KR101838821B1 - Heat treatment method of nickel base precipitation superalloy using replica - Google Patents

Abstract

The present invention relates to a heat treating method of nickel group precipitation hardening type alloy using surface replication. In gas turbine elements, the elements made of nickel group precipitation hardening type alloy are selected and microstructure is inspected using the surface replication which does not damage the elements. In addition, the present invention is intended to classify groups according to results of the microstructure analysis, and to perform effective material restoration work by performing different heat treatment methods for the respective groups.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for heat treatment of a precipitation hardening type nickel-

The present invention relates to a heat treatment method of a precipitation hardening type nickel alloy, and more particularly, to a heat treatment method for recovering a component made of a precipitation hardening alloy at the time of maintenance of a high temperature part of a gas turbine.

In general, components operating in a high temperature / high pressure environment, such as a gas turbine, will undergo microstructure changes with operating temperature and time.

During such operation, the microstructure of the component changes depending on the temperature of the actual component. The microstructure changes depending on the operating temperature and type of the gas turbine, the cooling technology applied to the component, and the coating.

During such operation, the mechanical properties of the parts are changed according to the microstructure change. Therefore, the parts are replaced after the operation for a predetermined time to perform the regeneration maintenance.

The restoration of parts is divided into two types of shape restoration and material restoration. The shape restoration is a technique to restore the worn parts by using welding or brazing, and the material restoration is performed through heat treatment do.

In particular, there are two types of heat treatment of precipitation hardening type alloys: solid solution heat treatment and aging heat treatment. The solid solution heat treatment is a heat treatment in which precipitates formed during operation or coarse precipitates are solidified as a matrix metal. Aging heat treatment is a heat treatment And the precipitated solid is re-precipitated again to restore the strength of the material.

On the other hand, materials mainly used for gas turbine parts are nickel-based superalloys, and these nickel-based superalloys are divided into a solid solution strengthening alloy and a precipitation hardening alloy.

Among them, the solid solution strengthening alloy is a material strengthening the material through strengthening of the solid solution, so that the material can not be strengthened through the heat treatment.

In addition, the precipitation hardening type alloy can strengthen the material through the heat treatment. In the past, when the gas turbine high-temperature parts are subjected to the material restoration after the operation for a predetermined period, they are restored by using only one heat treatment method determined for each material, .

However, since parts to be received for material restoration have various operation histories, the degree of deterioration of the materials is slightly different, so that there is a problem that the material can not be restored normally by only one heat treatment method.

That is, in the past, it was difficult to remove the specimen from the parts to be maintained and to conduct a separate heat treatment experiment. Therefore, the heat treatment parameters were used uniformly. Therefore, It was not possible to classify the microstructure and to perform the heat treatment suitable for the microstructure.

The present invention has been proposed in order to overcome the problems of the prior art described above. The present invention provides a gas turbine high-temperature part selected as a material restoration subject by inspecting the microstructure using surface replication technology, So that an optimal heat treatment restoration can be performed by performing a proper heat treatment.

According to an aspect of the present invention, there is provided a method of manufacturing a gas turbine component, A surface grinding step of grinding the surface of the selected part; A surface polishing step of polishing the portion where the grinding is performed with sandpaper; A diamond polishing step of polishing the polished portion using diamond powder; An etching step of spraying a corrosive liquid onto the polishing area; A step of attaching a surface replica film to the polishing region where the etching is performed; A clone film separating step of separating the clone film after the attached surface clone film is dried; A microscopic inspection step of attaching the separated surface replica film to a glass glass and observing the microstructure with a microscope; Grouping into four groups according to the microstructure type through the microscopic examination; And a heat treatment step of performing a heat treatment operation on the component according to the heat treatment method for each of the divided groups.

In the present invention, the parts made of the nickel-group precipitation hardening type alloy of the parts of the gas turbine are selected and the microstructure is inspected using the surface replica which does not damage the parts, and the group according to the analysis result of this microstructure is divided into four And by performing different heat treatment methods for each group, an effective material restoration work can be performed.

Particularly, since the biopsy is performed by the non-destructive surface replication method, the advantage of maximizing the restoration of physical properties is exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart of a precipitation hardening type alloy heat treatment process according to an embodiment of the present invention; FIG.
2 is a schematic view of an inspection process using a surface replication film in an embodiment of the present invention.
FIG. 3 is a block diagram of a heat treatment method for each group, which is divided in the embodiment of the present invention. FIG.
Figure 4 is a microstructure view of an alloy surface separated into Group 1 in the present invention.
Figure 5 is a microstructure view of an alloy surface separated into Group 2 in the present invention.
6 is a microstructure view of an alloy surface separated into Group 3 in the present invention.
Figure 7 is a microstructure view of an alloy surface separated into Group 4 in the present invention.

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

First, a heat treatment process of the precipitation hardening type nickel-based alloy according to an embodiment of the present invention will be described.

≪ Selection of duplication location > (ST 1)

First, a portion to be cloned is selected in the precipitation hardening type alloy 10, which is a component of the gas turbine.

At this time, it is preferable to select the high temperature deteriorated portion which is relatively heated by the heat of the entire portion of the precipitation hardening type alloy (10).

≪ Surface Grinding > (ST 2)

Thereafter, the surface is ground using a grinder to facilitate identification of the microstructure of the selected site.

≪ Surface polishing > (ST 3)

Then, when the grinder operation is completed, the grinding process is performed to polish the worn surface.

That is, at this time, the operator continuously carries out the surface grinding work manually by using the sandpaper having a gradually smaller thickness in the order of # 80, # 120, # 240, # 400, # 800 and # 1200.

<Diamond polishing> (ST 4)

Then, a secondary polishing operation is performed using diamond powder. Diamond powders of 6 μm, 1 μm, and 0.25 μm are successively used to achieve a finer polishing operation.

At this time, in order to increase the polishing effect, it is preferable to clean the polishing area once more with acetone after cleaning the polishing part with clean fusion after finishing the polishing.

&Lt; Etching > (ST 5)

Then, when the polishing operation is completed, the etchant is sprayed with a spray of a corrosive liquid to the replicated portion.

&Lt; Surface Reproduction Film Attachment > (ST 6)

Then, the surface replica film 20 is attached to the corresponding site as shown in FIG. 2. At this time, the surface of the film 20 is washed with an acetone solution so as not to cause air bubbles in the surface replication film 20, . Further, it is preferable to use a replica film as the surface replica film 20.

&Lt; Separation of surface replica film > (ST 7)

When the attached surface replica film 20 is completely dried, a separation operation for peeling off the film is performed.

<Microscope examination> (ST 8)

The separated surface replica film 20 is inspected by using an optical microscope 40 or an electron microscope after attaching the surface replica film 20 to the glass glass 30, and then the distribution of the microstructure including the precipitate 11 is examined.

At this time, the shape of the precipitate (11) is more clearly shown by spraying the carbon liquid on the surface of the surface replication film (20) before the microscopic examination and then performing the heat treatment for the ultraviolet ray for 1 to 5 minutes to further perform the carbon coating operation So that the surface replica film 20 is maintained in a flat state.

<Division of four groups> (ST 9)

As shown in FIG. 3, the work is divided into four groups according to the microstructure type that is observed through the microscopic examination.

That is, at this time, grouping is performed according to the distribution pattern of the precipitates appearing through the microstructure. As shown in FIG. 4, the precipitate 11 occupies 50% or more of the entire microstructure, and the circular precipitate 11a and the band- (11b) appear at the same time.

When the rectangular shaped precipitates 11c, the circular precipitates 11a, the band-shaped precipitates 11b, and the spot-like precipitates 11d appear at the same time as the precipitate 11 is less than 50% of the total microstructure as shown in Fig. 5 Group 2.

As shown in FIG. 6, when the rectangular precipitates 11c are uniformly distributed and the belt-shaped precipitates 11b appear irrespective of the distribution amount of the precipitates, the group 3 is determined.

In the case of the group 4, only the rectangular precipitate 11c and the spot type precipitate 11d appear while the band-like precipitate does not appear as shown in FIG.

&Lt; Heat Treatment by Group > (ST 10)

Then, when the grouping is performed, the heat treatment corresponding to each of the divided groups (1 group, 2 group, 3 group, 4 group) is performed as shown in FIG. At this time, the heat treatment is performed in a vacuum furnace (1 × 10 ^-3 torr).

That is, the group 1 is a group requiring a heat treatment for restoring a decrease in elongation due to the influence of the band-shaped precipitates 11b.

In this case, the heat treatment of Group 1 is performed by a HIP (Hot Isostatic Pressing) process of applying the pressure of 70 to 120 MPa at a temperature of 1,150 to 1,250 ° C. for 10 to 20 minutes and a HT (hot isostatic pressing) process of maintaining the component at a temperature of 1,150 to 1,250 ° C. for 2 to 4 hours Heat treatment 1, an HT2 process of maintaining at 1,050 to 1,150 ° C for 2 to 3 hours, and an HT3 process of maintaining at 820 to 900 ° C for 10 to 20 hours.

In the group 2, the effects of the circular precipitates 11a are relatively small, but various types of precipitates are present. Therefore, a heat treatment is performed so as to obtain a uniform structure as a whole, and a decrease in elongation due to the influence of the strip- It is necessary to perform the HIP process for applying the pressure of 70 to 120 MPa for 10 to 20 minutes at 1,150 to 1,250 ° C. and the HT process for maintaining the HTU at 1,050 to 1,150 ° C. for 4 to 6 hours, And the HT3 process of maintaining the temperature at 820 to 900 ° C. for 10 to 20 hours.

The group 3 does not require the employment of the rectangular precipitates 11c, but is a group requiring a heat treatment for restoring a decrease in elongation due to the belt-shaped precipitates 11b. Therefore, the heat treatment at this time is performed in a range of 1,150 to 1,250 The HIP process of applying 70 to 120 MPa pressure for 10 to 20 minutes, the HT2 process of maintaining the temperature at 1,050 to 1,150 DEG C for 2 to 3 hours, and the HT3 process of maintaining the temperature at 820 to 900 DEG C for 10 to 20 hours are sequentially performed do.

In the group 4, the employment of the prismatic precipitates 11c is not required, but the group of the precipitates 11d needs to be re-precipitated. In this case, the HT2 process for maintaining the components at 1,050 to 1,150 DEG C for 2 to 3 hours And the HT3 process of maintaining the temperature at 820 to 900 DEG C for 10 to 20 hours.

In the above, HIP is a heat treatment method that improves the microstructure of parts by making the environment of high temperature and high pressure using argon as the working fluid. It is necessary to confirm that the purity of argon is 99.9% or more before working.

Also, in HT1,2, the heating rate may vary depending on the performance of the vacuum furnace and should not exceed 50 ° C / min maximum. The cooling rate is a very important parameter, and HT1 and HT2 must have a cooling rate of 50 ° C / min or more from the heat treatment temperature to 200 ° C. If this cooling rate can not be maintained, reheat treatment should be performed.

Therefore, it can be understood that the material recovery of the turbine parts can be more effectively performed by performing the different heat treatment operations according to the distribution amount and the distribution form of the precipitate through the microstructure inspection as described above.

10: precipitation hardening type alloy 11: precipitate
11a: a circular precipitate 11b: a band-like precipitate
11c: square type precipitate 11d: point type precipitate
12: crack part 20: surface replication film
30: glass glass 40: optical microscope

Claims (6)

(ST1) for selecting a site to be surface-duplicated in a precipitation hardening alloy (10) which is a gas turbine component;
A surface grinding step of grinding the surface of the selected part; (ST 2)
A surface polishing step of polishing the portion where the grinding is performed with sandpaper; (ST 3)
A diamond polishing step of polishing the polished portion using diamond powder; (ST4)
An etching step of spraying a corrosive liquid onto the polishing area; and (ST 5)
(ST 6) attaching a surface replica film to the etched polishing region;
(ST 7) a step of separating the replica film after the attached surface replica film is dried;
A microscopic inspection step of attaching the separated surface replica film to a glass glass and observing the microstructure with a microscope; (ST 8)
According to the microscopic examination, the group 1, the group 2, the group 3, and the group 4 are divided into four groups according to the microstructure type, and the precipitate 11 occupies 50% or more of the entire microstructure, and the circular precipitate 11a and the band- And the precipitates 11b are simultaneously observed, and the precipitates 11 are less than 50% of the total microstructure and the rectangular precipitates 11c and the circular precipitates 11a, the band-shaped precipitates 11b and the spot- 11d are simultaneously observed, group 2 is determined. Regardless of the distribution of the precipitates, when the rectangular precipitates 11c are uniformly distributed and the band-like precipitates 11b appear, the group 3 is determined. When the band-shaped precipitates are not present, 11c and the pointed precipitate 11d are grouped into a group 4; (ST 9)
A heat treatment step of performing a heat treatment operation on the part according to the heat treatment method for each of the divided groups;
Wherein the heat treatment is performed at a temperature of at least &lt; RTI ID = 0.0 &gt; 100 C &lt; / RTI &gt; The method according to claim 1,
Wherein the step (ST1) includes a step of selecting a portion of the entire part of the component that is largely affected by thermal degradation. The method according to claim 1,
(ST 6), the film-attached surface is washed with an acetone solution in order to prevent the occurrence of bubbles on the adhered surface of the surface replica film. Way. The method according to claim 1,
In the microscopic examination step (ST 8), a carbon coating process is performed by spraying a carbon liquid onto the surface of the surface replication film before the microscopic inspection and then performing ultraviolet ray heat treatment, thereby performing heat treatment of the nickel group precipitation hardening type alloy . The method according to claim 1,
In the heat treatment step (ST 10), in the case of group 1, the heat treatment is performed by maintaining the HIP process at a temperature of 1,150 to 1,250 ° C. at a pressure of 70 to 120 MPa for 10 to 20 minutes and at a temperature of 1,150 to 1,250 ° C. for 2 to 4 hours HT1 process, an HT2 process for maintaining at 1,050 to 1,150 ° C for 2 to 3 hours, and an HT3 process for maintaining at 820 to 900 ° C for 10 to 20 hours;
The heat treatment of Group 2 is performed by HIP process which applies the pressure of 70 ~ 120MPa at 1,150 ~ 1,250 ℃ for 10 ~ 20minutes, HT2 process which keeps the components at 1,050 ~ 1,150 ℃ for 4 ~ 6 hours, Followed by HT3 for 20 hours;
The heat treatment of Group 3 is performed by HIP process which applies pressure of 70 ~ 120MPa at 1,150 ~ 1,250 ℃ for 10 ~ 20 minutes, HT2 process which maintains for 2 ~ 3 hours at 1,050 ~ 1,150 ℃, HT3 &lt; / RTI &gt;
In the heat treatment of group 4, the HT2 process for maintaining the component at 1,050 to 1,150 ° C for 2 to 3 hours and the HT3 process for maintaining the component at 820 to 900 ° C for 10 to 20 hours are sequentially performed. (Method for heat treatment of precipitation hardening type nickel alloy). The method of claim 5,
Wherein the HIP has a purity of argon of 99.9% or more and HT1,2 has a cooling rate of 50 DEG C / min or more up to 200 DEG C. Heat treatment method.

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