KR20170058065A - Ni base superalloy and Method of manufacturing thereof - Google Patents

Abstract

The nickel-base superalloy according to the present invention is characterized in that it contains 2.0 to 6.0 wt.% Of cobalt, 8.0 to 13.0 wt.% Of chromium (Cr), 6.0 to 9.0 wt.% Of tungsten (W) (Al), 2.0 wt.% Or less of titanium (Ti), 6.5 to 9.0 wt.% Of tantalum (Ta), 0.15 wt.% Or less of carbon (C) Boron (B) of 0.02 wt.% Or less, zirconium (Zr) of less than 0.02 wt.% And nickel (Ni) which is the remainder and other unavoidable impurities.

Description

TECHNICAL FIELD The present invention relates to a nickel base superalloy and a method of manufacturing the same,

The present invention relates to a nickel-base superalloy and a method of manufacturing the same, and more particularly, to a nickel-base superalloy having excellent high-temperature creep characteristics and oxidation resistance and having remarkably low production cost by adding rare elements Re, Ru and Mo, And a manufacturing method thereof.

In addition, the present invention provides a method for manufacturing a nickel-iron composite material, which is capable of maximizing solid solution strengthening effect while maintaining phase stability at a high temperature by optimizing an element composition ratio and controlling the fraction of gamma prime precipitate to thereby improve unidirectional solidification castability, Heat resistant alloys and a method of manufacturing the same.

The present invention relates to a nickel-base superalloy having a phase stability (Md) of 0.99 or more and containing no more than 56.93% by volume of the gamma prime phase relative to the total volume and capable of improving oxidation characteristics by adding no molybdenum (Mo) Alloy and a method for producing the same.

Nickel-base superalloys with excellent creep characteristics are widely used in structural components such as turbine blades, vanes, and combustors, which are major components of aircraft gas turbines and industrial gas turbines used for power generation.

Recently, as environmental problems such as global warming have emerged, there is a need for new methods for reducing or eliminating CO ₂ emissions, and for improving the efficiency of existing power generation methods. As a result, The operating temperature is constantly rising.

The gas turbine combusts the compressed air in the compressor with the fuel so that the expanded combustion gas rotates the turbine to generate power or to produce power.

Therefore, turbine blades, vanes, etc. have a complicated aerodynamic design in three dimensions including a complicated cooling passage inside a part to obtain higher efficiency under a given condition. For this reason, turbine blades, vanes and the like are manufactured by a casting process which is easy to shape.

In addition, the turbine blades of the gas turbine operating at high temperatures are subject to centrifugal force due to high-speed rotation of the turbine, and creep characteristics for enduring the centrifugal force at high temperatures become very important.

Since grain boundaries of cast alloy produced by general casting process are vulnerable to high-temperature creep characteristics, unidirectional solidification casting process which improved the creep characteristics of alloy by eliminating grain boundaries having a direction perpendicular to the stress since 1970's and single- A casting process has been developed and used to manufacture turbine blades.

Along with the development of such processes, alloys specialized in the respective polycrystalline, unidirectional solidification and single crystal casting processes have been developed and used.

Among them, a nickel-base superalloy is produced by a one-way solidification casting process. It is a special alloy requiring excellent oxidation resistance and mechanical properties at a high temperature of about 760 ° C or more. It is made of chromium (Cr), cobalt (Co) (Ti), molybdenum (Mo), tungsten (W), tantalum (Ta), niobium (Nb), carbon (C), boron (B), zirconium (Zr), rhenium (Re) ) Are added.

Such nickel-base superalloys have been continuously studied for designing alloy compositions having excellent properties because the characteristics of alloys to be exhibited vary depending on the kind, content and specific combination of alloying elements to be added.

Ni-based ultra heat resistance alloy by addition of Al, Ti, Ta, etc. L1 ₂ phase in a γ base (matrix) (W, Mo, Re, Cr, and Co), which is a strengthened phase lattice strengthening phase γ '(Ni ₃ (Al, Ti, Ta) Excellent high temperature creep strength is obtained. In addition, in the case of grain boundaries, fine precipitates are precipitated discontinuously at grain boundaries through the addition of alloying elements such as C, B, and Zr to maintain the high temperature creep strength of the grain boundaries.

In recent years, in order to satisfy the necessity of an alloy excellent in temperature water solubility and creep characteristics of an alloy, it is considered to be an effective alloy design method to control the addition amount of other alloying elements while minimizing the addition of high-priced alloying elements as much as possible.

Particularly in the case of parts used at high temperatures, the creep lifespan that reaches the creep rupture described above is also important, but if the shape of the part changes, it will not be able to be used continuously for the original purpose or the efficiency will be lowered. Is a very important factor to consider.

Accordingly, efforts have been made to obtain alloys excellent in tensile strength and creep characteristics at high temperature by controlling the amount of alloying elements. For example, in Korean Patent Laid-Open No. 10-2012-0105693, the content of aluminum or titanium is controlled There is disclosed a single-crystal nickel-base superalloy having improved creep characteristics.

The superabsorbent alloy according to the above-mentioned patent is characterized by containing 11.5 to 13.5% of Co, 3.0 to 5.0% of Cr, 0.7 to 2.0% of Mo, 8.5 to 10.5% of W, 3.5 to 5.5% of Al, 2.5 to 3.5% of Ta, 6.0 to 8.0% of Ta, 2.0 to 4.0% of Re and 0.1 to 2.0% of Ru, and the balance of Ni and other unavoidable impurities. However, the disclosed patent includes expensive Re and Ru, and since about 3% by weight of Re and Ru accounts for about half of the total alloy price, alloys containing Re and Ru increase the price There is a difficulty in suppressing.

U.S. Pat. No. 4,209,348 discloses a heat treated superalloy single crystal article having a high melting temperature by including a limited amount of cobalt without including carbon, boron and zirconium, and a manufacturing method thereof.

However, the prior art including the above-mentioned U.S. patent is an alloy designed only considering creep characteristics, which is a single stage blade (bucket) of a gas turbine for power generation, which contacts with a corrosive gas at a high temperature and is highly stressed due to centrifugal force of several thousands or tens of thousands of rpm Application of the same parts can shorten parts life due to high temperature oxidation and corrosion problems.

Therefore, in order to design the material for the first stage of the gas turbine for power generation, alloy design should be made considering not only creep characteristics but also various material characteristics such as high temperature corrosion resistance, oxidation resistance, casting of large parts, do.

An object of the present invention is to satisfy the demand for the development of a super heat resistant alloy as described above and to solve the problems of the prior arts, and it is an object of the present invention to provide a high temperature creep characteristic and oxidation resistance, And thus a manufacturing cost of the nickel-base superalloy is remarkably reduced.

Another object of the present invention is to optimize the compositional ratio of elements so as to maximize solid solution strengthening effect while maintaining phase stability at a high temperature and to control the fraction of gamma prime precipitate so as to improve unidirectional solidification castability, And a method of manufacturing the same.

It is a further object of the present invention to provide a process for the preparation of poly (vinylidene fluoride), which comprises incorporating at least 56.93% by volume of the gamma prime phase relative to the total volume and having a phase stability (Md) of 0.99 or less, And a method of manufacturing the same.

The nickel-base superalloy according to the present invention is characterized in that it contains 2.0 to 6.0 wt.% Of cobalt, 8.0 to 13.0 wt.% Of chromium (Cr), 6.0 to 9.0 wt.% Of tungsten (W) (Al), 2.0 wt.% Or less of titanium (Ti), 6.5 to 9.0 wt.% Of tantalum (Ta), 0.15 wt.% Or less of carbon (C) Boron (B) of 0.02 wt.% Or less, zirconium (Zr) of less than 0.02 wt.% And nickel (Ni) which is the remainder and other unavoidable impurities.

The nickel-base superalloy according to the present invention is a nickel-base superalloy having a composition comprising 3.8 to 4.3 wt.% Of cobalt, 9.6 to 10.5 wt.% Of chromium (Cr), 6.8 to 7.2 wt.% Of tungsten (W) (Al), 0.7 to 1.3 wt.% Of titanium (Ti), 7.2 to 7.6 wt.% Of tantalum (Ta), 0.039 to 0.121 wt.% Of carbon (C) , Boron (B) in an amount of 0.011 to 0.016 wt.%, Zirconium (Zr) in an amount of 0.002 to 0.011 wt.% And nickel (Ni) as a remainder, and other unavoidable impurities.

The nickel-base superalloy has a M ₂₃ C ₆ and M ₆ C type carbide at the grain boundary, and the γ 'precipitates are uniformly distributed in the matrix.

The γ 'precipitates are present in an amount of 56.93 to 69.23% by volume based on the total volume of the nickel-base superalloy.

The nickel base superalloy has a solid solution strengthening index of 1.60E + 18 to 1.92E + 18.

The M ₂₃ C ₆ and M ₆ C types of carbides and γ 'precipitates are characterized by a first aging step of inducing the formation of fine M ₂₃ C ₆ and M ₆ C carbides and γ' precipitates, the γ 'precipitates and the fine M ₂₃ And a second aging step of increasing the volume fraction of C ₆ and M ₆ C carbides.

A method of manufacturing a nickel-base superalloy according to the present invention is characterized by comprising the steps of: preparing a cobalt (Co) alloy containing 2.0 to 6.0 wt.%, Chromium (Cr) of 8.0 to 13.0 wt.%, Tungsten ), 4.0 to 6.0 wt.% Of aluminum (Al), 2.0 wt.% Or less of titanium (Ti), 6.5 to 9.0 wt.% Of tantalum (Ta), and 0.15 wt. ), A material preparation step of preparing an alloy material containing 0.02 wt.% Or less of boron (B), less than 0.02 wt.% Of zirconium (Zr) and nickel as a remainder and other unavoidable impurities A step of subjecting the alloy material to unidirectional solidification casting to produce a cast product; a solution treatment step of homogenizing the cast product at 1280 ° C for 4 hours; and a step of treating the alloy with fine M ₂₃ C ₆ and M ₆ C carbide and γ ' and the first aging step to induce a precipitate generated, γ 'precipitates and has a fine M ₂₃ C ₆ and M ₆ C carbides MC type carbide in the crystal grains by increasing the volume fraction of the interface, Eiji internal to the claim characterized by comprising a second aging step to complete the second Ni-based heat resistant alloy for the γ 'precipitates are uniformly distributed.

A method of manufacturing a nickel-base superalloy according to the present invention is characterized in that the cobalt (Co), the cobalt (Co), the cobalt (Cr) and the tungsten (W) in the range of 3.8 to 4.3 wt.%, 9.6 to 10.5 wt.% And 6.8 to 7.2 wt. , Aluminum (Al), 0.7 to 1.3 wt.% Of titanium (Ti), 7.2 to 7.6 wt.% Of tantalum (Ta), 0.039 to 0.121 wt.% Of carbon (C), 0.011 to 0.016 wt.% Of boron (B), 0.002 to 0.011 wt.% Of zirconium (Zr) and the remainder of nickel (Ni) and other inevitable impurities A solution preparing step of homogenizing the cast product at 1280 DEG C for 4 hours; a step of applying a solution containing fine M ₂₃ C ₆ and M ₆ C by increasing the 'first aging step and, γ inducing precipitate generated, and a fine precipitate M ₂₃ C ₆ and the volume fraction of M ₆ C carbide carbide and γ is a carbide of MC type in the grain interface Said, to the claim characterized in that comprising a second aging step of the γ 'precipitate completion of the second Ni-based heat resistant alloy are uniformly distributed within the base.

The solution treatment step is characterized in that it is a process of employing a coarse and irregularly shaped? 'Precipitate as a known γ phase.

The first aging step is performed at 1080 캜 for 4 hours, and the second aging step is performed at 871 캜 for 24 hours in a vacuum or an inert atmosphere.

The nickel-base superalloy according to the present invention and its manufacturing method are excellent in high-temperature creep characteristics and oxidation resistance, and have a merit that the production cost can be remarkably lowered by adding rare elements Re, Ru and Mo.

In addition, the present invention optimizes the composition ratio of the elements to maintain the phase stability at a high temperature, while the effect of solid solution strengthening is highly contrived, and the advantage that the unidirectional solidification castability, oxidation resistance and creep characteristics are simultaneously improved by controlling the fraction of? 'Precipitate have.

In addition, it has a phase stability (Md) of 0.99 or less and has an effect of further improving oxidation characteristics by adding no molybdenum (Mo).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a table showing compositions of preferred and comparative examples of a nickel-base superalloy according to the present invention;
2 is a transmission electron micrograph of a grain boundary interface of a nickel-base superalloy according to the present invention.
3 is a flow chart showing a process for producing a nickel-base superalloy according to the present invention.
FIG. 4 is a graph showing the temperature and time conditions at various stages in the method of manufacturing a nickel-base superalloy according to the present invention. FIG.
5 is a photograph of the microstructure of the dendritic core and the inter-dendritic region after one-directional solidification of the nickel-base superalloy according to the present invention.
6 is a table for comparison of heat treatment conditions according to Examples and Comparative Examples in a method of producing a nickel-base superalloy according to the present invention.
FIGS. 7 and 8 are graphs showing the creep characteristics measured according to the heat treatment conditions according to Examples and Comparative Examples in the method for producing a nickel-base superalloy according to the present invention.
9 to 12 are photographs of microstructures at each step of a preferred embodiment of the method for producing a nickel-base superalloy according to the present invention.
13 is a table comparing the phase stability (Md), gamma volume%, solid solubility index and oxidation characteristics of preferred embodiments of the nickel-base superalloy according to the present invention and Comparative Examples.
14 is a graph comparing the volume% of γ 'at 870 ° C. with respect to the preferred embodiments of the nickel-base superalloy according to the present invention and the comparative example.
FIG. 15 is a graph comparing and measuring the hardening hardening index with respect to the preferred embodiments of the nickel-base superalloy according to the present invention and the comparative example. FIG.
16 is a graph comparing and measuring oxidation characteristics with respect to preferred embodiments and comparative examples of a nickel-base superalloy according to the present invention.
17 is a table showing compositions in a more preferred embodiment of the nickel-base superalloy according to the present invention and a comparative example (comparative example including molybdenum).
18 is a graph comparing creep characteristics at 871 DEG C and 310 MPa with respect to a more preferred embodiment and a comparative example of the nickel-base superalloy according to the present invention.
19 is a graph comparing the creep characteristics of the comparative nickel-base superalloy with the nickel-base superalloy according to the present invention at 982 ° C and 187 MPa.
FIG. 20 is a table comparing the phase stability (Md), gamma volume percent, solid solubility index and oxidation characteristics of the example and comparative example shown in FIG.

Hereinafter, the composition and the internal structure of the nickel-base superalloy according to the present invention will be described with reference to FIGS. 1 and 2 attached hereto.

Prior to this, terms and words used in the present specification and claims should not be construed in a conventional and dictionary sense, and the inventor may appropriately define the concept of the term in order to describe its invention in the best possible way It should be construed as meaning and concept consistent with the technical idea of the present invention.

Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely preferred embodiments of the present invention, and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents It should be understood that water and variations may be present.

FIG. 1 is a table showing compositions of preferred embodiments and comparative examples of a nickel-base superalloy according to the present invention.

The super-heat-resistant alloy according to the present invention was developed to be applicable as a turbine blade of a gas turbine with an operating temperature of ultra-high temperature. As shown in FIG. 1, the composition ratio of the alloy element was optimized to improve the one- And it is designed to lower the manufacturing cost by adding no molybdenum (Mo), rhenium (Re) and ruthenium (Ru), which are rare elements, to the high temperature creep characteristics and oxidation resistance.

In particular, molybdenum (Mo) is not included because it degrades the oxidation characteristics, and the process is controlled to include 56.93 vol.% Or more of the total volume of the γ 'precipitate to improve oxidation resistance, creep characteristics, and phase stability .

As shown in the drawing, the super-refractory alloy of the preferred embodiment of the present invention has a composition of 2.0 to 6.0 wt.% Of cobalt, 8.0 to 13.0 wt.% Of chromium (Cr), 6.0 to 9.0 wt.% Of tungsten (W) (Al), 2.0 wt.% Or less of titanium (Ti), 6.5 to 9.0 wt.% Of tantalum (Ta), and 0.15 wt.% Or less of carbon (C) And boron (B) of 0.02 wt.% Or less, zirconium (Zr) of less than 0.02 wt.% And nickel (Ni) and other unavoidable impurities.

On the other hand, the comparative examples have the same components as those of the examples, and the composition ranges of the components are prepared by changing at least one of them to the boundary or not include the molybdenum (Mo) To see what characteristics are changing.

As shown in FIG. 2, the grain boundary of the super-refractory alloy has a structure in which fine carbides of the M ₂₃ C ₆ and M ₆ C types are discontinuously formed as shown in FIG. 2, whereby the high temperature creep characteristics, .

The super-heat-resistant alloys consider microstructure stability, oxidation resistance, unidirectional solidification, solidification index, and raw material cost associated with known solid solution strengthening and precipitation strengthening, brittle TCP topologically close-packed The alloy is derived from the design program for ultra-heat-resistant alloys (Program Registration No. C-2013-004753).

Cobalt (Co): 2.0 to 6.0 wt.%

Cobalt is known to enhance the high temperature strength by reducing the stacking defect energy of the base with the solid solution strengthening of the γ phase which is the base of the nickel base superalloy as an essential alloy element in the current nickel base superalloy. When the cobalt content is less than 2.0%, it is difficult to improve the creep characteristics due to the decrease of the solid solution strengthening effect of the alloy. When the cobalt content is more than 6.0%, the brittle TCP phase is promoted and the high temperature stability and mechanical properties Can be reduced.

Cr (Cr): 8.0 to 13.0 wt.%

The main purpose of chromium addition in the nickel base superalloy is to improve the high temperature corrosion resistance and oxidation resistance of the alloy. In addition, chromium has the role of improving creep characteristics by forming fine carbides in grain boundaries and suppressing grain boundary slip under high temperature creep.

If less than 8.0% of chromium is added, the high temperature corrosion resistance of the alloy is deteriorated. In addition, when the amount of chromium added is more than 13.0%, the alloy stability of the alloy is maintained. The generation on the TCP may increase sharply.

Tungsten (W): 6.0 to 9.0 wt.%

Tungsten, which is a refractory element with high density, is an element with a very low diffusion coefficient in nickel and contributes greatly to solid solution strengthening of a nickel-base superalloy and serves to increase the melting point of the alloy. In addition, tungsten is a major element for forming M ₆ C and M ₂₃ C ₆ carbides together with chromium and molybdenum, which contributes to strengthening the grain boundaries.

Despite these advantages, tungsten tends to produce a brittle TCP phase and tends to segregate to a solid phase during unidirectional solidification and single crystal solidification, increasing the likelihood of crystal defects such as freckle defects.

Therefore, more than 6.0% of tungsten is added to improve creep strength through proper solidification strengthening effect, and its content is limited to 9.0% in order to suppress the negative effects on casting and high temperature mechanical properties due to excessive addition.

Molybdenum (Mo): not included

Although molybdenum contributes to improvement of the high-temperature characteristics of the alloy through strengthening of the base, molybdenum is a main element for forming a TCP phase together with chromium and tungsten, and is not included in the embodiment of the present invention because it lowers phase stability and oxidation resistance .

In addition, changes in phase stability and oxidation characteristics depending on the presence or absence of molybdenum (Mo) will be described in detail below through Comparative Examples 13 to 17. [

Aluminum (Al): 4.0 to 6.0 wt.%

Aluminum is the main forming element on γ '(Ni ₃ Al), which is the main strengthening phase of the nickel base superalloy. In the nickel-base superalloy, aluminum improves the creep strength of the alloy by precipitation strengthening of the γ 'phase, and contributes to improving the oxidation resistance of the alloy by forming a dense oxide layer.

In the aluminum-added alloy of less than 4.0%, the precipitation fraction of the γ 'phase is lowered, thereby contributing to the creep strength. In the case of aluminum addition of more than 6.0%, the excessive amount of γ' phase is precipitated, (The temperature range between the incipient melting temperature of the alloy at the γ 'phase melting temperature) in which the solution heat treatment is possible by increasing the heating temperature of the γ' phase is drastically reduced, and the solution heat treatment becomes difficult.

Titanium (Ti): 2.0 wt.% Or less

Titanium plays a role in strengthening the γ 'phase by substituting aluminum with γ' phase as an element forming γ 'phase with aluminum. Titanium is also an element that improves the high temperature corrosion resistance of alloys.

As the amount of titanium added increases, the volume fraction of the γ 'phase increases to increase the creep strength of the alloy, but when added to an alloy having a high aluminum content exceeding 5.0%, the γ' phase fraction is excessively increased, It is possible to form a coarse Eta (Ni ₃ Ti) phase in the dendritic region to lower the phase stability and the mechanical properties. Therefore, the content is limited to 2.0%.

Tantalum (Ta): 6.5 to 9.0 wt.%

Tantalum is an element that not only contributes to solidification of the γ phase, but also strengthens the γ 'phase by replacing aluminum with γ'-phase with titanium. In addition, tantalum, which is a high-density heat-resistant element, is segregated as a liquid phase during solidification to increase the density of the liquid phase in the resin phase, thereby damping the buoyancy of the liquid phase in the resin phase during the unidirectional solidification or single crystal solidification.

Therefore, it is preferable to add more than 6.5% of tantalum in an alloy having a high tungsten content of 6.0 to 9.0%. However, the addition of tantalum in an amount of more than 9.0% promotes the TCP phase formation such as a Mu phase, Degrade the properties.

Carbon (C): 0.15 wt.% Or less

Carbon is deficient with Cr, Mo, W and the like, so that fine carbide particles of M ₂₃ C ₆ or M ₆ C type are formed discontinuously in grain boundaries to improve grain boundary strength. When carbon is not contained, carbide is not formed in grain boundaries. When carbon content higher than 0.15% is added, an excessive amount of coarse MC type carbide is formed in the crystal grains by bonding with Ti and Ta during coagulation, The maximum content of carbon is limited to 0.15% because it not only lowers the strength but also forms continuous M ₂₃ C ₆ or M ₆ C type carbides in the form of a film in grain boundaries and rather lowers grain boundary strength.

Boron (B): 0.02 wt.% Or less

Boron plays a role in strengthening the grain boundaries with carbon and plays a role of strengthening these carbides by substituting carbons from M ₂₃ C ₆ or M ₆ C type carbides generated at grain boundaries. However, if an excessive amount of boron is added, the local melting temperature of the alloy may be decreased to cause local melting near the process tissue during the solution heat treatment, so that the content is limited to 0.15% or less.

Zirconium (Zr): 0.02 wt.% Or less

Zirconium, together with carbon and boron, serves to strengthen the grain boundaries. In addition, zirconium contributes to prevention of strength deterioration due to grain boundary segregation of sulfur by forming a sulfide by binding with sulfur when sulfur, which is an impurity element that significantly reduces creep characteristics, is introduced in a nickel-base superalloy.

However, zirconium in an amount greater than 0.02% causes excessive grain boundary segregation of zirconium, which lowers the high temperature grain boundary strength, so that the maximum content is limited to 0.02%.

A method for manufacturing the super-high temperature alloy will be described with reference to FIGS.

FIG. 3 is a process flow chart showing a method of manufacturing a nickel-based superalloy according to the present invention, and FIG. 4 is a graph showing a temperature and a time condition according to a heat treatment step in the method of manufacturing a nickel-base superalloy according to the present invention.

As shown in the figure, the super-high-temperature alloy includes a material preparation step (S100) for preparing an alloy material having the above composition, a casting step (S200) for producing a cast product by unidirectionally solidifying the alloy material, A first aging step (S400) for aging treatment at 1080 DEG C for 4 hours (S400), and a heat treatment at 871 DEG C for 24 hours to complete a nickel base superalloy And a second aging step S500.

That is, the alloy of the above-described super alloy is prepared by unidirectional solidification, and then the solution is subjected to one solution treatment and two aging treatments.

Fig. 5 is a microstructure photograph of the dendritic core and the interdendritic region of the nickel-base superalloy in accordance with the present invention after unidirectional solidification. Fig. Due to the segregation of the alloying elements in the unidirectional solidification, there is a difference in composition between the dendritic core region and the dendritic phase. In particular, the formation of γ 'phase is promoted in the interdendritic region where γ' phase formation elements are segregated so that a large and high fraction of γ 'phase is generated compared with the dendritic core region. In the latter half of solidification, γ / As shown in FIG.

Accordingly, after the casting step (S200), the segregation of the alloy element is homogenized and the solution treatment step (S300) is performed to solidify the coarse? 'Precipitate. In the solution treatment step (S300), three conditions were selected in consideration of temperature and time related to the employment and diffusion of? 'Phase on the basis of the results of differential scanning calorimetry analysis.

FIG. 6 is a table for comparison of heat treatment conditions according to Examples and Comparative Examples in the method for producing a nickel-base superalloy according to the present invention. In the embodiment, the solution treatment step (S300) , The first aging step (S400) is performed at 1080 DEG C for 4 hours, the second aging step (S500) is performed at 871 DEG C for 24 hours, and the vacuum aging step or the inert gas atmosphere is performed.

In the manufacturing method of Comparative Example 1, the temperature was elevated in a stepwise manner in the solution treatment step, and the manufacturing method of Comparative Example 2 was a method in which only the aging treatment was performed without the solution treatment step.

The results are shown in FIGS. 7 and 8. FIG.

FIGS. 7 and 8 are graphs showing the creep characteristics measured according to the heat treatment conditions according to Examples and Comparative Examples in the method of manufacturing a nickel-base superalloy according to the present invention. It was confirmed that the life of the creep was much higher than that of the alloy of the comparative example.

More specifically, the nickel-base superalloy has a creep life of at least 600 hours at 871 ° C / 310 MPa and a creep life of at least 150 hours at 982 ° C / 187 MPa.

Hereinafter, microstructural changes at each step will be described with reference to FIGS. 9 to 12 attached hereto. 9 to 12 are microstructural photographs of each step of the preferred embodiment of the method for producing a nickel-base superalloy according to the present invention, and are classified into regions such as a dendritic core region, a dendritic region, and a grain boundary region.

As shown in FIG. 9, the coarse and irregularly shaped? 'Precipitates observed in the dendritic core and the interdendritic area in the casting state are employed as the known? Phase by the solution treatment step (S300) It can be seen from FIG. 10 that the size decreases. In addition, it can be seen that the grain boundaries are composed of coarse MC type carbide and? 'Precipitate without change by the above solution treatment step (S300).

11 is a microstructure after the first aging step (S400). As a result, unlike the casting state of FIG. 9, the γ 'precipitates, which have been solidified in the known γ phase through the solution treatment step (S300) S400), a γ 'phase having an average size of 0.3 to 0.4 μm is precipitated in the dendritic core region and the dendritic region.

In addition, it can be confirmed that the first aging step (S400) induces fine M ₂₃ C ₆ and M ₆ C type carbide precipitation in addition to the MC type carbide and the γ 'precipitate at the grain boundaries.

12 shows the microstructure after the second aging step (S500). The heat treatment performed at 871 占 폚 for 24 hours has no particular influence on the size and shape of the? 'Phase deposited on the dendritic core region and the dendritic region, It was confirmed that the volume fraction of the precipitate was further increased and the fine M ₂₃ C ₆ and M ₆ C type carbide fractions were increased at grain boundaries.

13, the solid solution strengthening index of 1.60E + 18 to 1.92E + 18 was higher than that of the comparative example as shown in FIG. 13, and the γ 'precipitate Was present in an amount of 56.93 to 69.23% by volume based on the total volume of the nickel-base superalloy, and it was found that the high-temperature oxidation characteristics were particularly improved.

That is, FIG. 13 is a table showing a comparison between the phase stability (Md), gamma volume percent, solid solubility index and oxidation characteristics of the preferred embodiments of the nickel-base superalloy according to the present invention and the comparative examples, The smaller the weight loss per area (mg / cm 2), the better the oxidation characteristics.

More specifically, FIG. 14 is a graph comparing the volume% of γ 'at 870 ° C. with respect to the preferred embodiments and comparative examples of the nickel-base superalloy according to the present invention. In the case of the samples thus prepared, the volume percentage of γ 'was uniformly shown at 870 ° C. However, in the comparative example, the volume percentage of γ' was significantly lower than that of the examples.

On the other hand, in the case of Comparative Example 6 and Comparative Example 9 in which the volume percentage of gamma prime a 'is higher than that of the sample of the present invention in FIG. 14, it can be confirmed that the solidification strengthening index is remarkably lowered as shown in FIG.

That is, when the volume percentage of γ 'is increased without limitation, the phase stability is relatively lowered. In a preferred embodiment of the present invention, by controlling the volume percentage of γ' to 56.93 to 69.23 volume% (Md) as shown below.

Also, as shown in FIG. 16, the super-heat-resistant alloy having the composition range of the preferred embodiment of the present invention has a significantly low weight loss when compared with the comparative example.

The composition and characteristics of a more preferred embodiment of the present invention will be described below with reference to FIGS. 17 to 20 attached hereto.

17 is a table showing compositions in a more preferred embodiment and a comparative example (a molybdenum-containing comparative example) of a nickel-base superalloy according to the present invention. Examples 6-1 to 6- a large number of samples were prepared on the basis of Example 6 in which the volume percent of γ 'and the oxidation characteristics were within the above ranges and the solid solubility index was the lowest.

More specifically, as shown in FIG. 17, the nickel-base superalloy according to a more preferred embodiment of the present invention comprises 3.8 to 4.3 wt.% Of cobalt, 9.6 to 10.5 wt.% Of chromium, (W), 4.6 to 5.3 wt.% Of aluminum (Al), 0.7 to 1.3 wt.% Of titanium (Ti), and 7.2 to 7.6 wt.% Of tantalum (Ta) (C), 0.011 to 0.016 wt.% Of boron (B), 0.002 to 0.011 wt.% Of zirconium (Zr) and the remaining nickel (Ni) and other inevitable impurities .

On the other hand, Comparative Examples 13 to 17 contain molybdenum (Mo) or a large amount of cobalt (Co). The alloys of Comparative Example 13 and Comparative Example 14 were Siemens-Westinghouse's 501F model and General Electric It is IN738LC and GTD-111, which are commercial unidirectional solidification super heat resistant alloys used for turbine blades of 7FA model.

18 and 19 are graphs showing creep characteristics measured for alloys of preferred embodiments and comparative examples. The nickel-base superalloy according to a more preferred embodiment of the present invention has a temperature of 871 DEG C / 310MPa for 630 hours And a creep life of at least 170 hours under the condition of 982 DEG C / 187 MPa. As a result, it was confirmed that the creep characteristics were significantly higher than those of the comparative examples.

20 is a table showing the comparison of phase stability (Md), gamma volume percent, solubility enhancing index and oxidation characteristics with respect to the examples and comparative examples shown in Fig. 17, and in addition to the oxidation characteristics described above, Contained no molybdenum (Mo), and thus showed a volume percentage of gamma prime of higher than Comparative Examples 13 to 15.

And the Employment Strength Index was also higher than the Comparative Example.

The scope of the present invention is not limited to the above-described embodiments, and many other modifications based on the present invention will be possible to those skilled in the art within the scope of the present invention.

S100. Material preparing step S200. Casting step
S300. Solution treatment step S400. First aging step
S500. Second aging step

Claims (10)

(Cr), 6.0 to 9.0 wt.% Of tungsten (W), 4.0 to 6.0 wt.% Of aluminum (Al), and the amount of cobalt (Co) (Ti), 6.5 to 9.0 wt.% Of tantalum (Ta), 0.15 wt.% Or less of carbon (C), 0.02 wt.% Or less of boron (B) , Less than 0.02 wt.% Of zirconium (Zr), and the remainder nickel (Ni) and other unavoidable impurities.
(Co), 9.6 to 10.5 wt.% Of chromium (Cr), 6.8 to 7.2 wt.% Of tungsten (W), and 4.6 to 5.3 wt.% Of aluminum (Al) And 0.011 to 0.016 wt.% Of boron (Ti), 0.7 to 1.3 wt.% Of titanium (Ti), 7.2 to 7.6 wt.% Of tantalum (Ta), 0.039 to 0.121 wt. B), 0.002 to 0.011 wt.% Of zirconium (Zr), and the balance nickel (Ni) and other unavoidable impurities.
The nickel-base superalloy according to claim 1 or 2, wherein the nickel-
The crystal grain interface ₂₃ M ₆ C and M ₆ C type carbide has a nickel-based ultra heat resistance alloy, it characterized in that the γ 'precipitates are uniformly distributed within the base.
The nickel base superalloy according to claim 3, wherein the? 'Precipitates are present in an amount of 56.93 to 69.23% by volume based on the total volume of the nickel base superalloy.
The nickel base superalloy according to claim 4, wherein the nickel base superalloy has a solid solution strengthening index of 1.60E + 18 to 1.92E + 18.
The method of claim 5, wherein the M ₂₃ C ₆ and M ₆ C types of carbide and γ '
A first aging step for inducing generation of fine M ₂₃ C ₆ and M ₆ C carbides and γ 'precipitates,
And a second aging step of increasing the volume fraction of the γ 'precipitates and the fine M ₂₃ C ₆ and M ₆ C carbides.
(Cr), 6.0 to 9.0 wt.% Of tungsten (W), 4.0 to 6.0 wt.% Of aluminum (Al), and the amount of cobalt (Co) of 2.0 to 6.0 wt.%, 8.0 to 13.0 wt. (Ti), 6.5 to 9.0 wt.% Of tantalum (Ta), 0.15 wt.% Or less of carbon (C), 0.02 wt.% Or less of boron (B) , Less than 0.02 wt.% Of zirconium (Zr), and the balance nickel (Ni) and other unavoidable impurities.
A casting step of producing a cast article by unidirectionally solidifying and casting the alloy material,
A solution treatment step of homogenizing the cast article at 1280 캜 for 4 hours,
A first aging step of inducing generation of fine M ₂₃ C ₆ and M ₆ C carbides and γ 'precipitates in the grain boundaries,
type superalloy having a MC type carbide at the grain boundary by increasing the volume fraction of γ 'precipitates and fine M ₂₃ C ₆ and M ₆ C carbides, and a γ-type superalloy having uniformly distributed γ' precipitates therein 2 < / RTI > aging step.
(Co), 9.6 to 10.5 wt.% Of chromium (Cr), 6.8 to 7.2 wt.% Of tungsten (W), and 4.6 to 5.3 wt.% Of aluminum (Al) And 0.011 to 0.016 wt.% Of boron (Ti), 0.7 to 1.3 wt.% Of titanium (Ti), 7.2 to 7.6 wt.% Of tantalum (Ta), 0.039 to 0.121 wt. B), 0.002 to 0.011 wt.% Of zirconium (Zr), and the balance nickel (Ni) and other unavoidable impurities.
A casting step of producing a cast article by unidirectionally solidifying and casting the alloy material,
A solution treatment step of homogenizing the cast article at 1280 캜 for 4 hours,
A first aging step of inducing generation of fine M ₂₃ C ₆ and M ₆ C carbides and γ 'precipitates in the grain boundaries,
type superalloy having a MC type carbide at the grain boundary by increasing the volume fraction of γ 'precipitates and fine M ₂₃ C ₆ and M ₆ C carbides, and a γ-type superalloy having uniformly distributed γ' precipitates therein 2 < / RTI > aging step.
9. The method according to claim 7 or 8,
Wherein the process is a process of solidifying γ 'precipitates in a coarse and irregular shape into a known γ phase.
10. The method of claim 9, wherein the first aging step is carried out at 1080 DEG C for 4 hours,
Wherein the second aging step is carried out at 871 캜 for 24 hours in a vacuum or an inert atmosphere.

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