Calculation method and verification method for batten width of batten-like structure in steel
By repeatedly tilting the sample stage under a transmission electron microscope and combining calculations with the cosine theorem, the problem of inaccurate measurement of lath martensite and bainite microstructures was solved, achieving high-precision lath width measurement and supporting process optimization and material performance evaluation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANGANG STEEL CO LTD
- Filing Date
- 2026-02-09
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies cannot accurately measure the lath width of lath martensite and lath bainite structures at the nanoscale, making it impossible to accurately judge the process effect and material properties.
Metal thin film samples were obtained under a transmission electron microscope. The sample stage was tilted and photographed using the electron microscope. The width of the slab was calculated using the cosine theorem. Multiple measurements and verification methods were used to improve the measurement accuracy.
It enables high-precision measurement of strip width, ensuring accurate evaluation of process optimization and material properties, and improving production consistency and reliability.
Smart Images
Figure CN122015722A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of microscopic property analysis technology of metallic materials, and relates to a method for calculating and verifying the width of laths in steel. Background Technology
[0002] The lath microstructure in steel mainly consists of lath martensite, lath bainite, and pearlite (lamellae). Among these, lath martensite, due to its extremely high strength and relatively high plasticity, has wide applications in quenched and tempered steel, ultra-high strength steel, and stainless steel. Lath bainitic steel is also more widely used due to its excellent strength, toughness, and weldability. Whether lath martensite or bainite, the size of the lath bundles directly affects the strength, toughness, plasticity, and weldability of the steel. The core practical significance of measuring lath martensite and lath bainite in steel lies in its role as a bridge connecting production process parameters with the final material properties. Through measurement, the result of process execution (what microstructure was obtained) can be known, thereby predicting or interpreting material properties. It is a necessary means to optimize production processes and ensure product quality and consistency. Without accurate measurement, it is impossible to determine whether the process is effective or the product is qualified. It is the scientific basis for understanding and improving material properties and developing new materials. It provides key data for establishing quantitative relationships and exploring new mechanisms. It is an important tool for diagnosing material failure and improving product reliability. Therefore, accurate qualitative and quantitative characterization of lath martensite and lath bainite in steel plays an indispensable role in the entire chain of steel material production, application, and research and development.
[0003] Since the width of laths containing martensite, bainite, pearlite, etc., is typically between tens and hundreds of nanometers, and some lath interfaces are indistinct, observation and statistical analysis can only be performed using transmission electron microscopy. Currently, no relevant measurement methods have been found. Therefore, exploring an accurate method for measuring the lath width of nanoscale lath-like structures and standardizing lath width measurement is of guiding significance for steel grade development and adjustment of mechanical properties. Summary of the Invention
[0004] To address the problem of inaccurate calculations in existing methods that rely solely on observation and statistical analysis using transmission electron microscopy, this invention provides a method for calculating the width of laths in steel, comprising the following steps:
[0005] Obtain the metal thin film sample to be tested; The metal thin film sample was observed under an electron microscope. After selecting an appropriate field of view to fully focus on the lath-like structure, the first image of the metal thin film lath bundle was taken from the direction perpendicular to the lath bundle. The first measurement of the projected image of the metal thin film lath bundle was then performed using an electron microscope. Keeping the position of the metal film unchanged, the sample stage is tilted by N°. After selecting a suitable field of view to fully focus on the lath structure, the lath morphology is photographed a second time and the projected image of the metal film lath bundle is measured a second time. Based on the first and second measurements of the lath bundle projection images, the actual width of the laths in the steel structure is calculated using the law of cosines.
[0006] Furthermore: the metal thin film sample is a metal disc with a thickness between 50-60 μm and a diameter of 2-4 mm. A central hole is formed in the center of the metal disc by electrolytic double-spray thinning.
[0007] Furthermore, the suitable field of view needs to meet the following conditions: The thickness of the thinned portion of the central hole is less than 100 nm; There are no sources of contamination on the surface of the thinned section of the central hole; There are no matte streaks at the thinned area of the central hole.
[0008] Furthermore, -15° <N<+15°。
[0009] Furthermore: the process of calculating the actual width of the laths in the steel using the law of cosines, based on the first and second measured lath bundle projection images, is as follows: Obtain the lath bundle width value A and the metal thin film sample thickness B from the projection image of the first measurement of the lath bundle. According to the Law of Cosines: (1) in: is the angle between the measured width and the actual width of the slat bundle; C is the actual value of the slat width. Because of C 2 =A 2 +B 2 We can obtain: (2) Obtain the slat bundle width value A1 from the projection image of the second measurement of the slat bundle; After the sample stage is tilted by +N° (3) Using the sum of cosines formula: (4) From equations (2), (3), and (4), given A and A1, the formula for calculating the actual value C of the slat width is obtained through trigonometric identities and algebraic derivation, as follows: (5).
[0010] This invention also provides a verification method for the calculation method of the width of the lath-like structure in steel as described above, comprising the following steps: Keeping the position of the metal thin film unchanged, the sample stage is tilted N° in the opposite direction. The metal thin film lath bundle is photographed for the third time and the projection image of the metal thin film lath bundle is measured for the third time. The lath bundle width value A2 in the projection image of the lath bundle measured in the third measurement is obtained. Based on the actual value C of the slat width, the slat bundle width value A in the projected image of the third measurement of the slat bundle is calculated through trigonometric identities and algebraic derivation. ’ 2; The lath bundle width value A2 in the projection image of the third measured lath bundle is compared with the lath bundle width value A calculated in the projection image of the third measured lath bundle. ’ 2. Compare, when When the value is less than the threshold M, it proves that the method for calculating the width of laths in steel is accurate; when... When the value is greater than or equal to the threshold M, the width of the steel slabs should be measured again.
[0011] The value of M ranges from 10 to 12 nm.
[0012] This invention provides a method for calculating and verifying the width of slabs in steel structures. The method involves measuring the projected width of the slab by tilting the steel at an angle, and then using the law of cosines (Pythagorean theorem) to calculate the actual width and projection angle, thus establishing a formula for calculating the slab width. If the calculated values are close to the actual values, and considering measurement errors, the calculated slab width can be considered reliable.
[0013] Lath width is one of the key microstructural parameters affecting the mechanical properties of metallic materials. Lath refinement (width reduction) can significantly alter the material's strength, toughness, and fatigue performance. Traditional measurement methods suffer from unclear lath boundaries and poor lath bundle orientation. If the lath bundle orientation is poor, the measured width is the width of the oblique section, which will overestimate the true width.
[0014] This invention obtains the true width of the slats by repeatedly measuring and verifying the tilt angle, which greatly improves the measurement accuracy and ensures the authenticity of the experimental data. This provides reliable experimental data for improving the accuracy of microstructure characterization, establishing process-performance correlation, and promoting quantitative materials science research. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 A schematic diagram of the projection of an electron beam penetrating a slab beam; Figure 2 The images show the slat bundle projection effects when the sample stage is tilted at different angles; (a) when the sample stage is not rotated, (b) when the sample stage is rotated by +5°, and (c) when the sample stage is rotated by -5°. Figure 3 Image showing the effect of electrolytic double-spraying to fabricate a Φ3mm metal thin film on a sample; Figure 4 Image showing the effect of transmission electron microscopy observation of lamellar tissue; Figure 5 The images show the measurement results of the width of martensitic laths in martensitic stainless steel; (a) Image I, (b) Image II, and (c) Image III. Figure 6 The images show the measurement results of the bainite lath width in the bainite weight rail; where (a) is the effect diagram I, (b) is the effect diagram II, and (c) is the effect diagram III. Figure 7 The images show the measurement results of the pearlite lamellar width in automotive cord steel, including (a) Image I, (b) Image II, and (c) Image III. Detailed Implementation
[0017] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.
[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0019] A method for calculating the width of steel slabs in a plate-like structure includes the following steps: S11: Obtain the metal thin film sample to be tested; S12: Place the metal thin film sample under an electron microscope for observation. After selecting an appropriate field of view and focusing the lath-like structure, take the first image of the projection of the metal thin film lath bundle from the direction perpendicular to the lath bundle. Use the DigitalMicrograph software built into the electron microscope to take the first measurement of the projection image of the metal thin film lath bundle. Figure 1 A schematic diagram of the projection of an electron beam penetrating a slab beam; S13: Keeping the metal film position unchanged, tilt the sample stage N°, select a suitable field of view to fully focus on the lath-like structure, then take a second picture of the lath morphology and perform a second measurement on the projected image of the metal film lath bundle; where: -15° <N<+15°; S14: Based on the first and second measured lath bundle projection images, the actual width of the laths in the steel is calculated using the cosine theorem.
[0020] Steps S11 / S12 / S13 / S14 are executed sequentially; Further: the metal thin film sample is a metal disc with a thickness between 50-60 μm and a diameter of 2-4 mm. A central hole is formed in the center of the metal disc by electrolytic double-spray thinning. Figure 2 As shown, Figure 2 The images show the slat bundle projection effects when the sample stage is tilted at different angles; (a) when the sample stage is not rotated, (b) when the sample stage is rotated by +5°, and (c) when the sample stage is rotated by -5°.
[0021] Furthermore, the suitable field of view needs to meet the following conditions: The thickness of the thinned portion of the central hole is less than 100 nm; There are no sources of contamination on the surface of the thinned section of the central hole; There are no matte streaks at the thinned area of the central hole.
[0022] Furthermore, the process of calculating the actual width of the laths in the steel using the law of cosines, based on the measured images of the first and second lath bundle projections, is as follows: Obtain the lath bundle width value A and the metal thin film sample thickness B from the projection image of the first measurement of the lath bundle. According to the Law of Cosines: (1) in: is the angle between the measured width and the actual width of the slat bundle; C is the actual value of the slat width. Because of C 2 =A 2 +B 2We can obtain: (2) Obtain the slat bundle width value A1 from the projection image of the second measurement of the slat bundle; After the sample stage is tilted by +N degrees (3) Using the sum of cosines formula: (4) From equations (2), (3), and (4), given A and A1, the formula for calculating the actual value C of the slat width is obtained through trigonometric identities and algebraic derivation, as follows.
[0023] (5) The verification method for calculating the width of a lath-like structure in steel, as described in any one of the above methods, includes the following steps: S21: Keep the position of the metal thin film unchanged, tilt the sample stage in the opposite direction by N degrees, take a third photograph of the slab morphology of the metal thin film slab bundle and take a third measurement of the projection image of the metal thin film slab bundle, and obtain the slab bundle width value A2 in the projection image of the slab bundle in the third measurement. S22: Based on the actual value C of the slat width, calculate the slat bundle width value A in the projected image of the slat bundle in the third measurement using trigonometric identities and algebraic derivation. ’ 2; Based on the actual value C of the slat width, the width A of the slat bundle in the projected image of the third measurement of the slat bundle is calculated through trigonometric identities and algebraic derivation. ’ The process of step 2 is as follows: After the sample stage is tilted -N°, (6) Using the sum of cosines formula: (7) From equations (2), (6), and (7), given A and C (obtained through formula 5), we can obtain the following results through trigonometric identities and algebraic derivation: The calculation formula is as follows: (8) S23: Combine the lath bundle width value A2 obtained from the projection image of the third measured lath bundle with the calculated lath bundle width value A in the projection image of the third measured lath bundle. ’ 2. Compare, when When the value is less than the threshold M, it proves that the method for calculating the width of laths in steel is accurate; when... When the value is greater than or equal to the threshold M, the width of the steel slabs should be measured again.
[0024] The value of M ranges from 10 to 12 nm.
[0025] Steps S21 / S22 / S23 are executed sequentially; Example 1: Taking martensitic stainless steel as an example, this example illustrates a method for measuring the width of martensitic laths using transmission electron microscopy, including the following steps: S11: Manually grind and polish both sides of the steel sample to be tested to reduce its thickness to 50-60 mm. m, and punched into A standard metal disc for a 3mm transmission electron microscope is electrolyzed and double-sprayed until a central hole is formed, thus preparing a metal thin film sample that can be observed by a transmission electron microscope. S12: Place the metal thin film sample under an electron microscope for observation. After selecting a suitable field of view and fully focusing on the lath-like structure, take the first photograph of the lath morphology (e.g., ...). Figure 3 Using the built-in DigitalMicrograph software of the electron microscope, the width of the lath bundle was measured for the first time from the direction perpendicular to the lath bundle, with a value of A=330nm; Figure 4 Image showing the effect of transmission electron microscopy observation of lamellar tissue; S13: Keep the sample position unchanged, tilt the sample stage by α angle +5°, focus and take a second photograph of the lath morphology, and measure the lath bundle width value A1 = 290 nm for the second time. S14: Based on the first and second measured lath bundle projection images, using the cosine theorem and formula (5), the actual width C≈553nm of the laths in the steel is calculated.
[0026] The verification method for calculating the width of a lath-like structure in steel, as described in any one of the above methods, includes the following steps: S21: Keep the sample position unchanged, tilt the sample stage by α angle -5°, focus and take a third photograph of the lath morphology and measure the lath bundle width value A2=370 nm for the third time; S22: After the sample stage is tilted by α angle -5°, the actual width C of the laths in the steel lath structure is calculated using trigonometric identities and algebraic derivation, and the lath bundle width A in the projection image of the third measurement of the lath bundle is calculated. ’ 2≈368nm; S23: The lath bundle width value A2 = 370 nm in the projection image of the third measured lath bundle is compared with the lath bundle width value A in the calculated projection image of the third measured lath bundle. ’ Compare 2 ≈ 368nm; 370 - 368 = 2nm < threshold M; The calculated value of the slat bundle width in the projection image of the third measurement of the slat bundle is close to the actual measured value, thus confirming that the actual slat width is about 553 nm.
[0027] like Figure 5 As shown, Figure 5 The images show the measurement results of the width of martensitic strips in martensitic stainless steel; (a) Image I, (b) Image II, and (c) Image III.
[0028] Example 2: Taking the bainite slab weight rail as an example, this example illustrates the method for calculating the width of bainite laths measured by transmission electron microscopy, including the following steps: S11: The steel sample to be tested is manually ground and polished on both sides to a thickness of 50-60μm, and punched into a Φ3mm standard metal disc for transmission electron microscopy. The disc is then electrolytically sprayed until the center is perforated to prepare a metal thin film sample that can be observed by transmission electron microscopy. S12: The metal thin film sample was placed under an electron microscope for observation. After selecting an appropriate field of view and focusing the lath-like structure, the lath morphology was photographed for the first time. Using the DigitalMicrograph software built into the electron microscope, the width of the lath bundle was measured for the first time from the direction perpendicular to the lath bundle, A=375nm. S13: Keep the sample position unchanged, tilt the sample stage by α angle +5°, focus, take a second photograph of the lath morphology and measure the lath bundle width value A1 = 360nm for the second time; S14: Based on the first and second measured lath bundle projection images, using the cosine theorem and formula (5), the actual width C≈389nm of the laths in the steel is calculated.
[0029] A verification method for calculating the width of slabs in steel lath structures includes the following steps: S21: Keep the sample position unchanged, tilt the sample stage by α angle -5°, focus, take a third photograph of the lath morphology and measure the lath bundle width value A2=380nm for the third time; S22: After the sample stage is tilted by α angle -5°, the actual width C of the laths in the steel lath structure is calculated using trigonometric identities and algebraic derivation, and the lath bundle width A in the projection image of the third measurement of the lath bundle is calculated. ’ 2≈383nm.
[0030] S23: Combine the lath bundle width value A2 = 380 nm in the projection image of the third measured lath bundle with the calculated lath bundle width value A in the projection image of the third measured lath bundle. ’ Comparing 2≈383nm; 383-380=3nm<threshold M, the calculation result is close to the actual measured value, thus confirming that the actual slat width is about 389nm.
[0031] like Figure 6 As shown, Figure 6The images show the measurement results of the bainite lath width in the bainite weight rail; where (a) is the effect diagram I, (b) is the effect diagram II, and (c) is the effect diagram III. Example 3: Taking automotive cord steel as an example, this describes a method for measuring pearlite lamellar spacing using transmission electron microscopy, including the following steps: S11: The automotive cord steel sample to be tested is manually ground and polished on both sides to thin it to 50-60μm, and punched into a Φ3mm standard metal disc for transmission electron microscopy. Electrolytic double spraying is performed until the center is perforated to prepare a metal thin film sample that can be observed by transmission electron microscopy. S12: Place the metal thin film sample under an electron microscope for observation. After selecting an appropriate field of view and focusing the pearlite lamellar structure, take the first photograph of the pearlite lamellar morphology. Using the DigitalMicrograph software built into the electron microscope, measure the width of the two lamellars A=177nm for the first time from the direction perpendicular to the pearlite lamellar bundle. S13: Keep the sample position unchanged, tilt the sample stage by α angle +5°, focus for the second time and take a picture of the lath morphology, and measure the lath bundle width value A1=173nm for the second time; S14: Based on the first measurement of the lath bundle projection image and the second measurement of the lath bundle projection image, using the cosine theorem and formula (5), the actual width C≈214nm of the laths in the steel is calculated.
[0032] A verification method for calculating the width of slabs in steel lath structures includes the following steps: S21: Keep the sample position unchanged, tilt the sample stage by α angle -5°, focus and take a third photograph of the lath morphology and measure the lath bundle width value A2=185nm for the third time; S22: After the sample stage is tilted by α angle -5°, the actual width C of the laths in the steel lath structure is calculated using trigonometric identities and algebraic derivation, and the lath bundle width A in the projection image of the third measurement of the lath bundle is calculated. ’ 2≈187nm; S23: Compare the lath bundle width value A2 = 185 nm in the projection image of the third measured lath bundle with the calculated lath bundle width value A in the projection image of the third measured lath bundle. ’ Comparing 2≈187nm; 185-187=2nm<threshold M, the calculation result is close to the actual measured value, thus confirming that the actual slat width is about 214nm.
[0033] Figure 7 The images show the measurement results of the pearlite lamellar width in automotive cord steel, including (a) Image I, (b) Image II, and (c) Image III.
[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for calculating the width of strips in steel slab structures, characterized in that: Includes the following steps: Obtain the metal thin film sample to be tested; The metal thin film sample was observed under an electron microscope. After focusing the lath-like structure by selecting the field of view, the first image of the metal thin film lath bundle was taken from the direction perpendicular to the lath bundle. The first measurement of the projected image of the metal thin film lath bundle was then performed using an electron microscope. Keeping the position of the metal film unchanged, the sample stage is tilted N°. After focusing the field of view on the lath structure, the lath morphology is photographed a second time and the projected image of the metal film lath bundle is measured a second time. Based on the first and second measurements of the lath bundle projection images, the actual width of the laths in the steel structure is calculated using the law of cosines.
2. The method for calculating the width of slab-type structural steel according to claim 1, characterized in that: The metal thin film sample is a metal disc with a thickness between 50-60 μm and a diameter of 2-4 mm. A central hole is formed in the center of the metal disc by electrolytic double-spray thinning.
3. The method for calculating the width of slab-type structural steel according to claim 1, characterized in that: The field of view needs to meet the following conditions: The thickness of the thinned portion of the central hole is less than 100 nm; There are no sources of contamination on the surface of the thinned section of the central hole; There are no matte streaks at the thinned area of the central hole.
4. The method for calculating the width of slabs in steel with a lath structure according to claim 1, characterized in that: -15°<N<+15°。 5. The method for calculating the width of slab-type structural steel according to claim 1, characterized in that: The process of calculating the actual width of the laths in the steel using the law of cosines, based on the first and second measured lath bundle projection images, is as follows: Obtain the lath bundle width value A and the metal thin film sample thickness B from the projection image of the first measurement of the lath bundle. According to the Law of Cosines: （1） in: is the angle between the measured width and the actual width of the slat bundle; C is the actual value of the slat width. Because of C 2 =A 2 +B 2 We can obtain: （2） Obtain the slat bundle width value A1 from the projection image of the second measurement of the slat bundle; After the sample stage is tilted by +N° （3） Using the sum of cosines formula: （4） From equations (2), (3), and (4), given A and A1, the formula for calculating the actual value C of the slat width is obtained through trigonometric identities and algebraic derivation, as follows: （5）。 6. A verification method for the calculation method of the width of a steel slab structure according to any one of claims 1-5, characterized in that: Includes the following steps: Keeping the position of the metal thin film unchanged, the sample stage is tilted N° in the opposite direction. A third photograph of the lath morphology of the metal thin film is taken and a third measurement is performed on the projected image of the metal thin film lath bundle. The lath bundle width value A2 in the third measured projection image of the lath bundle is obtained. Based on the actual value C of the slat width, the slat bundle width value A in the projected image of the third measurement of the slat bundle is calculated through trigonometric identities and algebraic derivation. ’ 2; The lath bundle width value A2 in the projection image of the third measured lath bundle is compared with the lath bundle width value A calculated in the projection image of the third measured lath bundle. ’ 2. Compare, when When the value is less than the threshold M, it proves that the method for calculating the width of laths in steel is accurate; when... When the value is greater than or equal to the threshold M, the width of the steel slabs should be measured again.
7. The verification method for the calculation method of the width of lath-like structures in steel according to claim 6, characterized in that: The value of M ranges from 10 to 12 nm.