Method for judging segregation elements and segregation degree of steel by using scanning electron microscope-energy disperse spectroscopy

Abstract

The invention belongs to the technical field of steel detection, and particularly discloses a method for judging segregation elements and segregation degree of steel by using a scanning electron microscope-energy disperse spectroscopy, and the method comprises the following steps: firstly, carrying out sample preparation on the cross section of to-be-detected steel, and carrying out acid pickling; identifying whether black spots exist at the center of the sample or not by naked eyes of a worker and screening; scanning and analyzing the black spots of the sample by using SEM-EDS, and determining segregation elements and segregation degree of the sample; carrying out sample preparation and acid pickling on the sample along the longitudinal section, then identifying whether the sample has a black line or not, and screening; and performing line scanning analysis along the black line of the sample to confirm segregation elements and contents of the longitudinal section of the sample. In order to solve the problems of complex operation and high cost of steel segregation detection by adopting an in-situ analyzer at present, the invention solves the common problems of high equipment requirement, complex operation and high cost of steel segregation detection means in the prior art in a manner of combining SEM-EDS with simple chemical treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel detection, and particularly relates to a method for determining steel segregation elements and segregation degree by using a scanning electron microscope-energy spectrometer. BACKGROUND

[0002] In the field of material science and metallurgy, segregation refers to the phenomenon that solute elements in an alloy are unevenly distributed in different parts of the microstructure. This phenomenon is a key factor affecting the performance and quality of materials. It usually occurs during solid-state phase transition and solidification, and its mechanism is closely related to the temperature gradient, solute diffusion rate and crystal growth mode during alloy solidification. When the alloy is in the solidification stage, the first solidified crystals tend to repel part of the solute elements, causing the solute concentration in the un-solidified liquid phase to gradually increase. With the continuous advancement of the solidification process, these solute-rich liquid phases eventually form composition segregation areas in the material, which significantly affect the overall performance of the material.

[0003] The negative effects of segregation on the performance of steel are widespread and far-reaching. From the perspective of mechanical properties, segregation can significantly reduce the ductility of steel, making it prone to brittle fracture when subjected to external forces. In terms of corrosion resistance, segregation areas often become weak links for corrosion, accelerating the corrosion process of steel and shortening its service life. At the same time, segregation also increases the risk of thermal cracking during hot working of steel, seriously affecting the product's qualification rate. For example, in the fields of automotive steel and construction steel, even slight segregation of steel can cause significant safety hazards, so accurate detection and effective control of steel segregation are of great significance.

[0004] Currently, the detection techniques used for steel segregation mainly rely on ultrasonic segregation detection and in-situ analyzer detection. Ultrasonic segregation detection technology is based on the differences in propagation speed and reflection characteristics of ultrasonic waves in different composition media, achieving rapid detection of internal segregation of steel. However, this technology requires high precision equipment, and the detection results are easily disturbed by the material surface state and internal structure, and it is difficult to accurately quantify the segregation degree. In-situ analyzer detection is through in-situ composition analysis of steel samples to obtain element distribution information. However, this type of equipment has high purchase cost and complex operation process, and requires professional technical personnel for maintenance and operation.

[0005] In summary, the detection means of the prior art for steel segregation generally exist the problems of high equipment requirement, complex operation and high cost, which is difficult to meet the needs of rapid, convenient and low-cost detection of steel segregation in industrial production. Therefore, in order to solve the above problems, it is necessary to design a method for determining the segregation elements and segregation degree of steel by using scanning electron microscope-energy spectrometer, which can not only effectively reduce the detection steps and workload, but also realize the determination of segregation elements and the quantification of segregation degree of steel, and reduce the detection threshold of some steel grades. SUMMARY

[0006] The purpose of the present application is to provide a method for determining the segregation elements and segregation degree of steel by using scanning electron microscope-energy spectrometer, in order to solve the problems of high equipment requirement, complex operation and high cost of the detection means of the prior art for steel segregation.

[0007] In order to achieve the above purpose, the basic scheme provided by the present application is: a method for determining the segregation elements and segregation degree of steel by using scanning electron microscope-energy spectrometer, comprising the following steps: S1: sample preparation: first, the cross section of the steel to be detected is prepared by metallographic sample by the staff, and then the sample is pickled with nitric acid solution; S2: screening: then the staff observes the pickled sample by naked eye, if there is a black dot in the center of the cross section of the sample, the sample with black dot is screened out; S3: scanning analysis: then the scanning electron microscope-energy spectrometer is used to scan and analyze the black dot of the cross section of the sample, to determine the segregation elements and segregation degree of the sample, and then line scanning is performed along the diameter of the cross section of the sample to check whether there is other segregation band; S4: longitudinal section sample preparation and screening: then the sample is prepared by metallographic sample along the longitudinal direction, and then the longitudinal section of the sample is pickled with nitric acid solution, and then the staff observes by naked eye to identify whether there is a black line on the longitudinal section of the sample and screen out the sample with black line; S5: longitudinal section scanning analysis: then the scanning electron microscope-energy spectrometer is used to perform line scanning along the black line on the longitudinal section of the sample to confirm the segregation elements and content of the longitudinal section of the sample to determine the segregation degree.

[0008] The beneficial effects of the present invention are as follows: (1) The present invention uses only scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) combined with simple chemical treatment to replace the in-situ analyzer for steel segregation detection, which reduces the detection cost of steel segregation. At the same time, the scanning electron microscope also lowers the threshold of analytical instruments and reduces the analysis steps and costs; (2) By using nitric acid to treat the sample, then visually identifying and marking the segregation black spots, the segregation area is directly located, avoiding blind scanning. Then, the element content of the black spot area is analyzed at a fixed point by scanning electron microscope-energy dispersive spectroscopy to accurately quantify the degree of steel segregation; (3) The present invention identifies the elements that cause steel segregation and verifies that in the later stage of solidification, as the temperature further decreases, elements with low melting points in the alloy tend to be repelled to the unsolidified liquid part, resulting in the chemical composition of the local area being different from the overall composition of the material. Thus, by identifying the segregation elements, the continuous casting parameters, such as cooling rate and electromagnetic stirring parameters, are optimized in a targeted manner to reduce the performance defects caused by segregation, reduce the risk of cracks in the subsequent rolling process, and improve the pass rate of high carbon steel and high performance steel.

[0009] Option 2, which is the preferred option of the basic option, involves the following metallographic sample preparation methods in S1 and S4: Step 1: First, the staff cuts the steel to be tested along the transverse or longitudinal section; Step Two: Then, the workers use sandpaper to polish the cut surfaces of the steel. Step 3: Next, use a polishing machine to polish the steel after grinding, so that the cut surface of the steel is flat and smooth.

[0010] Metallographic sample preparation involves cutting, sanding, and polishing the steel to ensure that the sample surface quality meets the observation requirements of scanning electron microscopy. Moreover, metallographic sample preparation only requires basic metallographic equipment, which lowers the implementation threshold.

[0011] Option 3, which is a preferred option of the basic option, is that in S1, the mass fraction of the nitric acid is 4.5%; using a nitric acid solution with a mass fraction of 4.5% can ensure that the segregated black spots are clearly visible and avoid excessive corrosion of the sample due to excessive concentration.

[0012] Option 4, which is the preferred option of the basic option, involves wiping the sample surface with cotton soaked in anhydrous ethanol after acid washing with nitric acid in S1 to ensure that there is no nitric acid solution residue on the surface. This thoroughly removes the nitric acid residue, avoids interference from the energy dispersive spectrometer for elemental analysis, and also reduces the corrosion of the equipment by the nitric acid solution when the sample comes into contact with the scanning electron microscope.

[0013] Option 5, an optimal choice of the basic option, involves marking the black spots or black lines on the sample's transverse cross-section and longitudinal cross-section using a marker pen in S2 and S4. After marking the black spots and black lines on the sample's transverse and longitudinal cross-sections, the scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) instrument can directly focus on the target area, thereby quickly finding the segregation points for detection and reducing scanning time.

[0014] Option 6 is an optimal alternative to the basic option. In S3, after performing a line scan along the sample diameter, if segregation exists, the segregating elements and their contents are determined by the composition provided by the scanning electron microscope-energy dispersive spectroscopy. After scanning and analyzing the black dots along the transverse cross section of the sample, a line scan is performed along the diameter direction and analyzed, which supplements the limitations of single-point analysis.

[0015] Option 7, which is the preferred option of the basic option, in S3, if the scanning electron microscope-energy dispersive spectroscopy detects that the content of a certain element at the black spot in the transverse section or the black line in the longitudinal section of the sample is ≥10%, then the element is determined to be a segregating element.

[0016] Option 8 is an optimal choice of the basic option. In S3, the degree of segregation is determined based on the percentage of segregated elements at the black dots in the transverse section and the black lines in the longitudinal section of the sample, as analyzed by scanning electron microscopy-energy dispersive spectroscopy. The higher the percentage, the more severe the segregation. Attached Figure Description

[0017] Figure 1 This is a schematic diagram showing black spots on the transverse cross section of a sample in a method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to the present invention. Figure 2 This is a scanning electron microscope (SEM) image of the first sample at one-quarter, center, and other locations in the transverse section of the first sample in the present invention, which uses a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) method to determine the segregated elements and degree of segregation in steel. Figure 3 This is a scanning electron microscope (SEM) image of the transverse cross section of sample No. 2 at one-quarter, center, and other locations in the method for determining segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy (EDS) of the present invention. Figure 4 This is a scanning electron microscope (SEM) image of the transverse cross section of sample No. 3 at one-quarter, center, and other locations in the method for determining segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy (EDS) of the present invention. Figure 5 This is a schematic diagram showing the presence of black lines in the longitudinal cross-section of a sample in a method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to the present invention. Figure 6This is a scanning electron microscope (SEM) image of the longitudinal section of sample No. 1 at the black line in the method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy (EDS) of the present invention. Figure 7 This is a scanning electron microscope (SEM) image of the longitudinal section of sample No. 2 at the black line in the method for determining segregated elements and the degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy (EDS) of the present invention. Figure 8 This is a scanning electron microscope (SEM) image of the longitudinal section of sample No. 3 at the black line in the method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy (EDS) of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below through specific embodiments: Example A method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy includes the following steps: S1: Sample Preparation: First, the staff will perform metallographic sample preparation on the transverse section of the steel to be tested. The metallographic sample preparation procedure is as follows: First, the staff will cut the steel to be tested along the transverse section. Then, the staff will use sandpaper to grind the cut surface of the steel. Next, the staff will use a polishing machine to polish the ground steel to make the cut surface of the steel smooth and flat. Then, the sample will be acid-washed with a 4.5% nitric acid solution. After acid washing, the staff will use cotton soaked in anhydrous ethanol to wipe the surface of the sample to remove any nitric acid solution residue. S2: Screening: Then, the staff will visually inspect the acid-washed samples. If there are black spots in the center of the cross-section of the sample, the samples with black spots will be screened out and marked with a marker pen at the black spots in the cross-section of the sample. S3: Scanning Analysis: Then, a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) is used to scan and analyze the black spots on the cross-section of the sample to determine the segregating elements and the degree of segregation. Next, a line scan is performed along the diameter of the cross-section of the sample to check for the presence of other segregation bands. If segregation is present, the segregating elements and their contents are determined by the composition provided by the SEM with EDS. If the content of a certain element is ≥10%, it is determined to be a segregating element. The degree of segregation is determined based on the percentage of the segregating elements at the black spots on the cross-section of the sample as analyzed by the SEM with EDS. The higher the percentage, the more severe the segregation. S4: Longitudinal Section Sample Preparation and Screening: The staff then cut the sample along its longitudinal section. Next, sandpaper is used to grind the cut surface of the steel, and then a polishing machine is used to polish the steel to make the cut surface smooth. Then, the longitudinal section of the sample is acid-washed with a 4.5% nitric acid solution. After acid washing, cotton soaked in anhydrous ethanol is used to wipe the sample surface to remove any nitric acid solution residue. Then, the staff visually inspects the longitudinal section of the sample to identify whether there are black lines. If there are black lines, they are marked with a marker. S5: Longitudinal section scanning analysis: Then, a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) is used to perform a line scan along the black line on the longitudinal section of the sample to confirm the segregated elements and their contents in the longitudinal section of the sample.

[0019] The segregation elements and degree of segregation were detected in the three samples using the methods described above. The results of the transverse and longitudinal sections of the samples are as follows: Table 1: Segregation Detection Data of Sample Transverse Section like Figure 3 The image shown is a scanning electron microscope (SEM) image of the transverse cross-section of sample No. 1. According to Table 1, the transverse cross-section of sample No. 1 contains more than 30% carbon at the quarter mark and the center, while no carbon is present in other areas. Furthermore, no chromium or manganese was detected. This indicates that carbon segregation exists at the quarter mark and the center of sample No. 1. Figure 4 The image shown is a scanning electron microscope (SEM) image of the transverse cross-section of sample No. 2. According to Table 1, the transverse cross-section of sample No. 2 contains 38.27% carbon at its center, while no carbon is present in other areas. Furthermore, no chromium or manganese was detected. This indicates that carbon segregation in sample No. 2 is only present at its center. Figure 5 The image shown is a scanning electron microscope image of the transverse cross section of sample No. 3. According to Table 1, sample No. 3 has a carbon content of more than 25% in both the quarter section and the center, while no carbon is present in other areas. At the same time, no chromium or manganese was detected. This indicates that carbon segregation exists in the quarter section and the center of sample No. 3.

[0020] Table 2: Segregation Detection Data of Sample Longitudinal Section like Figure 6 The image shown is a scanning electron microscope (SEM) image of the longitudinal section of sample 1. According to Table 2, sample 1 exhibits a carbon content of over 15% at both black lines along its longitudinal section, while no carbon is present in other areas. Furthermore, no chromium or manganese was detected. Therefore, it is evident that sample 1 exhibits only carbon segregation at the black lines. Figure 7The image shown is a scanning electron microscope (SEM) image of the longitudinal section of sample No. 2. According to Table 2, the longitudinal section of sample No. 2 shows a carbon content of over 15% at both black lines, while no carbon is present in other areas. Furthermore, no chromium or manganese was detected. Therefore, it can be seen that sample No. 2 only exhibits carbon segregation at the black lines. Figure 8 The image shown is a scanning electron microscope image of the longitudinal section of sample No. 3. According to Table 2, sample No. 3 has a carbon content of more than 10% at both black lines, while no carbon is present in other areas. At the same time, no chromium or manganese was detected. Therefore, it can be seen that sample No. 3 only has carbon segregation at the black lines.

[0021] In summary, the above method, employing scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and treating samples with nitric acid solution, replaces in-situ analyzers for steel segregation detection, reducing the detection cost. Furthermore, by visually identifying and marking segregation spots and lines on the samples, staff can quickly locate the segregation areas, avoiding blind scanning. SEM-EDS then allows for precise analysis of the elemental content in the spot and line areas, accurately quantifying the degree of segregation.

[0022] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy, characterized in that, Includes the following steps: S1: Sample preparation: First, the staff will prepare the metallographic sample by taking the transverse section of the steel to be tested, and then pickle the sample with nitric acid solution. S2: Screening: Then, the staff will visually inspect the acid-washed samples. If there are black spots in the center of the cross-section of the sample, the samples with black spots will be screened out. S3: Scanning Analysis: Then, the black spots on the cross section of the sample are scanned and analyzed using a scanning electron microscope-energy dispersive spectroscopy (SEM) to determine the segregated elements and the degree of segregation. Next, a line scan is performed along the diameter of the cross section of the sample to check for the presence of other segregation bands. S4: Longitudinal section sample preparation and screening: Then, the sample is prepared by metallographic sampling along the longitudinal direction. Next, the longitudinal section of the sample is acid-washed with nitric acid solution. Then, the staff visually observes the sample to identify whether there are black lines in the longitudinal section and screens out the samples with black lines. S5: Longitudinal section scanning analysis: Then, a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) is used to perform a line scan along the black line on the longitudinal section of the sample to confirm the segregated elements and their contents in the longitudinal section of the sample, so as to determine the degree of segregation.

2. The method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to claim 1, characterized in that, The metallographic sample preparation methods in S1 and S4 are as follows: Step 1: First, the staff cuts the steel to be tested along the transverse or longitudinal section; Step Two: Then, the workers use sandpaper to polish the cut surfaces of the steel. Step 3: Next, use a polishing machine to polish the steel after grinding, so that the cut surface of the steel is flat and smooth.

3. The method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to claim 1, characterized in that, In S1, the mass fraction of the nitric acid is 4.5%.

4. The method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to claim 1, characterized in that, In S1, the sample washed with nitric acid needs to be wiped with cotton soaked in anhydrous ethanol to ensure that there is no nitric acid solution residue on the surface.

5. The method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to claim 1, characterized in that, In S2 and S4, if there are black spots on the transverse section of the sample or black lines on the longitudinal section of the sample, mark the black spots on the transverse section and the black lines on the longitudinal section with a marker.

6. The method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to claim 1, characterized in that, In S3, after a line scan along the sample diameter, if segregation exists, the segregating elements and their contents are determined by the composition provided by scanning electron microscopy-energy dispersive spectroscopy.

7. The method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to claim 1, characterized in that, In S3, if the scanning electron microscope-energy dispersive spectroscopy detects that the content of a certain element at the black spot in the transverse section or the black line in the longitudinal section of the sample is ≥10%, then the element is determined to be a segregating element.

8. The method for determining the segregated elements and degree of segregation in steel using scanning electron microscopy-energy dispersive spectroscopy according to claim 1, characterized in that, In S3, the degree of segregation is determined based on the percentage of segregated elements at the black dots in the transverse section and the black lines in the longitudinal section of the sample, as analyzed by scanning electron microscopy-energy dispersive spectroscopy. The higher the percentage, the more severe the segregation.

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