JP5240168B2 - Steam turbine, steam turbine surface layer forming method, and steam turbine surface layer repairing method - Google Patents

Description

  The present invention relates to, for example, a steam turbine component that is a mechanical component requiring erosion resistance and a method for manufacturing the same.

Erosion in which a member is eroded when wet steam including water droplets collides at high speed is an important problem in steam turbine blades, pump piping, fluid injection parts, and the like. As described above, a coating process of a material having high erosion resistance by brazing, spraying, or the like, or a curing process by laser beam irradiation or the like is performed.
Further, when erosion occurs with long-term use, as shown in Patent Document 2, the base material is built up by overlay welding or the like, and then predetermined repair is performed.

JP 2004-027261 A JP 2007-182776 A

However, when an erosion-resistant film is applied by brazing, there are problems such as that it takes man-hours and that the brazed portion contains at least some defects (such as pores and insufficient penetration). In addition, in the case of welding, shape modification and heat treatment are required due to deformation of members due to excessive heat input and reduction in strength, manual work is required due to manual methods, and the manufacturing process is complicated. is there. In addition, in the case of thermal spraying, when it is newly manufactured, preheating and bond coat treatment are necessary so that the thermal sprayed film is easily attached, and the manufacturing process is complicated and the adhesiveness of the thermal sprayed coating itself is sufficient in the first place. It can not be said.
Further, in these film formation techniques, in the case of repair, since the erosion-resistant film is completely removed and the erosion occurrence site is removed and then restored to the original state, it takes more man-hours than new manufacturing.
Moreover, in the technique of removing the damaged part and filling it with overlay welding, the boundary part between the repaired part and the original member becomes poor in durability.

The present invention has been made to solve the above-described problems, and provides a method for manufacturing a turbine blade and a method for forming an erosion-resistant coating that can be easily repaired even if erosion occurs.
Specifically, a part where erosion is likely to occur is preliminarily raised from the surroundings by machining or overlaying, and an erosion-resistant film is formed on the raised part by discharge surface treatment, and erosion occurs when erosion occurs. After the part is excised, the discharge surface treatment is performed again so that the repair can be performed while eliminating the need for a process such as heat treatment or shape correction. Moreover, the mechanical strength of the base material is not impaired. Furthermore, the present invention provides a method capable of performing processing on a member automatically by a machine instead of relying on skill.

The steam turbine according to the present invention has a predetermined clearance from the front edge of the front end of the steam turbine blade, which is formed into a predetermined raised shape from the blade surface by machining or build-up processing. A discharge is generated between the arranged Si electrodes, and a Si surface layer having a surface roughness Rz of 20 μm or less and having a Si content of 1 to 20 wt% supplied from the Si electrodes is formed.

  According to the present invention, a surface layer exhibiting high erosion resistance can be formed because a good quality film can be stably formed on a member by discharge using an Si electrode, and erosion occurs. Can be repaired with minimal man-hours.

It is explanatory drawing of a discharge surface treatment system. It is the figure which showed the voltage and electric current waveform in discharge surface treatment. It is a figure showing the discharge phenomenon. It is a figure which shows the relationship between the resistance value R of an electrode, resistivity ρ, area S, and length L. It is the figure which showed the electric current waveform when discharge cannot be detected. It is a figure which shows the analysis result of the surface layer containing Si. It is the schematic of the evaluation test of erosion resistance. It is a figure which shows the evaluation test result of a stainless steel base material. It is a figure which shows the evaluation test result of a stellite. It is a figure which shows the evaluation test result of a TiC film | membrane. It is a figure which shows the evaluation test result of Si surface layer. It is a figure which shows the evaluation test result of Si surface layer. It is a condition list of Si surface layer. It is a surface photograph of Si surface layer. It is a cross-sectional photograph of the Si surface layer. It is the photograph which showed a mode that Si surface layer was destroyed. It is a photograph showing the state of erosion of Stellite. It is an erosion-resistant characteristic figure of Si surface layer. It is the photograph which the crack progressed in Si surface layer. It is an erosion-resistant characteristic figure of Si surface layer. It is an erosion-resistant characteristic figure of Si surface layer. 2 is an X-ray diffraction image of a Si surface layer. It is the figure which showed a mode that Si surface layer was formed with respect to the moving blade of a steam turbine. It is the figure which showed a mode that Si surface layer was formed with respect to the moving blade of a steam turbine. It is the figure which showed a mode that Si surface layer was formed with respect to the moving blade of a steam turbine. It is the cross-sectional schematic showing the cross section of the turbine blade in each process of the repair by the repair method of a steam turbine blade. It is the photograph which showed a mode that the erosion which generate | occur | produced in Si surface layer was repaired. It is a figure which shows the healthy minimum range of the height of the step part which forms Si surface layer. It is a figure which shows the healthy upper limit range of the height of the step part which forms Si surface layer. It is the figure which looked at an example of the curved surface which can apply the repair method of this invention from the cross section. It is the figure which looked at an example of the curved surface which can apply the repair method of this invention from the cross section.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 shows an outline of a discharge surface treatment method for generating a pulsed discharge between a Si electrode and a member to form a structure having an erosion resistance function on the member surface.
In the figure, 1 is a solid metal silicon (Si) electrode, 2 is a member to be treated, such as a steam turbine blade, 3 is an oil that is a working fluid, 4 is a DC power source, 5 is a voltage of a DC power source 4 A switching element for applying (or stopping) between the electrode 1 and the member 2, 6 a current limiting resistor for controlling the current value, 7 a control circuit for controlling on / off of the switching element 5, 8 Is a discharge detection circuit for detecting the voltage between the Si electrode 1 and the member 2 and detecting the occurrence of discharge.
The member 2 to be processed such as a steam turbine blade is an iron-based alloy such as SUS630, SUS410J1, SUS304, or SUS316.

Next, the operation will be described with reference to FIG. 2 showing voltage and current waveforms.
A voltage is applied between the Si electrode 1 and the member 2 by turning on the switching element 5 by the control circuit 7. An electrode feed mechanism (not shown) controls the distance between the Si electrode 1 and the member 2 to an appropriate distance (a distance at which discharge occurs). After a while, a discharge occurs between the Si electrode 1 and the member 2. Will occur. The current value ie, pulse width te (discharge duration) and discharge pause time t0 (time during which no voltage is applied) are set in advance and are determined by the control circuit 7 and the current limiting resistor 6.
When the discharge occurs, the discharge detection circuit 8 detects the occurrence of discharge from the voltage drop and timing between the Si electrode 1 and the member 2, and a predetermined time (pulse width te) from the time when the occurrence of discharge is detected. Later, the switching element 5 is turned off by the control circuit 7.
After a predetermined time (resting time t0) from when the switching element 5 is turned off, the control circuit 7 turns on the switching element 5 again.
By repeating the above operation, it is possible to generate a discharge having a continuously set current waveform.

In FIG. 1, the switching element is depicted as a transistor, but other elements may be used as long as the application of voltage can be controlled. Further, the current value is drawn as if it was controlled by a resistor, but it goes without saying that other methods may be used as long as the current value can be controlled.
In the description of FIG. 1, the current pulse waveform is a rectangular wave, but other waveforms may be used. Depending on the shape of the current pulse, the electrode can be consumed more to supply more Si material, and the electrode can be used more effectively by reducing the consumption of the electrode. I will not discuss it.

By continuously generating a discharge between the Si electrode 1 and the member 2 as described above, a layer containing a large amount of Si can be formed on the surface of the member 2.
However, in order to stably form a high-quality Si-containing layer for this purpose, any Si may be used, and the circuit shown in FIG. 1 has necessary conditions. This will be described in detail later.

First, before describing the conditions of the Si electrode and the circuit, a film forming technique by electric discharge machining will be described in order to clarify the difference between the conventional technique related to the discharge surface treatment and the present embodiment.
Japanese Patent Publication No. 5-13765 discloses a method of using silicon as an electrode for electric discharge machining to form a surface layer with high corrosion resistance and high heat resistance characteristics with an amorphous alloy layer or a fine crystal structure on the surface of the workpiece. ing.

The electric discharge machining with the Si electrode disclosed in the publication is a method of supplying energy with a peak value Ip of 1 A by a circuit system that periodically turns on and off the voltage with the voltage application time fixed at 3 μs and the pause time at 2 μs. is there.
Therefore, where the discharge occurs in the voltage pulse is all different in the period of 3 μs while the voltage is applied, and the current pulse width through which the current, which is the actual discharge duration, sequentially changes, and it is difficult to form a stable film. Become.

For example, as illustrated in FIG. 3, in a circuit-type power supply that periodically turns on and off the voltage, the voltage waveform and current waveform change, causing a phenomenon in which the energy of each pulse changes, and Si as an electrode material is supplied to the member The amount to be formed and the energy for melting the surface of the member to form the surface layer are different, and stable treatment becomes difficult.
In the figure, the discharge voltage is constant and the current is also constant, but in reality the voltage varies and the current also varies. Further, when a high-resistance material such as Si is used as the electrode, the voltage includes the voltage drop in Si, so that the voltage is high and the fluctuation is large.

Next, the reason why the publication has to periodically turn on and off the voltage as described above will be described.
In this publication, silicon, which is a high resistance material having a specific resistance value of about 0.01 Ωcm, is used, and a very small current pulse condition is used.
Therefore, in the conventional control method that detects the occurrence of discharge by detecting the arc potential of the discharge, when the discharge is generated when the electrode is a high resistance material, the voltage drop voltage when the current flows through the Si electrode is discharged. This is because, when the voltage of the voltage drop is high, the circuit cannot recognize that the discharge has occurred although the discharge has occurred.

In addition, the conventional silicon film formed by electric discharge machining has a problem that the treatment is greatly varied and cannot be stably performed.
This problem is also caused by the high resistance of Si.
For example, as shown in FIG. 4, the resistance value R of the electrode is expressed as R = ρ · L / S, where ρ is the resistivity, S is the area, and L is the length.
However, depending on the method of supplying power to the electrode, that is, the method of holding the electrode, the value of R will vary greatly if ρ is large.
Conventionally, silicon with ρ = 0.01 Ωcm is used as an electrode. However, in the case of such a high resistance material, processing cannot be performed unconditionally. For example, when the Si electrode is long and the power is fed by holding one end, when the electrode is long, the resistance of the electrode is high, and the resistance decreases as the length becomes short. If the electrode is long and has high resistance, the discharge cannot be detected as described above, and the probability of occurrence of an abnormal pulse increases, and even if no abnormality occurs, the resistance is high, so the discharge current value is low. .

According to the inventors' research, when silicon having a resistance value of about ρ = 0.01 Ωcm is used as an electrode, if the electrode length exceeds about several tens of millimeters, the voltage drop at the electrode due to the current when a discharge occurs increases. In some cases, abnormal discharge occurs and it is difficult to form a normal surface layer.
Further, it has been found that the conditions under which such abnormal discharge occurs are almost determined by the feeding position and the discharge position, that is, the length of the electrode, and are not so much related to the area (thickness) of the electrode.
This can be presumed to be because when the current flows through the electrode, it does not flow uniformly across the entire cross section of the electrode, but flows through a narrow path. Therefore, even when silicon having a resistivity of 0.01 Ωcm or more is used as an electrode, it is possible to generate a stable discharge if the position where the discharge is generated is close to the feeding point. For example, if a plate-like silicon having a thickness of about 1 mm is bonded to a metal and power is supplied, stable discharge is possible even with a resistance of about 0.05 Ωcm. However, even with an electrode of 0.01 Ωcm, when the length is about several tens mm or more, for example, about 100 mm, abnormal discharge may occur, and stable treatment is difficult.

As described above, the following was clarified from experiments by the inventors.
In order to form a surface layer containing Si on the surface of the member with silicon as an electrode at a high speed of about 10 μm so as to withstand industrial use, the resistance is low. A circuit of a system using Si and controlling the discharge pulse width (discharge current pulse) as shown in FIGS. 1 and 2 (equalizing to almost the same pulse width) must be used.

  In order to form a surface layer of about 10 μm on the surface of a member using silicon as an electrode, the resistance value (specific resistance) should be low. In consideration of industrial practical use, it is desirable that ρ is 0.005 Ωcm or less in consideration of the case where the electrode is used even when the electrode length is about 100 mm or more. In order to reduce the resistance value of Si, the concentration of so-called impurities may be increased, such as doping with other elements.

Even if ρ is 0.005 Ωcm or more, stable treatment is possible if the feeding point and the discharge position are close. The index at that time may be as follows including the case where ρ is 0.005 Ωcm or less.
That is, it is recognized that a discharge has occurred due to a decrease in the voltage applied between the electrodes, and the application of the voltage is stopped after a predetermined time (pulse width te) has elapsed since the time when the discharge was recognized to occur (that is, the discharge) When the surface layer containing Si is formed on the surface of the member using Si as an electrode, the interelectrode voltage including the voltage drop at the Si electrode, which is a resistor when a discharge occurs, is discharged Processing may be performed in a state where the level is lower than the detection level.

In general, the arc potential is about 25 V to 30 V, but the discharge detection level voltage may be set lower than the power supply voltage and higher than the arc potential. However, if the discharge detection level is set to a low value, it cannot be recognized that a discharge has occurred unless the resistance value of Si is low, and an abnormally long pulse as shown in FIG. 5 is generated. The danger increases.
If the discharge detection level is set high, even if the resistance of Si is slightly high, it becomes easy to fall below the discharge detection level when a discharge occurs. That is, when the resistance value of Si is low, the electrode may be long. When the resistance value of Si is high, the length of Si is shortened, and the voltage between the electrodes when discharge occurs is the discharge detection level. It is sufficient to make it lower. The discharge detection level may be set lower than the power supply voltage and higher than the arc potential, but from the above description, it is preferable to set the discharge detection level slightly lower than the power supply voltage.
In the experiments by the inventors, it has been found that setting the value about 10 to 30 V lower than the power supply voltage is most versatile in practice. More strictly, Si that can be used having a value lower than the power supply voltage by about 10V to 20V is convenient because it has a width.

  By satisfying the above conditions, it is possible to stably generate a free discharge pulse using Si, which is a high resistance material, as an electrode, and to form a surface layer containing Si on the member.

Now, a surface layer containing Si as described above can be formed, and when the properties thereof are examined, the following has been found.
FIG. 6 shows the analysis result of the surface layer containing Si. The upper left photo is the SEM image of the Si surface layer cross section, the upper middle is the Si surface analysis result, the upper right is the Cr surface analysis result, the lower left is the Fe surface analysis result, and the lower right (middle) is the Ni surface analysis result. It is.
Moreover, although it is a surface layer with a certain thickness from this result, the Si surface layer does not have Si on the base material, but Si is integrated with the base material. It can be seen that the surface layer is in a state where Si has permeated at a high concentration. Since this surface layer is an iron-based metallographic structure with an increased Si content and the expression “film” is not appropriate, it will be referred to as an Si surface layer for the sake of simplicity. In this surface layer, a portion where the Si amount is slightly increased by the component analysis is defined as a surface layer.
Since it is in such a state, the surface layer does not peel off the coating unlike the other surface treatment methods. As a result of examining the surface layer, it was found that when a certain condition is satisfied, the surface layer has extremely high erosion resistance. Erosion is a phenomenon in which water or the like hits and erodes a member, and is a phenomenon that causes failure of piping parts through which water or steam passes, or a moving blade of a steam turbine. As techniques for erosion resistance, there are various prior arts as described above, but each has a problem.

First, experimental results showing the high erosion resistance of the Si surface layer satisfying the predetermined conditions will be described. The predetermined condition will be described later.
The test results of the erosion resistance performance of this embodiment will be described below.
FIG. 7 is an outline of a test in which the state of erosion was compared by applying a water jet to a test piece as an evaluation of erosion resistance.
A water jet was applied at a pressure of 200 MPa. As test specimens, 1) stainless steel substrate, 2) stellite (generally used for erosion-resistant applications), 3) TiC film by discharge, and 4) a Si-rich surface layer according to the present invention is formed on stainless steel. 4 types were used.
The film 3) is a TiC film formed by the method disclosed in International Publication No. WO01 / 005545, and has a high hardness.
A water jet was applied to each test piece for 10 seconds, and erosion of the test piece was measured with a laser microscope.

8 shows the result of 1), FIG. 9 shows the result of 2), FIG. 10 shows the result of 3), and FIG. 11 shows the result of 4), that is, the surface layer according to the present embodiment.
As shown in FIG. 8, the stainless steel substrate is eroded to a depth of about 100 μm when a water jet is applied for 10 seconds.
On the other hand, as shown in FIG. 9, the stellite material has a different erosion state, but the depth is about 60 to 70 μm, and the erosion resistance of the stellite material was confirmed to some extent.
FIG. 10 shows the result of the TiC film having a very high hardness, but it was found that the erosion resistance was not solely due to the hardness of the surface because it was eroded to a depth of about 100 μm.

On the other hand, FIG. 11 shows the result in the case of the surface layer of Si according to the present embodiment.
The hardness of this surface layer is about 800 HV (the thickness of the surface layer was so thin that it was measured with a micro Vickers hardness tester with a load of 10 g. The hardness range was approximately 600 to 1100 Hv). The hardness is lower than that of the TiC film (about 1500 Hv) shown in 3), although it is higher than the stainless steel base material (about 350 Hv) shown in 2) and the stellite material (about 420 Hv) shown in 2).
That is, it can be seen that the erosion resistance is a combined effect that combines not only the hardness but also other properties.

In FIG. 10, although it is a hard coating, it seems to have been scooped out, so even if only the surface is hard, it is assumed that the thin coating with no toughness on the surface will be destroyed by the impact of the water jet. Is done.
On the other hand, the film of 4) in the present embodiment is tough according to another test and has a surface that can withstand deformation, and this point is presumed to be a cause of high erosion resistance. Experimentally, when a TiC film and a Si surface layer were formed on the surface of a thin plate and a bending test was performed, cracks immediately entered TiC, but did not easily enter the Si surface layer.

The surface layer of 4) was tested at a thickness of about 5 μm, but it was confirmed that when the coating was thin, the strength was not sufficient and erosion was likely to occur.
In Japanese Patent Publication No. 5-13765, which is a prior art, the coating of Si was studied and the high corrosion resistance was revealed, but the erosion resistance was not found but the surface layer could not be thickened. It can be inferred that this is one of the major causes.
In the case of erosion resistance, it is desirable that the surface layer has a thickness of 5 μm or more, although it depends on the collision speed of substances that cause erosion such as water. Of course, when the speed of the colliding substance is slow, a sufficient effect may be obtained if it is 2 to 3 μm or more.

Since almost no erosion was confirmed in the test for the Si surface layer shown in 4), FIG. 12 shows the result of extending the test for the Si surface layer and applying a water jet continuously for 60 seconds.
The place where the water jet hit is a little polished and can be distinguished, but it can be seen that there is almost no wear.
From the above, high erosion resistance of the surface layer of the present embodiment was confirmed.

Based on the above results, an experiment was conducted to find appropriate conditions for the steam turbine application. The state of erosion was examined by applying a water jet to the coating film under each condition shown in FIG.
FIG. 13 shows, for each processing condition, the value of time integration of the current value of the discharge pulse (A · μs), which is a value corresponding to the energy of the discharge pulse of the condition (current value ie × Pulse width te), the thickness of the Si surface layer under the processing conditions, and the presence or absence of cracks in the Si surface layer.
As the processing conditions, a rectangular current pulse having a current value ie on the horizontal axis and a pulse width te on the vertical axis was used. The substrate used for this test is SUS630.
A Si electrode having a size of ρ = 0.01 Ωcm was used, and an electrode having a size within a range in which a discharge pulse was normally generated was prepared and tested.

  From the figure, the presence or absence of cracks can be seen as one of the conditions for forming the Si surface layer. The presence or absence of cracks has a strong correlation with the energy of the discharge pulse, and the time integral value of the discharge current corresponding to the energy of the discharge pulse is in the range of 80 A · μs or less. It can be seen that it is.

Of course, whether or not cracks occur depending on the processing conditions is also somewhat affected by the substrate.
For example, among materials called stainless steel, a material that is a solid solution such as SUS304 is relatively hard to crack, and a precipitation hardening type material such as SUS630 tends to crack slightly. Since a precipitation hardening type stainless steel such as SUS630 is generally used for the steam turbine, a desirable range free from cracks is narrower than that of an austenitic stainless steel such as SUS304.

From FIG. 13, there is the thickness of the Si surface layer as another forming condition of the Si surface layer.
As can be seen from FIG. 13, the thickness of the Si surface layer also correlates with the time integral value of the discharge current, which is equivalent to the energy of the discharge pulse. It can be seen that the thickness increases as the integral value increases.
The thickness mentioned here refers to a range where Si, which is an electrode component, is melted by the energy of discharge and enters.
The range of the influence of heat is determined by the magnitude of the time integration value of the discharge current, which is an amount equivalent to the magnitude of the energy of the discharge pulse, but the amount of Si that enters also affects the number of occurrences of discharge. When the discharge is small, it is natural that Si cannot sufficiently enter, so the amount of Si in the Si surface layer is small. On the contrary, even if discharge occurs more than enough, the amount of Si in the Si surface layer is saturated at a certain value, and no more increases.
When the amount of Si is small, the effect of the Si surface layer as described later may not be sufficiently obtained. The amount of Si was 3 to 11 wt% when Si was sufficiently contained in the Si surface layer. The Si surface layer formed more stably was 6 to 9 wt%. The Si amount mentioned here is a value measured by energy dispersive X-ray spectroscopy (EDX), and the measurement conditions are an acceleration voltage of 15.0 kV and an irradiation current of 1.0 nA. Further, the amount of Si is a numerical value of a portion showing a substantially maximum value in the surface layer.

The optimum amount of Si in the Si surface layer is 6 to 9 wt%. In this range, the treated surface is smooth, and there is almost no surface roughness that is the starting point of erosion. When Si enters the surface in an appropriate amount, the base material melted by the discharge and the Si material of the electrode can be solidified smoothly. When the amount of Si decreases, the function of smoothing the melted material decreases, and when it is less than 3 wt%, the unevenness when the solidified material is melted by solidification becomes more noticeable, and when water droplets collide It was found that there was a starting point of damage and the erosion resistance was lowered.
Conversely, in order to increase the amount of Si, it is necessary to increase the pulse width te, and it has been found that the unevenness of the surface also increases depending on the condition when the pulse width is increased.
It was found that when the Si amount was increased to 11 wt% or more, the unevenness of the surface was large, and the portion that was the starting point of damage increased.
From the above, it was found that the Si amount in the Si surface layer was 3 to 11 wt%, more preferably 6 to 9 wt%. The hardness of the Si surface layer in the range where the above effects were obtained was 600 to 1100 Hv.

As described later in paragraph 0042, since the Si surface layer treated according to the present embodiment has an amorphous structure, the erosion resistance is improved. However, the erosion resistance cannot be ensured simply by having an amorphous structure, and the surface roughness is an important factor as described above. As a result of investigation by the inventors, the relationship between the erosion resistance and the surface roughness of the present invention has been investigated, and it has been found that the erosion resistance increases as the surface roughness decreases. It is known that the surface roughness of a steam turbine blade is 10 to 20 μm. Then, when the above-mentioned erosion resistance evaluation of the surface roughness of the substrate on which the Si surface layer is formed and the Si surface layer formed so that the Si amount is 3 to 11 wt% on the surface was performed, Rz (maximum height) It was confirmed that the erosion resistance was good when the thickness was 20 μm or less. From the viewpoint of reliability, Rz is preferably 8 μm or less.
Although explained later, the method for measuring the surface roughness is as follows. The measuring apparatus used was a foam holy surf manufactured by TaylorHobson, and a standard stylus was used. The measurement length was 4.8 mm, the high-frequency cut op length was 0.8 mm, the bandwidth ratio was 100: 1, and the filter type was Gaussian. The measured value was based on JIS B0601: 2001.

The point that the amount of Si in the Si surface layer affects the surface roughness of the surface has been described. One example is shown in FIGS.
The processing under the same processing conditions with the Si electrode was performed at different times, and the surface of the Si surface layer (FIG. 14) and the cross section of the Si surface layer (FIG. 15) were observed.
Since all the processing is performed under the constant processing conditions, it can be considered that the processing conditions are substantially the same as the ratio of the number of generated discharges. That is, when the processing time is short, the number of discharges is small, and when the processing time is long, the number of discharges is large. (However, since the processing time varies depending on conditions such as the pause time, the required processing time changes if the pause time changes in order to generate the same number of discharge pulses.)
The treatment times for the Si surface layer shown in the figure are 3, 4, 6, and 8 minutes. The following can be said from the figure.
When the treatment time is short (3 minutes), there are still many irregularities on the surface, and it is observed that there are small protrusions on the surface. (Although illustration is omitted, if the length is shorter, there are more protrusion-like parts, and the protrusions become inconspicuous in about 3 minutes of processing time.)
It can be seen that as the processing time is increased, these irregularities and protrusions decrease and become smoother.
On the other hand, the cross-sectional photograph shows that the thickness of the Si surface layer hardly changes in the cross section from the processing time of 3 minutes to 8 minutes. When the amount of Si in each coating is analyzed, the surface layer with a treatment time of 3 minutes is about 3 wt%, the surface layer with a treatment time of 4 minutes is about 6 wt%, the surface layer with a treatment time of 6 minutes is about 8 wt%, and the treatment time is 8 minutes. Was about 6 wt%. When the treatment time is short, Si is not sufficiently contained in the surface layer. However, when the treatment time has passed to some extent (4 minutes under this condition), it has been found that Si enters almost enough and the surface becomes smooth. From the above, it can be seen that when the amount of Si is small, the smoothness of the surface is poor and 3 wt% or more is necessary, and more desirably 6 wt% or more is necessary.

Although explained later, the performance of the Si surface layer is discussed below.
There are two major modes of erosion. One is a mode in which the surface is greatly scraped off by the impact of water, and the other is a mode in which the surface is scraped off when the water is strongly hit and flows through the surface.
FIG. 16 shows the result of destruction of the Si surface layer when a water jet was applied to the Si surface layer having a thickness of 3 μm at 200 MPa for 60 seconds. It can be seen that although the traces that were finely peeled off are not visible, they are destroyed so as to be largely scraped off. This is considered to be a result of the Si surface layer being destroyed without being able to withstand the impact caused by the application of a large amount of water with a water jet, not the scratches scraped off by the collision of water. That is, when the Si surface layer is as thin as 4 μm or less, it is effective for a mode in which water is strongly hit and scratches the surface when flowing through the surface, but for a mode in which the surface is greatly scraped off by the impact of water. Indicates that the effect is small.
FIG. 17 shows a result of Stellite No 6 alone, which is a material having high erosion resistance, when a 90 MPa water jet is applied for 60 seconds. The figure shows a mode in which the surface is scraped off when the water is strongly hit and flows through the surface.

Next, the relationship between the thickness of the Si surface layer and the erosion resistance is shown in FIG.
As shown in the figure, when the thickness of the Si surface layer is 4 μm or less, the Si surface layer is thin when a water jet is applied at a speed of about sonic speed corresponding to the speed at which water droplets collide with the turbine blades in the steam turbine. It was found that the phenomenon that the film could not be tolerated and the surface was destroyed occurred with high probability.
The reason why the Si surface layer is thin is weak against impact, and when the Si surface layer is thick, the reason for strong shock is presumed as follows. That is, when the Si surface layer is thin, strain is gradually accumulated on the base material when impact is applied, and finally the fracture occurs from the grain boundary of the base material. However, when the Si surface layer is thick, the strain is Is difficult to reach the base material, and the base material is protected. On the other hand, the Si surface layer has a structure close to an amorphous structure, so there is no grain boundary and no breakage occurs at the grain boundary.
From this point of view, in order to increase the thickness of the Si surface layer, it is necessary to increase the energy of the discharge pulse, and in order to increase the thickness to 5 μm or more, the energy of the discharge pulse needs to be 30 A · μs or more. It was.

As described above, the erosion resistance can be increased by increasing the film thickness of the Si surface layer, but there is also a problem associated with increasing the film thickness, which deteriorates the erosion resistance. There are things to do. As described above, in order to increase the thickness of the Si surface layer, it is necessary to increase the energy of the discharge pulse. However, as the discharge energy is increased, the influence of heat increases and cracks are generated on the surface. Become. The crack becomes easier to enter as the energy of the discharge pulse increases, and as described above, the crack is generated on the surface when the pulse is processed with a pulse of 80 A · μs or more.
It was found that the erosion resistance is remarkably lowered when cracks are formed on the surface. FIG. 19 shows a state in which a crack has progressed by applying a water jet. If it continues further, a film will be destroyed greatly within a certain range. It was found that when the film was processed under a pulse condition of energy of 80 A · μs, the film thickness was about 10 μm, and this was the practical upper limit value of the Si surface layer for erosion resistance.
From the viewpoint of cracks, the relationship between the film thickness of the Si surface layer and the erosion resistance is illustrated in FIG. 18 and 20, it was found that the relationship between the thickness of the Si surface layer and the erosion resistance is as shown in FIG.

The above is summarized as follows. In order to form a Si surface layer having erosion resistance, the Si surface layer needs to be 5 μm or more, and for this purpose, the energy of the discharge pulse needs to be 30 A · μs or more.
On the other hand, in order to prevent cracks on the surface, the energy of the discharge pulse needs to be 80 A · μs or less, and therefore the Si surface layer is 10 μm or less.
As described above, in order to obtain erosion resistance, the thickness of the Si surface layer is increased to 5 to 10 μm with respect to the substrate having a surface roughness Rz of 20 μm or less, and the Si amount is set to 3 to 11 wt%. I found it necessary. The energy of the discharge pulse for forming the Si surface layer having this layer thickness was 30 A · μs to 80 A · μs, and the Si surface layer hardness at that time was in the range of 600 Hv to 1100 Hv.

By the way, the reason why the Si surface layer according to the present invention is excellent as the erosion resistance is considered as follows. The erosion resistance is generally said to have a strong correlation with hardness. However, as can be seen from the above evaluation results, there are many points that cannot be explained only by hardness. As an element other than hardness, the surface properties have an influence, and it has been found that the erosion resistance is improved closer to a mirror surface than a rough surface. The surface properties can be cited as the reason why the erosion resistance is excellent in the Si surface layer. The Si surface layer has a hardness of 600Hv to 1100Hv to some extent, and has a smooth surface. This is thought to affect the erosion resistance.
Furthermore, ordinary hard coatings (eg, hard coatings such as the above-mentioned TiC coating, PVD, CVD, etc.) have low toughness and the coating is destroyed by slight deformation, whereas the Si surface layer has high toughness and deformation. It is considered that one of the causes of the high erosion resistance is that it has a property that cracks and the like are not easily generated even if added. Further, it is considered that the crystal structure of the Si surface layer is also affected. The X-ray diffraction results of the Si surface layer formed under the conditions within the scope of the present invention are shown in FIG. In the figure, a diffraction image in the case where SUS630 as a base material and a Si surface layer are formed thereon is shown. As can be seen from the diffraction pattern of the Si surface layer, although the peak of the substrate is visible, a wide background in which formation of an amorphous structure is recognized is observed. In other words, the Si surface layer is amorphous, so that it can be considered that the fracture at the crystal grain boundaries, which are likely to occur with ordinary materials, hardly occurs.
In order to have an amorphous structure which is one of the conditions necessary for having the erosion resistance, the amount of Si is 1 to 20 wt%. If it is 1 wt% or less, an amorphous structure is not formed, and if it is 20 wt% or more, crystallization occurs.

Now, since it turned out that a high erosion-resistant surface layer is obtained by this Embodiment, an actual application technique is demonstrated.
In the following application technologies, the basic technology described so far will be described as a technology that is applied to actual applications, so it will not be repeated in the following description, but it is assumed that the technology described so far will be used. I refuse to be there.

  Prior to describing the manufacturing method and repair method of the steam turbine blade of the present invention, the actual state of the current steam turbine will be described. As described in the aforementioned patent document, erosion occurs in the steam turbine at a portion such as a leading edge portion of the moving blade. A portion where erosion of the current steam turbine occurs, particularly a front edge portion and a tip portion of a low-pressure turbine rotor blade, is coated with an erosion-resistant material such as stellite by brazing or welding. In the case of brazing, the part to be brazed on the wing side is recessed so that the plate can be accommodated, and a plate of erosion resistant material such as stellite is brazed so that the plate is accommodated. Is about 0.5 mm bulkier than the surface of the steam turbine blade. Usually, it is often used as it is. In some cases, stellite is built up at the tip by welding, but after that, a curved surface is created manually, so the shapes are almost different from each other.

Then, the manufacturing method and repair method of the steam turbine blade of this invention are demonstrated.
FIG. 23 shows how the Si surface layer of the present invention is formed on the rotor blade of a steam turbine, where erosion often causes a problem.
In the figure, 11 is a Si electrode, 12 is a steam turbine blade that is a member to be treated, and 13 is a surface layer containing Si formed on the surface of the steam turbine blade 12. The steam turbine rotor blade 12 is positioned and fixed by a jig (not shown). Although emphasized in the figure, the surface of the steam turbine rotor blade 12 on which the surface layer containing Si is formed is raised in a step of 0.5 mm. The material of the steam turbine blade 2 used in the present embodiment is SUS630.
In actual processing, if the root tree portion is fixed, it can be stably fixed.
When forming the surface layer by electric discharge, it is necessary to immerse the portion to be discharged in oil, so it is practically convenient to install a jig (not shown) in the processing tank for storing the oil.

In the figure, a Si electrode matching the shape of a part requiring erosion resistance is made and opposed to a steam turbine rotor blade in oil (not shown).
Even if the discharge is performed between the Si electrode and the counterpart material (turbine rotor blade) for a long time, the counterpart member (turbine rotor blade) is not damaged, and the shape may be made uniform by discharge. When coating with an erosion resistant material by welding, thermal spraying or brazing, the heat input is large and the member is deformed. However, with the method using this discharge surface treatment, there is almost no deformation, so if an electrode that matches the shape of the member can be formed, it is repeated as it is. Can be used.
Therefore, while the conventional method is a method that requires manual skill, in the present embodiment, since the machine performs the work, stable processing can be performed regardless of the person.

Although the surface layer having high erosion resistance can be automatically formed on the steam turbine rotor blade by the above method, it may be difficult to form a large area electrode.
In such a case, a thin electrode as shown in FIG. 24 is formed, and the entire necessary portion can be processed by scanning the electrode as the processing proceeds. In FIG. 24, the scanning direction is from the tip of the blade toward the root, but it goes without saying that the scanning direction is not particularly limited as long as a portion requiring processing can be processed.
Because the front edge of the steam turbine blade is curved, the electrode shape does not match the cross-sectional shape of the blade by simply scanning with the same shape of the electrode, but reducing the electrode thickness reduces the consumption of the electrode. It can be promoted and can easily follow the shape of the treated surface.

By the above method, a surface layer having high erosion resistance can be automatically formed on the steam turbine rotor blade. However, when the processing area is large, there is a problem that it takes a long processing time. In that case, the processing time can be shortened by dividing the electrodes as shown in FIG.
By treating the gap between the electrodes while moving the electrode slightly beyond the gap between the electrodes, a coating can be formed without gaps.

  Normally, a steam turbine blade is made by forging, then a detailed shape is created by cutting, etc., and then brazing or welding is performed to give erosion resistance, and then for distortion removal. After processing and heat treatment, it is finally manufactured in a process called finishing. By using the technique of the present invention, after making a rough shape by forging, make a detailed shape by cutting, etc., finish processing, and finally perform a process to form a Si surface layer, erosion resistance Can be granted. The process can be shortened and the cost can be greatly reduced. Further, as will be described later, by creating a shape that swells the portion that imparts erosion resistance, the subsequent repair can be performed only by excision of the damaged portion, and the repair work is simplified. The portion to be raised may be formed by cutting after making a rough shape by forging, or may be raised by overlay welding or the like on a blade having a shape as usual.

Next, the steam turbine blade manufactured by the above method and repaired at the place where the surface layer containing Si was formed (the place raised in a 0.5 mm step) and the repair method The turbine blades that can be reused will be described with reference to FIG.
FIG. 26 is a schematic diagram of one cross section in each process of repairing a portion where a surface layer containing Si is formed, and FIG. 26A shows a damaged Si surface layer. FIG. 26B shows a state in which the stepped portion is removed to the damaged depth by electric discharge machining, grinder, polishing, grinding, or the like. In the case of grinders, polishing, and grinding, the surface roughness of the base material before forming the Si surface layer is particularly important in order to further improve the erosion resistance of the Si surface layer and shorten the processing time for forming the subsequent Si surface layer. Although not specified, it is desirable that the surface roughness is equal to or less than that of the portion where the Si surface layer is not formed. The same applies to surface removal by electric discharge machining. In particular, when removing by electrical discharge machining using the Si electrode used in the present invention, the process of FIG. 26B can be omitted and the number of processes can be further reduced. An Si surface layer is formed on the surface finished in FIG. 26B as shown in FIG. In FIG. 26, a state in which damage has progressed to a deeper part than the Si surface layer is depicted, but when damage remains in the Si surface layer, if a discharge surface treatment is performed with the Si electrode, The surface is smooth and can be repaired. FIG. 27 shows a state in which cracks and damage generated by the water jet test are repaired by the above method as an example of repairing the generated erosion part.

  As described above, a layer having a micrometer order erosion resistance by discharge surface treatment as in the present invention is provided at the front edge of the tip of the steam turbine blade in advance (higher) in a step shape. This makes it possible to repair easily (reducing repair man-hours) many times until the stepped bulge disappears, and to fill the missing part of the material like overlay welding Therefore, there is no concern about a decrease in mechanical strength of the member, particularly at the boundary between the member and the built-up portion. As described above, the brazing of the erosion-resistant material is about 0.5 mm bulky. It won't be a big problem. Furthermore, the Si surface layer eliminates problems such as defects and delamination that are a concern during brazing.

  In this embodiment, the height of the raised portion that forms the Si surface layer is set to 0.5 mm. However, the height of the step is somewhat free, and is largely due to the convenience of parts that require erosion resistance. . As shown in FIG. 28, in the case of a steam turbine, if the bulge is 0.005 mm, the thickness of the Si surface layer is about 5 to 10 μm. Therefore, when there is no damage, a healthy Si surface layer without damage is formed. When it is formed again, it can be repaired only once. Further, as shown in FIG. 29, when the height is increased by 3 mm or more, the flow of steam flowing in the turbine is disturbed, so that the efficiency as a machine is lowered, which causes a problem. Therefore, the rise of the portion forming the Si surface layer of the steam turbine blade is preferably in the range of 0.005 mm to 3.0 mm.

The shape of the surface on which the Si surface layer is formed may not be a plane. Even if it is a curved surface adapted to the design of the steam turbine, the discharge surface of the Si electrode used for processing may be made to the shape or processed into the shape in advance. The same applies when creating a surface that forms the Si surface layer during repair (cutting out and creating a new surface). Although the swelled end is also represented as a right angle in FIG. 26, it may be gentle. In the case of a complicated curved surface such as the tip of a steam turbine, it may be thickened in advance as shown in FIGS. 30 and 31, for example.
As mentioned in paragraph 0044, since the steam turbine blade is somewhat free in shape, if it is in the range of 0.005 mm to 3 mm for the reason described in paragraph 0052, the blade as shown in FIGS. 30 and 31. Even if the tip becomes thick, it does not become a big problem.
However, in the free curved surface portion of the steam turbine blade, its dimensional shape must be taken into account. For example, if the diameter is raised to about 3 mm in a portion having a diameter of Φ10 mm, the curved surface shape is greatly changed. Since it will adversely affect the efficiency, it is better to keep it to about 0.500 mm which is about 5% of the diameter.

In the above paragraphs 0045 to 0053, the case where the portion where the Si surface layer of the steam turbine blade is formed is described as being raised, but repairing is also similarly performed for those that do not have a raised shape as in the conventional steam turbine blade. Is possible. However, in the case of repairing such a member, the portion where the Si surface layer is formed falls below the surroundings each time the repair is repeated.
If the drop is 2 mm or more, the flow of steam flowing through the turbine is disturbed, and the efficiency of the turbine is greatly reduced. If it is not 2 mm or more, the mechanical strength of the blade is reduced if it is thinner than half the original thickness of the blade. Therefore, such a repairing method can be carried out if the depth is 0 to 2 mm or the thickness ratio is 0.5 or more as a result of progressing by erosion or dropping by repairing.

As an embodiment, the case where the erosion-resistant component is applied to a moving blade of a steam turbine has been described, but it goes without saying that the erosion-resistant component can be similarly applied to other erosion-resistant components that require erosion resistance. .
For example, the same method can be used for a portion where the fluid inside the pipe is strongly hit or a portion that is likely to cause cavitation. Other applications include fuel injection components.

  The surface layer forming method according to the present invention is useful for application to anti-erosion parts.

  1 Si electrode, 2 member, 3 machining fluid, 4 DC power supply, 5 switching element, 6 current limiting resistor, 7 control circuit, 8 discharge detection circuit, 11 Si electrode, 12 steam turbine blade, surface layer containing 13 Si, 14 Si-containing surface layer damage, 15 Si-containing surface layer, 16 Swelled portion where steam turbine blade Si surface layer is formed, 17 Steam turbine blade main body, 18 Cut away so as to eliminate the damaged portion Further, a raised portion where the Si surface layer of the steam turbine blade is formed, 19 a newly formed surface layer containing Si, 20 members, 21 fleshing portions, 22 members, 23 fluffing portions, 24 members, 25 fluffing portions.

Claims (6)

Between the Si electrode arranged at a predetermined gap from the front edge of the tip arranged in the machining liquid, at the front edge of the tip of the steam turbine blade, which has been raised from the blade surface by machining or build-up processing. A steam turbine characterized in that an electric discharge is generated to form an Si surface layer having a surface roughness Rz of 20 μm or less and having an Si content of 1 to 20 wt% supplied from the Si electrode . The Si surface layer, a steam turbine according to claim 1, characterized in that it has a thickness 5~10μm to the tip leading edge. The Si surface layer, Si content 3~11wt%, the steam turbine according to claim 1 or claim 2, characterized in that the amorphous layer in the range of hardness 600～1100HV. The steam turbine according to any one of claims 1 to 3, wherein the leading edge of the tip is raised in a range of 0.005 to 3 mm from a blade surface. A method for forming a surface layer of the steam turbine,
A step raised to form a raised portion of a predetermined shape from the blade surface by machining or overlaying process,
The steam turbine in which the raised portion is formed is placed in the machining fluid, with respect to the raised portion, the Si electrode disposed a predetermined gap apart from the value of the time integral of the current value of the discharge pulse 30~80A A step of supplying a Si component from the Si electrode to the raised portion by generating a discharge pulse in the range of μs, and forming the Si surface layer having a Si content of 1 to 20 wt% with a surface roughness Rz of 20 μm or less. When,
The method for forming a surface layer of a steam turbine according to claim 1, comprising : A method for repairing a surface layer of the steam turbine ,
Grinding and polishing a raised portion formed in a predetermined shape from the blade surface by machining or electric discharge machining; and
Grinding, the raised portion which is polished and placed in a processing solution, the Si electrode disposed a predetermined gap spaced, discharge pulse value of the time integral of the current value of the discharge pulse is in the range of 30~80A · μs by generating the the steps of the supplying Si component into the raised portion of the Si electrode, forming the Si surface layer of the Si content 1 to 20 wt% or less surface roughness Rz20myuemu,
The method for repairing a surface layer of a steam turbine according to claim 1, comprising :

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