CN113106378A - Heat treatment method of medium carbon alloy steel fitting - Google Patents

Heat treatment method of medium carbon alloy steel fitting Download PDF

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Publication number
CN113106378A
CN113106378A CN202110371276.0A CN202110371276A CN113106378A CN 113106378 A CN113106378 A CN 113106378A CN 202110371276 A CN202110371276 A CN 202110371276A CN 113106378 A CN113106378 A CN 113106378A
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treatment
nitriding
furnace
alloy steel
carbon alloy
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CN113106378B (en
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王浩存
李治宾
高中楠
张登坡
郭全海
张希平
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Weifang Fengdong Heat Treatment Co ltd
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Weifang Fengdong Heat Treatment Co ltd
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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
    • C23C8/08—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
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • 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
    • 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
    • C23C8/12—Oxidising using elemental oxygen or ozone
    • C23C8/14—Oxidising of ferrous surfaces
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

Abstract

The invention provides a heat treatment method of a medium carbon alloy steel fitting, belongs to the technical field of heat treatment, and can solve the technical problems of poor product nitriding appearance, blackening and the like in the existing gas nitriding process. The heat treatment method comprises the following steps: (1) ultrasonic cleaning and drying; (2) pre-oxidation treatment; (3) nitriding treatment; (4) nitriding and preserving heat; (5) cooling; (6) and discharging, wherein the nitriding treatment further comprises a primary nitriding treatment and a secondary nitriding treatment. The invention has the characteristics of simple and convenient operation, high product wear resistance, high surface hardness and the like. The invention can be applied to the gas nitriding treatment process of the medium carbon alloy steel fittings.

Description

Heat treatment method of medium carbon alloy steel fitting
Technical Field
The invention belongs to the technical field of heat treatment, and particularly relates to a heat treatment method of a medium carbon alloy steel fitting.
Background
The gas nitriding process is a chemical heat treatment process for making nitrogen atoms penetrate into the surface layer of a workpiece in a certain medium at a certain temperature. The product after nitriding treatment has excellent wear resistance, fatigue resistance, corrosion resistance and high temperature resistance, and the process is widely applied to the fields of automobiles, machinery, molds and the like.
However, when the conventional gas nitriding process is adopted to treat accessory products, the problems of poor nitriding appearance, blackening and the like of the treated products exist due to the long-term use of the gas-nitrogen furnace, untimely and incomplete cleaning of the furnace chamber or the problems of cleaning residues and the like of the products when the products enter the furnace, and the product performance is further influenced. Therefore, how to develop a treatment process which is simple and convenient to operate and has ideal properties such as wear resistance, fatigue resistance and the like by optimizing a gas nitriding process is a key point for solving the problems.
Disclosure of Invention
Aiming at the technical problems of poor nitrided appearance, blackening and the like of products in the existing gas nitriding process, the invention provides a heat treatment method which has the characteristics of simple and convenient operation, high product wear resistance, high surface hardness and the like.
In order to achieve the purpose, the invention adopts the technical scheme that:
a heat treatment method of a medium carbon alloy steel fitting comprises the following steps:
ultrasonically cleaning oil stains on the surface of the medium carbon alloy steel fitting and in the gap, and drying cleaning liquid on the surface of the medium carbon alloy steel fitting and in the gap;
after the dried medium carbon alloy steel fittings enter a well type gas nitrogen furnace, raising the temperature of the furnace to 200-450 ℃ for pre-oxidation treatment;
after the pre-oxidation treatment is finished, a vacuum pump is used for pumping the interior of the furnace to the limit vacuum, nitrogen is repressed to positive pressure, then hard nitriding atmosphere is introduced into the furnace for primary nitriding treatment, and then oxygen is introduced into the furnace for secondary nitriding treatment;
nitriding the medium carbon alloy steel fittings subjected to the secondary nitriding treatment in a furnace for heat preservation;
after the nitriding heat preservation is finished, starting cooling treatment, stopping introducing the hard nitriding atmosphere and oxygen, introducing protective atmosphere into the furnace, starting cooling treatment, stopping introducing oxygen, reducing the introduction amount of the hard nitriding atmosphere, and reducing the flow to 6-12m3And h, when the temperature is reduced to 350 +/-50 ℃, closing the hard nitriding atmosphere, opening the protective atmosphere to continue to reduce the temperature, and discharging the steel when the temperature is reduced to below 100 ℃.
Preferably, the pre-oxidation treatment is pre-oxidation treatment of the dried medium carbon alloy steel fittings for 50-100min at the furnace temperature of 200-450 ℃, and air is introduced into the furnace in the whole process.
Preferably, a hard nitriding atmosphere is introduced in the whole process of the primary nitriding treatment and the secondary nitriding treatment.
Preferably, the hard nitriding atmosphere introduced in the primary nitriding treatment and the secondary nitriding treatment is ammonia gas, and the flow rates of the ammonia gas are respectively 5-15m3/h、15-30m3/h。
Preferably, the conditions of the primary nitridation treatment are treatment at the temperature of 450-550 ℃ for 100-120min, and the conditions of the secondary nitridation treatment are treatment at the temperature of 500-550 ℃ for 850-960 min.
Preferably, the decomposition rate of the primary nitriding treatment and the decomposition rate of the secondary nitriding treatment are both 20 to 50%.
Preferably, in the secondary nitriding treatment process, the proportion of oxygen is controlled to be 1-5%, and the balance is hard nitriding atmosphere.
Preferably, the protective atmosphere is nitrogen.
Compared with the prior art, the invention has the advantages and positive effects that:
1. the invention provides a heat treatment method of a medium carbon alloy steel fitting, which organically combines a conventional gas nitriding process and a pre-oxidation treatment process and arranges the process before the gas nitriding process, wherein the process can form a compact oxide film on the surface of the fitting, and the film is reduced at the initial stage of nitriding, so that a clean new surface presents high chemical activity, the adsorption rate and the adsorption quantity of a penetrating agent are increased, and the function of a catalyst is played, so that the molecular bond breaking of the penetrating agent is promoted, and the active nitrogen atom penetration is accelerated;
2. the invention provides a heat treatment method of a medium carbon alloy steel fitting, which is characterized in that a hard nitriding atmosphere and oxygen are introduced simultaneously in the hard nitriding treatment process, and proper oxygen is added in the hard nitriding treatment process, so that hydrogen can be firstly combined with oxygen, the hydrogen partial pressure in the atmosphere can be reduced, the nitrogen potential of the atmosphere is improved, and the aim of improving the nitriding speed is fulfilled;
3. the invention provides a heat treatment method of a medium carbon alloy steel fitting, which can also play a role in accelerating dehydrogenation of a surface layer by adding proper oxygen in the hard nitriding treatment process, can obviously reduce the hydrogen content of the surface layer of a product, and further accelerates the diffusion speed of nitrogen atoms in the fitting due to the increase of the nitrogen potential of the atmosphere and the reduction of the hydrogen content of the surface.
Drawings
FIG. 1 is a schematic view of the appearance of a product after being treated by a heat treatment method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the appearance of a product treated by the method described in comparative example 1 according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a heat treatment method of a medium carbon alloy steel fitting, which comprises the following steps:
s1, ultrasonically cleaning oil stains on the surface of the medium carbon alloy steel fitting and in the gap, and drying the cleaning liquid on the surface of the medium carbon alloy steel fitting and in the gap;
in the step S1, the ultrasonic technique is first used to thoroughly remove rust preventive oil, dust and other substances on the surfaces of the fittings and in the gaps, and compressed air is used to blow out and blow dry the residual cleaning solution on the surfaces of the fittings and in the gaps, so that the surfaces and the gaps of the fittings are thoroughly cleaned and dried before the nitrogen furnace is fed, which is beneficial to improving the appearance of the product.
S2, after the blow-dried medium carbon alloy steel fitting enters a well type gas nitrogen furnace, raising the temperature of the furnace to 200 ℃ and 450 ℃ and carrying out pre-oxidation treatment;
in the step S2, the furnace temperature may be 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃ or any value selected from the above-mentioned limited ranges according to actual requirements falls within the protection scope of the present invention; in addition, the reason why the fitting is subjected to the pre-oxidation treatment in the embodiment of the present invention is that: the surface of the accessory obtains a compact oxidation film, the film is reduced at the initial stage of nitriding, the clean new surface presents high chemical activity, the adsorption rate and the adsorption quantity of the penetrating agent are increased, the function of a catalyst is played, the molecular bond breaking of the penetrating agent is promoted, and the penetration of active nitrogen atoms is accelerated.
S3, after the pre-oxidation treatment is finished, the furnace is pumped to the limit vacuum by using a vacuum pump, nitrogen is repressed to the positive pressure, then hard nitriding atmosphere is introduced into the furnace for primary nitriding treatment, and then oxygen is introduced into the furnace for secondary nitriding treatment;
in the step S3, a hard nitriding atmosphere and oxygen are introduced simultaneously during the secondary nitriding treatment, and a proper amount of oxygen is added during the secondary nitriding treatment, so that hydrogen is firstly combined with oxygen, the partial pressure of hydrogen in the atmosphere can be reduced, the nitrogen potential of the atmosphere can be increased, and the purpose of increasing the nitriding speed can be achieved; meanwhile, proper oxygen is added in the treatment process to play a role in accelerating dehydrogenation of the surface layer, so that the hydrogen content of the surface layer of the product can be obviously reduced, and the diffusion speed of nitrogen atoms in the accessory is further accelerated due to the increase of the nitrogen potential of the atmosphere and the reduction of the surface hydrogen content.
S4, nitriding the medium carbon alloy steel fitting subjected to the secondary nitriding treatment in a furnace for heat preservation;
in the above step S4, the reason why the nitriding insulation time is not specifically limited in the embodiments of the present invention is that: the duration of the nitriding heat preservation is closely related to the thickness of the infiltration layer, and in the practical application, the duration of the nitriding heat preservation needs to be adjusted according to the actual thickness requirement of the infiltration layer, for example, when the infiltration layer is required to be 0.2-0.3mm, the heat preservation duration is 8-12h, when the infiltration layer is required to be 0.3-0.4mm, the heat preservation duration is 12-16h, when the infiltration layer is required to be 0.4-0.5mm, the heat preservation duration is 20-24 h.
S5, after the nitriding heat preservation is finished, cooling treatment is started, protective atmosphere is introduced into the furnace while the introduction of the hard nitriding atmosphere and the oxygen is stopped, the cooling treatment is started, the introduction of the oxygen is stopped, the introduction amount of the hard nitriding atmosphere is reduced, and the flow rate of the hard nitriding atmosphere is reduced to 6-12m3And h, when the temperature is reduced to 350 +/-50 ℃, closing the hard nitriding atmosphere, opening the protective atmosphere to continue to reduce the temperature, and discharging the steel when the temperature is reduced to below 100 ℃.
In a preferred embodiment, the pre-oxidation treatment is pre-oxidation treatment for 50-100min for the dried medium carbon alloy steel fittings at the furnace temperature of 200-450 ℃, and air is introduced into the furnace in the whole process.
In the above preferred embodiment, the time of the pre-oxidation treatment can be selected from 50, 60, 70, 80, 90min or any value within the above-mentioned limit range according to actual requirements, and the time falls within the protection scope of the present invention.
In a preferred embodiment, the hard nitriding atmosphere is introduced all the way during the primary nitriding treatment and the secondary nitriding treatment.
In a preferred embodiment, the hard nitriding atmosphere introduced in the primary nitriding treatment and the secondary nitriding treatment is ammonia gas, and the flow rates of the ammonia gas are respectively 5-15m3/h、15-30m3/h。
In the preferred embodiment, the flow rate of ammonia gas in the course of one nitriding treatment can be selected from 5m3/h、6m3/h、7m3/h、8m3/h、9m3/h、10m3/h、11m3/h、12m3/h、13m3/h、14m3/h、15m3The protection range of the invention is within the protection range of the invention; the flow rate of ammonia gas in the secondary nitridation treatment process can be selected from 15m3/h、16m3/h、17m3/h、18m3/h、19m3/h、20、21m3/h、22m3/h、23m3/h、24m3/h、25m3/h、26m3/h、27m3/h、28m3/h、29m3/h、30m3The protection scope of the invention is within the scope of the present invention, and any value within the above-defined range may be selected according to actual requirements.
In a preferred embodiment, the condition of the first nitridation treatment is treatment at a temperature of 450-550 ℃ for 100-120min, and the condition of the second nitridation treatment is treatment at a temperature of 500-550 ℃ for 850-960 min.
In the above preferred embodiment, the temperature of the primary nitridation may be selected to be 450 ℃, 460 ℃, 470 ℃, 480, 490 ℃, 500 ℃, 510 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃ or any value selected from the above-mentioned limited range according to actual requirements, and fall within the protection range of the present invention, the temperature of the secondary nitridation may be selected to be 500 ℃, 510 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃ or any value selected from the above-mentioned limited range according to actual requirements, and fall within the protection range of the present invention, and the processing time may be selected to be 850min, 860min, 870min, 880min, 890min, 900min, 910min, 920min, 940min, 950min, 960min or any value selected from the above-mentioned limited range according to actual requirements, and fall within the protection range of the present invention 930.
In a preferred embodiment, the decomposition rates of the first nitridation treatment and the second nitridation treatment are 20-50%, and specifically, 20%, 30%, 40%, 50% or any value within the above-mentioned limit range according to actual requirements is within the protection scope of the present invention.
In the above preferred embodiment, the reason why the decomposition rates of the primary nitriding treatment and the secondary nitriding treatment are controlled to 20 to 50% is that: the primary nitridation is to establish a nitrogen potential and prepare for secondary nitridation; the purpose of secondary nitridation is to precisely control the nitrogen potential so as to ensure that each index of the product is qualified.
In a preferred embodiment, during the secondary nitridation treatment, the ratio of oxygen is controlled to be 1% -5%, and the rest is a hard nitridation atmosphere, wherein the ratio of oxygen may be specifically selected to be 1%, 2%, 3%, 4%, 5%, or any value within the above-mentioned limited range according to actual requirements, and falls within the protection scope of the present invention.
In the preferred embodiment, during the hard nitriding treatment, a proper amount of oxygen is introduced into the furnace, and the affinity of hydrogen and oxygen is far greater than that of nitrogen and oxygen, so that hydrogen can be firstly combined with oxygen, the partial pressure of hydrogen in the atmosphere can be reduced, the nitrogen potential of the atmosphere can be improved, and the aim of improving the nitriding speed can be further achieved.
In a preferred embodiment, the protective atmosphere is nitrogen.
In order to more clearly and specifically describe the heat treatment method of the medium carbon alloy steel fitting provided by the embodiment of the invention, the following description is given with reference to the specific embodiment.
Comparative example 1
The comparative example selects a gear ring made of 42CrMo as a processing object, a well type gas nitrogen furnace with 230kW power is used as processing equipment, and provides a heat treatment method of the 42CrMo gear ring, which comprises the following steps:
(1) ultrasonic cleaning and drying: cleaning impurities such as rust preventive oil on the surface of the 42CrMo gear ring and dust in the gap by adopting ultrasonic waves, blowing out cleaning liquid remained on the surface of the 42CrMo gear ring and in the threaded hole by using compressed air, and drying;
(2) pre-oxidation treatment: after the blow-dried gear ring enters a well type gas nitrogen furnace, the furnace temperature is raised to 200 ℃, pre-oxidation treatment is carried out for 100min, air is introduced into the furnace in the whole process, air is not introduced into the furnace in the process, and the specific operation is as follows: heating to the pre-oxidation temperature, preserving heat, and fully opening an exhaust valve in the heat preservation stage;
(3) nitriding treatment: after the pre-oxidation treatment is finished, ammonia gas is introduced into the furnace, the flow rate of the ammonia gas is 5m3/h, the decomposition rate is controlled to be 20%, the nitriding treatment is carried out for one time at the temperature of 450 ℃, the treatment time is 100min, and after the nitriding treatment is finished, the flow rate of the ammonia gas is adjusted to be 15m3Controlling the decomposition rate at 20%, and performing secondary nitriding treatment at 500 ℃ for 850 min;
(4) nitriding and preserving heat: nitriding the gear ring subjected to the hard nitriding treatment in a furnace for heat preservation;
(5) cooling treatment: after the nitridation heat preservation is finished, starting cooling treatment, reducing the furnace temperature to 350 ℃, and introducing nitrogen into the furnace while stopping introducing ammonia and oxygen;
(6) discharging: and discharging the cooled gear ring out of the furnace to finish the heat treatment process of the gear ring.
Example 1
In the embodiment, a gear ring made of 42CrMo is selected as a processing object, a well type gas nitrogen furnace with 230kW power is selected as processing equipment, and a heat treatment method for the 42CrMo gear ring is provided, which specifically comprises the following steps:
(1) ultrasonic cleaning and drying: cleaning impurities such as rust preventive oil on the surface of the 42CrMo gear ring and dust in the gap by adopting ultrasonic waves, blowing out cleaning liquid remained on the surface of the 42CrMo gear ring and in the threaded hole by using compressed air, and drying;
(2) pre-oxidation treatment: after the dried gear ring enters a well type gas nitrogen furnace, the furnace temperature is raised to 200 ℃, pre-oxidation treatment is carried out for 100min, and air is introduced into the furnace in the whole process;
(3) nitriding treatment: after the pre-oxidation treatment is finished, ammonia gas is introduced into the furnace, and the flow velocity of the ammonia gas is 5m3H, controlling the decomposition rate to be 20%, performing primary nitridation treatment at the temperature of 450 ℃ for 100min, then introducing oxygen into the furnace at the oxygen introduction ratio of 1%, continuously introducing ammonia gas and controlling the flow rate to be 15m3Controlling the decomposition rate at 20%, and performing secondary nitriding treatment at 500 ℃ for 850 min;
(4) nitriding and preserving heat: nitriding the gear ring subjected to the hard nitriding treatment in a furnace for heat preservation;
(5) cooling treatment: after the nitridation heat preservation is finished, starting cooling treatment, reducing the furnace temperature to 350 ℃, and introducing nitrogen into the furnace while stopping introducing ammonia and oxygen;
(6) discharging: and discharging the cooled gear ring out of the furnace to finish the heat treatment process of the gear ring.
Example 2
In the embodiment, a gear ring made of 42CrMo is selected as a processing object, a well type gas nitrogen furnace with 230kW power is selected as processing equipment, and a heat treatment method for the 42CrMo gear ring is provided, which specifically comprises the following steps:
(1) ultrasonic cleaning and drying: cleaning impurities such as rust preventive oil on the surface of the 42CrMo gear ring and dust in the gap by adopting ultrasonic waves, blowing out cleaning liquid remained on the surface of the 42CrMo gear ring and in the threaded hole by using compressed air, and drying;
(2) pre-oxidation treatment: after the dried gear ring enters a well type gas nitrogen furnace, the furnace temperature is raised to 450 ℃, pre-oxidation treatment is carried out for 50min, and air is introduced into the furnace in the whole process;
(3) nitriding treatment: after the pre-oxidation treatment is finished, ammonia gas is introduced into the furnace, wherein the flow rate of the ammonia gas is 15m3H, controlling the decomposition rate to be 50%, performing primary nitridation treatment at the temperature of 550 ℃ for 120min, then introducing oxygen into the furnace at the oxygen introduction ratio of 5%, continuously introducing ammonia gas and controlling the flow rate to be 30m3The decomposition rate is controlled to be 50%, secondary nitriding treatment is carried out at the temperature of 550 ℃, and the treatment time is 960 min;
(4) nitriding and preserving heat: nitriding the gear ring subjected to the hard nitriding treatment in a furnace for heat preservation;
(5) cooling treatment: after the nitridation heat preservation is finished, starting cooling treatment, reducing the furnace temperature to 400 ℃, and introducing nitrogen into the furnace while stopping introducing ammonia and oxygen;
(6) discharging: and discharging the cooled gear ring out of the furnace to finish the heat treatment process of the gear ring.
Example 3
In the embodiment, a gear ring made of 42CrMo is selected as a processing object, a well type gas nitrogen furnace with 230kW power is selected as processing equipment, and a heat treatment method for the 42CrMo gear ring is provided, which specifically comprises the following steps:
(1) ultrasonic cleaning and drying: cleaning impurities such as rust preventive oil on the surface of the 42CrMo gear ring and dust in the gap by adopting ultrasonic waves, blowing out cleaning liquid remained on the surface of the 42CrMo gear ring and in the threaded hole by using compressed air, and drying;
(2) pre-oxidation treatment: after the dried gear ring enters a well type gas nitrogen furnace, raising the temperature of the furnace to 300 ℃, carrying out pre-oxidation treatment for 80min, and introducing air into the furnace in the whole process;
(3) nitriding treatment: after the pre-oxidation treatment is finished, introducing ammonia gas into the furnace at the flow velocity of 10m3H, controlling the decomposition rate to be 40%, performing primary nitridation treatment at the temperature of 500 ℃ for 110min, then introducing oxygen into the furnace at the oxygen introduction ratio of 3%, continuously introducing ammonia gas and controlling the flow rate to be 25m3The decomposition rate is controlled to be 40 percent, secondary nitridation treatment is carried out at the temperature of 520 ℃, and the treatment time is 900 min;
(4) nitriding and preserving heat: nitriding the gear ring subjected to the hard nitriding treatment in a furnace for heat preservation;
(5) cooling treatment: after the nitridation heat preservation is finished, starting cooling treatment, reducing the furnace temperature to 380 ℃, and introducing nitrogen into the furnace while stopping introducing ammonia and oxygen;
(6) discharging: and discharging the cooled gear ring out of the furnace to finish the heat treatment process of the gear ring.
And (3) performance testing:
the invention respectively tests the performances of surface hardness, infiltrated layer thickness, compound layer thickness, brittleness and the like of the gear rings obtained after the treatment of the above examples and comparative examples, and the test methods and results are as follows:
(1) the test method comprises the following steps:
the surface hardness detection method refers to GB 4340.1 part 1 of Vickers hardness test of metal materials: test methods, and reference GB/T11354 method for detecting the thickness of a permeated layer, the thickness of a compound, brittleness, porosity and the level of pulse-shaped nitride to the depth determination of a nitrided layer of a steel part and metallographic structure inspection.
(2) And (3) testing results:
TABLE 1 statistics of performance test results of gear rings obtained in various proportions and examples
Surface hardness Thickness of infiltrated layer Thickness of compound layer Brittleness Porosity of the pipe Pulse nitride grade
Example 1 687.6HV0.3 0.368mm 12μm Level 1 Level 1 Level 1
Example 2 680.6HV0.3 0.362mm 13μm Level 1 Level 1 Level 1
Example 3 685.1HV0.3 0.370mm 15μm Level 1 Level 1 Level 1
Comparative example 1 609.6HV0.3 0.328mm 8μm Stage 2 Grade 3 Grade 3
On the basis of the above experimental results, it can be seen from fig. 1-2 that the surface hardness, the coating thickness, the thickness of the compound layer and other properties of the parts treated by the method provided in comparative example 1 cannot reach ideal states, and as can be seen from fig. 2, the surface of the parts treated by the method provided in comparative example 1 still has the problems of poor appearance, blackening and the like, while the parts treated by the treatment method provided in embodiments 1-3 of the present invention have various properties and no blackening phenomenon on the surface of the parts, so that the heat treatment method provided in the present invention can thoroughly solve the technical problems of poor product nitriding appearance, blackening and the like in the existing gas nitriding process.

Claims (8)

1. A heat treatment method of a medium carbon alloy steel fitting is characterized by comprising the following steps:
ultrasonically cleaning oil stains on the surface of the medium carbon alloy steel fitting and in the gap, and drying cleaning liquid on the surface of the medium carbon alloy steel fitting and in the gap;
after the dried medium carbon alloy steel fittings enter a well type gas nitrogen furnace, raising the temperature of the furnace to 200-450 ℃ for pre-oxidation treatment;
after the pre-oxidation treatment is finished, a vacuum pump is used for pumping the interior of the furnace to the limit vacuum, nitrogen is repressed to positive pressure, then hard nitriding atmosphere is introduced into the furnace for primary nitriding treatment, and then oxygen is introduced into the furnace for secondary nitriding treatment;
nitriding the medium carbon alloy steel fittings subjected to the secondary nitriding treatment in a furnace for heat preservation;
after the nitriding heat preservation is finished, starting cooling treatment, stopping introducing the hard nitriding atmosphere and oxygen, introducing protective atmosphere into the furnace, starting cooling treatment, stopping introducing oxygen, reducing the introduction amount of the hard nitriding atmosphere, and reducing the flow to 6-12m3And h, when the temperature is reduced to 350 +/-50 ℃, closing the hard nitriding atmosphere, opening the protective atmosphere to continue to reduce the temperature, and discharging the steel when the temperature is reduced to below 100 ℃.
2. The heat treatment method for the medium carbon alloy steel fitting as claimed in claim 1, wherein the pre-oxidation treatment is pre-oxidation treatment for 50-100min at the furnace temperature of 200-450 ℃, and air is introduced into the furnace in the whole process.
3. The method for heat treating a medium carbon alloy steel fitting according to claim 1, wherein a hard nitriding atmosphere is introduced during the primary and secondary nitriding treatments all the way.
4. The method for heat treating a medium carbon alloy steel fitting according to claim 3, wherein the hard nitriding atmosphere is ammonia gas at a flow rate of 5 to 15m in each of the primary nitriding treatment and the secondary nitriding treatment3/h、15-30m3/h。
5. The method for heat treatment of a medium carbon alloy steel fitting as claimed in claim 1, wherein the conditions of the primary nitriding treatment are treatment at a temperature of 450-.
6. The method of heat treating a medium carbon alloy steel part according to claim 1, wherein the decomposition rate of each of the primary nitriding treatment and the secondary nitriding treatment is 20 to 50%.
7. The method for heat treating a medium carbon alloy steel fitting according to claim 1, wherein during the secondary nitriding treatment, the proportion of oxygen is controlled to be 1% to 5%, and the balance is a hard nitriding atmosphere.
8. The method of heat treating a medium carbon alloy steel fitting of claim 1, wherein the protective atmosphere is nitrogen.
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