JP3776549B2 - Low cycle corrosion fatigue resistant steam turbine rotor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steam turbine rotor made of a low alloy steel excellent in low cycle corrosion fatigue resistance.
[0002]
[Prior art]
Steam turbine rotors are typically manufactured from low alloy steels such as 3.5NiCrMoV steel and used with a machined finish without any surface treatment such as coating.
Further, in the screw type pump, electroless nickel plating with a thickness of 50 μm or less is applied to the rotor surface for the purpose of imparting corrosion resistance and wear resistance (Japanese Patent Laid-Open Nos. 2-108888 and 3-290086). Gazette).
Wet steam which is a working fluid of a steam turbine is generally corrosive. When a low-alloy turbine rotor is used for a long time in such a corrosive environment, the blade mounting groove, pressure balance hole, etc. may become high due to repeated loads resulting from changes in centrifugal force due to turbine start / stop and turbine blade vibration. In the part which receives repeated stress, corrosion fatigue (low cycle corrosion fatigue) occurs, and the malfunction that the soundness of the turbine rotor is impaired occurs.
[0003]
When coating a steam turbine rotor for the purpose of providing corrosion resistance and wear resistance, the coating of the steam turbine rotor should withstand long-term use for several decades, and the processing tolerance of the steam turbine is an accuracy of the order of 1/100 mm. The accuracy of the coating thickness must be on the order of 1/1000 mm, satisfying strict requirements such as being able to withstand repeated high stresses in a corrosive environment, and having a significant impact on cost. Thus, no suitable coating method has been found. That is, the parts to which the conventional corrosion resistance and abrasion resistance coating is applied are containers, shafts, and the like, to which no large stress acts, and in this case, the function is sufficiently exhibited if the coating layer is in close contact. However, since the steam turbine rotor targeted by the present invention is repeatedly subjected to large strains, the conventional coating is damaged or can only be used a few times and cannot be used.
[0004]
[Problems to be solved by the invention]
In view of the actual state of the prior art, the present invention can be easily applied to a portion of a steam turbine rotor used in a corrosive environment where high stress repeatedly acts, and the high stress repeatedly acts in a corrosive environment. It is an object of the present invention to provide a steam turbine rotor on which a coating film having excellent resistance against corrosion fatigue (low cycle corrosion fatigue) generated in the case is formed.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the inventors of the present invention have made extensive studies on the formation of a coating film on the steam turbine rotor, and the electroless nickel plating in which the phosphorus content is appropriately controlled is excellent for low cycle corrosion fatigue. The present invention was completed by finding that it exhibits resistance.
[0006]
That is, according to the present invention, an electroless nickel plating layer containing 7.5 to 9.5% by weight of phosphorus is formed on the surface of a site where high stress of a low-alloy steel turbine rotor repeatedly acts in a corrosive environment. It is a steam turbine rotor characterized by being formed with a thickness of ˜30 μm.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The steam turbine rotor of the present invention has a phosphorus content of 7.5 to 9.5% by weight on the surface of a portion where the high stress of a turbine rotor made of a low alloy steel such as 3.5NiCrMoV steel repeatedly acts in a corrosive environment. The electroless nickel plating layer controlled in the range of 10 to 30 μm is formed. The electroless nickel plating may be applied to a portion where high stress repeatedly acts in a corrosive environment such as a blade mounting groove of a turbine rotor, but of course, depending on conditions, the electroless nickel plating may be applied to the entire turbine rotor surface.
[0008]
Since nickel plating changes its resistance to low cycle corrosion fatigue depending on the phosphorus content, it must be controlled within an appropriate phosphorus content range for application to high stress sites. If the content of phosphorus in the electroless nickel plating layer is out of the above range, the fatigue resistance is deteriorated, and the plating layer is cracked by a few repetitions and the corrosion resistance is lost.
[0009]
If the thickness of the electroless nickel plating layer is less than 10 μm, the effect of imparting low cycle corrosion fatigue resistance is not sufficient, and if it exceeds 30 μm, the adhesion between the plating layer and the substrate becomes weak, and it becomes easy to peel off. It is not preferable.
[0010]
Next, the steam turbine rotor of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing an example in which phosphorus-containing electroless nickel plating is applied to a blade mounting groove of a turbine rotor of a blade mounting structure called a tangential entry type which is one embodiment of a steam turbine rotor of the present invention. 1 (a) is a cross-sectional view, FIG. 1 (b) is an enlarged view of a portion A in FIG. 1 (a), and FIG. 1 (c) is a cross-sectional view showing a state of a blade groove subjected to electroless nickel plating. In this example, blade grooves 2 called T-routes are continuously provided in the circumferential direction on the outer periphery of the turbine rotor 1, and the blades 3 are inserted into the blade grooves 2 and sequentially implanted in the circumferential direction of the turbine rotor. ing.
[0011]
As a construction method for forming the electroless nickel plating layer 10 on the inner surface of the blade groove 2, an annular plating solution tank 5 is attached to the outer periphery of the rotor via a seal 4 as shown in the explanatory diagram of FIG. 3. The plating solution 6 prepared to a predetermined concentration is circulated to the plating solution tank 5 by a pump 7. In order to allow the plating to proceed stably, the rotor surface and the outer surface of the plating solution tank 5 are structured to be kept at a constant temperature by a heater 9 having a temperature controller 8. By this method, a steam turbine rotor having an electroless nickel plating layer 10 formed as shown in FIG.
[0012]
The steam turbine rotor of the present invention formed with the electroless nickel plating layer has improved low cycle corrosion fatigue resistance, and the degree of corrosion dissolution due to strain induction is reduced even when high strain is repeated. The generation life is extended.
As described above, the electroless nickel plating itself having a phosphorus content of 5 to 10% by weight has been conventionally used as a coating film for anticorrosion and abrasion resistance. Among them, the phosphorus content is 7.5 to 9.5 % by weight . It was not known that those prepared in the range could be used as a coating that withstands low cycle corrosion fatigue at sites where high stress is repeated on the order of 10 ⁴ times.
[0013]
【Example】
The effects of the present invention will be demonstrated by the following examples.
(Example)
An electroless nickel plating layer with varying phosphorus content was formed on the surface of a test piece made of a low alloy material, and a low cycle corrosion fatigue life measurement test was conducted in simulated environment water simulating a steam turbine operating environment.
The test piece used is a 3.5NiCrMoV steel having the shape and dimensions shown in FIG. 4 (the unit of the numerical values is mm) (composition is Ni: 3.5%, Cr: 1.8%, Mo: 0% by weight). .3%, V: 0.1%), and a plating solution prepared by adjusting the phosphorus content so that the phosphorus content in the plating layer is 2, 6 and 8% by weight, respectively (mainly The component used was nickel sulfate, sodium hypophosphite, alkylhydroxycarboxylic acid, etc.) to form an electroless nickel plating layer having a thickness of 20 μm. The test was carried out using these test pieces and the test pieces made of the low alloy steel material in which the electroless nickel plating layer was not formed for comparison.
[0014]
The test method is as follows. First, these test pieces are attached to a fatigue test apparatus, an environmental chamber is attached to the test piece, and environmental water (pure water at a temperature of 130 ° C.) is sent into the chamber at a flow rate of 100 ml / min. I let you. In that state, a single-sided repeated bending load is continuously applied to the test piece in a triangular waveform with a notch bottom strain rate of 0.014% / min, and continued until a crack with a depth of 0.5 mm occurs on the test piece. did.
[0015]
FIG. 2 shows the relationship between the strain range loaded on the test piece and the number of repeated crack initiations. In FIG. 2, a large number of crack initiation repetitions indicates a long life, that is, excellent low cycle corrosion resistance. The results of FIG. 2 show that the phosphorus content of 2% by weight and 6% by weight has a slightly longer life than the low alloy steel material as it is, but the effect is small, whereas the phosphorus content The amount of 8% by weight and the formation of an electroless nickel plating layer containing high phosphorus shows that the lifetime is remarkably increased.
[0016]
From the above test results, low cycle corrosion fatigue resistance can be remarkably improved by forming a high phosphorus content electrolytic nickel plating layer on the surface of the site where the high stress of the turbine rotor made of low alloy steel repeatedly acts. Recognize.
[0017]
【The invention's effect】
An electroless nickel plating layer containing 7.5 to 9.5% by weight of phosphorus is formed on the surface of a site where high stress of the low-alloy steel turbine rotor of the present invention repeatedly acts in a corrosive environment. The steam turbine rotor formed with a thickness of 5 mm has excellent resistance to corrosion fatigue (low cycle corrosion fatigue) that occurs when high stress is repeatedly applied in a corrosive environment. The service life can be extended. The electroless nickel plating layer can be easily applied to a site where high stress of the steam turbine rotor repeatedly acts in a corrosive environment .
[Brief description of the drawings]
FIG. 1 is an explanatory view showing one embodiment of a steam turbine rotor of the present invention.
FIG. 2 is a diagram showing a relationship between a strain range loaded on a test piece and the number of repeated crack generations in Examples.
FIG. 3 is an explanatory diagram showing an example of a construction method for forming an electroless nickel plating layer on the steam turbine rotor of the present invention.
FIG. 4 is an explanatory view showing the shape and size of a test piece used in Examples.

Claims (1)

An electroless nickel plating layer containing 7.5 to 9.5% by weight of phosphorus on the surface of a portion where high stress of a low alloy steel turbine rotor repeatedly acts in a corrosive environment has a thickness of 10 to 30 μm. A steam turbine rotor characterized by being formed by

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