JPS6396233A - Steam turbine moving blade and its production - Google Patents

Abstract

PURPOSE:To obtain a steam turbine moving blade having excellent strength characteristics and showing superior erosion resistance comparable to that of stellite, by precipitating a hard phase in an alpha-phase in the vicinity of a surface, to be in contact with working steam, of a steam turbine moving blade having an alpha+beta structure of a Ti-6Al-4V alloy as base material. CONSTITUTION:A material for a steam turbine moving blade composed of an alpha+beta phase of a Ti-6Al-4V alloy is formed. Subsequently, the surface, of this moving blade, to be in contact with working steam is subjected to dry polishing work, e.g., by dry belt polishing of grain size No.80. In this way, the hard phase 2 is precipitated in the alpha-phase 1', in the vicinity of the polished surface, in the alpha+beta phase 3 constituting the material as illustrated. As a result, the steam turbine moving blade having superior characteristics as mentioned above can easily be manufactured in high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a titanium alloy rotor blade for a steam turbine, and particularly to a rotor blade with improved erosion resistance and a method for manufacturing the same.

[Conventional technology]

Conventionally, measures to prevent erosion in the final stage of the titanium alloy rotor blades of thermal power steam turbines have been taken using titanium β alloys, as described in "Nuclear Thermal Power Generation" Vol. 31, No. 9, "Experience with Titanium Used in Turbines". Thermal spray overlay technology for rotor blades is well known.

In recent years, in the steam turbines of commercial power generation plants,
Capacity is increasing to improve efficiency.

Along with this, the size of steam turbines has progressed, and in particular, it has become necessary to make the final stage blades of the steam turbine longer. Currently, 12% Cr1H1 is often used as a rotor blade material, but it is limited by the allowable rotation speed due to its centrifugal strength.
The limit that can be designed is that the centrifugal force is approximately several thousand times the weight of the blade due to its specific gravity and strength, that is, the blade length is approximately 31 to 35 inches for 3600 rpm, and 4 inches for 3000 rpm.
It is about 0 inch. For longer blades, it is necessary to use a material instead of 12% Cr steel, that is, a titanium alloy. Since titanium alloy has a high specific strength, that is, a ratio of strength/density, the blade can be made longer than 12% Crfi.

Steam turbines for thermal power are usually high-pressure turbines.

It consists of an intermediate pressure turbine and a low pressure turbine.

The steam generated in the boiler converts thermal energy into kinetic energy and performs work in each of the above turbines in order, but as a result, near the final stage, the steam reaches a wet region, and water droplets are present in the steam. Become.

These water droplets cause erosion of the rotor blades, and in the worst case, lead to damage to the rotor blades. As a countermeasure for this, 12
In the case of a %Cr steel rotor blade, Go-based alloy Stellite is attached to the tip of the rotor blade by silver brazing or welding to prevent erosion.

For titanium alloy blades, as a measure to prevent erosion, a low-density titanium-based β alloy instead of Stellite, such as T i -15M o -5Z β alloy, is thermally sprayed overlay on the titanium alloy blade to prevent erosion. There is.

Regarding the above-mentioned techniques for preventing erosion of titanium alloys, deformation of the rotor blade by performing thermal spray overlay, or
If the adhesion between the built-up part and the rotor blade is not perfect, there will be problems such as cracks occurring in the joint during operation.

[Problem that the invention seeks to solve]

As mentioned above, in order to make the blades of a steam turbine longer, titanium alloy rotor blades, that is, Ti, -6Al-4V alloy, are used because of their manufacturability and workability.

FIG. 3 is a chart showing the relationship between the results of a cavitation test commonly used to evaluate erosion resistance and the hardness of the target material. Ti-6Al-4v alloy contains 12% Cr
It has better erosion resistance than M alloy, but as shown in the figure, it is more susceptible to erosion than Stellite (indicated by Δ), which is the erosion prevention material for conventional 12% Cr rotor blades. It is also an erosion prevention material for titanium alloys. Ti-15Mo-52r-3An or T
i-15Mo-5Zr also has inferior erosion resistance compared to stellite.

FIG. 3 shows the relationship between erosion resistance and hardness, and the tendency is that the higher the hardness, the better the cavitation resistance. However, for example, 12%Cr
Steel and Ti-6AA-4V alloy or stellite and β
Alloy (Ti-15M.

-5Zr-3AQ, Ti-15Mo-5Zr), some have excellent cavitation resistance even if they have low hardness, and as shown in this figure, Stellite, which has lower hardness than β alloy, Excellent cavitation resistance.

Therefore, as a titanium alloy cavitation prevention material, it is desired to develop a titanium material that has a cavitation resistance mechanism similar to that of stellite.

The present invention has been made in view of the above-mentioned circumstances, and has a base material strength suitable for use as a steam turbine rotor blade.

Moreover, it is an object of the present invention to provide a steam turbine rotor blade having a surface layer with excellent erosion resistance, and a method for manufacturing the same.

[Means for solving problems]

Ti-6A Q- used for steam turbine rotor blade material
4V alloy becomes various structures by heat treatment.

Usually, it is manufactured by the manufacturing process shown in FIG. 4, and its structure becomes a pro-eutectoid α phase and an acicular α+β structure shown in FIG.

This structure is the best as a base material for steam turbine rotor blades in terms of strength, toughness, fatigue strength, etc. In order to improve erosion resistance, it is desirable that the structure of this base material is not changed.

The steam turbine rotor blade of the present invention, which was created in response to these demands, has a steam turbine rotor blade whose base material is the α+β structure of Ti-6AI2 4V alloy, in which the blade is in the α phase near the surface where the rotor blade contacts the working steam. It is characterized by forming a thin layer with excellent erosion resistance by precipitating a hardened phase.

Further, the method for manufacturing a steam turbine rotor blade of the present invention, which has been created to be suitable for manufacturing the rotor blade according to the above-mentioned invention, first
The material of the steam turbine rotor blade is made of the α+β phase of i-6Al-4V alloy, and the surface of the rotor blade that comes into contact with the working steam is dry polished, and the polished surface of the α+β phase that made up the material is It is characterized in that a hardened phase is precipitated in the adjacent α phase.

[Effect]

The α+β phase base material has strength characteristics suitable for a rotor blade, and the precipitated hardened layer exhibits excellent erosion resistance.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure shows Ti manufactured by the manufacturing process shown in Figure 4.
- The surface of steam turbine rotor blades made of 6Al-4V alloy has a grain size of 8
The structure is shown after being finished polished by No. 0 dry belt polishing. This structure is similar to the T i -6A shown in FIG. 2 without polishing (or with surface finishing by wet polishing).
Unlike the structure of Q-4V alloy (that is, the set m consisting of α phase 1 and α + β phase 2), a hardened phase 2 is generated in the α phase 1. The erosion resistance of the structure in which this hardened phase 2 is generated is ,
As shown by the mark ◎ in FIG. 3, it is significantly improved compared to the Ti-6Al-4v alloy and comparable to Stellite. That is, the effect of this structure is comparable to the erosion-resistant mechanism of stellite, and it works effectively as a titanium-based erosion-resistant material.

The depth at which this structure is formed can be arbitrarily selected up to a depth of about 0.1 m+11 m, depending on the pressing force during belt polishing and the polishing time. Therefore, erosion-resistant surface treatment can be performed without impairing the integrity of the base material.

〔Effect of the invention〕

The steam turbine rotor blade of the present invention has the excellent strength properties of Ti-6AΩ-4v alloy, and exhibits erosion resistance comparable to Stellite.

According to the method of the present invention, the steam turbine rotor blade according to the above invention can be manufactured easily and with high quality, and since thermal spraying, welding, etc. are not used, there is no undesirable thermal effect on the base material. or cause poor weld penetration,
There is no risk of the formation of an oxide film or its entrainment, and uniform product quality can be guaranteed.

[Brief explanation of the drawing]

FIG. 1 is a microscopic structure diagram showing the structure near the surface of a T i -6A Q-4V alloy steam turbine rotor blade material polished by a dry belt. FIG. 2 is a microscopic microstructure diagram of a turbine rotor blade material made of Ti-6Al-4V alloy and subjected to no treatment and wet polishing. FIG. 3 is a chart showing the relationship between cavitation weight loss and hardness, and FIG. 4 is a block diagram showing the manufacturing process of a steam turbine rotor blade. 1.1'...α phase, 2... hardened phase, 3... α+β
phase.

Claims (1)

[Claims] 1. In a steam turbine rotor blade whose base material is an α+β structure of a Ti-6Al-4V alloy, a hardened phase is precipitated in the α phase near the surface of the rotor blade in contact with the working steam to improve durability. A steam turbine rotor blade characterized by the formation of a thin layer with excellent erosion resistance. 2. The material of the steam turbine rotor blade is made of the α+β phase of Ti-6Al-4V alloy, and the surface of the rotor blade that comes into contact with the working steam is dry polished to polish the α+β phase that made up the material. A method for manufacturing a steam turbine rotor blade, characterized in that a hardened phase is precipitated in an α phase close to a surface.