CN114150258B - Carbon steel nitrocarburizing surface porosity improvement method - Google Patents
Carbon steel nitrocarburizing surface porosity improvement method Download PDFInfo
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- CN114150258B CN114150258B CN202111483338.3A CN202111483338A CN114150258B CN 114150258 B CN114150258 B CN 114150258B CN 202111483338 A CN202111483338 A CN 202111483338A CN 114150258 B CN114150258 B CN 114150258B
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- 238000000034 method Methods 0.000 title claims abstract description 32
- 229910000975 Carbon steel Inorganic materials 0.000 title claims abstract description 27
- 239000010962 carbon steel Substances 0.000 title claims abstract description 27
- 230000006872 improvement Effects 0.000 title description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 96
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 50
- 238000005121 nitriding Methods 0.000 claims abstract description 15
- 238000001816 cooling Methods 0.000 claims abstract description 14
- 239000007789 gas Substances 0.000 claims abstract description 12
- 238000000197 pyrolysis Methods 0.000 claims abstract description 11
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 20
- 229910052799 carbon Inorganic materials 0.000 claims description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 7
- 229910001315 Tool steel Inorganic materials 0.000 claims description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 5
- 229910021529 ammonia Inorganic materials 0.000 claims description 5
- 239000001257 hydrogen Substances 0.000 claims description 5
- 229910052739 hydrogen Inorganic materials 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 230000007797 corrosion Effects 0.000 abstract description 5
- 238000005260 corrosion Methods 0.000 abstract description 5
- 239000002184 metal Substances 0.000 abstract description 2
- 230000001105 regulatory effect Effects 0.000 abstract 1
- 230000008569 process Effects 0.000 description 19
- 239000010410 layer Substances 0.000 description 14
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 5
- 125000004433 nitrogen atom Chemical group N* 0.000 description 5
- 238000005336 cracking Methods 0.000 description 4
- 238000001514 detection method Methods 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000000149 penetrating effect Effects 0.000 description 2
- 229910001295 No alloy Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
-
- 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
- C23C8/28—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 more than one element being applied in one step
- C23C8/30—Carbo-nitriding
- C23C8/32—Carbo-nitriding of ferrous surfaces
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D27/00—Simultaneous control of variables covered by two or more of main groups G05D1/00 - G05D25/00
- G05D27/02—Simultaneous control of variables covered by two or more of main groups G05D1/00 - G05D25/00 characterised by the use of electric means
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Automation & Control Theory (AREA)
- General Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
- Measuring Volume Flow (AREA)
- Flow Control (AREA)
Abstract
The invention relates to a method for improving the surface porosity of carbon steel nitrocarburizing, which comprises the following steps: putting a workpiece made of carbon steel into a gas nitriding furnace with the temperature of 560-580 ℃ for nitrocarburizing treatment; the nitrocarburizing treatment comprises a replacement stage, a nitrocarburizing stage and a cooling stage, and is characterized in that: in the replacement stage, firstly introducing N 2 to replace air in the furnace, and then introducing pyrolysis NH 3 to replace N 2 in the furnace; NH 3、N2 and CO 2 are introduced in the nitrocarburizing stage to obtain the required nitrogen potential; in the cooling stage, NH 3 and pyrolysis NH 3 are introduced first, the isothermal temperature is reduced to 380+/-10 ℃, then N 2 is introduced until the carbon steel workpiece is discharged. The method of the invention ensures that the surface porosity grade of the metal part made of carbon steel is controlled to be 1 class standard regulated by AMS 2759/12A after nitrocarburizing treatment, thereby effectively improving the corrosion resistance of the carbon steel after nitrocarburizing.
Description
Technical Field
The invention belongs to the technical field of metal heat treatment, and relates to a method for improving nitrocarburizing surface porosity of carbon steel.
Background
The process of simultaneously penetrating nitrogen and carbon into the surface of a workpiece at the temperature of 500-600 ℃ is called ferrite nitrocarburizing, and is a low-temperature chemical heat treatment process widely applied at present. The carbon steel has no alloy element for generating alloy nitride, and the diffusion layer of the carbon steel is not high in hardness after nitrocarburizing, so that the carbon steel has little contribution to wear resistance. Therefore, the main purpose of the carbon steel after nitrocarburizing is to form a compact white bright layer of about 6-20um on the outer surface so as to obtain good corrosion resistance.
One major factor affecting the corrosion resistance of the white light layer is the porosity of the white light layer. Loosening refers to the density of micropores in a white layer on the surface of a nitriding part and is a defective tissue generated in a nitrocarburizing process. The AMS 2759/12A nitrocarburizing standard divides the loose grade into 2 grades, and the loose grade 1 refers to the loose thickness not exceeding 15% of the thickness of the white bright layer; the loose grade 2 refers to a loose thickness exceeding 10% but not exceeding 50% of the thickness of the white bright layer. The mechanism of loosening is generally considered to be that the parameters of the nitrocarburizing process are improper, and the concentration of nitrogen in the epsilon phase of the surface layer greatly fluctuates, so that nitrogen atoms are easy to combine into nitrogen molecules to escape from the surface to form holes. The level of carbon steel surface porosity after the existing nitrocarburizing process is 2, and in order to improve the surface porosity, how to reasonably set and control the nitrocarburizing process parameters can prevent the outward diffusion of nitrogen atoms in the white bright layer as little as possible, which is a great difficulty of the existing nitrocarburizing process.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the method for improving the surface porosity of the carbon steel nitrocarburizing, which effectively solves the problem of out-of-tolerance surface porosity grade generated by the original nitrocarburizing process and improves the corrosion resistance of the carbon steel nitrocarburizing.
The technical scheme adopted by the invention is as follows:
The method for improving the surface porosity of the carbon steel nitrocarburizing comprises the following steps: putting a workpiece made of carbon steel into a gas nitriding furnace with the temperature of 560-580 ℃ for nitrocarburizing treatment; the nitrocarburizing treatment comprises a replacement stage, a nitrocarburizing stage and a cooling stage, and is characterized in that: in the replacement stage, firstly introducing N 2 to replace air in the furnace, and then introducing pyrolysis NH 3 to replace N 2 in the furnace; NH 3、N2 and CO 2 are introduced in the nitrocarburizing stage to obtain the required nitrogen potential; in the cooling stage, NH 3 and pyrolysis NH 3 are introduced first, the isothermal temperature is reduced to 380+/-10 ℃, then N 2 is introduced until the carbon steel workpiece is discharged.
The carbon steel material is carbon tool steel.
The displacement stage first evacuates the furnace atmosphere with N 2 at low temperature. And (3) raising the temperature in the furnace to 450+/-10 ℃, introducing pyrolysis NH 3 to empty the N 2 in the furnace, and ensuring that a white bright layer is not formed on the surface in the temperature raising stage.
The nitrocarburizing stage is the main process of nitrocarburizing treatment, the gas is three mixed gases of N 2、NH3 and CO 2, the nitrocarburizing temperature is 560-580 ℃, the nitrocarburizing potential is 1.6-2.0, and the nitriding time is 2-5h, so as to obtain the white bright tissue required by nitrocarburizing.
And in the cooling stage, pyrolysis NH 3 and small flow NH 3 are simultaneously introduced, so that the atmosphere still maintains a certain nitrogen potential in the cooling stage, and the nitrogen concentration difference between the nitrogen concentration on the surface of the part and the nitrogen potential of the atmosphere is reduced.
An intelligent nitrogen potential control system is arranged in the gas nitriding furnace and comprises a laser nitrogen potential sensor and an intelligent flow controller; the laser nitrogen potential sensor measures the partial pressure of ammonia and the partial pressure of hydrogen in the furnace in real time and calculates the nitrogen potential by utilizing the results of the partial pressure and the partial pressure of hydrogen; the intelligent flow controller is used for accurately controlling and adjusting the gas flow and accurately controlling the nitrogen potential in the furnace.
Compared with the prior art, the invention has the following advantages: the cracking of NH 3 during the warm-up phase has two benefits: firstly, N 2 in the furnace is replaced in advance, so that the time for establishing the atmosphere in the nitrocarburizing stage is reduced. Secondly, surface nitriding in the temperature rising stage is avoided, and a white bright layer with uncontrollable nitrogen concentration is formed. The lower nitrogen potential is adopted in the nitrocarburizing stage, so that the overlarge fluctuation of the nitrogen potential caused by overlarge nitrogen potential is avoided, and the overlarge fluctuation of the nitrogen concentration of the white bright layer is prevented from being influenced. And in the cooling stage, cracking NH 3 and small flow NH 3 are introduced, so that the atmosphere is kept with a certain nitrogen potential, and the loosening caused by diffusion of nitrogen atoms in the white bright layer to the outside of the atmosphere due to rapid drop of the nitrogen potential of the atmosphere of the suddenly cut-off NH 3 is prevented. Meanwhile, the invention also adopts an intelligent nitrogen potential control system, wherein the laser nitrogen potential sensor is particularly suitable for measuring the atmosphere nitrogen potential when N 2 is introduced into the nitrocarburizing atmosphere, and solves the problem that the nitrogen potential is not accurately calculated by only using a hydrogen probe or only using a bubble bottle in the nitrocarburizing atmosphere of NH 3、N2 and CO 2 in the past. The intelligent flow controller controls the atmosphere nitrogen potential within the nitrogen potential range required by the process all the time through accurate control and adjustment of the NH 3、N2 and CO 2 flows.
Drawings
FIG. 1 is a graph of a conventional nitrocarburizing process.
FIG. 2 is a graph of a nitrocarburizing process according to an embodiment of the present invention.
Fig. 3 is a metallographic photograph of a conventional nitrocarburizing process with a loose surface (500X).
Fig. 4 is a metallographic photograph of nitrocarburized surface porosity (500X) of an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and examples. The intelligent nitrogen potential control system comprises a laser nitrogen potential sensor and an intelligent flow controller, which are both of the existing structure and technology.
Example 1
A method for improving the surface porosity of carbon steel nitrocarburizing comprises the following steps:
And (3) putting the workpiece made of the carbon tool steel material into a gas nitriding furnace for nitrocarburation treatment, heating the nitriding furnace, and introducing N 2 to replace air, wherein the flow rate of N 2 is 5m 3/h.
When the furnace temperature is raised to 450+/-5 ℃, N 2 is closed, and simultaneously cracking NH 3 is introduced to replace N 2, wherein the flow rate of the cracking NH 3 is 3m 3/h.
When the furnace temperature is raised to 570+/-5 ℃, 50% NH 3、45％N2 and 5% C0 2 are simultaneously introduced for nitrocarburizing, the intelligent nitrogen potential control system automatically controls the nitrogen potential to be 1.6-2, and the temperature is kept for 3.5H.
After nitrocarburizing is finished, the fast air cooler is opened, CO 2 and N 2 are closed, pyrolysis NH 3 and small-flow NH 3 are continuously introduced for cooling, NH 3 flow is 2m 3/h, and pyrolysis ammonia flow is 3m 3/h.
The furnace temperature was cooled to 380.+ -.5 ℃, NH 3 was closed and NH 3 was cleaved while N 2,N2 flow was opened for 2m 3/h.
And (5) when the temperature is cooled to 150+/-5 ℃, the fast cooling fan and the N 2 are closed, and the carbon tool steel workpiece is discharged.
The graph of the nitriding method is shown in fig. 2.
Comparative example 1
And (3) putting the workpiece made of the carbon tool steel material into a gas nitriding furnace for nitrocarburation treatment, heating the nitriding furnace, and introducing N 2 to replace air, wherein the flow rate of N 2 is 5m 3/h.
When the furnace temperature is raised to 450+/-5 ℃, N 2 is closed, and NH 3 is introduced to replace N 2,NH3 with the flow rate of 3m 3/h.
When the furnace temperature is raised to 570+/-5 ℃, 50% NH 3、45％N2 and 5% C0 2 are simultaneously introduced for nitrocarburizing, a bubble bottle is used for manually controlling the ammonia decomposition rate to be 70% -75%, and the temperature is kept for 3.5H.
After nitrocarburizing is finished, the fast air cooler is opened, CO 2 and NH 3 are closed, N 2 is continuously introduced for cooling, and the flow of N 2 is 2m 3/h.
And (5) when the temperature is cooled to 150+/-5 ℃, the fast cooling fan and the N 2 are closed, and the carbon tool steel workpiece is discharged.
The nitriding process is shown in fig. 1.
Result detection
Taking the samples produced by the two processes of the example 1 and the comparative example 1, carrying out metallographic detection on the samples of the two processes according to the AMS 2759/12A nitrocarburizing standard, wherein the metallographic result of the process of the example 1 shows that the surface porosity grade is 1 grade, and a specific metallographic structure detection photo is shown in fig. 4. The metallographic result of the traditional process, namely the comparative example 1, shows that the surface porosity level is 2, and a specific metallographic structure detection photo is shown in fig. 3.
Analysis shows that the NH3 is replaced by the cracked NH3 in the heating stage, so that nitrogen atoms are prevented from penetrating into the surface of the workpiece, and a white bright layer with uncontrollable nitrogen concentration is avoided. In the nitrocarburizing stage, the accurate measurement and control of the atmosphere nitrogen potential are carried out by an intelligent nitrogen potential control system, so that the error area of the nitrocarburizing atmosphere nitrogen potential is corrected by a method of singly measuring and controlling the decomposition rate by using a bubble bottle, and the process adopts lower nitrogen potential in the nitrocarburizing stage, thereby reducing the fluctuation of the nitrogen potential and being beneficial to the stability of the nitrogen concentration on the surface of a workpiece. The cooling section is simultaneously introduced with pyrolysis NH3 and NH3, so that the difference of the nitrogen concentration on the surface of the workpiece and the nitrogen potential of the atmosphere is further reduced, and the possibility that nitrogen atoms in the white bright layer are outwards diffused to form looseness is reduced. The porosity grade of the carbon steel surface after nitrocarburizing is improved from the original grade 2 to the grade 1, so that the corrosion resistance of the carbon steel material can be effectively improved.
The technical scheme and the conception are only simple text description of the design idea of the invention, but not limitation of the design idea of the invention, and any combination, addition or modification not exceeding the design idea of the invention falls within the protection scope of the invention.
Claims (2)
1. The method for improving the surface porosity of the carbon steel nitrocarburizing comprises the following steps: putting a workpiece made of carbon steel into a gas nitriding furnace with the temperature of 560-580 ℃ for nitrocarburizing treatment; the nitrocarburizing treatment comprises a replacement stage, a nitrocarburizing stage and a cooling stage, and is characterized in that: in the replacement stage, firstly introducing N 2 to replace air in the furnace, and then introducing pyrolysis NH 3 to replace N 2 in the furnace; NH 3、N2 and CO 2 are introduced in the nitrocarburizing stage to obtain the required nitrogen potential; introducing NH 3 and splitting NH 3 at the cooling stage, and introducing N 2 until the workpiece made of carbon steel is discharged after the isothermal temperature is reduced to 380+/-10 ℃; the carbon steel material is carbon tool steel;
In the replacement stage, firstly, evacuating air in the furnace by using N 2 at low temperature, raising the temperature in the furnace to 450+/-10 ℃, introducing pyrolysis NH 3 to evacuate N 2 in the furnace, and ensuring that a white bright layer is not formed on the surface in the temperature raising stage;
The gases used in the nitrocarburizing stage are NH 3、N2 and CO 2, the temperature is 560-580 ℃, the nitrogen potential is controlled to be 1.6-2.0, and the nitriding time is 2-5h.
2. The method for improving the nitrocarburizing surface porosity of the carbon steel according to claim 1, wherein the method comprises the following steps: an intelligent nitrogen potential control system is arranged in the gas nitriding furnace, the intelligent nitrogen potential control system comprises a laser nitrogen potential sensor and an intelligent flow controller, and the laser nitrogen potential sensor measures the partial pressure of ammonia and the partial pressure of hydrogen in the furnace in real time and calculates the nitrogen potential by utilizing the results of the partial pressure of ammonia and the partial pressure of hydrogen in the furnace; the intelligent flow controller is used for accurately controlling and adjusting the gas flow and accurately controlling the nitrogen potential in the furnace.
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| CN2020230465780 | 2020-12-17 | ||
| CN202023046578 | 2020-12-17 |
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| CN114150258A CN114150258A (en) | 2022-03-08 |
| CN114150258B true CN114150258B (en) | 2024-04-26 |
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| CN202111430682.6A Active CN114107876B (en) | 2020-12-17 | 2021-11-29 | White-layer-free nitriding method for inner gear ring of wind power speed increasing box |
| CN202111483338.3A Active CN114150258B (en) | 2020-12-17 | 2021-12-07 | Carbon steel nitrocarburizing surface porosity improvement method |
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| CN202111430682.6A Active CN114107876B (en) | 2020-12-17 | 2021-11-29 | White-layer-free nitriding method for inner gear ring of wind power speed increasing box |
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| CN115404434A (en) * | 2022-07-26 | 2022-11-29 | 厦门真冈热处理有限公司 | A rapid nitriding method for planet carrier of automatic transmission of automobile |
| CN116640912A (en) * | 2023-05-11 | 2023-08-25 | 浙江大学 | A heat treatment surface strengthening method for inner curve hydraulic motor stator guide rail |
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- 2021-11-05 CN CN202122694884.3U patent/CN216201077U/en active Active
- 2021-11-29 CN CN202111430682.6A patent/CN114107876B/en active Active
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| CN114107876A (en) | 2022-03-01 |
| CN216201077U (en) | 2022-04-05 |
| CN114150258A (en) | 2022-03-08 |
| CN114107876B (en) | 2024-03-26 |
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