CN117947364A - Recovery heat treatment method for repairing creep damage of K439B nickel-based superalloy - Google Patents
Recovery heat treatment method for repairing creep damage of K439B nickel-based superalloy Download PDFInfo
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 101
- 238000011084 recovery Methods 0.000 title claims abstract description 55
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 title claims abstract description 44
- 238000000034 method Methods 0.000 title claims abstract description 37
- 229910052759 nickel Inorganic materials 0.000 title claims abstract description 22
- 229910000601 superalloy Inorganic materials 0.000 title claims abstract description 16
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 125
- 239000000956 alloy Substances 0.000 claims abstract description 125
- 238000011282 treatment Methods 0.000 claims description 73
- 230000032683 aging Effects 0.000 claims description 60
- 238000001816 cooling Methods 0.000 claims description 32
- 230000000630 rising effect Effects 0.000 claims description 23
- 238000010791 quenching Methods 0.000 claims description 13
- 230000000171 quenching effect Effects 0.000 claims description 13
- 238000004321 preservation Methods 0.000 claims description 6
- 238000005086 pumping Methods 0.000 claims description 5
- 230000015556 catabolic process Effects 0.000 abstract description 3
- 238000006731 degradation reaction Methods 0.000 abstract description 3
- 238000012423 maintenance Methods 0.000 abstract description 3
- 210000001787 dendrite Anatomy 0.000 description 41
- 239000000243 solution Substances 0.000 description 27
- 101000912561 Bos taurus Fibrinogen gamma-B chain Proteins 0.000 description 20
- 230000000052 comparative effect Effects 0.000 description 18
- 238000012360 testing method Methods 0.000 description 18
- 230000007774 longterm Effects 0.000 description 16
- 239000006104 solid solution Substances 0.000 description 12
- 238000005728 strengthening Methods 0.000 description 12
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 8
- 238000000227 grinding Methods 0.000 description 8
- 238000005498 polishing Methods 0.000 description 8
- 238000001556 precipitation Methods 0.000 description 8
- 230000008569 process Effects 0.000 description 7
- 230000002045 lasting effect Effects 0.000 description 6
- 230000007797 corrosion Effects 0.000 description 5
- 238000005260 corrosion Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 229910000905 alloy phase Inorganic materials 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- 235000011187 glycerol Nutrition 0.000 description 4
- 230000001788 irregular Effects 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 230000008439 repair process Effects 0.000 description 4
- 238000005266 casting Methods 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
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- 230000009467 reduction Effects 0.000 description 3
- 230000006978 adaptation Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000008520 organization Effects 0.000 description 2
- 238000001226 reprecipitation Methods 0.000 description 2
- 208000031361 Hiccup Diseases 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000001010 compromised effect Effects 0.000 description 1
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- 230000008034 disappearance Effects 0.000 description 1
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- 238000001035 drying Methods 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000001513 hot isostatic pressing Methods 0.000 description 1
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- 239000011159 matrix material Substances 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
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Abstract
The invention relates to the technical field of cast nickel-based superalloy, in particular to a recovery heat treatment method for repairing creep damage of K439B nickel-based superalloy. The invention provides a practical and available recovery heat treatment method capable of repairing a nickel-based superalloy K439B degradation structure for a turbine casing, which eliminates gamma' phase, grain boundary M 23C6 carbide and eta phase, so that the structure of the alloy basically reaches a heat treatment state level, and room temperature tensile property and high temperature durability are close to or even exceed the heat treatment state level, thereby ensuring service safety of an aeroengine, prolonging the service life of the engine casing and reducing maintenance cost of the aeroengine.
Description
Technical Field
The invention relates to the technical field of cast nickel-based superalloy, in particular to a recovery heat treatment method for repairing creep damage of K439B nickel-based superalloy.
Background
The nickel-based superalloy has excellent middle-high temperature strength, heat resistance, corrosion resistance and the like, is a main material for key components of the hot end of an advanced aeroengine and a gas turbine, and is used in a high-temperature and high-pressure complex environment. The main strengthening modes of the alloy are gamma' phase precipitation strengthening, grain boundary precipitation strengthening, second phase strengthening, solid solution strengthening and the like. In the service process, a series of tissue degradation of the material, such as coarsening and raft treatment of gamma' phase, carbide decomposition, precipitation of TCP phase and the like, is generated, so that the mechanical property is obviously reduced, the service life of the casting is seriously damaged, and the parts are required to be replaced regularly. The recovery heat treatment can be effectively adjusted to the size, the number and the distribution of precipitated phases in the life part, the organization and the mechanical property of the alloy are recovered to a certain extent, the service life of the part is prolonged, the service safety is improved, the capacity of reinstalling and using is realized, the manufacturing cost is reduced, and the economic benefit is great.
K439B is used as a novel nickel-based superalloy and is intended for manufacturing 800 ℃ level complex thin-wall casing castings of fifth-generation turbofan engines. The casting is easy to produce metallurgical defects such as loosening, hiccups, inclusions and the like in the manufacturing process, and needs welding treatment. Therefore, the grain boundary strengthening effect of the K439B alloy is also extremely important, and when M 23C6 carbide at the grain boundary is in granular distribution, the inter-grain deformation can be coordinated, so that the alloy has higher strength. After the K439B alloy is subjected to long-term aging test of simulated service, the gamma' -phase is coarsened in size, MC carbide at the grain boundary is degraded to form a small amount of eta phase, meanwhile, M 23C6 carbide at the grain boundary is linked to be long-strip-shaped and further grows up, the grain boundary width is increased, and at the moment, the room-temperature tensile property and the high-temperature durability of the alloy are obviously reduced. At present, no report is made on a recovery heat treatment method of the K439B alloy degenerated structure.
The recovery heat treatment method is to re-solutionize the alloy strengthening phase into the matrix for re-precipitation after heat treatment at different temperatures and time, so that the degenerated structure is basically or completely recovered to the original shape, and the purpose of recovering the mechanical property is achieved. Chinese patent CN103643188B discloses a heat treatment method for K465 alloy that is very remarkable in the recovery performance effect of K465 turbine blades after a period of use. Chinese patent CN104878329B discloses a hot isostatic pressing method for repairing creep damage of DZ125 single crystal alloy, and the microstructure and mechanical properties of the alloy are effectively recovered after recovery treatment; chinese patent CN110284087A carries out recovery treatment on creep damage tissue of K403 alloy blade, and after the recovery heat treatment process treatment, the tissue and performance can be recovered to new product state; chinese patent CN115584455A heat treatment is a recovery heat treatment for single crystal alloys, the second solution treatment temperature is Tf, γ ' ±5 ℃, tf, γ ' is the complete solution temperature of γ ' phase±5 ℃ which is the solution temperature. Unlike other alloys, the lower content of the gamma 'phase of K439B weakens the strengthening effect of the alloy, and the re-dissolution of the grain boundary precipitation phase eta and the recovery of M 23C6 carbide are considered to promote the grain boundary strengthening effect, so that the temperature and time setting in the recovery heat treatment process are particularly important, and the temperature and time setting is required to effectively control the precipitation of the gamma' phase of the alloy and the grain boundary M 23C6 carbide and the elimination of a small amount of eta phase.
Disclosure of Invention
The invention aims to provide a practical and available recovery heat treatment method capable of repairing a nickel-based superalloy K439B degradation structure for a turbine casing, which eliminates coarsened gamma' -phase, grain boundary M 23C6 carbide and eta phase, so that the structure of the alloy basically reaches a heat treatment state level, and room-temperature tensile property and high-temperature durability are close to or even exceed the heat treatment state level, thereby ensuring the service safety of an aeroengine, prolonging the service life of the engine casing and reducing the maintenance cost of the aeroengine. The invention aims at realizing the following process steps:
a recovery heat treatment method for repairing creep damage of a K439B nickel-based superalloy comprises the following steps:
S1, solution treatment: controlling the temperature rising speed in the furnace at 8-10 ℃ per minute, rising the furnace temperature, stopping heating and preserving heat, vacuumizing, and cooling at the air cooling rate;
S2, primary aging treatment: on the basis of the treatment of S1, controlling the temperature rising speed in the furnace to be 8-12 ℃ per minute, rising the furnace temperature, stopping heating and preserving heat, vacuumizing, and cooling at the air cooling rate:
S3, secondary aging treatment: on the basis of the S2 treatment, controlling the temperature rising speed in the furnace to be 8-10 ℃ per minute, rising the furnace temperature, stopping heating and preserving heat, vacuumizing, and controlling the cooling rate to be the air cooling speed;
s4, three-stage aging treatment, wherein on the basis of the treatment of S3, the temperature rising speed in the furnace is controlled to be 6-8 ℃ per minute, the furnace temperature is raised, heating is stopped, heat preservation is carried out, vacuumizing is carried out, and the cooling rate is the air cooling rate, so that the repaired K439B nickel-based alloy is obtained.
The solid solution temperature defined by the invention is K439B alloy gamma '-phase complete solid solution temperature +80-110 ℃ (aiming at effectively dissolving eta phase and other harmful phases and promoting grain boundary to separate out more granular M 23C6 carbide), and the different alloy gamma' -phases have different complete solid solution temperatures. The gamma 'phase in the damaged structure is seriously coarsened after long-term aging for 5000 hours, and the solid solution time is selected according to the time for completely dissolving the coarse gamma' phase and eta phase in the alloy structure at the temperature. If the solution temperature is not suitable, long-form γ' and η phases occur at the grain boundaries.
The primary aging temperature and time have larger influence on the structure of the alloy, when the primary aging heat preservation time is changed to 5 hours, gamma' in the alloy structure precipitates coarse phase change secondarily, the grain boundary becomes coarse and irregular, at the moment, the room temperature stretchability of the alloy is 1140MPa, the durability is 61 hours, and when the primary aging temperature is changed to 1060 ℃, the room temperature stretchability of the alloy is 1100MPa, and the durability is 69 hours.
In the prior art, alloy is often repaired by solid solution and multiple aging treatments, but the technical scheme is different from that of the invention because of different repaired alloy objects, for example, the temperature of a step three furnace in CN103643188B is kept at 1230 ℃ for 4-4.5 hours, and then the alloy is cooled along with the furnace, so that the K439B alloy of the invention is not influenced in a beneficial way, but the gamma' secondary precipitation phase change of the alloy is coarse, and the mechanical property of the alloy is reduced; for example, when the furnace temperature of CN110284087A reaches 1220-1240 ℃, the solution temperature is used for primary melting of K439B alloy, irreversible damage of the alloy occurs, and the alloy structure and mechanical properties cannot be recovered; for example, the CN104878329B heat treatment is a recovery heat treatment for single crystal alloy, the solid solution temperature used is 1235-1255 ℃, the process also generates primary melting for K439B alloy, the alloy structure is irreversibly damaged, and the structure and mechanical properties cannot be recovered; for example, the heat treatment of CN115584455A is a recovery heat treatment for single crystal alloy, the second solution treatment temperature is Tf, γ ' ±5 ℃, tf, γ ' is γ ' phase complete solution temperature±5 ℃, and if the complete solution temperature±5 is used for K439B alloy, the temperature cannot completely eliminate η phase in the alloy structure, grain boundary cannot precipitate granular carbide, so that the alloy structure and mechanical properties cannot be completely recovered.
Therefore, none of the prior art restoration heat treatment processes is effective in restoring the organization and performance of the compromised K439B.
In some embodiments, the furnace temperature is raised to 1170 ℃ to 1200 ℃ in the step S1, heating is stopped, and the temperature is kept for 2 to 4 hours.
In some embodiments, the furnace temperature is raised to 1060 ℃ to 1090 ℃ in the step S2, heating is stopped, and the temperature is kept for 3 to 5 hours.
In some embodiments, the furnace temperature is raised to 830 ℃ to 850 ℃ in the step S3, heating is stopped, and the temperature is kept for 20 to 24 hours.
In some embodiments, the furnace temperature is raised to 800 ℃ in S4, heating is stopped and the temperature is maintained for 15 to 17 hours.
The applicant finds out in a large number of experiments that when the furnace temperature is increased to 1180 ℃ in S1, long-strip carbide is precipitated at the grain boundary, and eta phase is precipitated at the grain boundary, so that the mechanical property of the alloy is reduced; when the primary aging time in S2 is 5h, the secondary gamma' phase in the alloy structure is larger in size and irregular in shape, and further the room temperature tensile property of the alloy and the lasting life under 815 ℃/379MPa are seriously reduced; when the secondary aging temperature in S3 is 800 ℃, the secondary gamma 'phase size in the alloy structure is far smaller than the critical size, the gamma' phase volume fraction is smaller, the precipitation strengthening is weakened, and the lasting life of the alloy at 815 ℃/379MPa is seriously reduced; when the secondary aging temperature is 870 ℃, the secondary gamma' phase in the alloy structure is larger in size and extremely irregular in shape after recovery treatment, and the coarsening of the grain boundary is serious, so that the room-temperature tensile property of the alloy and the lasting life at 815 ℃/379MPa are seriously reduced; and when the three-stage aging time in S4 is 4 hours, the morphology of the secondary gamma 'phase cannot be effectively optimized due to the short three-stage aging time, and the size of the secondary gamma' phase is small, and the volume fraction is small, so that the lasting life of the alloy at 815 ℃/379MPa is reduced.
In some embodiments, the repaired K439B nickel-based alloy has a 30-40% increase in total creep rupture life over a damaged test bar.
In some embodiments, the dendrite trunk and inter-dendrite region gamma 'phase morphology of the repaired K439B nickel-based alloy microstructure are spherical, the average size of the gamma' phase is not more than 60nm, granular M 23C6 carbide is precipitated at the grain boundary, and the eta phase at the grain boundary completely disappears.
In some embodiments, the solution treatment, primary aging treatment, secondary aging treatment, and tertiary aging treatment are all performed in a vacuum gas quenching furnace.
In some embodiments, the furnace temperature uniformity of the vacuum gas quenching furnace is not less than the requirements specified by HB5354 for a class iii furnace.
In some embodiments, the initial furnace temperature of the vacuum gas quenching furnace is not more than 150 ℃, and the furnace is vacuumized to below 10 - 2 Pa.
Compared with the prior art, the invention has the following beneficial effects:
The invention provides a practical and available recovery heat treatment method capable of repairing a nickel-based superalloy K439B degradation structure for a turbine casing, which eliminates gamma' phase, grain boundary M 23C6 carbide and eta phase, so that the structure of the alloy basically reaches a heat treatment state level, and room temperature tensile property and high temperature durability are close to or even exceed the heat treatment state level, thereby ensuring service safety of an aeroengine, prolonging the service life of the engine casing and reducing maintenance cost of the aeroengine.
Drawings
FIG. 1 is a graph showing the results of heat treatment microstructure examination of the K439B alloy of example 1, wherein the left graph shows the dendrite trunk gamma 'phase and the right graph shows the interdendritic gamma' phase.
Fig. 2 is a graph of the microstructure test result of the K439B alloy of example 1 after long-term aging at 800 ℃ for 5000 hours, wherein the left graph of fig. 2A shows dendrite trunk γ 'phase, the right graph of fig. 2A shows dendrite inter γ' phase, and fig. 2B shows grain boundary morphology.
Fig. 3 is a graph showing the microstructure of the alloy of example 1K439B after solution treatment, wherein the left graph of fig. 3A shows dendrite dry γ 'phase, the right graph of fig. 3A shows interdendritic γ' phase, and the shape of grain boundary of fig. 3B.
Fig. 4 is a graph showing the microstructure of the repaired alloy of example 1K439B, wherein the left graph of fig. 4 shows the dendrite trunk gamma 'phase and the right graph of fig. 4 shows the inter-dendrite gamma' phase.
Fig. 5 is a graph of the microstructure of the K439B alloy of example 2 after solution treatment, wherein the left graph of fig. 5A shows dendrite drying γ 'phase, the right graph of fig. 5A shows interdendritic γ' phase, and the fig. 5B shows grain boundary morphology.
FIG. 6 is a graph showing the results of the microstructure test of the K439B alloy of example 2 after repair, wherein the left graph of FIG. 6 shows the dendrite trunk gamma 'phase and the right graph of FIG. 6 shows the interdendritic gamma' phase.
Fig. 7 is a scanning electron microscope image of the repair of the K439B alloy in comparative example 1, wherein the left image of fig. 7A is a dendrite trunk γ 'phase, the right image of fig. 7A is an inter-dendrite γ' phase, and fig. 7B is a repaired grain boundary morphology, wherein the left image is a grain boundary morphology, long-strip carbides are precipitated at the grain boundary, and the right image is a precipitated strip η phase.
FIG. 8 is a photomicrograph of the alloy of comparative example 2 at a K439B solution temperature of 1210 ℃.
FIG. 9 is a scanning electron microscope image of the K439B alloy repair of comparative example 3, wherein the left image of 9 is the alloy dendrite trunk gamma 'phase and the right image of 9 is the alloy interdendritic gamma' phase.
FIG. 10 is a scanning electron microscope image of the K439B alloy repair of comparative example 4, wherein the left image of FIG. 10A shows the dendrite trunk gamma 'phase and the right image shows the interdendritic gamma' phase. Fig. 10B is a graph of grain boundary morphology.
Detailed Description
The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
And (3) performing heat treatment on the K439B alloy test bar by adopting a DC-B30/16 type box type heat treatment furnace, heating the alloy to a temperature above the solid solution temperature, and then performing two-stage aging to obtain the alloy heat treatment test bar. And cutting a cylindrical sample with the diameter of 15mm multiplied by 5mm from the heat-treated test bar, grinding and polishing (adopting a UNIPOL-830 metallographic sample pre-grinding machine and a polishing machine), corroding the sample for 15-120 s by adopting an HNO 3:HF (glycerin=1:2:1) corrosion solution, and preparing the metallographic sample for observing dendrite morphology and alloy phase. The heat treated structure was then observed, and the gamma prime phase size and volume fraction, as well as grain boundary width were measured. And then carrying out 800 ℃/5000h long-term aging on the K439B alloy test rod after heat treatment, wherein the equipment adopts a DC-B30/16 type box-type heat treatment furnace, a thermocouple is adopted to monitor the temperature of the sample in real time in the experimental process, a cylindrical sample with the diameter of 15mm multiplied by 5mm is cut from the long-term aging test rod, grinding and polishing treatment is carried out (a UNIPOL-830 type metallographic sample pre-grinding machine and polishing machine are adopted), and a HNO 3:HF corrosion solution with the ratio of glycerin=1:2:1 is adopted to corrode the sample for 15-120 s, so that the metallographic sample for observing dendrite morphology and alloy phase is prepared. The heat treated structure was then observed, and the gamma prime phase size and volume fraction, as well as grain boundary width were measured. Obtaining a sample after 800 ℃/5000h long-term aging, then placing the sample in a vacuum gas quenching furnace, and starting recovery heat treatment.
The K439B alloy comprises the following components: cr, co, al, ti, nb, W, ta, B, zr, C, ni, the main strengthening phases of the alloy are gamma' phase and carbide. The gamma ' phase is mainly spherical, has fine size and regular shape, the average size of the gamma ' phase of the dendrite of the heat-treated alloy is 47nm, and the average size of the gamma ' phase among dendrites is 50nm. And granular M 23T6 is evenly precipitated at the grain boundary, the room temperature tensile strength of the alloy after heat treatment is 1175.0MPa, and the lasting life is 116.83h.
A recovery heat treatment method for repairing creep damage of a K439B nickel-based superalloy comprises the following steps:
S1, solution treatment: controlling the temperature rising speed in the furnace at 10 ℃ per minute, rising the furnace temperature to 1205 ℃, stopping heating, preserving heat for 4 hours, vacuumizing to below 10 -2 Pa, and enabling the cooling rate to be the air cooling rate;
S2, primary aging treatment: on the basis of the treatment of S1, controlling the temperature rising speed in the furnace at 10 ℃ per minute, rising the furnace temperature to 1086 ℃, stopping heating and preserving heat for 4 hours, vacuumizing to below 10 -2 Pa, and cooling at the air cooling rate:
S3, secondary aging treatment: on the basis of the treatment of S2, controlling the temperature rising speed in the furnace at 8 ℃ per minute, rising the furnace temperature to 850 ℃, stopping heating and preserving heat for 20 hours, vacuumizing to below 10 -2 Pa, and controlling the cooling rate to be the air cooling speed;
S4, three-stage aging treatment, wherein on the basis of the treatment of S3, the temperature rising speed in the furnace is controlled to be 8 ℃ per minute, the furnace temperature is raised to 805 ℃, heating is stopped, heat preservation is carried out for 17 hours, vacuum pumping is carried out until the pressure is lower than 10 -2 Pa, and the cooling rate is the air cooling rate, so that the repaired K439B nickel-based alloy is obtained.
The solution treatment, the primary aging treatment, the secondary aging treatment and the tertiary aging treatment are all carried out in a vacuum gas quenching furnace, the uniformity of the furnace temperature of the vacuum gas quenching furnace is not lower than the related requirements about a III type furnace specified by HB5354, the initial furnace temperature of the vacuum gas quenching furnace is not higher than 150 ℃, and the vacuum pumping is carried out to below 10 -2 Pa.
Example 2
And (3) performing heat treatment on the K439B alloy test bar by adopting a DC-B30/16 type box type heat treatment furnace, heating the alloy to a temperature above the solid solution temperature, and then performing two-stage aging to obtain the alloy heat treatment test bar. And cutting a cylindrical sample with the diameter of 15mm multiplied by 5mm from the heat-treated test bar, grinding and polishing (adopting a UNIPOL-830 metallographic sample pre-grinding machine and a polishing machine), corroding the sample for 15-120 s by adopting an HNO 3:HF (glycerin=1:2:1) corrosion solution, and preparing the metallographic sample for observing dendrite morphology and alloy phase. The heat treated structure was then observed, and the gamma prime phase size and volume fraction, as well as grain boundary width were measured. And then carrying out 800 ℃/5000h long-term aging on the K439B alloy test rod after heat treatment, wherein the equipment adopts a DC-B30/16 type box-type heat treatment furnace, a thermocouple is adopted to monitor the temperature of the sample in real time in the experimental process, a cylindrical sample with the diameter of 15mm multiplied by 5mm is cut from the long-term aging test rod, grinding and polishing treatment is carried out (a UNIPOL-830 type metallographic sample pre-grinding machine and polishing machine are adopted), and a HNO 3:HF corrosion solution with the ratio of glycerin=1:2:1 is adopted to corrode the sample for 15-120 s, so that the metallographic sample for observing dendrite morphology and alloy phase is prepared. The heat treated structure was then observed, and the gamma prime phase size and volume fraction, as well as grain boundary width were measured. Obtaining a sample after 800 ℃/5000h long-term aging, then placing the sample in a vacuum gas quenching furnace, and starting recovery heat treatment.
A recovery heat treatment method for repairing creep damage of a K439B nickel-based superalloy comprises the following steps:
S1, solution treatment: controlling the temperature rising speed in the furnace at 10 ℃ per minute, rising the furnace temperature to 1190 ℃, stopping heating, preserving heat for 4 hours, vacuumizing to below 10 -2 Pa, and cooling at the air cooling rate;
S2, primary aging treatment: on the basis of the treatment of S1, controlling the temperature rising speed in the furnace at 10 ℃ per minute, rising the furnace temperature to 1075 ℃, stopping heating and preserving heat for 4 hours, vacuumizing to below 10 -2 Pa, and cooling at the air cooling rate:
s3, secondary aging treatment: on the basis of the treatment of S2, controlling the temperature rising speed in the furnace at 8 ℃ per minute, rising the furnace temperature to 840 ℃, stopping heating and preserving heat for 20 hours, vacuumizing to below 10 -2 Pa, and controlling the cooling rate to be the air cooling speed;
S4, three-stage aging treatment, wherein on the basis of the treatment of S3, the temperature rising speed in the furnace is controlled to be 8 ℃ per minute, the furnace temperature is raised to 795 ℃, heating is stopped, heat preservation is carried out for 17 hours, vacuumizing is carried out to be less than 10 -2 Pa, and the cooling rate is the air cooling rate, so that the repaired K439B nickel-based alloy is obtained.
The solution treatment, the primary aging treatment, the secondary aging treatment and the tertiary aging treatment are all carried out in a vacuum gas quenching furnace, the uniformity of the furnace temperature of the vacuum gas quenching furnace is not lower than the related requirements about a III type furnace specified by HB5354, the initial furnace temperature of the vacuum gas quenching furnace is not higher than 150 ℃, and the vacuum pumping is carried out to below 10 -2 Pa.
Comparative example 1
The alloy was subjected to recovery treatment in the same manner as in example 1, except that the solution temperature was set at 1180 ℃.
Comparative example 2
The alloy was subjected to recovery treatment in the same manner as in example 1, except that the solid solution temperature was set at 1210 ℃.
Comparative example 3
The alloy was subjected to recovery treatment as in example 1, except that the holding time in S2 was 3h.
Comparative example 4
The alloy was subjected to recovery treatment as in example 1, except that the holding time in S2 was 5h.
Performance testing
The K439B alloys repaired by the above examples and comparative examples were subjected to microscopic observation, and the results were as follows:
FIG. 1 shows the dendrite and inter-dendrite structures of the K439B alloy of example 1, and shows that the alloy structure precipitates spherical gamma ' phases, which are fine in size and regular in shape, and the average size of the gamma ' phases of the dendrite of the heat-treated alloy is 47nm, and the average size of the gamma ' phases of the inter-dendrite is 50nm.
FIG. 2 shows the structure of the K439B alloy of example 1 after long-term aging at 800 ℃ for 5000 hours, and it can be found that the gamma '-phase of the K439B alloy coarsens after long-term aging, the coarsening degree among dendrites is more obvious than that of dendrites, the spherical gamma' -phase evolves into a cube shape, the average size of the gamma '-phase of the dendrites is 133.9nm, the average size of the gamma' -phase among dendrites is 137.9nm, long-strip-shaped carbide is precipitated at the grain boundary, and MC carbide at the grain boundary degenerates to form a small amount of eta-phase.
FIG. 3 shows the structure of the repaired alloy dendrites and interdendritic grains at 1205℃for the K439B alloy of example 1, showing complete disappearance of the internal coarse, cubic gamma 'phase after the recovery heat treatment, and re-precipitation of the smaller size spherical gamma' phase. At a solution temperature of 1205 ℃, the dendrite stems and inter-dendrite gamma' -phase sizes were 54.7nm and 58.5nm, respectively, with a volume fraction of 23%. The gamma' -phase is substantially uniform in size, morphology, distribution and heat treatment. Grain boundary re-precipitates granular M 23C6 carbide, eta phase at the grain boundary completely disappears, and the alloy structure is basically recovered.
FIG. 4 shows that S2 of example 1 shows that after recovery heat treatment, the dendrite stems and the inter-dendrite gamma' phase sizes are 54.6nm and 58.7nm, respectively, and the volume fraction is 23.3% at a primary aging temperature of 1085 ℃. The grain boundary morphology and the heat treatment state are basically consistent.
In step S3 of example 1, it can be seen that after the recovery heat treatment, the dendrite stems and the inter-dendrite gamma' phase sizes were 54.9nm and 58.5nm, respectively, and the volume fraction was 23.3% when the secondary aging temperature was 850 ℃. The grain boundary morphology and the heat treatment state are basically consistent.
In step S4 of example 1, it can be seen that after the recovery heat treatment, the dendrite stems and the inter-dendrite gamma' phase sizes were 54.3nm and 58.9nm, respectively, and the volume fraction was 23% when the three-stage aging temperature was 805 ℃. The grain boundary morphology and the heat treatment state are basically consistent.
FIG. 5 shows the structure of the dendrites and inter-dendrites of the repaired alloy when the solution temperature of the K439B alloy is 1195 ℃, and the sizes of the gamma' phases between the dendrites and the inter-dendrites are 54.0nm and 58.0nm, respectively, and the volume fraction is 22.8% when the solution temperature is 1195 ℃. The grain boundary morphology and the heat treatment state are basically consistent.
FIG. 6 shows the structure of the repaired alloy dendrites and inter-dendrites of the K439B alloy at 1075℃and the size of the gamma' -phase between dendrites and inter-dendrites of 54.1nm and 58.0nm, respectively, with a volume fraction of 23%. The grain boundary morphology and the heat treatment state are basically consistent.
The K439B alloy of example 2 had a repaired alloy dendrite trunk and inter-dendrite structure at a solid solution temperature of 1195 c, and had dendrite trunk and inter-dendrite gamma' -phase sizes of 54.0nm and 58.0nm, respectively, and a volume fraction of 22.8% at a solid solution temperature of 1195 c. The grain boundary morphology and the heat treatment state are basically consistent.
The K439B alloy in example 2 had a repaired alloy dendrite and inter-dendrite structure at 1075 ℃ and dendrite and inter-dendrite gamma' phase sizes of 54.1nm and 58.0nm, respectively, and a volume fraction of 23%. The grain boundary morphology and the heat treatment state are basically consistent.
In example 2, step S3, it was found that after the recovery heat treatment, the dendrite stems and the inter-dendrite gamma' phase had dimensions of 53.5nm and 58.0nm, respectively, and a volume fraction of 22.8%, when the secondary aging temperature was 840 ℃. The grain boundary morphology and the heat treatment state are basically consistent.
In example 2, step S4, it can be seen that after the recovery heat treatment, the dendrite stems and the inter-dendrite gamma' phase sizes were 53.3nm and 58.9nm, respectively, and the volume fraction was 22.9%, when the three-stage aging temperature was 795 ℃. The grain boundary morphology and the heat treatment state are basically consistent.
FIG. 7 is a graph of the morphology of the repaired alloy of comparative example 1, after recovery treatment, the dendrite stems and inter-dendrite gamma prime phase sizes were 53.3nm and 56.5nm, respectively, with a volume fraction of 22.3%. It was found that the eta phase present in the alloy was not completely eliminated and that elongated carbides were present at the alloy grain boundaries, resulting in a severe reduction in the long-term life of the alloy at 815 deg.c/379 MPa.
FIG. 8 shows the structure of the alloy after the recovery treatment in comparative example 2, after the recovery treatment, the alloy is initially melted, and the initial melting results in serious reduction of the mechanical properties of the alloy at room temperature and the endurance life at 815 ℃/379 MPa.
FIG. 9 shows the morphology of the alloy structure after recovery treatment in comparative example 4, after recovery treatment, the dendrite and inter-dendrite gamma ' -phase sizes were 43.0nm and 46.0nm, respectively, and the volume fraction was 19.4%, and it was found that the secondary gamma ' -phase size in the alloy structure was much smaller than the critical size, the gamma ' -phase volume fraction was smaller, and the precipitation strengthening was weakened, resulting in a decrease in the endurance life of the alloy at 815 ℃/379 MPa.
FIG. 10 is a graph of the morphology of the repaired alloy of comparative example 3, after recovery treatment, it can be seen that dendrite stems and inter-dendrite gamma prime phase sizes are 120.0nm and 125.1nm, respectively, with a volume fraction of 24%. The secondary gamma' phase in the alloy structure is found to be larger in size and irregular in shape, the grain boundary width is larger, the grain boundary carbide is larger, the degree of irregularity of the grain boundary is increased, and the combined action causes the serious reduction of the room temperature mechanical property of the alloy and the lasting life at 815 ℃/379 MPa.
The K439B alloys repaired in the above examples and comparative examples were subjected to room temperature tensile and 815 ℃/379MPa durability tests, room temperature tensile properties were tested according to GB/T228-2002 standard (method for tensile test of metallic materials at room temperature), and durability was tested according to GB/T2039-1997 standard (method for tensile creep and durability test). The test equipment is a 3382 type electronic universal tester and a SATEC M3 type high-temperature creep-rupture tester respectively. The results are shown in tables 1-3.
Table 1 shows the room temperature elongation and 815 ℃/379MPa durability of the alloy in the heat treated state. The alloy was simulated in service using long-term aging (800 ℃ C./5000 h) and tested for room temperature tensile and high temperature durability properties as shown in Table 2. The room temperature stretching and 815 ℃/379MPa durability of the alloy treated by the recovery heat treatment method provided by the invention are shown in Table 3. From Table 2, it can be seen that the long-term aging (800 ℃/5000 h) of the alloy reduces the durable life of 815 ℃/379MPa to 90.6h, and the long-term aging treatment of the alloy by the recovery heat treatment method provided by the invention improves the durable life of 815 ℃/379MPa to 122.6h, improves the aging state for a long period by 35%, and improves the room-temperature tensile property by 45%. Therefore, the structure, the room temperature tensile property and the durability of 815 ℃/379MPa of the alloy after being treated by the recovery heat treatment method provided by the invention are basically recovered to the level of the heat treatment state.
Table 1K439B alloy heat treated room temperature tensile properties and 815 ℃/379MPa durability properties
| σb/MPa | τ/h | |
| Example 1 | 1175.0 | 116.83 |
Table 2K439B alloy has room temperature tensile properties and 815 ℃/379MPa durability after long-term aging at 800 ℃ for 5000 hours
| σb/MPa | τ/h | |
| Example 1 | 803.3 | 90.60 |
Table 3K439B alloy after recovery heat treatment, room temperature tensile properties and 815 ℃/379MPa durability properties
| σb/MPa | τ/h | |
| Example 1 | 1165.0 | 122.60 |
| Example 2 | 1160.0 | 119.10 |
| Comparative example 1 | 1020.0 | 39.50 |
| Comparative example 2 | 1060.0 | 58.00 |
| Comparative example 3 | 1090 | 63 |
| Comparative example 4 | 1140 | 61 |
From the above experimental data, it can be seen that the solution treatment and the multistage aging treatment at specific temperatures and times adopted in the invention can significantly improve the durability of the alloy, and the experimental effect of example 1 is the best.
While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the present invention.
Claims (10)
1. The recovery heat treatment method for repairing the creep damage of the K439B nickel-based superalloy is characterized by comprising the following steps of:
S1, solution treatment: placing the K439B nickel-based superalloy to be repaired in a furnace, controlling the temperature rising speed in the furnace at 8-10 ℃ per minute, rising the furnace temperature, stopping heating and preserving heat, vacuumizing, and cooling at the air cooling rate;
S2, primary aging treatment: on the basis of the treatment of S1, the furnace temperature is raised, heating is stopped, heat preservation is carried out, vacuum pumping is carried out, and the cooling rate is the air cooling rate:
S3, secondary aging treatment: on the basis of the treatment of the step S2, the furnace temperature is raised, heating is stopped, heat preservation is carried out, vacuum pumping is carried out, and the cooling rate is controlled to be the air cooling rate;
S4, three-stage aging treatment, namely raising the furnace temperature, stopping heating and preserving heat on the basis of the treatment of S3, vacuumizing, and obtaining the repaired K439B nickel-based alloy, wherein the cooling rate is the air cooling rate.
2. The recovery heat treatment method according to claim 1, wherein the furnace temperature in S1 is raised to 1170 ℃ to 1200 ℃, heating is stopped, and the temperature is kept for 2 to 4 hours.
3. The recovery heat treatment method according to claim 1, wherein the furnace temperature is raised to 1060 ℃ to 1090 ℃ in S2, heating is stopped, and heat is kept for 3 to 5 hours.
4. The recovery heat treatment method according to claim 1, wherein the furnace temperature is raised to 830 ℃ to 850 ℃ in S3, and the heating is stopped and the heat is kept for 20 to 24 hours.
5. The recovery heat treatment method according to claim 1, wherein the furnace temperature is raised to 780-820 ℃ in S4, heating is stopped, and heat is kept for 15-17 hours.
6. The recovery heat treatment method according to claim 1, wherein the temperature rise rate in the furnace of the primary aging treatment is 8 to 12 ℃ per minute.
7. The recovery heat treatment method according to claim 1, wherein the temperature rise rate in the secondary aging treatment furnace is 8 to 10 ℃ per minute.
8. The recovery heat treatment method according to claim 1, wherein the temperature rise rate in the furnace of the three-stage aging treatment is 6 to 8 ℃ per minute.
9. The recovery heat treatment method according to claim 1, wherein the solution treatment, the primary aging treatment, the secondary aging treatment, and the tertiary aging treatment are performed in a vacuum gas quenching furnace.
10. The recovery heat treatment method according to claim 9, wherein the initial furnace temperature of the vacuum gas quenching furnace is not more than 150 ℃, and the furnace is evacuated to 10 -2 Pa or less.
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