In-situ identification analysis method for superfine non-metallic inclusions in steel

Abstract

The invention discloses an in-situ identification analysis method for superfine non-metallic inclusions in steel, and mainly solves the technical problems that the superfine non-metallic inclusions in the existing steel are difficult to identify and extract and the microstructure and phase composition of the inclusions are difficult to characterize. According to the technical scheme, the method for detecting and analyzing the small-size non-metallic inclusions in the steel by using the scanning electron microscope comprises the following steps: (1) preparing a metallographic sample; 2) preparing a transmission electron microscope sample, and determining an area where the inclusion of the metallographic sample is located by using a scanning electron microscope; carrying out accurate positioning and in-situ micro-nano thinning and cutting on the area where the inclusion of the metallographic sample is located by using a focused ion beam double-beam electron microscope system, and extracting the superfine non-metallic inclusion; and 3) analyzing the ultrafine non-metallic inclusions in the transmission electron microscope sample, and detecting the grain orientation of the ultrafine inclusions by using a transmission-type electron back scattering diffractometer. The method provided by the invention can accurately identify and extract the superfine non-metallic inclusions and the phase composition, components and grain orientation thereof in situ.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material inclusion analysis, and in particular to an in-situ identification and analysis method for ultrafine non-metallic inclusions in steel, and belongs to the technical field of steel material analysis and detection. Background Art

[0002] With the development of steelmaking technology, especially the application of new technologies for inclusion modification such as secondary purification and calcium treatment, magnesium treatment, and magnesium-calcium composite treatment, the purity of steel has been significantly improved, and the size and content of non-metallic inclusions in steel have been reduced. High purity, high homogeneity, and high performance have also become the key development directions of steel materials in the future.

[0003] At present, metallurgical technology can control harmful elements such as oxygen, nitrogen, and sulfur below 10ppm and the size of inclusions below 1μm, but this is a time-consuming, labor-intensive process with high production costs. The type, quantity, size, shape, and distribution of inclusions all affect the mechanical properties of steel, and the higher the strength of the steel, the more significant the impact of inclusions on its performance. The smaller the size of inclusions in the steel, the smaller the impact on fatigue performance. However, the unlimited pursuit of inclusion refinement has led to a significant increase in the production cost of steel.

[0004] The traditional characterization method of inclusion characteristics in steel is mainly to observe its morphology using a scanning electron microscope, analyze the composition of the inclusions using an energy dispersive spectrometer, and analyze it using special inclusion analysis equipment. For small complex inclusions, a transmission electron microscope can be used to analyze its internal structure and phase composition; however, the sample preparation process for a transmission electron microscope is relatively complicated, and sometimes the transmission electron microscope sample cannot observe the corresponding inclusion area, and the area that needs to be observed is highly random, making it difficult to observe and characterize ultrafine inclusions in a specific area in situ.

[0005] By observing the sample to be tested in metallographic phase, the size range of inclusions is determined, and the test parameters of the scanning electron microscope are adjusted according to this range to perform scanning electron microscope test and EDS spectrum analysis on the sample to be tested, so as to obtain the size, shape and composition data of inclusions in steel. This method adjusts different test parameters and scanning areas of the scanning electron microscope according to the different inclusion sizes observed in metallographic phase. The working distance of the scanning electron microscope is 15-20mm, and the operation process needs to be switched continuously. The working voltage and working distance range vary greatly, which has a great impact on the accuracy and reproducibility of the results.

[0006] A Chinese patent application with application publication number CN113899763A discloses a method for detecting and analyzing small-sized non-metallic inclusions in steel using a scanning electron microscope. The method obtains the number, size, shape and composition information of the inclusions by observing the sample to be tested in metallography, adjusting the scanning electron microscope and energy spectrum parameters, and setting inclusion classification standards. The method mainly performs a statistical analysis on the number, type and size of non-metallic inclusions on the overall detection surface of small-sized non-metallic inclusions in steel, and mainly analyzes the observation surface of inclusions larger than 1 μm, and cannot analyze the internal structure and phase composition of the inclusions.

[0007] In the prior art, the analysis and detection of ultrafine non-metallic inclusions in steel cannot analyze the internal structure and phase composition of the inclusions; the sample preparation process of transmission electron microscopy technology is relatively complicated and the required observation area is highly random, which cannot meet the detection requirements of ultrafine non-metallic inclusions in steel. Summary of the invention

[0008] The purpose of the present invention is to provide an in-situ identification and analysis method for ultrafine non-metallic inclusions in steel, which mainly solves the technical problems of difficulty in identifying and extracting ultrafine non-metallic inclusions in existing steel and difficulty in characterizing the microstructure and phase composition of inclusions.

[0009] The technical concept of the present invention is to use a scanning electron microscope to determine the area where the ultrafine non-metallic inclusions in the steel are located; use a focused ion beam double-beam electron microscope system to accurately locate and in-situ micro-nano thinning and cutting of the area where the ultrafine non-metallic inclusions in the steel are located to prepare a transmission electron microscope sample; characterize the ultrafine non-metallic inclusions through a transmission electron microscope; use a transmission electron backscatter diffractometer to detect the grain orientation of the ultrafine inclusions to obtain the microstructural characteristics of the ultrafine non-metallic inclusions in the steel.

[0010] The technical solution of the present invention is an in-situ identification and analysis method for ultrafine non-metallic inclusions in steel, comprising the following steps:

[0011] 1) preparing a metallographic sample, and mounting the surface of the steel sample to be tested using a hot mounting machine; grinding, polishing, and cleaning the mounted sample to obtain a metallographic sample;

[0012] 2) Prepare a transmission electron microscope sample and use a scanning electron microscope to determine the area where the metallographic sample inclusions are located; use a focused ion beam double-beam electron microscope system to accurately locate and in-situ micro-nano thinning and cutting of the area where the metallographic sample inclusions are located, extract ultrafine non-metallic inclusions, and obtain a transmission electron microscope sample;

[0013] 3) Analyze the ultrafine non-metallic inclusions in the transmission electron microscope samples, and use the transmission electron microscope to detect the morphology, size, crystal structure, composition and phase composition of the ultrafine non-metallic inclusions; use the transmission electron backscatter diffractometer to detect the grain orientation of the ultrafine inclusions to obtain the microstructural characteristics of the ultrafine non-metallic inclusions in the steel.

[0014] Further, step 1) of grinding, polishing and cleaning the mounted sample comprises:

[0015] 1.1) The mounted samples were ground and polished. The sandpaper grits were selected from 180 to 1200 meshes in the grinding and polishing machine, and the grinding time for each grit was 1.5-2 min. The polishing liquid was 3 μm and 0.05 μm diamond suspensions in turn, and the polishing time was 2-3 min.

[0016] 1.2) Place the polished metallographic sample in alcohol and perform ultrasonic cleaning for 10-15 minutes.

[0017] Further, the step 2) of preparing the transmission electron microscope sample comprises:

[0018] 2.1) Use the scanning electron microscope mode of the focused ion beam dual beam electron microscope system to accurately locate the area where the inclusions are located in the metallographic sample;

[0019] 2.2) Using a focused ion beam of a focused ion beam dual-beam electron microscope system to etch and mark the area where the ultrafine inclusions are located, and deposit a layer of metal platinum protective layer, and perform ion beam thinning and cutting on the area around the metal platinum layer to obtain the target sample;

[0020] 2.3) Extract the target sample with a nanomanipulator; weld the target sample to a metal conductive copper mesh;

[0021] 2.4) The target sample on the conductive copper mesh is further finely thinned using the focused ion beam of the focused ion beam dual-beam electron microscope system until the final thickness of the ultrafine inclusion sample is less than 100 nm, thereby obtaining a transmission electron microscope sample.

[0022] Further, the step 3) of analyzing ultrafine non-metallic inclusions in the transmission electron microscope sample comprises:

[0023] 3.1) Observe ultrafine non-metallic inclusions using a transmission electron microscope to obtain the morphology and size of non-metallic inclusions in the sample;

[0024] 3.2) Use a transmission electron microscope to perform electron diffraction on different areas of the transmission electron microscope sample to obtain the crystal structure and phase composition of non-metallic inclusions in the sample;

[0025] 3.3) Use a transmission electron microscope energy spectrometer to analyze the composition of the transmission electron microscope sample to obtain the element composition and element surface distribution of the non-metallic inclusions in the sample;

[0026] 3.4) Use a transmission electron backscatter diffractometer to collect transmission electron diffraction patterns of transmission electron microscope samples, and perform crystallographic analysis to determine the grain orientation of non-metallic inclusions in the samples.

[0027] Compared with the prior art, the present invention has the following positive effects: 1) The focused ion beam of the focused ion beam dual-beam electron microscope system is used for in-situ micro-nano processing of ultrafine non-metallic inclusions in steel, which can extract specific ultrafine non-metallic inclusions and prepare high-quality transmission electron microscope samples of ultrafine non-metallic inclusions, with high processing efficiency, accurate inclusion positioning, and accurate and reliable analysis results. 2) Combining the focused ion beam in-situ micro-nano processing and transmission electron microscope characterization of the focused ion beam dual-beam electron microscope system, the crystal structure and phase of ultrafine non-metallic inclusions can be accurately analyzed in situ, and the analysis is accurate and high in precision. 3) Combined with transmission electron microscopy and transmission electron backscatter diffractometer analysis, the phase composition, composition and grain orientation of ultrafine non-metallic inclusions can be accurately obtained. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described and elaborated below in conjunction with embodiments.

[0029] Example 1: Ultrafine non-metallic inclusions in B500LF steel with a thickness of 8 mm were detected. The model of the focused ion beam double beam electron microscope was Zeiss Auriga.

[0030] An in-situ identification and analysis method for ultrafine non-metallic inclusions in steel comprises the following steps:

[0031] 1) preparing a metallographic sample, mounting the surface of the steel sample to be tested with a hot mounting machine; grinding, polishing and cleaning the mounted sample to obtain a metallographic sample; including,

[0032] 1.1) Select the position of 1 / 4 of the width of the hot-rolled plate, cut a sample of 20mm×20mm, take two pieces of its longitudinal section of 8mm×20mm, and mount them by hot mounting method using a hot mounting machine; grind and polish the mounted samples, and use sandpaper with a particle size ranging from 180 mesh to 1200 mesh in the grinding process on the grinding and polishing machine, and the grinding time for each particle size is 1.5min; during polishing, the polishing liquid is selected in turn as 3μm and 0.05μm diamond suspension, and the polishing time is 2min;

[0033] 1.2) Place the polished metallographic sample in alcohol and perform ultrasonic cleaning for 10 minutes;

[0034] 2) Prepare a transmission electron microscope sample, and use a scanning electron microscope to determine the area where the metallographic sample inclusions are located; use a focused ion beam double-beam electron microscope system to accurately locate and in-situ micro-nano thinning and cutting of the area where the metallographic sample inclusions are located, extract ultrafine non-metallic inclusions, and obtain a transmission electron microscope sample; including,

[0035] 2.1) Place the metallographic sample of B500LF steel to be tested on the adjustable sample stage of the focused ion beam dual-beam electron microscope system, and scan and observe the metallographic sample in the scanning electron microscope mode of the focused ion beam dual-beam electron microscope system to preliminarily determine and locate the ultrafine non-metallic inclusion area in the steel;

[0036] 2.2) Adjust the tilt angle of the sample stage in the focused ion beam dual-beam electron microscope system to 54o, use the focused ion beam in the focused ion beam dual-beam electron microscope system to accurately locate the ultrafine non-metallic inclusions in the B500LF steel sample, and etch and mark the area where the ultrafine inclusions are located, and deposit a long strip of metal platinum protective layer on the surface of the area to be processed, with a thickness of 800nm, a width of 2mm, and a length of 8mm; use a gallium ion beam, adopt a trapezoidal mode, and etch the area to be processed around the ultrafine inclusions deposited with the platinum protective layer at a high current of 18nA to remove the material around the target sample; then adjust the high current to a low current of 600pA, adopt the cross-section refinement mode, and refine the two surfaces of the sample to make the surface of the processed sample smooth and the inclusions clearly visible; and rotate the ion beam window 180 degrees to facilitate the next step of sampling to obtain the target sample;

[0037] 2.3) Extract the target sample with a nanomanipulator, move the nanomanipulator in the focused ion beam dual beam electron microscope system close to the top of the sample, and weld the sample and the nanomanipulator with deposited metal platinum; then further perform ion beam thinning and cutting on the sample, so that the nanomanipulator takes the ultrafine inclusion sample to be analyzed away from the entire initial sample, and transfers the target sample to the manipulator; move the ultrafine inclusion sample cut from the sample close to the copper mesh, and spot weld the target sample to the metal conductive copper mesh using deposited metal platinum; then use the ion beam to separate the nanomanipulator from the ultrafine inclusion sample to be analyzed, and obtain the target sample on the conductive copper mesh;

[0038] 2.4) Using the focused ion beam of the focused ion beam dual-beam electron microscope system, the target sample on the conductive copper mesh is further finely thinned. The cross-section refinement mode is used to further finely thin the sample at a low current of 120pA until the thickness is penetrable by the electron beam. After the focused ion beam thinning, the sample thickness is 80nm, and a transmission electron microscope sample is obtained;

[0039] 3) Analyze the ultrafine non-metallic inclusions in the transmission electron microscope sample, use the transmission electron microscope to detect the shape, size, crystal structure, composition and phase composition of the ultrafine non-metallic inclusions; use the transmission electron backscatter diffractometer to detect the grain orientation of the ultrafine inclusions, and obtain the microstructural characteristics of the ultrafine non-metallic inclusions in the steel; including,

[0040] 3.1) Observe the ultrafine non-metallic inclusions obtained after focused ion beam in-situ cutting by transmission electron microscopy to obtain the morphology and size of the non-metallic inclusions in the sample;

[0041] 3.2) Perform electron diffraction on different areas of the TEM sample using a transmission electron microscope to obtain electron diffraction patterns, and analyze the electron diffraction patterns to obtain the crystal structure and phase composition of non-metallic inclusions in the sample;

[0042] 3.3) Scan the TEM sample with a TEM spectrometer to obtain the element composition and element distribution of non-metallic inclusions in the sample;

[0043] 3.4) Use a transmission electron backscatter diffractometer to collect transmission electron diffraction patterns of transmission electron microscope samples, and perform crystallographic analysis to determine the grain orientation of non-metallic inclusions in the samples.

[0044] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. An in-situ identification and analysis method for ultrafine non-metallic inclusions in steel, characterized in that: The method comprises the following steps: 1) preparing a metallographic sample, and mounting the surface of the steel sample to be tested using a hot mounting machine; grinding, polishing, and cleaning the mounted sample to obtain a metallographic sample; 2) Prepare a transmission electron microscope sample and use a scanning electron microscope to determine the area where the metallographic sample inclusions are located; use a focused ion beam double-beam electron microscope system to accurately locate and in-situ micro-nano thinning and cutting of the area where the metallographic sample inclusions are located, extract ultrafine non-metallic inclusions, and obtain a transmission electron microscope sample; 3) Analyze the ultrafine non-metallic inclusions in the transmission electron microscope sample, use the transmission electron microscope to detect the shape, size, crystal structure, composition and phase composition of the ultrafine non-metallic inclusions; use the transmission electron backscatter diffractometer to detect the grain orientation of the ultrafine inclusions, and obtain the microstructural characteristics of the ultrafine non-metallic inclusions in the steel; including, 3.1) Observe ultrafine non-metallic inclusions using a transmission electron microscope to obtain the morphology and size of non-metallic inclusions in the sample; 3.2) Use a transmission electron microscope to perform electron diffraction on different areas of the transmission electron microscope sample to obtain the crystal structure and phase composition of non-metallic inclusions in the sample; 3.3) Use a transmission electron microscope energy spectrometer to analyze the composition of the transmission electron microscope sample to obtain the element composition and element surface distribution of the non-metallic inclusions in the sample; 3.4) Use a transmission electron backscatter diffractometer to collect transmission electron diffraction patterns of transmission electron microscope samples, and perform crystallographic analysis to determine the grain orientation of non-metallic inclusions in the samples.

2. The in-situ identification and analysis method for ultrafine non-metallic inclusions in steel according to claim 1, characterized in that: Step 1) grinding, polishing and cleaning the mounted sample comprises: 1.1) The mounted samples were ground and polished. The sandpaper grits were selected from 180 to 1200 meshes in the grinding and polishing machine, and the grinding time for each grit was 1.5-2 min. The polishing liquid was 3 μm and 0.05 μm diamond suspensions in turn, and the polishing time was 2-3 min. 1.2) Place the polished metallographic sample in alcohol and perform ultrasonic cleaning for 10-15 minutes.

3. The in-situ identification and analysis method for ultrafine non-metallic inclusions in steel according to claim 1, characterized in that: Step 2) preparing a transmission electron microscope sample comprises: 2.1) Use the scanning electron microscope mode of the focused ion beam dual beam electron microscope system to accurately locate the area where the inclusions are located in the metallographic sample; 2.2) Using a focused ion beam of a focused ion beam dual-beam electron microscope system to etch and mark the area where the ultrafine inclusions are located, and deposit a layer of metal platinum protective layer, and perform ion beam thinning and cutting on the area around the metal platinum layer to obtain the target sample; 2.3) Extract the target sample with a nanomanipulator; weld the target sample to a metal conductive copper mesh; 2.4) The target sample on the conductive copper mesh is further finely thinned using the focused ion beam of the focused ion beam dual-beam electron microscope system until the final thickness of the ultrafine inclusion sample is less than 100 nm, thereby obtaining a transmission electron microscope sample.