A method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD

Abstract

This invention discloses a method for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD, relating to the field of high-strength steel phase transformation characterization technology. The method involves cutting the target steel into cylindrical samples; immersing the polished sample in an electrolyte for electrolytic polishing to remove the stress layer on the sample surface; placing the field of view of a high-temperature in-situ confocal laser microscope close to a specific region of a marked point and heating it; then performing electron backscatter diffraction observation on a specific region within the marked point of the sample after high-temperature in-situ confocal testing, observing the lath collision phenomenon; analyzing the bainitic lath collision behavior based on the electron backscatter data of the selected region combined with in-situ confocal morphology analysis; and employing phase-field simulation to simulate the growth and collision process of bainitic laths. This invention, by combining phase-field simulation and multiple microscopic characterization techniques, conducts a comprehensive study from microscopic to macroscopic levels, fully revealing the growth mechanism and collision behavior of bainitic laths.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel phase transformation characterization technology, specifically to a method for analyzing bainite lath collision behavior using high-temperature in-situ observation combined with EBSD. Background Technology

[0002] Under the national "dual carbon" goals, green and high-quality development has become the main theme of many industries. With the rapid development of the automotive industry, the contradiction between automobiles and the environment and energy is becoming increasingly prominent. While continuously improving vehicle safety, how to achieve lightweighting has become a crucial issue that the automotive industry must address. Advanced high-strength steel (AHSS), due to its combination of high strength, good plasticity, and high energy absorption capacity during collisions, has become the preferred material for lightweighting automobiles. Bainite, as a typical non-equilibrium phase transformation structure, possesses a better strength-toughness balance due to its high-density dislocations and multi-level microstructure, and has been widely used in the automotive, natural gas pipeline, and aerospace industries. Therefore, it is necessary to conduct in-depth research on the phase transformation behavior of bainite.

[0003] During the growth of bainite laths, an "interlocking structure" of lath interactions often forms. The growth of bainite laths is temporarily halted due to collisions / intersections with other laths, but new laths continue to grow after this brief pause. However, to date, different understandings of the bainite lath growth and impact mechanisms remain controversial, and the growth mechanism of new laths cannot be determined. Previous studies on bainite phase transformation in steel have mostly relied on traditional optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. These techniques cannot monitor bainite lath growth behavior in real time, and the lack of determination of crystallographic relationships of lath collision behavior and the establishment of key models hinders the observation and subsequent analysis of bainite lath collision behavior. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technologies, this invention provides a method for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD. This method combines phase-field simulation and various microscopic characterization techniques to conduct a comprehensive study from the microscopic to the macroscopic level, fully revealing the growth mechanism and collision behavior of bainitic laths. This invention not only overcomes the deficiencies of traditional research methods but also provides theoretical basis and technical support for the design and optimization of novel low-temperature bainitic steels, thereby improving the application performance of bainitic steels.

[0005] To achieve the above objectives, the first objective of this invention is to provide a method for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD, comprising the following steps:

[0006] Cut the target steel into cylindrical shapes;

[0007] The cylindrical sample is polished until the top and bottom surfaces are parallel and the surface is smooth and free of scratches, forming a mirror-like surface.

[0008] The polished sample is placed in an electrolyte for electrolytic polishing to remove the stress layer on the sample surface.

[0009] A diamond-shaped marking point was used to calibrate a specific area of ​​the electropolished sample using a microhardness tester.

[0010] The labeled sample was placed in the heating chamber of the in-situ confocal laser microscope, a vacuum was drawn, and helium gas was introduced.

[0011] The field of view of the in-situ confocal laser microscope is brought close to the specific area of ​​the marked point and heated. The temperature of the heating chamber is 950±5 ℃ and held for 5~10 min. After complete austenitization, the temperature is cooled to the bainite transformation temperature of 370~430 ℃ and held for 5~10 min. The growth morphology of bainite laths is observed and recorded in the bainite phase transformation range.

[0012] Electron backscatter diffraction observation was performed on a specific region within the marked point of the sample after in-situ confocal testing, where lath collisions were observed.

[0013] Based on electron backscattering data of the selected region and in-situ confocal morphology analysis, the collision behavior of bainite laths was analyzed, and the phase field simulation method was used to simulate the growth and collision process of bainite laths.

[0014] Preferably, the electrolyte is prepared by mixing 9-11% perchloric acid and alcohol by volume.

[0015] Preferably, during the electrolytic polishing process, the electrolytic voltage is 15 kV, the current is 0.5~0.6 A, the electrolyte temperature is controlled to be maintained at 0~5 ℃, and the electrolysis time is 10~12 s.

[0016] Preferably, the in-situ confocal laser microscope field of view is close to a specific area of ​​the marked point and is heated at a heating rate of 300 ℃ / min and a cooling rate of 600 ℃ / min. The observation is recorded by video recording and photography, with a shooting interval of 1 s.

[0017] Preferably, electron backscattering data analysis is performed using Aztec Crystal in conjunction with the MTEX ​​toolbox.

[0018] Preferably, during electron backscatter diffraction observation, the test voltage is 20 kV, the scan step is 0.08 μm, a 60 μm aperture is used, and the sample stage is tilted at 70°.

[0019] Preferably, during the polishing process, the sample surface is sequentially polished with 400-grit, 800-grit, 1200-grit, 1500-grit, 2000-grit, 3000-grit, and 5000-grit sandpaper, then water-polished with 2.5 μm polishing paste, and then rinsed and dried with water and alcohol in sequence; wherein, when polishing with sandpaper, the goal is to completely remove the polishing marks from the previous sandpaper polishing.

[0020] Preferably, the target steel has the following chemical composition by mass percentage: C: 0.19%, Mn: 3.09%, Si: 1.46%, V: ≤0.005%, S: ≤0.005%, with the balance being Fe and unavoidable impurities.

[0021] Preferably, the target steel is obtained according to the following steps:

[0022] Raw materials are melted in a vacuum according to a certain composition ratio to form ingots;

[0023] The ingot temperature is raised to 1150~1250 ℃ and maintained for 2~4 h to obtain a steel billet;

[0024] The steel billet is freely forged at around 1050~1200 ℃ to achieve a thickness of 40~60 mm, thus obtaining a cast billet.

[0025] The billet is held at 1050~1200 ℃ for 2~4 h, then hot rolled to 9~11 mm thick, and then air cooled to room temperature to form hot-rolled martensitic steel plate.

[0026] A is determined based on the phase diagram. c1 A c3 And Ms point, Bs point is calculated based on MUCGU3, and the cooling rate is determined;

[0027] Martensitic steel plates are processed into thermal expansion samples;

[0028] The thermally expanding sample is first heated to 900~1000 ℃ and held for 10~20 min, then cooled to room temperature to obtain the target steel.

[0029] The first objective of this invention is to provide an application of the above-described method in the analysis of bainitic lath collision behavior.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] This invention provides a method for analyzing the collision behavior of bainite laths using high-temperature in-situ observation combined with electron backscatter diffraction (EBSD). The invention aims to study the growth behavior of bainite laths by employing high-temperature in-situ confocal microscopy combined with electron backscatter diffraction (EBSD). This method overcomes the limitations of traditional optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in observing the microstructure after bainite phase transformation, and compensates for the inability to monitor bainite lath growth behavior in real time and determine crystallographic relationships. Furthermore, this invention introduces a phase-field simulation method to simulate the growth and collision processes of bainite laths, effectively describing the evolution of the microstructure and providing a deeper understanding of lath growth dynamics and phase transformation mechanisms.

[0032] By combining phase-field simulation and various microscopic characterization techniques, a comprehensive study from the microscopic to the macroscopic level is conducted to fully reveal the growth mechanism and collision behavior of bainitic laths. This invention not only overcomes the shortcomings of traditional research methods but also provides theoretical basis and technical support for the design and optimization of novel low-temperature bainitic steels, thereby improving the application performance of bainitic steels. Attached Figure Description

[0033] Figure 1 The following are the high-temperature in-situ confocal topography and corresponding EBSD orientation data in Example 1: where, ab) high-temperature in-situ confocal image; c) IPF orientation distribution map; d) variant distribution map; e) CP group distribution map; f) orientation difference distribution map along the X-X' direction in figure d).

[0034] Figure 2 The following are the high-temperature in-situ confocal morphology and corresponding EBSD orientation data in Example 2: where, ac) high-temperature in-situ confocal image; d) CP group distribution map; e) variant distribution map.

[0035] Figure 3 The results are from the phase-field simulation of the bainitic lath collision process. Detailed Implementation

[0036] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0037] The first aspect of this invention provides a method for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD, comprising the following steps:

[0038] Cut the target steel into cylindrical shapes;

[0039] The cylindrical sample is polished until the top and bottom surfaces are parallel and the surface is smooth and free of scratches, forming a mirror-like surface.

[0040] The polished sample is placed in an electrolyte for electrolytic polishing to remove the stress layer on the sample surface.

[0041] A diamond-shaped marking point was used to calibrate a specific area of ​​the electropolished sample using a microhardness tester.

[0042] The labeled sample was placed in the heating chamber of a high-temperature in-situ confocal laser microscope, a vacuum was drawn, and helium gas was introduced.

[0043] The field of view of the high-temperature in-situ confocal laser microscope is brought close to a specific area of ​​the marked point and heated. The heating chamber temperature is 950±5 ℃ and held for 5~10 min. After complete austenitization, the temperature is cooled to the bainite transformation temperature of 370~430 ℃ and held for 5~10 min. The growth morphology of bainite laths is observed and recorded in the bainite phase transformation range.

[0044] Electron backscatter diffraction observation was performed on a specific region within the marked point of the sample after high-temperature in-situ confocal testing, where lath collisions were observed.

[0045] Based on electron backscattering data of the selected region and in-situ confocal morphology analysis, the collision behavior of bainite laths was analyzed, and the phase field simulation method was used to simulate the growth and collision process of bainite laths.

[0046] The electrolyte is prepared by mixing perchloric acid and alcohol at a volume percentage of 9-11%.

[0047] During the electrolytic polishing process, the electrolysis voltage is 15 kV, the current is 0.5~0.6 A, the electrolyte temperature is controlled at 0~5 ℃, and the electrolysis time is 10~12 s.

[0048] Among them, the field of view of the high-temperature in-situ confocal laser microscope is close to a specific area of ​​the marked point and is heated. The heating rate is 300 ℃ / min and the cooling rate is 600 ℃ / min. The observation and recording are done by video recording and photography, with a shooting interval of 1 s.

[0049] According to the present invention, electron backscattering data analysis is performed using Aztec Crystal in conjunction with the MTEX ​​toolbox.

[0050] During electron backscatter diffraction observation, the test voltage was 20 kV, the scan step size was 0.08 μm, a 60 μm aperture was used, and the sample stage was tilted at 70°.

[0051] During the polishing process, the sample surface is sequentially polished with 400-grit, 800-grit, 1200-grit, 1500-grit, 2000-grit, 3000-grit, and 5000-grit sandpaper, followed by water polishing with 2.5 μm polishing paste, and then rinsed and dried with water and alcohol. The sanding process is carried out until all the sanding marks from the previous sanding are completely removed.

[0052] The target steel has the following chemical composition by mass percentage: C: 0.19%, Mn: 3.09%, Si: 1.46%, V: ≤0.005%, S: ≤0.005%, with the balance being Fe and unavoidable impurities.

[0053] The target steel is obtained according to the following steps:

[0054] Raw materials are melted in a vacuum according to a certain composition ratio to form ingots;

[0055] The ingot temperature is raised to 1150~1250 ℃ and maintained for 2~4 h to obtain a steel billet;

[0056] The steel billet is freely forged at around 1050~1200 ℃ to achieve a thickness of 40~60 mm, thus obtaining a cast billet.

[0057] The billet is held at 1050~1200 ℃ for 2~4 h, then hot rolled to 9~11 mm thick, and then air cooled to room temperature to form hot-rolled martensitic steel plate.

[0058] A is determined according to the phase diagram. c1 A c3 And Ms point, Bs point is calculated based on MUCGU3, and the cooling rate is determined;

[0059] Martensitic steel plates are processed into thermal expansion samples;

[0060] The thermally expanding sample is first heated to 900~1000 ℃ and held for 10~20 min, then cooled to room temperature to obtain the target steel.

[0061] In one embodiment, a method is provided for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD. The target steel has the following chemical composition by mass percentage: C: 0.19%, Mn: 3.09%, Si: 1.46%, V: ≤0.005%, S: ≤0.005%, with the balance being Fe and unavoidable impurities. The method includes the following steps:

[0062] (1) The raw materials are melted in vacuum to form ingots according to the above composition. The ingots are homogenized using a muffle furnace, and the temperature is raised to 1200 °C and held for two hours. Then, the billet is free-forged at about 1100 °C to make its thickness reach 40-60 mm;

[0063] (2) The billet is held at 1150℃ for 2 hours, then hot-rolled to a thickness of 10 mm, ensuring that the final rolling temperature is not lower than 850-900℃. It is then air-cooled to room temperature to form a hot-rolled martensitic steel plate.

[0064] (3) Determine A based on the phase diagram c1 A c3 And Ms point, Bs point is calculated based on MUCGU3, and the cooling rate is determined; where A c1 The point is the temperature at which the curve begins to expand significantly during the heating process, indicating that ferrite (or pearlite) begins to transform into austenite. A c3 The first point (Ms) is the temperature at which the curve shows a significant change again during heating, indicating the complete transformation of ferrite into austenite. The second point (Ms) is the temperature at which the curve suddenly contracts during cooling, indicating the beginning of the transformation of austenite into martensite.

[0065] (4) The steel plate was cut into thermal expansion samples with a diameter of 5 mm and a height of 10 mm by wire cutting and lathe processing;

[0066] (5) Place the thermal expansion sample in a rapid quenching thermal expansion apparatus and heat it to 950 °C for 10 min isothermal, then cool it to room temperature to achieve composition homogenization.

[0067] (6) Cut the thermally expanded sample into cylindrical pieces with a diameter of 5 mm and a height of 3 mm. Grind the top and bottom surfaces parallel to each other, and polish the top surface to a smooth, scratch-free mirror finish. Observe the polishing effect under a metallographic microscope.

[0068] (7) The polished sample is placed in an electrolyte solution for electrolytic polishing to remove the stress layer on the sample surface;

[0069] (8) Use a microhardness tester to mark specific areas of the electropolished sample with rhomboid markers for subsequent fixed-point observation in experiments;

[0070] (9) Place the marked sample into the heating chamber of the high-temperature confocal laser microscope, evacuate the vacuum chamber, and introduce helium gas.

[0071] (10) Place the field of view of the high-temperature confocal laser microscope close to the specific area of ​​the marked point, raise the temperature of the heating chamber to 950±5 ℃, hold for 5-10 min, and after complete austenitization, cool down to the bainite transformation temperature of 370 ℃-430 ℃ and hold for 5-10 min. Observe and record the growth morphology of bainite laths in the bainite phase transformation range.

[0072] (11) Electron backscatter diffraction observation was performed on a specific region within the marked point of the sample after high-temperature in-situ confocal testing, where lath collisions were observed.

[0073] (12) Based on the electron backscattering data of the selected area and in-situ confocal morphology analysis, the collision behavior of bainite laths was analyzed;

[0074] (13) The phase field simulation method was used to simulate the growth and collision process of bainite laths.

[0075] It should be noted that phase field simulation mainly combines the latest in-situ and EBSD technologies. Specifically, it simulates martensitic transformation through an elastoplastic phase field model, using the Allen-Cahn phase field equation and the total Gibbs free energy of the system, combined with chemical free energy, gradient energy and elastic strain energy, and uses COMSOL multiphysics finite element software for two-dimensional simulation to study the growth and collision behavior of martensite / bainite in the austenite parent phase.

[0076] The polishing process described in step (6) involves first grinding the sample surface with sandpaper, using 400 grit, 800 grit, 1200 grit, 1500 grit, 2000 grit, 3000 grit and 5000 grit sandpaper in sequence. Then, water polishing is performed using 2.5 μm polishing paste, followed by rinsing with water and alcohol and drying.

[0077] In step (7), the electropolishing process uses an electrolyte of 80 ml of a 10% perchloric acid + alcohol mixture, an electrolysis voltage of 15 kV, a current of 0.5-0.6 A, and maintains the electrolyte temperature at 0-5 ℃ for 10-12 s. The electrolyte is continuously stirred during the electropolishing process. The electrolyzed sample is then ultrasonically cleaned to remove dust, dirt, or chemical residues.

[0078] During the high-temperature in-situ confocal heating process described in step (10), the heating rate was 300 ℃ / min and the cooling rate was 600 ℃ / min. Observation and recording were conducted by recording video and taking photos, with a shooting interval of 1 s.

[0079] The electron backscattering experiment described in step (11) uses a test voltage of 20 kV, a scan step of 0.08 μm, a 60 μm aperture, and a sample stage tilted at 70°.

[0080] Subsequent data analysis of EBSD was performed using Aztec Crystal in conjunction with the MTEX ​​toolkit.

[0081] The specific parameters for phase-field simulation used in step (13) are shown in Table 1 below:

[0082] Table 1. Simulation parameters of elastoplastic phase field

[0083]

[0084] This invention utilizes high-temperature in-situ confocal laser microscopy to observe the growth and collision processes of bainite laths in real time, and combines this with electron backscatter diffraction (EBSD) technology to analyze their crystallographic orientation and phase composition, thereby obtaining detailed microstructural information. This method allows for direct observation of the dynamic evolution of bainite laths at the microscopic level. Simultaneously, by combining phase-field simulation methods, the evolutionary laws of the microstructure can be predicted and explained, providing theoretical support and verification. This method, through the comprehensive application of high-temperature in-situ observation, EBSD analysis, and phase-field simulation, comprehensively reveals the growth mechanism and collision behavior of bainite laths from the microscopic to the macroscopic levels, providing important theoretical basis and technical support for the design and optimization of advanced high-strength steels.

[0085] A second aspect of the present invention provides an application of the above-described method in the analysis of bainitic lath collision behavior.

[0086] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0087] Example 1

[0088] A method for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD includes the following steps:

[0089] The target steel was selected with the following chemical composition by mass percentage: C: 0.19%, Mn: 3.09%, Si: 1.46%, V: ≤0.005%, S: ≤0.005%, with the balance being Fe and unavoidable impurities. The method includes the following steps:

[0090] (1) The raw materials are made into ingots by vacuum melting according to the above composition. The ingots are homogenized using a muffle furnace, and the temperature is raised to 1200 °C and held for two hours. Then, the steel billet is free-forged at about 1100 °C to make its thickness reach 40-60 mm;

[0091] (2) The billet is held at 1150 ℃ for 2 h, and then hot rolled to a thickness of 10 mm, ensuring that the final rolling temperature is not lower than 850-900 ℃. Then it is air-cooled to room temperature to form a hot-rolled martensitic steel plate;

[0092] (3) Determine A based on the phase diagram c1 A c3 And Ms point, Bs point is calculated based on MUCGU3, and the cooling rate is determined;

[0093] (4) The steel plate was cut into thermal expansion samples with a diameter of 5 mm and a height of 10 mm by wire cutting and lathe processing;

[0094] (5) Place the thermal expansion sample in a rapid quenching thermal expansion apparatus and heat it to 950 °C for 10 min isothermal, then cool it to room temperature to achieve composition homogenization.

[0095] (6) Cut the thermal expansion sample into cylindrical specimens with a diameter of 5 mm and a height of 3 mm. Then, grind the surface of the specimen with sandpaper, successively using 400 grit, 800 grit, 1200 grit, 1500 grit, 2000 grit, 3000 grit and 5000 grit sandpaper. Then, water polish with 2.5 μm polishing paste, followed by rinsing with water and alcohol and drying. Observe the polishing effect under a metallographic microscope until the surface is polished to a mirror finish with parallel top and bottom surfaces, and no scratches.

[0096] (7) The polished sample is placed in an electrolyte solution for electrolytic polishing to remove the stress layer on the sample surface. The electrolyte solution is a mixture of 10% perchloric acid and alcohol with a volume ratio of 80 ml. The electrolysis voltage is 15 kV, the current is 0.5-0.6 A, the electrolyte temperature is controlled at 0-5 ℃, and the electrolysis time is 10-12 s. The electrolyte solution is continuously stirred during the electrolytic polishing process. The sample after electrolysis is ultrasonically cleaned to remove dust, dirt or chemical residues.

[0097] (8) Use a microhardness tester to mark specific areas of the electropolished sample with rhomboid markers for subsequent fixed-point observation in experiments;

[0098] (9) Place the marked sample into the heating chamber of the high-temperature confocal laser microscope, evacuate the vacuum chamber, and introduce helium gas.

[0099] (10) The field of view of the high-temperature confocal laser microscope is brought close to the specific area of ​​the marked point. The temperature of the heating chamber is raised to 950±5 ℃ at a rate of 300 ℃ / min. The temperature is held for 5-10 min. After complete austenitization, the temperature is lowered to the bainite transformation temperature of 370 ℃ at a rate of 600 ℃ / min. Then the temperature is raised to 430 ℃. The bainite growth behavior is observed by changing the temperature. The bainite lath growth morphology is observed and recorded in the bainite phase transformation range.

[0100] (11) Electron backscatter diffraction observation was performed on a specific region within the marked point of the sample after high-temperature in-situ confocal testing. The test voltage was 20 KV, the scanning step size was 0.08 μm, a 60 μm aperture was used, and the sample stage was tilted at 70°.

[0101] (12) Based on the electron backscattering data of the selected area and the in-situ confocal morphology, the collision behavior of bainite laths was analyzed using Aztec crystal combined with the MTEX ​​toolbox.

[0102] (13) The phase field simulation method was used to simulate the growth and collision process of bainite laths.

[0103] Results from the examples Figure 1 As shown, this invention can clearly observe the lath growth morphology during bainitic lath collisions and analyze lath collision behavior by combining EBSD information. It effectively combines in-situ observation results with crystallographic orientation information to illustrate the tendency characteristics of the new lath variants (BF3) and (BF1) after collisions, explaining the growth of the new laths after collisions and their tendency to generate new nuclei with similar tendencies and consistent growth directions as the original lath variants. Combined with simulation work not disclosed in this patent, it can effectively reveal the bainitic lath collision behavior. This provides an economical and effective method for studying the bainitic phase transformation process in advanced high-strength steels. It can be applied to the observation and mechanism investigation of phase transformation behavior in non-equilibrium phase transformation microstructures, providing reliable observation and analysis data for revealing material phase transformation processes.

[0104] Example 2

[0105] A method for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD includes the following steps:

[0106] The target steel was selected with the following chemical composition by mass percentage: C: 0.19%, Mn: 3.09%, Si: 1.46%, V: ≤0.005%, S: ≤0.005%, with the balance being Fe and unavoidable impurities. The method includes the following steps:

[0107] (1) The raw materials are made into ingots by vacuum melting according to the above composition. The ingots are homogenized using a muffle furnace, and the temperature is raised to 1200℃ and held for two hours. Then, the billet is free-forged at about 1100℃ to make its thickness reach 40-60 mm;

[0108] (2) The billet is held at 1150 ℃ for 2 h, and then hot rolled to a thickness of 10 mm, ensuring that the final rolling temperature is not lower than 850-900 ℃. Then it is air-cooled to room temperature to form a hot-rolled martensitic steel plate;

[0109] (3) Determine A based on the phase diagram c1 A c3 And Ms point, Bs point is calculated based on MUCGU3, and the cooling rate is determined;

[0110] (4) The steel plate was cut into thermal expansion samples with a diameter of 5 mm and a height of 10 mm by wire cutting and lathe processing;

[0111] (5) Place the thermal expansion sample in a rapid quenching thermal expansion apparatus and heat it to 950 °C for 10 min isothermal, then cool it to room temperature to achieve composition homogenization.

[0112] (6) Cut the thermal expansion sample into cylindrical specimens with a diameter of 5 mm and a height of 3 mm. Then, grind the surface of the specimen with sandpaper, successively using 400 grit, 800 grit, 1200 grit, 1500 grit, 2000 grit, 3000 grit and 5000 grit sandpaper. Then, water polish with 2.5 μm polishing paste, followed by rinsing with water and alcohol and drying. Observe the polishing effect under a metallographic microscope until the surface is polished to a mirror finish with parallel top and bottom surfaces, and no scratches.

[0113] (7) The polished sample is placed in an electrolyte solution for electrolytic polishing to remove the stress layer on the sample surface. The electrolyte solution is 80 ml of a 10% perchloric acid + alcohol mixture (volume ratio), the electrolysis voltage is 15 kV, the current is 0.5-0.6 A, the electrolyte temperature is controlled at 0-5 ℃, and the electrolysis time is 10-12 s. The electrolyte solution is continuously stirred during the electrolytic polishing process. The sample after electrolysis is ultrasonically cleaned to remove dust, dirt or chemical residues.

[0114] (8) Use a microhardness tester to mark specific areas of the electropolished sample with rhomboid markers for subsequent fixed-point observation in experiments;

[0115] (9) Place the marked sample into the heating chamber of the high-temperature confocal laser microscope, evacuate the vacuum chamber, and introduce helium gas.

[0116] (10) Place the field of view of the high-temperature confocal laser microscope close to the specific area of ​​the marked point, raise the temperature of the heating chamber to 950±5 ℃ at a heating rate of 300 ℃ / min, hold for 5-10 min, and after complete austenitization, cool down to the bainite transformation temperature of 430±5 ℃ at a cooling rate of 600 ℃ / min, observe the bainite growth behavior isothermally, and observe and record the bainite lath growth morphology in the bainite phase transformation range.

[0117] (11) Electron backscatter diffraction observation was performed on a specific region within the marked point of the sample after high-temperature in-situ confocal testing. The test voltage was 20 KV, the scanning step size was 0.08 μm, a 60 μm aperture was used, and the sample stage was tilted at 70°.

[0118] (12) Based on the electron backscattering data of the selected area and the in-situ confocal morphology, the collision behavior of bainite laths was analyzed using Aztec crystal combined with the MTEX ​​toolbox.

[0119] (13) The phase field simulation method was used to simulate the growth and collision process of bainite laths.

[0120] Compared to Example 1, the results of the high-temperature in-situ observation stage in Example 2, measured during the isothermal process of bainite, are as follows: Figure 2 As shown, the lath collision process can be observed in real time. Combined with in-situ observation results and EBSD data analysis, it can be found that the newly generated laths and the original laths belong to the same CP group and have similar variant tendencies.

[0121] Based on the observations from the embodiments, combined with phase-field simulations Figure 3 As shown, the evolution of equivalent stress and equivalent plastic strain reveals that before lath collision, the surrounding stress and plastic strain fields interact, either inhibiting or blocking the growth of the corresponding laths. Collisions of laths of the same Bain variant do not affect the growth of existing laths; only stress accumulation occurs, slowing the lath growth rate, allowing new laths to pass through existing laths. However, collisions of different Bain variants mutually block each other, further catalyzing nucleation and growth in the original stress / strain influence zone. The simulation results are consistent with experimental results of collisions of different Bain variants; laths cannot pass through each other and can only re-nucleate and grow in the strain accumulation zone on the other side.

[0122] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0123] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for analyzing the collision behavior of bainitic laths using high-temperature in-situ observation combined with EBSD, characterized in that, Includes the following steps: Cut the target steel into cylindrical shapes; The cylindrical sample is polished until the top and bottom surfaces are parallel and the surface is smooth and free of scratches, forming a mirror-like surface. The polished sample is placed in an electrolyte for electrolytic polishing to remove the stress layer on the sample surface. A diamond-shaped marking point was used to calibrate a specific area of ​​the electropolished sample using a microhardness tester. The labeled sample was placed in the heating chamber of the in-situ confocal laser microscope, a vacuum was drawn, and helium gas was introduced. The field of view of the in-situ confocal laser microscope is brought close to the specific area of ​​the marked point and heated. The heating chamber temperature is 950±5 ℃ and held for 5~10 min. After complete austenitization, the temperature is cooled to the bainite transformation temperature of 370~430 ℃ and held for 5~10 min. The growth morphology of bainite laths is observed and recorded in the bainite phase transformation range. Electron backscatter diffraction observation was performed on a specific region within the marked point of the sample after in-situ confocal testing, where lath collisions were observed. Based on electron backscattering data of the selected region and in-situ confocal morphology analysis, the collision behavior of bainite laths was analyzed, and the phase field simulation method was used to simulate the growth and collision process of bainite laths.

2. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD as described in claim 1, characterized in that, The electrolyte is prepared by mixing perchloric acid and alcohol at a volume percentage of 9-11%.

3. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD as described in claim 1, characterized in that, During the electrolytic polishing process, the electrolysis voltage is 15 kV, the current is 0.5~0.6 A, the electrolyte temperature is controlled at 0~5 ℃, and the electrolysis time is 10~12 s.

4. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD as described in claim 1, characterized in that, The in-situ confocal laser microscope field of view was close to a specific area marked on the microscope and heated at a rate of 300 ℃ / min and a rate of 600 ℃ / min. The observation was recorded by video and photographs at 1 s intervals.

5. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD according to claim 1, characterized in that, Electron backscattering data analysis was performed using Aztec Crystal in conjunction with the MTEX ​​toolbox.

6. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD according to claim 1, characterized in that, During electron backscatter diffraction observation, the test voltage was 20 kV, the scanning step size was 0.08 μm, a 60 μm aperture was used, and the sample stage was tilted at 70°.

7. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD according to claim 1, characterized in that, During the polishing process, the sample surface is sequentially polished with 400-grit, 800-grit, 1200-grit, 1500-grit, 2000-grit, 3000-grit, and 5000-grit sandpaper, followed by water polishing with 2.5 μm polishing paste, and then rinsed and dried with water and alcohol. The sanding process is carried out until all the sanding marks from the previous sanding are completely removed.

8. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD according to claim 1, characterized in that, The target steel has the following chemical composition by mass percentage: C: 0.19%, Mn: 3.09%, Si: 1.46%, V: ≤0.005%, S: ≤0.005%, with the balance being Fe and unavoidable impurities.

9. The method for analyzing bainitic lath collision behavior using high-temperature in-situ observation combined with EBSD according to claim 1, characterized in that, The target steel is obtained according to the following steps: Raw materials are melted in a vacuum according to a certain composition ratio to form ingots; The ingot temperature is raised to 1150~1250 ℃ and maintained for 2~4 h to obtain a steel billet; The steel billet is freely forged at around 1050~1200 ℃ to achieve a thickness of 40~60 mm, thus obtaining a cast billet. The billet is held at 1050~1200 ℃ for 2~4 h, then hot rolled to 9~11 mm thick, and then air cooled to room temperature to form hot-rolled martensitic steel plate. A is determined based on the phase diagram. c1 A c3 And Ms point, Bs point is calculated based on MUCGU3, and the cooling rate is determined; Martensitic steel plates are processed into thermal expansion samples; The thermally expanding sample is first heated to 900~1000 ℃ and held for 10~20 min, then cooled to room temperature to obtain the target steel.

10. The application of the method described in any one of claims 1 to 9 in the analysis of bainitic lath collision behavior.

Images