CN114921638A - Accurate heat treatment method for low-carbon low-alloy high-strength thin steel plate - Google Patents
Accurate heat treatment method for low-carbon low-alloy high-strength thin steel plate Download PDFInfo
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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
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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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
- C21D1/185—Hardening; Quenching with or without subsequent tempering from an intercritical temperature
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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
- C21D1/26—Methods of annealing
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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
- C21D11/00—Process control or regulation for heat treatments
- C21D11/005—Process control or regulation for heat treatments for cooling
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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
- C21D2211/005—Ferrite
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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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- 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
- C21D2211/009—Pearlite
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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
- C21D2241/00—Treatments in a special environment
- C21D2241/01—Treatments in a special environment under pressure
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- 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
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Abstract
The invention provides a precise heat treatment method of a low-carbon low-alloy high-strength thin steel plate, and relates to the technical field of material processing. The precise heat treatment method comprises the steps of sequentially carrying out annealing treatment, austenitizing treatment, clamping quenching treatment and tempering treatment, and sequentially converting the structure of the steel plate into a ferrite structure, a pearlite structure, an austenite structure, a martensite structure and a tempered martensite structure, wherein the clamping force of the steel plate is changed in the clamping quenching treatment. The method realizes precise cooperative shape control, and the obtained steel plate has small deformation, no obvious indentation on the surface and good mechanical property, and reduces the production cost and simplifies the process steps.
Description
Technical Field
The invention relates to the technical field of material processing, in particular to a precise heat treatment method of a low-carbon low-alloy high-strength thin steel plate.
Background
The low-carbon low-alloy high-strength thin steel plate is widely applied to key fields of national defense war industry, engineering machinery, mining and metallurgy engineering, rail transit and the like. With the development of heavy-duty, high-speed and long-life in these key fields, the required low-carbon, low-alloy and high-strength thin steel plate also needs to be developed in the directions of large scale, complicated structure, integrated form, light weight of material and precise quality. The method puts forward more rigorous requirements on various performance indexes of the steel plate: the alloy not only needs to meet the conventional performances of high strength, easy welding and the like, but also needs to have the appearance performances of excellent plate shape, low residual stress, excellent surface quality and the like.
In order to obtain the desired properties of the low carbon low alloy high strength steel sheet, it must be heat treated. Further, the steel sheet is rapidly quenched and cooled in a quenching stage of the final heat treatment process to obtain a full martensite structure, thereby ensuring that the steel sheet obtains a desired strength and toughness. Because the low-carbon low-alloy high-strength thin steel plate has the characteristics of extremely large length (width) to thickness ratio, weak rigidity and the like, large quenching distortion is easily generated in the rapid quenching stage of the heat treatment process. The conventional water-through free quenching is adopted, the thin steel plate is easy to generate severe deformation such as tortoise back, bulge, warping and the like, and generally needs to be corrected by post-treatment, while the low-carbon low-alloy high-strength thin steel plate after heat treatment has high strength, and the required plate shape can be obtained after the low-carbon low-alloy thin steel plate after heat treatment needs to be corrected, polished and corrected by fire for many times. After many times of correction and grinding, the steel plate generates larger residual stress, and various properties of the thin plate, especially fatigue property, can be reduced, so that the service life of the thin steel plate is greatly shortened. By adopting constant clamping quenching, the thin steel plate is easy to generate defects such as local indentation, plastic deformation, microcrack and the like, the apparent quality of the thin steel plate is influenced, and even the thin steel plate is directly scrapped.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
An object of the present invention is to provide a method for precisely heat treating a low-carbon low-alloy high-strength thin steel sheet, which solves at least one of the problems of the prior art.
The second purpose of the invention is to obtain the low-carbon low-alloy high-strength thin steel plate prepared by the method.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
a precise heat treatment method of a low-carbon low-alloy high-strength thin steel plate comprises the following steps:
annealing treatment for transforming the structure of the steel sheet into a ferrite and pearlite structure;
step (b) of austenitizing the ferrite and pearlite structures in step (a) to an austenite structure;
a step (c) of performing a clamping quenching process for transforming the austenitic structure of the step (b) into a martensitic structure, wherein the clamping force of the steel sheet is varied;
tempering treatment in step (d) to transform the martensitic structure in step (c) into a tempered martensitic structure.
Further, in the step (c) of the clamping quenching treatment, the application of the clamping force is divided into the following stages (1) to (3):
the clamping force in the stage (1) is the maximum value of the deformation force in the austenite structure stage;
the clamping force in the stage (2) is the maximum value of the deformation force in the austenite transformation martensite stage;
the clamping force in the stage (3) is the maximum value of the deformation force in the martensite structure stage;
preferably, the deformation force is determined from a deformation force evolution history of the steel sheet during quenching.
Further, the operation of the clamping quenching treatment in the step (c) comprises: quenching the clamped steel plate at the water spraying flow rate and the water spraying pressure which are higher than the minimum cooling speed of the martensite structure, and cooling to the temperature T4 which is lower than the martensite finish transformation temperature;
preferably, the temperature T4 is at least 50-80 ℃ below the martensite finish transition temperature.
Further, the annealing in the step (a) includes: the steel plate is heated to a temperature T1 above the austenite finish transition temperature for a holding time T1 and subsequently cooled to a temperature T2 below the bainite start transition temperature.
Further, the temperature T1 is 80-100 ℃ higher than the austenite finish transformation temperature, and the time T1 is 1.5-5 times of the millimeter-thickness of the steel plate;
preferably, said temperature T2 is at least 80-100 ℃ below the bainite start transition temperature.
Further, the operation of the austenitizing treatment in step (b) comprises: the steel plate is heated to a temperature T3 higher than the austenite finish transition temperature for a holding time T2.
Further, the temperature T3 is 30-80 ℃ higher than the austenite finish transformation temperature, and the time T2 is 1.5-2 times of the millimeter thickness of the steel plate.
Further, the tempering in the step (d) includes: and heating the steel plate to the temperature of 180-680 ℃, and keeping the temperature for t3, wherein the time t3 is 10-30 times of the millimeter thickness of the steel plate.
Further, the method further comprises the step of detecting an isothermal transformation curve and a continuous cooling transformation curve of the steel sheet before the step (a).
The low-carbon low-alloy high-strength thin steel plate is prepared by the accurate heat treatment method.
Compared with the prior art, the invention has the technical effects that:
the heat treatment method provided by the invention can solve the problems of deformation, indentation, large residual stress and the like easily occurring in the heat treatment process of the high-strength thin steel plate in the prior art, realize precise cooperative shape control, and the obtained steel plate has small deformation, no obvious indentation on the surface and good mechanical property, and reduces the production cost and simplifies the process steps.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic size diagram of a low-carbon low-alloy high-strength thin steel plate provided by an embodiment of the invention;
FIG. 2 is a photograph showing the quenching deformation of a steel plate under the free quenching condition in comparative example 1 of the present invention;
FIG. 3 is a photograph showing defects such as indentation of a steel sheet under constant-clamping quenching conditions in comparative example 2 of the present invention;
FIG. 4 is a continuous cooling transformation curve of a low carbon low alloy steel sheet material according to an embodiment of the present invention, wherein Ac1 is the austenite start transformation temperature, Ac3 is the austenite finish transformation temperature, Ms: martensite start transition temperature, Mf: a martensite finish transition temperature;
FIG. 5 is a low-carbon low-alloy thin steel sheet material isothermal transformation curve according to an example of the present invention, wherein Ac1 represents an austenite start transformation temperature, Ac3 represents an austenite finish transformation temperature, Ms: martensite start temperature, Mf: a martensite finish transition temperature;
FIG. 6 is a graph showing the temperature of the core of the steel plate varying with time under different quenching flow conditions according to the embodiment of the present invention;
FIG. 7 is a graph showing the deformation force of a steel plate according to the embodiment of the present invention with respect to time;
FIG. 8 is a graph of the change of the clamping force of a quenched steel plate with a variable clamping force over time according to an embodiment of the invention;
FIG. 9 is a steel sheet obtained after precision heat treatment in the example of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be apparent that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a precise heat treatment method of a low-carbon low-alloy high-strength thin steel plate, which comprises the following steps of:
the annealing treatment of step (a) converts the structure of the steel sheet into ferrite and pearlite structures.
In the step, the structure of the annealed steel plate is changed into a uniform ferrite and pearlite structure, so that the components and the structure uniformity of the steel plate are improved, the uniformity of structure transformation in the step (c) is further improved, the structure stress is reduced, and the deformation of the steel plate is reduced.
And (b) carrying out austenitizing treatment to transform the ferrite and pearlite structures in the step (a) into austenite structures.
In this step, the structure of the austenitic steel sheet is transformed from ferrite and pearlite after annealing treatment to an austenitic structure, and is prepared for the structure of the pinch quenching treatment in step (c).
And (c) performing clamping quenching treatment to transform the austenite structure in the step (b) into a martensite structure, wherein the clamping force of the steel plate is changed.
In the step, the structure of the steel plate is completely changed into a martensite structure from austenite during austenitizing treatment, and the clamping force of the steel plate can be adjusted to ensure that the steel plate is limited from deforming and can freely stretch and contract during clamping quenching treatment.
The pressure-variable clamping scheme can limit the deformation of the conventional free quenching cooling method of the steel plate and can avoid surface defects such as indentation, scratch and the like of the conventional constant-clamping-force quenching cooling method. The quenching process analysis of the steel plate shows that the steel plate is mainly divided into the following three stages in the clamping quenching process:
(1) and (3) a primary setting stage: the steel plate at the stage is treated in an austenite undercooling area, the strength is low, the plasticity is good, only thermal stress is generated, and the steel plate shrinks from the periphery of the steel plate to the center of the steel plate due to cooling, so that continuous small clamping force (the specific clamping force is different along with the treated steel plate) can be applied to limit deformation and avoid indentation defects on the surface of the steel plate at the stage, and meanwhile, the steel plate can shrink towards the center to avoid the defects of scratches, surface tensile stress and the like caused by overlarge clamping force.
(2) And (3) cooling and shape control stage: in the stage, the steel plate structure is changed from austenite to martensite, the steel plate strength is increased, and meanwhile, the structure stress and the thermal stress are generated, the stress is larger and is the key stage of the shape control of the steel plate, in the stage, the steel plate is cooled to cause the steel plate to contract from the periphery of the steel plate to the center of the steel plate, the steel plate is changed from austenite to martensite to cause the volume expansion of the steel plate from the center of the steel plate to the periphery of the steel plate, and the steel plate and the martensite can offset each other, so that larger clamping force (the specific clamping force is different along with the treatment of the steel plate) can be applied to prevent the deformation of the steel plate in the stage.
(3) And (3) a dimensional stabilization stage: the steel plate structure is martensite at this stage, the strength of the steel plate is high, but the temperature difference still exists inside and outside the steel plate, and the steel plate is continuously cooled to generate thermal stress, so that relatively large stress (the specific clamping force is different along with the processed steel plate) is applied at this stage to prevent the steel plate from deforming.
Tempering treatment in step (d) to transform the martensitic structure in step (c) into a tempered martensitic structure.
In the step, the steel plate is converted from a martensite structure into tempered martensite or tempered sorbite, so that the steel plate obtains better comprehensive performance matching of strength and toughness.
In a preferred embodiment, in the step (c) of the clamp quenching treatment, the application of the clamping force may specifically adopt the following mode:
the clamping force in the stage (1) is the maximum value of the deformation force in the austenite structure stage;
the clamping force in the stage (2) is the maximum value of the deformation force in the austenite transformation martensite stage;
the clamping force in the stage (3) is the maximum value of the deformation force in the martensite structure stage.
Specifically, the change of the clamping force is six-stage clamping, which is respectively the clamping force changed to the stage (1), the clamping force maintenance of the stage (1), the clamping force changed to the stage (2) by the stage (1), the clamping force maintenance of the stage (2), the clamping force changed to the stage (3) by the stage (2) and the clamping force maintenance of the stage (3), wherein the switching of the clamping forces is switched in a manner as fast as possible, and particularly can be adjusted according to the performance of the quenching equipment used.
In a preferred embodiment, before the steel sheet is precisely heat-treated, preparation work is required as follows:
(i) and (3) obtaining an isothermal transformation curve and a continuous cooling transformation curve of the steel plate so as to obtain the key transformation temperatures of the full martensite structure, such as the minimum cooling speed, the austenite finish transformation temperature, the bainite start transformation temperature, the martensite finish transformation temperature and the like, and guiding the optimization of the heating temperature and the tapping cooling temperature of annealing treatment in the step (a), the heating temperature of austenitizing treatment in the step (b), the water cooling temperature in the step (c) and the like of the precise shape control of the high-strength thin steel plate based on physical and chemical tests and data simulation processes.
(ii) And obtaining optimized quenching technological parameters of the steel plate by using a numerical simulation method, wherein the technological parameters are used for converting the steel plate into a full martensite structure, namely, the minimum cooling speed of the steel plate is higher than the parameters such as water spray flow, water spray pressure and the like corresponding to the minimum cooling speed for obtaining the full martensite structure.
(iii) And (4) determining the deformation force evolution process of the steel plate in the quenching process by using a numerical simulation method, thereby determining the deformation force in the stages (1) - (3).
In a preferred embodiment, the operation of the pinch quenching process in the step (c) includes: the clamped steel sheet is quenched at a water jet flow rate and a water jet pressure which are higher than the minimum cooling rate of the martensite structure, and cooled to a temperature T4 which is lower than the martensite finish transformation temperature. The temperature T4 is preferably at least 50-80 ℃ below the martensite finish temperature, and the temperature T4 may be, but is not limited to, at least 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃ below the martensite finish temperature.
In a preferred embodiment, the annealing in step (a) comprises: the steel plate is heated to a temperature T1 above the austenite finish transition temperature for a holding time T1 and then cooled to a temperature T2 below the bainite start transition temperature. The temperature T1 is preferably 80-100 ℃ higher than the austenite finish transition temperature, e.g., 80 ℃, 85 ℃, 90 ℃, 95 ℃ or 100 ℃, etc.; the time t1 is preferably 1.5 to 5 times the thickness of the steel plate made of millimeters, and the time t1 is minutes, for example, if the thickness of the steel plate is 10mm, the time t1 is 15 to 50 minutes; the temperature T2 is preferably at least 80-100 ℃ lower than the bainite onset temperature, for example 80 ℃, 85 ℃, 90 ℃, 95 ℃ or 100 ℃.
In a preferred embodiment, the operation of the austenitizing treatment in step (b) comprises: the steel plate is heated to a temperature T3 higher than the austenite finish transition temperature for a holding time T2. The temperature T3 is preferably 30-80 ℃ above the austenite finish transition temperature, e.g., 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃, and the time T2 is preferably 1.5-2 times the millimeter thickness of the steel sheet.
In a preferred embodiment, the tempering in step (d) comprises: and heating the steel plate to the temperature of 180-680 ℃, and keeping the temperature for t3, wherein the time t3 is 10-30 times of the millimeter thickness of the steel plate. The heating temperature of the steel sheet may be, but is not limited to, 180 ℃, 280 ℃, 380 ℃, 480 ℃, 580 ℃, or 680 ℃.
In a more preferred embodiment, the precise heat treatment method of the low carbon low alloy high strength steel sheet is as follows:
the first stage, based on physicochemical experiment and data simulation process optimization:
step 1, obtaining an isothermal transformation curve and a continuous cooling transformation curve of materials corresponding to a low-carbon low-alloy high-strength thin steel plate; and (4) guiding the optimization of the heating temperature and the tapping cooling temperature of the annealing treatment in the step (a), the heating temperature of the austenitizing treatment in the step (b) and the water cooling temperature in the step (c) in the shape control of the high-strength thin steel plate precision based on physicochemical tests and data simulation processes (second stage).
Step 2, obtaining optimized quenching technological parameters of the low-carbon low-alloy thin steel plate by using a numerical simulation method; the design of the parameters of the spraying system in the step (c) in the second stage of the precise shape control of the high-strength thin steel plate can be optimized based on physical and chemical tests and data simulation processes.
Step 3, determining the deformation force evolution process of the steel plate in the quenching process by using a numerical simulation method;
and 4, obtaining the optimal value of the clamping force of the low-carbon low-alloy high-strength thin plate by combining a steel plate quenching cooling theory and an acting force and reaction force principle on the basis of the step 3. The optimization design of the clamping force in the step (c) in the precise shape control (second stage) of the high-strength thin steel plate can be guided to be optimized based on physical and chemical tests and data simulation processes.
And in the second stage, the high-strength thin steel plate is clamped, clamped and quenched under variable pressure:
step (a), annealing treatment, namely heating the steel plate to a certain temperature T1, preserving heat for a period of time T1, and then cooling the steel plate to a certain temperature T2 along with a furnace, discharging and cooling the steel plate;
austenitizing, namely heating the steel plate to a certain temperature T3 and keeping the temperature for a period of time T2;
clamping and quenching, namely quickly transferring the steel plate to quenching equipment, clamping the steel plate by the quenching equipment, and starting a spraying system to cool the steel plate to a certain temperature T4; the quenching intensity is determined according to the step 2 based on physicochemical experiments and numerical simulation process optimization (the first stage), so that the steel plate is completely transformed into martensite in the clamping and quenching treatment process of the step (c) and large quenching distortion caused by large stress generated by overlarge cooling speed can be avoided; the clamping force applied to the steel plate by the quenching equipment is determined and an optimized variable-pressure clamping and variable-pressure clamping mode is designed according to the steps 3 and 4 based on physicochemical experiments and numerical simulation process optimization (first stage), so that the steel plate is limited in deformation and can freely stretch and contract in the clamping and quenching treatment process of the step (c).
And (d) tempering, namely heating the steel plate to a certain temperature and preserving the temperature for a period of time t3, so that the steel plate obtains better comprehensive performance matching of strength and toughness.
In the method provided by the invention, the structure/performance of the steel plate can be regulated and controlled by the quenching technological parameters in the clamping quenching treatment, so that the low-carbon low-alloy thin steel plate is integrally quenched into high-strength martensite. The change of the clamping force can prevent the steel plate from generating large heat treatment deformation, surface indentation, scratch and other problems in the quenching process.
The invention also provides a low-carbon low-alloy high-strength thin steel plate prepared by the method, and the low-carbon low-alloy high-strength thin steel plate has excellent performance and appearance.
The invention is further illustrated by the following examples. The materials in the examples are prepared according to known methods or are directly commercially available, unless otherwise specified.
Examples
The low-carbon low-alloy steel sheet has the dimensions shown in FIG. 1, and has a length of 12000mm, a width of 2000mm and a thickness of 10 mm. The steel plate chemical composition is shown in table 1.
TABLE 1 Low carbon low alloy steel sheet chemical composition (mass fraction, wt%)
| C | Si | Mn | Cr | Ni | Mo |
| 0.28 | 0.2~0.5 | 0.75~1.1 | 0.75~1.1 | 1-1.3 | 0.25~0.45 |
The process optimization (first stage) based on physicochemical experiments and numerical simulations comprises the following steps:
step 1, obtaining a continuous cooling transformation curve (figure 4) and an isothermal transformation curve (figure 5) of a low-carbon low-alloy high-strength steel plate material through a physicochemical experiment; the austenite finish transformation temperature of the obtained steel plate material is 820 ℃, the bainite start transformation temperature is 500 ℃, the martensite start transformation temperature is 340 ℃, the martensite finish transformation temperature is 200 ℃, and the minimum cooling speed V of the full martensite structure is obtained Face Is 40 ℃/s.
Step 2, obtaining optimized quenching technological parameters of the low-carbon low-alloy thin steel plate by using a numerical simulation method; three quenching process schemes are designed, namely a quenching process scheme I: the quenching flow is 5L/m 2 S and quenching pressure of 0.2 MPa; and a second quenching process scheme: the quenching flow is 10L/m 2 S and quenching pressure of 0.2 MPa; a third quenching process scheme: the quenching flow is 15L/m 2 S and quenching pressure of 0.2 MPa. The temperature profile of the core of the steel plate with time under different quenching process schemes is shown in fig. 6.
It can be seen that the quenching process scheme is 5L/m 2 S, the cooling speed of the steel plate core is about 25 ℃/s, which is less than the minimum cooling speed V for obtaining the full martensite structure in the continuous cooling transformation curve in the step 1 Face 40 ℃/s, the steel plate can not obtain the required martensite structure under the quenching process condition; the quenching process scheme is 10L/m 2 S, the cooling rate of the steel plate core is about 48 ℃/s, which is slightly larger than the minimum cooling rate V for obtaining the full martensite structure in the continuous cooling transformation curve in the step 1 Face The temperature is 40 ℃/s, so the steel plate can obtain the required martensite structure under the process condition; the quenching process scheme is 20L/m 2 When the temperature is s, the cooling speed of the core of the steel plate is about 98 ℃/s and is larger than the minimum cooling speed V for obtaining the full martensite structure in the continuous cooling transformation curve in the step 1 Face The temperature is 40 ℃/s, and the steel plate can obtain the required martensite structure under the process condition. Combined with actual production, to save quenching water and excrementThe operation in the quenching process, the quenching process selects a second quenching process scheme, and the quenching flow is 10L/m 2 S and quenching pressure of 0.2 MPa.
And 3, determining the deformation force evolution process of the steel plate in the quenching process by using a numerical simulation method, as shown in figure 7. The maximum deformation force in quenching is 158KN, and the deformation force is changed continuously.
And 4, combining a steel plate quenching cooling theory and an action force and reaction force principle on the basis of the step 3, and obtaining an optimal value of the clamping force of the low-carbon low-alloy high-strength thin plate as shown in fig. 8 (which is the maximum value of the deformation force in three states of austenite, austenite transformation martensite and martensite), wherein the clamping force is increased to 70KN within 0s to 1s, the clamping force is maintained to 70KN within 1s to 5s, the clamping force is increased to 158KN from 70KN within 5s to 10s, the clamping force is maintained to 158KN within 10s to 16s, the clamping force is reduced to 90KN from 158KN within 16s to 20s, and the clamping force is maintained to 90KN within 20s to 30 s.
The variable-pressure clamping quenching treatment (the second stage) of the high-strength thin steel plate comprises the following steps:
annealing treatment, namely heating the steel plate to 900 ℃, preserving heat for 30min, and then cooling the steel plate to 400 ℃ along with a furnace, discharging and cooling;
step (b), carrying out austenitizing treatment, namely heating the steel plate to a certain temperature of 860 ℃ and preserving the temperature for 18 min;
and (c) clamping and quenching treatment, namely quickly transferring the steel plate to quenching equipment, clamping the steel plate by the quenching equipment, and setting the clamping force as follows: increasing the clamping force to 70KN from 0s to 1s, maintaining the clamping force at 70KN from 1s to 5s, increasing the clamping force from 70KN to 158KN from 5s to 10s, maintaining the clamping force at 158KN from 10s to 16s, decreasing the clamping force from 158KN to 90KN from 16s to 20s, and maintaining the clamping force at 90KN from 20s to 30 s; starting the spraying system (quenching flow is 10L/m) 2 S, the quenching pressure is 0.2 MPa) cooling the steel plate by water for 30s, and cooling the steel plate to 30 ℃;
and (d) tempering, namely heating the steel plate to 200 ℃, and keeping the temperature for 200 min.
Through detection, the steel plate obtained by applying the technology of the embodiment has small deformation of 10mm at most, no obvious defects such as indentation on the surface and the like, and as shown in figure 9, the yield strength is about 1500MPa, the tensile strength is about 1750MPa, the elongation is 15% -17%, and the accurate heat treatment of the low-carbon low-alloy high-strength thin steel plate is realized.
Comparative example 1
Using the steel sheets as in the examples, the operational procedures were carried out with reference to the examples (step (a) to step (d)), except that in step (c), free quenching of the steel sheets was carried out, specifically, at a quenching flow rate of 10L/m 2 Free quenching was performed under the quenching process conditions with an s and quenching pressure of 0.2MPa, and the steel plate quenching numerical simulation and the actual heat-treated steel plate are shown in fig. 2. Therefore, the steel plate is obviously deformed under the quenching process, and the use requirement cannot be met.
Comparative example 2
Using the steel sheets as in the examples, the operation flow was conducted with reference to the examples (step (a) to step (d)), except that in step c, constant pinch quenching of the steel sheets was used at a quenching flow rate of 10L/m 2 S, quenching pressure of 0.2MPa, constant clamping force of 158000N in the quenching process, and the numerical simulation of steel plate quenching and the actual heat treatment of the steel plate are shown in figure 3. Therefore, under the quenching process condition, obvious defects such as indentation and the like are generated on the surface of the steel plate, the appearance quality is influenced, and the use requirement is not met.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A precise heat treatment method for a low-carbon low-alloy high-strength thin steel plate is characterized by comprising the following steps:
annealing treatment for transforming the structure of the steel sheet into a ferrite and pearlite structure;
step (b) of austenitizing the ferrite and pearlite structures in step (a) to an austenite structure;
a step (c) of a pinch quenching treatment for converting the austenite structure in the step (b) into a martensite structure, wherein the pinch force of the steel sheet is varied;
tempering treatment in step (d) to transform the martensitic structure in step (c) into a tempered martensitic structure.
2. The precision heat treatment method according to claim 1, wherein in the step (c) clamp quenching process, the application of the clamping force is divided into the following stages (1) to (3):
the clamping force in the stage (1) is the maximum value of the deformation force in the austenite structure stage;
the clamping force in the stage (2) is the maximum value of the deformation force in the austenite transformation martensite stage;
the clamping force in the stage (3) is the maximum value of the deformation force in the martensite structure stage;
the deformation force is determined by the deformation force evolution process of the steel plate in the quenching process.
3. The precision heat treatment method according to claim 2, wherein the operation of the clamping quenching process in the step (c) comprises: quenching the clamped steel plate at the water spraying flow rate and the water spraying pressure which are higher than the minimum cooling speed of the martensite structure, and cooling to the temperature T4 which is lower than the martensite finish transformation temperature;
the temperature T4 is at least 50-80 ℃ below the martensite finish transition temperature.
4. A precision thermal processing method according to claim 1, characterized in that said operation of annealing in step (a) comprises: the steel sheet is heated to a temperature T1 above the austenite finish transition temperature for a holding time T1 and subsequently cooled to a temperature T2 below the bainite start transition temperature.
5. The precision heat treatment method according to claim 5, characterized in that the temperature T1 is 80-100 ℃ higher than the austenite finish transformation temperature, the time T1 is 1.5-5 times the millimeter thickness of the steel sheet;
the temperature T2 is at least 80-100 ℃ below the bainite onset temperature.
6. The precision thermal processing method according to claim 1, wherein the operation of the austenitizing treatment in the step (b) comprises: the steel plate is heated to a temperature T3 higher than the austenite finish transition temperature for a holding time T2.
7. The precision heat treatment method according to claim 6, characterized in that said temperature T3 is 30-80 ℃ above the austenite finish transition temperature, and said time T2 is 1.5-2 times the millimetric thickness of the steel sheet.
8. The precision heat treatment method according to claim 1, wherein the tempering in the step (d) comprises: and heating the steel plate to the temperature of 180-680 ℃, and keeping the temperature for t3, wherein the time t3 is 10-30 times of the millimeter thickness of the steel plate.
9. The precision heat treatment method according to any one of claims 1 to 8, further comprising a step of detecting an isothermal transformation curve and a continuous cooling transformation curve of the steel sheet before the step (a).
10. A low carbon low alloy high strength steel sheet produced by the precision heat treatment method as set forth in any one of claims 1 to 9.
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| PCT/CN2023/075923 WO2023213109A1 (en) | 2022-05-06 | 2023-02-14 | Accurate heat treatment method for low-carbon low-alloy high-strength thin steel plate |
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| WO2023213109A1 (en) * | 2022-05-06 | 2023-11-09 | 中国机械总院集团北京机电研究所有限公司 | Accurate heat treatment method for low-carbon low-alloy high-strength thin steel plate |
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