CN114774840A - Nitriding process for powder metallurgy products - Google Patents
Nitriding process for powder metallurgy products Download PDFInfo
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- CN114774840A CN114774840A CN202210491823.3A CN202210491823A CN114774840A CN 114774840 A CN114774840 A CN 114774840A CN 202210491823 A CN202210491823 A CN 202210491823A CN 114774840 A CN114774840 A CN 114774840A
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- 238000005121 nitriding Methods 0.000 title claims abstract description 108
- 238000000034 method Methods 0.000 title claims abstract description 65
- 238000004663 powder metallurgy Methods 0.000 title claims abstract description 42
- 238000010438 heat treatment Methods 0.000 claims abstract description 10
- 239000007789 gas Substances 0.000 claims description 37
- 238000004140 cleaning Methods 0.000 claims description 15
- 238000005086 pumping Methods 0.000 claims description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 10
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 6
- 238000013020 steam cleaning Methods 0.000 claims description 6
- 238000007599 discharging Methods 0.000 claims description 5
- 238000005507 spraying Methods 0.000 claims description 5
- 229910001873 dinitrogen Inorganic materials 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 3
- 238000001035 drying Methods 0.000 claims description 3
- 238000002791 soaking Methods 0.000 claims description 3
- 238000010407 vacuum cleaning Methods 0.000 claims description 3
- 239000000843 powder Substances 0.000 claims 1
- 238000012805 post-processing Methods 0.000 abstract description 5
- 238000000227 grinding Methods 0.000 abstract description 4
- 150000001875 compounds Chemical class 0.000 description 13
- 238000009792 diffusion process Methods 0.000 description 7
- 238000001514 detection method Methods 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 239000002173 cutting fluid Substances 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 239000003599 detergent Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000005187 foaming Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000005555 metalworking Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- CWQXQMHSOZUFJS-UHFFFAOYSA-N molybdenum disulfide Chemical compound S=[Mo]=S CWQXQMHSOZUFJS-UHFFFAOYSA-N 0.000 description 1
- 229910052982 molybdenum disulfide Inorganic materials 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 235000020610 powder formula Nutrition 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Images
Classifications
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- 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
- C23C8/36—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 using ionised gases, e.g. ionitriding
- C23C8/38—Treatment of ferrous surfaces
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
-
- 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
- C23C8/02—Pretreatment of the material to be coated
Abstract
The embodiment of the invention provides a nitriding process method of a powder metallurgy product, which relates to the technical field of heat treatment. Compared with the prior art, the method has the advantages that through the pulse gas nitriding process, the surface hardness of the workpiece can be improved, the phenomenon of uneven white bright layers is improved, the working noise is reduced, the wear-resisting and corrosion-resisting properties are improved, the application of the powder metallurgy product can be further expanded, compared with other nitriding processes, the method is a good way for improving the nitriding quality of the powder metallurgy product, the powder metallurgy product is not required to be directly assembled and used by grinding, and the post-processing cost is reduced.
Description
Technical Field
The invention relates to the technical field of heat treatment, in particular to a nitriding process method of a powder metallurgy product.
Background
The powder metallurgy product can reduce the machining amount and improve the productivity, so the powder metallurgy product is increasingly widely applied to hardware and electronic industries. In order to further improve the deformation load resistance and the wear resistance and abrasion resistance of the powder metallurgy product, the powder metallurgy product needs to be subjected to nitriding treatment.
In the prior art, a well-type nitriding furnace is usually adopted to realize nitriding of a workpiece, nitriding is usually performed for one time after a nitriding gas is introduced, the nitrogen content ratio or the nitrogen-hydrogen content ratio in the atmosphere is difficult to control, a thicker (more than 20 micrometers) compound layer usually appears on the surface of the workpiece subjected to gas nitriding treatment, and the thicker compound layer is an uneven mixture layer formed by two phases of e + gamma', and the inner layer is a diffusion layer. Therefore, a three-phase microstress is generated in the compound, and if an external force is slightly applied in the direction, micro cracks are generated, the cracks gradually expand to peel off the whole compound layer, the compound layer of the chromium-containing and aluminum nitriding steel is very brittle, and the compound layer is generally ground after gas nitriding for use.
Disclosure of Invention
The invention aims to provide a nitriding process method of a powder metallurgy product, which can improve the surface hardness of a workpiece, improve the uneven phenomenon of a white layer, reduce the working noise, improve the wear-resisting and corrosion-resisting properties, further expand the application range of the powder metallurgy product, avoid the need of grinding and direct installation and reduce the post-processing cost.
Embodiments of the invention may be implemented as follows:
in a first aspect, the present invention provides a nitriding process for a powder metallurgy product, comprising:
cleaning the workpiece;
feeding the workpiece into a vacuum furnace;
periodically carrying out vacuum pumping operation and nitrogen gas introducing operation on the vacuum furnace at a nitriding temperature so as to carry out vacuum pulse nitriding on the workpiece;
and cooling the workpiece and discharging.
In an alternative embodiment, the step of periodically subjecting the vacuum furnace to a vacuum pumping operation and a nitriding gas introducing operation at a nitriding temperature comprises:
pumping out the gas in the vacuum furnace until the vacuum degree in the vacuum furnace reaches a first preset value;
heating the vacuum furnace to a nitriding temperature;
stopping pumping the gas in the vacuum furnace, and introducing nitriding gas into the vacuum furnace until the gas pressure in the vacuum furnace reaches a second preset value, thereby completing a nitriding cycle;
the cycle completes a plurality of nitridation cycles.
In an alternative embodiment, said first preset value is 1.33 Pa.
In an alternative embodiment, the step of heating the vacuum furnace to a nitriding temperature comprises:
heating the vacuum furnace to 530-540 ℃, and preserving heat.
In an alternative embodiment, said second preset value is 1000 mbar.
In an alternative embodiment, each of the nitridation cycles is between 80 and 140 ss.
In an alternative embodiment, cycling through the steps of a plurality of nitridation cycles comprises:
the cycle completed 60 nitridation cycles.
In an alternative embodiment, the step of cleaning the workpiece comprises:
conveying the workpiece into a vacuum cleaning machine;
steam cleaning the workpiece;
circularly spraying the workpiece;
soaking the workpiece;
and drying the workpiece and discharging.
In an alternative embodiment, before the step of steam cleaning the workpiece 400s, the method further comprises:
adding a Cl ion neutralizer to the vacuum cleaner;
pre-spraying the workpiece.
In an alternative embodiment, the nitriding gas is ammonia.
The beneficial effects of the embodiment of the invention include, for example:
according to the nitriding process method of the powder metallurgy product, provided by the embodiment of the invention, the workpiece is cleaned firstly, then the workpiece is sent into the vacuum furnace, and the vacuum furnace is subjected to vacuumizing operation and nitrogen gas introducing operation periodically at the nitriding temperature, so that the workpiece is subjected to vacuum pulse nitriding, and finally the workpiece is cooled and discharged from the furnace. Compared with the prior art, the method can obtain an epsilon-phase single-phase layer with less brittleness of 5-15um or a tough gamma' -phase single-phase layer with 0-8um thickness by controlling the nitrogen content ratio or the nitrogen-hydrogen ratio in the atmosphere through a pulse gas nitriding process, and can also obtain a diffusion layer with better toughness, which has no compound layer and only has a diffusion layer, so that the surface hardness of a workpiece can be improved, the phenomenon of uneven white layer can be improved, the working noise can be reduced, the wear-resisting and corrosion-resisting properties can be improved, the application of a powder metallurgy product can be further expanded, compared with other nitriding processes, the method is a good way for improving the nitriding quality of the powder metallurgy product, a grinding direct-loading machine is not needed, and the post-processing cost can be reduced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Fig. 1 is a block diagram of the steps of a nitridation process method for a powder metallurgy product according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. indicate an orientation or a positional relationship based on that shown in the drawings or that the product of the present invention is used as it is, this is only for convenience of description and simplification of the description, and it does not indicate or imply that the device or the element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention.
Furthermore, the appearances of the terms "first," "second," and the like, if any, are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.
As disclosed in the background art, the nitridation process in the prior art is usually implemented by using a well-type nitriding furnace, firstly, a protective gas needs to be merged for replacement, then, a nitriding gas is introduced, and continuous nitridation is maintained at an auditive temperature for a certain time, wherein the nitriding speed is slow, the nitriding time is long, and the total nitriding period is as long as 24 hours. Meanwhile, because nitriding gas cannot be controlled after being introduced into the furnace, the atmosphere in the furnace cannot be controlled, and a thicker (more than 20 um) compound layer usually appears on the surface of a workpiece subjected to gas nitriding treatment under the continuous nitriding action, because the non-uniform mixture layer consisting of two phases of e + gamma' is formed, and the inner layer is a diffusion layer. Therefore, a three-phase microstress is generated in the compound, and if an external force is slightly applied in the direction, micro cracks are generated, the cracks gradually expand to peel off the whole compound layer, the compound layer of the chromium-containing and aluminum nitriding steel is very brittle, and the compound layer is generally ground after gas nitriding for use.
Furthermore, for steel parts, cleaning with gasoline, detergents may be performed before nitriding, whereas for porous powder metallurgy, the use of conventional cleaning methods is not appropriate.
In order to solve the above problems, the present invention provides a novel nitriding process for powder metallurgy products, and it should be noted that the features of the embodiments of the present invention can be combined with each other without conflict.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
Referring to fig. 1, the embodiment provides a nitriding process method for a powder metallurgy product, which improves the nitriding quality of the powder metallurgy product, and reduces the post-processing cost because the metallurgy product is directly installed and used without grinding.
The nitriding process method of the powder metallurgy product provided by the embodiment is used for realizing the nitriding process of the powder metallurgy product, and can further improve the anti-deformation load capacity and the wear-resisting and wear-resisting properties of the powder metallurgy product. Wherein the powder formula of the powder metallurgy product is as follows: 2.5 percent of copper, 1.5 percent of graphite, 1 percent of hard zinc, 0.5 percent of molybdenum disulfide, 0.1 percent of spindle oil and 94.4 percent of 100-mesh iron powder, wherein the carbon content of the fired product is 0.68 percent, the metallographic structure is pearlite, ferrite and graphite, and the hardness is 93 HRB.
The nitriding process of the powder metallurgy product provided by the embodiment specifically comprises the following steps:
s1: and cleaning the workpiece.
Specifically, the powder metallurgy product can be cleaned by using a vacuum solvent cleaning machine, a workpiece is firstly placed into the vacuum solvent cleaning machine, then a Cl ion neutralizer is added into the vacuum cleaning machine, then the workpiece is pre-sprayed to achieve a primary cleaning effect, then the workpiece is cleaned by a steam cleaning process, then the workpiece is circularly sprayed, then the workpiece is soaked, and finally the workpiece is taken out of the furnace after being dried.
It should be noted that, in this embodiment, the vacuum solvent cleaning machine can clean fully, suppress the greasy dirt in the gap of powder metallurgy spare, avoid the surface to contain oxide absorption and in the later stage reducing atmosphere and generate oxygen, reduce the interior oxidation cleaning system and adopt the hydrocarbon organic solvent of environmental protection of pure environment, have splendid solubility to metal working and various quenching oil, can guarantee the cleaning performance.
Preferably, the vacuum solvent cleaning machine can be adopted for cleaning in the embodiment, and the oil stain, the water, the cutting fluid, the adsorption of oxide on the surface and the generation of oxygen in the later reducing atmosphere can be sufficiently removed by performing steam cleaning on the workpiece for 400 seconds, spraying for 400 seconds, soaking for 300 seconds (including foaming and ultrasonic waves) and quick drying for 800 seconds.
S2: the workpiece is fed into a vacuum furnace.
Specifically, the cleaned workpiece is sent into the vacuum furnace, the vacuum furnace is provided with a vacuumizing device and a nitriding gas introducing device, the vacuumizing device can be a mechanical pump and can realize the extraction action of gas in the vacuum furnace, so that the gas pressure in the furnace is reduced, and the nitriding gas introducing device is used for introducing nitriding gas into the vacuum furnace in a pulse mode, so that the workpiece is conveniently nitrided.
S3: and periodically carrying out vacuum pumping operation and nitrogen gas introducing operation on the vacuum furnace at the nitriding temperature so as to carry out vacuum pulse nitriding on the workpiece.
Specifically, after a workpiece is loaded into a vacuum furnace, firstly, gas in the vacuum furnace is pumped out until the vacuum degree in the vacuum furnace reaches a first preset value, then the vacuum furnace is heated to a nitriding temperature, then, the gas in the vacuum furnace is stopped being pumped out, nitriding gas is introduced into the vacuum furnace until the gas pressure in the vacuum furnace reaches a second preset value, a nitriding period is completed, and then, a plurality of nitriding periods are completed in a circulating mode.
It should be noted that, during the process of completing a plurality of nitriding cycles, the vacuum furnace is always in the range of nitriding temperature, so as to ensure that the temperature is always in the nitriding condition.
Preferably, the first predetermined value here may be 1.33Pa, that is, the initial vacuum pumping action needs to be continued until the vacuum degree in the vacuum furnace reaches 1.33Pa, and then the subsequent heating action is started. Meanwhile, the nitriding temperature may be 530 ℃ to 540 ℃, that is, the vacuum furnace is heated to 530 ℃ to 540 ℃, preferably to 535 ℃, and heat is preserved until the end of nitriding. Meanwhile, the second preset value can be 1000mbar, namely the pressure in the furnace can be increased by introducing the nitriding gas, and the introduction can be stopped until 1000 mbar. In addition, each nitridation period is 80-140s, and 60 nitridation periods are required to be completed in the whole nitridation process. Of course, the data presented herein are merely exemplary and certain modifications may be made based on the actual nitriding environment.
In this embodiment, the nitriding gas may be ammonia gas, and the ammonia gas may be introduced at a rate of 5m3And h, when the step S3 is actually executed, ammonia gas can be introduced into the vacuum furnace in a pulse mode, namely, after the workpiece is loaded into the vacuum furnace, a mechanical pump is started to pump air, when the vacuum degree reaches a first preset value (for example, 1.33Pa), the vacuum furnace is electrified to heat up, and is heated, meanwhile, the vacuum degree is continuously pumped, the vacuum degree in the furnace is kept, after the furnace temperature reaches the required nitriding temperature of 530-. The furnace temperature was kept constant throughout the nitriding process.
In the embodiment, after vacuum pulse nitriding, the surface hardness of the workpiece is higher, the nitriding speed is much faster than that of common gas nitriding, the nitriding time is shortened, the total period is 14 hours, the total period is reduced by 10 hours compared with the total period of gas nitriding for 24 hours, and the diffusion layer is uniformly distributed.
S4: and cooling the workpiece and discharging.
Specifically, after the infiltrated layer meets the requirement, the heating is stopped, the vacuum furnace is cooled to 80 ℃, and then the nitriding operation is finished after the vacuum furnace is discharged.
It is noted that, in the conventional process, the specific process parameters thereofThe following: igniting the well type nitriding furnace at the temperature of 525 ℃ for 10min, and keeping the nitriding temperature at 525 ℃ for 9h, wherein NH is generated at the moment3The decomposition rate is 18% -22%, and then the nitriding temperature is kept for 525 ℃ for 11h, at the moment, NH3The decomposition rate is 30-35 percent, and finally the nitriding temperature is kept for 525 ℃ for 7h, at the moment, NH3Decomposition rate is 18% -22%, NH3The flow rate is 15-25m3The process cycle is about 27 hours. The required specifications are as follows: surface hardness is not less than 550HV0.05(ii) a The nitrided layer-spline is more than or equal to 0.1 mm; white layer-spline: 5-15 μm; the brittleness is less than or equal to grade 2; the porosity is less than or equal to 2 grade; the pulse nitride is less than or equal to 2 levels. The detection result of the workpiece subjected to nitriding treatment by using the conventional process is as follows: surface hardness 456, 634, 493HV0.05And nitrided layer-spline: 0.037DN(280HV0.1) (ii) a White layer-spline: 6-10 μm, brittleness grade 3; loosening by 3 grades; pulsed nitride 3 level. The detection result proves that the product is not qualified.
After the nitriding process method of the powder metallurgy product provided by the invention, the detection results of the workpiece are as follows: surface hardness 643, 631, 656HV0.05And nitrided layer-spline: 0.951DN(280HV0.1) White layer-spline: 5-12 μm, brittleness grade 1; loosening for grade 2; pulse nitride level 1. The detection result proves that the product is qualified. Therefore, the workpiece nitrided by the method of the embodiment has better quality than the workpiece nitrided by the conventional process.
In summary, the nitridation process method for the powder metallurgy product provided by the embodiment is to clean the workpiece, send the workpiece into the vacuum furnace, and periodically perform the vacuum pumping operation and the operation of introducing the nitriding gas into the vacuum furnace at the nitriding temperature, so as to realize the vacuum pulse nitridation of the workpiece, and finally cool the workpiece and discharge the workpiece from the furnace. Compared with the prior art, the pulse gas nitriding process can obtain an epsilon-phase single-phase layer with less brittleness of 5-15 mu m or a toughness gamma' -phase single-phase layer with thickness of 0-8 mu m by controlling the nitrogen content ratio or the nitrogen-hydrogen ratio in the atmosphere, and can also obtain a diffusion layer with better toughness, which has no compound layer and only a diffusion layer, so that the surface hardness of a workpiece can be improved, the phenomenon of uneven white layer can be improved, the working noise can be reduced, the wear-resisting and corrosion-resisting properties can be improved, the application of a powder metallurgy product can be further expanded, compared with other nitriding processes, the pulse gas nitriding process is a good way for improving the nitriding quality of the powder metallurgy product, the pulse gas nitriding process does not need to be directly installed for use, and the post-processing cost can be reduced.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (10)
1. A nitriding process method of a powder metallurgy product is characterized by comprising the following steps:
cleaning the workpiece;
feeding the workpiece into a vacuum furnace;
periodically carrying out vacuum pumping operation and nitrogen gas introducing operation on the vacuum furnace at a nitriding temperature so as to carry out vacuum pulse nitriding on the workpiece;
and cooling the workpiece and discharging.
2. The powder metallurgy product nitriding process method according to claim 1, wherein the step of periodically subjecting the vacuum furnace to a vacuum-pumping operation and a nitriding gas-introducing operation at a nitriding temperature comprises:
pumping out the gas in the vacuum furnace until the vacuum degree in the vacuum furnace reaches a first preset value;
heating the vacuum furnace to a nitriding temperature;
stopping pumping the gas in the vacuum furnace, and introducing nitriding gas into the vacuum furnace until the gas pressure in the vacuum furnace reaches a second preset value, so as to finish a nitriding cycle;
the cycle completes a plurality of nitridation cycles.
3. The nitriding process method of a powder metallurgy product according to claim 2, wherein the first predetermined value is 1.33 Pa.
4. The method for nitriding powder metallurgy products according to claim 2, wherein the step of heating the vacuum furnace to a nitriding temperature comprises:
heating the vacuum furnace to 530-540 ℃, and preserving heat.
5. The nitriding process of a powder metallurgical product according to claim 2, wherein said second predetermined value is 1000 mbar.
6. The nitriding process method for powder metallurgy products according to claim 2, wherein each nitriding cycle is 80-140 ss.
7. The method of nitriding a powder metallurgy product according to claim 2, wherein the step of cyclically completing a plurality of nitriding cycles comprises:
the cycle completed 60 nitridation cycles.
8. The nitriding process method for the powder metallurgy product according to claim 1, wherein the step of cleaning the workpiece comprises:
conveying the workpiece into a vacuum cleaning machine;
steam cleaning the workpiece;
circularly spraying the workpiece;
soaking the workpiece;
and drying the workpiece and discharging.
9. The method of nitriding of powder metallurgy products according to claim 8, wherein before the step of steam cleaning the workpiece, the method further comprises:
adding a Cl ion neutralizer to the vacuum cleaner;
and pre-spraying the workpiece.
10. The powder metallurgy product nitriding process according to claim 1, wherein the nitriding gas is ammonia gas.
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