CN-122016909-A - In-situ dynamic observation method for austenitic stainless steel sensitization process

Abstract

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

Inventors

• JIN XING
• YU JIAYAO
• WANG XIAOFENG
• YANG JING
• XU RONGJIE
• HUANG LEI

Assignees

• 鞍钢股份有限公司

Dates

Publication Date

20260512

Application Date

20260209

Claims (8)

1. 1. The in-situ dynamic observation method for the austenitic stainless steel sensitization process is characterized by comprising the following steps of: s1, sample preparation, namely grinding and polishing an austenitic stainless steel sample and electropolishing to obtain a mirror observation surface without a surface deformation layer; S2, in-situ thermal cycle experiment, namely placing the sample in an HT-CLSM high-temperature furnace, and carrying out solution treatment and sensitization isothermal treatment under the protection of inert atmosphere; s3, dynamic image acquisition, namely, in the sensitization isothermal stage, carrying out time sequence image acquisition on a fixed view field, and recording the dynamic process of carbide precipitation.
2. 2. The method for in-situ dynamic observation of an austenitic stainless steel sensitization process according to claim 1, wherein in the 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. 3. The method for in-situ dynamic observation of an austenitic stainless steel sensitization process according to claim 1, wherein in the step S1, a perchloric acid-glacial acetic acid mixed solution is adopted as an electrolyte for electrolytic polishing, 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. 4. The method for in-situ dynamic observation of an austenitic stainless steel sensitization process according to claim 1, wherein in step S2, the solution treatment comprises heating to 1100-1150 ℃ at a heating rate of not lower than 100 ℃ per second, and preserving heat for 3-5min.
5. 5. The method for in-situ dynamic observation of an austenitic stainless steel sensitization process according to claim 1, wherein in step S2, the sensitization isothermal treatment comprises cooling from a solid solution temperature to a target temperature within a range of 450-850 ℃ at a cooling rate of 40-60 ℃ per minute, and isothermal heat preservation is performed at the temperature for more than 10 minutes.
6. 6. The method for in-situ dynamic observation of an austenitic stainless steel sensitization process according to claim 1, wherein in step S3, an automatic time sequence recording mode is adopted for image acquisition, one frame of image is acquired every 15-30S 30min before isothermal heat preservation, and then the acquisition frequency is reduced to one frame every 2-5 min.
7. 7. The method of in-situ dynamic observation of austenitic stainless steel sensitization process of claim 6, wherein the resolution of the acquired image is not lower than 1024 x 1024 pixels, and the laser power and detector gain are kept constant throughout the acquisition process.
8. 8. The method according to claim 1, wherein in step S3, the fixed field of view is achieved by locking X, Y, Z coordinates of the HT-CLSM stage, ensuring that all images are from the same viewing area.

Description

In-situ dynamic observation method for austenitic stainless steel sensitization process Technical Field The invention relates to the technical field of austenitic stainless steel sensitization processes, in particular to an in-situ dynamic observation method for an austenitic stainless steel sensitization process. Background Sensitization of austenitic stainless steel is a major cause of deterioration or even failure of the austenitic stainless steel due to intergranular corrosion during use. The sensitization nature is caused by the fact that supersaturated solid-solution carbon combines with chromium at grain boundaries to form chromium-rich M 23C6 carbides, resulting in chromium depletion in the peripheral regions of the grain boundaries. The process occurs in a temperature range of 450-850 ℃, and is difficult to avoid particularly in the processes of welding, hot working and the like. In the prior art, national standard (GB/T) or ASTM standard methods for evaluating the sensitization degree of stainless steel, such as sulfuric acid-copper sulfate corrosion test, electrolytic etching method and the like, belong to an end point method and destructive inspection. That is, the heat-treated sample is subjected to chemical or electrolytic corrosion, and whether or not it is "sensitized" is qualitatively judged by metallographic observation or weight loss after bending. The traditional methods have the obvious defects that firstly, the dynamic process of carbide precipitation, such as the initial position and growth rate of nucleation and the connection mode along grain boundaries, cannot be reproduced and recorded, secondly, the result is seriously dependent on the experience of operators, the subjectivity is strong, only qualitative conclusions of yes or no can be given, the time-space evolution of the process cannot be quantified, thirdly, the tested sample is destroyed, cannot be used for subsequent other analysis, and cannot be monitored in situ in the real heat treatment process. The appearance of a high-temperature laser confocal microscope (HT-CLSM) provides a powerful in-situ, real-time and visual platform for the research of the high-temperature process of materials, and is widely applied to the research of metal recrystallization, phase transformation, grain growth and the like. However, the systematic study of HT-CLSM directly for austenitic stainless steel sensitization processes still faces the following key challenges and limitations: First, there is a lack of dedicated sample preparation methods for sensitization observations. The mechanical polishing deformation layer existing on the surface of the conventional metallographic sample is easy to recrystallize in the HT-CLSM heating process, a large number of new and non-original crystal boundaries are generated, and the actual observation of carbide precipitation behavior on the original austenite crystal boundaries is seriously interfered. A standardized set of sample pretreatment procedures that ensure that only the original grain boundaries are exposed at high temperatures has not been established in the prior art. Second, thermal cycling programs lack a targeted design for sensitization kinetics. Sensitization is a kinetic process that is strongly dependent on temperature and time. If the cooling rate is too slow, carbide may precipitate in advance in a higher temperature interval during the cooling process, so that the actual nucleation behavior at the target temperature cannot be observed, and if the cooling rate is too fast, thermal stress may be introduced or the furnace temperature control may be unstable. The conventional HT-CLSM experiment usually directly adopts a simpler heating-heat preservation-cooling program, and a thermal circulation path which rapidly enters an isothermal sensitization zone from a solid solution state cannot be finely designed so as to 'freeze' a high-temperature state, so that carbide precipitation is ensured to mainly occur in a set isothermal stage, and the starting point of an accurate capturing process is ensured. Third, the image acquisition strategy fails to match the dynamics of the sensitization process. The nucleation and early growth of carbide in the initial sensitization stage are faster, and the later connection and networking process is slower. If a fixed and lower-frequency image acquisition mode is adopted, key details of initial instant and early evolution of nucleation are very easy to miss, so that an observation sequence is discontinuous and incomplete, and a complete dynamic image cannot be constructed. Disclosure of Invention In order to overcome the defects of the prior art, the invention provides an in-situ dynamic observation method for an austenitic stainless steel sensitization process. The whole process of dynamic precipitation of carbide on the original grain boundary is clearly captured through systematic optimization from sample preparation and thermal cycle to image acquisition