KR100340806B1 - Method for extending lifetime of gas turbine hot parts by hot isostatic pressing - Google Patents

Abstract

The present invention uses a Ni-based superalloy to remove defects in the interior of high temperature parts such as gas turbine blades, which are made by vacuum precision casting, and to optimize the microstructure, thereby increasing the service life of the high temperature parts. The present invention relates to a method for extending the service life of gas turbine high temperature parts using isocompression technology. The high temperature isocompression treatment method is composed of four stages: vacuum heating, elevated temperature boost, constant temperature maintenance, and cooling. In particular, in the present invention, by performing the cooling process divided into two stages to finely precipitate the grain boundary and the γ 'strengthening phase to improve the high temperature strength. Accordingly, in the first step, the controlled cooling step 410, the cooling rate is minimized to 5 ° C. or less per minute in a temperature range of 1200 ± 20 ° C. to 1120 ± 20 ° C. to deform the grain boundary of the material into a sawtooth shape so as to be high temperature. Increases creep strength. Thereafter, in the second step, the uniform rapid cooling step 420, by uniformly rapid cooling to more than 100 ℃ per minute in a temperature range of 1120 ± 20 ℃ to 30 ℃ fine precipitates the high temperature enhanced phase γ 'to increase the high temperature strength . In addition, after the high temperature isocompression treatment is further performed after the heat treatment (500) for 8 hours or more at 850 ± 30 ° C. in a vacuum atmosphere, the secondary γ 'is further finely precipitated to further improve the high temperature strength. It has the advantage of being able to.

Description

Method for extending lifetime of gas turbine hot parts by hot isostatic pressing}

The present invention is to control the cooling process in the high temperature isocompression process and to apply the post-heat treatment process in combination to effectively remove the defects in the gas turbine blade material and to optimize the microstructure to extend the life of high temperature gas turbine components It is about a method. In particular, the present invention is to improve the high temperature isostatic compression process consisting of vacuum heating, elevated temperature, constant temperature, cooling process to effectively remove the defects present in the gas turbine blade, optimize the microstructure to improve the mechanical properties A method for improving the mechanical properties by further modifying the secondary γ 'phase by further modifying the grain boundary by controlling the cooling process, and further applying a method of finely depositing γ' phase, which is a high temperature strengthening image, and post-heat treatment. will be.

In general, since the gas turbine blades are used at a high temperature, defects on the surface as well as defects occur in the material when they are used for a long time, and microstructures are also transformed and deteriorated. Conventionally, the vacuum heat treatment was performed as a method of removing defects and microstructures in the material, but these techniques can control the γ 'phase and the microstructure, but defects formed in the material cannot be completely removed. There is this.

Therefore, in order to solve the above problems, the present invention improves the high temperature isothermal compression process to remove the defects in the material and at the same time optimize the shape control of the grain boundary and the precipitation of the γ 'reinforcement phase, and the post heat treatment process. The purpose is to extend the service life of high temperature parts used in gas turbines by carrying out the combined process of applying them together.

1 is an overall process diagram for the high temperature isocompression treatment according to the present invention,

Figure 2 is a detailed process diagram for the cooling process and the post-heat treatment process in Figure 1,

3 is a graph showing a relationship of temperature, pressure, and time for each process of FIG. 1;

Figure 4 is a graph showing the relationship between temperature, vacuum degree and time for the post-heat treatment process shown in FIG.

5 is a picture showing the effect of the present invention is a photograph showing a state in which the shape of the grain boundary is controlled in the shape of a sawtooth,

Figure 6 is a picture showing the effect of the present invention is a photo finely formed primary γ 'in the material,

7 is a view showing the effect of the present invention on the fatigue (fatigue) strength,

8 is a view showing the effect of the present invention on the creep strength.

<Explanation of symbols for main parts of drawing>

A: Controlled cooling process curve B: Uniform rapid cooling process curve

10: tooth shape grain boundary 20: finely deposited γ 'shape

30: second precipitated γ 'shape

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 shows an overall flow chart of the high temperature isocompression treatment process of the present invention.

As shown in the drawing, the high temperature isocompression treatment process is a process for discharging harmful gases largely, the vacuum heating process 100 for heating at 300 ° C. for at least 30 minutes in a vacuum atmosphere, and a temperature section of 1200 ± 50 ° C. Temperature raising step to raise the temperature to 100MPa or more, and to maintain a constant temperature for more than 4 hours in the temperature range to remove defects by plastically deforming casting bonds and pores at a temperature below which local melting proceeds. The constant temperature maintenance process 300 and the cooling process 400 is made up.

The cooling process 400 and the post-heat treatment process 500 after finishing the cooling process will be described in detail with reference to FIGS. 2 to 8.

2 is a flowchart schematically illustrating a cooling process 400 and an additional post-heat treatment process 500. Figure 3 is a high temperature isostatic compression process consisting of the vacuum heating process 100, the temperature rising step 200, the constant temperature holding step 300, the cooling step 400 of the present invention as a relationship between time, temperature and pressure It is a graph. 4 is a graph showing the post-heat treatment process in relation to time, temperature, and pressure after the high temperature isothermal compression treatment. This will be described with reference to FIGS. 2 to 4.

First, as shown in Figure 2, the cooling process 400 is made of a process of greatly improving the high temperature strength by controlling in two stages of the control cooling 410 and uniform rapid cooling (420).

That is, in the control cooling step 410, which is the first step, after maintaining constant temperature for 4 hours or more at 1200 ± 20 ° C, γ ', which contributes to improving the high temperature strength of the Ni-based superalloy, as shown in the' A 'part of FIG. By dissolving in the γ-base and slowly cooling (minimizing) to 1120 ± 20 ° C to 5 ° C or less per minute and then maintaining it for 30 minutes or more, the grain boundary shape can be deformed into a sawtooth shape to increase the high temperature creep strength.

Then, in the second step, the uniform rapid cooling step 420, as in the 'B' portion of Figure 3, in the temperature section (1120 ± 20 ℃ to 30 ℃) or less in the uniform rapid cooling above 100 ℃ per minute Therefore, the deformation of the material is suppressed, the grain boundary of the sawtooth shape is not deformed, and the high temperature strength of the material is improved by suppressing the fine distribution by inhibiting the growth of the γ 'phase, which is a high temperature strengthening image that precipitates during the cooling process. In the uniform rapid cooling step 420, in order to maintain the maximum strength of the Ni-based superalloy at high temperature, the γ'-reinforced phase is finely precipitated to an average size of about 0.5 μm and then uniformly cooled to 100 ° C. or more so as not to grow.

After performing the two-step control cooling process (400) as described above, γ 'remaining in the microstructure of the gas turbine blade material is not completely precipitated by rapid cooling, thereby transforming the matrix into an equilibrium state, and the fine secondary γ In order to further improve the high temperature strength in phase, as shown in Figure 4, by further performing a post-heat treatment (500) that is heated to 850 ± 30 ℃ in a vacuum atmosphere and maintained for more than 8 hours, it is possible to further improve the high temperature strength have. Such a heat treatment process of the present invention is made by using a specially made high temperature high pressure heat treatment apparatus is a heat treatment operation corresponding to this according to the set pressure, temperature, time.

FIG. 5 is a photograph analyzing the effect of the present invention. As a result of observing the microstructure using an optical microscope after high temperature isostatic compression treatment, it can be seen that the grain boundary is deformed into a sawtooth shape 10.

Figure 6 shows that the microstructure of the gas turbine blade after high temperature isostatic compression treatment in the present invention by using a scanning electron microscope it can be seen that the γ 'enhanced phase is fine and uniformly distributed. Here, reference numeral '20' denotes a finely precipitated γ 'shape and' 30 'denotes a secondary precipitated γ' shape.

FIG. 7 shows that the fatigue property is greatly improved by more than 6 times due to the removal of internal defects and the optimization of the microstructure after the high temperature isothermal compression treatment and the post heat treatment.

Figure 8 shows that the creep properties are improved by more than three times due to the removal of internal defects and the optimization of microstructure after high temperature isothermal compression and post heat treatment.

As described above, in the present invention, by controlling the cooling process in two stages, as shown in FIG. 5, the grain boundary, which is the main factor of high temperature strength, is transformed into a sawtooth shape as desired, and the γ 'enhanced image is finely controlled. (See Fig. 6), by applying a vacuum heat treatment process at 850 ± 30 ℃ after high temperature isostatic compression as shown in Figure 4, the secondary γ 'phase as shown in the reference numeral' 30 'of FIG. It is further precipitated in between, and can significantly improve fatigue characteristics by six times or more (see FIG. 7), and high temperature creep strength by three times or more (see FIG. 8). Therefore, the present invention can extend the service life of the hot parts by removing defects existing in the gas turbine blades and the hot parts and optimizing the microstructure.

Claims (4)

To extend the service life of high temperature parts by eliminating defects inside high temperature parts such as gas turbine blades using Ni-based superalloys and optimizing microstructures to greatly improve the high temperature strength of materials. A vacuum heating process of heating the high temperature part at 300 ° C. for at least 30 minutes in a vacuum atmosphere; After the vacuum heating process, the temperature raising step of raising the temperature to a temperature section of 1200 ± 20 ℃ and the pressure to 100MPa or more; A constant temperature maintaining process for maintaining the constant temperature for at least 4 hours in the temperature section for removing defects by plastically deforming casting bonds and pores at a temperature where local melting proceeds (1200 ° C.) or lower; And A method of extending the life of gas turbine high temperature parts using a high temperature isothermal compression technique, after maintaining a constant temperature, performing a controlled cooling step to minimize a cooling rate and then performing a uniform rapid cooling step. The method of claim 1, The control cooling step, After slowly cooling from 1200 ± 20 ℃ to 1120 ± 20 ℃ to 5 ℃ or less per minute and maintaining it for more than 30 minutes, the grain boundary shape is transformed into saw tooth shape. The uniform rapid cooling step, Gas turbine using high temperature isothermal compression technology characterized by uniformly rapid cooling at 100 ° C./min or more in the temperature range of 1120 ± 20 ° C. to 30 ° C. so that the γ 'phase, which is a high temperature strengthened image, does not precipitate and grow finely. How to extend the life of high temperature parts. The method of claim 2, The uniform rapid cooling step, the extended life cycle of the gas turbine hot parts using high temperature isocompression technology, characterized in that the γ 'reinforced phase is finely deposited to an average size of 0.5㎛. The method of claim 1, After the cooling process, further heat treatment to maintain at least 8 hours by heating to a temperature of 850 ± 30 ℃ in a vacuum atmosphere in order to further precipitate a fine secondary γ 'phase in the Ni-based superalloy microstructure Life extension of gas turbine high temperature parts using high temperature isocompression technology.