CN114150258A - Carbon steel nitrocarburizing surface porosity improvement method - Google Patents
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- CN114150258A CN114150258A CN202111483338.3A CN202111483338A CN114150258A CN 114150258 A CN114150258 A CN 114150258A CN 202111483338 A CN202111483338 A CN 202111483338A CN 114150258 A CN114150258 A CN 114150258A
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- 238000000034 method Methods 0.000 title claims abstract description 35
- 229910000975 Carbon steel Inorganic materials 0.000 title claims abstract description 30
- 239000010962 carbon steel Substances 0.000 title claims abstract description 30
- 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 94
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 52
- 238000001816 cooling Methods 0.000 claims abstract description 19
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 12
- 239000007789 gas Substances 0.000 claims abstract description 11
- 238000005121 nitriding Methods 0.000 claims abstract description 10
- 238000005336 cracking Methods 0.000 claims abstract description 6
- 238000006073 displacement reaction Methods 0.000 claims abstract description 6
- 229910000069 nitrogen hydride Inorganic materials 0.000 claims description 25
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical group N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 23
- 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
- 229910021529 ammonia Inorganic materials 0.000 claims description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 5
- 239000001257 hydrogen Substances 0.000 claims description 5
- 229910052739 hydrogen Inorganic materials 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
- 230000003628 erosive effect Effects 0.000 abstract 1
- 230000008569 process Effects 0.000 description 19
- 239000010410 layer Substances 0.000 description 15
- 125000004433 nitrogen atom Chemical group N* 0.000 description 5
- 238000001514 detection method Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000006467 substitution reaction Methods 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
- 238000005516 engineering process Methods 0.000 description 1
- 239000000463 material Substances 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
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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
- C23C8/28—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
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
- Measuring Volume Flow (AREA)
- Flow Control (AREA)
Abstract
The invention relates to a carbon steel nitrocarburizing surface porosity improving method, which comprises the following steps: putting a workpiece made of carbon steel into a gas nitriding furnace at the temperature of 560-; the nitrocarburizing treatment comprises a displacement stage, a nitrocarburizing stage and a cooling stage, and is characterized in that: introducing N in the replacement stage2Replacing air in the furnace and then introducing cracked NH3To N in the furnace2Carrying out replacement; NH is introduced at the nitrocarburizing stage3、N2And CO2To obtain the desired nitrogen potential; NH is firstly introduced in the cooling stage3And cracking NH3After the temperature is reduced to 380 +/-10 ℃, N is introduced2Until the workpiece made of carbon steel is discharged. The method of the invention controls the surface porosity grade of the metal parts made of carbon steel to be in the 1-class standard specified by AMS 2759/12A after nitrocarburizing treatment, thereby effectively improving the corrosion resistance of the carbon steel after nitrocarburizingAnd (4) eroding.
Description
Technical Field
The invention belongs to the technical field of metal heat treatment, and relates to a carbon steel nitrocarburizing surface porosity improving method.
Background
The process of simultaneously permeating nitrogen and carbon into the surface of a workpiece within the temperature range of 500-600 ℃ is called ferrite nitrocarburizing, and is a low-temperature chemical heat treatment process which is widely applied at present. The carbon steel has no alloy elements for generating alloy nitrides, and the hardness of a diffusion layer of the carbon steel is not high after nitrocarburizing, so that the carbon steel has little contribution to the wear resistance. So the main purpose of the carbon steel after nitrocarburizing is to form a compact white layer of about 6-20um on the outer surface to obtain good corrosion resistance.
One of the main factors affecting the corrosion resistance of the bright layer is the looseness of the bright layer. The porosity refers to the density of micropores in a white layer on the surface of a nitrided piece, and is a defect structure generated in the nitrocarburizing process. The AMS 2759/12A nitrocarburizing standard divides the loosening grade into 2 grades, and the loosening grade 1 means that the loosening thickness does not exceed 15% of the thickness of the white layer; by loose grade 2 is meant that the loose thickness exceeds 10% of the thickness of the white layer but does not exceed 50% of the thickness of the white layer. The mechanism of the loosening is generally considered to be that the nitrocarburizing process parameters are not proper, and the nitrogen concentration in the epsilon phase of the surface layer generates large fluctuation, so that nitrogen atoms are easy to combine into nitrogen molecules to escape from the surface to form holes. The surface porosity grade of carbon steel after the existing nitrocarburizing process is 2 grades, and how to reasonably set and control nitrocarburizing process parameters for improving the surface porosity can prevent the nitrogen atoms in the white and bright layer from diffusing outwards as little as possible, which is a big difficulty of the existing nitrocarburizing process.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for improving the surface porosity of carbon steel nitrocarburizing, which effectively solves the problem of the poor level of surface porosity generated by the original nitrocarburizing process and improves the corrosion resistance of the carbon steel after nitrocarburizing.
The technical scheme adopted by the invention is as follows:
a carbon steel nitrocarburizing surface porosity improving method comprises the following steps: putting a workpiece made of carbon steel into a gas nitriding furnace at the temperature of 560-; the nitrocarburizing treatment comprises a displacement stage, a nitrocarburizing stage and a cooling stage, and is characterized in that: introducing N in the replacement stage2Replacing air in the furnace and then introducing cracked NH3To N in the furnace2Carrying out replacement; NH is introduced at the nitrocarburizing stage3、N2And CO2To obtain the desired nitrogen potential; NH is firstly introduced in the cooling stage3And cracking NH3After the temperature is reduced to 380 +/-10 ℃, N is introduced2Until the workpiece made of carbon steel is discharged.
The carbon steel is carbon tool steel.
The displacement stage is preceded by N at low temperature2And evacuating the air in the furnace. The temperature in the furnace is raised to 450 +/-10 ℃, and cracked NH is introduced3To furnace N2Evacuation is carried out and it is ensured that no white bright layer is formed on the surface during the temperature rise phase.
The nitrocarburizing stage is the main process of nitrocarburizing treatment, and the gas is N2、NH3And CO2The temperature of nitrocarburizing is 560-.
Introducing cracked NH at the same time in the cooling stage3And a small flow NH3And a certain nitrogen potential is still kept in the atmosphere at 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 installed in the gas nitriding furnace, and comprises a laser nitrogen potential sensor and an intelligent flow controller; the laser nitrogen potential sensor measures the ammonia partial pressure and the hydrogen partial pressure in the furnace in real time and calculates the nitrogen potential by using the results of the ammonia partial pressure and the hydrogen partial pressure; the intelligent flow controller accurately controls and adjusts the gas flow and accurately controls the nitrogen potential in the furnace.
Compared with the prior art, the invention has the following advantages: NH cracking at the temperature rising stage3Has two advantages: firstly, N in the furnace is put in advance2Displacement, reducing the time for atmosphere establishment during the nitrocarburizing stage. And secondly, surface nitriding is avoided in the temperature rise stage, and a brilliant layer with uncontrollable nitrogen concentration is formed. The nitrocarburizing stage adopts lower nitrogen potential, thereby avoiding the too big fluctuation of the nitrogen potential caused by too high nitrogen potential and influencing the too big fluctuation of the nitrogen concentration of the white bright layer. Introducing cracked NH in the cooling stage3And a small flow NH3To maintain a certain nitrogen potential in the atmosphere and prevent NH from being suddenly cut off3The nitrogen potential of the atmosphere drops too fast, which leads to loosening caused by the diffusion of nitrogen atoms in the white layer to the outside of the atmosphere. Meanwhile, the invention also adopts an intelligent nitrogen potential control system, wherein the laser nitrogen potential sensor is particularly suitable for introducing N into nitrocarburizing atmosphere2The measurement of the nitrogen potential of the atmosphere solves the problem of the prior NH3、N2And CO2The problem that the nitrogen potential cannot be accurately calculated by using only a hydrogen probe or only a bubble bottle in the nitrocarburizing atmosphere. The intelligent flow controller is used for controlling the flow of NH3、N2And CO2The flow is precisely controlled and adjusted, and the nitrogen potential of the atmosphere is always controlled within the nitrogen potential range required by the process.
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 surface porosity (500X) of a conventional nitrocarburizing process.
FIG. 4 is a metallographic photograph of a nitrocarburized surface porosity (500X) of an example of the invention.
Detailed Description
The invention is further described below with reference to the figures and examples. The intelligent nitrogen potential control system comprises a laser nitrogen potential sensor and an intelligent flow controller, which are both in the existing structure and technology.
Example 1
A carbon steel nitrocarburizing surface porosity improving method comprises the following steps:
putting a workpiece made of carbon tool steel into a gas nitriding furnace for nitrocarburizing treatment, heating the nitriding furnace and introducing N2Replacement of air, N2The flow rate is 5m3/h。
When the furnace temperature rises to 450 +/-5 ℃, N is closed2While introducing cracked NH3Substitution of N2Cracking of NH3The flow rate is 3m3/h。
When the furnace temperature rises to 570 +/-5 ℃, 50 percent of NH is simultaneously introduced3、45％N2And 5% C02And (3) carrying out nitrocarburizing, automatically controlling the nitrogen potential to be 1.6-2 by an intelligent nitrogen potential control system, and keeping the temperature for 3.5H.
After the nitrocarburizing is finished, the quick cooling fan is turned on, and CO is turned off2And N2Continuously introducing cracked NH3And a small flow NH3Cooling is carried out, NH3Flow 2m3H, cracked ammonia flow 3m3/h。
Cooling the furnace to 380 +/-5 ℃, and closing NH3And cracking NH3While simultaneously turning on N2，N2Flow 2m3/h。
Cooling to 150 +/-5 ℃, turning off the quick cooling fan and N2And discharging the carbon tool steel workpiece.
The graph of the nitridation method is shown in fig. 2.
Comparative example 1
Putting a workpiece made of carbon tool steel into a gas nitriding furnace for nitrocarburizing treatment, heating the nitriding furnace and introducing N2Replacement of air, N2The flow rate is 5m3/h。
When the furnace temperature rises to 450 +/-5 ℃, N is closed2While introducing NH3Substitution of N2，NH3The flow rate is 3m3/h。
When the furnace temperature rises to 570 +/-5 ℃, 50 percent of NH is simultaneously introduced3、45％N2And 5% C02And (3) carrying out nitrocarburizing, manually controlling the ammonia decomposition rate to be 70-75% by using a bubble bottle, and keeping the temperature for 3.5H.
After the nitrocarburizing is finished, the quick cooling fan is turned on, and the C is turned offO2And NH3Continuously introducing N2Cooling is carried out, N2Flow 2m3/h。
Cooling to 150 +/-5 ℃, turning off the quick cooling fan and N2And discharging the carbon tool steel workpiece.
The graph of the nitridation process is shown in fig. 1.
Result detection
The samples produced by the two processes of example 1 and comparative example 1 are taken, metallographic detection is carried out on the samples produced by the two processes according to the AMS 2759/12A nitrocarburizing standard, the metallographic result of the process of 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 conventional process, namely comparative example 1, shows that the surface porosity level is 2, and a specific metallographic structure detection photograph is shown in fig. 3.
Analysis shows that cracked NH3 is used to replace NH3 in the temperature raising stage, so that nitrogen atoms are prevented from permeating into the surface of the workpiece, and a white bright layer with uncontrollable nitrogen concentration is avoided in the temperature raising stage. In the nitrocarburizing stage, the accurate measurement and control of the nitrogen potential of the atmosphere are performed by the intelligent nitrogen potential control system, the error zone that the nitrogen potential of the nitrocarburizing atmosphere is controlled by the traditional method of measuring and controlling the decomposition rate by using a bubble bottle alone is corrected, and the process adopts lower nitrogen potential in the nitrocarburizing stage, reduces the fluctuation of the nitrogen potential and is beneficial to the stability of the nitrogen concentration on the surface of a workpiece. Cracked NH3 and NH3 are introduced into the cooling section at the same time, so that the difference between 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 layer diffuse outwards to form porosity is reduced. The surface porosity grade of the carbon steel 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 solutions and concepts described above are only simple words for describing the design idea of the present invention, and are not limitations of the design idea of the present invention, and any combination, addition, or modification that does not exceed the design idea of the present invention falls within the protection scope of the present invention.
Claims (5)
1. A method for improving the surface porosity of carbon steel by nitrocarburizingThe method comprises the following steps: putting a workpiece made of carbon steel into a gas nitriding furnace at the temperature of 560-; the nitrocarburizing treatment comprises a displacement stage, a nitrocarburizing stage and a cooling stage, and is characterized in that: introducing N in the replacement stage2Replacing air in the furnace and then introducing cracked NH3To N in the furnace2Carrying out replacement; NH is introduced at the nitrocarburizing stage3、N2And CO2To obtain the desired nitrogen potential; NH is firstly introduced in the cooling stage3And cracking NH3After the temperature is reduced to 380 +/-10 ℃, N is introduced2Until the workpiece made of carbon steel is discharged.
2. The carbon steel nitrocarburizing surface porosity improving method according to claim 1, characterized in that: the carbon steel is carbon tool steel.
3. The carbon steel nitrocarburizing surface porosity improving method according to claim 1, characterized in that: the displacement stage is preceded by N at low temperature2Evacuating the air in the furnace, raising the temperature in the furnace to 450 +/-10 ℃, and introducing cracked NH3To furnace N2Evacuation is carried out and it is ensured that no white bright layer is formed on the surface during the temperature rise phase.
4. The carbon steel nitrocarburizing surface porosity improving method according to claim 1, characterized in that: the gas used in the nitrocarburizing stage is NH3、N2And CO2The temperature is 560-.
5. The carbon steel nitrocarburizing surface porosity improving method according to claim 1, characterized in that: an intelligent nitrogen potential control system is installed 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 ammonia partial pressure and the hydrogen partial pressure in the furnace in real time and calculates the nitrogen potential by using the results of the ammonia partial pressure and the hydrogen partial pressure; the intelligent flow controller accurately controls and adjusts the gas flow and accurately controls the nitrogen potential in the furnace.
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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 | Rapid nitriding method for planet carrier of automatic transmission of automobile |
| CN116640912A (en) * | 2023-05-11 | 2023-08-25 | 浙江大学 | Heat treatment surface strengthening method for inner curve hydraulic motor stator guide rail |
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| CN114150258B (en) | 2024-04-26 |
| CN216201077U (en) | 2022-04-05 |
| CN114107876A (en) | 2022-03-01 |
| CN114107876B (en) | 2024-03-26 |
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