In-situ dynamic observation method for sensitization process of austenitic stainless steel

Abstract

The invention relates to the technical field of an austenitic stainless steel sensitization process, in particular to an in-situ dynamic observation method for the austenitic stainless steel sensitization process. Aiming at the problem that dynamic precipitation of carbides on an original grain boundary cannot be clearly and continuously captured by the existing observation means, the method is realized by the following steps of: firstly, carrying out electrolytic polishing on a sample to obtain an observation surface without a deformation layer, and ensuring that only the original austenite grain boundary is shown at high temperature; secondly, executing a thermal cycle program including rapid solid solution and controllable cooling to a sensitization temperature in the HT-CLSM, and locking a precipitation process in a target isothermal stage; finally, automatic timing image acquisition is performed on the fixed field of view during an isothermal period. The method realizes clear, dynamic and visual observation of the whole sensitization process, especially initial nucleation, reveals carbide precipitation kinetics, provides an effective tool for research of a sensitization mechanism and material evaluation, and is suitable for austenitic stainless steel.

Description

Technical Field

[0001] This invention relates to the field of austenitic stainless steel sensitization process technology, specifically to an in-situ dynamic observation method for the austenitic stainless steel sensitization process. Background Technology

[0002] Sensitization is a major cause of intergranular corrosion in austenitic stainless steel during use, leading to performance degradation and even failure. Sensitization essentially occurs when supersaturated carbon in solid solution combines with chromium at grain boundaries to form chromium-rich Mg2+. 23 C6-type carbides cause chromium depletion in the grain boundary region. This process occurs in the temperature range of 450~850℃ and is particularly difficult to avoid during welding, hot working and other processes.

[0003] In existing technologies, national standards (GB / T) or ASTM standard methods for evaluating the degree of sensitization of stainless steel, such as the sulfuric acid-copper sulfate corrosion test and electrolytic etching, are all endpoint methods and destructive tests. This involves chemically or electrolytically corroding heat-treated samples and qualitatively determining whether they are "sensitized" by observing the metallographic structure after bending or by weight loss. These traditional methods have significant drawbacks: First, they cannot reproduce and record the dynamic process of carbide precipitation, such as the initial nucleation location, growth rate, and grain boundary connectivity; second, the results heavily rely on operator experience, are highly subjective, and can only provide a qualitative "yes" or "no" conclusion, failing to quantify the spatiotemporal evolution of the process; third, the samples are destroyed after the test, making them unusable for subsequent analyses, and in-situ monitoring during actual heat treatment is impossible.

[0004] The advent of high-temperature laser confocal microscopy (HT-CLSM) has provided a powerful in-situ, real-time, and visualization platform for studying high-temperature processes in materials, and it has been widely applied to the study of recrystallization, phase transformation, and grain growth in metals. However, the systematic study of the sensitization process of austenitic stainless steel using HT-CLSM directly still faces the following key challenges and limitations: First, there is a lack of dedicated sample preparation methods for sensitization observation. The mechanically polished deformation layer on the surface of conventional metallographic samples is prone to recrystallization during HT-CLSM heating, generating a large number of new, non-primary grain boundaries, which severely interferes with the accurate observation of carbide precipitation behavior on the original austenite grain boundaries. Currently, there is no standardized sample pretreatment procedure that can ensure the exposure of only the original grain boundaries at high temperatures.

[0005] Second, the thermal cycling program lacks a targeted design for sensitization kinetics. Sensitization is a kinetic process strongly correlated with temperature and time. If the cooling rate is too slow, carbides may precipitate prematurely in the higher temperature range during cooling, making it impossible to observe the actual nucleation behavior at the target temperature; if the cooling rate is too fast, it may introduce thermal stress or lead to unstable furnace temperature control. Existing HT-CLSM experiments often directly adopt a relatively simple heating-holding-cooling procedure, failing to finely design the thermal cycling path from the solid solution state to the isothermal sensitization range, in order to "freeze" the high-temperature state and ensure that carbide precipitation mainly occurs in the set isothermal stage, thereby accurately capturing the starting point of the process.

[0006] Third, the image acquisition strategy failed to match the dynamic characteristics of the sensitization process. Carbides exhibit rapid nucleation and early growth in the initial stages of sensitization, while the later process of forming a network is slower. If a fixed, low-frequency image acquisition method is used, it is easy to miss the initial moment of nucleation and key details of early evolution, resulting in discontinuous and incomplete observation sequences, making it impossible to construct a complete dynamic picture. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides an in-situ dynamic observation method for the sensitization process of austenitic stainless steel. It achieves systematic optimization from sample preparation and thermal cycling to image acquisition, clearly capturing the entire process of dynamic carbide precipitation at the original grain boundaries.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A method for in-situ dynamic observation of the sensitization process of austenitic stainless steel, specifically including the following steps: S1. Sample preparation: Austenitic stainless steel samples are ground, polished and electrolytically polished to obtain a mirror-like observation surface without surface deformation layer; S2. In-situ thermal cycling experiment: The sample was placed in the HT-CLSM high-temperature furnace and subjected to solution treatment and sensitization isothermal treatment under inert atmosphere protection. S3. Dynamic Image Acquisition: During the sensitization isotherm stage, time-series images are acquired on a fixed field of view to record the dynamic process of carbide precipitation.

[0009] Furthermore, in step S1, the austenitic stainless steel sample is a cylindrical sample with a diameter of 6-8 mm and a height of 2-3 mm.

[0010] Further, in step S1, the electrolytic polishing uses a perchloric acid-glacial acetic acid mixed solution as the electrolyte, wherein the volume ratio of perchloric acid to glacial acetic acid is 1:(8~10), the polishing voltage is 15~20V, and the polishing time is 60~90s.

[0011] Further, in step S2, the solution treatment includes: heating to 1100~1150℃ at a heating rate of not less than 100℃ / s, and holding at that temperature for 3~5 minutes.

[0012] Further, in step S2, the sensitization isothermal treatment includes: cooling from the solution temperature to a target temperature in the range of 450~850℃ at a cooling rate of 40~60℃ / min, and isothermally holding at that temperature for more than 10 minutes.

[0013] Furthermore, in step S3, the image acquisition adopts an automatic time-series recording mode, acquiring one frame of image every 15-30 seconds for the first 30 minutes of isothermal insulation, and then reducing the acquisition frequency to one frame every 2-5 minutes.

[0014] Furthermore, the acquired image resolution is no less than 1024×1024 pixels, and the laser power and detector gain remain constant throughout the acquisition process.

[0015] Furthermore, in step S3, the fixed field of view is achieved by locking the X, Y, and Z coordinates of the HT-CLSM stage to ensure that all images come from the same observation area.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention enables dynamic, visualized, and quantitative observation of the entire sensitization process, especially carbide nucleation and growth, overcoming the limitations of traditional endpoint-based and destructive methods. Traditional corrosion tests can only provide an endpoint judgment of "whether sensitization has occurred." However, this invention, through high-frequency time-series image acquisition (e.g., one frame every 15-30 seconds in the first 30 minutes), successfully captures the nucleation cores and early growth processes of carbides at grain boundaries down to the 50-100 nm scale. This allows for in-situ quantitative measurement of key kinetic parameters such as the nucleation incubation period and early growth rate, providing direct evidence for mechanistic research.

[0017] 2. The clarity and reliability of the observation results are fundamentally improved, ensuring that the observed behavior is the true original grain boundary behavior. The deformation layer present on the surface of traditional metallographic samples or conventional HT-CLSM samples will generate recrystallized grain boundaries upon heating, with an interference rate as high as 70% or more. This invention, through an optimized electrolytic polishing process (e.g., 20V, 70s), prepares a mirror surface with a surface roughness of less than 10nm and no residual stress. Combined with the thermal etching effect of high-temperature solid solution (1150℃), the original austenite grain boundaries are clearly revealed, thus ensuring the authenticity of the carbide precipitation behavior observation scenario and avoiding misobservations.

[0018] 3. Through precise thermal cycling program design, strict control over sensitization temperature and time is achieved, resulting in high experimental reproducibility. Existing methods struggle to control precipitation interference during the cooling process. This invention, by designing a program of rapid solution heating at ≥100℃ / s and controlled cooling to the isothermal temperature at 50℃ / min, ensures that carbides precipitate primarily at the target isothermal stage (e.g., 650℃). This cooling rate is significantly higher than the typical precipitation rate of carbides above 700℃, thus locking the "timing zero point" of the precipitation process at the isothermal start moment, greatly improving the comparability of experimental data from different laboratories or different batches.

[0019] 4. A complete spatiotemporal evolution data chain is provided, supporting subsequent in-depth quantitative analysis. Traditional methods can only provide metallographic images of the final state. This invention uses continuous acquisition with a fixed field of view (e.g., acquiring more than 60 high-resolution images within 60 minutes) and synchronously stores each image with a timestamp accurate to the second and temperature data within ±1℃, forming a complete spatiotemporal database. This makes it possible to quantitatively analyze the changes in carbide nucleation density over time, the measurement of growth rate, and the evolution of network structure connectivity.

[0020] 5. The method is scalable and instructive. By systematically changing the isothermal temperature (e.g., 550℃, 650℃, 750℃) and repeating this observation procedure, a "sensitization kinetic spectrum" (TTP spectrum) for specific stainless steel materials can be efficiently constructed, intuitively revealing the most sensitive temperature range. This provides direct experimental evidence for formulating anti-sensitization heat treatment processes or welding process parameters, which is incomparable to the statistical results obtained by traditional methods that rely on a large number of discrete and destructive samples. Attached Figure Description

[0021] Figure 1 This is an image taken 5 minutes before the start of heat preservation in Embodiment 1 of the present invention.

[0022] Figure 2 This is an image from Embodiment 1 of the present invention, showing the temperature maintained for 8 minutes.

[0023] Figure 3 This is an image from Embodiment 1 of the present invention, showing the temperature maintained for 15 minutes.

[0024] Figure 4 This is an image from Embodiment 1 of the present invention, showing the temperature maintained for 30 minutes.

[0025] Figure 5 This is an image from Embodiment 1 of the present invention, showing the temperature maintained for 60 minutes. Detailed Implementation

[0026] This invention discloses an in-situ dynamic observation method for the sensitization process of austenitic stainless steel. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0027] A method for in-situ dynamic observation of the sensitization process of austenitic stainless steel, specifically including the following steps: S1. Sample preparation: The purpose of this step is to obtain a stress-free, strain-free, and smooth observation surface, which is a prerequisite for obtaining high-resolution in-situ observation results. Any plastic deformation layer on the surface will recrystallize during heating, generating new grain boundaries, which seriously interferes with the observation of carbide precipitation behavior on the original austenite grain boundaries.

[0028] Sampling: Use wire cutting to take a standard cylindrical sample with a diameter of 7.5 mm and a height of 2~3 mm from the austenitic stainless steel plate to be tested.

[0029] Rough grinding and fine grinding: Mechanical grinding is performed sequentially using metallographic sandpaper of progressively finer grades (e.g., 120#, 400#, 800#, 1200#). Each grinding step must completely remove the scratches from the previous process and ensure that the sample surface is parallel to the grinding and polishing plane.

[0030] Fine polishing: Use diamond polishing paste (e.g., 2.5μm) on a fully automatic polishing machine equipped with a velvet polishing cloth for final polishing until the sample surface is free of any visible scratches and presents a mirror effect.

[0031] Electropolishing: The mechanically polished sample is placed in an electropolishing apparatus, using a perchloric acid-glacial acetic acid mixed solution (volume ratio 1:9) as the electrolyte, and polished for 60-90 seconds at a DC voltage of 15-20V and room temperature. This step completely eliminates the surface deformation layer introduced by mechanical polishing, obtaining a strain-free, crystal-structure-complete original surface, thus ensuring that only the original austenite grain boundaries of the material are visible during the HT-CLSM heating process, rather than recrystallized grain boundaries or scratches.

[0032] S2, In-situ thermal cycling experiment: This step is one of the core aspects of the invention, aiming to precisely control the heat treatment process to induce and capture the sensitization process. The experiment was conducted in an HT-CLSM equipped with a vacuum high-temperature furnace.

[0033] Sample loading and initial state recording: The prepared sample was placed in a high-temperature resistant alumina ceramic crucible and then placed on the sample holder of the high-temperature furnace. After closing the furnace lid, the furnace was repeatedly evacuated three times and filled with high-purity argon as a protective gas. A clean, impurity-free surface was selected as the observation field for in-situ analysis. The sample was heated to 200°C at a heating rate not exceeding 200°C / min. This stage was the light source preheating stage, preparing for the rapid heating in the subsequent solution treatment stage.

[0034] Solution treatment stage: The sample is rapidly heated to 1100-1150℃ at a limiting rate of ≥100℃ / s and held for 3-5 minutes. This stage serves three purposes: first, to ensure that all existing carbides are completely dissolved, and that carbon and chromium are fully dissolved in the austenite matrix, obtaining a single initial state; second, to utilize the thermal etching effect at high temperatures to make the original austenite grain boundaries significantly concave, thus becoming exceptionally clear in optical contrast, facilitating subsequent identification and tracking; and third, to eliminate any previous thermal history of the sample, ensuring that the starting point for all experiments is absolutely consistent.

[0035] Sensitization Observation Stage: This is the core stage of dynamic observation. The sample is rapidly cooled from the solution treatment temperature to the pre-set target sensitization temperature (450-850℃) at a rate of 50℃ / min. Upon reaching this temperature, a long isothermal holding period is immediately initiated (usually 10 minutes to several hours, depending on the steel grade). The set cooling rate must be faster than the precipitation rate of carbides in the high-temperature range to prevent precipitation during cooling and ensure that precipitation mainly occurs at the target isothermal temperature; however, it must not be too fast, which could lead to unstable furnace temperature control or thermal stress on the sample.

[0036] S3, Dynamic Image Acquisition: This step aims to record the complete dynamic sequence of the sensitization process with high quality.

[0037] Parameter settings: Throughout the sensitization observation phase, optical parameters such as laser power and detector gain are kept constant to ensure that the grayscale values ​​of all image sequences are comparable.

[0038] Automatic time-series recording: Activate the automatic time-series recording function of the CLSM system. During the initial stage of heat preservation (first 30 minutes), due to the rapid nucleation and early growth of carbides, set a high acquisition frequency, automatically acquiring a high-resolution image of 2048x2048 pixels every 15-30 seconds. Subsequently, the frequency can be gradually reduced to one frame every 2-5 minutes.

[0039] Fixed field-of-view tracking: Throughout the experiment, the X, Y, and Z coordinates of the microscope stage must be strictly locked to ensure that all acquired images come from the absolutely identical field of view. This is an absolute prerequisite for achieving dynamic tracking and analysis of carbides at the same location from scratch.

[0040] Data recording: The system automatically stores each frame of image along with precise temperature and timestamp, forming a complete spatiotemporal evolution database, providing a solid foundation for subsequent mechanism analysis.

[0041] Example 1: In-situ dynamic observation of the sensitization process of 316L austenitic stainless steel 1. Sample preparation: Cylindrical samples with dimensions Φ7.5mm × H2.5mm were cut from 316L stainless steel sheet (chemical composition: C: 0.08%, Si: 0.7%, Mn: 2.1%, Cr: 18.7%, Ni: 8.5%, Mo: 0.43%, balance Fe) using wire cutting. The samples were mechanically polished sequentially using 120#, 400#, 800#, and 1200# metallographic sandpaper, followed by polishing to a mirror finish using 2.5μm diamond polishing paste on an automatic polishing machine. The polished samples were then used as anodes and placed in a perchloric acid-glacial acetic acid electrolytic polishing solution with a volume ratio of 1:9, and electrolyzed for 70 seconds at 20V DC voltage and room temperature. After removal, the samples were rinsed with anhydrous ethanol and dried for later use.

[0042] 2. In-situ thermal cycling experiment and dynamic observation: The prepared sample was placed in an alumina ceramic crucible of a high-temperature laser confocal microscope (model: VL2000DX-SVF17SP). After being evacuated and repeatedly cleaned three times with high-purity argon gas (purity >99.999%), the experiment was conducted under argon protection. The thermal cycling program was set as follows: Heat to 200℃ at 50℃ / min, preheat, and select the observation field.

[0043] The temperature was rapidly increased to 1150℃ at a maximum rate of 100℃ / s, held for 3 minutes, and then subjected to solution treatment.

[0044] The temperature was reduced to the target sensitization temperature of 650°C at a cooling rate of 50°C / min.

[0045] The sample was kept at 650℃ for 60 minutes under isothermal conditions.

[0046] 3. Image Acquisition: During the isothermal holding phase at 650℃, automatic time-series recording was initiated. To capture the rapid nucleation phase, for the first 10 minutes after the start of the holding phase, a high-resolution image of 1024×1024 pixels was automatically acquired every 30 seconds; thereafter, until the end of the holding phase, a frame was acquired every 1 minute. The microscope stage coordinates were locked throughout the entire process to ensure a fixed field of view.

[0047] 4. Observation results: like Figures 1 to 5As shown, the playback image sequence clearly shows the dynamic evolution of the entire sensitization process of 316L stainless steel at 650℃.

[0048] Figure 1 (5 minutes before the start of heat preservation): The original austenite grain boundaries after solution treatment are clear and straight, and no precipitates are seen in the grain boundaries and within the grains.

[0049] Figure 2 (Hold for 8 minutes): At the junction of several triangular grain boundaries, fine, bright white dot-like precipitates begin to appear; this is M. 23 Initial nucleation of C6 carbides.

[0050] Figure 3 (Hold for 15 minutes): The initial nucleation sites grow to both sides along the grain boundaries, forming short rods. At the same time, new point-like nucleation sites also appear in the straight grain boundary segments.

[0051] Figure 4 (Hold for 30 min): The carbide particles on the grain boundaries coarsen significantly and begin to approach and connect with each other, forming a discontinuous chain structure.

[0052] Figure 5 (Hold for 60 minutes): Most grain boundaries are covered by continuous or nearly continuous network carbides, indicating that the material has reached a fully sensitized state.

[0053] Example 2: In-situ dynamic observation of the sensitization process of 304 austenitic stainless steel 1. Sample preparation: Samples were taken from 304 stainless steel plate (chemical composition: C: 0.07%, Si: 0.6%, Mn: 1.5%, Cr: 18.2%, Ni: 8.1%, balance Fe). The sample size and preparation process were the same as in Example 1, and the electropolishing parameters were kept consistent (1:9 perchloric acid-glacial acetic acid, 20V, 70s).

[0054] 2. In-situ experiments and observations: The experimental equipment and protective atmosphere were the same as in Example 1. The thermal cycling program was adjusted as follows: heating at 100℃ / s to 1100℃ for solution treatment and holding for 3 min, followed by cooling at 50℃ / min to 550℃ and isothermal holding for 90 min. The image acquisition strategy was: one frame every 45 s for the first 20 min, and one frame every 2 min thereafter.

[0055] 3. Observation results: During the isothermal process at 550°C, the preferential nucleation of carbides at the triangular grain boundaries was also observed, followed by their expansion along the grain boundaries. Compared with Example 1, at the lower temperature (550°C), the incubation period for carbide nucleation was extended to about 12 minutes, and the precipitate particles were finer, more densely distributed, and grew at a slower rate. However, a continuous grain boundary carbide network was still formed at 90 minutes, clearly revealing the characteristics of low-temperature long-term sensitization.

[0056] Example 3: In-situ dynamic observation of the sensitization process of 321 austenitic stainless steel 1. Sample preparation: Samples were taken from a 321 stainless steel plate (chemical composition: C: 0.08%, Si: 0.5%, Mn: 1.2%, Cr: 17.5%, Ni: 9.0%, Ti: 0.4%, balance Fe). The preparation process was the same as in Example 1. Due to the addition of Ti, the surface condition of the sample was good after electrolytic polishing.

[0057] 2. In-situ experiments and observations: The experimental conditions were the same as in Example 1. The thermal cycling program was set as follows: solution treatment at 1150℃ for 3 min, followed by cooling at 50℃ / min to 750℃ and isothermal holding for 30 min. The image acquisition frequency was set to one frame every 20 seconds for the first 10 min, and one frame every 1 min thereafter.

[0058] 3. Observation results: At a higher temperature of 750℃, the incubation period for carbide nucleation is significantly shortened, with precipitates observed at grain boundaries approximately 3 minutes after the start of the holding period. The precipitates grow rapidly and are relatively large in size; however, at the end of the 30-minute holding period, the continuity of the grain boundary carbide network is lower than that of 316L at 650℃ / 60 minutes. This indicates that the stabilizing element Ti, to some extent, delays the precipitation and bonding process of carbides, and this method successfully captures this difference.

[0059] Comparative example: HT-CLSM observation of conventional metallographic samples To illustrate the importance of the sample preparation method of this invention, 316L stainless steel samples that were conventionally mechanically polished (without electrolytic polishing) were observed under the same HT-CLSM equipment and thermal cycling procedure (same as Example 1).

[0060] Sample preparation: Only mechanical polishing with 1200# sandpaper and 2.5μm diamond polishing paste was performed; electrolytic polishing was not performed.

[0061] Observation results: During the solution treatment and holding stage at 1150℃, the sample surface underwent intense recrystallization due to the residual deformation layer, generating numerous fine new grains and meandering recrystallization grain boundaries within the original field of view, completely obscuring the original austenite grain boundaries. In the subsequent isothermal process at 650℃, precipitates were observed appearing on these newly formed, unstable grain boundaries, and their precipitation behavior was chaotic and disordered, making it impossible to trace the true precipitation kinetics of carbides on the original grain boundaries, rendering the observation results meaningless. This fully demonstrates that traditional sample preparation methods that do not eliminate the surface deformation layer cannot be used to study the sensitization behavior of the original microstructure, highlighting the necessity and crucial role of the electropolishing step in this invention.

[0062] The above embodiments and comparative examples demonstrate that the method provided by the present invention is reliable and can clearly, realistically, and dynamically reveal the entire sensitization process of different types of austenitic stainless steel at different temperatures, thus possessing significant scientific research and application value.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for in-situ dynamic observation of the sensitization process of austenitic stainless steel, characterized in that, Specifically, the following steps are included: S1. Sample preparation: Austenitic stainless steel samples are ground, polished and electrolytically polished to obtain a mirror-like observation surface without surface deformation layer; S2. In-situ thermal cycling experiment: The sample was placed in the HT-CLSM high-temperature furnace and subjected to solution treatment and sensitization isothermal treatment under inert atmosphere protection. S3. Dynamic Image Acquisition: During the sensitization isotherm stage, time-series images are acquired on a fixed field of view to record the dynamic process of carbide precipitation.

2. The in-situ dynamic observation method for the sensitization process of austenitic stainless steel according to claim 1, characterized in that, In step S1, the austenitic stainless steel sample is a cylindrical sample with a diameter of 6-8 mm and a height of 2-3 mm.

3. The in-situ dynamic observation method for the sensitization process of austenitic stainless steel according to claim 1, characterized in that, In step S1, the electrolytic polishing uses a perchloric acid-glacial acetic acid mixed solution as the electrolyte, wherein the volume ratio of perchloric acid to glacial acetic acid is 1:(8~10), the polishing voltage is 15~20V, and the polishing time is 60~90s.

4. The in-situ dynamic observation method for the sensitization process of austenitic stainless steel according to claim 1, characterized in that, In step S2, the solution treatment includes heating to 1100~1150℃ at a heating rate of not less than 100℃ / s and holding at that temperature for 3~5 minutes.

5. The in-situ dynamic observation method for the sensitization process of austenitic stainless steel according to claim 1, characterized in that, In step S2, the sensitization isothermal treatment includes: cooling from the solution temperature to a target temperature in the range of 450 to 850°C at a cooling rate of 40 to 60°C / min, and isothermally holding at that temperature for more than 10 minutes.

6. The in-situ dynamic observation method for the sensitization process of austenitic stainless steel according to claim 1, characterized in that, In step S3, the image acquisition adopts an automatic time-series recording mode, acquiring one frame of image every 15-30 seconds for the first 30 minutes of isothermal insulation, and then reducing the acquisition frequency to one frame every 2-5 minutes.

7. The in-situ dynamic observation method for the sensitization process of austenitic stainless steel according to claim 6, characterized in that, The acquired images have a resolution of no less than 1024×1024 pixels, and the laser power and detector gain remain constant throughout the acquisition process.

8. The in-situ dynamic observation method for the sensitization process of austenitic stainless steel according to claim 1, characterized in that, In step S3, the fixed field of view is achieved by locking the X, Y, and Z coordinates of the HT-CLSM stage to ensure that all images come from the same observation area.

Images