JPS59180003A - Moving blade of steam turbine - Google Patents

Abstract

PURPOSE:To obtain a blade that is excellent in strength at the joined section and will not be formed with an embrittled layer on the blade base due to the melting, by joining a Co base alloy, which is excellent in resistance to cavitation erosion, to the forward edge of the forward end section of the blade using the diffusion bonding process. 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 can occur more thereby protecting the forward edge. The diffusion bonding technique is used to join the shield (a) to the vane base (b). Therefore, a vane that is excellent in strength at the joined section and will not be formed with an embrittled layer due to the melting of the vane base (b).

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a rotor blade equipped with an erosion 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 cavitation erosion wear due to high-speed collisions of condensed water droplets containing C2 in the steam. For this reason, there is a lot of wear and tear on the starch, and the front edge of the tip is
As shown in Fig. 1, the erosion shield (a) is made of an alloy commonly known as stellite, which contains about 50% Co and has excellent cavitation erosion resistance. (b) is At brazed or welded (two-way jointed and secured. In the figure (c)
) is the wing embedded part.

By the way, in the above-mentioned erosion shield joining C, in the conventional AI brazing, the AI brazing is corroded by the water contained in the steam at 1 m during use, and the joint strength decreases. The stress at the joint due to vibration increases and the erosion shield peels off.

In addition, when TIG welding or BB wide welding is performed, the joint strength of C2 is higher than that of At brazing L2, but there is a brittle layer at the molten joint between the Co-based alloy of the erosion shield and the 120R-based copper of the wing base. During use, vibrations may cause cracks to form in the brittle layer of this joint, causing the erosion shield to peel off.

In particular, when a wing base C containing Fe as the main component and an erosion shield containing Co as the main component are provided, Fθ ions and CO ions mutually cause an electrode reaction at the joint C2.
As a result, the entire blade is eroded, further accelerating the growth of cracks.

[Object of the present invention] The present invention has been made in view of the above points, and includes an erosion shield formed by diffusion bonding a cobalt-based alloy having excellent cavitation erosion resistance at least in a portion of the leading edge of the blade tip. This provides a distinctive steam turbine final stage rotor blade.

[Summary of the present invention] The present inventors have developed a dynamic system having the above-mentioned erosion shield.
After intensive research, we found that if a cO-based alloy with excellent cavitation erosion resistance is bonded to the wing base using the diffusion bonding method, the strength of the joint will be superior to C2, and the wing base f unit will be bonded. It was discovered that a good blade without the formation of a brittle layer due to molten S2 could be obtained, and the present invention was invented. In particular, for the entire blade C2 of Fe-based alloy, Fe, CO
By performing diffusion bonding using a filler metal other than the N1 group, for example, a useful method for suppressing erosion of the wing base due to the electrode reaction C2 can be obtained.

Diffusion bonding is a method of joining metals by heating the joint to a temperature lower than the melting point of the base material, mainly utilizing the diffusion phenomenon of elements, and obtaining a joint with a strong K equivalent to that of the base material. . Diffusion bonding methods can be roughly divided into two types: in-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. This is a method in which the base metals are deformed and brought into close contact with each other, and then a diffusion heat treatment is applied to homogenize the joint.
uid PhaBeBondlnp ) l AD method (
Actlv, 2tea Diffusion BOnd
This method is also called ``inp'', and the method that has been mainly used in the past is as follows.

First, as a filler metal for liquid phase diffusion bonding, a filler metal having a thickness of several tens of micrometers is typically used to add melting point lowering elements such as Ni-based alloy c, B, p, and st. Two intervening. These filler metals are
It melts at a temperature several tens of degrees lower than the melting point of the base metal (for example, N1-based alloy, Fe-based alloy, etc.), and therefore the joint is heated to a temperature higher than the melting point of the filler metal and lower than the melting point of the base metal. From step 2, the filler metal is melted and wetted onto the base metal to first obtain the effect of the C2 filler metal. B, Si, P
etc. are diffused 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.
Since only a small pressing force is required, members with complex shapes can be easily joined. There are many others. In particular, in the liquid phase diffusion bonding method, compared to the solid phase diffusion bonding method, the C filler metal melts during bonding and fills the minute gaps in the bonded area, so there is no need for pressurization in principle. In addition, since the joining surface finish accuracy can be relaxed, it is more effective for joining complex-shaped members.

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

The joint surfaces of the desired wing base material and the Co-based alloy member with excellent cavitation erosion resistance f2 are polished without being separated, and then washed together with the filler metal using lubricant.

Next, each of the materials is fixed in close contact with each other. As a filler metal supply method.

Usually, this amorphous thin plate or alloy powder hardened into a sheet shape with an organic binder or the like is used, but there are cases where special cleanliness is required or the shape of the joint surface is complicated, and the filler metal is used. If it is difficult to fix a thin plate, for example, vapor deposition method (Japanese Patent Application No. 87429/1989) may be used.
There is also a method of supplying using the LPC method.

In addition, for filler metal rods, for example, Fe is used for the currently widely used s 120r m '2.

For example, it is useful to use filler metals other than metals mainly composed of CO, such as filler metals mainly composed of Ni. That is, when diffusion bonding is performed using a filler metal containing ll1e or co as a main component, either the Fe-based wing base or the OO-based erosion shield material becomes F.
Since it is adjacent to the e- or aO-based filler metal, when the blade is used (-5Fe ions and O.

An electrode reaction of ions occurs, resulting in the inconvenience that the F'e base material is eaten away. However, for example, by performing diffusion bonding using a filler metal containing Ni as a main component, a Ni-rich layer is formed between the Fθ-based base thread base and the CO-based erosion shield, and this 1- layer plays the role of a barrier. The filler metal used here can be any metal as long as it can act as a barrier between the wing base and the erosion shield and is suitable for diffusion bonding.

Next, the tightly fixed members are heated and held in an inert atmosphere. The pressure may be 0101 to 50 Kt/j. The pruning atmosphere may be an oxidation-preventing atmosphere such as vacuum or inert gas. The temperature is selected from two types, 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 600° to 1300°C.The holding time is also selected in the same way. However, it usually takes 1 minute or more.
It takes about 100 hours.

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 transferred to another inert atmosphere and reheated to perform diffusion heat treatment.

The present invention has a CO-based erosion shield as described above. A steam turbine final stage rotor blade can be obtained.

Of course, the base material of the final stage driving shaft of the steam turbine according to the present invention 1'' may include, in addition to the above-mentioned 12 Or base steel, a Ti alloy.

[Example of the Invention] The effectiveness of the present invention 11 was investigated using a simple-shaped test piece.

120r fl14 (11,
30r -2,5N1-o, 3v 0.6Mo -0
,13c -1,6Mn -0,2Si-0,03N-
A test piece with the remainder Fe -) and a CO with a diameter of 13 mm and a length of 5 mm.
Base alloy (commonly known as stellite: 5.ONi -28,00
A test piece of r-20, Ow-0,90a-remainder co-) was prepared, and the joint surfaces of both were polished with #600 emery paper, and then thoroughly degreased and cleaned with trichloride and acetone.

Also, a 40 μm thick filler metal with a composition of 150r 4B 'l'i part N1 was degreased and cleaned using trichlene and acetone. Next, these test pieces and filler metal were closely fixed and s2XIOTO
rr vacuum hot press. Further, in C2, the joint portion was pressurized to 0.1 V4/- and held at 1180° C. for 1 hour.

Thereafter, heat treatment was performed at 1050°C for 2 hours and at 620°C for 2 hours, followed by gas cooling.

In the thus obtained bonding material, a Ni-rich layer of approximately 40 μm was formed between the 512or steel test piece and the Stellite test piece, and no brittle layer was observed in the test piece.

Further, the bonding strength is 10 to 30 Kf/- or more at room temperature, which is 3 to 10 times the strength of conventional Ap solder.

Furthermore, when a corrosion test was conducted on the joint, there was almost no corrosion due to moisture, as seen in AJ brazing, and the corrosion test results were good.

RuO Figure 1

Claims (1)

[Claims] (1) A steam turbine rotor blade characterized by having at least an erosion shield formed by diffusion bonding a CO-based alloy with excellent cavitation erosion resistance at the leading edge of the blade tip.