CN114908242B - Film-shaped retained austenite control method suitable for heavy-load carburized gear - Google Patents
Film-shaped retained austenite control method suitable for heavy-load carburized gear Download PDFInfo
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- CN114908242B CN114908242B CN202210391496.4A CN202210391496A CN114908242B CN 114908242 B CN114908242 B CN 114908242B CN 202210391496 A CN202210391496 A CN 202210391496A CN 114908242 B CN114908242 B CN 114908242B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/32—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for gear wheels, worm wheels, or the like
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/04—Hardening by cooling below 0 degrees Celsius
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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
- C23C8/20—Carburising
- C23C8/22—Carburising of ferrous surfaces
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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
- C23C8/80—After-treatment
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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
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F17/00—Multi-step processes for surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by subclass C21D or C22F or class C25
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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Abstract
A film-shaped retained austenite control method suitable for a heavy-duty carburized gear belongs to the technical field of heat treatment tissue control of heavy-duty carburized gears. By combining chemical components of the heavy-duty gear and the transformation rules of austenite with different carbon contents after carburization, the organization structure of the heavy-duty carburized gear is controlled by optimizing a heat treatment process, and a complex phase structure of which the carburized layer of the gear is mainly martensite and contains 1-10% of film-shaped residual austenite is obtained; the intermediate transition zone is a mixed structure of twin martensite and lath martensite; the core is a gradient structure of low-carbon lath martensite or lower bainite. By controlling the content and the form of the residual austenite, the high wear resistance, the high bearing capacity and the high fatigue performance of the heavy-duty gear part are realized, and the quality consistency, the size and the precision stability of the heavy-duty gear part are obviously improved.
Description
Technical Field
The invention belongs to the technical field of heat treatment tissue control of heavy-duty carburized gears, and particularly relates to a film-shaped residual austenite content control method of a heavy-duty carburized gear.
Background
The heavy-duty carburized gear is a key for determining the bearing capacity and the service life of a transmission device, is widely applied to various transmission devices, such as heavy-duty special vehicle transmission devices, aeroengine transmission devices, ship power system transmission devices, engineering machinery transmission devices, wind power gear boxes, high-speed trains and the like, and is a core component for ensuring the safety and the reliability of the transmission devices. The heavy-duty carburized gear is served in the environments of wide load range, wide temperature range, strong impact and complex vibration, and the components are required to have the comprehensive properties of high surface hardness, high wear resistance and high toughness of the core.
The composition of the steel material is the basis for determining the structural performance of the steel material, and the heat treatment process is the key for obtaining reasonable structural performance, and the reasonable structural performance is an important factor for influencing the performance of the heavy-duty carburized gear. The heavy duty carburized gears in various countries in the world are selected from a large number of gear steels mainly comprising Cr-Ni-Mo, mainly comprising Cr-Mo in the United states and mainly comprising Mn-Cr in the Germany, and the heavy duty carburized gears in China are selected from a large number of gear steels, cr-Ni-Mo, cr-Mo, mn-Cr-Ti and the like. At present, the heavy-duty carburized gear in China is generally manufactured by adopting materials such as 20Cr2Ni4A, 20CrNiMoA, 17Cr2Ni2MoVNb, 18Cr2Ni4WA and the like, and the manufacturing process route is as follows: blanking, forging, normalizing and tempering, rough machining, quenching and tempering, rough machining, carburizing, high-temperature tempering, quenching, low-temperature tempering, sand blasting/shot blasting, finish machining and finished product warehousing, wherein the carburizing, quenching and tempering processes are key to influencing the comprehensive performance of the heavy-duty carburized gear.
Carburization is a common surface strengthening means for heavy-duty gears, and after rough machining, the gear part is carburized, so that the carbon content of the surface is increased to 0.80% -1.20%, and the carbon content distribution gradient which is gradually reduced from the surface to the core part is obtained; then quenching treatment is carried out to ensure that the surface carburized layer of the gear part obtains a mixed structure of high-hardness twin martensite and residual austenite; the transition zone obtains twin martensite and lath martensite; the core obtains a lath martensite and lower bainite mixed structure, thereby achieving the goals of high wear resistance, high bearing capacity, high fatigue performance, high precision and high quality consistency of the gear component. After the treatment, the stability of austenite is obviously improved due to the higher surface carbon content of the surface of the heavy-duty gear, and the austenite which is converted first has an inhibition effect on the non-converted austenite, so that after the gear part is cooled to room temperature, more residual austenite exists in the surface carburized layer, and the residual austenite is mainly blocky, as shown in fig. 1.
The blocky residual austenite is of a face-centered cubic structure and has the characteristics of low hardness, low strength, instability and the like, so that the existence of the blocky residual austenite can reduce the hardness, the strength and the wear resistance of a material, and can influence the strength, the plasticity, the toughness, the fatigue and other mechanical properties of parts, and the blocky residual austenite can be converted into martensite and film-shaped residual austenite along with the extension of time in the use process of the parts, and the macroscopic volume change of a heavy-duty gear can be caused in the conversion process, so that the precision of a workpiece is reduced and the size of the workpiece is unstable.
Taking a heavy-duty gear manufactured by using 20Cr2Ni4A and 17Cr2Ni2MoVNb steel as an example, carrying out X-ray diffraction measurement by using a Co-K alpha target, calculating the volume fraction of the retained austenite in a carburized layer after carburization and the morphology thereof, and calculating the volume fraction of the retained austenite by using a formula (1) and combining diffraction peaks of (110) alpha (200) alpha (211) alpha and (111) gamma (200) gamma (220) gamma (311) gamma, wherein V gamma is the volume fraction of the retained austenite.
Vγ=1.4iγ/(iα+1.4iγ) formula (1)
According to the results shown in fig. 2 and 3, the residual austenite content of the surface carburized layer of the heavy-duty carburized gear is 15% -30%, the existence of a large amount of block-shaped residual austenite not only can lower the surface hardness and influence the wear resistance of the heavy-duty gear, but also can influence the dimensional accuracy and the quality stability of the heavy-duty gear along with the occurrence of strain-induced martensitic transformation in the service process of the heavy-duty gear, and the heavy-duty gear can be seriously broken and failed early. Therefore, the method eliminates the blocky residual austenite of the surface carburized layer after carburization of the heavy-duty gear, reasonably controls the form and the content of the residual austenite, and is the key for obtaining the heavy-duty gear parts with high bearing capacity, high fatigue life and high quality consistency.
Currently, most of the views suggest that the retained austenite in the microstructure of the high carbon content material cannot be completely eliminated. The applicant believes that the retained austenite cannot be completely eliminated, but the content and the morphology of the retained austenite are controllable, so that a large amount of blocky retained austenite is further converted into martensite+film-shaped retained austenite, a smaller and more uniformly distributed lath martensite structure can be obtained, precipitation of nano-scale ultrafine dispersed carbides can be promoted, the remaining film-shaped retained austenite is in an equiaxial compressive stress state, and when the retained austenite exists in the middle of the lath martensite, the structure is stable, plastic deformation is not easy to occur, and the retained austenite exists in a ductile phase in the service process, so that the effects of relieving stress and preventing fatigue crack growth are achieved. Meanwhile, the existence of martensite formed secondarily and nano-scale carbide distributed in a dispersing way can generate residual compressive stress on the surface when the heavy-duty gear is restored to a room temperature state, and the residual compressive stress can reduce the damage of defects to the local strength of the material, and finally, the bearing capacity and the wear resistance are improved.
Disclosure of Invention
The invention aims to provide a residual austenite control method suitable for a heavy-duty carburized gear, which combines chemical components of the heavy-duty gear and transformation rules of austenite with different carbon contents after carburization, controls the structure of the heavy-duty carburized gear by optimizing a heat treatment process, changes the form of the residual austenite and reduces the content of the residual austenite, and obtains a complex phase structure of which a carburized layer of the gear is mainly martensite and contains 1-10% of film-shaped residual austenite; the intermediate transition zone is a mixed structure of twin martensite and lath martensite; the core is a gradient structure of low-carbon lath martensite or lower bainite. Not only can the surface hardness be increased to improve the wear resistance, but also the bearing capacity, the fatigue life, the precision stability and the quality consistency of the parts can be improved. By controlling the content and the form of the residual austenite, the high wear resistance, the high bearing capacity and the high fatigue performance of the heavy-duty gear part are realized, and the quality consistency, the size and the precision stability of the heavy-duty gear part are obviously improved.
The technical proposal of the invention
The invention completes the control of the residual austenite of the heavy-duty carburized gear by the following method: taking a hot rolled steel bar (optionally 20Cr2Ni4A, 17Cr2Ni2MoVNb, 20CrNiMoA, 18Cr2Ni4WA and other heavy-duty carburized gear steel), carrying out rough machining to obtain a gear blank, and carrying out heat treatment according to the following sequence:
step 1) carburizing: the gas carburizing process or the low-pressure pulse carburizing process can be selected.
And (3) a gas carburizing process: performing carburizing treatment on the gear blank by adopting a Yi Pusen controlled atmosphere multipurpose furnace, and introducing 200L (160+/-5 kg) propane and 20L BH-5 direct-growth type catalyst mixed carburizing medium into a carburizing furnace for carburizing according to the flow of 0.5-1.0L/h; strong osmosis period: carburizing temperature 930℃ + -10 ℃, carbon potential 1.00-1.10%wt, time 170min + -5 min; diffusion period: the carburization temperature is 890+/-10 ℃, the carbon potential is 0.85-0.90%wt, the time is 120 min+/-5 min, the furnace is cooled to 400+/-5 ℃ after carburization is completed, and the furnace is taken out for air cooling.
Low-pressure pulse carburizing process: and (3) performing carburization treatment on the gear blank by adopting an ALD low-pressure high-temperature carburizing furnace, introducing acetylene into the carburizing furnace for carburization according to the flow of 128-130L/h, wherein the carburization temperature is 950 ℃ plus or minus 10 ℃, introducing acetylene medium for nine times in the strong infiltration period, wherein the first medium introduction time is 160s plus or minus 2s, the rest introduction time is 45s plus or minus 2s, the strong infiltration time is 90min plus or minus 3min, the diffusion time is 50min plus or minus 3min, and cooling to 400 ℃ plus or minus 5 ℃ along with the furnace after carburization is completed, and discharging and air cooling.
Step 2) finish machining:
tempering the carburized heavy-duty gear blank at 680+/-10 ℃, air-cooling, and then carrying out finish machining according to the size requirement of the part.
Step 3) quenching:
and carrying out sectional quenching treatment on the gear after finish machining. The quenching temperature is 880+/-10 ℃ and is kept for 30-35 min, after the heat preservation is finished, the quenching temperature is cooled to 450+/-5 ℃ at a cooling speed of more than or equal to 20 ℃/s, the quenching medium is nitrogen or quenching oil at a cooling speed of more than or equal to 10 ℃/s below 450+/-5 ℃ and is cooled to room temperature.
Step 4) low-temperature tempering:
after the gear quenching is finished, tempering treatment is finished within 24 hours by using a well tempering furnace or a box tempering furnace, wherein the tempering temperature is 200+/-5 ℃, and the tempering time is 240+/-10 minutes.
Step 5) cryogenic treatment:
after the gear tempering is finished, the gear is subjected to cryogenic treatment by utilizing liquid nitrogen, the cryogenic temperature is minus 150+/-10 ℃, the time is 120 minutes+/-5 minutes, and the gear is subjected to low-temperature tempering at 150+/-10 ℃ and the time is 120 minutes+/-5 minutes after the cryogenic treatment.
The cryogenic medium selected by the cryogenic treatment is liquid nitrogen, and the purpose is to convert 15% -30% of block residual austenite into 1% -10% of film-shaped residual austenite and secondary martensite, so that a carburized layer of the heavy-duty carburized gear is made to obtain a complex phase structure which is mainly made of martensite and contains 1% -10% of film-shaped residual austenite; the intermediate transition zone has a mixed structure of twin martensite and lath martensite; the core is a gradient structure of low-carbon lath martensite or lower bainite.
Advancement of the invention
According to the invention, the microstructure of the surface carburized layer of the heavy-duty carburized gear is controlled by optimizing the heat treatment process, 15% -30% of residual austenite is further converted into 1% -10% of film-shaped residual austenite and secondarily refined martensite, so that the carburized layer obtains a complex phase structure which mainly comprises martensite and contains 1% -10% of film-shaped residual austenite; the intermediate transition zone has a mixed structure of twin martensite and lath martensite; the core is organized in a gradient of low carbon lath martensite or lower bainite. The film-shaped residual austenite exists between martensite laths, can exist in a ductile phase in the service process of the heavy-duty gear, and plays a role in relaxing stress and preventing fatigue crack growth. Meanwhile, the invention increases the cryogenic treatment process and adopts liquid nitrogen as a cooling medium. The liquid nitrogen is a byproduct of industrial oxygen production, has wide source, easy storage, high chemical stability, no damage to parts, no toxicity or corrosion, no pollution to gear parts, economy and convenience, and is a green technology.
Drawings
FIG. 1 is a diagram showing a structure of twinned martensite and film-like retained austenite.
FIG. 2 is a diagram showing a structure of twinned martensite and bulk retained austenite.
FIG. 3 is a graph of the residual austenite content of a heavy-duty gear made of 20Cr2Ni4A steel.
FIG. 4 is a graph of the residual austenite content of a heavy duty gear made of 17Cr2Ni2MoVNb steel.
Detailed Description
The invention is further described in connection with the following detailed description. It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Example 1
The method comprises the steps of blanking a heavy-duty carburized gear by adopting a hot rolled 20Cr2Ni4A steel bar (the chemical components are C0.19-0.21%, si 0.17-0.37%, mn 0.30-0.60%, cr 1.25-1.65%, ni 3.25-3.65%, P less than or equal to 0.010% and S less than or equal to 0.005%), forging, normalizing and tempering, roughing, tempering and roughing, and carrying out the following heat treatment after roughing into a heavy-duty gear blank:
1) Carrying out gas atmosphere carburization on heavy-duty gear blanks by using a Yi Pusen controlled atmosphere multipurpose furnace, and introducing a mixed carburization medium of 200L propane and 20L BH-5 catalyst into a carburization furnace for carburization according to the flow of 0.8L/h, wherein the specific carburization process parameters are as follows: strong infiltration period, carburizing temperature 930 ℃, carbon potential 1.10%wt, time 170min; and in the diffusion period, the carburization temperature is 890 ℃, the carbon potential is 0.85%wt, the time is 120min, and the furnace is cooled to 400 ℃ after carburization is completed, and the furnace is taken out for air cooling.
2) Tempering the heavy-duty gear blank subjected to carburization in the step at a high temperature of 680 ℃, air-cooling, and then carrying out finish machining according to the size requirement of the part.
3) Quenching: heating the finished heavy-duty gear to 880 ℃ in a Yi Pusen controlled atmosphere multipurpose furnace, preserving heat for 30min, introducing 20# special quenching oil after the heat preservation is finished, cooling to 450 ℃ at a cooling rate of 45 ℃/s, and cooling to room temperature at a cooling rate of 25 ℃/s below 450 ℃.
4) And (3) carrying out a low-temperature tempering process on the heavy-duty gear after quenching is finished: tempering temperature is 200 ℃, tempering and heat preservation is carried out for 240min.
5) After tempering the heavy-duty gear, carrying out cryogenic treatment by utilizing liquid nitrogen, wherein the cryogenic temperature is-150 ℃ for 120min, and carrying out low-temperature tempering treatment at 150 ℃ for 120min after the cryogenic treatment.
The depth of a carburized layer of the heavy-duty gear obtained by the process is 1.09mm, the hardness of a working surface is 60HRC, and the surface carburized layer is a complex phase structure mainly comprising martensite and containing 7% of film-shaped residual austenite; the intermediate transition zone is a mixed structure of twin martensite and lath martensite; the core is a gradient structure mainly comprising low-carbon lath martensite, so that the fatigue strength, service life, precision stability and quality consistency of the heavy-duty gear are remarkably improved.
Example 2
The hot rolling is adopted to carry out blanking of the heavy-duty carburized gear by adopting a hot rolled 17Cr2Ni2MoVNb steel bar (the chemical components are C:0.16-0.20%, si: less than or equal to 0.37%, mn:0.50-0.90%, cr 1.50-1.80%, ni 1.50-1.70%, mo 0.25-0.35%, nb 0.02-0.06%, V0.01-0.10%, P: less than or equal to 0.010% and S: less than or equal to 0.005%), forging, normalizing and tempering, rough machining, and carrying out the following heat treatment after rough machining into a heavy-duty gear blank:
1) Carburizing the heavy-load carburized gear by using a German ALD vacuum carburizing furnace, wherein a carburizing medium is acetylene, and specific carburization process parameters are as follows: the carburization temperature is 950 ℃, the acetylene flow is 129L/h, the strong infiltration period is divided into 9 times of acetylene medium, wherein the first medium is introduced for 160s, the other 8 times of medium is introduced for 45s, the strong infiltration time is 90min, the diffusion time is 50min, and the furnace is cooled to 400 ℃ along with the furnace after carburization is completed, and the furnace is discharged for air cooling.
2) Tempering the heavy-duty gear blank subjected to carburization in the step at a high temperature of 680 ℃, air-cooling, and then carrying out finish machining according to the size requirement of the part.
3) Quenching: heating the finished heavy-duty gear to 880 ℃ in a German ALD vacuum furnace, preserving heat for 30min, introducing nitrogen for cooling after the heat preservation is finished, cooling to 450 ℃ at a cooling rate of 40 ℃/s, and cooling to room temperature at a cooling rate of 20 ℃/s below 450 ℃.
4) And (3) carrying out a low-temperature tempering process on the heavy-duty gear after quenching is finished: tempering temperature is 200 ℃, tempering and heat preservation is carried out for 240min.
5) After tempering the heavy-duty gear, carrying out cryogenic treatment by utilizing liquid nitrogen, wherein the cryogenic temperature is-150 ℃ for 120min, and carrying out low-temperature tempering treatment at 150 ℃ for 120min after the cryogenic treatment.
The depth of a carburized layer of the heavy-duty gear obtained by the process is 1.12mm, the hardness of a working surface is 61HRC, and the surface carburized layer is a complex phase structure mainly comprising martensite and containing 8% of film-shaped residual austenite; the intermediate transition zone is a mixed structure of twin martensite and lath martensite; the core is a gradient structure mainly comprising low-carbon lath martensite, so that the fatigue strength, service life, precision stability and quality consistency of the heavy-duty gear are remarkably improved.
Example 3
The method comprises the steps of blanking a heavy-duty carburized gear by adopting a hot rolled 18Cr2Ni4WA steel bar (the chemical components are C0.13-0.19%, si 0.17-0.37%, mn 0.30-0.60%, cr 1.35-1.65%, ni 4.00-4.50%, W0.80-1.20%, P less than or equal to 0.015% and S less than or equal to 0.005%), forging, normalizing and tempering, roughing, and performing the following heat treatment after roughing into a heavy-duty gear blank:
1) Carrying out gas atmosphere carburization on heavy-duty gear blanks by using a Yi Pusen controlled atmosphere multipurpose furnace, and introducing a mixed carburization medium of 200L propane and 20L BH-5 catalyst into a carburization furnace for carburization according to the flow of 0.75L/h, wherein the specific carburization process parameters are as follows: strong infiltration period, carburizing temperature 930 ℃, carbon potential 1.05%wt, time 170min; and in the diffusion period, the carburization temperature is 880 ℃, the carbon potential is 0.85%wt, the time is 120min, and the furnace is cooled to 400 ℃ after carburization is completed, and the furnace is taken out for air cooling.
2) Tempering the heavy-duty gear blank subjected to carburization in the step at a high temperature of 680 ℃, air-cooling, and then carrying out finish machining according to the size requirement of the part.
3) Quenching: heating the finished heavy-duty gear to 880 ℃ in a Yi Pusen controlled atmosphere multipurpose furnace, preserving heat for 30min, introducing 20# special quenching oil after the heat preservation is finished, cooling to 450 ℃ at a cooling rate of 40 ℃/s, and cooling to room temperature at a cooling rate of 20 ℃/s below 450 ℃.
4) And (3) carrying out a low-temperature tempering process on the heavy-duty gear after quenching is finished: tempering temperature is 200 ℃, tempering and heat preservation is carried out for 240min.
5) After tempering the heavy-duty gear, carrying out cryogenic treatment by utilizing liquid nitrogen, wherein the cryogenic temperature is-150 ℃ for 120min, and carrying out low-temperature tempering treatment at 150 ℃ for 120min after the cryogenic treatment.
The depth of a carburized layer of the heavy-duty gear obtained by the process is 1.05mm, the hardness of a working surface is 61HRC, and the surface carburized layer is a complex phase structure mainly comprising martensite and containing 6% of film-shaped residual austenite; the intermediate transition zone is a mixed structure of twin martensite and lath martensite; the core is a gradient structure mainly comprising low-carbon lath martensite, so that the fatigue strength, service life, precision stability and quality consistency of the heavy-duty gear are remarkably improved.
Claims (3)
1. A control method of the film-shaped residual austenite content of a heavy-duty carburized gear is characterized in that a hot rolled steel bar is taken, and is subjected to heat treatment after being roughly processed into a gear blank; the technical parameters of the steps and control are as follows:
step 1) carburizing: the method comprises the following steps: gas carburizing process or low-pressure pulse carburizing process
And (3) a gas carburizing process: performing carburizing treatment on the gear blank by adopting a Yi Pusen controlled atmosphere multipurpose furnace, and introducing a mixed carburizing medium of 200L propane+20L BH-5 direct-growth type catalyst into a carburizing furnace for carburizing according to the flow of 0.5-1.0L/h; strong osmosis period: carburizing temperature is 920-940 ℃, carbon potential is 1.00-1.10%wt, and time is 165-175 min; diffusion period: the carburization temperature is 880-900 ℃, the carbon potential is 0.85-0.90%wt, the time is 115-125 min, the carburization is cooled to 395-405 ℃ along with the furnace after the carburization is completed, and the furnace is discharged for air cooling;
low-pressure pulse carburizing process: performing carburization treatment on a gear blank by adopting an ALD low-pressure high-temperature carburizing furnace, introducing acetylene into the carburizing furnace for carburization according to the flow of 128-130L/h, wherein the carburization temperature is 940-960 ℃, introducing acetylene medium into the high-pressure carburizing period for nine times, wherein the first medium introducing time is 158-162 s, the rest introducing time is 43-47 s, the high-pressure carburizing time is 87-93 min, the diffusion time is 47-53 min, and cooling to 395-405 ℃ along with the furnace after carburization is completed, and discharging and air cooling;
step 2) finish machining:
tempering the carburized heavy-duty gear blank at 670-690 ℃, air-cooling, and then finishing according to the size requirement of the part;
step 3) quenching:
and carrying out sectional quenching treatment on the gear after finish machining. The quenching temperature is 870 ℃ to 890 ℃ for 30min to 35min, after the heat preservation is finished, the quenching temperature is cooled to 445 ℃ to 455 ℃ at a cooling rate of more than or equal to 20 ℃/s, the quenching medium is nitrogen or quenching oil at a cooling rate of more than or equal to 10 ℃/s below 445 ℃ to 455 ℃;
step 4) low-temperature tempering:
after the gear is quenched, tempering treatment is completed within 24 hours by using a well tempering furnace or a box tempering furnace, wherein the tempering temperature is 195-205 ℃, and the tempering time is 230-250 min;
step 5) cryogenic treatment:
after the gear tempering is finished, the gear is subjected to cryogenic treatment by utilizing liquid nitrogen, the cryogenic temperature is between minus 160 ℃ and minus 140 ℃, the time is between 115 and 125 minutes, and the gear is subjected to low-temperature tempering at 145 to 155 ℃ after the cryogenic treatment, and the time is between 115 and 125 minutes.
2. The method for controlling the retained austenite content in a film form of a heavy duty carburized gear according to claim 1, wherein in step 1), the hot rolled steel rod is 20Cr2Ni4A, 20CrNiMoA or 17Cr2Ni2MoVNb, 18Cr2Ni4WA gear steel.
3. The method for controlling the content of the film-shaped retained austenite of the heavy-duty carburized gear according to claim 1, wherein in the step 5), the cryogenic medium selected for the cryogenic treatment is liquid nitrogen, so that 15% -30% of the block retained austenite is converted into 1% -10% of film-shaped retained austenite and secondary martensite, and a carburized layer of the heavy-duty carburized gear is made into a complex phase structure which is mainly martensite and contains 1% -10% of film-shaped retained austenite; the intermediate transition zone has a mixed structure of twin martensite and lath martensite; the core is a gradient structure of low-carbon lath martensite or lower bainite.
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| CN103290419A (en) * | 2013-06-25 | 2013-09-11 | 清华大学 | Gear treatment method |
| CN105400944A (en) * | 2015-12-01 | 2016-03-16 | 张贺佳 | Cryogenic heat treatment technology for improving performances of countershaft gear |
| CN106222606A (en) * | 2016-08-31 | 2016-12-14 | 中车戚墅堰机车车辆工艺研究所有限公司 | A kind of process controlling the carburized workpiece non-martensite degree of depth |
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| CN110951962A (en) * | 2019-12-16 | 2020-04-03 | 武汉理工大学 | High-performance gear heat treatment method for realizing fine and homogenized structure |
| CN111304581A (en) * | 2020-03-21 | 2020-06-19 | 哈尔滨工程大学 | Circulating carburization treatment method for carburization layer on surface of heavy-duty gear |
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| CN103290419A (en) * | 2013-06-25 | 2013-09-11 | 清华大学 | Gear treatment method |
| CN105400944A (en) * | 2015-12-01 | 2016-03-16 | 张贺佳 | Cryogenic heat treatment technology for improving performances of countershaft gear |
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