CN111850439B - Bolt heat treatment process for Nimonic 80A alloy material - Google Patents
Bolt heat treatment process for Nimonic 80A alloy material Download PDFInfo
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- CN111850439B CN111850439B CN202010754145.6A CN202010754145A CN111850439B CN 111850439 B CN111850439 B CN 111850439B CN 202010754145 A CN202010754145 A CN 202010754145A CN 111850439 B CN111850439 B CN 111850439B
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 71
- 239000000956 alloy Substances 0.000 title claims abstract description 65
- 229910001235 nimonic Inorganic materials 0.000 title claims abstract description 46
- 238000000034 method Methods 0.000 title claims abstract description 40
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 41
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 29
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 22
- 230000003647 oxidation Effects 0.000 claims abstract description 18
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 18
- 230000003068 static effect Effects 0.000 claims abstract description 13
- 238000001816 cooling Methods 0.000 claims description 23
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 20
- 239000007789 gas Substances 0.000 claims description 17
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims description 16
- 229910052786 argon Inorganic materials 0.000 claims description 10
- 235000019270 ammonium chloride Nutrition 0.000 claims description 8
- 239000000843 powder Substances 0.000 claims description 8
- 238000009792 diffusion process Methods 0.000 abstract description 6
- 230000001681 protective effect Effects 0.000 abstract description 4
- 229910052751 metal Inorganic materials 0.000 abstract description 2
- 239000002184 metal Substances 0.000 abstract description 2
- 239000000463 material Substances 0.000 description 9
- 238000002156 mixing Methods 0.000 description 8
- 238000012545 processing Methods 0.000 description 7
- 238000009413 insulation Methods 0.000 description 6
- 238000005070 sampling Methods 0.000 description 6
- 239000010410 layer Substances 0.000 description 5
- 238000004321 preservation Methods 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- 239000011651 chromium Substances 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 229910018487 Ni—Cr Inorganic materials 0.000 description 1
- 229910052774 Proactinium Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium chloride Substances Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- VNNRSPGTAMTISX-UHFFFAOYSA-N chromium nickel Chemical compound [Cr].[Ni] VNNRSPGTAMTISX-UHFFFAOYSA-N 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 230000003313 weakening effect Effects 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
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- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Powder Metallurgy (AREA)
- Heat Treatment Of Articles (AREA)
Abstract
The invention relates to a Nimonic 80A alloyThe heat treatment process of the bolt comprises the following steps: carrying out solution heat treatment on a hot-rolled or forged bar of Nimonic 80A alloy of a bolt to be manufactured at 1080-1100 ℃; after the bar is processed into finished bolts meeting the specification requirements, the bolts are placed in AlClnHeating to 750-760 ℃ in atmosphere to carry out chemical-aging heat treatment. The heat treatment process of the Nimonic 80A alloy bolt can improve the aluminum content of the bolt surface within the depth of 2 mu m by not less than 15 percent and far higher than the aluminum content of an alloy parent metal by 1 to 1.8 percent while ensuring the high-temperature strength and the low expansion performance of the alloy; the yield strength at room temperature is not lower than 740 MPa; the surface hardness is improved to be not less than 320HB and higher than HB of a bolt>298; al in the Al-rich diffusion layer can form Al in high-temperature environment2O3The thickness of the oxide film of 850 ℃/100h in static air of the protective film is not higher than 0.1 mu m, and the complete oxidation resistance level is achieved, so that the problem of insufficient oxidation resistance of the Nimonic 80A alloy bolt in the service process is solved, and the wear resistance of the bolt is obviously improved.
Description
Technical Field
The invention belongs to the field of metal heat treatment, and particularly relates to a heat treatment process for a bolt made of a Nimonic 80A alloy material.
Background
The Nimonic 80A alloy is a gamma' phase dispersion strengthened high-temperature alloy which is developed by American special metal material company, takes nickel-chromium as a matrix, is added with aluminum and titanium, and has good creep resistance at the use temperature of 700-800 ℃ and between 650-850 ℃. The alloy has low alloying degree, contains Al (1.0-1.8% (mass fraction) and Ti (1.8-2.7% (mass fraction)) as generating elements of a gamma' phase to strengthen the alloy, contains Cr (18-21% (mass fraction)) to enable the alloy to have good corrosion resistance, has relatively pure alloy matrix, reduces the possibility of weakening plasticity due to brittleness of a crystal boundary caused by excessive carbide because of no carbide forming elements such as W, Mo and Nb, has good cold and hot processing performance, is in the form of bars, plates, strips, annular pieces and the like, and is used for manufacturing parts such as engine rotor blades, guide blade supports, bolts, blade locking plates and the like.
The high-temperature bolt is a part for fastening and connecting in the generator set which works under the high-temperature and stress state for a long time, and the high-temperature bolt generates certain pressing force on a valve joint surface, so that the connected part is kept sealed and does not leak in the service cycle, and the high-temperature bolt plays a vital role in the normal operation of the high-temperature fastening part of the power plant and the safety of equipment. Generally, the design life of high-temperature bolts is about 20 years, and the oxidation problem is serious in the long-term service process, which causes great trouble to the normal maintenance work of a power plant and sometimes even necessitates destructive removal. Therefore, the high-temperature oxidation resistance of the bolt is improved, the overhaul efficiency of a power plant can be improved to a certain extent, the overhaul time is shortened, the reuse rate of the bolt can be improved, the purchase and use of new spare parts are reduced, and the economic benefit of the power plant is improved.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a bolt heat treatment process for a Nimonic 80A alloy material, which can be used for solving the problem of insufficient oxidation resistance of a Nimonic 80A alloy bolt in the service process by obviously improving the aluminum content of the surface of the Nimonic 80A alloy while ensuring the high-temperature strength and low-expansion performance of the alloy.
The invention is realized by the following technical scheme:
a bolt heat treatment process for a Nimonic 80A alloy material comprises the following steps:
step 1, carrying out solution heat treatment on a hot-rolled or forged bar of Nimonic 80A alloy of a bolt to be manufactured at 1080-1100 ℃, wherein the heat preservation time is as follows: keeping the temperature of a bar with the diameter less than 60mm for 2-5 hours, and cooling the bar to room temperature by air; keeping the temperature of the bar with the diameter larger than 60mm for 5-8 hours, and cooling the oil to room temperature;
step 2, after the bar in the step 1 is processed into a finished bolt meeting the specification requirement, the bolt is placed in AlClnHeating to 750-760 ℃ in atmosphere to carry out chemical-aging heat treatment, wherein the heat preservation time is as follows: keeping the temperature of the bolts with the diameter smaller than 60mm for 4-6 hours, and keeping the temperature of the bolts with the diameter larger than 60mm for 6-8 hours; cooling to room temperature with high purity argon.
The invention is further improved in that in the step 2, the purity of the high-purity argon is not lower than 99.99 percent, and the cooling rate is not lower than 10 ℃/min through flow rate control.
The invention is further improved in that in the step 2, AlCl is adoptednThe atmosphere is composed of AlCl and AlCl2And AlCl3The mixed gas is prepared by mixing pure aluminum powder and ammonium chloride powder according to the mass ratio of 1 (2-6) and heating to 650 ℃.
The invention is further improved in that in the step 2, the bolt to be heat-treated is placed in the workpiece chamber, and when the vacuum degree of the workpiece chamber is not less than 1 x 10-5Heating to 750-760 ℃ at Pa, and in the heating and heat preservation process, adding AlClnThe gas is introduced into the workpiece chamber to ensure that the pressure in the workpiece chamber is not lower than 0.4 MPa.
The further improvement of the invention is that the heat treatment process can improve the mass ratio of the aluminum content in the depth of 2 mu m on the surface of the bolt to be not less than 15 percent and the hardness to be not less than 320 HB; the yield strength at room temperature is not lower than 740 MPa; the thickness of the oxide film at 850 ℃/100h in static air is not higher than 0.1 mu m, and the complete oxidation resistance level is achieved.
Compared with the prior art, the invention has at least the following beneficial technical effects:
the heat treatment process of the Nimonic 80A alloy bolt can improve the mass ratio of the aluminum content in the depth of 2 mu m on the surface of the bolt while ensuring the high-temperature strength and the low expansion performance of the alloyThe content of aluminum is lower than 15 percent and is far higher than that of the alloy base metal by 1-1.8 percent; can improve the surface hardness not less than 320HB and obviously higher than HB of a bolt>298; al in the Al-rich diffusion layer can form Al in high-temperature environment2O3The protective film is adopted, so that the problem that the oxidation resistance of the Nimonic 80A alloy bolt is insufficient in the service process is solved, and the wear resistance of the bolt is obviously improved.
Drawings
FIG. 1 is a scanning electron microscope sectional view (secondary electron mode photograph) of a bolt core of Nimonic 80A alloy material obtained after heat treatment in example 3 of the present invention.
Fig. 2 is a scanning electron microscope cross-sectional view (photographed by a backscatter mode) of the bolt surface of the Nimonic 80A alloy material obtained after the heat treatment in example 3 of the present invention.
FIG. 3 is a graph comparing the oxide film thickness in 850 deg.C/static air for examples of the present invention and a reference.
FIG. 4 is a graph comparing the surface hardness of examples of the present invention with that of a reference.
FIG. 5 is a graph comparing the room temperature yield strength of examples of the present invention with that of a reference.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples.
Example 1:
carrying out heat treatment on the bolt made of the Nimonic 80A alloy material with the diameter of the threaded end being 50mm, wherein the heat treatment process comprises the following steps and parameters:
(1) heating a Nimonic 80A alloy bar of a bolt to be manufactured to 1080 ℃ in a normal-pressure atmospheric environment, preserving heat for 5 hours, and cooling air to room temperature;
(2) processing the bar subjected to the heat treatment in the step (1) into a finished bolt with qualified specification;
(3) placing the bolt in the step (2) into a closed workpiece chamber, vacuumizing through a pipeline communicated with the bolt until the vacuum degree is not less than 1 x 10-5Pa；
(4) Mixing pure aluminum powderAnd ammonium chloride powder are put into an atmosphere generator according to the proportion of 1:6, and heated to 650 ℃ to generate AlClnA gas;
(5) and (4) mixing the AlCl generated in the step (4)nConveying the gas into the closed workpiece chamber in the step (3) through a heat insulation pipeline to enable the pressure in the workpiece chamber to be not lower than 0.4 MPa;
(6) heating the workpiece chamber provided with the bolts in the step (4) to 750 ℃, and preserving heat for 6 hours, wherein the step and the step (5) are carried out synchronously;
(7) and (3) cooling the bolt subjected to the heat treatment in the step (6) to room temperature by using high-purity argon with the purity not lower than 99.99%, and controlling the cooling rate to be not lower than 10 ℃/min through the flow rate.
In the bolt made of the Nimonic 80A alloy material obtained by the process of the embodiment, the mass percentage of the aluminum content in the depth of 2 mu m on the surface of the bolt is 15.4 percent, and the rest components are alloy base material elements; the surface hardness is 325 HB; sampling is carried out on the bolt core part along the axial direction, and the room-temperature yield strength is 748 MPa; the thickness of the oxide film at 850 ℃/100h in static air is 0.08 mu m, and the complete oxidation resistance level is achieved.
Example 2:
carrying out heat treatment on the bolt made of the Nimonic 80A alloy material with the diameter of the threaded end being 50mm, wherein the heat treatment process comprises the following steps and parameters:
(1) heating the Nimonic 80A alloy bar of the bolt to be manufactured to 1100 ℃ in a normal-pressure atmospheric environment, preserving heat for 2 hours, and cooling air to room temperature;
(2) processing the bar subjected to the heat treatment in the step (1) into a finished bolt with qualified specification;
(3) placing the bolt in the step (2) into a closed workpiece chamber, vacuumizing through a pipeline communicated with the bolt until the vacuum degree is not less than 1 x 10-5Pa；
(4) Pure aluminum powder and ammonium chloride powder are put into an atmosphere generator according to the proportion of 1:2, and heated to 650 ℃ to generate AlClnA gas;
(5) and (4) mixing the AlCl generated in the step (4)nConveying the gas to the closed workpiece in the step (3) through a heat insulation pipelineIn the chamber, the pressure in the workpiece chamber is not lower than 0.4 MPa;
(6) heating the workpiece chamber provided with the bolts in the step (4) to 760 ℃, and preserving heat for 4 hours, wherein the step and the step (5) are carried out synchronously;
(7) and (3) cooling the bolt subjected to the heat treatment in the step (6) to room temperature by using high-purity argon with the purity not lower than 99.99%, and controlling the cooling rate to be not lower than 10 ℃/min through the flow rate.
In the bolt made of the Nimonic 80A alloy material obtained by the process of the embodiment, the mass percentage of the aluminum content in the depth of 2 mu m on the surface of the bolt is 18.7 percent, and the rest components are alloy base material elements; the surface hardness is 336 HB; sampling the bolt core part along the axial direction, wherein the room-temperature yield strength is 766 MPa; the thickness of the oxide film at 850 ℃/100h in static air is 0.07 mu m, and the complete oxidation resistance level is achieved.
Example 3:
carrying out heat treatment on the bolt made of the Nimonic 80A alloy material with the diameter of the threaded end being 50mm, wherein the heat treatment process comprises the following steps and parameters:
(1) heating the Nimonic 80A alloy bar of the bolt to be manufactured to 1090 ℃ in a normal-pressure atmospheric environment, preserving heat for 4 hours, and cooling air to room temperature;
(2) processing the bar subjected to the heat treatment in the step (1) into a finished bolt with qualified specification;
(3) placing the bolt in the step (2) into a closed workpiece chamber, vacuumizing through a pipeline communicated with the bolt until the vacuum degree is not less than 1 x 10-5Pa；
(4) Pure aluminum powder and ammonium chloride powder are put into an atmosphere generator according to the proportion of 1:3, and heated to 650 ℃ to generate AlClnA gas;
(5) and (4) mixing the AlCl generated in the step (4)nConveying the gas into the closed workpiece chamber in the step (3) through a heat insulation pipeline to enable the pressure in the workpiece chamber to be not lower than 0.4 MPa;
(6) heating the workpiece chamber provided with the bolts in the step (4) to 755 ℃, and preserving heat for 5 hours, wherein the step and the step (5) are carried out synchronously;
(7) and (3) cooling the bolt subjected to the heat treatment in the step (6) to room temperature by using high-purity argon with the purity not lower than 99.99%, and controlling the cooling rate to be not lower than 10 ℃/min through the flow rate.
In the bolt made of the Nimonic 80A alloy material obtained by the process of the embodiment, the mass percentage of the aluminum content in the depth of 2 mu m on the surface of the bolt is 16.3 percent, and the rest components are alloy base material elements; the surface hardness is 330 HB; sampling the bolt core part along the axial direction, wherein the room-temperature yield strength is 760 MPa; the thickness of the oxide film at 850 ℃/100h in static air is 0.07 mu m, and the complete oxidation resistance level is achieved.
Example 4:
carrying out heat treatment on the bolt made of Nimonic 80A alloy with the diameter of the threaded end of 80mm, wherein the heat treatment process comprises the following steps and parameters:
(1) heating a Nimonic 80A alloy bar of a bolt to be manufactured to 1080 ℃ in a normal-pressure atmospheric environment, preserving heat for 8 hours, and cooling air to room temperature;
(2) processing the bar subjected to the heat treatment in the step (1) into a finished bolt with qualified specification;
(3) placing the bolt in the step (2) into a closed workpiece chamber, vacuumizing through a pipeline communicated with the bolt until the vacuum degree is not less than 1 x 10-5Pa；
(4) Pure aluminum powder and ammonium chloride powder are put into an atmosphere generator according to the proportion of 1:6, and heated to 650 ℃ to generate AlClnA gas;
(5) and (4) mixing the AlCl generated in the step (4)nConveying the gas into the closed workpiece chamber in the step (3) through a heat insulation pipeline to enable the pressure in the workpiece chamber to be not lower than 0.4 MPa;
(6) heating the workpiece chamber provided with the bolts in the step (4) to 750 ℃, and preserving heat for 8 hours, wherein the step and the step (5) are carried out synchronously;
(7) and (3) cooling the bolt subjected to the heat treatment in the step (6) to room temperature by using high-purity argon with the purity not lower than 99.99%, and controlling the cooling rate to be not lower than 10 ℃/min through the flow rate.
In the bolt made of the Nimonic 80A alloy material obtained by the process of the embodiment, the mass percentage of the aluminum content in the depth of 2 mu m on the surface of the bolt is 15.9 percent, and the rest components are alloy base material elements; the surface hardness is 329 HB; sampling the bolt core part along the axial direction, wherein the room-temperature yield strength is 750 MPa; the thickness of the oxide film at 850 ℃/100h in static air is 0.07 mu m, and the complete oxidation resistance level is achieved.
Example 5:
carrying out heat treatment on the bolt made of Nimonic 80A alloy with the diameter of the threaded end of 80mm, wherein the heat treatment process comprises the following steps and parameters:
(1) heating the Nimonic 80A alloy bar of the bolt to be manufactured to 1100 ℃ in a normal-pressure atmospheric environment, preserving heat for 6 hours, and cooling air to room temperature;
(2) processing the bar subjected to the heat treatment in the step (1) into a finished bolt with qualified specification;
(3) placing the bolt in the step (2) into a closed workpiece chamber, vacuumizing through a pipeline communicated with the bolt until the vacuum degree is not less than 1 x 10-5Pa；
(4) Pure aluminum powder and ammonium chloride powder are put into an atmosphere generator according to the proportion of 1:2, and heated to 650 ℃ to generate AlClnA gas;
(5) and (4) mixing the AlCl generated in the step (4)nConveying the gas into the closed workpiece chamber in the step (3) through a heat insulation pipeline to enable the pressure in the workpiece chamber to be not lower than 0.4 MPa;
(6) heating the workpiece chamber provided with the bolts in the step (4) to 760 ℃, and preserving heat for 6 hours, wherein the step and the step (5) are carried out synchronously;
(7) and (3) cooling the bolt subjected to the heat treatment in the step (6) to room temperature by using high-purity argon with the purity not lower than 99.99%, and controlling the cooling rate to be not lower than 10 ℃/min through the flow rate.
In the bolt made of the Nimonic 80A alloy material obtained by the process of the embodiment, the mass percentage of the aluminum content in the depth of 2 mu m on the surface of the bolt is 19.2 percent, and the rest components are alloy base material elements; the surface hardness is 340 HB; sampling the bolt core part along the axial direction, wherein the room-temperature yield strength is 778 MPa; the thickness of the oxide film at 850 ℃/100h in static air is 0.07 mu m, and the complete oxidation resistance level is achieved.
Example 6:
carrying out heat treatment on the bolt made of Nimonic 80A alloy with the diameter of the threaded end of 80mm, wherein the heat treatment process comprises the following steps and parameters:
(1) heating the Nimonic 80A alloy bar of the bolt to be manufactured to 1090 ℃ in a normal-pressure atmospheric environment, preserving heat for 7 hours, and cooling air to room temperature;
(2) processing the bar subjected to the heat treatment in the step (1) into a finished bolt with qualified specification;
(3) placing the bolt in the step (2) into a closed workpiece chamber, vacuumizing through a pipeline communicated with the bolt until the vacuum degree is not less than 1 x 10-5Pa；
(4) Pure aluminum powder and ammonium chloride powder are put into an atmosphere generator according to the proportion of 1:3, and heated to 650 ℃ to generate AlClnA gas;
(5) and (4) mixing the AlCl generated in the step (4)nConveying the gas into the closed workpiece chamber in the step (3) through a heat insulation pipeline to enable the pressure in the workpiece chamber to be not lower than 0.4 MPa;
(6) heating the workpiece chamber provided with the bolts in the step (4) to 755 ℃, and preserving heat for 7 hours, wherein the step and the step (5) are carried out synchronously;
(7) and (3) cooling the bolt subjected to the heat treatment in the step (6) to room temperature by using high-purity argon with the purity not lower than 99.99%, and controlling the cooling rate to be not lower than 10 ℃/min through the flow rate.
In the bolt made of the Nimonic 80A alloy material obtained by the process of the embodiment, the mass percentage of aluminum in the depth of 2 mu m on the surface of the bolt is 17.1 percent, and the rest components are alloy base material elements; the surface hardness is 327 HB; sampling is carried out on the bolt core part along the axial direction, and the room-temperature yield strength is 768 MPa; the thickness of the oxide film at 850 ℃/100h in static air is 0.07 mu m, and the complete oxidation resistance level is achieved.
For comparison, step (4) and step (5) in examples 3 and 6 are specifically removed and used as reference examples one and two. In both the reference example I and the reference example II, the aluminum content of the bolt surface within 2 μm depth is not increased, and is maintained within the aluminum content range of 1% -1.8% of the base material.
The preparation processes of examples 1 to 6 of the present invention and reference examples 1 to 2 are shown in Table 1. From the examples 1-6, the heat treatment process can improve the aluminum content mass ratio within 2 μm depth of the bolt surface by not less than 15%, which is far higher than the aluminum content of the alloy base material mass ratio of 1% -1.8%; al in the Al-rich diffusion layer can form Al in high-temperature environment2O3The protective film is adopted, so that the problem that the oxidation resistance of the Nimonic 80A alloy bolt is insufficient in the service process is solved, and the wear resistance of the bolt is obviously improved.
TABLE 1 preparation parameters for the examples and reference proportions and 2 μm deep aluminum content of the surface layer
FIG. 1 is a scanning electron microscope sectional view (secondary electron mode photograph) of a bolt core portion of Nimonic 80A alloy material obtained after heat treatment in example 3 of the present invention, and it can be seen that the alloy mainly consists of a gamma phase, a gamma' phase and a carbide phase after the bolt heat treatment process of the Nimonic 80A alloy material by the method of the present invention. The heat treatment process of the invention keeps the strengthening of the gamma' phase in the alloy and avoids Ni2The precipitation temperature of the Cr phase ensures the obdurability, and the yield strength at room temperature is not lower than 740 MPa.
FIG. 2 is a scanning electron microscope cross-sectional view (photographed by a back scattering mode) of the bolt surface of the Nimonic 80A alloy material obtained after the heat treatment in example 3 of the present invention, and it can be seen that after the bolt heat treatment process of the Nimonic 80A alloy material by the method of the present invention, an aluminum-rich diffusion layer with a depth of about 2 μm is obtained on the alloy surface, and the mass ratio of the aluminum content in the diffusion layer is not less than 15%, which is much higher than the mass ratio of the alloy base material of 1% -1.8%; al in the Al-rich diffusion layer can form Al in high-temperature environment2O3The protective film is adopted, so that the problem that the oxidation resistance of the Nimonic 80A alloy bolt is insufficient in the service process is solved, and the wear resistance of the bolt is obviously improved.
An oxidation test of 850 ℃/100h in static air shows that after the bolt made of the Nimonic 80A alloy material is subjected to the heat treatment process by the method, the oxidation rate of the bolt in the 850 ℃/static air is obviously reduced. FIG. 3 is a graph comparing the thickness of the oxide film in 850 deg.C/static air in the examples of the present invention with that of the reference, and it can be seen that the thickness of the oxide film is reduced by about 5 times or more compared with the comparative example. Fig. 4 and 5 are graphs comparing the surface hardness and the room temperature yield strength of examples of the present invention with reference values, respectively. Compared with the comparative example, the invention can obviously improve the surface hardness not less than 320HB, which is obviously higher than the surface hardness of the reference example after heat treatment, and also obviously higher than the requirement that the HB of the bolt is more than 298, and the improvement of the surface hardness can obviously improve the wear resistance of the bolt. The room temperature yield strength of the embodiment and the reference ratio is not lower than 740MPa, and the strength requirement of the service of the bolt is met.
While the invention has been described in connection with specific embodiments thereof, it will be understood that these should not be construed as limiting the scope of the invention, which is defined in the appended claims, any modifications to which this invention pertains being applicable being within the scope of this invention.
Claims (3)
Priority Applications (1)
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