KR20190140286A - Nickel-based alloy with excellent creep property and oxidation resistance at high temperature and method for manufacturing the same - Google Patents

Abstract

An objective of the present invention is to provide a nickel-based super heat-resistant alloy having a higher temperature resistant oxidation resistance and creep characteristics than to a prior art; and a manufacturing method thereof. According to one aspect of the present invention, provided is a nickel-based super heat-resistant alloy casting having excellent high temperature creep characteristics and oxidation resistance comprising: 16.6-20.0 wt% of cobalt (Co); 15.0-17.2 wt% of chromium (Cr); greater than 0 wt% and less than 2.0 wt% of molybdenum (Mo); 7.3-10.0 wt% of tungsten (W); 2.2-2.7 wt% of aluminum (Al); 2.4-3.2 wt% of titanium (Ti); 0.5-3.0 wt% of tantalum (Ta); 0.04-0.1 wt% of carbon (C); greater than 0 wt% and less than 0.01 wt% of boron (B); and the remaining balance consisting of nickel (Ni) and other unavoidable impurities.

Description

Nickel-based alloy with excellent creep property and oxidation resistance at high temperature and method for manufacturing the same

The present invention relates to a nickel-based super heat-resistant alloy used in aircraft engines, generator gas turbines, and the like, and more particularly, a nickel-based super heat-resistant alloy having both excellent creep properties and oxidation resistance suitable for high temperature oxidation environments and its manufacture It's about how.

Super heat-resistant alloy may be classified into nickel (Ni) group, iron (Fe) group, cobalt (Co) group alloy group. Among them, the most important and widely used industrially is nickel (Ni) super heat resistant alloys. Nickel (Ni) super heat-resistant alloys use nickel (Ni) as the matrix, and chromium (Cr), cobalt (Co), aluminum (Al), tungsten (W), tantalum (Ta) and molybdenum It is an alloy group that has optimized high temperature mechanical and environmental resistance by adding 10 kinds of alloying elements such as (Mo), carbon (C) and rhenium (Re). Nickel-based superalloys have been applied to many industries requiring high temperature corrosion resistance and heat resistance, but the most important applications are aircraft engines and power generation gas turbines.

Recently, as environmental problems such as global warming have emerged, the necessity for increasing the efficiency of existing power generation methods is increasing along with the study of new power generation methods to reduce or eliminate carbon dioxide (CO ₂ ) emissions. As a result, in the case of gas turbines, the operating temperature is continuously increasing to improve efficiency. The gas turbine burns the compressed air together with the fuel in the compressor so that the expanded combustion gas rotates the turbine to generate power or produce power.

Thus, turbine blades or nozzle guide vanes and the like have a three-dimensional complex aerodynamic design that includes complex shaped cooling passages inside the part to achieve higher efficiency at a given condition. For this reason, turbine blades and vanes and the like are produced by a casting process that is easy to manufacture shapes. In addition, the turbine blade of the gas turbine operating at high temperature is subjected to centrifugal force due to the high speed rotation of the turbine, and the creep characteristic to withstand the centrifugal force at high temperature is very important. In addition, the components used in the oxidizing atmosphere, such as nozzle guide vanes for a turbojet engine as a component used at high temperatures should also have excellent oxidation resistance.

The super heat-resistant alloy for components used in such a high temperature oxidation atmosphere should be designed in consideration of the material properties and economics including creep resistance, oxidation resistance, weldability, and the like.

Domestic Patent No. 10-0725624

The present invention has been made to solve various problems including the above problems, and an object of the present invention is to provide a nickel-based super heat-resistant alloy having a superior high temperature oxidation resistance and creep characteristics and a method of manufacturing the same. However, these problems are exemplary, and the scope of the present invention is not limited thereby.

According to one aspect of the invention, in weight percent, 16.6 to 20.0 cobalt (Co), 15.0 to 17.2 chromium (Cr), greater than 0 or less than 2.0 or less molybdenum (Mo), 7.3 to 10.0 tungsten (W) , Aluminum (Al) of 2.2 to 2.7, titanium (Ti) of 2.4 to 3.2, tantalum (Ta) of 0.5 to 3.0, carbon (C) of 0.04 to 0.1, boron (B) of more than 0 and 0.01, and the balance A nickel-based super heat resistant alloy casting having excellent oxidation resistance including nickel (Ni) and other unavoidable impurities is provided.

In the nickel-based superheat-resistant alloy casting material, the parameter P represented by Equation 1 may have a value of 150 or more.

Equation 1: P = α ₁ exp (α ₂ (M _d -0.97)) + bfγ '+ cI _sss + d

α ₁ = -124.27

α ₂ = 119.90

         b = 18.928

c = 3.965 × 10 ^-16

         d = -1338.89

M _d = average energy level of the _d -orbital

         fγ '= volume fraction of gamma prime phase (%)

I _sss = Employment Reinforcement Index

The nickel-based super-heat-resistant alloy casting material is a phase having a spinel structure on the top layer of the surface (((Ni, Co)) when 50 cycles are repeated with one cycle of cooling to room temperature after holding for 1 hour at 1100 ° C. in the air. Cr ₂ O ₄ ) and a chromium oxide (Cr ₂ O ₃ ) layer is formed, the titanium tantalum composite oxide (TiTaO ₄ ) or nickel aluminum composite oxide (NiAl ₂ O ₄ ) below the chromium oxide (Cr ₂ O ₃ ) layer ) May be present.

In the nickel-based super heat-resistant alloy casting material having excellent oxidation resistance, the thickness of the chromium oxide (Cr ₂ O ₃ ) layer may have a range of 5 to 10㎛.

In the nickel-based super heat-resistant alloy cast material having excellent oxidation resistance, the volume fraction of the gamma prime phase may be in the range of 0.249 to 0.298. In addition, the size of the first gamma prime phase in the dendritic center may be in the range of 0.162 μm to 0.172 μm, and the size of the second gamma prime prime in the dendritic center may be in the range of 0.0405 μm to 0.0429 μm.

According to another aspect of the present invention, there is provided a method for producing a nickel-based superheat-resistant alloy casting material having excellent oxidation resistance.

The method for producing the nickel-based superheat-resistant alloy cast material is, by weight, cobalt (Co) of 16.6 to 20.0, chromium (Cr) of 15.0 to 17.2, molybdenum (Mo) of more than 0 and 2.0 or less, tungsten of 7.3 to 10.0. (W), aluminum (Al) from 2.2 to 2.7, titanium (Ti) from 2.4 to 3.2, tantalum (Ta) from 0.5 to 3.0, carbon (C) from 0.04 to 0.1, boron (B) above 0 and 0.01 and Preparing a molten alloy of an alloy having a balance including nickel (Ni) and other unavoidable impurities; Casting the molten metal; Solution casting the cast alloy casting material at a temperature of more than 1200 ° C. and less than 1250 ° C. for 4 hours to 6 hours; A first aging treatment for 3 to 5 hours in the range of 950 ° C. to 1050 ° C. after the solution treatment is completed; And a second aging treatment for 7 to 9 hours in the range of 800 ° C. to 900 ° C. after the first aging treatment.

According to an embodiment of the present invention, it is possible to implement a nickel-based super heat resistant alloy having excellent creep properties and excellent high temperature oxidation resistance and a method of manufacturing the same. Of course, the scope of the present invention is not limited by these effects.

1 is a view showing the conditions of the first heat treatment method performed after the casting of the alloy is completed.
2 and 3 are the results of observing the microstructure of the alloy treated by the first heat treatment method.
4 is a view showing the conditions of the second heat treatment method performed after the casting of the alloy is completed.
5 and 6 show the results of observing the microstructure of the alloy treated by the second heat treatment method.
7 is a graph showing the size (maximum diameter) distribution of the gamma prime phase (γ'phase) deposited in the alloy according to the solution time in the alloy treated according to the second heat treatment method.
8 is a graph showing the volume fraction of the gamma prime phase at the dendritic center in the alloy treated according to the second heat treatment method.
Fig. 9 is a graph showing the average size of the primary gamma prime phase at the dendritic center in the alloy treated according to the second heat treatment method.
FIG. 10 is a graph showing the average size of the secondary gamma prime phase at the dendritic center in the alloy treated according to the second heat treatment method.
FIG. 11 is a graph showing creep properties of alloys treated by the first and second heat treatment methods. FIG.
12 to 14 show the creep properties of the examples and comparative examples having the composition shown in Table 1.
FIG. 15 shows the results of Larson-Miller index analysis for Examples and Comparative Examples 5 and 6. FIG.
FIG. 16 shows repeated oxidation test results for Examples and Comparative Examples 5 and 6. FIG.
17 to 19 are the results of observing the surface after repeated oxidation experiments of Examples, Comparative Examples 5 and 6, respectively.
20 shows the result of plotting the parameter P with respect to the breaking life.
21 is a result of plotting the value of the parameter P according to the composition range for each alloy composition constituting the embodiment.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms, and the following embodiments are intended to complete the disclosure of the present invention, the scope of the invention to those skilled in the art It is provided to inform you completely. In addition, the components may be exaggerated or reduced in size in the drawings for convenience of description.

), 니켈 기지 내에 원자반경이 다른 치환형 및 침입형 원자의 고용으로 인해 전위 (dislocation)이동을 방해함으로써 고온에서의 크리프 강도를 증가시키는 정도를 나타내는 고용강화 지수 (Isss)를 계산하였으며, 이렇게 도출된 Md, fγ', Isss를 변수로 하는 파라메터로서, 크리프 수명(즉, 합금의 파단까지의 시간, rupture time)과 실질적으로 직선적 관계를 나타내는 파라메터 P를 도출하였다. 구체적인 파라메터 P의 도출 과정에 대해서는 후술하도록 한다. Nickel-based super heat-resistant alloy according to an embodiment of the present invention has excellent oxidation resistance in a high temperature oxidation atmosphere and at the same time excellent creep characteristics. The present inventors have cobalt (Co), chromium (Cr), molybdenum (Mo), tungsten (W), aluminum (Al), tantalum (Ta), Carbon (C) and boron (B) were selected. Md value and the volume fraction of gammaprime expressed as the sum of the d-electron orbital energy level of each alloying element and the atomic fraction of the plurality of specimens manufactured by changing the composition range of the selected alloying elements. (

), The solid solution strengthening index (Isss), which represents the degree of increase in creep strength at high temperatures by preventing dislocation movement due to the dissolution of substituted and invasive atoms with different atomic radiuses in the nickel matrix, was derived. As parameters having Md, fγ ', and Isss as variables, a parameter P representing a substantially linear relationship with creep life (ie, rupture time) is derived. The derivation process of the specific parameter P will be described later.

The inventors have found that when the value of the derived parameter P is 150 or more, it exhibits excellent creep characteristics and high temperature oxidation resistance compared to conventional commercially available superheat-resistant alloys. Based on this, the parameter P satisfies 150 or more. The composition range of the alloying elements could be derived.

 Accordingly, the nickel-based superheat-resistant alloy according to the embodiment of the present invention, in weight percent, cobalt (Co) of 16.6 to 20.0, chromium (Cr) of 15.0 to 17.2, molybdenum (Mo) greater than 0 and less than 2.0, 7.3 Tungsten (W) of 1 to 10.0, aluminum (Al) of 2.2 to 2.7, tantalum (Ta) of 0.5 to 3.0, carbon (C) of 0.04 to 0.1, boron (B) of more than 0 and 0.01 or less, and the balance It contains nickel (Ni) and other unavoidable impurities.

Hafnium (Hf) is an expensive refractory element that bends grain boundaries in nickel-based superheat alloys to strengthen grain boundaries.However, hafnium (Hf) tends to segregate into a liquid phase during solidification. And form an Eta phase of block-shaped Ni ₃ (Ti, Hf). Due to the slow diffusion rate, once formed Eta phase is difficult to remove through heat treatment. In addition, hafnium is not included in the examples of the present invention because it reacts with the mold at high temperatures during casting to produce undesirable products at the mold-casting interface.

Niobium (Nb) is an element that strengthens the γ '(Ni ₃ (Al, Ti, Ta, Nb)) phase together with aluminum, titanium, tantalum, and the like in a nickel-based superheat-resistant alloy. However, in this embodiment, which is properly designed in consideration of high temperature creep strength, oxidation characteristics, and welding characteristics, niobium addition may form a La ₂ phase of Ni ₂ Nb during solidification, and a δ phase of Ni ₃ Nb during thermal treatment after casting. It is not included in the present embodiment because of the high possibility of forming and inhibiting the toughness of the alloy.

On the other hand, the nickel-based super heat-resistant alloy according to an embodiment of the present invention can implement the optimum creep characteristics by casting the molten metal having the above-described composition range and then heat treatment appropriately.

The heat treatment includes a solution treatment for homogenizing the microstructure of the cast material after casting is completed, and an aging treatment for depositing a gamma prime phase (γ 'phase), which is a reinforcement phase, on the base of the solution-treated alloy.

When the solution treatment temperature is low or the solution treatment time is short, the solution solution is not sufficiently formed so that the shape of the precipitated phase after aging treatment has a very irregular shape and the tissue is not homogenized sufficiently. On the other hand, if the solution treatment temperature is too high or the treatment time is too long, local melting of the alloy (incipient melting) may occur, the creep properties may be greatly reduced. In the case of the alloy according to the embodiment of the present invention, the solution treatment is carried out in the range of 4 hours to 6 hours at a temperature higher than 1200 ℃ and 1250 ℃ or less.

The aging treatment includes a first aging step for depositing a primary gamma prime phase and a second aging step for depositing a secondary gamma prime phase. In order to exhibit good creep properties at high temperatures, it is important to optimize the shape and volume fraction of the primary and secondary gammaprime phases. In the case of the super heat-resistant alloy according to an embodiment of the present invention, the first aging treatment is performed for 3 to 5 hours in the range of 950 ° C. to 1050 ° C., and 7 to 9 hours in the range of 800 ° C. to 900 ° C. after the primary aging treatment. During the second aging process.

Hereinafter will be described experimental examples for determining the characteristics of the nickel-based super heat-resistant alloy prepared according to the technical idea of the present invention. However, the following experimental examples are only to help understanding of the present invention, the technical spirit of the present invention is not limited to the following experimental examples.

Table 1 shows the alloy composition of the alloy according to the embodiment of the present invention and comparative examples (Comparative Examples 1 to 6) for comparison thereto. In particular, Comparative Example 5 is the same composition as MGA-2400 commercial alloy, Comparative Example 6 is the same composition as GTD-222 commercial alloy.

Co Cr Mo W Al Ti Ta Nb C B Ni Example 18 16 One 8 2.5 3 2 0 0.07 0.005 Balance Comparative Example 1 17 20 0 7 2.5 3 One 0 0.07 0.005 Balance Comparative Example 2 16 16 One 8 1.5 3.5 3 0 0.07 0.015 Balance Comparative Example 3 12 20 0 8 1.5 3.5 2 0 0.07 0.015 Balance Comparative Example 4 16 20 0 8 1.5 3.5 2 0 0.07 0.005 Balance Comparative Example 5 19 19.1 0 6 1.9 3.7 1.4 One 0.17 0.005 Balance Comparative Example 6 19 22.5 <1 2 1.3 2.3 One 0.8 0.1 0.008 Balance

Examples and Comparative Examples (Comparative Examples 1 to 6) of Table 1 are casting materials which were prepared by melting the molten metal having the above-described composition and then pouring it into a mold, and after the solidification was completed, a predetermined heat treatment was performed. . The heat treatment included solution treatment and aging treatment.

Specifically, FIG. 1 shows heat treatment conditions following the first heat treatment method. Referring to FIG. 1, after the solidification of the alloy was charged into a heat treatment furnace, the temperature was raised to 1200 ° C. and maintained for 2 hours. Next, after cooling at a cooling rate of 100 ℃ / hr to 1030 ℃ in the heat treatment furnace and maintained for 2 hours. Next, the mixture was removed from the heat treatment furnace and cooled to room temperature by gas fan cooling. Next, as the primary aging treatment, the alloy after the solution treatment was added to the heat treatment furnace again, the temperature was raised to 1000 ° C and maintained for 4 hours, then taken out of the heat treatment furnace and air cooled to room temperature. Next, as a secondary aging treatment, the temperature was raised to 850 ° C. in the heat treatment furnace and maintained for 8 hours, and then air-cooled to room temperature.

2 and 3 show the microstructure when the alloy of the composition corresponding to the embodiment of Table 1 was treated according to the first heat treatment method. FIG. 2 is a microstructure of a dendrite core portion formed in the alloy, and FIG. 3 is a microstructure of an interdendritic region.

2 and 3, in the case of the first heat treatment method, it is understood that the solution phase is not sufficiently formed so that the shape of the precipitated phase after the aging treatment is not spherical but has a very irregular shape. In addition, it can be seen that the microstructure difference in the dendritic center and the dendritic region is very severe.

In order to solve this problem, heat treatment was performed on the same alloy by a second heat treatment method in which the conditions of the solution treatment were changed in comparison with the first heat treatment method. 4 shows the conditions of the second heat treatment method. Specifically, according to the second heat treatment method, the alloy was maintained for 2 hours, 4 hours, and 6 hours after heating up to 1240 ° C. Next, the mixture was removed from the heat treatment furnace and cooled to room temperature by gas fan cooling. The aging treatment thereafter was the same as in the first heat treatment method.

FIG. 5 shows the microstructure of the dendritic central portion according to the solution treatment time of the alloy treated by the second heat treatment method, and FIG. 6 shows the microstructure of the interdendritic region according to the solution treatment time.

5 and 6, in the case of the second heat treatment method, it is confirmed that the solution is sufficiently formed to form a generally uniform spherical precipitated phase. Also, there was no significant difference in the microstructure in the dendritic center and the dendritic region.

Figure 7 shows the distribution of the size of the gamma prime phase (γ 'phase) precipitated in the alloy with the solution treatment time. It can be seen that as the solution treatment time increases, the size of the gamma prime phase increases as a whole.

FIG. 8 shows the volume fraction of the gamma prime phase at the dendritic center with the solution treatment time (volume fraction of the first and second gammapri phases). As the solution treatment time increases, it can be seen that the volume fraction of gammaprime increases.

FIG. 9 shows the average size of the primary gammaprime phase (primary γ'phase) at the dendritic center with time of solution treatment. FIG. 10 shows the average size of the secondary gamma prime phase at the dendritic center with solution treatment time. Both tend to increase in size as the solution time increases.

Table 2 summarizes the results of the change in gamma prime according to the solution treatment time shown in FIGS. 8 to 10.

Solution time 2 hours 4 hours 6 hours γ 'volume fraction 0.249 0.263 0.298 Average size of 1st γ '(㎛) 0.162 0.167 0.172 Average size of the second γ '(㎛) 0.0405 0.0422 0.0429

11 shows the creep properties of the alloy treated by the first and second heat treatment methods. The creep test is performed at 900 ° C and 200 MPa, and the graph shows the time at which the alloy breaks under each condition.

Referring to FIG. 11, the creep characteristics of the alloys heat-treated by the second heat treatment method are superior to those of the alloys heat-treated by the first heat treatment method. Particularly, in the second heat treatment method, creep characteristics of 4 hours or 6 hours of solution treatment are relatively better than those of 2 hours of solution treatment of 219 hours of breakdown time of 241 hours and 237 hours, respectively. Indicated.

The results of the examples and comparative examples described below are the results after being processed by the above-described second heat treatment method both after casting.

12 to 14 show results of creep characteristics of Examples and Comparative Examples. Comparative Examples 5 (EQ) and Comparative Examples 5 (DS) shown in FIGS. 12 to 14 refer to polycrystalline casting structures and directional solidification casting structures respectively manufactured by a general casting process. In addition, all of the comparative examples not shown have a unidirectional solidification casting structure.

 12 is a test result at 850 ° C. and 300 MPa creep condition, FIG. 13 is a creep test result at 900 ° C. and 200 MPa condition, and FIG. 14 is a creep test result at 900 ° C. and 150 MPa condition. The results in the examples showed the best under all conditions.

Hereinafter, a method of deriving the above-described parameter P and a process of deriving an optimal alloy composition having excellent creep characteristics and high temperature oxidation resistance characteristics using the same will be described in detail.

Table 3 shows the results of rupture life time at Md, fγ '(%), Isss, and 900 ° C, 200 MPa creep conditions of Examples and Comparative Examples.

Md fγ '(%) Isss (× 10 ¹⁸⁾ Breaking life
(900 ℃ -200MPa) Example 0.9654 33.18 2.41 183.1 Comparative Example 1 0.9654 30.42 2.30 76.3 Comparative Example 2 0.9569 27.59 2.35 86.1 Comparative Example 3 0.9599 25.19 2.28 19 Comparative Example 4 0.9624 25.2 2.41 33.4 Comparative Example 5 0.9654 32.12 2.22 68.8 Comparative Example 6 0.9245 14.94 1.75 -

In Table 3, Md is the sum of the d-electron orbital energy levels of each alloy element and the atomic fraction, fγ '(%) is the volume fraction (%) of the decay prime phase, and Isss is the solid solution strengthening index. Means.

Referring to Table 3, fγ '(%) and Isss of the alloy according to the embodiment of the present invention showed the highest value, and it can be seen that the break life also indicates the longest time during creep test.

FIG. 15 shows the results of Larson-Miller index analysis for Examples and Comparative Examples 5 and 6. FIG. Referring to FIG. 15, it was analyzed that the examples have better creep properties than Comparative Examples 5 and 6, which are actual commercial alloys.

The alloy according to the embodiment of the present invention shows excellent oxidation resistance at high temperature, and repeated oxidation experiments were performed to prove this. Repeated oxidation test is a method of observing the change in weight of the alloy as a change in oxidation resistance while repeating the step of oxidizing for a predetermined time at a predetermined temperature in a plurality of cycles. When the oxidation of the alloy proceeds, it shows a sharp change in the weight of the alloy, and thus shows a rapid weight change rate.

Repeated oxidation experiments were repeated for 1 cycle (50 cycles) by keeping the temperature at 1100 ℃ for 1 hour and then cooling to room temperature (cyle). 16 shows the results of repeated oxidation experiments for Examples and Comparative Examples 1 and 5. Referring to FIG. 16, both Comparative Example 1 and Comparative Example 5 showed a sudden change in weight when the number of repetitions exceeded 30 cycles, which means that the oxidation proceeded rapidly. That is, the oxide produced while being maintained at a high temperature undergoes repeated heating / cooling process, and the weight is increased at the initial stage of repeated oxidation, and then the weight decreases rapidly as the oxide is released. The greater the reduction in weight, the worse the oxidation resistance, and the closer the weight loss is to zero, the better the repeat oxidation characteristics. In contrast, in the case of the embodiment, even if the number of repetitions reached 50 cycles, there was no sudden change in weight. From this, it can be seen that the alloy according to the embodiment of the present invention exhibits excellent oxidation resistance.

FIG. 17 shows the results of observing the surface of an example in which the above-described repeated oxidation experiment is completed with a backscattered electron image in a scanning electron microscope. 18 and 19 are the results of observing the surface after the same heat treatment in Comparative Example 1 and Comparative Example 5, respectively.

Referring to FIGS. 18 and 19, in Comparative Example 1 and Comparative Example 5, both thick nickel oxide (NiO) is present on the top layer of the surface, and a porous spinel structure phase ((Ni, Co) Cr ₂ O is located below. ₄ ) and nickel and tungsten composite oxide (NiWO ₄ ) were mixed. In addition, the lower portion thereof shows a structure in which nickel and tungsten composite oxide (NiWO ₄ ) particles are contained in a chromium oxide (Cr ₂ O ₃ ) layer.

In contrast, in the embodiment, a thin spinel-structured phase ((Ni, Co) Cr ₂ O ₄ ) was formed on the uppermost layer, and a chromium oxide (Cr ₂ O ₃ ) layer 5 capable of inhibiting oxidation of the base material was formed at the bottom thereof. A structure having a thickness of 10 μm and continuously formed without a uniform short circuit area is shown. In addition, titanium, tantalum composite oxide (TiTaO ₄ ) or nickel and aluminum composite oxide (NiAl ₂ O ₄ ) were present in the lower portion thereof. Underneath was alumina (Al ₂ O ₃ ).

When exposed to such a high temperature oxidizing atmosphere, the alloy according to the embodiment of the present invention is interpreted to prevent the rapid progress of oxidation by suppressing the reaction of oxygen with the metal base material while forming a uniform and stable chromium oxide on the surface. Can be.

In order to derive a parameter that can directly represent the creep characteristics of the examples and comparative examples of the present invention, the properties of the total six alloys of the examples shown in Table 3, Comparative Examples 1 to 5 (Md, fγ ', Isss) was fitted to derive a parameter P represented by Equation (1).

Equation 1: P = α ₁ exp (α ₂ (M _d -0.97)) + bfγ '+ cI _sss + d

α ₁ = -124.27

α ₂ = 119.90

         b = 18.928

c = 3.965 × 10 ^-16

         d = -1338.89

M _d = average energy level of the _d -orbital

         fγ '= volume fraction of gamma prime phase (%)

I _sss = Employment Reinforcement Index

20 shows a graph plotting the relationship between creep life and parameter P. FIG. As shown in FIG. 20, parameter P has a nearly linear relationship with creep life. In other words, the parameter P is a parameter directly related to the creep life (ie, the time to break). As the value of P increases, the creep life increases.

Referring to FIG. 20, in the case of Comparative Examples 1 to 5, the value of the parameter P did not exceed 100. In contrast, in the case of the embodiment, the value of the parameter P exceeded 170.

The present inventors confirmed that the alloy having excellent creep properties compared to the conventional case exhibits a high value of the parameter P, and sets the parameter P to 150 or more as a reference for the alloy having excellent creep properties compared to the prior art.

FIG. 21 shows a composition range (% by weight) when the value of the parameter P for each of the alloying elements constituting the alloy according to the embodiment is 150 or more. In addition, Table 4 shows a composition range in which the P value is 150 or more in the data for each element shown in FIG. 20.

Furtherance Co Cr Mo W Al Ti Ta C B Maximum (% by weight) 1.66 15 0 7.3 2.2 2.4 0.5 0.04 0 Minimum (% by weight) 24.8 17.2 2.0 10 2.7 3.2 3.0 0.1 0.01

Hereinafter, based on the composition range derived from the parameter P, it is derived by considering the effect of each alloying element on the metallic properties of nickel-based super heat-resistant alloy, for example, castability, high temperature phase stability, strength characteristics, etc. An optimal composition range should be suggested.

Cobalt (Co) is known to improve the high temperature strength by reducing the lamination defect energy of the matrix together with the solid solution strengthening on the gamma phase of the nickel-based superheat-resistant alloy as an essential alloy element in the nickel-based superheat-resistant alloy currently commercially available. According to the embodiment of the present invention, when the cobalt content is less than 16.6% by weight, it is difficult to expect an improvement in creep characteristics due to a decrease in the solid solution strengthening effect of the alloy. On the other hand, when a large amount is added, brittle TCP phase formation may be promoted, thereby lowering the high temperature phase stability and mechanical properties of the alloy. Therefore, the upper limit of the addition is limited to 20% by weight or less. In consideration of creep properties and high temperature phase stability, more preferably, it may have a range of 17.0 wt% to 19.0 wt%.

The main purpose of the addition of chromium (Cr) is to improve the high temperature corrosion resistance and oxidation resistance of the alloy. In addition, chromium forms a fine carbide in the grain boundary and serves to improve creep characteristics by suppressing grain boundary slipping under high temperature creep. When less than 15.0% by weight of chromium is added, creep properties and high temperature corrosion resistance of the alloy are lowered. On the other hand, when a large amount is added, not only the solid-solution strengthening effect is reduced in the alloy composition in which the phase stability of the alloy is maintained, but also the production of the TCP phase may be increased rapidly when exposed at high temperature. Therefore, the upper limit of the addition is limited to 17.2% by weight or less. In consideration of creep properties and high temperature phase stability, it may be more preferably in the range of 15.5% by weight to 16.5% by weight.

Molybdenum (Mo) contributes to improving the high temperature properties of the alloy through solid solution strengthening of the matrix and is a major element to form M ₆ C and M ₂₃ C ₆ carbides together with chromium and tungsten. In addition, referring to Figure 16, it is determined that the addition of a small amount of molybdenum in order to improve the oxidation resistance in the alloy according to the embodiment of the present invention. On the other hand, molybdenum has a strong tendency to volatilize at high temperature, so when added too much, it may have a negative effect on oxidation resistance. Therefore, molybdenum may be added to improve creep strength through proper solidification effect, but its content is limited to 2.0% by weight to suppress negative effects in casting and high temperature mechanical properties and oxidation resistance due to excessive addition. More preferably 1.5% by weight.

Tungsten (W) is an element having a very low diffusion coefficient in nickel, which greatly contributes to the solid solution strengthening of the nickel-based superheat-resistant alloy, and increases the melting point of the alloy. In addition, tungsten, together with chromium and molybdenum, is a major element that forms M ₆ C and M ₂₃ C ₆ type carbides, thereby contributing to grain boundary strengthening. Despite these advantages, tungsten tends to produce brittle TCP phases and tends to segregate into solid phases, increasing the likelihood of creating crystal defects such as freckles defects. Therefore, 7.3 wt% or more of tungsten is added to improve creep strength through proper solidification effect, and its content is limited to 10.0 wt% to suppress negative effects on castability and high temperature mechanical properties due to excessive addition.More Preferably limited to 9.0% by weight.

Aluminum (Al) is the main forming element of γ '(Ni ₃ Al) phase, which is the main reinforcement phase of nickel-based super heat-resistant alloys. In nickel-based super heat-resistant alloys, aluminum enhances the creep strength of the alloy by strengthening the precipitation on γ 'phase, and induces the formation of a dense oxide layer, thereby contributing to the improvement of oxidation resistance of the alloy. In the aluminum addition alloy of less than 2.2% by weight, the precipitation fraction of the γ 'phase is lowered, thereby reducing the contribution to creep strength.In addition, the addition of aluminum in an amount greater than 2.7% by weight increases the solid solution temperature of the γ' phase, thereby allowing solution heat treatment. The temperature range (the temperature range between the incipient melting temperature of the alloy at the solid solution temperature of γ ') is drastically reduced, making solution heat treatment difficult and the weldability deteriorated due to excessive γ' phase precipitation.

Titanium (Ti) is a representative γ 'phase forming element together with aluminum and serves to strengthen the γ' phase by substituting aluminum on the γ 'phase. As the amount of titanium added increases, the volume fraction of the γ 'phase increases to improve the creep strength of the alloy. In titanium-added alloys less than 2.4% by weight, the precipitation fraction of the γ 'phase is lowered, thereby reducing the contribution to creep strength. Titanium additions in excess of 3.2% by weight may cause coarse Eta (Ni ₃ Ti) form the phase stability and mechanical properties can be lowered, high temperature oxidation resistance is greatly reduced.

Tantalum (Ta) is an element that not only contributes to solid solution strengthening of the phase γ, but also strengthens the γ 'phase by replacing aluminum of the γ' phase with titanium. Therefore, in order to improve creep properties, tantalum is preferably added at least 0.5% by weight, more preferably at least 1.0% by weight, but addition of more than 3.0% by weight of tantalum may result in the formation of a TCP phase such as a Mu phase. Accelerates and degrades high temperature mechanical properties. Therefore, the content is limited to 3.0% by weight, more preferably 2.5% by weight.

Carbon (C) defects with Cr, Mo, W and the like to discontinuously form fine carbide particles of the form of M ₂₃ C ₆ or M ₆ C at the grain boundary improves the grain boundary strength. If the carbon content is less than 0.04% by weight, carbides are not sufficiently formed in the grain boundary, and when carbon with a content of more than 0.1% by weight is added, an excessive amount of coarse MC in the grains is combined with Ti and Ta during solidification. The formation of carbides not only reduces the strength of the matrix but also forms a continuous M ₂₃ C ₆ or M ₆ C type carbide in the form of a film at the grain boundaries, which in turn lowers the grain strength, so the maximum content of carbon is 0.1% by weight, more Preferably it is limited to 0.07% by weight.

Boron (B) plays a role of reinforcing grain boundaries together with carbon, and serves to reinforce these carbides by substituting carbon in M ₂₃ C ₆ or M ₆ C type carbides formed at the grain boundaries. However, when an excessive amount of boron is added, the local melting temperature of the alloy may be reduced to cause local melting near the process structure during the solution heat treatment, so the content thereof may be 0.01% by weight or less, more preferably 0.005% by weight or less. Limited to

 Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (5)

By weight, cobalt (Co) of 16.6 to 20.0, chromium (Cr) of 15.0 to 17.2, molybdenum (Mo) greater than 0 or less than 2.0, tungsten (W) of 7.3 to 10.0, aluminum of 2.2 to 2.7 (Al ), Titanium (Ti) of 2.4 to 3.2, tantalum (Ta) of 0.5 to 3.0, carbon (C) of 0.04 to 0.1, boron (B) of more than 0 and less than 0.01, and the balance of nickel (Ni) and other unavoidable impurities Including;
Parameter P represented by Equation 1 has a value of 150 or more,
Nickel-based super heat-resistant alloy cast material with excellent high temperature creep properties and oxidation resistance.
Equation 1: P = α ₁ exp (α ₂ (M _d -0.97)) + bfγ '+ cI _sss + d
α ₁ = -124.27
α ₂ = 119.90
b = 18.928
c = 3.965 × 10 ^-16
d = -1338.89
M _d = average energy level of the _d -orbital
fγ '= volume fraction of gamma prime phase (%)
I _sss = Employment Reinforcement Index The method of claim 1,
If 50 cycles were repeated with 1 cycle of maintaining the temperature at 1100 ° C. for 1 hour in the air and then cooling to room temperature,
A phase ((Ni, Co) Cr ₂ O ₄ ) having a spinel structure is formed on the top layer of the surface, and a chromium oxide (Cr ₂ O ₃ ) layer is formed on the bottom thereof.
Titanium, tantalum composite oxide (TiTaO ₄ ) or nickel, aluminum composite oxide (NiAl ₂ O ₄ ) is present below the chromium oxide (Cr ₂ O ₃ ) layer,
Nickel-based super heat-resistant alloy cast material with excellent high temperature creep properties and oxidation resistance. The method of claim 2,
The thickness of the chromium oxide (Cr ₂ O ₃ ) layer has a range of 5 to 10㎛,
Nickel-based super heat-resistant alloy cast material with excellent high temperature creep properties and oxidation resistance. The method of claim 1,
The volume fraction of the gamma prime phase is in the range of 0.249 to 0.298,
The size of the first gammaprime phase at the dendritic center is in the range of 0.162 μm to 0.172 μm,
The size of the second gammaprime phase at the dendritic center is in the range of 0.0405 μm to 0.0429 μm,
Nickel-based super heat-resistant alloy cast material with excellent high temperature creep properties and oxidation resistance. By weight, cobalt (Co) of 16.6 to 20.0, chromium (Cr) of 15.0 to 17.2, molybdenum (Mo) greater than 0 or less than 2.0, tungsten (W) of 7.3 to 10.0, aluminum of 2.2 to 2.7 (Al ), Titanium (Ti) of 2.4 to 3.2, tantalum (Ta) of 0.5 to 3.0, carbon (C) of 0.04 to 0.1, boron (B) of more than 0 and less than 0.01, and the balance of nickel (Ni) and other unavoidable impurities Preparing a molten alloy of an alloy comprising a;
Casting the molten metal;
Solution casting the cast alloy casting material at a temperature of more than 1200 ° C. and less than 1250 ° C. for 4 hours to 6 hours;
A first aging treatment for 3 to 5 hours in the range of 950 ° C. to 1050 ° C. after the solution treatment is completed; And
A second aging treatment for 7 to 9 hours in the range of 800 ° C. to 900 ° C. after the first aging treatment;
Including,
A method for producing a nickel-based super heat-resistant alloy cast material having excellent high temperature creep properties and oxidation resistance.

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