JPS59180004A - Moving blade of steam turbine - Google Patents

Abstract

PURPOSE:To produce efficiently a moving blade that has a shield and is excellent in strength at the joined section, by joining an erosion shield and a shield support using the diffusion bonding technique, and welding the shield support and a blade base. CONSTITUTION:The last stage moving blades of a steam turbine will be wasted due to cavitation erosion by high speed impingement of condensed water droplets contained in steam. To overcome this, an erosion shield (a) of a stellite alloy containing about 50% Co that is excellent in resistance to cavitation erosion is joined to a 12-Cr base steel of the blade base (b) at the forward edge of the forward end section of the blade where wastage will occur more thereby protecting the forward edge. To join the shield (a) to the blade base (b), first the shield (a) is joined to the shield support (c) by the diffusion bonding technique, and then the shield support (c) and the blade base (b) are welded. Thus, an article that is high in strength at the joined section can be obtained highly efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical distribution of the invention] The present invention relates to a rotor blade equipped with a two-lotion shield used as a low-pressure final stage rotor blade of a steam turbine.

[Technical background of the invention and its problems]

The final stage rotor blades of a steam turbine suffer from cavitation erosion due to high-speed collisions of condensed water droplets contained in the steam. For this reason, the leading edge of the blade tip, which is subject to a lot of wear and tear, is equipped with an erosion shield (as shown in Figure 1) made of an alloy commonly known as stellite, which contains about 50% Co, which has excellent cavitation erosion resistance. a)
It is protected by bonding it to the 12Cr base (BL), which is the wing base, using Ag solder or welding.

By the way, in the conventional Ag brazing method used to join the erosion shield, the Ag solder is corroded by the moisture contained in the steam during use, reducing the joint strength. The stress at the joint increases and the erosion shield peels off.

Also, if TIG welding or IDE welding is performed,
Although the joint strength is higher than g-brazing, an embrittled layer forms at the molten joint between the CO-based alloy of the erosion shield and the T2 Cr-based steel of the wing base, and vibrations during use cause the embrittled layer to break away from the joint. There are inconveniences such as cracks occurring and the two lotion shields peeling off.

On the other hand, diffusion bonding can be considered as an alternative to conventional Ag brazing and welding, but the length is approximately 17 mm.
M. When diffusion bonding an erosion shield to the final stage rotor blade, which has a width of 20 to 30 cm, the vacuum chamber for diffusion bonding is very large, making it difficult to work, and it takes a long time to remove surface absorption gas. There are industrial disadvantages such as high heat consumption and large heat loss due to the large size of the heated object.

[Object of the present invention]

The present invention is based on the above-mentioned points, and is made of a CO-based alloy having excellent cavitation erosion resistance.A two-layer erosion shield and an erosion shield support are diffusion-bonded, and the two-lotion shield support and The present invention provides a steam turbine final stage rotor blade characterized by having a structure in which a blade base body is welded and joined.

As a filler metal for liquid phase diffusion bonding, a filler metal with a thickness of several tens of micrometers, typically made by adding melting point lowering elements such as B, P, and 8i to an alloy mainly composed of Ni, is interposed in the bonding part. . These filler metals are
For example, Ni-based alloys, Fe-based alloys, etc.) are melted at a temperature several tens of degrees lower than the melting point of the filler metal. Wet the base metal by melting it to obtain the effect of soldering. Thereafter, the temperature is maintained for a longer period of time to diffuse B, 8i, P, etc. into the base material. At that time, the filler metal undergoes an isothermal solidification phenomenon and forms a strong joint.

The characteristics of the diffusion bonding method are: (1) No brittle layer is created due to melting of the base material. ■Excellent joint strength. ■Compared to pressure welding, etc., the pressing force is small, making it easy to join complex-shaped members. There are many others.

In particular, the liquid phase diffusion bonding method, compared to the same phase diffusion bonding method,
During joining, the filler metal melts and fills the minute gaps in the joint, so in principle there is no need to apply pressure, and the joining surface finish accuracy can be relaxed, making it more effective for joining complex-shaped parts. .

[Summary of the invention]

That is, the steam turbine final stage rotor blade according to the present invention
As shown in the figure, this is a steam turbine final stage rotor blade having a structure in which the erosion shield (a) and the erosion shield support (C1) are diffusion bonded, and then the erosion shield support is welded to the blade base (b). .

Diffusion bonding is a method in which the base metals are heated to a temperature lower than the melting point of the base metal (g), and the base metals are joined using the diffusion phenomenon of the elements to obtain a joint that has the same strength as the base metal. . Diffusion bonding methods can be roughly divided into two types: solid phase diffusion bonding and liquid phase diffusion bonding. In the former method, the base metals are connected directly or a thin filler metal is interposed between the base metals, and then the joint is heated and pressurized to a temperature below the melting point of the base metal, causing the surface of the base metal or filler metal at the joint to creep. In this method, after the base materials are deformed and brought into close contact with each other, a diffusion heat treatment is further performed to homogenize the joint.

The latter is the TLP method (Trasient Liquid
Phase Bonding), AD method (A
activated Diffusion Bondin
g), etc., and the methods commonly used in the past are as follows.

Next, a steam turbine final stage rotor blade having an erosion shield according to the present invention will be explained.

First, the desired erosion shield support and anti-cavity 7-
After polishing the joint surfaces of CO-based alloy members with excellent erosion properties, the joint surfaces of each member and the filler metal are degreased and cleaned. Next, each of the materials is fixed in close contact with each other. The filler metal supply method is several tens of μm.
Amorphous thin plate materials with a thickness of 14 mm or sheets made of alloy powder with an organic binder are often used, but special cleanliness is required or the joint surface shape is 14 mm.
If it is difficult to fix the thin filler metal due to roughness, for example, vapor deposition method (Japanese Patent Application No. 87429/1988) may be used.For example, in contrast to the currently widely used 12Cr base, Fe may be used.

For example, it is useful to use filler metals other than metals containing CO as a main component, such as filler metals containing N1 as a main component. In other words, when diffusion bonding is performed using a filler metal containing Fe or CO as the main component, either the Fe-based wing base or the CO-based erosion seal)' JFA,
Since it is adjacent to Fe or Co-based filler metal, an electrode reaction between Fe ions and Co ions occurs during use, resulting in the inconvenience that the Fe-based base thread substrate is eroded. However, for example, by performing diffusion bonding using a filler metal containing Ni as a main component, Fe base and Co
A Ni-rich layer is formed in the middle of the base erosion shield, which acts as a barrier and suppresses electrode reactions. The filler metal used here is of any type as long as it can serve as a barrier between the wing base and the lotion shield and is suitable for diffusion bonding.

Then, it is heated and held in a clean, inert atmosphere while being tightly fixed. The pressure is 0. 9/- is fine for O1-50. Further, the atmosphere may be an oxidation-preventing atmosphere such as a vacuum or an inert gas. The temperature is selected depending on the type of filler metal and the type of diffusion bonding (solid phase or liquid phase diffusion bonding), but is usually in the range of about 6000 to 1300°C. The retention time is chosen similarly, but typically ranges from 1 minute to 100 minutes.
It takes about an hour.

Note that during this bonding, when the bonding is completed at the bonded portion, the pressure may be removed and the integrated structure may be moved to another inert atmosphere and reheated to perform diffusion heat treatment.

In the manner described above, an erosion shield support having a Co-based erosion shield can be obtained.

Next, the erosion shield support is welded to the wing base by conventional 'I'IG welding or EB welding. In this way, a steam turbine final stage rotor blade according to the present invention equipped with an anti-cavitation erosion shield is obtained.

Note that, of course, the base body of the steam turbine final stage rotor blade according to the present invention includes Ti alloys in addition to the above-mentioned 12cr base steel.

[Example of the present invention]

CO-based alloy (Stellite:
5.0Ni-28,0Cr-20,0W-0,9C-remaining Co) member, and 1 of the shape shown in FIG. 2(C)
2cr@(L 1.3Cr-2,5N i -0,3
V-0,6Mo-0,13C-1,6Mn-0,2S
The bonding surface of the (7) John shield support made of i-0,03N (balance of Fe) was polished with #600 emery paper, and then degreased and washed with trichlene and acetone.

Further, a filler metal of 15cr-48-remainder Nj having a thickness of 40 μm was similarly degreased and cleaned with trichlene and acetone. Next, these members and filler metal were closely fixed and heated at 1180° C. for 1 hour in a 2×10 −’ vacuum. Pressure was applied at an average of 0.2 Ky/-. Thereafter, heat treatment was performed at 1050°C for 2 hours and at 620°C for 2 hours, followed by gas cooling.

The thus obtained bonding material has approximately 40 μm of N1 between the 12 cr copper support and the stellite erosion shield.
A layer rich in silver is formed, no brittle layer is observed, and the bonding strength is 3 to 10 times that of conventional Ag soldered products.
It had a strength of 0q/- or more.

Further, when a corrosion test was conducted on the joint, there was no corrosion due to moisture, which is the case with Ag solder, and the results of the corrosion test were also good.

Next, the support body with the erosion shield diffusion bonded was EB welded to a model blade base made of 12Cr steel similar to the support body in the atmosphere to obtain a steam turbine final stage model blade according to the present invention equipped with an erosion shield. .

[Brief explanation of the drawing]

FIG. 2 is a perspective view of a conventional rotor blade, and FIG. 2 is a perspective view of the rotor blade of the present invention. Agent: Patent attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 2

Claims (1)

[Claims] An erosion shield made of a cobalt-based alloy with excellent cavity erosion resistance and an erosion shield support are diffusion bonded, and the erosion shield support and the substrate are welded and bonded. steam turbine rotor blades.