CN116606989A - Heat treatment method of stainless steel - Google Patents
Heat treatment method of stainless steel Download PDFInfo
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 76
- 238000000034 method Methods 0.000 title claims abstract description 54
- 239000010935 stainless steel Substances 0.000 title claims abstract description 23
- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 23
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 211
- 239000010959 steel Substances 0.000 claims abstract description 211
- 238000001816 cooling Methods 0.000 claims abstract description 176
- 238000011282 treatment Methods 0.000 claims abstract description 84
- 230000032683 aging Effects 0.000 claims abstract description 50
- 239000000243 solution Substances 0.000 claims abstract description 39
- 239000006104 solid solution Substances 0.000 claims abstract description 29
- 238000004321 preservation Methods 0.000 claims abstract description 20
- 239000000463 material Substances 0.000 claims description 27
- 229910000734 martensite Inorganic materials 0.000 abstract description 34
- 230000008569 process Effects 0.000 abstract description 13
- 230000009286 beneficial effect Effects 0.000 abstract description 2
- 238000006243 chemical reaction Methods 0.000 abstract description 2
- 229910001566 austenite Inorganic materials 0.000 description 19
- 230000000052 comparative effect Effects 0.000 description 19
- 238000010791 quenching Methods 0.000 description 12
- 230000000171 quenching effect Effects 0.000 description 11
- 230000009466 transformation Effects 0.000 description 11
- 239000002245 particle Substances 0.000 description 7
- 238000004881 precipitation hardening Methods 0.000 description 7
- 229910001563 bainite Inorganic materials 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 238000011010 flushing procedure Methods 0.000 description 5
- 238000003756 stirring Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 238000007599 discharging Methods 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 230000001427 coherent effect Effects 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 239000007769 metal material Substances 0.000 description 3
- 230000002431 foraging effect Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 238000012797 qualification Methods 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 238000005275 alloying Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/02—Hardening by precipitation
-
- 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
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- 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
-
- 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
-
- 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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- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
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- Materials Engineering (AREA)
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Abstract
The application discloses a heat treatment method of stainless steel, which sequentially comprises solution treatment, oil cooling and aging treatment; in the solid solution treatment, putting the steel into a solid solution furnace for heat preservation; in the oil cooling, the steel after solution treatment is rapidly put into cooling oil for cooling; the cooling speed of the cooling oil is more than or equal to 95 ℃/s; in the aging treatment, aging treatment is carried out on the steel after oil cooling. The application adopts the cooling oil with high cooling speed to rapidly cool the steel after solution treatment, is beneficial to more fully converting the austenitic structure in the steel into the lath martensitic structure, avoids the step of continuous cooling treatment due to insufficient conversion, and omits the subsequent cryogenic treatment process.
Description
Technical Field
The application relates to a heat treatment method of a metal material, in particular to a heat treatment method of high-strength high-toughness steel.
Background
With the rapid development of the national industrialization field at present, the performance requirements on metal materials are also somewhat and more high, particularly in large-scale vessels related to the fields of aviation, aerospace and the like, high-strength and high-toughness metal materials are often required, and only precipitation hardening type high-strength steel can meet the use requirements in the conventional steel, but the obtained precipitation hardening type steel has strict requirements on the heat treatment process of the steel.
At present, the heat treatment of the steel is generally carried out in three steps of solid solution and deep cooling and time efficiency, the structure of the steel is generally converted into lath martensite and residual austenite after the solid solution treatment, the residual austenite in the steel is further converted into lath martensite after the deep cooling, a large amount of reverse-transformed austenite and second-phase particles are separated out from the lath martensite in the steel after the time efficiency, the steel has higher strength and toughness, the three heat treatment processes are closely connected, and the steel is buckled in a ring mode if one step of treatment is improper, so that the steel cannot reach the required performance index. The general specific solution treatment process is as follows: heating the steel to austenitizing temperature, preserving heat, and then putting the steel into oil for cooling; the specific cryogenic process comprises the following steps: transferring the sample subjected to solution treatment into a cryogenic device for further cooling, and then carrying out rewarming in the air; the specific aging process comprises the following steps: transferring the sample after deep cooling into an aging furnace for aging treatment, wherein the whole process is about 12-14 hours.
Because the heat treatment process has more steps and longer time, and the prior domestic enterprises have different placement methods, cryogenic time, cryogenic medium, temperature control of the steel after cryogenic, and the like, the same steel materials can often have different performance results in different unit heat treatments, and great trouble is caused to the using units of the materials.
There is therefore a great need for a simple, rapid heat treatment process for producing high strength, high toughness precipitation hardening steels.
Disclosure of Invention
The present application has been made to overcome the problems occurring in the prior art, and an object of the present application is to provide a heat treatment method for precipitation hardening steel, which can simply and rapidly produce a precipitation hardening steel having high strength and high toughness.
Through intensive researches, the inventor of the application discovers that when steel is in solid solution, the steel is reasonably placed at the austenitizing temperature and fully preserved, then the steel is placed into cooling oil with extremely high cooling speed for cooling, the steel is fully cooled in the cooling oil with extremely high cooling speed, so that the austenite content in the steel is converted into lath martensite as much as possible, and the steel after oil cooling directly enters an aging furnace for reasonable placement and full aging treatment, and finally the high-strength high-toughness steel can be obtained. Thus, the application provides a simple and rapid heat treatment method for producing high-strength high-toughness steel.
In order to achieve the above purpose, the present application adopts the following technical scheme.
The heat treatment method of stainless steel sequentially comprises solution treatment, oil cooling and aging treatment; wherein,,
in the solid solution treatment, placing the steel into a solid solution furnace for heat preservation;
in the oil cooling, the steel after solution treatment is rapidly put into cooling oil for cooling; the cooling speed of the cooling oil is more than or equal to 95 ℃/s;
in the aging treatment, aging treatment is carried out on the steel after oil cooling.
In the above heat treatment method, as a preferable embodiment, the steel material is added to the solution furnace in a suspended manner for solution treatment. Preferably, the solutionizing furnace may employ a well-type solutionizing furnace; still preferably, the interval gap between the steel materials is more than or equal to 20mm; so as to ensure that each steel can be fully subjected to solution treatment.
In the above heat treatment method, as a preferred embodiment, in the solid solution treatment, the solid solution treatment is performed by heating the solid melting furnace to the austenitizing temperature of the steel material and then maintaining the temperature at 900-1040 ℃ (for example, 910 ℃, 920 ℃, 950 ℃, 970 ℃, 980 ℃, 1000 ℃, 1020 ℃, 1040 ℃), and the temperature maintaining time is not less than 1 hour, so that the alloying elements in the steel can be uniformly dispersed in the steel, and the uniformity of the structure of the steel material can be ensured.
In the conventional art, steel is solution treated in a solution furnace in a stacked manner. In the application, the steel is subjected to solution treatment in a hanging manner instead of the conventional stacking manner, so that the steel can be ensured to be fully and uniformly dissolved in the solution furnace.
According to the application, during the solution treatment, the steel is discharged in a hanging manner, so that the steel is in a uniform temperature field and the steel is not contacted with each other, and further, during the solution treatment, the alloy elements in the steel can be ensured to be more uniformly dispersed into the steel, so that the structure of the steel is more uniform, and further, the more uniform structure can be obtained in the subsequent cooling process.
In the heat treatment method, as a preferable implementation mode, in the oil cooling, the time for transferring the steel into the cooling oil is required to be within 10 seconds, the temperature of the cooling oil is required to be less than or equal to 38 ℃, and the cooling time of the steel in the cooling oil is required to be more than or equal to 20 minutes; preferably, the cooling time is 30min to 60min (e.g., 35min, 40min, 45min, 50min, 55min, 58 min).
The present application requires that the steel material obtain a lath martensitic structure during cooling. After the steel is discharged from the furnace, as the ambient temperature is reduced below the austenitizing temperature, the structure in the steel starts to change, if the transfer time in the air is longer than 10s, the cooling speed of the surface temperature of the steel is slower, and the bainite and other structures can appear in the steel, thereby influencing the performance of the subsequent steel. Therefore, the steel is quickly transferred into the cooling oil to be quickly cooled by shortening the transfer time of the steel in the air, so that the steel is prevented from having undesirable structures such as bainite in air cooling, and the performance of the steel is improved.
In the application, if the oil cooling time is less than 20min, the austenitic structure in the steel cannot be thoroughly converted into the lath martensitic structure, and the performance index of the steel is seriously affected, so that the time is more than 20min for ensuring that the austenite in the steel is fully converted into the lath martensitic structure.
In the above heat treatment method, as a preferred embodiment, the oil-cooled steel material is subjected to aging treatment in an aging furnace in a suspended manner. Preferably, the ageing treatment is carried out in a well ageing oven; discharging the steel after aging treatment, and air-cooling to room temperature; preferably, the temperature of the aging treatment is 480 to 620 ℃ (e.g., 490 ℃, 500 ℃, 510 ℃, 525 ℃, 550 ℃, 560 ℃, 580 ℃, 600 ℃, 610 ℃).
According to the application, the steel after oil cooling replaces the conventional stacking mode in a hanging mode, so that the steel is in a uniform temperature field and is not contacted with each other, and the full and uniform aging is ensured.
The heat treatment method can obtain high-strength high-toughness precipitation hardening type steel, and in addition, the heat treatment method has few steps (omits a cryogenic treatment process), is simple to operate, has short time, and can greatly improve the working efficiency and the product qualification rate.
In the above heat treatment method, as a preferred embodiment, the heat treatment method is applied to heat treatment of Cr13Ni8 type, cr17Ni4 type and Cr15Ni5 type stainless steel.
In the above heat treatment method, as a preferred embodiment, the heat treatment method is applied to heat treatment of stainless steel having a diameter of less than 40mm (e.g., 10mm, 15mm, 20mm, 25mm, 30mm, 35 mm).
For cooling oil, it is now possible to produce oil at cooling rates above 95 ℃/s far above 50 ℃/s for the 20 th century.
Further, as is known from the study of the mechanism of the heat treatment process of the high-strength and high-toughness steel, the mechanism of the high-strength and high-toughness steel is that a large amount of reverse transformation austenite and second phase particles are precipitated in lath martensite when the steel is aged, and the premise of obtaining a large amount of lath martensite is that the austenite in the steel is transformed as much as possible, so that the deep cooling treatment is required after the solution treatment in order to obtain a large amount of lath martensite structure of the steel. However, as described above, in view of the fact that the cooling rate of the cooling oil which can be produced in China can reach 95 ℃/s at present, the cooling oil with the cooling rate of 95 ℃/s is adopted to quench the steel after solution treatment, and the steel can obtain more lath martensitic structure after full oil quenching without further cryogenic treatment. In addition, the well type heat treatment furnace is adopted to preserve heat of the steel, so that the condition that the heat preservation effect of the box type heat treatment furnace on the steel is not ideal is avoided.
In the application, the technical characteristics can be freely combined to form a new technical scheme under the condition of no conflict.
Compared with the prior art, the application has the following beneficial technical effects.
1. The steel subjected to solution treatment is rapidly cooled by adopting cooling oil with high cooling speed, so that austenite structure in the steel is more fully converted into lath martensite structure, the step of continuing cooling treatment due to insufficient conversion is avoided, and the subsequent cryogenic treatment process is omitted;
2. the steel is subjected to solution treatment in a hanging mode, so that the solution treatment of the steel is more sufficient and uniform, alloy elements in the steel are more uniform, and the alloy elements are dispersed in the steel, so that the structure of the steel is more uniform, and the mechanical property of the final steel is further ensured.
3. The steel is subjected to aging treatment in a hanging mode, so that the aging treatment of the steel is more sufficient and uniform, lath martensite in the steel is uniform and dispersed, reverse transformation austenite and second phase particles which are coherent with a matrix are precipitated, and the final steel is ensured to have higher strength and toughness.
4. By adopting the technical scheme of the application, the heat treatment operation links can be reduced, the production cost is reduced, and the efficiency is improved; meanwhile, the qualification rate of the product can be improved.
Drawings
FIG. 1 shows a lath martensite structure of a steel product obtained by cooling with a cooling oil having a cooling rate of 98 ℃ per second and a temperature of 32 ℃ in example 2 of the present application.
FIG. 2 shows the reverse transformation austenite structure precipitated in lath martensite of the steel product after aging treatment in example 2 of the present application.
FIG. 3 shows the second phase particles precipitated in lath martensite of the steel product after aging treatment in example 2 of the present application.
FIG. 4 is a diagram showing a metallographic structure of a steel material obtained by cooling with a cooling oil in example 2 of the present application.
FIG. 5 is a lath martensite count in the steel obtained after cooling with the cooling oil in example 2 of the present application.
FIG. 6 is a lath martensite count in the steel product obtained after cooling with a quenching oil in comparative example 1 of the present application.
FIG. 7 is a metallographic structure of a steel material obtained by cooling with a cooling oil according to comparative example 4 of the present application.
FIG. 8 is a metallographic structure of a steel material obtained by cooling with a cooling oil according to comparative example 5 of the present application.
Detailed Description
The technical solutions of the present application will be clearly and completely described below in connection with specific embodiments, and it is obvious that the described embodiments are only some embodiments of the present application, but not all embodiments. It should be understood that the detailed description and specific examples, while indicating and illustrating the application, are not intended to limit the application. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the application, fall within the scope of protection of the application.
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other.
A heat treatment method of steel, comprising solution treatment, oil cooling and aging treatment; the solid solution treatment comprises the steps of placing steel into a well type heat treatment furnace in a hanging mode, transferring the steel into cooling oil (quenching oil) within 10 seconds after the steel is fully dissolved in the furnace, and cooling the steel in the cooling oil for at least 20 minutes at room temperature, wherein the aging treatment comprises the steps of placing the steel after oil cooling into the well type heat treatment furnace in a hanging mode for full aging treatment, then discharging and air cooling, and finally obtaining the steel with high strength and high toughness.
According to the application, the heat treatment furnace adopts a well type heat treatment furnace, the precision requirement of the furnace is within +/-5 ℃, and the cooling speed of the cooling oil is more than 95 ℃/s; and the temperature of the cooling oil is less than or equal to 35 ℃.
According to the application, the steel is put in a heat treatment furnace in a hanging manner, the steel can be fully subjected to the solution treatment by preserving the heat for a certain period of time, preferably, different steel products are separated by a certain gap (the interval is more than or equal to 20 mm) to ensure the solution effect, the heat treatment furnace is preferably used for carrying out the heat preservation after the heat treatment furnace is heated to the required austenitizing temperature with the precision within +/-5 ℃, and the heat preservation time is more than or equal to 1h.
And (3) putting the steel subjected to solid solution heat preservation into cooling oil within 10 seconds for cooling treatment, wherein the cooling oil is preferably uniformly stirred in advance, the temperature of the cooling oil is less than or equal to 38 ℃, preferably less than or equal to 35 ℃, the cooling speed is more than 95 ℃ per second, and the oil cooling time is more than 20 minutes.
According to the present application, aging of steel is performed by placing the steel in a heat treatment furnace in a suspended manner and maintaining the steel for a predetermined period of time to allow the steel to be sufficiently aged. Preferably, different steel materials should be separated by a certain gap, and the preferable interval is more than or equal to 20mm; so as to ensure the aging treatment effect of the steel. Still preferably, the heat treatment furnace should employ a heat treatment furnace having an accuracy within + -5 deg.c, preferably + -3 deg.c. And preferably, the heat treatment furnace is heated to the aging temperature and then kept for at least 4 hours.
The application adopts oil rapid quenching of more than or equal to 95 ℃ per second to ensure that a large amount of lath martensite with high strength and high toughness is formed in the steel, and after aging at 480-620 ℃, high-toughness reverse transformation austenite and second phase particles which are coherent with a matrix can be separated out from the lath martensite, and after air cooling to room temperature, the lath martensite, the reverse transformation austenite and the second phase particles which are coherent with the matrix are formed in the steel, and the three tissues jointly act to ensure that the steel has high strength and high toughness.
Therefore, the steel treated by the method can obtain high strength, high toughness and high impact property, and has the advantages of few steps, short time and strong operability.
Example 1
This example illustrates the heat treatment method of the present application using a phi 30mm Cr13-Ni8 steel.
A heat treatment method for steel comprises solution treatment, oil cooling and aging treatment, and concretely comprises the following steps.
(1) Solution treatment of
Firstly, heating a well type solid solution furnace to 925 ℃, then placing steel materials into the furnace in a hanging manner, wherein the interval between different steel materials is 25mm, and preserving heat for 1h and 20min after the steel materials enter the furnace;
(2) Oil cooling
Placing a cooling oil groove beside a well type solid solution furnace while preserving heat of steel, wherein the cooling speed of cooling oil is 98 ℃/s, the temperature is 32 ℃, rapidly placing the steel after solid solution treatment into the cooling oil within 5 seconds, stirring the cooling oil, and cooling the steel in the cooling oil for 25 minutes; cooling the steel to room temperature; wherein the cooling oil is quick bright quenching oil (KR-H28Y, kerun Co.);
(3) Aging treatment
And taking out the steel after oil cooling, flushing greasy dirt on the surface by using clear water, then placing the steel into an aging furnace which is heated to 510 ℃ in advance in a hanging mode, preserving heat for 4h30min after the steel enters the furnace, and then discharging the steel.
Table 1 shows the properties and the total heat treatment time of the Cr13-Ni8 steel obtained in this example.
TABLE 1 Room temperature mechanical Properties and Total Heat treatment time of different steels
Example 2
The difference between this example and example 1 is that the steel having a different composition is used, and specifically, this example describes the heat treatment method of the present application by taking as an example a steel having a specification of phi 30mmCr17-Ni 4.
A heat treatment method for steel comprises solution treatment, oil cooling and aging treatment, and concretely comprises the following steps.
(1) Solution treatment of
Firstly, heating a well type solid solution furnace to 1040 ℃, then placing steel into the furnace in a hanging manner, wherein the interval between different steel is 25mm, and preserving heat for 1h and 30min after the steel enters the furnace;
(2) Oil cooling
Placing a cooling oil groove beside a well type solid solution furnace while preserving heat of steel, wherein the cooling speed of cooling oil is 98 ℃/s, the temperature is 32 ℃, placing the steel subjected to solid solution treatment in the cooling oil for 5s, stirring the cooling oil, and cooling the steel in the cooling oil for 25min to room temperature;
(3) Aging treatment
And taking out the steel after oil cooling, flushing greasy dirt on the surface by using clear water, then placing the steel into an aging furnace which is heated to 605 ℃ in advance in a hanging mode, preserving heat for 4h30min after the steel enters the furnace, and then discharging the steel. The properties of the resulting stainless steel are shown in table 1.
FIG. 1 shows the lath martensite structure of the steel product obtained after cooling with a cooling oil having a cooling rate of 98 ℃/s and a temperature of 32℃in this example. Figures 2 and 3 show the reverse transformed austenite structure and second phase particles, respectively, precipitated in the lath martensite of the steel after ageing treatment in this example. FIGS. 4 and 5 show metallographic structure diagrams and lath martensite counts in the steel material obtained after cooling with the cooling oil in this example.
As can be seen from fig. 4, the steel material was cooled by the rapid quenching oil for 25 minutes, and the structure was completely changed to the lath martensitic structure.
Comparative example 1
Compared with the example 2, the comparative example adopts conventional cooling oil (25 # transformer oil) for quenching and heat preservation for 1h and 30min, adopts air cooling after quenching, and air cooling time is 2h, and is put into the cooling oil for heat preservation for 25min after air cooling, then adopts 0 ℃ for heat preservation for 2h (namely, deep cooling), and needs to rewarming in air for 2h after heat preservation at 0 ℃, wherein the cooling speed of the cooling oil is 50 ℃/min, the temperature is 32 ℃, and the rest steps are the same as the example 2. The properties of the resulting stainless steel are shown in table 1. FIG. 6 shows the lath martensite count in the steel obtained after cooling with the cooling oil in this comparative example.
In this comparative example, the steel material has high strength by having a microstructure such as martensite, austenite, and bainite in the steel after air cooling, and then converting austenite and bainite into lath martensite again after heat preservation at 0 ℃.
As can be seen from FIGS. 5 and 6, the lath martensite count in the steel is between 3000 and 3500, and the number is small, using conventional quenching oil cooling at a cooling rate of 50 ℃/s. And rapid quenching oil with cooling speed of 98 ℃/s is adopted for cooling, the lath martensite count in the steel is more than 4000, and the number is more.
As is clear from a comparison of example 2 and comparative example 1 in Table 1, the properties of the obtained stainless steel according to the technical scheme of the present application (example 2) are comparable to those of the stainless steel according to the technical scheme of deep cooling after quenching (comparative example 1), that is, by adopting the technical scheme of the application, the conventional deep cooling process can be omitted, the heat treatment process steps of the stainless steel are simplified, and the heat treatment time is saved.
Comparative example 2
This comparative example illustrates a conventional heat treatment method for obtaining a precipitation hardening type steel, taking a phi 30mmCr13-Ni8 type steel as an example. The heat treatment method comprises solution treatment, oil cooling, deep cooling, tempering and aging, and is concretely as follows.
Firstly, heating a box-type solid solution furnace to 925 ℃, then placing Cr13-Ni8 steel into the furnace in a stacking manner, and preserving heat for 1h and 30min after the steel enters the furnace; placing a cooling oil groove beside a solid solution furnace while preserving heat of steel, wherein the cooling speed of cooling oil is 50 ℃/s, and the temperature is 32 ℃; after the heat preservation is finished, rapidly placing the steel into cooling oil for 5 seconds, stirring the cooling oil, cooling the steel for 10 minutes, taking out the steel, and flushing greasy dirt on the surface with clear water; then, the oil-cooled sample is put into an incubator at 0 ℃ for heat preservation for 2 hours and 30 minutes, the sample is rewarmed in the air for 3 hours after being discharged from the incubator at 0 ℃, then the sample is put into a box-type aging furnace which is heated to 510 ℃ in advance for aging treatment in a stacking mode, the steel is insulated for 5 hours after being fed into the furnace, and the performance of the obtained steel is shown in a table 1.
Comparative example 3
A heat treatment method of Cr13-Ni8 steel includes solution treatment, oil cooling and aging, and differs from example 1 in steel stacking as follows.
Firstly, heating a box-type solid solution furnace to 925 ℃, then placing Cr13-Ni8 steel into the furnace in a stacking manner, and preserving heat for 1h and 30min after the steel enters the furnace; placing a cooling oil groove beside a solid solution furnace while preserving heat of steel, wherein the cooling speed of cooling oil is 98 ℃/s, and the temperature is 32 ℃; after the heat preservation is finished, rapidly placing the steel into cooling oil for 5 seconds, stirring the cooling oil, cooling the steel for 25 minutes, taking out the steel, and flushing greasy dirt on the surface with clear water; then put into a box type ageing furnace which is heated to 510 ℃ in advance in a stacking mode for ageing treatment, and keep the temperature for 4.5 hours after the steel is fed into the furnace and discharged, wherein the performances of the obtained steel are shown in a table 1.
Comparative example 4
A heat treatment method of phi 30mmCr13-Ni8 steel comprises solution treatment, oil cooling, deep cooling, tempering and aging, and concretely comprises the following steps.
Firstly, heating a well type solid solution furnace to 925 ℃, then placing steel materials into the furnace in a hanging manner, wherein the interval between different steel materials is 25mm, and preserving heat for 1h and 20min after the steel materials enter the furnace; placing a cooling oil groove beside a solid solution furnace while preserving heat of steel, wherein the cooling speed of cooling oil is 50 ℃/s, and the temperature is 32 ℃; after the heat preservation is finished, rapidly placing the steel into cooling oil for 5 seconds, stirring the cooling oil, cooling the steel for 10 minutes, taking out the steel, and flushing greasy dirt on the surface with clear water; then, the oil-cooled sample is put into an incubator at 0 ℃ for heat preservation for 2 hours and 30 minutes (namely, deep cooling), the sample is rewarmed in the air for 3 hours after being taken out of the incubator at 0 ℃, then the sample is put into an aging furnace which is heated to 510 ℃ in advance in a hanging mode, and the steel is kept for 4 hours and 30 minutes after being put into the furnace, and then is taken out of the furnace. The properties of the steel product obtained are shown in Table 1. FIG. 7 is a diagram showing a metallographic structure of a steel material obtained by cooling with a cooling oil in this comparative example.
As is clear from fig. 7, in this comparative example, when the oil cooling time is 10 minutes, the metallographic structure of the steel obtained is lath martensite+bainite or the like, and therefore the transformation effect of the steel structure is not good.
Comparative example 5
The difference between the present application and example 1 is that after the steel is solid-dissolved, air cooling is performed for 10min and then oil cooling is performed by transferring cooling oil. The properties of the steel product obtained are shown in Table 1. FIG. 8 is a diagram showing a metallographic structure of a steel material obtained by cooling with a cooling oil in this comparative example.
As can be seen from fig. 8, the comparative example uses air cooling and then oil cooling, and the metallographic structure of the obtained steel is pearlite+bainite+a small amount of lath martensite, so that the metallographic structure of the obtained steel is not good in transformation effect by air cooling and then oil cooling.
In general, as can be seen from table 1, the steel material after heat treatment can obtain high strength, high toughness and high impact property, and has the advantages of few steps, short time and strong operability by adopting the technical scheme of the application.
The main principle of the increase of the Charpy impact and the fracture toughness of the obtained stainless steel is that the content of the reverse transformation austenite (precipitated from lath martensite) in the steel is increased, the content of the reverse transformation austenite in the oil with the cooling speed of 50 ℃/s and the deep-cooling steel with the temperature of 0 ℃ is 0.94 percent (comparative example 1) measured by a test, the content of the reverse transformation austenite in the steel is 1.74 percent after the cooling speed is more than or equal to 95 ℃/s, and the Charpy impact and the fracture toughness of the steel are both increased after the content of the reverse transformation austenite is increased.
Claims (10)
1. The heat treatment method of the stainless steel is characterized by sequentially comprising solution treatment, oil cooling and aging treatment; wherein,,
in the solid solution treatment, placing the steel into a solid solution furnace for heat preservation;
in the oil cooling, the steel after solution treatment is rapidly put into cooling oil for cooling; the cooling speed of the cooling oil is more than or equal to 95 ℃/s;
in the aging treatment, aging treatment is carried out on the steel after oil cooling.
2. The method for heat treatment of stainless steel according to claim 1, wherein in the solution treatment, steel is added to a solution furnace in a hanging manner for solution treatment; preferably, the spacing gap between the steel materials is more than or equal to 20mm.
3. The method of heat treatment of stainless steel according to claim 1 or 2, wherein said solution furnace is a well-type solution furnace.
4. A heat treatment method for stainless steel according to any one of claims 1 to 3, wherein in the solid solution treatment, the solid solution treatment is performed with heat preservation after heating the solid solution furnace to the austenitizing temperature of the steel, and the heat preservation temperature of the solid solution treatment is 900 to 1040 ℃, and the heat preservation time is not less than 1 hour.
5. The method according to any one of claims 1 to 4, wherein the time required for transferring the steel material into the cooling oil in the oil cooling is 10 seconds or less, the temperature of the cooling oil is not more than 38 ℃, and the cooling time of the steel material in the cooling oil is not less than 20 minutes; preferably, the cooling time is 30min to 60min.
6. The method for heat treatment of stainless steel according to any one of claims 1 to 5, wherein the oil-cooled steel is aged in a hanging manner in an aging furnace;
preferably, the temperature of the aging treatment is 480-620 ℃.
7. The method of heat treatment of stainless steel according to any one of claims 1-6, characterized in that the aging treatment is performed in a well aging oven.
8. The method for heat treatment of stainless steel according to any one of claims 1 to 7, wherein the steel after aging treatment is discharged from the furnace and cooled to room temperature by air.
9. The heat treatment method of stainless steel according to any one of claims 1 to 8, wherein the heat treatment method is applicable to heat treatment of Cr13Ni8 type, cr17Ni4 type and Cr15Ni5 type stainless steel.
10. The heat treatment method of stainless steel according to any one of claims 1 to 9, wherein the heat treatment method is suitable for heat treatment of stainless steel having a diameter of less than 40 mm.
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