CN115233147A - Heat treatment process for improving surface hardness of Cr-Ni steel - Google Patents
Heat treatment process for improving surface hardness of Cr-Ni steel Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 70
- 238000010438 heat treatment Methods 0.000 title claims abstract description 63
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 26
- 239000010959 steel Substances 0.000 title claims abstract description 26
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 54
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 54
- 238000010791 quenching Methods 0.000 claims abstract description 44
- 230000000171 quenching effect Effects 0.000 claims abstract description 44
- 238000005496 tempering Methods 0.000 claims abstract description 24
- 238000009792 diffusion process Methods 0.000 claims abstract description 18
- 238000005255 carburizing Methods 0.000 claims abstract description 17
- 238000001816 cooling Methods 0.000 claims description 19
- 238000004321 preservation Methods 0.000 claims description 12
- 150000003839 salts Chemical class 0.000 claims description 8
- 238000007599 discharging Methods 0.000 claims description 5
- 230000008595 infiltration Effects 0.000 claims description 5
- 238000001764 infiltration Methods 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 238000002791 soaking Methods 0.000 claims description 3
- 238000005507 spraying Methods 0.000 claims description 3
- 150000002823 nitrates Chemical class 0.000 claims description 2
- 229910045601 alloy Inorganic materials 0.000 abstract description 12
- 239000000956 alloy Substances 0.000 abstract description 12
- 229910001566 austenite Inorganic materials 0.000 abstract description 5
- 229910000734 martensite Inorganic materials 0.000 abstract description 5
- 238000005261 decarburization Methods 0.000 abstract description 4
- 239000011159 matrix material Substances 0.000 abstract description 2
- 238000003303 reheating Methods 0.000 abstract description 2
- 230000009466 transformation Effects 0.000 abstract description 2
- 238000009941 weaving Methods 0.000 abstract 1
- LBPGGVGNNLPHBO-UHFFFAOYSA-N [N].OC Chemical compound [N].OC LBPGGVGNNLPHBO-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 229910002651 NO3 Inorganic materials 0.000 description 6
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 6
- 238000009826 distribution Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 239000006229 carbon black Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
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- 238000005272 metallurgy Methods 0.000 description 1
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- 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
- 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
- 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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- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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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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- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/004—Dispersions; Precipitations
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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Abstract
The invention discloses a heat treatment process for improving the surface hardness of Cr-Ni steel without cold treatment. The invention realizes the slow reduction of the hardness of the effective hardened layer by adopting the carburizing process of strong carburizing, diffusion (performed in two sections) and carbon potential regulation (different in three sections); adopts the heat treatment process of carburizing, high-temperature tempering and quenching to make the metallographic phase group of the workpieceForming spherical alloy carbide as much as possible during weaving, thereby reducing the carbon content and the alloy element content of the martensite matrix during reheating quenching, and increasing the martensite transformation starting temperature M s Point and end temperature M f The content of residual austenite during quenching is reduced, and the surface hardness of the workpiece is increased; the mode of quenching in the atmosphere furnace is adopted, the occurrence of surface decarburization phenomenon in the quenching process is reduced, and the phenomenon of lower surface hardness of the workpiece is avoided.
Description
Technical Field
The invention relates to heat treatment of Cr-Ni steel, in particular to a heat treatment process for improving the surface hardness of Cr-Ni steel.
Background
According to the specification of national standard GB/3077-2015, the mass percent (%) of the alloy elements of the Cr-Ni steel material is as follows: c0.17-0.23, si 0.17-0.37, mn 0.30-0.60, cr 1.25-1.65, ni 3.25-3.65; residual elements: p is less than or equal to 0.030, S is less than or equal to 0.030, cu is less than or equal to 0.30, mo is less than or equal to 0.10, and the austenite grain size is not coarser than 5 grade.
The Cr-Ni steel belongs to medium-alloy high-Ni carburizing steel, has good hardenability, high core hardness and good toughness, is commonly used for heavy-duty gears, high-speed gears and gears bearing larger impact load, and is widely applied to the fields of chemical industry, metallurgy, mining machinery, power stations, ships, aviation, military industry and the like. However, because the alloy content of the material is high, the surface of the material after carburizing and quenching has more retained austenite, so that the hardness is low, and the requirement of 58-62HRC of the surface hardness of a workpiece is difficult to meet. In order to increase the surface hardness, cold treatment is usually used to reduce the residual austenite content on the surface of the workpiece. On one hand, the cost of manufacturing enterprises is greatly increased due to the fact that cold treatment equipment is expensive and high in operation cost, and large cold treatment equipment is relatively short, so that the cold treatment of large workpieces cannot be met; it has also been found that the cold treatment process sometimes promotes the formation of martensitic microcracks, resulting in increased brittleness of the material, so that some parts are not allowed to be cold treated during production.
Disclosure of Invention
The invention aims to provide a heat treatment process for improving the surface hardness of Cr-Ni steel without cold treatment.
In order to achieve the purpose, the invention can adopt the following technical scheme:
the heat treatment process for improving the surface hardness of the Cr-Ni steel comprises a carburizing process, a tempering process and a quenching process; the carburizing process is carried out in a well-type atmosphere furnace, and specifically comprises the following steps:
first, a temperature rise stage
Firstly, heating to 450-500 ℃, preserving heat for 1-2h, then continuously heating to 600-700 ℃, preserving heat for 1-2h, and then heating to 750-850 ℃, preserving heat for 1-2h;
second, exhaust stage
Heating to 920 to 940 ℃, preserving the temperature for 20 to 60min, adjusting the carbon potential in the furnace to 0.3 percent, opening an exhaust hole and exhausting the air in the furnace;
the third step, the strong infiltration stage
Closing the vent hole, adjusting the carbon potential in the furnace to 1.15 to 1.25 percent, and determining the heat preservation time T according to the depth of the carburized effective hardened layer 1 : when the effective hardening layer depth D is less than or equal to 1.4mm, T 1 Less than or equal to 6 hours; t when the effective hardened layer depth D is greater than 1.4mm 1 ＞6h；
The fourth step, diffusion stage
Keeping the temperature at 920 to 940 ℃:
firstly, adjusting the carbon potential in the furnace to be 0.95 to 1.05 percent, and determining the heat preservation time T 2 : when T is 1 When the time is less than or equal to 6 hours, T 2 =0h; when T is 1 When is more than 6h, T 2 =（T 1 -3) h, this stage being the first stage diffusion stage;
then adjusting the carbon potential in the furnace to be 0.85 to 0.95 percent, and determining the heat preservation time T 3 : when T is 1 When the time is less than or equal to 6 hours, T 3 =（T 1 -3) h; when T is 1 When more than 6h, T 3 =3h, this stage is the secondary diffusion stage;
step five, cooling stage
Keeping the carbon potential in the furnace at 0.85-0.95%, reducing the temperature to 810-830 ℃, preserving the heat for 1-2h, then discharging the furnace and air-cooling to the room temperature.
The tempering process of the invention is carried out in a tempering furnace: and (4) heating to 600-700 ℃, preserving the heat for 3-6 h, taking out of the furnace, and cooling to room temperature in air.
The quenching process of the invention is still carried out in a well-type atmosphere furnace: heating to 400 to 450 ℃, and keeping the temperature for 1 to 2 hours; then heating to 600-700 ℃, and preserving heat for 1-2h; heating to 800 to 830 ℃, and keeping the temperature for 2 to 4 hours, wherein the carbon potential is controlled to be 0.85 to 0.95 percent; finally, the workpiece is placed in nitrate salt to be subjected to salt quenching to the temperature of 150 to 180 ℃, the workpiece is taken out of a salt tank to be air-cooled to the temperature of 70 to 90 ℃, and then the workpiece is soaked in water and sprayed.
And after the quenching procedure, the workpiece is placed in a tempering furnace for low-temperature tempering for 15h.
The invention realizes the slow reduction of the hardness of the effective hardened layer by adopting the carburizing process of strong carburizing, diffusion (performed in two sections) and carbon potential regulation (different in three sections); by adopting the heat treatment process of carburizing, high-temperature tempering and quenching, spherical alloy carbides are formed in the metallographic structure of the workpiece as much as possible, thereby reducing the carbon content and the alloy element content of a martensite matrix during reheating and quenching, and improving the martensite transformation starting temperature M s Point and end temperature M f The content of residual austenite during quenching is reduced, and the surface hardness of the workpiece is increased; the mode of quenching in the atmosphere furnace is adopted, the occurrence of surface decarburization phenomenon in the quenching process is reduced, and the phenomenon of lower surface hardness of the workpiece is avoided.
In the heat treatment process of the invention, the determination principle of the diffusion carbon potential at the end of the carburization process is as follows:
in order to improve the hardness of the surface of the Cr-Ni steel workpiece, the corresponding relation between the carbon content and the hardness of the surface of the Cr-Ni steel is determined so as to determine the carbon potential in the furnace in the final diffusion stage, so that the surface of the workpiece reaches the required process carbon potential. For this purpose the present application has determined the relationship between the quench hardness of Cr-Ni steels at different carbon contents, as shown in Table 1:
TABLE 1
The relationship between the carbon content and the hardness in Cr-Ni steels is shown in FIG. 1.
And (4) conclusion: the surface carbon content of the workpiece is controlled to be more than 0.78% to ensure that the surface hardness of the workpiece reaches more than 58HRC, and the optimal surface carbon content is 0.83-0.95%.
The relationship between the carbon content of the workpiece surface and the final diffused carbon potential can be estimated using the alloy coefficients:
C s =f×C p
wherein, C s Surface carbon content, f- -alloy coefficient, C p - -furnace gas carbon potential;
the alloy coefficients can be expressed by the formula s. Gunnarson:
the alloy coefficient of the surface carbon content of the Cr-Ni steel during carburization is about 1.002 by calculation when the alloy is calculated by the formula of logf =0.013Mn% +0.04Cr% +0.013Mo% -0.055Si% -0.014 Ni.
Through the calculation, the carbon content of the workpiece surface is controlled to be 0.83-0.95%, and the carbon potential of the furnace atmosphere in the final diffusion stage and the quenching stage is controlled to be 0.83-0.95%.
The determination principle of the carbon potential in the furnace during quenching is as follows:
in order to obtain the optimal quenching temperature of the Cr-Ni steel, the surface hardness and the structure of the Cr-Ni steel after quenching at different temperatures are analyzed, and A of the Cr-Ni steel c3 The point is 780 ℃, and the quenching temperature is above 800 ℃ in order to ensure the complete austenitization of the core during quenching. The test results are shown in Table 2.
TABLE 2
And (4) conclusion: the optimal quenching temperature of the Cr-Ni steel is between 800 and 830 ℃.
The well type atmosphere furnace used in the present invention was a nitrogen methanol atmosphere well type furnace, and the correspondence between the temperature and the carbon black limit in this atmosphere is shown in table 3.
TABLE 3
And (4) conclusion: in order to prevent the carbon black limit in the furnace, the carbon potential in the furnace is controlled to be between 0.85 and 0.95 percent under the quenching temperature of 800 to 830 ℃.
Drawings
FIG. 1 is a graph showing the relationship between the carbon content and the hardness in Cr-Ni steel.
FIG. 2 is a diagram of a workpiece carburizing process with an effective hardened layer depth of less than or equal to 1.4 mm.
FIG. 3 is a diagram of a workpiece carburizing process with an effective hardened layer depth > 1.4 mm.
FIG. 4 is a quenching process with a furnace atmosphere.
FIG. 5 is a distribution curve of hardened layers of the gear part treated by the heat treatment process, wherein the effective hardened layer depth is less than or equal to 1.4 mm.
FIG. 6 is a profile of the hardened layer of a gear part treated by the heat treatment process of the present application for an effective hardened layer depth of > 1.4 mm.
FIG. 7 is an original carburization process.
Fig. 8 is an original quenching process.
FIG. 9 is a hardened layer distribution curve of a gear part with an effective hardened layer depth of less than or equal to 1.4mm by adopting an original heat treatment process.
FIG. 10 is a graph of the profile of the hardened layer of a gear part having an effective hardened layer depth of greater than 1.4mm using an original heat treatment process.
Detailed Description
To facilitate understanding of those skilled in the art, the present invention compares and verifies the processing effects of two parts (gear part with module M =3, which requires an effective hardened layer depth of 0.8-1.2mm; gear part with module M =5, which requires an effective hardened layer depth of 1.5-1.8 mm) by heat treatment according to the method of the present invention and the conventionally employed method, respectively. The two selected gear parts are gears for the gearbox and are made of Cr-Ni steel.
Example 1
The gear part with the modulus M =3 and the technical requirement that the effective hardening layer depth is 0.8-1.2mm is subjected to heat treatment according to the method of the application:
a carburizing process: the method is carried out in an Aiyilin VBEs-160/160 nitrogen methanol atmosphere well type furnace, and the specific steps comprise:
first, a temperature rise stage
Firstly, heating to 470 ℃, preserving heat for 1.5h, then continuously heating to 650 ℃, preserving heat for 1.5h, and then heating to 800 ℃, preserving heat for 1.5h;
second, exhaust stage
Heating to 930 deg.C, maintaining for 1h, adjusting carbon potential in the furnace to 0.3%, opening the exhaust hole, and exhausting air in the furnace;
the third step, the strong infiltration stage
Closing the exhaust hole, adjusting the carbon potential in the furnace to 1.2 percent and keeping the temperature for T 1 Is 5h;
the fourth step, diffusion stage
Keeping the temperature at 930 ℃, adjusting the carbon potential in the furnace to be 0.9 percent, and determining the heat preservation time T 3 =（T 1 -3) h =2h; because the depth D of the effective hardening layer of the workpiece is less than or equal to 1.4mm, T2 is zero (primary diffusion is not needed);
the fifth step, the cooling stage
Keeping the carbon potential in the furnace at 0.9 percent, reducing the temperature to 820 to 830 ℃, preserving the heat for 1.5h, then discharging the furnace and air-cooling the furnace to the room temperature.
A tempering procedure: in an Aiyilin DZLE-200/250 tempering furnace: the temperature is raised to 650 ℃, the temperature is kept for 4.5 hours, and the mixture is discharged from the furnace and cooled to the room temperature by air.
A quenching procedure: still in an AiXielin VBEs-160/160 nitrogen methanol atmosphere shaft furnace: firstly, raising the temperature to 400 ℃, and preserving the heat for 1.5h; then heating to 650 ℃, and preserving heat for 1.5h; then heating to 830 ℃, and preserving the heat for 2.5 hours, wherein the carbon potential is controlled at 0.9%; placing the workpiece in a nitrate tank for salt quenching to 160 ℃, taking the workpiece out of the salt tank, air cooling to 70-90 ℃, and then soaking and spraying the workpiece in water; and finally, putting the mixture into a tempering furnace for tempering for 15 hours at low temperature (180 ℃), and cooling the mixture to room temperature in air. The whole heat treatment process is shown in fig. 2 and 4.
The distribution curve of the hardened layer of the processed gear part is shown in figure 5, the effective hardened layer depth is 0.9-1.0mm, and the hardness within 0.4mm from the surface reaches 58HRC.
Comparative example 1 a gear part with a modulus M =3, requiring an effective hardened layer depth of 0.8-1.2mm was heat treated in a conventional manner:
the carburizing process is carried out in an Epoxicillin VBEs-160/160 nitrogen methanol atmosphere shaft furnace as shown in FIG. 7, and comprises the following steps:
first, temperature raising stage
Firstly, heating to 470 ℃, preserving heat for 1.5h, then continuously heating to 650 ℃, preserving heat for 1.5h, and then heating to 800 ℃, preserving heat for 1.5h;
second, exhaust stage
Heating to 930 deg.C, maintaining for 1h, adjusting carbon potential in the furnace to 0.3%, opening the exhaust hole, and exhausting air in the furnace;
the third step, the strong infiltration stage
Closing the exhaust hole, adjusting the carbon potential in the furnace to 1.2%, and preserving the heat for 5 hours;
the fourth step, diffusion stage
Keeping the temperature at 930 ℃, adjusting the carbon potential in the furnace to 0.8%, and preserving the heat for 2h;
the fifth step, the cooling stage
And (4) reducing the temperature to 820-830 ℃, preserving the heat for 1.5h, and then discharging from the furnace and air-cooling to room temperature.
A tempering procedure: in an Aiyilin DZLE-200/250 tempering furnace: the temperature is raised to 650 ℃, the temperature is kept for 4.5 hours, and the mixture is discharged from the furnace and cooled to the room temperature by air.
The quenching process is shown in fig. 8: still in an AiXielin VBEs-160/160 nitrogen methanol atmosphere shaft furnace: firstly, raising the temperature to 400 ℃, and preserving the heat for 1.5h; then heating to 650 ℃, and preserving heat for 1.5h; then heating to 830 ℃, and preserving the heat for 2.5h; and (3) placing the workpiece in an oil groove, performing oil quenching to 60 ℃, then performing air cooling to room temperature, finally placing the workpiece in a tempering furnace for tempering at low temperature (180 ℃) for 15h, and performing air cooling to room temperature.
The distribution curve of the hardened layer of the processed gear part is shown in figure 9, the depth of the effective hardened layer is 0.9-1.0mm, the hardness is maximum at a position 0.3mm away from the surface, the maximum hardness is 57.4HRC, and the hardness of the outermost surface is 57.0HRC.
As can be seen by comparing the heat treatment process of example 1 with the conventionally used heat treatment process, the main differences are: the method is based on the relation between the carbon content and the hardness in the Cr-Ni steel shown in figure 1, and adopts a higher carbon potential of 0.9 percent in a diffusion stage, so that the carbon content on the surface of a part is ensured; in the quenching stage, the surface decarburization of the part is prevented by adjusting the carbon potential in the furnace to be 0.9 percent; compared with the traditional oil quenching process, the heat treatment process adopts 160 ℃ isothermal nitrate quenching, and compared with quenching oil, the nitrate quenching property is better.
Example 2 a gear component with a modulus M =5 and a technical requirement that the effective depth of the hardened layer is 1.5-1.8mm is heat treated according to the method of the present application:
a carburizing process: the method is carried out in an Aiyilin VBEs-160/160 nitrogen methanol atmosphere well type furnace, and the specific steps comprise:
first, a temperature rise stage
Firstly, heating to 470 ℃, preserving heat for 1.5h, then continuously heating to 650 ℃, preserving heat for 1.5h, and then heating to 800 ℃, preserving heat for 1.5h;
second, exhaust stage
Heating to 930 deg.C, maintaining for 1h, adjusting carbon potential in the furnace to 0.3%, opening the exhaust hole, and exhausting air in the furnace;
the third step, the strong infiltration stage
Closing the vent hole, adjusting the carbon potential in the furnace to 1.2%, and preserving the heat for 9h (the heat preservation time T) 1 Taking for 9 h);
the fourth step, diffusion stage
Maintaining the temperature at 930 ℃:
firstly, adjusting the carbon potential in the furnace to be 1.0 percent and determining the heat preservation time T 2 ：T 2 =（T 1 -3) h =6h, performing a first stage diffusion;
then adjusting the carbon potential in the furnace to be 0.9 percent, and determining the heat preservation time T 3 ：T 3 =3h（T1＞6h）；
Step five, cooling stage
Keeping the carbon potential in the furnace at 0.9%, reducing the temperature to 820-830 ℃, preserving the heat for 1.5h, and then discharging from the furnace and air-cooling to room temperature.
The tempering process of the present invention was performed in the same manner as in example 1 in an Aielin DZLE-200/250 tempering furnace: the temperature is raised to 650 ℃, the temperature is kept for 4.5 hours, and the mixture is discharged from the furnace and cooled to the room temperature by air.
The quenching process of the invention is the same as example 1, and is still carried out in an Aiyilin VBEs-160/160 nitrogen methanol atmosphere shaft furnace: firstly, raising the temperature to 400 ℃, and preserving the heat for 1.5h; then heating to 650 ℃, and preserving heat for 1.5h; then heating to 830 ℃, and preserving the heat for 2.5h; putting the workpiece in a nitrate tank, performing salt quenching to 160 ℃, taking the workpiece out of the salt tank, air-cooling to 70-90 ℃, and then soaking and spraying the workpiece in water; and finally, putting the mixture into a tempering furnace for tempering for 15 hours at low temperature (180 ℃), and cooling the mixture to room temperature in air.
The whole heat treatment process is shown in fig. 3 and 4.
The distribution curve of the hardened layer of the processed gear part is shown in figure 6, the effective hardened layer depth is 1.7-1.8mm, and the hardness within 0.6mm from the surface reaches 58HRC.
Comparative example 2 a gear component with a modulus M =5, requiring an effective hardened layer depth of 1.5-1.8mm was heat treated in a conventional manner: the heat treatment process is the same as the comparative example 1, wherein the strong permeation heat preservation time is adjusted to 9 hours; the diffusion heat preservation time is adjusted to 8h.
The distribution curve of the hardened layer of the processed gear part is shown in figure 10, the depth of the effective hardened layer is 1.6-1.8mm, the hardness is maximum at a position 0.3mm away from the surface and is 56.7HRC, and the hardness of the outermost surface is 56.3HRC.
As can be seen by comparing the heat treatment process of example 2 with the conventionally used heat treatment process, the main differences are:
the diffusion stage is divided into two sections from one section, so that the smoothness of the depth curve of the effective hardened layer is ensured; the higher carbon potential is adopted at the second diffusion stage, so that the carbon content of the surface of the part is ensured; in the quenching stage, the surface decarburization of the part is prevented by adjusting the carbon potential in the furnace to be 0.9 percent; compared with the traditional oil quenching process, the heat treatment process adopts 160 ℃ isothermal nitrate quenching, and compared with quenching oil, the hardenability of the nitrate is better.
Claims (4)
1. A heat treatment process for improving the surface hardness of Cr-Ni steel comprises a carburizing process, a tempering process and a quenching process, and is characterized in that: the carburizing process is carried out in a well-type atmosphere furnace, and specifically comprises the following steps:
first, a temperature rise stage
Firstly, heating to 450-500 ℃, preserving heat for 1-2h, then continuously heating to 600-700 ℃, preserving heat for 1-2h, and then heating to 750-850 ℃, preserving heat for 1-2h;
second, exhaust stage
Heating to 920 to 940 ℃, preserving the temperature for 20 to 60min, adjusting the carbon potential in the furnace to 0.3%, opening an exhaust hole, and exhausting the air in the furnace;
the third step, the strong infiltration stage
Closing the vent hole, adjusting the carbon potential in the furnace to 1.15 to 1.25 percent, and determining the heat preservation time T according to the depth of the carburized effective hardened layer 1 : when the effective hardening layer depth D is less than or equal to 1.4mm, T 1 Less than or equal to 6 hours; t when the effective hardened layer depth D is greater than 1.4mm 1 ＞6h；
The fourth step, diffusion stage
Keeping the temperature at 920 to 940 ℃:
firstly, adjusting the carbon potential in the furnace to be 0.95 to 1.05 percent, and determining the heat preservation time T 2 : when T is 1 When the time is less than or equal to 6 hours, T 2 =0h; when T is 1 When is more than 6h, T 2 =（T 1 -3）h；
Then adjusting the carbon potential in the furnace to be 0.85 to 0.95 percent, and determining the heat preservation time T 3 : when T is 1 When the time is less than or equal to 6 hours, T 3 =（T 1 -3) h; when T is 1 When is more than 6h, T 3 =3h；
The fifth step, the cooling stage
Keeping the carbon potential in the furnace at 0.85-0.95%, reducing the temperature to 810-830 ℃, preserving the heat for 1-2h, and then discharging from the furnace and air-cooling to room temperature.
2. The heat treatment process for improving the surface hardness of the Cr-Ni steel as claimed in claim 1, wherein:
the tempering process is carried out in a tempering furnace: and (4) heating to 600-700 ℃, preserving the heat for 3-6 h, taking out of the furnace, and cooling to room temperature in air.
3. The heat treatment process for improving the surface hardness of Cr-Ni steel according to claim 1, wherein:
the quenching process is carried out in a well-type atmosphere furnace: firstly heating to 400-450 ℃, and preserving heat for 1-2h; then heating to 600-700 ℃, and preserving heat for 1-2h; then heating to 800-830 ℃, and keeping the temperature for 2-4h, wherein the carbon potential is controlled to be 0.85-0.95%; and finally, putting the workpiece into nitrate salt for salt quenching to 150-180 ℃, taking the workpiece out of a salt tank for air cooling to 70-90 ℃, and then soaking and spraying the workpiece in water.
4. A heat treatment process for improving the surface hardness of Cr-Ni steel according to claim 1, 2 or 3, characterized in that: after the quenching procedure, the workpiece is placed in a tempering furnace for tempering for 15 hours at the low temperature of 180 ℃.
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