and Patent Document 2 and Patent Document 3 have a plating treatment. Since the process of carrying out the process occurs, there is a concern about an increase in manufacturing cost and manufacturing time.

  In thermal power plants and nuclear power plants, the power generation output can be improved by lengthening the turbine blades. On the other hand, the stress that the turbine rotor receives from the turbine blades increases accordingly. Further, since the length of the turbine blade increases as it approaches the steam outlet, the stress generated at the attachment portion of the turbine rotor to the turbine blade is larger on the steam outlet side. As countermeasures against the increase in stress, it is conceivable to use a higher-strength material or increase the size of the turbine rotor. Since it is necessary to set an upper limit value for the strength of the material used for the rotor, it is necessary to take measures to reduce the stress received by the turbine rotor by enlarging the groove of the turbine rotor. In this case, depending on the set upper limit value, it is necessary to enlarge the axial length and outer diameter of the turbine rotor, and further increase the size of the cabin in which the turbine is mounted. There is concern about the increase.

  Accordingly, in view of the above circumstances, the present invention is a heat treatment of a turbine rotor capable of providing a turbine rotor having excellent SCC resistance without reducing the size, manufacturing cost, and manufacturing time of equipment and reducing the strength. It is to provide a method.

In one aspect of the present invention, in order to achieve the above object, in a heat treatment method for a turbine rotor that is a component of a low-pressure turbine used in a thermal power plant or a nuclear power plant,
The heat treatment method includes a quenching process,
The holding time at the quenching treatment temperature in the quenching treatment step is the temperature of the environment in which the turbine rotor is used is over 20 ° C. and 250 ° C. or less, regardless of the dimensions of the turbine rotor and the strength of the turbine rotor material. Provided is a turbine rotor heat treatment method characterized in that when it is over 0% and 18% or less, it is 85 hours or longer.

According to the present invention, provides limiting enlargement and manufacturing costs and manufacturing time of the equipment, without decreasing the strength, the heat treatment how the turbine rotor capable of providing a turbine rotor having excellent SCC resistance can do.

It is a cross-sectional schematic diagram which shows an example of a part of low pressure turbine which can apply the heat processing method of the turbine rotor which concerns on this invention. It is a schematic diagram which shows an example of the temperature profile of the tempering heat treatment process (quenching / tempering process) of a turbine rotor material. It is a graph which shows the relationship between the holding time in the quenching process temperature of the turbine rotor material of Example 1, and the presence or absence of SCC generation | occurrence | production. It is a graph which shows the relationship between the holding time in the quenching process temperature of the turbine rotor material of Example 2, and the presence or absence of SCC generation | occurrence | production.

The turbine rotor heat treatment method and the turbine rotor according to the present invention can optionally include the following aspects.
( I ) The turbine rotor is made of 3.5NiCrMoV steel or 2.5NiCrMoV steel.
( Ii ) The low pressure turbine is a low pressure turbine of a thermal power plant or a nuclear power plant used in a 60 Hz region.
( Iii ) The low-pressure turbine is newly manufactured for application to a newly constructed plant.
( Iv ) The low-pressure turbine is newly manufactured for replacement of a turbine used in an existing plant.

  Hereinafter, embodiments according to the present invention will be described more specifically. However, the present invention is not limited to the embodiment taken up here, and can be appropriately combined and improved without departing from the scope of the invention.

As described above, the heat treatment method of a turbine rotor according to the invention comprises a quenching process step, the retention time at the quenching treatment temperature in the hardening treatment process, irrespective of the strength of the dimensions of the turbine rotor and the turbine rotor materials, the When the temperature of the environment in which the turbine rotor is used is more than 20 ° C. and 250 ° C. or less and the wetness is more than 0% and 18% or less, it is characterized in that it is 85 hours or more.

FIG. 2 is a schematic diagram showing an example of a temperature profile of a tempering heat treatment process (quenching / tempering process) of the turbine rotor material. As shown in FIG. 2, the turbine rotor material, which is a forged steel product mainly composed of iron (Fe), is subjected to a tempering heat treatment for the purpose of adjusting its mechanical properties (strength, hardness, toughness, etc.) Quenching / tempering heat treatment) is performed. Specifically, the tempering heat treatment is performed by (1) raising the temperature of the turbine rotor material to the quenching treatment temperature (900 ° C. in FIG. 2), holding it for a certain time (holding time T _{1 in} FIG. 2), and then performing rapid cooling. After the quenching treatment step for increasing the strength of the steel and the quenching treatment steps (2) and (1), the turbine rotor material is heated to the tempering treatment temperature (600 ° C. in FIG. 2), and is kept for a certain time (FIG. 2). in after holding time T ₂₎ holding, and a tempering step of high toughness of the steel by performing slow cooling.

The present invention, in the manufacturing process of the turbine rotor material is obtained by focusing on the retention time T ₁ of the at quenching temperature shown in FIG. The inventors of the present invention have made extensive studies on the relationship between the heat treatment process conditions of the turbine rotor and the presence or absence of SCC generation in the turbine rotor. As a result, the holding time at the quenching treatment temperature is set to be higher than 20 ° C. and 250 ° C. or lower in the environment in which the turbine rotor is used regardless of the size of the turbine rotor and the strength of the turbine rotor material , and the wetness is 0%. It has been found that the SCC generation of the turbine rotor can be suppressed by setting it to 85 hours or more when the content is 18% or less . The present invention is based on this finding.

  Holding at the quenching treatment temperature (specific temperature) during the quenching process has the purpose of making the material structure a predetermined structure (austenite) and solidifying the elements in the material. By increasing the length, it is considered that austenitization and solid solution of elements are further promoted, and thus the SCC resistance of the material is improved. Therefore, the SCC resistance can be improved regardless of the strength of the material by setting the holding time at the time of quenching sufficiently long (30 hours or more) corresponding to the use environment (temperature, wetness). it is conceivable that. Specifically, the higher the temperature of the environment in which the turbine rotor is used, the higher the wetness, the longer the holding time during the quenching process, thereby improving the SCC resistance while maintaining the strength of the material. Can do.

  In the prior art, as in Non-Patent Document 1 described above, the conditions of the tempering process are optimized in order to balance the SCC resistance and strength of the turbine rotor material. Since the present invention does not change the conditions of the tempering process that directly affects the strength of the turbine rotor material, the SCC resistance can be improved with minimal influence (decrease) on the strength. Therefore, as in Non-Patent Document 1 described above, it is necessary to increase the size (dimensions) of the turbine rotor or the like in order to set an upper limit value for the strength of the material and reduce the stress applied to the turbine rotor or the like. There is no. As a result, it is possible to manufacture a high-output turbine rotor having excellent SCC resistance while keeping the strength equal to or higher than that of the conventional one by suppressing the increase in size of the facility, the manufacturing cost, and the manufacturing time.

  The quenching treatment temperature is not particularly limited, but it is preferable to apply general tempering heat treatment conditions for the turbine rotor material. Specifically, it is preferably 800 ° C. or higher and 900 ° C. or lower.

The retention time at the quenching temperature, regardless of the intensity of the size of the turbine rotor and the turbine rotor material, the temperature of the environment is 20 ° C. than the use of data Binrota, at 250 ° C. or less, wetness 0 percent, 18 percent If it is less than 85 hours . The retention time in the quenching process temperature by setting like this, it is possible to prevent the occurrence of SCC of the turbine rotor under the environment.

  Even if the holding time at the quenching temperature is increased, there is no significant difference in the strength of the material. Therefore, this invention can provide the turbine rotor which has the outstanding SCC resistance, without reducing the intensity | strength of material.

  In addition, about the holding time in the tempering process temperature in a tempering process, the tendency like the holding time in the quenching process temperature is not seen. That is, the occurrence of SCC cannot be suppressed only by lengthening the holding time at the tempering temperature.

  Moreover, the general conditions at the time of manufacturing a turbine rotor can be used for the conditions of “rapid cooling” in the quenching process and “slow cooling” in the tempering process. The main point of the present invention is the holding time at the quenching treatment temperature, and the heat treatment conditions other than that are not limited. Therefore, detailed description thereof is omitted here.

  FIG. 1 is a schematic view showing an example of a part of a low-pressure turbine to which a heat treatment method for a turbine rotor according to the present invention can be applied. As shown in FIG. 1, a turbine rotor 1 to which the present invention is applied has a configuration in which a number of stages in which turbine blades 2 are planted in the circumferential direction are configured in several stages in the axial direction. The material of the turbine rotor is not particularly limited, but is preferably made of 3.5NiCrMoV steel or 2.5NiCrMoV steel. The turbine is preferably a low-pressure turbine used in a thermal power plant or a nuclear power plant. The present invention can be applied to any turbine of high pressure, medium pressure, or low pressure, but is particularly suitable for a low pressure turbine having high wetness in a use environment.

In general, the holding time at the quenching temperature is often set according to the dimensions of the parts. The size of the turbine rotor is basically set according to the output of the plant, but in addition to this, it is also affected by the frequency band of the applied region. Specifically, since the generated stress differs depending on the rotational speed between the one used in the 50 Hz region and the one used in the 60 Hz region, the one used in the 50 Hz region is more than the one used in the 60 Hz region. The size tends to increase. Accordingly, when the conventional heat treatment methods are used, the turbine rotor used in the 60 Hz region inevitably tends to have a shorter holding time for the quenching treatment temperature than that used in the 50 Hz region. In the present invention, the holding time at the quenching treatment temperature is set to 30 hours or more regardless of the material and strength of the turbine rotor. For this reason, conventionally, it was not considered to heat-treat the turbine rotor used in the 60 Hz region for 85 hours or more. However, in the present invention, the temperature of the environment in which the turbine rotor is used exceeds 20 ° C. and 250 ° C. or less. In the case where the wetness is over 0% and 18% or less, the turbine rotor used in the 60 Hz region is subjected to heat treatment for 85 hours or more.

  Further, the turbine rotor heat treatment method according to the present invention is applicable to a newly manufactured plant for application to a newly constructed plant, and is used for replacement of a turbine used in an existing plant. It can also be applied to newly manufactured products.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.

( Reference Example 1)
Holding time and SCC at the quenching treatment temperature in use environment condition 1 (temperature of 50 ° C. or more and 150 ° C. or less and wetness of more than 0%, 12% or less) which is a use environment outside the scope of the present invention of the turbine rotor The presence or absence of occurrence was investigated. 3.5NiCrMoV steel was used for the turbine rotor material, and the size was the same as the actual machine used in the power plant. The presence or absence of SCC in each turbine rotor material was evaluated by performing a nondestructive test. Further, the strength of the turbine rotor material was evaluated by performing a tensile test.

  FIG. 3 is a graph showing the relationship between the holding time at the quenching temperature of the turbine rotor material in this embodiment and the presence or absence of occurrence of SCC. As shown in FIG. 3, in the use environment condition 1, SCC may occur when the holding time at the quenching treatment temperature is less than 30 hours. However, by setting the holding time to 30 hours or more, the SCC It has been found that the occurrence of can be suppressed. In addition, from the evaluation results of the tensile test, it was confirmed that the strength of each turbine rotor material was approximately the same.

(Example 1 )
Holding time and SCC generation at the quenching treatment temperature in use environment condition 2 (temperature of over 20 ° C., 250 ° C. or less, wetness of over 0%, 18% or less) which is the use environment of the scope of the present invention of the turbine rotor The presence or absence of was investigated. 3.5NiCrMoV steel was used for the turbine rotor material, and the size was the same as the actual machine used in the power plant. The presence or absence of SCC in each turbine rotor material was evaluated by performing a nondestructive test. Further, the strength of the turbine rotor material was evaluated by performing a tensile test.

FIG. 4 is a graph showing the relationship between the holding time at the quenching temperature of the turbine rotor material in this embodiment and the presence or absence of occurrence of SCC. As shown in FIG. 4, it was found that the use environment condition 2 can suppress the occurrence of SCC by setting the holding time at the quenching treatment temperature to 85 hours or longer. In addition, from the evaluation results of the tensile test, it was confirmed that the strength of each turbine rotor material was approximately the same.

  As described above, according to the present invention, it is possible to provide a turbine rotor having excellent SCC resistance without reducing the size, manufacturing cost, and manufacturing time of the equipment, and reducing the strength. It has been shown that a heat treatment method can be provided.

  The above-described embodiments and examples have been described for the purpose of facilitating understanding of the present invention, and the present invention is not limited to the specific configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. That is, according to the present invention, a part of the configurations of the embodiments and examples of the present specification can be deleted, replaced with other configurations, and added with other configurations.

DESCRIPTION OF SYMBOLS 1 ... Turbine rotor, 2 ... Turbine blade, 3 ... Turbine rotor central axis.

Claims (5)

In a heat treatment method for a turbine rotor that is a component of a low-pressure turbine used in a thermal power plant or a nuclear power plant,
The heat treatment method includes a quenching process ,
The holding time at the quenching treatment temperature in the quenching treatment step is such that the temperature of the environment in which the turbine rotor is used is more than 20 ° C. and 250 ° C. or less, regardless of the dimensions of the turbine rotor or the strength of the turbine rotor material. greater than 0%, when 18% or less, a heat treatment method features and to filter Binrota to be at least 85 hours. The turbine rotor, the heat treatment method of the turbine rotor of claim 1 Symbol mounting characterized by comprising the 3.5NiCrMoV steel or 2.5NiCrMoV steel. The heat treatment method for a turbine rotor according to claim 1 or 2 , wherein the low-pressure turbine is a low-pressure turbine of a thermal power plant or a nuclear power plant used in a 60 Hz region. The turbine rotor heat treatment method according to any one of claims 1 to 3 , wherein the low-pressure turbine is newly manufactured for application to a newly constructed plant. The low-pressure turbine, a heat treatment method of the turbine rotor according to any one of claims 1 to 4, characterized in that is manufactured in the new for the replacement of the turbine used in existing plants .

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