KR20130133365A - Method of manufacturing welds with good creep properties in polycrystalline nickel-based superalloys - Google Patents

Abstract

Disclosed is a method of manufacturing a welded portion of a polycrystalline nickel base super heat resistant alloy having excellent creep properties. According to an embodiment of the present invention, a method for manufacturing a welded portion of a nickel base superheat resistant alloy includes a first step of causing plastic deformation by applying an external force to the welded portion of a base material and a welded portion formed by joining welding of a nickel based super heat resistant alloy; And a second step of heat-treating the weld to refine the grain size of the weld to the grain size of the base material.

Description

METHOD OF MANUFACTURING WELDS WITH GOOD CREEP PROPERTIES IN POLYCRYSTALLINE NICKEL-BASED SUPERALLOYS}

The present invention relates to a method for manufacturing a welded portion of a polycrystalline nickel-based super heat-resistant alloy, and more particularly, after welding using a nickel-based super heat-resistant alloy, the polycrystalline nickel improves creep characteristics by miniaturizing the coarse columnar structure of the welded portion. It relates to a welding part manufacturing method of the base heat-resistant alloy.

Superalloys are widely used as structural materials in high-tech industries such as aerospace, nuclear power, and power plant industries. Among these superalloys, nickel-based superalloys are processable and weldable. Because of its excellent corrosion resistance and high temperature mechanical properties, it is generally used in parts such as gas turbine casings and combtion liners.

The joining method that is widely used in structuring the nickel-based super heat-resistant alloy is a welding method. In this regard, Figure 1 is a schematic view showing the junction of the super heat-resistant alloy. Referring to FIG. 1, in the case of joining both ends of the super-heat-resistant alloy formed of a sheet material or joining both ends of two or more super-heat-resistant alloys, the joining portion of the super-heat-resistant alloy is largely the base material (1) and the heat-affected portion (2). And the weld metal part 3. In this case, the heat affected zone 2 and the weld metal 3 may be collectively referred to as a weld zone a.

The base material 1 means the superheat-resistant alloy part which is not influenced by the welding heat etc. in the welding of the junction part of a superheat-resistant alloy. The heat affected zone 2 is also called HAZ (Heat Affected Zone), which is not directly welded and solidified by welding like the weld metal 3, but is affected by heat generated in the welding operation. It means the receiving part.

By the way, in the welding operation of the super heat-resistant alloy as described above, the problem that the physical properties of the welding portion (a) is weak compared to the base material (1) has been pointed out. This is because the weld metal part 3 is melted and solidified by the welding heat generated during the welding operation to produce a coarse columnar structure, and the heat affected part 2 is coarse in structure by heat. This is because the weld portion a has coarse grains. This acts as a cause of local weakness in parts using super heat resistant alloys, and therefore, researches for improving the physical properties of the welded portion (a) in the welding work of super heat resistant alloys are being actively conducted.

Embodiments of the present invention to provide a method for manufacturing a welded portion of a polycrystalline nickel-based super heat-resistant alloy that can improve the properties of the welded portion to the base material level.

According to an aspect of the present invention, a first step of causing a plastic deformation by applying an external force to the weld portion of the base material and the weld portion formed by welding the joint portion of the nickel-based super-heat-resistant alloy; And a second step of heat-treating the weld to refine the grain size of the weld to the grain size of the base material.

In this case, an external force may be applied to the welding part so as to satisfy Equation 1 below.

[Formula 1]

0.2t1≤R≤0.7t1

(Where t1 is the initial height of the protruding portion on the base material surface in the weld, R is the change in height of the weld due to external force)

In addition, the method of applying an external force to the weld may be a rolling method, a pressing method or a short peening method.

On the other hand, the second step may be characterized in that it comprises a step 2-1 to solution-treat the weld.

At this time, the solution treatment of the step 2-1 may be characterized in that it is carried out above the recrystallization temperature of the base material.

At this time, the temperature in the solution treatment may be characterized in that 1100 ℃ to 1200 ℃.

On the other hand, the second step may further comprise a step 2-2 of aging the weld.

At this time, the temperature in the aging treatment of the second step 2 may be characterized in that 750 ℃ to 850 ℃.

In the embodiments of the present invention it is possible to improve the physical properties of the weld to the base material level by first applying an external force to the weld to cause plastic deformation and second heat treatment to refine the crystal grains of the weld.

1 is a view schematically showing a joint of a super heat resistant alloy.
2 is a flow chart of a method for manufacturing a welded portion of a polycrystalline nickel-based super heat-resistant alloy according to an embodiment of the present invention.
FIG. 3 is a view schematically illustrating an external force applied to the weld metal part according to the method of FIG. 2.
4A to 4C are photographs of microstructures of portions of the Nimonic 263 alloy according to the test example.

Hereinafter, embodiments of the present invention will be described in detail.

FIG. 2 is a flowchart illustrating a method for controlling grains of a nickel-based superheat-resistant alloy welded part according to an embodiment of the present invention, and FIG. 3 is a view schematically showing an external force applied to the welded portion A according to the method of FIG. 2. .

2 and 3, the welded part manufacturing method of the polycrystalline nickel-based super heat-resistant alloy (hereinafter, referred to as a welded part manufacturing method) is the welded portion (A) of the nickel-based super-alloy alloy including the base material 10 and the welded portion (A) A first step of causing plastic deformation by applying external force to the weld portion (A) after the welding is performed; And a second step of heat-treating the weld A in order to refine the grain size of the weld A to the grain size of the base material 10.

In the present specification, 'nickel-based super heat-resistant alloy' refers to a Ni-Cr-based polycrystalline alloy having a gamma (γ) phase having an FCC (face centered cubic) structure, and includes Al (aluminum) and Ti (titanium). ), Co (cobalt), Mo (molybdenum) and the like. The kind of such nickel-based super heat-resistant alloy may vary, and it is noted that the term 'nickel-based super heat-resistant alloy' is used as a concept including all known nickel-based super heat-resistant alloys.

Examples of nickel-based super heat-resistant alloys include Nimonic 263, and the Nimonic 263 is widely used as a structure of a gas turbine casing, liner, etc. because of its high temperature characteristics and good moldability.

The nickel-based superheat-resistant alloy includes the base material 10 and the weld portion A formed by welding the joint. For example, in order to join the nickel-based superheat-resistant alloy in the form of a tube, the joining portion may be a joining portion when joining both ends of the nickel-based superheat-resistant alloy, or when joining two or more end portions of the nickel-based superheat-resistant alloy. Junctions and the like.

The base material 10 means a main portion of the nickel-based superheat-resistant alloy, and means a portion which is not affected by welding heat or the like in welding the joint of the nickel-based superheat-resistant alloy.

Weld portion (A) means a portion where welding is directly performed at the junction of the nickel-based superheat-resistant alloy. The welded portion A may be further divided into a heat affected portion 20 and a welded metal portion 30. The welding metal part 30 refers to a part in which welding is directly performed, and the heat affected part 20 is not a part in which a welding operation is directly performed like the welding metal part 30 but is affected by heat generated in the welding operation. It means the receiving part. The heat affected part 20 may be formed between the weld metal part 30 and the base material 10.

Hereinafter, each step will be described.

(1) First step ( S110 )

First, welding is performed at the junction of the nickel-based superheat-resistant alloy. At this time, the welding method is not limited, and a known welding method can be used. Examples of the welding method include gas tungsten arc welding (GTAW) or gas metal arc welding (GMAW). When the welding is finished, the nickel-based super heat-resistant alloy may be divided into the base material 10 and the weld portion A, and the weld portion A may be further divided into the heat affected portion 20 and the weld metal portion 30.

Next, an external force is applied to the weld portion A to cause plastic deformation. Applying the external force to the welding portion (A), as shown in Figure 3, using the external force processing apparatus 100 that can apply an external force to the welding portion (A), the heat affected zone 20 except for the base material 10 and It means that the external force is applied only to the weld metal part 30.

A method of applying an external force to the weld portion A may include a rolling method, a press method, or a short peening method, but is not limited thereto. More specifically, the external force processing device 100 may be a rolling device when the external force is applied to the weld portion A using the rolling method. In this case, the weld A can be processed by passing between two rolls. In the case of applying an external force to the weld portion A using the press method, the external force processing device 100 may be a press machine. In this case, the weld A can be processed by being pressed by a press. When the external force is applied to the weld portion A using the shot peening method, the external force processing device 100 may be a shot peening device. In this case, the welding portion A can be processed by hitting by shot balls or the like projected by the shot peening apparatus.

As described above, when an external force is applied to the weld portion A, plastic deformation of the weld portion A occurs. In this case, the external force may be applied to the weld portion A until the thickness change of the base material 10 does not occur. Can be. The plastic deformation of the welded portion A here means that the grains are severely crushed inside the metal and the density of internal dislocations is increased. This state of the weld A increases the internal stored energy, so that after the heat treatment (annealing), it promotes recrystallization and nucleation so that the tissue of the weld A is formed. Contribute to miniaturization to (10) level. At this time, the microstructure of the welded portion A is reduced to the level of the base metal 10, and the grain size of the heat-affected portion 20 and the weld metal portion 30 and the base metal 10 forming the welded portion A are similar. Means.

On the other hand, the degree of applying the external force of the welding portion (A) can be performed to satisfy the following [Equation 1].

[Formula 1]

0.2t1≤R≤0.7t1

Here, t1 means the initial height of the portion projecting on the surface of the base material 10 in the welded portion A, and R means the amount of change in the height of the welded portion A by the external force.

Specifically, immediately after welding to the welded portion A of the nickel-based superheat-resistant alloy, a part of the welded portion A protrudes onto the surface of the base material 10 based on the surface of the base material 10 (mainly, Weld metal part 30). At this time, when a part of the welded portion A protrudes onto the surface of the base material 10 is referred to as a “projection portion” for convenience, when the external force is applied to the welded portion A, the height of the protruding portion is lowered. Therefore, [Equation 1] specifies the range of the height change amount of the protrusion changed by applying an external force, which ranges from 20% to 70% of the initial height of the protrusion.

If the height variation R of the welded portion A due to external force is less than 20% of the initial height of the portion protruding on the surface of the base material 10 from the welded portion A, the plastic deformation is not sufficient, so that the recrystallization does not occur properly. A) It is difficult to achieve the microstructure of the tissue, and if it is more than 70%, recrystallization may be promoted to achieve the microstructure of the tissue, but the shape of the nickel-based superheat-resistant alloy component may change (above S110).

(2) second step ( S120 )

Next, the welded portion A in which plastic deformation has occurred is heat treated. In the method for controlling grain size of a nickel-based super-alloy welded weld according to an embodiment of the present invention, plastic deformation occurs in the welded portion A, and then the welded portion A is heat-treated to measure the grain size of the welded portion A. It is characterized in that the micronized to a grain size of).

The heat treatment can be divided into two stages. The first step is a step of solid solution treatment of the weld A, and through this step, the grains of the weld A can be miniaturized to the level of the base material 10. On the other hand, if necessary, a second step may be introduced. For example, in the case where the nickel-based superheat-resistant alloy is a gamma prime (γ ') precipitation hardening alloy, the aging treatment may be performed on the welding portion A following the first step described above. aging treatment) may be performed. That is, the aging treatment can be selected as necessary.

Through the solution treatment, the welded portion A in which the internal accumulation energy is increased by the external force applied in the first step may be recrystallized to refine the structure of the welded portion A. FIG. In addition, it is possible to reduce the fine segregation present in the welded portion (A) that is quickly melted and solidified again.

The solution treatment may be performed above the recrystallization temperature of the base material 10. For example, the temperature in the solution treatment may be carried out at 1100 ° C to 1200 ° C, preferably about 1150 ° C. On the other hand, the solution treatment time may be performed in the range of about 10 minutes to about 1 hour, preferably about 30 minutes. If the solution treatment time is shorter than 10 minutes, recrystallization does not occur completely and only partial recovery occurs. If the solution treatment time is longer than 1 hour, recrystallization occurs completely but grain growth ( There is a problem that grain growth occurs to coarse grains.

As such, the recrystallization phenomenon is rapidly promoted in the welded portion A through the solution treatment, and thus the grain size can be reduced to the grain size level of the base material 10. It can be improved to the level of the base metal 10 (more than S121).

On the other hand, the aging treatment is selectively performed in the case where the nickel-based super heat-resistant alloy is a gamma prime (γ?) Precipitation-reinforced alloy as described above. A) means heat treatment again. At this time, the temperature in the aging treatment may be carried out at 750 ℃ to 850 ℃. The aging treatment time is not limited. For example, the aging treatment time may be performed for 8 hours or more corresponding to a time when the gamma prime γ 'is sufficiently precipitated.

As such, after the aging treatment, the grain size of the weld portion A does not change, but since the gamma prime γ 'is deposited inside the grain, the high temperature strength can be improved to the level of the base material 10 (S122). .

Hereinafter, the present invention will be described in more detail with reference to the test examples of the present invention. It should be understood, however, that the following test examples are illustrative only to illustrate the present invention, and do not limit the scope of the present invention.

Test Example

The joints of Nimonic 263 sheet specimens (Haynes, USA) were TIG welded (tungsten inert gas welding), and plastic deformation was performed by pressing 10 times the welds appearing according to the joint welding through a press equipment. The plastic deformation was performed such that the welded portion had a height of approximately 50% based on the initial height of the welded portion projected onto the base material surface. Next, the plate specimen was subjected to solution treatment at 1150 ° C. for 30 minutes, and then aged at 800 ° C. for 8 hours.

The microstructure of the plate specimen treated as described above was observed with an optical microscope (OM, Optical Microscope) for the weld metal part, the heat affected part and the base material (see Fig. 3). In this regard, Figures 4a to 4c is a photograph of the microstructure of the portion of the Nimonic 263 plate specimens according to the test example.

Figure 4a corresponds to the weld metal portion of the specimen, Figure 4b corresponds to the heat affected zone (HAZ) of the specimen, Figure 4c corresponds to the base material of the specimen. As can be seen in Figures 4a to 4c, as a result of processing the plate specimen by the weld grain control method according to an embodiment of the present invention, it was confirmed that the grain size difference of the weld metal portion, heat affected zone and the base material hardly come out. . Therefore, it was confirmed that the crystal graining phenomenon appeared as a whole.

Next, in order to determine the degree of creep characteristics improvement of the nickel-based superheat-resistant alloy according to an embodiment of the present invention, Example 1, in which the Nimonic 263 plate specimen was treated as in the embodiment of the present invention as described above, The creep test was done about the comparative example which performed only 2 and welding (temperature 870 degreeC, stress 113 MPa conditions). The results are shown in the following [Table 1].

Creep Break Time (hr) Creep Elongation (%) Example 1 85.5 48.1 Example 2 95.3 51.2 Comparative Example 63.2 40.9

As can be seen in Table 1, it was confirmed that the creep life was improved by about 35 to 51% compared to the comparative example in the Examples. Therefore, it can be seen that the creep characteristics of the welded portion of the nickel-based super heat-resistant alloy according to the embodiments of the present invention are superior to those of the prior art.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the invention as set forth in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

1, 10: base material
2, 20: heat affected zone
3, 30: welded metal part
A, a: seam
100: external force processing device

Claims (8)

A first step of forming a plastic deformation by applying an external force to the welding portion among the base metal and the welding portion formed by welding the joint portion of the nickel-based superheat-resistant alloy; And
And a second step of heat-treating the weld to refine the grain size of the weld to the grain size of the base material. The method according to claim 1,
The welding part manufacturing method of the nickel-based super heat-resistant alloy, characterized in that to apply an external force to the weld to satisfy the following formula 1.
[Formula 1]
0.2t1≤R≤0.7t1
(Where t1 is the initial height of the protruding portion on the base material surface in the weld, R is the change in height of the weld due to external force) The method according to claim 1,
The method of applying an external force to the weld is a welding method of the nickel-based super heat-resistant alloy, characterized in that the rolling method, the press method or the shot peening method. The method according to claim 1,
The second step comprises:
The welding part manufacturing method of the nickel-based super heat-resistant alloy, characterized in that it comprises a step 2-1 to the solution solution. The method of claim 4,
Wherein the solution treatment of the step 2-1 is welded manufacturing method of the nickel-based super heat-resistant alloy, characterized in that carried out above the recrystallization temperature of the base material. The method of claim 4,
The temperature in the solution treatment is 1100 ℃ to 1200 ℃ weld section manufacturing method of nickel-based super heat-resistant alloy, characterized in that. The method of claim 4,
The second step comprises:
The welding method of the nickel-based super heat-resistant alloy further comprises a step 2-2 of aging the weld. The method of claim 6,
The temperature in the aging treatment of the step 2-2 is a welding part manufacturing method of nickel-based super heat-resistant alloy, characterized in that 750 ℃ to 850 ℃.

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