JP4959316B2 - Corrosion-resistant covering member and rotating machine - Google Patents

Description

  The present invention relates to a corrosion-resistant covering member and a rotary machine that are excellent in corrosion resistance in an environment where a sodium chloride aqueous solution exists.

Conventionally, steam turbine plants have been frequently used as power plants. FIG. 10 shows a moving blade 100 of a steam turbine used in a steam turbine plant. The moving blade 100 includes a blade portion 102 that collides with circulating steam, and a blade root portion 103 provided on the root side of the blade portion 102. As shown in FIG. 11, the blade root portion 103 is fitted and fixed to a plurality of fitting portions 107 formed on the outer periphery of the rotor disk 105 rotating around the rotation axis. .
In the steam turbine configured as described above, when the steam flows, the steam temperature decreases as the low pressure stage is reached. When the steam temperature is close to the saturation temperature, a part of the steam is condensed and enters between the blade root portion 103 and the fitting portion 107. When the state where the condensed water enters in this way continues intermittently, sodium chloride (NaCl) contained in the condensed water is concentrated. When NaCl is concentrated, pits (small holes) are formed in the blade root portion 103 or the fitting portion 107 due to corrosion, and there is a possibility that fatigue failure will proceed starting from this pit.

  On the other hand, in order to improve the corrosion resistance of a metal, a technique for coating a Ni-based alloy layer on a base material is known (see Patent Document 1).

JP-A-8-74506

However, the technique described in Patent Document 1 takes into account corrosion resistance and oxidation resistance, but does not consider corrosion resistance in a sodium chloride aqueous solution environment.
Moreover, when applying to rotary machines, such as a steam turbine, as mentioned above, it is requested | required that it is excellent in fatigue strength.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the corrosion-resistant coating | coated member and rotary machine which were excellent in corrosion resistance in the sodium chloride aqueous solution environment, and were excellent in fatigue strength.

In order to solve the above problems, the corrosion-resistant covering member and rotating machine of the present invention employ the following means.
That is, the corrosion-resistant covering member according to the present invention comprises a base material on which a nitrogen-containing nitride layer is formed on the surface side, and a corrosion-resistant film coated on the surface of the base material. It has a Ni-PB alloy layer.

As the corrosion resistant film, a Ni-PB alloy layer, which is a Ni-based alloy, was provided. The Ni-PB alloy layer, since it contains P, resistant Cl ^- and a sex. Thereby, the corrosion-resistant film excellent in the sodium chloride aqueous solution environment is realized.
Further, since the Ni-PB alloy layer contains B, it has toughness.
Furthermore, the fatigue strength is improved by forming a nitride layer on the surface side of the substrate. Thereby, the fall of the fatigue strength by a Ni-PB alloy layer can be compensated.
The Ni—PB alloy layer is preferably provided as the uppermost layer.
The Ni—PB alloy layer is preferably formed by electroless plating.

  The nitride layer is preferably a radical nitride layer.

  Furthermore, according to the corrosion-resistant covering member of the present invention, the radical nitride layer has a thickness of 30 μm or more.

  When the thickness of the radical nitride layer is less than 30 μm, the thickness is insufficient and improvement in fatigue strength is not recognized. The thickness of the radical nitride layer is preferably 40 μm or more.

  Furthermore, according to the corrosion-resistant covering member of the present invention, the P concentration of the Ni-PB alloy layer is 4.0 wt% or more, and the B concentration of the Ni-PB alloy layer is 0.5 wt% or more. It is characterized by being.

When the P concentration of the Ni—PB alloy layer is less than 4.0 wt%, improvement in Cl ⁻ resistance cannot be expected.
When the B concentration of the Ni-PB alloy layer is less than 0.5 wt%, improvement in toughness cannot be expected.

  Further, according to the corrosion-resistant covering member of the present invention, the corrosion-resistant coating includes the Ni-PB alloy layer and a Ni-P alloy layer provided between the Ni-PB alloy layer and the base material. It is characterized by.

By providing the Ni-P alloy layer between the Ni-PB alloy layer and the base material, the adhesion between the Ni-PB alloy layer and the base material is improved.
The Ni—P alloy layer is preferably formed by electroless plating.

  In addition, the rotating machine of the present invention includes a rotor disk that rotates about a rotation axis, and a plurality of blades that have a blade root portion fitted and fixed to a plurality of fitting portions formed on the outer periphery of the rotor disk. The blade root portion of the rotor blade or the fitting portion of the rotor disk is provided with any one of the above corrosion-resistant covering members.

Between the blade root portion and the fitting portion, moisture in the fluid is likely to condense and enter, so that an environment in which sodium chloride is easily concentrated is obtained. In the present invention, since any one of the above corrosion-resistant covering members is provided at the blade root portion or the fitting portion, corrosion can be prevented even when this region is exposed to a sodium chloride environment. Moreover, since said corrosion-resistant coating | coated member is excellent in toughness and fatigue strength characteristic, fatigue failure can also be prevented.
As a rotating machine, a steam turbine is mentioned as a thing which sodium chloride tends to concentrate between a blade root part and a fitting part, and it is especially suitable for a low pressure stage steam turbine in the environment where steam is easy to condense.

The corrosion-resistant coated member of the present invention is an environment in which an aqueous sodium chloride solution is present because the corrosion-resistant coating 4 having Cl− resistance and toughness is coated on a substrate on which a radical nitride layer having high fatigue strength is formed. However, sufficient corrosion resistance and fatigue strength can be exhibited.
In addition, since the rotating machine of the present invention is provided with the corrosion-resistant covering member of the present invention at the blade root part or the fitting part, corrosion can be prevented even when this region is exposed to a sodium chloride environment. It is possible to prevent fatigue failure by the corrosion-resistant clothing member having excellent toughness and fatigue strength characteristics.

Embodiments according to the present invention will be described below with reference to the drawings.
As shown in FIGS. 10 and 11, the corrosion-resistant covering member of the present invention is particularly suitable for use in the blade root portion 103 of the moving blade 100 of the low-pressure stage of the steam turbine. In addition, it is good also as using for the fitting part 107 of the rotor disk 105. FIG.

FIG. 1 shows a cross section of the corrosion-resistant covering member 1.
The corrosion-resistant covering member 1 includes a substrate 3 and a corrosion-resistant coating 4 that is coated on the surface of the substrate.

As the base material 3, for example, stainless steel such as SUS410J1 is used.
A radical nitride layer 3 a is provided on the surface side of the substrate 3. Fatigue strength is improved by the compressive stress imparting effect of the radical nitride layer 3a.
The thickness of the radical nitride layer 3a is 30 μm or more, preferably 40 μm or more. This is because if the thickness is less than 30 μm, the amount of compressive stress applied becomes insufficient, and improvement in fatigue strength cannot be expected. As shown in FIG. 9, the thickness of the radical nitride layer 3a is a dimension from the surface of the base material 3 to a position where the hardness is equivalent to that of the base material. The Hv hardness of the radical nitride layer 3a is generally 800 to 1200.

The radical nitriding layer 3a is formed by the radical nitriding apparatus 10 shown in FIG.
The radical nitriding apparatus 10 includes a chamber 12, an external heater 13 that covers the outer periphery of the chamber 12, a vacuum pump 14 that evacuates the chamber 12, a process gas supply unit 16 that supplies process gas into the chamber 12, and a chamber 12 includes a cooling gas supply means 18 for supplying a cooling gas and a DC power source 20.
An installation shelf 24 for installing the base material 3 to be processed is provided in the chamber 12. The installation shelf 24 is connected to the negative electrode of the DC power supply 20. A positive electrode of the DC power supply 20 is connected to the chamber 12.

Formation of the radical nitride layer by the radical nitriding apparatus 10 having the above-described configuration is performed as follows.
The base material 3 installed on the installation shelf 24 is heated to about 400 ° C. by the external heater 13. Further, the inside of the chamber 12 is maintained at a predetermined degree of vacuum by the vacuum pump 14. A glow discharge is generated in the chamber 12 by supplying a direct current from the direct current power source 20. In this state, process gases of ammonia and hydrogen are introduced by the process gas supply means 16 to generate plasma in the chamber 12. NH radicals generated by the plasma cause N to enter the substrate 3 to form a nitride with Fe or the like, thereby forming the radical nitrided layer 3a.

The corrosion resistant coating 4 in FIG. 1 is a Ni—PB alloy layer 5. The Ni—PB alloy layer 5 is preferably formed by electroless plating.
The Ni-PB alloy layer 5 is obtained by adding a small amount of P and B to a Ni-based alloy.
By adding P in Ni-PB alloy, resistance to Cl ^- is improved. Thereby, the corrosion-resistant film excellent in the sodium chloride aqueous solution environment is realized. The P concentration of the Ni—PB alloy layer 5 is 4.0 wt% or more and 7.0 wt% or less. This is because when the P concentration is less than 4.0 wt%, improvement in Cl ⁻ resistance cannot be expected. On the other hand, if the P concentration exceeds 7.0 wt%, the plating solution becomes unstable when performing electroless plating.
Moreover, toughness is improved by adding B to the Ni-PB alloy. The B concentration of the Ni—PB alloy layer 5 is 0.5 wt% or more and 1.0 wt% or less. This is because if it is less than 0.5 wt%, improvement in toughness cannot be expected. On the other hand, if it exceeds 1.0 wt%, the plating solution becomes unstable when performing electroless plating.

  As shown in FIG. 2, the corrosion-resistant film 4 includes a Ni—PB alloy layer 5 provided on the outermost layer, and a Ni—P alloy layer 7 provided between the Ni—PB alloy layer 5 and the substrate 3. It is good also as a structure provided with. The Ni—P alloy layer 7 is used to enhance the adhesion between the base material 3 and the Ni—P—B alloy layer 5. The Ni-P alloy layer 7 is obtained by adding a small amount of P to a Ni-based alloy. The Ni—P alloy layer 7 is preferably formed by electroless plating. The P concentration of the Ni—P alloy layer 7 is 3 wt% or more and 13 wt% or less.

  As described above, the corrosion-resistant covering member 1 according to the present embodiment coats the corrosion-resistant coating 4 having Cl− resistance and toughness on the substrate 3 on which the radical nitrided layer 3a having high fatigue strength is formed. Even in an environment where a sodium chloride aqueous solution is present, sufficient corrosion resistance and fatigue strength can be exhibited.

Next, examples of the present invention will be described.
[Radical nitride layer thickness evaluation]
The thickness of the radical nitride layer 3a formed on the surface side of the substrate 3 was evaluated.
A radical nitriding layer was formed on the test piece shown in FIG. 4 using the radical nitriding apparatus 10 shown in FIG. SUS401J1 was used for the test piece.
A rotating bending fatigue test was performed on the test piece on which the nitride layer was formed. In this fatigue test, a smooth test piece was used as the shape of the test piece, the repetition rate was 3600 rpm, and the test temperature was room temperature. Then, the fatigue strength at 10 ⁷ times in the rotating bending test was measured, and the ratio to the comparative test piece in which the radical nitride layer was not formed (fatigue strength improvement multiple) was determined.
FIG. 5 shows this fatigue strength enhancement factor with respect to the radical nitride layer depth (μm). As shown in FIG. 9, the thickness of the radical nitride layer 3a is a dimension from the surface of the base material 3 to a position where the hardness is equivalent to that of the base material. The Hv hardness of the radical nitride layer 3a is generally 800 to 1200.
As can be seen from FIG. 5, when the radical nitride layer depth is 30 μm or more, the fatigue strength improvement factor is remarkably increased. Therefore, the radical nitride layer depth is preferably 30 μm or more, more preferably 40 μm or more. Even if the radical nitride layer depth exceeds 70 μm, the multiple of improvement in fatigue strength is constant at about 1.4. Therefore, it can be said that the radical nitride layer depth is 70 μm or less.

[Ni-PB alloy layer]
Next, the Ni—PB alloy layer 5 as the corrosion resistant film 4 formed on the substrate 3 was examined.
As a test piece of the base material 3, SUS410J1 having a size of 20 mm × 20 mm × 5 mm was used, and a Ni—PB alloy layer was formed to a thickness of 50 μm by the following process.
The Ni-PB alloy layer 5 was formed by electroless plating in the step shown in FIG.
First, the test piece was degreased for 15 minutes at 60 ° C. using a commercially available alkaline solution. Next, acid treatment was carried out using hydrochloric acid (35 wt%) at 500 ml / L (500 ml of 35 wt% hydrochloric acid in 1 liter of aqueous solution) at 25 ° C. for 3 minutes. Then, activation treatment was carried out using sulfuric acid (95 wt%) at 50 ml / L (50 ml of 95 wt% sulfuric acid in 1 liter of aqueous solution) at 25 ° C. for 30 seconds. Thereafter, the test piece was immersed in a Ni—PB ternary plating solution maintained at 80 ° C. to perform electroless plating.

The corrosion resistance was evaluated using the test piece on which the Ni—PB alloy layer was formed as described above.
Specifically, anode / cathode polarization characteristics were measured by an electrochemical method, and pitting corrosion resistance was evaluated by the following method. Pitting corrosion resistance was evaluated by pitting potential measurement at a corrosion current density of 100 μA / cm ² . The conditions used for this test are as follows.
<Electrochemical test conditions>
Test solution: 22% NaCl aqueous solution Test temperature: 80 ° C
Atmosphere: Deaeration measurement method: Sweep the potential from the natural potential in the direction of the cathode and anode at 20mV / min, measure the value of the current flowing through the test piece (□ 15mm), and obtain the polarization curve.

FIG. 7 shows the test results. The horizontal axis represents the phosphorus (P) concentration (wt%) in the plating solution, and the vertical axis represents the anode current potential (V) at 100 μA / cm ² . The B concentration in the plating solution is shown for 0, 0.5, and 1.0 wt%, respectively. In the figure, the higher the anode current potential, the higher the corrosion resistance.
As can be seen from the figure, the anode current potential increases as the P concentration increases.
It can be seen that the potential of the anode current is higher when the B concentration is 0.5 wt% and 1.0 wt% compared to 0 wt%. Further, the potential of the anode current is higher when the B concentration is 0.5 wt% than when 1.0 wt%.
Further, it can be seen that when the B concentration is 0.5 wt% and 1.0 wt% and the P concentration is 4 to 7 wt%, the potential of the anode current is significantly increased. Therefore, it is judged that the P concentration is 4 to 7 wt% and the B concentration is 0.5 to 1.0 wt%.
In addition, the plating solution added by Ni-PB plating with P concentration of 4-7wt% exceeding B concentration of 3.0wt% became unstable because the plating solution became cloudy and unstable 1 hour after the bathing. The data in are not shown in the figure. Similarly, the plating solution added with P concentration exceeding 10wt% in Ni-PB plating with B concentration of 0.5 ~ 3.0wt% became turbid and unstable 1 hour after the bathing. Data in this area is not shown in the figure.

[Corrosion fatigue characteristics]
Next, corrosion fatigue characteristics were examined using a test piece in which a Ni—PB alloy layer was formed on a substrate by electroless plating shown in FIG.
As the base material of the test piece, SUS410J1 was used, and the shape was the smooth test piece shown in FIG.
A radical nitriding layer having a thickness of 60 μm was formed on the surface of the substrate using the radical nitriding apparatus shown in FIG. Then, a Ni—PB alloy layer was formed to a thickness of 50 μm by electroless plating. Regarding the P concentration and B concentration of the Ni-PB alloy, the P concentration was 7 wt% and the B concentration was 0.5 wt% based on the test results shown in FIG. Thereafter, heat treatment was performed at 300 ° C. for 1 hour.
As a comparative material, a material in which no treatment was applied to the base material, that is, a material in which a radical nitride layer and a Ni—PB alloy layer were not formed was used.
The specifications of each specimen are summarized below.
Table 1 Corrosion fatigue test piece specifications

The conditions of the corrosion fatigue test are as follows.
<Corrosion fatigue test conditions>
Rotating bending fatigue test
22% NaCl aqueous solution dripping
22% NaCl aqueous solution temperature: 80 ℃
Repetition frequency: 60Hz
Fatigue strength evaluation of up to 1 × 10 ⁸ cycles

FIG. 8 shows the results of the corrosion fatigue test.
From the figure, it can be seen that the stress amplitude σa is larger in the example having the Ni-PB alloy layer than in the comparative material at any number of repetitions Nf. Therefore, it can be seen that even in the environment of sodium chloride (Nacl) aqueous solution, the corrosion-resistant covering member provided with the Ni-PB alloy layer of the example has sufficient corrosion resistance and high fatigue strength.

It is sectional drawing which showed typically the cross section of the corrosion-resistant coating | coated member concerning one Embodiment of this invention. It is sectional drawing which showed the modification of FIG. It is sectional drawing which showed the outline of the radical nitriding apparatus which forms a radical nitride layer in the base-material surface. It is the front view which showed the test piece which performs a fatigue test. It is the graph which showed the fatigue strength improvement multiple with respect to the radical nitride layer thickness. It is the flowchart which showed the process of the electroless plating which forms a Ni-P-B alloy layer. It is the graph which showed the electric potential of the anode current with respect to P density | concentration. It is the graph which showed the stress amplitude (fatigue strength) with respect to the repetition number of fracture about the test piece of an Example, and the test piece of a comparative material. It is the graph which showed the hardness of the base material with respect to the distance from the base material surface. It is the perspective view which showed the moving blade which has a blade root. It is a front view which shows the state which fitted and fixed the several moving blade with respect to the rotor disk.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Corrosion-resistant coating member 3 Base material 3a Radical nitride layer 4 Corrosion-resistant film 5 Ni-PB alloy layer 7 Ni-P alloy layer

Claims (5)

A base material on which a nitride layer containing nitrogen is formed on the surface side;
A corrosion-resistant film coated on the surface of the substrate,
The corrosion-resistant film includes a Ni-PB alloy layer ,
The P concentration of the Ni-PB alloy layer is 4.0 wt% or more,
A corrosion-resistant covering member, wherein the B concentration of the Ni-PB alloy layer is 0.5 wt% or more .   The corrosion-resistant covering member according to claim 1, wherein the nitrided layer is a radical nitrided layer.   The corrosion-resistant covering member according to claim 2, wherein the radical nitride layer has a thickness of 30 μm or more. The said corrosion-resistant film | membrane is equipped with the said Ni-PB alloy layer and the Ni-P alloy layer provided between this Ni-PB alloy layer and the said base material, The Claim 1 to 3 characterized by the above-mentioned. The corrosion-resistant covering member according to any one of the above. A rotor disk that rotates about the axis of rotation;
A plurality of blades that are fitted and fixed to a plurality of fitting portions formed on the outer periphery of the rotor disk; and
The blade root of the rotor blade, or to the fitting portion of the rotor disk is provided with a corrosion resistance coating member,
The corrosion-resistant coating member includes a base material on which a nitrogen-containing nitride layer is formed on the surface side, and a corrosion-resistant film coated on the surface of the base material,
The rotary machine characterized in that the corrosion-resistant film includes a Ni-PB alloy layer .

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