CN114921638B - 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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- CN114921638B CN114921638B CN202210483543.8A CN202210483543A CN114921638B CN 114921638 B CN114921638 B CN 114921638B CN 202210483543 A CN202210483543 A CN 202210483543A CN 114921638 B CN114921638 B CN 114921638B
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- 238000000034 method Methods 0.000 title claims abstract description 79
- 238000010438 heat treatment Methods 0.000 title claims abstract description 44
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 32
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 29
- 239000000956 alloy Substances 0.000 title claims abstract description 29
- 238000010791 quenching Methods 0.000 claims abstract description 92
- 230000000171 quenching effect Effects 0.000 claims abstract description 92
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 58
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 36
- 238000000137 annealing Methods 0.000 claims abstract description 12
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 9
- 238000005496 tempering Methods 0.000 claims abstract description 9
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- 239000007921 spray Substances 0.000 claims description 5
- 230000008646 thermal stress Effects 0.000 claims description 5
- 230000001131 transforming effect Effects 0.000 claims description 3
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- 238000004088 simulation Methods 0.000 description 15
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Classifications
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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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
Abstract
The invention provides an accurate 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 sequentially comprises annealing treatment, austenitizing treatment, clamping quenching treatment and tempering treatment, wherein the structure of the steel plate is sequentially transformed into ferrite and pearlite structure, austenite structure, martensite structure and tempered martensite structure, and the clamping force of the steel plate in the clamping quenching treatment is changed. The method realizes precise cooperative control of the shape, the obtained steel plate has small deformation, no obvious indentation on the surface and good mechanical property, the production cost is reduced, and the process steps are simplified.
Description
Technical Field
The invention relates to the technical field of material processing, in particular to an accurate 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 important fields such as national defense war industry, engineering machinery, mining and metallurgy engineering, rail transit and the like. With the development of the important fields towards heavy load, high speed and long service life, the required low-carbon low-alloy and high-strength thin steel plate also needs to develop towards the directions of large scale, complex structure, integrated form, light material and accurate quality. The more severe requirements are put on each performance index of the steel plate: the product has the conventional properties of high strength, easy welding and the like, and has the apparent properties 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 is necessary to heat treat it. Further, the steel sheet is rapidly quenched and cooled in the quenching stage of the final heat treatment process to obtain a fully martensitic structure, thereby ensuring that the steel sheet has 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 extremely easy to generate in the rapid quenching stage of the heat treatment process. By adopting conventional water-penetrating free quenching, the thin steel plate is easy to generate serious deformation such as tortoise back, bulge, warping and the like, usually needs post-treatment for correction, and the low-carbon low-alloy high-strength thin steel plate is high in strength after heat treatment, and can obtain a required plate shape after repeated correction, polishing and fire correction of the low-carbon low-alloy thin steel plate after heat treatment. However, after repeated correction and grinding, the steel plate generates larger residual stress, and various properties of the thin plate, especially fatigue properties, are 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 this, the present invention has been made.
Disclosure of Invention
The invention aims to provide an accurate heat treatment method for a low-carbon low-alloy high-strength steel sheet, which at least solves one of the technical problems in the prior art.
The second purpose of the invention is to obtain the low-carbon low-alloy high-strength thin steel plate by the method.
In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:
an accurate heat treatment method of a low-carbon low-alloy high-strength thin steel plate comprises the following steps:
step (a) of annealing treatment to transform the structure of the steel sheet into ferrite and pearlite structures;
a step (b) of austenitizing the ferrite and pearlite structure in the step (a) into an austenite structure;
a step (c) of a clamp quenching treatment of transforming the austenite structure in the step (b) into a martensite structure, wherein a clamp force of the steel sheet is varied;
and (d) tempering treatment, wherein the martensitic structure in the step (c) is transformed into a tempered martensitic structure.
Further, in the step (c) of the clamp quenching treatment, the application of the clamp 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 austenitic 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 martensitic structure stage;
preferably, the deformation force is determined by the deformation force evolution history of the steel sheet during quenching.
Further, the step (c) of the clamp quenching treatment includes: quenching the clamped steel plate at a water spraying flow rate and a water spraying pressure which are higher than the minimum cooling speed of the martensitic structure, and cooling to a temperature T4 lower than the martensite finish transition 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 sheet is heated to a temperature T1 above the austenite finish transformation temperature for a holding time T1 and then cooled to a temperature T2 below the bainite start transformation temperature.
Further, the temperature T1 is 80-100 ℃ higher than the austenite finish transition 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 starting transition temperature.
Further, the operation of the austenitizing in the step (b) includes: the steel sheet is heated to a temperature T3 above the austenite finish transition temperature for a hold time T2.
Further, the temperature T3 is 30-80 ℃ higher than the austenite finish transition temperature, and the time T2 is 1.5-2 times of the millimeter thickness of the steel plate.
Further, the tempering treatment in the step (d) includes: heating the steel plate to 180-680 ℃, and preserving heat for a time t3, wherein the time t3 is 10-30 times of the millimeter thickness of the steel plate.
Further, before the step (a), a step of detecting an isothermal transformation curve and a continuous cooling transformation curve of the steel plate is further included.
The low-carbon low-alloy high-strength thin steel plate 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 easy deformation, indentation, large residual stress and the like in the heat treatment process of the high-strength thin steel plate in the prior art, realizes precise cooperative control of shape, has small deformation of the obtained steel plate, no obvious indentation on the surface and good mechanical property, 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 that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic view of a low-carbon low-alloy high-strength thin steel plate according to an embodiment of the present invention;
FIG. 2 is a drawing showing the quenching deformation of a steel sheet under the free quenching condition of comparative example 1 of the present invention;
FIG. 3 is a photograph showing defects such as steel plate indentation under constant clamping quenching in comparative example 2 of the present invention;
FIG. 4 is a graph showing a continuous cooling transformation curve of a low carbon low alloy steel sheet material according to an embodiment of the present invention, wherein Ac1 represents an austenite start transformation temperature, ac3 represents an austenite end transformation temperature, ms: martensite start temperature, mf: martensite finish transition temperature;
FIG. 5 is an isothermal transformation curve of a low carbon low alloy sheet material according to an embodiment of the present invention, wherein Ac1: austenite start transformation temperature, ac3: austenite end transformation temperature, ms: martensite start temperature, mf: martensite finish transition temperature;
FIG. 6 is a graph showing the temperature of the core of the steel plate with time under different quenching flow conditions in the embodiment of the present invention;
FIG. 7 is a graph showing the deformation force of a steel sheet according to the embodiment of the present invention with time;
FIG. 8 is a graph showing the change of clamping force with time of a quenched steel sheet with variable clamping force according to an embodiment of the present invention;
fig. 9 is a steel sheet obtained after the precision heat treatment in the example of the present invention.
Detailed Description
The technical solutions of the present invention will be clearly and completely described in connection with the embodiments, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The accurate heat treatment method of the low-carbon low-alloy high-strength thin steel plate provided by the invention comprises the following steps of:
and (a) annealing treatment, namely converting the structure of the steel plate into ferrite and pearlite structures.
In the step, the structure of the annealed steel plate is changed into uniform ferrite and pearlite structure, so that the composition and 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) an austenitizing treatment to transform the ferrite and pearlite structure in step (a) into an austenite structure.
In this step, the steel sheet structure after the austenitizing treatment is transformed from ferrite and pearlite after the annealing treatment to an austenite structure, and a structure preparation is made for the clamp quenching treatment in step (c).
And (c) a clamping quenching treatment, namely converting the austenitic structure in the step (b) into a martensitic structure, wherein the clamping force of the steel plate is changed.
In this step, the structure of the steel sheet is entirely transformed from austenite to martensite during the austenitizing treatment, and the steel sheet is allowed to freely expand and contract while being restrained from deformation during the clamping quenching treatment by the adjustment of the clamping force of the steel sheet.
The pressure variable clamping scheme can limit the deformation of the steel plate by the conventional free quenching cooling method and avoid the surface defects such as indentation, scratch and the like of the conventional constant clamping force quenching cooling method. Analysis of the quenching process of the steel plate shows that the steel plate is mainly divided into the following three stages in the clamping quenching process:
(1) Preliminary setting stage: the austenitic supercooling zone is treated by the steel plate in the stage, the strength is low, the plasticity is good, only thermal stress is generated, and the steel plate in the stage is contracted from the periphery of the steel plate to the core of the steel plate due to cooling shrinkage, so that continuously smaller clamping force (the specific clamping force varies with the treated steel plate) can be applied to limit deformation and avoid indentation defects on the surface of the steel plate in the stage, and meanwhile, the steel plate can be contracted towards the core to avoid the defects such as scratches and surface tensile stress caused by overlarge clamping force.
(2) Cooling and shape control: the steel plate structure is changed from austenite to martensite, the steel plate strength is increased, meanwhile, the structural stress and the thermal stress are generated, the stress is larger, the steel plate shape control key stage is that the steel plate is cooled in the stage to cause the steel plate to shrink from the periphery of the steel plate to the core of the steel plate, the steel plate is changed from austenite to martensite to expand in volume, the steel plate expands from the core of the steel plate to the periphery of the steel plate, and the austenite and the martensite can offset the parts, so that larger clamping force (the size of the specific clamping force is different according to the processed steel plate) can be applied in the stage to prevent the steel plate from deforming.
(3) Dimensional stabilization stage: the steel plate structure is martensite at this stage, the steel plate strength is high, but the temperature difference still exists between the inside and outside of the steel plate, and the heat stress is generated by continuous cooling, so that relatively large stress (the specific clamping force is different according to the processed steel plate) is applied at this stage to prevent the steel plate from deforming.
And (d) tempering treatment, wherein the martensitic structure in the step (c) is transformed into a tempered martensitic structure.
In the step, the steel plate is transformed from a martensitic structure into tempered martensite or tempered sorbite, so that the steel plate obtains better toughness and comprehensive performance matching.
In a preferred embodiment, in the clamping quenching treatment in the step (c), the clamping force may be applied in the following manner:
the clamping force in the stage (1) is the maximum value of the deformation force in the austenitic 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 martensitic structure stage.
Specifically, the change of the clamping force is six-stage clamping, namely the clamping force changed to the stage (1), the clamping force maintenance of the stage (1), the clamping force changed to the stage (2), the clamping force maintenance of the stage (2), the clamping force changed to the stage (3) and the clamping force maintenance of the stage (3), wherein the conversion of the clamping forces is changed in a way as fast as possible, and the conversion of the clamping forces is particularly adjustable according to the performance of the quenching equipment used.
In a preferred embodiment, the preparation work is as follows before the steel sheet is precisely heat treated:
(i) The isothermal transformation curve and the continuous cooling transformation curve of the steel plate are obtained, so that the minimum cooling speed, the austenite finish transformation temperature, the bainite start transformation temperature, the martensite finish transformation temperature and other key transformation temperatures of a full martensitic structure are obtained, and 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 high-strength steel plate are guided to be optimized based on a physicochemical test and a data simulation process.
(ii) And obtaining optimized quenching process parameters of the steel plate by using a numerical simulation method, wherein the process parameters are used for converting the steel plate into a full martensitic structure, namely obtaining the parameters such as water spraying flow, water spraying pressure and the like, wherein the minimum cooling speed of the steel plate is larger than the minimum cooling speed of the full martensitic structure.
(iii) And (3) 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 clamp quenching treatment in step (c) comprises: the clamped steel plate is quenched at a water spray flow rate and a water spray pressure corresponding to a minimum cooling rate greater than the martensitic structure, and cooled to a temperature T4 lower than the martensite finish transition temperature. The temperature T4 is preferably at least 50-80 ℃ below the martensite finish transition 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 transition temperature.
In a preferred embodiment, the annealing in step (a) comprises: the steel sheet is heated to a temperature T1 above the austenite finish transformation temperature for a holding time T1 and then cooled to a temperature T2 below the bainite start transformation temperature. The temperature T1 is preferably 80-100deg.C above the austenite finish transition temperature, such as 80 ℃, 85 ℃, 90 ℃, 95 ℃, or 100 ℃, etc.; the time t1 is preferably 1.5 to 5 times the millimeter thickness of the steel plate, and it is noted that the time t1 is made in 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 c below the bainite start transition temperature, such as 80 c, 85 c, 90 c, 95 c or 100 c, etc.
In a preferred embodiment, the operation of the austenitizing treatment in step (b) comprises: the steel sheet is heated to a temperature T3 above the austenite finish transition temperature for a hold time T2. The temperature T3 is preferably 30-80 ℃ higher than the austenite finish transition temperature, for example 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 treatment in step (d) comprises: heating the steel plate to 180-680 ℃, and preserving heat 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 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:
in the first stage, process optimization is simulated based on physicochemical tests and data:
step 1, isothermal transformation curves and continuous cooling transformation curves of materials corresponding to low-carbon low-alloy high-strength steel plates are obtained; guiding to optimize 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 precise control shape control (second stage) of the high-strength steel sheet based on physical and chemical tests and data simulation technology.
Step 2, obtaining optimized quenching process 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 precise control shape control (second stage) of the high-strength steel sheet can be guided to be optimized based on physical and chemical tests and a data simulation process.
Step 3, determining the deformation force evolution process of the steel plate in the quenching process by using a numerical simulation method;
and 4, based on the step 3, combining a steel plate quenching cooling theory and an acting force and reaction force theory to obtain an optimal value of the clamping force of the low-carbon low-alloy high-strength sheet. The optimization design of the clamping force in the step (c) in the precise control shape control (second stage) of the high-strength steel sheet based on the physicochemical test and data simulation process can be guided.
And in the second stage, the high-strength steel sheet is subjected to variable-pressure clamping and quenching treatment:
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 to a certain temperature T2 along with a furnace, and discharging and cooling;
step (b), performing austenitizing treatment, namely heating the steel plate to a certain temperature T3 and preserving heat for a period of time T2;
step (c), clamping and quenching treatment, namely rapidly transferring the steel plate into 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 optimization (the first stage) of a physicochemical experiment and numerical simulation process, so that the steel plate can be completely converted into martensite in the clamping quenching treatment process of the step (c), and large quenching distortion caused by large stress generated by excessive cooling speed can be avoided; the clamping force applied to the steel plate by the quenching equipment is determined and designed according to the steps 3 and 4 based on physicochemical experiment and numerical simulation process optimization (first stage), and the optimized variable-pressure clamping mode is designed, so that the steel plate is limited to deform and can freely stretch in the clamping quenching treatment process of the step (c).
And (d) tempering, namely heating the steel plate to a certain temperature and preserving heat for a period of time t3, so that the steel plate obtains better combination property matching of toughness.
In the method provided by the invention, the quenching process parameters in the clamping quenching treatment can regulate and control the structure/performance of the steel plate, so that the low-carbon low-alloy thin steel plate is integrally quenched into high-strength martensite. The clamping force is changed, so that the problems of large heat treatment deformation, surface indentation, scratch and the like of the steel plate in the quenching process can be prevented.
The invention also provides the low-carbon low-alloy high-strength steel sheet prepared by the method, and the steel sheet has excellent performance and appearance.
The invention is further illustrated by the following examples. The materials in the examples were prepared according to the existing methods or were directly commercially available unless otherwise specified.
Examples
The dimensions of the low-carbon low-alloy steel sheet are shown in FIG. 1, and the steel sheet is 12000mm long, 2000mm wide and 10mm thick. The chemical compositions of the steel sheets are shown in Table 1.
TABLE 1 chemical composition (weight fraction, wt%) of low carbon low alloy steel sheet
| 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 simulation comprises the following steps:
step 1, obtaining a continuous cooling transition curve (figure 4) and an isothermal transition curve (figure 5) of a low-carbon low-alloy high-strength steel plate material through a physicochemical experiment; thus, the austenitic steel sheet material can be obtainedThe volume end transformation temperature is 820 ℃, the bainite start transformation temperature is 500 ℃, the martensite start transformation temperature is 340 ℃, the martensite end transformation temperature is 200 ℃, and the minimum cooling speed V of the full martensitic structure is obtained Temporary face (L) 40 ℃/s.
Step 2, obtaining optimized quenching process 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: quenching flow rate is 5L/m 2 * s, the quenching pressure is 0.2MPa; the quenching process scheme II is as follows: quenching flow rate is 10L/m 2 * s, the quenching pressure is 0.2MPa; and a quenching process scheme III: quenching flow is 15L/m 2 * s, the quenching pressure is 0.2MPa. The temperature change curve of the core part of the steel plate with time under different quenching process schemes is shown in fig. 6.
As can be seen from the above, the quenching process scheme is 5L/m 2 * s, the cooling rate of the core of the steel sheet is about 25 ℃ per second, which is less than the minimum cooling rate V for the continuous cooling transition curve in step 1 to obtain a fully martensitic structure Temporary face (L) 40 ℃/s, so that the steel plate cannot obtain the required martensitic structure under the quenching process condition; the quenching process scheme is 10L/m 2 * s, the cooling rate of the core of the steel sheet is about 48 ℃/s, which is slightly greater than the minimum cooling rate V for the continuous cooling transition curve in step 1 to achieve a fully martensitic structure Temporary face (L) 40 ℃/s, so that the steel plate can obtain the required martensitic structure under the process condition; the quenching process scheme is 20L/m 2 * s, the cooling rate of the core of the steel sheet is about 98 ℃/s, which is greater than the minimum cooling rate V for the continuous cooling transition curve in step 1 to obtain a fully martensitic structure Temporary face (L) At 40 deg.c/s, the steel sheet may obtain a desired martensitic structure under the process conditions. In combination with actual production, in order to save quenching water and facilitate the operation of the quenching process, a quenching process scheme II is selected in the quenching process, and the quenching flow is 10L/m 2 * s, the quenching pressure is 0.2MPa.
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 fig. 7. The maximum deformation force in quenching is 158KN, and the deformation force is continuously changed.
And 4, on the basis of the step 3, combining the quenching theory of the steel plate and the principle of acting force and reaction force, obtaining the optimal value of the clamping force of the low-carbon low-alloy high-strength thin plate, wherein the optimal value is shown in fig. 8 (the maximum value of deformation force in the three states of austenite, austenite transformation martensite and martensite), the clamping force is increased to 70KN in 0s to 1s, the clamping force is kept to 70KN in 1s to 5s, the clamping force is increased to 158KN in 5s to 10s, the clamping force is kept to 158KN in 10s to 16s, the clamping force is reduced to 90KN in 16s to 20s, and the clamping force is kept to 90KN in 20s to 30 s.
The high-strength steel sheet pressure-swing-clamping quenching process (second stage) includes the steps of:
step (a), annealing treatment, namely heating the steel plate to 900 ℃ and preserving heat for 30min, and then cooling to 400 ℃ along with a furnace, and discharging and cooling;
step (b), carrying out austenitizing treatment, namely heating the steel plate to a certain temperature of 860 ℃ and preserving heat for 18min;
step (c), clamping and quenching treatment, namely rapidly transferring the steel plate into quenching equipment, wherein the quenching equipment clamps the steel plate, and the set clamping force is as follows: increasing the clamping force to 70KN within 0s to 1s, maintaining the clamping force to 70KN within 1s to 5s, increasing the clamping force to 158KN within 5s to 10s, maintaining the clamping force to 158KN within 10s to 16s, decreasing the clamping force to 90KN within 16s to 20s, and maintaining the clamping force to 90KN within 20s to 30 s; starting the spray system (quenching flow 10L/m) 2 * s, quenching pressure is 0.2 MPa) cooling the steel plate with water for 30s, and cooling the steel plate to 30 ℃;
and (d) tempering, namely heating the steel plate to 200 ℃ and preserving heat for 200min.
Through detection, the obtained steel plate has small deformation, the maximum is 10mm, the surface has no obvious defects such as indentation and the like, as shown in fig. 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 steel plate is realized.
Comparative example 1
The procedure is described in reference to examples (step (a) -stepd) Wherein, except that the steel sheet is free quenched in step (c), specifically at a quenching flow of 10L/m 2 * And (3) carrying out free quenching under the quenching process condition that the quenching pressure is 0.2MPa, wherein the steel plate quenching numerical simulation and the actual heat treatment steel plate are shown in figure 2. Therefore, under the quenching process, the steel plate is obviously deformed, and the use requirement cannot be met.
Comparative example 2
With the steel sheet as in the examples, the operation flow was carried out with reference to the examples (steps (a) - (d)), except that the steel sheet was subjected to constant clamp quenching in step c at a quenching flow rate of 10L/m 2 * And s, carrying out constant clamping quenching under the quenching process conditions that the quenching pressure is 0.2MPa and the constant clamping force in the quenching process is 158000N, wherein the steel plate quenching numerical simulation and the actual heat treatment 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 affected, and the use requirement is not met.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (9)
1. The accurate heat treatment method of the low-carbon low-alloy high-strength thin steel plate is characterized by comprising the following steps of:
step (a) of annealing treatment to transform the structure of the steel sheet into ferrite and pearlite structures;
a step (b) of austenitizing the ferrite and pearlite structure in the step (a) into an austenite structure;
a step (c) of a clamp quenching treatment of transforming the austenite structure in the step (b) into a martensite structure, wherein a clamp force of the steel sheet is varied;
a tempering treatment of step (d) for transforming the martensitic structure in step (c) into a tempered martensitic structure;
in the step (c) of the clamp quenching treatment, the application of the clamp force is divided into the following stages (1) to (3):
stage (1) is a preliminary shaping stage: the steel plate in the stage is processed in an austenite supercooling region, has low strength and good plasticity, only generates thermal stress, and the clamping force is the maximum value of deformation force in the austenite structure stage;
the stage (2) is a cooling shape control stage: the steel plate structure is transformed from austenite to martensite, the strength of the steel plate is increased, and meanwhile, the structural stress and the thermal stress are generated, and the clamping force is the maximum value of the deformation force of the austenite transformation martensite phase;
stage (3) is a dimensionally stable stage: the steel plate structure at the stage is martensitic, the steel plate strength is high, but the temperature difference exists between the inside and the outside of the steel plate, the steel plate is continuously cooled to generate thermal stress, and the clamping force is the maximum value of deformation force at the martensitic structure stage;
the deformation force is determined by the deformation force evolution process of the steel plate in the quenching process;
the step (c) of the clamp quenching treatment includes: the clamped steel plate is quenched at a water spray flow rate and a water spray pressure corresponding to a minimum cooling rate greater than the martensitic structure, and cooled to a temperature T4 lower than the martensite finish transition temperature.
2. The precision heat treatment method according to claim 1, wherein,
the temperature T4 is 50 ℃ below the martensite finish transition temperature.
3. The precision heat treatment method according to claim 1, wherein the annealing treatment in step (a) comprises: the steel sheet is heated to a temperature T1 above the austenite finish transformation temperature for a holding time T1 and then cooled to a temperature T2 below the bainite start transformation temperature.
4. A precision heat treatment method according to claim 3, wherein the temperature T1 is 80-100 ℃ higher than the austenite finish transition temperature, and the time T1 is 1.5-5 times the millimeter thickness of the steel sheet;
the temperature T2 is 80 ℃ below the bainite starting transition temperature.
5. The precision heat treatment method according to claim 1, wherein the operation of the austenitizing treatment in step (b) comprises: the steel sheet is heated to a temperature T3 above the austenite finish transition temperature for a hold time T2.
6. The precision heat treatment method according to claim 5, wherein the temperature T3 is 30-80 ℃ higher than the austenite finish transition temperature, and the time T2 is 1.5-2 times the millimeter thickness of the steel sheet.
7. The precision heat treatment method according to claim 1, wherein the tempering treatment in step (d) comprises: heating the steel plate to 180-680 ℃, and preserving heat for a time t3, wherein the time t3 is 10-30 times of the millimeter thickness of the steel plate.
8. The precision heat treatment method according to any one of claims 1 to 7, further comprising the step of detecting an isothermal transformation curve and a continuous cooling transformation curve of the steel sheet before the step (a).
9. The low-carbon low-alloy high-strength steel sheet manufactured by the precise heat treatment method according to any one of claims 1 to 8.
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