Method for identifying martensite phase in ferrite steel based on energy spectrum analysis

Abstract

The invention discloses a method for identifying a martensite phase in ferritic steel based on energy spectrum analysis, and relates to the technical field of iron and steel material structure identification, and the method comprises the following steps: sequentially carrying out mechanical grinding and electrolytic double spraying on a ferritic stainless steel sample to prepare a sample with a thin region; loading the sample into a transmission electron microscope, vacuumizing to a working vacuum degree, and observing the microtopography of different phases in a thin region of the sample in an imaging mode; switching the transmission electron microscope to a diffraction mode, focusing an electron beam in a selected area in the thin area, collecting diffraction spot patterns of different phases in the thin area, and calculating lattice parameters of the different phases; respectively carrying out EDS energy spectrum analysis on each phase of the collected diffraction spot patterns, and calculating corresponding chemical components; and determining a ferrite phase and a martensite phase according to the microstructure, lattice parameters and chemical components of different phases in the thin region. According to the method, the martensite phase with relatively small lattice distortion can be accurately identified, and meanwhile, the lattice parameters of the martensite phase can be represented.

Description

Technical Field

[0001] The present invention relates to the technical field of steel material tissue identification, and in particular to an identification method of a martensite phase in ferrite steel based on energy spectrum analysis. Background Art

[0002] Among ferritic stainless steels, Cr12 stainless steel is a typical ultra-low carbon product with a wide range of applications, including coal, railways, and electric power systems. However, different application scenarios require Cr12 stainless steel to have different performance characteristics due to different service environments, which puts forward more detailed requirements on the production process and microstructure of the material. Ultra-low carbon ferritic stainless steel undergoes different heat treatment processes to generate a certain proportion of martensite phase on the ferrite matrix through phase transformation, making the steel a ferrite-martensite dual-phase structure. Different heat treatment processes achieve different two-phase ratios, and ultimately it is suitable for service environments under different working conditions. Therefore, how to accurately identify the martensite phase in ferritic stainless steel under different heat treatment processes is a key issue in the production and research and development of ferritic stainless steel.

[0003] At present, the main methods for identifying the phase structure of steel materials are microstructure observation and electron backscatter diffraction (EBSD) imaging. Among them, the microstructure observation method selects a suitable etchant and uses the morphological characteristics of optical microscopes and scanning electron microscopes to identify simple two-phase or multi-phase structures; the EBSD imaging method analyzes the diffraction pattern images of different phases and identifies them based on the clarity of the imaging, which usually requires large crystal structure differences between different tissues.

[0004] However, in ultra-low carbon ferritic stainless steel, due to the ultra-low carbon content, the corrosion resistance of the martensite structure generated by the phase transformation of ultra-low carbon ferritic stainless steel is very close to that of the ferrite structure. At the same time, the lattice distortion is small, which makes it difficult to distinguish the diffraction pattern images of the martensite phase and the ferrite phase. Therefore, it is difficult to identify the ferrite phase and the martensite phase in ultra-low carbon ferritic stainless steel using the existing microstructure observation method and EBSD technology imaging method. Summary of the Invention

[0005] In order to solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a method for identifying the martensite phase in ferrite steel based on energy spectrum analysis.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for identifying martensite phase in ferritic steel based on energy spectrum analysis is provided, comprising:

[0008] Ferritic stainless steel samples were subjected to mechanical grinding and electrolytic double spraying in sequence to prepare specimens with thin areas;

[0009] Place the sample into the transmission electron microscope, evacuate to the working vacuum, set the electron gun acceleration voltage, beam current, objective lens aperture and working distance, and observe the microscopic morphology of different phases in the thin area of ​​the sample in the imaging mode;

[0010] Switch the transmission electron microscope to diffraction mode, focus the electron beam on a selected area in the thin region, adjust the beam spot size, phosphor screen current, and CCD exposure time, collect diffraction spot patterns of different phases in the thin region, and calculate the lattice parameters of different phases;

[0011] In the imaging mode or scanning mode of the transmission electron microscope, perform EDS energy spectrum analysis on each phase of the collected diffraction spot pattern, obtain each corresponding X-ray energy spectrum, and calculate the corresponding chemical composition;

[0012] Based on the micromorphology, lattice parameters and chemical composition of different phases in the thin area of ​​the sample, a comprehensive analysis was carried out to determine the ferrite phase and martensite phase.

[0013] In some optional embodiments, the mechanical grinding includes: using a plurality of sandpapers with gradually finer grain sizes to grind the ferritic stainless steel sample in sequence, so that the sample reaches a set thickness.

[0014] In some optional embodiments, the electrolytic double spray includes: placing the mechanically ground ferritic stainless steel sample in a special electrolytic double spray instrument, using the sample as an anode, installing cathode nozzles on both sides of the sample, and passing a set electrolyte into the cathode nozzle to electrolytically corrode the sample.

[0015] In some optional embodiments, the working vacuum is set to 10 -4 ~10 -6 Pa, the electron gun acceleration voltage is set to 180-200 kV, the beam current is set to 5-10 nA, the objective lens aperture is set to 10-20 μm, and the working distance is set to 1-2 mm.

[0016] In some optional implementations, the beam spot size is set to 6-7, the phosphor screen current is set to 0.4-0.6 nA, and the CCD exposure time is set to 0.3-0.5 s.

[0017] In some optional implementations, when performing EDS energy spectrum analysis, the energy range of the energy spectrometer is set to 0-10 keV, the acquisition time is set to 60-90 s, and the dead time is set to 20-30%.

[0018] In some optional embodiments, the ferrite phase and the martensite phase are determined by:

[0019] If a phase exhibits lath-like features in microscopic morphology, a body-centered tetragonal structure is shown by lattice parameter calculation, and its chemical composition is similar to that of the matrix ferrite, then the current phase is determined to be martensite;

[0020] If a phase is equiaxed grains in microscopic morphology, shows a body-centered cubic structure through lattice parameter calculation, and has a chemical composition similar to that of the matrix ferrite, then the current phase is determined to be a ferrite phase.

[0021] The main advantages of the technical solution of the present invention are as follows:

[0022] The method for identifying the martensite phase in ferrite steel based on energy spectrum analysis of the present invention obtains the micromorphology, lattice parameters and chemical composition of the ferrite phase and the martensite phase for comprehensive analysis by combining transmission electron microscope electron selected area diffraction spot calibration and energy spectrum analysis. It can accurately identify the martensite phase with smaller lattice distortion and characterize the lattice parameters of the martensite phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the embodiments of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0024] Figure 1 A flow chart of a method for identifying martensite phase in ferrite steel based on energy spectrum analysis provided in an embodiment of the present invention;

[0025] Figure 2 A ferrite phase diffraction pattern provided by an embodiment of the present invention;

[0026] Figure 3 for Figure 2 The energy spectrum corresponding to ferrite;

[0027] Figure 4 A martensite phase diffraction pattern provided by an embodiment of the present invention;

[0028] Figure 5 for Figure 4 The energy spectrum corresponding to martensite. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] The technical solutions provided by the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] refer to Figure 1 The embodiment of the present invention provides a method for identifying the martensite phase in ferritic steel based on energy spectrum analysis. The method is used to identify the ferrite phase and the martensite phase in ultra-low carbon ferritic stainless steel, comprising the following steps:

[0032] Step 1: mechanically grinding and electrolytic double spraying are performed on the ferritic stainless steel sample in sequence to prepare a sample with a thin area;

[0033] In the embodiment of the present invention, the thin area refers to a region that can be penetrated by an electron beam of a transmission electron microscope, so as to facilitate subsequent observation by the transmission electron microscope.

[0034] Step 2: Place the sample into a transmission electron microscope, evacuate to the working vacuum, set the electron gun acceleration voltage, beam current, objective lens aperture, and working distance, and observe the microscopic morphology of different phases in the thin area of ​​the sample in imaging mode;

[0035] In the embodiment of the present invention, since there are certain differences in the microscopic morphological characteristics of ferrite and martensite, by observing the microscopic morphology of different phases in the thin area of ​​the sample, the ferrite phase and martensite phase can be preliminarily identified and located, and the area of ​​interest can be selected for subsequent selected area diffraction and energy spectrum analysis.

[0036] Step 3: Switch the transmission electron microscope to diffraction mode, focus the electron beam on a selected area in the thin region, adjust the beam spot size, screen current, and CCD exposure time, collect diffraction spot patterns of different phases in the thin region, and calculate the lattice parameters of the different phases;

[0037] In an embodiment of the present invention, the transmission electron microscope is switched to the diffraction mode, and based on the ferrite phase and martensite phase preliminarily identified and located in step 2, diffraction spot patterns are collected for different phases respectively to obtain different corresponding diffraction spot patterns, and the corresponding lattice parameters are calculated and determined based on the diffraction spot patterns.

[0038] In the embodiment of the present invention, the distance between the diffraction spots is measured and combined with the camera constant to calculate the lattice parameters, including the interplanar spacing (d value) and the lattice constants (a, b, c). The lattice constants a, b, and c represent the side lengths of the unit cell, specifically the lengths along the three edges of the unit cell.

[0039] Step 4: Under the imaging mode or scanning mode of the transmission electron microscope, perform EDS energy spectrum analysis on each phase of the collected diffraction spot pattern, obtain each corresponding X-ray energy spectrum, and calculate the corresponding chemical composition;

[0040] In an embodiment of the present invention, in the imaging mode or scanning mode of the transmission electron microscope, an energy spectrometer is used to perform energy spectrum analysis on each phase of the collected diffraction spot pattern, obtain each corresponding X-ray energy spectrum, and calculate the corresponding element content based on the X-ray energy spectrum.

[0041] Step 5: Perform a comprehensive analysis based on the micromorphology, lattice parameters, and chemical composition of different phases in the thin area of ​​the sample to determine the ferrite phase and martensite phase.

[0042] In an embodiment of the present invention, the micromorphology, lattice parameters and chemical composition of different phases in the thin area of ​​the sample obtained above are combined for comprehensive analysis and judgment, which can accurately distinguish the ferrite phase and the martensite phase, thereby achieving effective identification of the martensite phase in ferrite steel.

[0043] The method for identifying the martensite phase in ferrite steel based on energy spectrum analysis provided in an embodiment of the present invention obtains the micromorphology, lattice parameters and chemical composition of the ferrite phase and the martensite phase for comprehensive analysis by combining transmission electron microscope electron selected area diffraction spot calibration and energy spectrum analysis. It can accurately identify the martensite phase with smaller lattice distortion and characterize the lattice parameters of the martensite phase.

[0044] It should be noted that, in the embodiments of the present invention, ultra-low carbon ferritic stainless steel refers to ferritic stainless steel with a carbon content of less than or equal to 0.01%.

[0045] Furthermore, in an embodiment of the present invention, the mechanical grinding includes: using a plurality of sandpapers with gradually finer grain sizes to grind the ferritic stainless steel sample in sequence, so that the sample reaches a set thickness.

[0046] The particle sizes of the multiple sandpapers are specifically set according to actual conditions.

[0047] The thickness is set according to actual conditions, and is set to 50-80 μm in the embodiment of the present invention.

[0048] Furthermore, in an embodiment of the present invention, the electrolytic double-spraying includes: placing the mechanically ground ferritic stainless steel sample in a dedicated electrolytic double-spraying instrument, using the sample as an anode, installing cathode nozzles on both sides of the sample, and passing a set electrolyte into the cathode nozzle to electrolytically corrode the sample.

[0049] In an embodiment of the present invention, when performing electrolytic double spraying, under the action of the electrolyte jets ejected simultaneously from the two cathode nozzles, the central area of ​​the sample is selectively electrolytically corroded and thinned until perforation occurs. The edge area of ​​the perforation is the thin area that can be penetrated by the electron beam of the transmission electron microscope and can be used for subsequent transmission electron microscope observation.

[0050] In the embodiment of the present invention, the thin region is an extremely thin region with a thickness less than 100 nm.

[0051] The electrolyte is specifically set according to actual conditions, and is set to a perchloric acid alcohol solution in the embodiment of the present invention.

[0052] In the embodiments of the present invention, mechanical grinding of the sample can be performed to rapidly thin the sample, providing a sample of suitable thickness for subsequent electrolytic double-spraying. Electrolytic double-spraying of the mechanically ground sample can produce a thin region that is "transparent" to the electron beam, facilitating subsequent transmission electron microscopy observation. Electrolytic double-spraying also better preserves the sample's original microstructure, preventing phase changes or deformation caused by mechanical stress, which could affect the accuracy of subsequent analytical results.

[0053] Furthermore, in the embodiment of the present invention, in step 2, the working vacuum degree is set to 10 -4 ~10 -6 Pa to ensure stable transmission of the electron beam and reduce interference from gas molecules; the electron gun acceleration voltage is set to 180-200 kV to ensure that the electron beam can penetrate the sample and produce a high-resolution image; the beam current is set to 5-10 nA to reduce irradiation damage to the sample while ensuring image brightness; the objective lens aperture is set to 10-20 μm to improve imaging contrast; and the working distance is set to 1-2 mm to ensure image resolution.

[0054] In the embodiment of the present invention, a clear microscopic morphology can be obtained by performing imaging using a transmission electron microscope based on the parameters set above.

[0055] Furthermore, in an embodiment of the present invention, in step 3, the beam spot size (Spot Size) is set to 6-7, the fluorescent screen current is set to 0.4-0.6 nA, and the CCD exposure time is set to 0.3-0.5 s. In this way, sufficient beam intensity can be provided to obtain clear diffraction spots, while ensuring that the beam spot is small enough to accurately select a single phase for single crystal diffraction analysis and obtain a clear and calibrable diffraction spot pattern.

[0056] Furthermore, in an embodiment of the present invention, in step 4, the energy range of the energy spectrometer is set to 0-10 keV to ensure that the characteristic X-ray peaks of the main chemical elements can be covered; the acquisition time is set to 60-90 s, and the dead time is set to 20-30% to ensure that a sufficiently high counting rate can be obtained, the spectral peak intensity and statistical accuracy can be guaranteed, the noise can be reduced, and the signal loss can be controlled at an acceptable level to ensure the accuracy of quantitative analysis of chemical elements.

[0057] Furthermore, since ferrite usually has equiaxed or polygonal grains, while martensite usually has lath-shaped, lens-shaped features or has substructures such as high-density dislocations inside; ferrite has a typical body-centered cubic structure, while martensite usually has a body-centered tetragonal structure.

[0058] To this end, in an embodiment of the present invention, in step 5, the ferrite phase and the martensite phase are determined in the following manner:

[0059] If a phase exhibits lath-like features in microscopic morphology, shows a body-centered tetragonal structure (c / a>1) through lattice parameter calculation, and has a chemical composition similar to that of the matrix ferrite, then the current phase is determined to be martensite;

[0060] If a phase is equiaxed grains in microscopic morphology, shows a body-centered cubic structure (c / a=1) through lattice parameter calculation, and has a chemical composition similar to that of the matrix ferrite, then the current phase is determined to be a ferrite phase.

[0061] To make the above technical solution of the present invention clearer, the technical solution of the present invention will be described clearly and completely in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0062] Example 1

[0063] The specific steps of Example 1 are as follows:

[0064] Step 1: mechanically grinding and electrolytic double spraying are performed on the ferritic stainless steel sample in sequence to prepare a sample with a thin area;

[0065] Step 2: Place the sample into the transmission electron microscope and evacuate to 10 -6 Pa, set the electron gun acceleration voltage to 180 kV, the beam current to 5 nA, the objective lens aperture to 10 μm, and the working distance to 1 mm, and observe the microscopic morphologies of different phases in the thin area of ​​the sample in the imaging mode;

[0066] Step 3: Switch the transmission electron microscope to diffraction mode, focus the electron beam on the selected area in the thin region, adjust the beam spot size to 6, set the phosphor screen current to 0.4 nA, and the CCD exposure time to 0.3 s, collect the diffraction spot patterns of different phases in the thin region, and calculate the lattice parameters of the different phases;

[0067] Step 4: In the imaging mode or scanning mode of the transmission electron microscope, set the energy range of the spectrometer to 0-10 keV, the acquisition time to 60 seconds, and the dead time to 20%. Perform EDS energy spectrum analysis on each phase of the collected diffraction spot pattern, obtain each corresponding X-ray energy spectrum, and calculate the corresponding chemical composition;

[0068] Step 5: Perform a comprehensive analysis based on the micromorphology, lattice parameters, and chemical composition of different phases in the thin area of ​​the sample; if a phase has lamellar features in micromorphology, a body-centered tetragonal structure is shown by lattice parameter calculation, and the chemical composition is similar to that of the matrix ferrite, then the current phase is determined to be a martensite phase; if a phase has equiaxed grains in micromorphology, a body-centered cubic structure is shown by lattice parameter calculation, and the chemical composition is similar to that of the matrix ferrite, then the current phase is determined to be a ferrite phase.

[0069] refer to Figure 2-5 , Figure 2 A ferrite phase diffraction pattern provided by an embodiment of the present invention; Figure 3 for Figure 2 The energy spectrum corresponding to ferrite; Figure 4 A martensite phase diffraction pattern provided by an embodiment of the present invention; Figure 5 for Figure 4 The energy spectrum corresponding to martensite.

[0070] It can be seen that the method for identifying the martensite phase in ferritic steel based on energy spectrum analysis provided by the embodiment of the present invention can accurately identify the martensite phase with smaller lattice distortion and can characterize the lattice parameters of the martensite phase.

[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In addition, "front", "back", "left", "right", "upper" and "lower" in this document are all referenced to the placement states shown in the accompanying drawings.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for identifying martensite phase in ferritic steel based on energy spectrum analysis, characterized in that: include: Ferritic stainless steel samples were subjected to mechanical grinding and electrolytic double spraying in sequence to prepare specimens with thin areas; Place the sample into the transmission electron microscope, evacuate to the working vacuum, set the electron gun acceleration voltage, beam current, objective lens aperture and working distance, and observe the microscopic morphology of different phases in the thin area of ​​the sample in the imaging mode; Switch the transmission electron microscope to diffraction mode, focus the electron beam on a selected area in the thin region, adjust the beam spot size, phosphor screen current, and CCD exposure time, collect diffraction spot patterns of different phases in the thin region, and calculate the lattice parameters of different phases; In the imaging mode or scanning mode of the transmission electron microscope, perform EDS energy spectrum analysis on each phase of the collected diffraction spot pattern, obtain each corresponding X-ray energy spectrum, and calculate the corresponding chemical composition; Based on the micromorphology, lattice parameters and chemical composition of different phases in the thin area of ​​the sample, a comprehensive analysis was carried out to determine the ferrite phase and martensite phase.

2. The method for identifying the martensite phase in ferrite steel based on energy spectrum analysis according to claim 1, characterized in that: The mechanical grinding includes: using a plurality of sandpapers with gradually finer grain sizes to grind the ferritic stainless steel sample in sequence, so that the sample reaches a set thickness.

3. The method for identifying martensite phase in ferrite steel based on energy spectrum analysis according to claim 1, characterized in that: The electrolytic double-spray method includes placing a mechanically ground ferritic stainless steel sample in a dedicated electrolytic double-spray instrument, using the sample as an anode, installing cathode nozzles on both sides of the sample, and introducing a set electrolyte into the cathode nozzles to electrolytically corrode the sample.

4. The method for identifying martensite phase in ferrite steel based on energy spectrum analysis according to claim 1, characterized in that: The working vacuum is set to 10 -4 ~10 -6 Pa, the electron gun acceleration voltage is set to 180-200 kV, the beam current is set to 5-10 nA, the objective lens aperture is set to 10-20 μm, and the working distance is set to 1-2 mm.

5. The method for identifying martensite phase in ferrite steel based on energy spectrum analysis according to claim 1, characterized in that: The beam spot size is set to 6-7, the phosphor screen current is set to 0.4-0.6 nA, and the CCD exposure time is set to 0.3-0.5 s.

6. The method for identifying martensite phase in ferrite steel based on energy spectrum analysis according to claim 1, characterized in that: When performing EDS spectrum analysis, the energy range of the spectrometer is set to 0-10 keV, the acquisition time is set to 60-90 s, and the dead time is set to 20-30%.

7. The method for identifying martensite phase in ferrite steel based on energy spectrum analysis according to claim 1, characterized in that: The ferrite and martensite phases are determined by: If a phase exhibits lath-like features in microscopic morphology, a body-centered tetragonal structure is shown by lattice parameter calculation, and its chemical composition is similar to that of the matrix ferrite, then the current phase is determined to be martensite; If a phase is equiaxed grains in microscopic morphology, shows a body-centered cubic structure through lattice parameter calculation, and has a chemical composition similar to that of the matrix ferrite, then the current phase is determined to be a ferrite phase.

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