Carbon steel material ultrahigh-temperature austenite in-situ EBSD test method

Abstract

The invention discloses an in-situ EBSD (electron back-scattered diffraction) test method for ultrahigh-temperature austenite of a carbon steel material. The in-situ EBSD test method specifically comprises the following steps: firstly, carrying out a heating and cooling test on a sample through an in-situ SEM + EBSD test system to obtain an influence rule of a cooling speed on an austenite phase transformation point; and then, a high-temperature prevention device is arranged in front of an EBSD cabin door, an EBSD in-situ high-temperature test is started, cooling is carried out after the temperature is increased till complete austenite phase change occurs to the matrix structure of the carbon steel, the high-temperature prevention device is started, and EBSD high-temperature in-situ characterization operation is carried out. According to the testing method, the problem that in an existing method, ultrahigh-temperature austenite structure information and the transformation process of the ultrahigh-temperature austenite structure information cannot be obtained through the EBSD technology is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature deformation and fracture, and particularly relates to a method for in-situ EBSD testing of ultra-high-temperature austenite of carbon steel materials. Background Art

[0002] Clarifying the deformation and fracture behavior of materials at high or ultra-high temperatures is of great significance for improving the high-temperature service life of materials or understanding how materials fail at high temperatures. Among them, in-situ observation tests are an important way to study material deformation and cracking. Currently, researchers hope to obtain more crystallographic and mechanical information through a test method combining one or several characterization means. By mounting an EBSD probe on a scanning electron microscope, the material can be characterized at high temperatures to obtain SEM crystal morphology maps, crystal orientation information, phase structure information, grain boundary information, etc. SEM+EBSD combined with DIC technology can also additionally obtain stress and strain information during the high-temperature deformation process of the material.

[0003] Currently, the test temperature range of the in-situ high-temperature tensile system of a scanning electron microscope is generally 20°C to 1200°C. The in-situ high-temperature tensile system of a scanning electron microscope can perform EBSD analysis by mounting an EBSD probe. However, the current temperature resistance limit of the EBSD phosphor screen is about 800°C. Considering equipment safety and service life, EBSD in-situ analysis is generally only allowed within 750°C, and in special cases, short-term data acquisition can be performed within 750°C to 800°C. The existing in-situ test equipment mainly measures the temperature by welding or contacting a thermocouple probe on the back of the sample. The test temperature refers to the test temperature of the thermocouple probe, and the observation surface of the sample is the upper surface. Currently, it is still difficult to directly monitor the temperature change of the upper surface of the sample through the thermocouple probe. Affected by factors such as the heating system and sample heat dissipation, there is generally a certain temperature difference between the upper and lower surfaces of the sample. Literature or foreign manufacturers have reported in-situ EBSD tests near 1000°C, but the actual operation is difficult, the failure rate is high, and the damage to the probe life is large. Moreover, the reported test temperature generally refers to the test temperature of the thermocouple probe on the lower surface of the specimen, and it is generally difficult for the upper surface of the specimen to reach such a high temperature. The phase transformation point temperature of carbon steel is about 770°C, and in order to observe a stable austenite phase structure, it is generally necessary to keep warm for a period of time above the phase transformation point temperature to completely transform the carbon steel matrix structure into austenite phase and achieve austenite homogenization before observing and characterizing austenite. However, it is difficult to observe stable high-temperature austenite tissue information using in-situ EBSD technology based on existing equipment conditions. Under some special working conditions, researchers hope to obtain parameters such as the morphology and orientation information of the ultra-high-temperature (800-1300°C) austenite phase, and be able to observe the dynamic phase transformation process of the ultra-high-temperature austenite transforming into ferrite, bainite, martensite and other tissues based on EBSD technology. Limited by the current temperature resistance limit of the EBSD phosphor screen, the above research is difficult to achieve. Summary of the Invention

[0004] The object of the present invention is to provide a method for in-situ EBSD testing of ultra-high temperature austenite in carbon steel materials, which solves the problem that in the existing methods, it is impossible to obtain the information of ultra-high temperature austenite structure and its transformation process through EBSD technology.

[0005] The technical solution adopted by the present invention is a method for in-situ EBSD testing of ultra-high temperature austenite in carbon steel materials. The specific process is as follows: First, perform a heating and cooling test on the sample through an in-situ SEM+EBSD testing system to obtain the influence law of the cooling rate on the austenite phase transformation point; Then, set up a high-temperature protection device in front of the EBSD chamber door, heat the specimen to a temperature at which the matrix structure of the carbon steel undergoes complete austenite phase transformation and then cool it down, open the high-temperature protection device, and perform EBSD high-temperature in-situ characterization operation.

[0006] The present invention is also characterized in that

[0007] It is specifically implemented according to the following steps:

[0008] Step 1: Place the specimen on the in-situ SEM+EBSD testing system, perform a heating and cooling test, and obtain the influence law of the cooling rate on the austenite phase transformation point;

[0009] Step 2: Set up a high-temperature protection device in front of the EBSD chamber door, start the EBSD in-situ high-temperature test, heat the sample to a specific temperature and hold it until the matrix structure of the carbon steel undergoes complete austenite phase transformation, and keep the high-temperature protection device closed during this process;

[0010] Step 3: After cooling the sample to the target temperature, open the high-temperature protection device and perform EBSD high-temperature in-situ characterization operation;

[0011] Step 4: Determine whether the current structure is the austenite phase with FCC structure. If so, use the EBSD system to perform in-situ characterization of crystallographic information. If not, the test fails;

[0012] Step 5: If in-situ characterization of the austenite phase transformation process is required, perform a cooling operation and perform in-situ characterization of the phase transformation behavior based on the SEM or EBSD high-temperature in-situ observation system. If the in-situ observation of the austenite phase transformation process is not required, the test ends.

[0013] In Step 1, during the heating and cooling test, control the cooling rate to ensure that the austenite phase transformation point temperature during the cooling process does not exceed 700°C.

[0014] The specific process of Step 1 is as follows:

[0015] Step 1.1: Paste the specimen onto the ultra-flat specimen block for grinding and mechanical polishing. Then, further polish the observation surface by vibration polishing until the observation surface meets the EBSD observation requirements.

[0016] Step 1.2: Mark the observation position of the specimen.

[0017] Step 1.3: Immerse the ultra-flat specimen block with the specimen in acetone solution for 6h - 12h. After the acetone dissolves the binder, remove the specimen, and use sandpaper to remove the residual binder on the back. During this process, spray alcohol solution on the specimen surface to protect the observation surface from oxidation. Then, place the specimen in alcohol solution for ultrasonic cleaning and dry it for storage.

[0018] Step 1.4: Install the processed specimen on the high-temperature in-situ tensile test bench of the in-situ SEM system. Heat it up to 1200°C and hold for 5 minutes, then cool it at a rate of 0.1°C / s - 10°C / s to determine the phase transformation temperature of austenite during the cooling process, so as to obtain the influence law of the cooling rate on the austenite phase transformation point.

[0019] In Step 2, the high-temperature protection device includes a lead screw. One end of the lead screw meshes with a gear, and the gear is connected to the output shaft of the driving motor. A sliding module is sleeved on the lead screw. The top of the sliding module is connected to one end of the tin foil board. The other end of the tin foil board is arranged on Track I. The bottom end of the sliding module is arranged in Track II. Track I and Track II are arranged in parallel and are both arranged on the EBSD hatch shell. The driving motor is connected to a motor control module, and the motor control module is respectively connected to the power supply and the remote control device.

[0020] In Step 2, the heating rate is 0.5°C / s - 3°C / s, the specific temperature is 1200°C, and the holding time is 5 minutes.

[0021] In Step 3, the cooling rate during cooling is 0.1°C / s - 10°C / s, and the target temperature is 800°C.

[0022] The specific process of Step 4 is as follows:

[0023] Step 4.1: Turn on the high-temperature protection device, move the EBSD probe to the observation position, set the acquisition parameters, and perform pre-acquisition.

[0024] Step 4.2: According to the pre-acquisition result of Step 4.1, determine whether the organizational structure in the observation area is the austenite phase of the FCC structure at this time, and judge whether the EBSD resolution rate of this observation area meets the requirements.

[0025] Step 4.3: If the organizational structure in the observation area is the austenite phase with an FCC structure, no phase transformation has occurred, and the EBSD resolution is 70% - 100%, then directly conduct in-situ EBSD high-temperature characterization; if the austenite phase in the observation area has undergone a phase transformation or has completely transformed into a structure with a BCC structure, the test is determined to have failed.

[0026] In Step 5, when using an SEM or an in-situ EBSD high-temperature observation system for in-situ characterization of phase transformation behavior, the acquisition step size needs to be controlled at 0.1 to 0.2 times the grain size.

[0027] In Step 5, the cooling rate during the cooling operation is 0.1 °C / s to 10 °C / s.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel materials in the present invention proposes to install a high-temperature device that can be automatically opened and closed in front of the EBSD phosphor screen. The opening and closing method is a left-right sliding, so that it does not interfere with other devices inside the electron microscope. This opening and closing device can be opened after the ultra-high temperature austenite cools down to below 800 °C and a relatively stable austenite phase is obtained. Using the EBSD technology, the morphology and orientation information of the retained ultra-high temperature austenite can be characterized. At the same time, in cooperation with the subsequent cooling operation, the in-situ observation of austenite phase transformation behavior can also be carried out based on the EBSD technology, thus breaking through the problems that existing high-temperature in-situ EBSD devices are difficult to characterize the crystallographic information of austenite at high temperature or ultra-high temperature and are difficult to characterize the phase transformation behavior during the cooling of high-temperature austenite, providing new ideas for understanding and clarifying the crystallographic information of high-temperature austenite and studying the high-temperature information of materials, and having important engineering application value;

[0030] (2) The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel materials in the present invention, based on the difference in austenite phase transformation temperature of carbon steel materials during heating and cooling, that is, the austenite phase transformation temperature increases with the increase of the heating rate during heating, and decreases with the increase of the cooling rate during cooling, proposes that a fully austenitized structure can be observed during the cooling process. At the same time, when austenite cools down, it retains the morphology and orientation information of austenite at ultra-high temperature (such as 1200 °C) before the phase transformation, which provides new ideas for obtaining the crystallographic information of ultra-high temperature austenite. Description of the Drawings

[0031] Figure 1 It is a flow chart of the in-situ EBSD testing method for ultra-high temperature austenite of carbon steel materials in the present invention;

[0032] Figure 2 It is a structural schematic diagram of the high-temperature protection device in the in-situ EBSD testing method for ultra-high temperature austenite of carbon steel materials in the present invention.

[0033] In the figure, 1. EBSD hatch cover, 2. foil board, 3. sliding module, 4. lead screw, 5. drive motor, 6. gear, 7. motor control module, 8. power supply, 9. remote control device, 10. track I, 11. track II. Specific embodiments

[0034] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] The method for in-situ EBSD testing of ultra-high temperature austenite in carbon steel materials of the present invention specifically comprises the following steps: First, perform a heating and cooling test on a sample through an existing in-situ SEM (scanning electron microscope) + EBSD (electron backscatter diffraction) test system to obtain the influence law of the cooling rate on the austenite phase transformation point; then, set up a high-temperature protection device in front of the EBSD hatch, heat the specimen to a temperature at which the matrix structure of the carbon steel undergoes complete austenite phase transformation and then cool it down, open the high-temperature protection device, and utilize the characteristic that the austenite phase transformation temperature is lower during the cooling process to collect information on the high-temperature austenite phase and perform EBSD high-temperature in-situ characterization operations.

[0036] As Figure 1 shown, it is specifically implemented according to the following steps:

[0037] Step 1, place the specimen on an existing in-situ SEM + EBSD test system, perform a heating and cooling test, and obtain the influence law of the cooling rate on the austenite phase transformation point;

[0038] The specific process of Step 1 is as follows:

[0039] Step 1.1, paste the specimen onto a super-flat specimen block, perform grinding and mechanical polishing, and further polish the observation surface by vibration polishing until the observation surface meets the EBSD observation requirements;

[0040] Step 1.2, mark the observation position of the specimen;

[0041] Step 1.3, immerse the super-flat specimen block with the specimen in acetone solution for 6h - 12h. After the acetone dissolves the binder, remove the specimen, use sandpaper to remove the residual binder on the back, and spray an alcohol solution on the specimen surface to protect the observation surface from oxidation. Then, place the specimen in an alcohol solution for ultrasonic cleaning and drying for storage;

[0042] Step 1.4, install the processed specimen on the high-temperature in-situ tensile test bench of the in-situ SEM system, heat it to 1200°C and hold for 5 minutes, and then cool it at a rate of 0.1°C / s - 10°C / s to determine the austenite phase transformation temperature during the cooling process, so as to obtain the influence law of the cooling rate on the austenite phase transformation point;

[0043] Among them, during the heating and cooling test, the cooling rate needs to ensure that the austenite phase transformation temperature does not exceed 700 °C.

[0044] Step 2, set up a high-temperature protection device in front of the EBSD chamber door, start the in-situ high-temperature EBSD test, heat the sample to be tested at a heating rate of 0.5 °C / s to 3 °C / s until it reaches 1200 °C and hold for 5 minutes until the matrix structure of the carbon steel undergoes complete austenite phase transformation. During this process, keep the high-temperature protection device closed, and at this time, keep the high-temperature protection device closed so that the temperature received by the EBSD phosphor screen will not increase significantly;

[0045] Among them, the high-temperature protection device includes a lead screw 4. One end of the lead screw 4 meshes with a gear 6, and the gear 6 is connected to the output shaft of a driving motor 5. A sliding module 3 is sleeved on the lead screw 4. The top of the sliding module 3 is connected to one end of a tin foil plate 2. The other end of the tin foil plate 2 is arranged on a track I10. The bottom end of the sliding module 3 is arranged in a track II11. The track I10 and the track II11 are arranged in parallel and are both arranged on the EBSD chamber door housing 1. The driving motor 5 is connected to a motor control module 7. The motor control module 7 is respectively connected to a power supply 8 and a remote control device 9; the remote control device 9 is connected to the motor control module 7 by means of infrared remote control. The motor control module 7 is driven by the remote control device 9, and the motor control module 7 controls the driving motor 5 to rotate, thereby driving the gear 6 to rotate. The gear 6 meshes with the lead screw 4, then drives the lead screw 4 to rotate, and the lead screw 4 drives the sliding module 3 to move left and right, and the sliding module 3 drives the tin foil plate 2 to move, so as to realize the opening and closing of the tin foil plate 2 outside the EBSD chamber door;

[0046] Step 3, cool the sample to be tested at a cooling rate of 0.1 °C / s to 10 °C until it reaches 800 °C, then open the high-temperature protection device and perform the EBSD high-temperature in-situ characterization operation;

[0047] Step 4, determine whether the current tissue is an austenite phase with an FCC structure. If so, use the EBSD system to perform in-situ characterization of crystallographic information. If not, the test fails;

[0048] The specific process of Step 4 is as follows:

[0049] Step 4.1, open the high-temperature protection device, move the EBSD probe to the observation position, set the acquisition parameters, and perform pre-acquisition;

[0050] Step 4.2, according to the pre-acquisition result of Step 4.1, determine whether the organizational structure in the observation area at this time is an austenite phase with an FCC structure, and determine whether the EBSD resolution rate of this observation area meets the requirements;

[0051] Step 4.3, if the organizational structure in the observation area is an austenite phase with an FCC (face-centered cubic) structure, no phase transformation has occurred, and the EBSD resolution is 70% to 100%, then directly conduct in-situ high-temperature EBSD characterization; if the austenite phase in the observation area has undergone a phase transformation or has been completely transformed into a BCC (body-centered cubic) structure, the test is determined to fail.

[0052] Step 5, if in-situ characterization of the austenite phase transformation process is required, perform a cooling operation. The cooling rate can be controlled at 0.1 to 10 °C / s according to research requirements, and in-situ characterization of the phase transformation behavior is carried out based on the SEM or EBSD high-temperature in-situ observation system. During the in-situ characterization process, the acquisition step size needs to be controlled at 0.1 to 0.2 times the grain size. If the austenite phase transformation process does not need to be observed, the test ends.

[0053] It has been found through research that the austenite phase transformation point temperature is affected by the heating and cooling rates, and the austenite phase transformation point temperature during the cooling process is lower than that during the heating process. Taking a certain carbon steel as an example, when the heating rate is increased from 0.1 °C / s to 10 °C / s, the phase transformation point (Ac1) temperature increases from 773 °C to 827 °C. After complete austenitization, when the austenite is cooled, the austenite requires a certain degree of supercooling to undergo a phase transformation. That is to say, the austenite phase transformation temperature during the cooling process is lower than the austenite phase transformation temperature during the heating process, and the faster the cooling rate, the lower the phase transformation point temperature. The data shows that when a certain carbon steel that has undergone complete austenitization is cooled, after the cooling rate is increased from 0.05 °C / s to 0.5 °C / s, the phase transformation point temperature decreases from 766 °C to 690 °C. This indicates that the existing EBSD phosphor screen can observe the completely austenitized structure during the cooling process, but it is very difficult to observe the completely austenitized structure during the heating process. At the same time, during cooling, the austenite retains the morphology and orientation information of austenite at ultra-high temperatures (such as 1200 °C) before the phase transformation occurs. This shows that the crystal morphology and orientation of the ultra-high temperature austenite phase can be obtained by observing the austenite during the cooling process, which provides a new idea for obtaining the crystallographic information of ultra-high temperature austenite. The key point of the present invention is to combine the above phase transformation point law with the improvement of the EBSD in-situ high-temperature observation system to protect the EBSD phosphor screen during the heating process so that the EBSD phosphor screen is not affected by high temperatures. After the specimen is heated to a specific high temperature and sufficiently insulated, the specimen is rapidly cooled. When the temperature drops to 800 °C and no austenite phase transformation has occurred yet, the high-temperature protection device of the EBSD phosphor screen is opened to characterize the austenite at this time.

[0054] Example 1

[0055] Taking X65 pipeline steel as an example, the specific process is as follows:

[0056] Step 1: Place the specimen on the in-situ SEM + EBSD test system and conduct heating and cooling tests to obtain the influence law of cooling rate on the austenite phase transformation point.

[0057] The specific process of Step 1 is as follows:

[0058] Step 1.1: Paste the specimen onto the ultra-flat specimen block with 502 glue, perform grinding and mechanical polishing, and further polish the observation surface by vibration polishing until the observation surface meets the EBSD observation requirements. The observation surface is not corroded after polishing. A total of 8 specimens are processed according to the process, among which 6 are used to explore the influence law of heating and cooling on the austenite phase point, and 2 are used for in-situ high-temperature characterization of SEM + EBSD of high-temperature austenite.

[0059] Step 1.2: Use nano-indentation, microhardness method or other methods to mark the observation position of the specimen so that the marked position can be found more quickly during subsequent observations.

[0060] Step 1.3: Immerse the ultra-flat specimen block with the specimen in acetone solution for 6h - 12h. After the acetone dissolves the 502 glue, remove the specimen, and use sandpaper to remove the residual glue on the back. During this process, an alcohol solution needs to be sprayed on the specimen surface to protect the observation surface from oxidation. Then, place the specimen in the alcohol solution for ultrasonic cleaning and drying for storage.

[0061] Step 1.4: Install the processed specimen on the high-temperature in-situ tensile test bench of the in-situ SEM system, heat it to 1200°C at the fastest heating rate allowed by the equipment and hold for 5 minutes, then cool it at a rate of 0.1°C / s to determine the phase transformation temperature of austenite during the cooling process, so as to obtain the influence law of cooling rate on the austenite phase transformation point.

[0062] Among them, during the heating and cooling test process, ensure that the austenite phase transformation point temperature does not exceed 700°C by controlling the cooling rate.

[0063] Step 2: Set up a high-temperature protection device in front of the EBSD chamber door, start the EBSD in-situ high-temperature test, heat the 2 specimens to 1200°C at a heating rate of 0.5°C / s and hold for 5 minutes until the matrix structure of the carbon steel undergoes complete austenite phase transformation. Keep the high-temperature protection device closed during this process.

[0064] Step 3: Cool the 2 specimens at a cooling rate of 0.1°C / s to 800°C, then open the high-temperature protection device and perform EBSD high-temperature in-situ characterization operations.

[0065] Step 4: Determine whether the current tissue is the austenite phase with FCC structure. If so, use the EBSD system for in-situ characterization of crystallographic information. If not, the test fails.

[0066] The specific process of Step 4 is as follows:

[0067] Step 4.1: Turn on the high-temperature protection device, move the EBSD probe to the observation position, set the acquisition parameters, and perform pre-acquisition.

[0068] Step 4.2: According to the pre-acquisition results in Step 4.1, determine whether the microstructure in the observation area is the austenite phase with FCC structure, and judge whether the EBSD resolution rate in this observation area meets the requirements.

[0069] Step 4.3: If the microstructure in the observation area is the austenite phase with FCC structure, no phase transformation has occurred, and the EBSD resolution rate is above 70%, then directly perform EBSD high-temperature in-situ characterization; if the austenite phase in the observation area has undergone phase transformation or has completely transformed into the structure with BCC structure, then the test is judged to fail.

[0070] Step 5: If in-situ characterization of the austenite phase transformation process is required, perform a cooling operation. The cooling rate can be controlled at 0.1 °C / s according to research requirements, and perform in-situ characterization of the phase transformation behavior based on the SEM or EBSD high-temperature in-situ observation system. During the in-situ characterization process, the acquisition step size needs to be controlled at 0.1 to 0.2 times the grain size. If the austenite phase transformation process does not need to be observed, the test ends.

[0071] Example 2

[0072] Taking X65 pipeline steel as an example, the specific process is as follows:

[0073] Step 1: Place the specimen on the in-situ SEM+EBSD test system, perform heating and cooling tests, and obtain the influence law of the cooling rate on the austenite phase transformation point.

[0074] The specific process of Step 1 is as follows:

[0075] Step 1.1: Paste the specimen onto the ultra-flat specimen block with 502 glue, perform grinding and mechanical polishing, and further polish the observation surface by vibration polishing until the observation surface meets the EBSD observation requirements. The observation surface is not corroded after polishing. A total of 8 specimens are processed according to the process, among which 6 are used to explore the influence law of heating and cooling on the austenite phase point, and 2 are used for SEM+EBSD in-situ high-temperature characterization of high-temperature austenite.

[0076] Step 1.2: Use nano-indentation, microhardness method or other methods to mark the observation position of the specimen, so as to be able to find the marked position faster during subsequent observations.

[0077] Step 1.3: Immerse the super-flat specimen block with the specimen attached in acetone solution for 6 to 12 hours. After the acetone dissolves the 502 glue, remove the specimen, and use sandpaper to remove the remaining glue on the back. During this process, spray alcohol solution on the specimen surface to protect the observation surface from oxidation. Then, place the specimen in alcohol solution for ultrasonic cleaning and dry it for storage.

[0078] Step 1.4: Install the processed specimen on the high-temperature in-situ tensile test bench of the in-situ SEM system. Heat it to 1200 °C at the fastest heating rate allowed by the equipment and hold for 5 minutes, then cool it at a rate of 1 °C / s to determine the phase transformation temperature of austenite during the cooling process, so as to obtain the influence law of the cooling rate on the austenite phase transformation point.

[0079] Among them, during the heating and cooling test process, ensure that the austenite phase transformation point temperature does not exceed 700 °C by controlling the cooling rate.

[0080] Step 2: Set up a high-temperature protection device in front of the EBSD chamber door and start the EBSD in-situ high-temperature test. Heat 2 specimens to 1200 °C at a heating rate of 2 °C / s and hold for 5 minutes until the matrix structure of the carbon steel undergoes complete austenite phase transformation. Keep the high-temperature protection device closed during this process.

[0081] Step 3: Cool the 2 specimens at a cooling rate of 1 °C / s to 800 °C, then open the high-temperature protection device and perform EBSD high-temperature in-situ characterization operations.

[0082] Step 4: Determine whether the current tissue is the austenite phase with FCC structure. If so, use the EBSD system for in-situ characterization of crystallographic information. If not, the test fails.

[0083] The specific process of Step 4 is as follows:

[0084] Step 4.1: Open the high-temperature protection device, move the EBSD probe to the observation position, set the acquisition parameters, and perform pre-acquisition.

[0085] Step 4.2: According to the pre-acquisition results in Step 4.1, determine whether the tissue structure in the observation area is the austenite phase with FCC structure and whether the EBSD resolution rate of this observation area meets the requirements.

[0086] Step 4.3: If the tissue structure in the observation area is the austenite phase with FCC structure, no phase transformation has occurred, and the EBSD resolution rate is above 70%, then directly perform EBSD high-temperature in-situ characterization. If the austenite phase in the observation area has undergone phase transformation or has been completely transformed into the BCC structure tissue, then determine that the test fails.

[0087] Step 5, if in-situ characterization of the austenite phase transformation process is required, perform a cooling operation. The cooling rate can be controlled at 1 °C / s according to research requirements, and in-situ characterization of the phase transformation behavior is carried out based on the SEM or EBSD high-temperature in-situ observation system. During the in-situ characterization process, the acquisition step size needs to be controlled at 0.1 to 0.2 times the grain size. If the austenite phase transformation process does not need to be observed, the test ends.

[0088] Example 3

[0089] Taking X65 pipeline steel as an example, the specific process is as follows:

[0090] Step 1, place the specimen on the in-situ SEM+EBSD test system, perform heating and cooling tests, and obtain the influence law of the cooling rate on the austenite phase transformation point;

[0091] The specific process of Step 1 is as follows:

[0092] Step 1.1, paste the specimen onto the ultra-flat specimen block with 502 glue, perform grinding and mechanical polishing, and further polish the observation surface by vibration polishing until the observation surface meets the EBSD observation requirements. The observation surface is not corroded after polishing. A total of 8 specimens are processed according to the above process, 6 of which are used to explore the influence law of heating and cooling on the austenite phase point, and 2 are used for SEM+EBSD in-situ high-temperature characterization of high-temperature austenite;

[0093] Step 1.2, use nano-indentation, microhardness method or other methods to mark the observation positions of the specimens so that the marked positions can be found more quickly during subsequent observations;

[0094] Step 1.3, immerse the ultra-flat specimen block with the specimen in acetone solution for 6h - 12h. After the acetone dissolves the 502 glue, remove the specimen, and use sandpaper to remove the residual glue on the back. During this process, an alcohol solution needs to be sprayed on the specimen surface to protect the observation surface from oxidation. Then, place the specimen in an alcohol solution for ultrasonic cleaning and drying for storage;

[0095] Step 1.4, install the processed specimen on the high-temperature in-situ tensile test bench of the in-situ SEM system, heat it to 1200 °C at the fastest heating rate allowed by the equipment, hold for 5 minutes, and then cool it at a rate of 10 °C / s to determine the phase transformation temperature of austenite during the cooling process, so as to obtain the influence law of the cooling rate on the austenite phase transformation point;

[0096] Among them, during the heating and cooling test process, the cooling rate needs to ensure that the austenite phase transformation point temperature does not exceed 700 °C.

[0097] Step 2: Set up a high-temperature protection device in front of the EBSD chamber door and start the in-situ high-temperature EBSD test. Heat two specimens at a heating rate of 3 °C / s to 1200 °C and hold for 5 minutes until the matrix structure of the carbon steel undergoes complete austenite phase transformation. Keep the high-temperature protection device closed throughout this process.

[0098] Step 3: Cool the two specimens at a cooling rate of 10 °C / s to 800 °C, then open the high-temperature protection device and perform the in-situ high-temperature EBSD characterization operation.

[0099] Step 4: Determine whether the current structure is the austenite phase with an FCC structure. If so, use the EBSD system to perform in-situ characterization of crystallographic information. If not, the test fails.

[0100] The specific process of Step 4 is as follows:

[0101] Step 4.1: Open the high-temperature protection device, move the EBSD probe to the observation position, set the acquisition parameters, and perform pre-acquisition.

[0102] Step 4.2: Based on the pre-acquisition results in Step 4.1, determine whether the organizational structure in the observation area is the austenite phase with an FCC structure and whether the EBSD resolution rate in this observation area meets the requirements.

[0103] Step 4.3: If the organizational structure in the observation area is the austenite phase with an FCC structure, no phase transformation has occurred, and the EBSD resolution rate reaches over 70%, directly perform the in-situ high-temperature EBSD characterization. If the austenite phase in the observation area has undergone phase transformation or has completely transformed into a BCC-structured tissue, the test fails.

[0104] Step 5: If in-situ characterization of the austenite phase transformation process is required, perform a cooling operation. The cooling rate can be controlled at 10 °C / s according to research needs, and perform in-situ characterization of the phase transformation behavior based on the SEM or in-situ high-temperature EBSD observation system. During the in-situ characterization process, control the acquisition step size to be 0.1 to 0.2 times the grain size. If the austenite phase transformation process does not need to be observed, the test ends.

Claims

1. In-situ EBSD testing method for ultra-high temperature austenite of carbon steel material, characterized in that: The specific process is as follows: first, the sample is subjected to a temperature rise and fall test through the in-situ SEM+EBSD testing system to obtain the influence of cooling rate on the austenite phase transformation point; then, a high-temperature protection device is set in front of the EBSD cabin door, the sample is heated to the point where the matrix structure of the carbon steel undergoes a complete austenite phase transformation, then cooled and the high-temperature protection device is turned on to perform EBSD high-temperature in-situ characterization operations.

2. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 1, characterized in that: Follow the steps below to implement it: Step 1, placing the sample on an in-situ SEM+EBSD test system, performing a temperature rise and fall test, and obtaining the influence of cooling rate on the austenite phase transformation point; Step 2: Set up a high temperature protection device in front of the EBSD cabin door, start the EBSD in-situ high temperature test, heat the sample to be tested to a specific temperature and keep it warm until the matrix structure of the carbon steel undergoes a complete austenite phase transformation. During this process, keep the high temperature protection device closed; Step 3, after cooling the sample to be tested to the target temperature, turn on the high temperature protection device and perform EBSD high temperature in-situ characterization operation; Step 4, determine whether the current organization is an austenite phase of FCC structure. If so, use the EBSD system to perform in-situ characterization of crystallographic information. If not, the test fails. Step 5: If in-situ characterization of the austenite phase transformation process is required, the temperature is lowered and in-situ characterization of the phase transformation behavior is performed based on a SEM or EBSD high-temperature in-situ observation system. If the austenite phase transformation process does not need to be observed, the experiment ends.

3. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: In step 1, during the temperature rise and fall test, the cooling rate must be controlled to ensure that the austenite transformation point temperature does not exceed 700°C.

4. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: The specific process of step 1 is: Step 1.1, the sample is pasted onto an ultra-flat sample block for grinding and mechanical polishing, and the observation surface is further polished by vibration polishing until the observation surface meets the EBSD observation requirements; Step 1.2, marking the observation position of the sample; Step 1.3, soak the ultra-flat specimen block with the specimen in an acetone solution for 6 to 12 hours. After the acetone dissolves the adhesive, remove the specimen and use sandpaper to remove the residual adhesive on the back. This process requires spraying an alcohol solution on the surface of the specimen to protect the observation surface from oxidation. Then, place the specimen in an alcohol solution for ultrasonic cleaning and dry it for storage. Step 1.4, install the treated sample on the high-temperature in-situ tensile test bench of the in-situ SEM system, heat it to 1200℃ and keep it for 5 minutes, then cool it down at a rate of 0.1℃ / s to 10℃ / s, determine the phase transformation temperature of austenite during the cooling process, and obtain the influence of cooling rate on the phase transformation point of austenite.

5. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: In step 2, the high temperature protection device comprises a screw rod (4), one end of which is meshed with a gear (6), and the gear (6) is connected to the output shaft of the drive motor (5). A sliding module (3) is sleeved on the screw rod (4), and the top of the sliding module (3) is connected to one end of a tin foil plate (2), and the other end of the tin foil plate (2) is arranged on a track I (10). The bottom end of the sliding module (3) is arranged in a track II (11), and the track I (10) and the track II (11) are arranged in parallel and are both arranged on the EBSD cabin door shell (1). The drive motor (5) is connected to a motor control module (7), and the motor control module (7) is respectively connected to a power supply (8) and a remote control device (9).

6. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: In step 2, the heating rate is 0.5°C / s to 3°C / s, the specific temperature is 1200°C, and the holding time is 5 minutes.

7. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: In step 3, the cooling rate is 0.1°C / s to 10°C / s, and the target temperature is 800°C.

8. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: The specific process of step 4 is: Step 4.1, turn on the high temperature protection device, move the EBSD probe to the observation position, set the acquisition parameters, and perform pre-acquisition; Step 4.2, based on the pre-collection results of step 4.1, determine whether the organizational structure in the observation area at this time is an austenite phase of the FCC structure, and determine whether the EBSD resolution of this observation area meets the requirements; Step 4.3: If the microstructure in the observation area is an austenite phase with an FCC structure, no phase change has occurred, and the EBSD resolution is 70% to 100%, EBSD high-temperature in-situ characterization is performed directly; if the austenite phase in the observation area has undergone a phase change or has been completely transformed into a BCC structure, the test is judged to have failed.

9. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: In step 5, when using SEM or EBSD high-temperature in-situ observation system to perform in-situ characterization of phase change behavior, the acquisition step length needs to be controlled to be 0.1 to 0.2 times the grain size.

10. The in-situ EBSD testing method for ultra-high temperature austenite of carbon steel material according to claim 2, characterized in that: In step 5, the cooling rate during the cooling operation is 0.1°C / s to 10°C / s.

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