Method for realizing accurate control on structure evolution of high-strength steel based on controllable cooling

Abstract

The invention discloses a method for realizing accurate control of structure evolution of high-strength steel based on controllable cooling, relates to the technical field of structure evolution regulation and phase change regulation of metal materials, and aims to solve the problems of narrow process window, easiness in cracking, non-uniform structure property and the like of a traditional quenching process of 22MnB5 steel. Continuous in-situ observation from melt solidification to phase change ending is achieved for the first time, and the regulation and control rule of the cooling rate on the structure type is defined by combining microstructure correlation analysis at different cooling rates of 1-30 DEG C / s; meanwhile, the starting and ending temperature and time of delta-gamma, gamma-alpha or martensite phase transformation are accurately determined by combining DSC thermal analysis with microscopic image contrast, and the error caused by the fact that a traditional CCT curve depends on experience derivation is overcome; according to the technology, the structure stability and performance reliability of the 22MnB5 steel are improved, and the technology can be popularized to high-strength steel systems with the liquid-solid-solid transformation characteristic such as hot forming steel and die steel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material organization evolution regulation and phase change regulation, and particularly relates to a method for realizing accurate regulation of microstructure of high-strength steel, especially 22MnB5 high-strength steel, by precisely controlling continuous cooling rate. The method can be widely applied to organization regulation and performance optimization of hot forming steel, and is particularly suitable for optimization of microstructure and improvement of comprehensive performance in hot stamping process of automobile safety structural parts. BACKGROUND

[0002] With the increasing demand for light weight and high strength of automobiles, 22MnB5 steel is increasingly widely used in the automobile industry due to its excellent hot formability and high strength performance. However, the current organization regulation method of 22MnB5 steel mostly adopts traditional quenching process, which has the defects of narrow process window, easy cracking, and uneven organization performance. More importantly, the existing research method focuses on static analysis of the final organization morphology, and lacks real-time observation and regulation analysis from liquid solidification to room temperature, which is difficult to meet the high requirements of material consistency for high-precision industrial production.

[0003] To solve the above technical problems, it is urgent to develop an accurate control technology based on cooling rate to realize a real-time organization regulation method of 22MnB5 steel from liquid state to room temperature, which can not only improve the organization stability and performance reliability of the material, but also help to provide effective protection for industrial production, and has important significance for promoting the technical upgrading of automobile steel. SUMMARY

[0004] The purpose of the application is to overcome the shortcomings of the prior art, and to provide a method for accurately regulating the organization structure of high-strength steel, especially 22MnB5 high-strength steel, by precisely controlling the continuous cooling rate, so as to solve the problem of difficult accurate control of organization performance in the existing process, and significantly improve the performance stability and consistency of hot stamping parts.

[0005] To achieve the above purpose, the technical solution provided by the application is as follows:

[0006] A method for accurately controlling the organization evolution of high-strength steel based on controllable cooling, comprising the following steps:

[0007] Step S1, sample preparation: Select industrial grade 22MnB5 steel as raw material, the chemical composition (mass percent) is: C: 0.20-0.27%, Mn: 1.10-1.40%, Si: 0.15-0.35%, Cr: 0.20-0.25%, Ti: 0.010-0.045%, B: 0.0005-0.003%, P: ≤0.02%, S: ≤0.007%, the rest is iron (Fe); Then use electric spark wire cutting to process the steel sample into a cylinder with a diameter of 3-6mm and a height of 2-4mm; Then use 400#-1500# sandpaper to polish, and then use diamond polishing liquid on the polishing machine to polish, finally into a mirror surface, then put into anhydrous ethanol for cleaning, and put into paraffin oil for preservation;

[0008] Step S2, sample installation and atmosphere replacement: the sample taken out from the paraffin oil is first immersed in anhydrous ethanol for cleaning, and the surface residues are removed, and a dust-free cloth is used to wipe dry; Then the sample is transferred to an Al2O3 ceramic crucible, and is fixed in the internal furnace cavity of a high-temperature laser confocal scanning microscope (HT-CLSM) system, to ensure that the sample is coaxially aligned with the laser light path and the optical observation window; Before the experiment, the HT-CLSM furnace cavity needs to be subjected to atmosphere replacement treatment; High-purity argon gas (purity ≥99.999%, flow rate 500sccm) is introduced into the system, and at least three rounds of charging and replacement procedures are performed;

[0009] Step S3, melting and heating treatment: after completing the sample installation and atmosphere replacement, the heating program of the HT-CLSM system is started, and the sample is heated in stages according to the following steps:

[0010] S31, heat from room temperature to 200℃ at a heating rate of 50℃ / min, slowly preheat and remove surface adsorbed water, and stabilize the furnace cavity thermal field; Then increase the heating rate to 200℃ / min, and heat quickly to 1300℃;

[0011] S32, continue to heat at a heating rate of 100℃ / min to 1540-1560℃, which is higher than the liquidus temperature of 22MnB5 steel;

[0012] S33, keep the temperature at this high temperature for 30-50 seconds, to ensure that the melt is fully stable, and to provide a repeatable initial state for subsequent cooling treatment;

[0013] Step S4, cooling treatment: after the sample is heated to a completely molten state, the cooling system of the high-temperature laser confocal scanning microscope (HT-CLSM) device is accurately controlled by a computer program, so that the sample realizes continuous controlled cooling; The cooling rate ranges from 1 to 40℃ / s, which is suitable for microstructure regulation under different requirements.

[0014] Preferably, the 22MnB5 steel sample selected in the step S1 has a chemical composition adjusted according to a specific processing process, wherein the content of C is preferably 0.20-0.27%, the content of Mn is preferably 1.10-1.40%, and the content of B is preferably 0.0005-0.003%, so as to balance the hardenability and crack resistance.

[0015] Preferably, the polishing treatment of the sample in the step S1 can be performed by using sandpaper with a mesh size of 400-1500, and the surface roughness is controlled to be less than 0.05 μm after polishing, so as to ensure that the subsequent high-temperature observation image is clear.

[0016] Preferably, in the step S2, the crucible is made of Al2O3 to ensure high-temperature stability and no reaction with the steel sample; and the argon replacement time is not less than 3 minutes per round.

[0017] Preferably, the melting and holding time in the step S3 can be adjusted according to the size of the sample, and is selected in the range of 30-60 seconds, so as to ensure that the melt is fully uniform.

[0018] Preferably, in the step S4, the cooling rate range can be further expanded to 1-40 ℃ / s to adapt to the regulation and control requirements of different phase transition behaviors.

[0019] Compared with the prior art, the present application has the following beneficial effects

[0020] The whole process of microstructure evolution starting from the melt state is observed in situ: the present application realizes continuous real-time observation of the whole process from melting to solidification to phase transition through a laser confocal microscopic system.

[0021] The clear correlation between the cooling rate and the microstructure regulation and control is established: under different cooling rates (1-30 ℃ / s), the 22MnB5 steel shows obviously different microstructure types (such as ferrite, upper bainite, lower bainite, and martensite), which provides a reliable reference for regulating the final microstructure.

[0022] The accuracy of the phase transition behavior determination is improved: combined with DSC thermal analysis (attached Figure 2 ) and microscopic image (attached Figure 6 to attached Figure 9 ) verification, the phase transition start and end time and temperature of δ→γ, γ→α or martensite are accurately determined, and the error problem of the traditional CCT curve depending on empirical derivation is overcome.

[0023] The present application has high universality and engineering expandability: the present application is not only suitable for 22MnB5 steel, but also suitable for other high-strength steel systems with liquid-solid-solid transformation characteristics, and can be widely used in the fields of hot forming steel, die steel, low-alloy high-strength steel, etc. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 for the method flowchart of the present application;

[0025] Figure 2 for the DSC thermal analysis diagram of 22MnB5 steel;

[0026] Figure 3 for the EBSD grain boundary distribution diagram and KAM diagram of different cooling rates;

[0027] Figure 4 for the Vickers hardness diagram of the sample after cooling at different cooling rates;

[0028] Figure 5 for the nanoindentation load-displacement curve of the sample after cooling at different cooling rates;

[0029] Figure 6 for the high-temperature confocal micrograph of ferrite;

[0030] Figure 7 for the high-temperature confocal micrograph of upper bainite;

[0031] Figure 8 for the high-temperature confocal micrograph of lower bainite;

[0032] Figure 9 for the high-temperature confocal micrograph of martensite structure.

[0033] Figure 3 Middle: (a1, b1, c1, d1) grain boundary diagram, (a2, b2, c2, d2) grain average orientation difference (KAM) diagram DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the preferred embodiments of the present application, not all. Based on the embodiments in the present application, other embodiments obtained by those of ordinary skill in the art without creative labor should be considered to fall within the protection scope of the present application.

[0035] The present application provides a method for precise regulation of continuous cooling structure of 22MnB5 high-strength steel, which comprises the following steps:

[0036] Step S1, sample preparation:

[0037] Select industrial-grade 22MnB5 steel as raw material, and the chemical composition (mass percent) is:

[0038] C: 0.20-0.27%, Mn: 1.10-1.40%, Si: 0.15-0.35%, Cr: 0.20-0.25%, Ti: 0.010-0.045%, B: 0.0005-0.003%, P: ≤0.02%, S: ≤0.007%, the rest is iron (Fe). Then the steel sample is processed into a cylinder with a diameter of 3-6 mm and a height of 2-4 mm by wire electrical discharge machining. Then it is polished by using 400-1500 mesh sandpaper, and then polished on a polishing machine by using diamond polishing liquid to finally form a mirror surface, and then placed in anhydrous ethanol for cleaning. To prevent surface oxidation, it is placed in paraffin oil for storage.

[0039] Step S2, sample installation and atmosphere replacement:

[0040] The sample taken out from the paraffin oil is first immersed in anhydrous ethanol for cleaning to remove surface residues, and then wiped dry with a dust-free cloth. Then, the sample is transferred to an Al2O3 ceramic crucible and fixed inside the furnace cavity of the high-temperature laser confocal scanning microscopy (HT-CLSM) system, ensuring that the sample is coaxially aligned with the laser light path and the optical observation window. To ensure the reducing environment during the high-temperature experiment and prevent oxidation interference, the HT-CLSM furnace cavity needs to be subjected to atmosphere replacement treatment before the experiment. High-purity argon gas (purity ≥ 99.999%, flow rate 500 sccm) is introduced into the system, and at least three rounds of charging and replacement procedures are performed to effectively remove residual air and oxygen and create a stable inert protective environment.

[0041] Step S3, melting and heating treatment:

[0042] After completing sample installation and atmosphere replacement, the heating program of the HT-CLSM system is started, and the sample is heated in stages as follows: first, heat from room temperature to 200°C at a heating rate of 50°C / min to achieve slow preheating of the sample, remove surface adsorbed water, and stabilize the furnace cavity thermal field; then increase the heating rate to 200°C / min and quickly heat to 1300°C; then continue to heat at a heating rate of 100°C / min to 1540-1560°C, which is higher than the liquidus temperature of 22MnB5 steel, to ensure complete melting of the sample; keep the temperature at this high temperature for 30-50 seconds to ensure that the melt is fully stable and provide a repeatable initial state for subsequent cooling treatment.

[0043] Step S4, cooling treatment:

[0044] After the sample is heated to a completely molten state, the cooling system of the high-temperature laser confocal scanning microscope (HT-CLSM) device is precisely controlled by a computer program to achieve continuous controlled cooling of the sample.

[0045] The present application is described below by means of specific examples, which should not be interpreted as limiting the scope of the present application in any way. In addition, in the following examples, unless otherwise specified, the reagents or instruments used are conventional products that can be obtained commercially. The units used in the specification are international standard units, and the values and value ranges appearing in the present application should be understood to include systematic errors that are unavoidable in industrial production. If the specific processing conditions and methods are not explicitly described in the following examples, the conditions and methods known in the art can be used for processing.

[0046] Example 1

[0047] (1) Sample preparation: Select industrial grade 22MnB5 steel as raw material, the chemical composition (mass percentage) is: C 0.217%, Mn 1.224%, Si 0.24%, B 0.003%, Cr 0.232%, Ti 0.041%, P: ≤0.02%, S: ≤0.007%, the rest is Fe. The steel sample is processed into a cylinder with a diameter of 5 mm and a height of 3 mm by wire electrical discharge machining. Then polish it with 400#-1500# sandpaper, and then polish it with diamond polishing liquid, and then put it into anhydrous ethanol for cleaning. To prevent surface oxidation, put it into paraffin oil for storage.

[0048] (2) Sample installation and atmosphere replacement: The sample obtained in step (1) is first soaked and cleaned in anhydrous ethanol to remove surface residues, and then wiped dry with a dust-free cloth. Then transfer the sample to an Al2O3 ceramic crucible and fix it inside the furnace cavity of the high-temperature laser confocal scanning microscopy system (HT-CLSM), ensuring that the sample is coaxially aligned with the laser light path and the optical observation window. Perform atmosphere replacement on the HT-CLSM furnace cavity. Introduce high-purity argon (purity ≥ 99.999%, flow rate 500 sccm) into the system and perform at least three rounds of charge and replacement procedures.

[0049] (3) Melting and heating: After completing sample installation and atmosphere replacement, start the heating program of the HT-CLSM system and heat the sample in stages as follows: first heat from room temperature to 200°C at a rate of 50°C / min; then increase the heating rate to 200°C / min and rapidly heat to 1300°C; then continue to heat at a rate of 100°C / min to 1540-1560°C, which is higher than the liquidus temperature of 22MnB5 steel, to ensure complete melting of the sample; keep the temperature at this high temperature for 30 seconds to ensure that the melt is fully stable.

[0050] (4) Cooling treatment: After the sample is heated to a completely molten state, the cooling system of the high temperature laser confocal scanning microscope (HT-CLSM) device is precisely controlled by a computer program to cool the sample at a cooling rate of 1℃ / s.

[0051] As attached Figure 6 As shown, the morphology of strip-shaped ferrite can be clearly observed in the sample obtained at a cooling rate of 1℃ / s, and this was verified by measuring its Vickers hardness, with a result of 250 HV (see appendix). Figure 4 ), exhibiting low intensity, electron backscatter diffraction (EBSD) (attached) Figure 3 Analysis of the grain morphology revealed a large average grain size and dispersed microstructure orientation. In this embodiment, a diamond pyramidal indenter with a maximum loading force of 50 mN was used to apply in-situ loading to the sample, and the relationship between the nanoindentation load and the indentation depth was recorded (see attached curve). Figure 5 a) The curve rises gently overall, with a large indentation depth, indicating that the material has weak local resistance to deformation and exhibits typical soft ferrite-dominated microstructure characteristics.

[0052] Example 2

[0053] (1) Sample preparation: Industrial grade 22MnB5 steel was selected as the raw material. The chemical composition (mass percentage) was: C 0.217%, Mn 1.224%, Si 0.24%, B 0.003%, Cr 0.232%, Ti 0.041%, P: ≤0.02%, S: ≤0.007%, and the remainder was Fe. The steel sample was then processed into a cylinder with a diameter of 5 mm and a height of 3 mm using wire EDM. It was then polished with 400#-1500# sandpaper, followed by polishing with diamond polishing liquid, and then cleaned in anhydrous ethanol. To prevent surface oxidation, it was stored in paraffin oil.

[0054] (2) Sample installation and atmosphere replacement: The sample obtained in step (1) was first immersed in anhydrous ethanol to remove surface residues and then wiped dry with a lint-free cloth. The sample was then transferred to an Al2O3 ceramic crucible and fixed inside the high-temperature laser confocal scanning microscopy (HT-CLSM) furnace cavity, ensuring that the sample, laser path, and optical observation window remained coaxially aligned. Atmosphere replacement was then performed on the HT-CLSM furnace cavity. High-purity argon gas (purity ≥99.999%, flow rate 500 sccm) was introduced into the system, and at least three cycles of purging and replacement were performed.

[0055] (3) Melting heating: After the sample installation and atmosphere replacement are completed, the heating program of the HT-CLSM system is started, and the sample is subjected to staged heating according to the following steps: first, heating from room temperature to 200°C at a temperature increasing rate of 50°C / min; then, increasing the temperature increasing rate to 200°C / min, rapidly heating to 1300°C; then, continuing to heat to 1540-1560°C at a temperature increasing rate of 100°C / min, which is higher than the liquidus temperature of the 22MnB5 steel, to ensure that the sample is completely melted; and keeping the temperature at the high temperature for 30 seconds to ensure that the melt is fully stable.

[0056] (4) Cooling treatment: after the sample is heated to a completely melted state, the cooling system of the high-temperature laser confocal scanning microscope (HT-CLSM) device is accurately controlled by a computer program, so that the sample is cooled at a cooling rate of 7°C / s.

[0057] As shown in FIG. 6, the morphology of upper bainite can be clearly observed in the sample obtained at a cooling rate of 7°C / s, and verified by measuring the Vickers hardness, the obtained result is about 360HV (see FIG. 7), and the EBSD (FIG. 8) result shows that the degree of grain refinement is significantly improved, and the proportion of high-angle grain boundaries is increased. In this embodiment, a diamond pyramid indenter with a maximum load of 50mN is used to load the sample in situ, and the relationship curve between the nanoindentation load and the indentation depth is recorded (FIG. 9). Figure 7 Figure 4 As shown in FIG. 6, the morphology of upper bainite can be clearly observed in the sample obtained at a cooling rate of 7°C / s, and verified by measuring the Vickers hardness, the obtained result is about 360HV (see FIG. 7), and the EBSD (FIG. 8) result shows that the degree of grain refinement is significantly improved, and the proportion of high-angle grain boundaries is increased. In this embodiment, a diamond pyramid indenter with a maximum load of 50mN is used to load the sample in situ, and the relationship curve between the nanoindentation load and the indentation depth is recorded (FIG. 9). Figure 3 Figure 5 As shown in FIG. 6, the morphology of upper bainite can be clearly observed in the sample obtained at a cooling rate of 7°C / s, and verified by measuring the Vickers hardness, the obtained result is about 360HV (see FIG. 7), and the EBSD (FIG. 8) result shows that the degree of grain refinement is significantly improved, and the proportion of high-angle grain boundaries is increased. In this embodiment, a diamond pyramid indenter with a maximum load of 50mN is used to load the sample in situ, and the relationship curve between the nanoindentation load and the indentation depth is recorded (FIG. 9).

[0058] Example 3

[0059] (1) Sample preparation: an industrial grade 22MnB5 steel is selected as the raw material, and the chemical composition (mass percentage) is: C 0.217%, Mn 1.224%, Si 0.24%, B 0.003%, Cr 0.232%, Ti 0.041%, P: ≤0.02%, S: ≤0.007%, and the rest is Fe. Then, the steel sample is processed into a cylinder with a diameter of 5mm and a height of 3mm by using electric spark wire cutting. Then, the sample is polished by using 400-1500 mesh sandpaper, and then polished by using diamond polishing liquid, and then cleaned in anhydrous ethanol. In order to prevent surface oxidation, the sample is stored in paraffin oil.

[0060] ​​(2) Sample installation and atmosphere replacement: The sample obtained in step (1) was first immersed in anhydrous ethanol to remove surface residues and then wiped dry with a lint-free cloth. Afterward, the sample was transferred to an Al2O3 ceramic crucible and fixed inside the high-temperature laser confocal scanning microscopy (HT-CLSM) furnace cavity, ensuring that the sample, laser path, and optical observation window remained coaxially aligned. Atmosphere replacement was then performed on the HT-CLSM furnace cavity. High-purity argon gas (purity ≥99.999%, flow rate 500 sccm) was introduced into the system, and at least three cycles of purging and replacement were performed.

[0061] (3) Melting and heating: After the sample installation and atmosphere replacement are completed, the heating program of the HT-CLSM system is started, and the sample is heated in stages according to the following steps: First, the sample is heated from room temperature to 200℃ at a heating rate of 50℃ / min; then the heating rate is increased to 200℃ / min and rapidly heated to 1300℃; then the sample is heated to 1540–1560℃ at a heating rate of 100℃ / min, which is higher than the liquidus temperature of 22MnB5 steel, to ensure that the sample is completely melted; the sample is held at this high temperature for 30 seconds to ensure that the melt is sufficiently stable and to provide a repeatable initial state for subsequent cooling treatment.

[0062] (4) Cooling treatment: The cooling system of the high temperature laser confocal scanning microscope (HT-CLSM) is precisely controlled by a computer program to cool the sample at a cooling rate of 15℃ / s.

[0063] As attached Figure 8 As shown, the morphology of lower bainite can be clearly observed in the sample obtained at a cooling rate of 15℃ / s, and this is verified by measuring its Vickers hardness, with a result of approximately 460 HV (see appendix). Figure 4 This falls within the medium-to-high strength range and is suitable for manufacturing high-strength, long-fatigue-life components. EBSD (with attached) Figure 3 The analysis results showed further grain refinement and a dense, uniform microstructure. In this embodiment, a diamond pyramidal indenter with a maximum loading force of 50 mN was used to perform in-situ loading on the sample, and the relationship curve between the nanoindentation load and the indentation depth was recorded (see attached figure). Figure 5 c): It can be clearly seen that the load increases rapidly and the displacement depth decreases. This is because the microstructure is mainly bainite, which has better resistance to indentation.

[0064] Example 4

[0065] (1) Sample preparation: Selecting industrial grade 22MnB5 steel as raw material, the chemical composition (mass percent) is: C 0.217%, Mn 1.224%, Si 0.24%, B 0.003%, Cr 0.232%, Ti 0.041%, P: ≤0.02%, S: ≤0.007%, the rest is Fe. Then use wire electrical discharge machining to process the steel sample into a cylinder with a diameter of 5 mm and a height of 3 mm. Then use 400#-1500# sandpaper to polish, then use diamond polishing liquid to polish, then put it into anhydrous ethanol for cleaning, to prevent surface oxidation, put it into paraffin oil for preservation.

[0066] (2) Sample installation and atmosphere replacement: The sample obtained in step (1) is first immersed in anhydrous ethanol for cleaning to remove surface residues, and then dried with a dust-free cloth. Then, the sample is transferred to an Al2O3 ceramic crucible and fixed inside the furnace cavity of the high-temperature laser confocal scanning microscopy (HT-CLSM) system, ensuring that the sample is coaxially aligned with the laser light path and the optical observation window. The HT-CLSM furnace cavity is subjected to atmosphere replacement treatment. High-purity argon gas (purity ≥ 99.999%, flow rate 500 sccm) is introduced into the system, and at least three rounds of charging and replacement procedures are performed.

[0067] (3) Melting and heating: Start the heating program of the HT-CLSM system and heat the sample in stages as follows: first heat from room temperature to 200°C at a rate of 50°C / min; then increase the heating rate to 200°C / min and quickly heat to 1300°C; then continue to heat at a rate of 100°C / min to 1540-1560°C, which is higher than the liquidus temperature of 22MnB5 steel, to ensure complete melting of the sample; keep the temperature at this high temperature for 30 seconds to ensure that the melt is fully stable and provide a reproducible initial state for subsequent cooling treatment.

[0068] (4) Cooling treatment: After heating the sample to a completely molten state, the cooling system of the high-temperature laser confocal scanning microscope (HT-CLSM) device is precisely controlled by computer program to cool the sample at a cooling rate of 30°C / s.

[0069] As shown in FIG. 1, the morphology of lath-shaped martensite can be clearly observed in the sample obtained at a cooling rate of 30°C / s, and the results exceed 570HV (see FIG. 2), showing excellent strength performance, suitable for manufacturing high safety automobile structural parts. Figure 8 Figure 4 As shown in FIG. 1, the morphology of lath-shaped martensite can be clearly observed in the sample obtained at a cooling rate of 30°C / s, and the results exceed 570HV (see FIG. 2), showing excellent strength performance, suitable for manufacturing high safety automobile structural parts. Figure 3 ​) analysis shows that the grain is very fine, the grain boundary distribution is dense, and the orientation is relatively dispersed, showing the characteristics of rapid non-equilibrium solidification. In this embodiment, the diamond triangular pyramid indenter with a maximum loading force of 50 mN is used to load the sample in situ, and the relationship curve between the nanoindentation load and the indentation depth is recorded (Fig. 6 Figure 5 d) Compared with examples 1, 2 and 3, the indentation depth of example 4 is the smallest, and the curve slope is the largest, the main reason is that the structure is mainly lath martensite with high strength, which gives the material the strongest local hardness and load bearing capacity.

[0070] Through the system verification of the above embodiments, the method of the present application can accurately and effectively realize the microstructure regulation of high-strength steel, especially 22MnB5 steel, and improve the overall performance stability of the material, which has important industrial application value.

[0071] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for precisely controlling the microstructure evolution of high-strength steel based on controllable cooling, characterized in that: Comprising the following steps: Step S1, sample preparation: select industrial grade 22MnB5 steel as raw material, the chemical composition (mass percent) is: C: 0.20-0.27%, Mn: 1.10-1.40%, Si: 0.15-0.35%, Cr: 0.20-0.25%, Ti: 0.010-0.045%, B: 0.0005-0.003%, P: ≤0.02%, S: ≤0.007%, the rest is iron (Fe); then use electric spark wire cutting to process the steel sample into a cylinder with a diameter of 3-6mm and a height of 2-4mm; then use 400#-1500# sandpaper to polish, then use diamond polishing liquid on the polishing machine to polish, finally into a mirror surface, then put into anhydrous ethanol for cleaning, put into paraffin oil for preservation; Step S2, sample installation and atmosphere replacement: the sample taken out from the paraffin oil is first soaked and cleaned in anhydrous ethanol to remove surface residues, and then dried with a dust-free cloth; then the sample is transferred to an Al2O3 ceramic crucible and fixed inside the high-temperature laser confocal scanning microscopic system (HT-CLSM) furnace cavity, ensuring that the sample is coaxially aligned with the laser light path and the optical observation window; before the experiment, the HT-CLSM furnace cavity needs to be subjected to atmosphere replacement treatment; high-purity argon gas (purity ≥99.999%, flow rate 500sccm) is introduced into the system and at least three rounds of charging and replacement procedures are performed; Step S3, melting and heating treatment: after completing sample installation and atmosphere replacement, start the heating program of the HT-CLSM system and heat the sample in stages as follows: S31, heat from room temperature to 200℃ at a rate of 50℃ / min, slowly preheat and remove surface adsorbed moisture, stabilize the furnace cavity thermal field; then increase the heating rate to 200℃ / min, rapidly heat to 1300℃; S32, continue to heat at a rate of 100℃ / min to 1540-1560℃, which is higher than the liquidus temperature of 22MnB5 steel; S33, keep the temperature at this high temperature for 30-50 seconds to ensure that the melt is fully stable, providing a repeatable initial state for subsequent cooling treatment; Step S4, cooling treatment: after heating the sample to a completely molten state, the cooling system of the high-temperature laser confocal scanning microscope (HT-CLSM) device is precisely controlled by a computer program to achieve continuous controlled cooling of the sample; the cooling rate ranges from 1 to 40℃ / s, which is suitable for microstructure regulation under different requirements.

2. The method of claim 1, wherein the method is characterized by: The 22MnB5 steel sample selected in step S1 can have its chemical composition adjusted according to specific processing techniques, with the C content preferably being 0.20-0.27%, the Mn content preferably being 1.10-1.40%, and the mass fraction of B element preferably being 0.0005-0.003%.

3. The method of claim 1, wherein the method is characterized by: The sample polishing process in step S1 can use sandpaper with a mesh size of 400 to 1500, and each time the sandpaper is replaced, the direction is rotated by 90°, and the final surface roughness is controlled to be Ra<0.05μm.

4. The method of claim 1, wherein the method is characterized by: The crucible is made of Al2O3 material to ensure high temperature stability and no reaction with the steel sample; the argon replacement time is not less than 3 minutes per round.

5. The method of claim 1, wherein the method is characterized by: The melting and holding time in step S3 can be adjusted according to the sample size, and is selected in the range of 30-60 seconds.

6. The method of claim 1, wherein the method is characterized by: In step S4, the cooling rate range can be further expanded to 1-40 ℃ / s to meet the regulation requirements of different phase change behaviors.

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