Quantitative evaluation method for surface indentation of peritectic steel cast slab
By combining the area method and the depth method to calculate the depression index R, the problem of quantitative evaluation of depressions on the surface of peritectic steel billets has been solved, achieving rapid and accurate depression quantification and improving production efficiency and billet quality control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TANGSHAN IRON & STEEL GROUP
- Filing Date
- 2026-03-30
- Publication Date
- 2026-07-17
AI Technical Summary
Existing technologies fail to effectively quantify and evaluate the degree of surface depressions in peritectic steel billets and their impact on billet quality, leading to potential production hazards and quality risks.
The method combines the area method and the depth method. The depression area S and depth L are calculated, and the depression index R=S×L×δ is used for quantitative evaluation. δ is the depression coefficient, and its value is determined according to the depression area and depth level. The size of the depression is measured by combining the ellipse approximation method.
It enables rapid and accurate quantitative evaluation of surface depressions in peritectic steel billets, improving production efficiency, reducing unnecessary billet surface cleaning, lowering production costs, and enhancing billet quality control.
Smart Images
Figure CN122408690A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metallurgical continuous casting technology, and in particular to a method for quantitatively evaluating surface depressions in peritectic steel billets. Background Technology
[0002] The formation of surface depressions on peritectic steel billets is caused by a combination of factors. Firstly, the steel grade, influenced by its composition, undergoes a peritectic reaction, resulting in significant volume shrinkage during solidification and a tendency to form depressions. Secondly, poor heat transfer uniformity between the initial billet shell and the crystallizer exacerbates the peritectic shrinkage, leading to pits on the thinner billet surface. Furthermore, the superposition of these depressions and surface oscillation marks on the billet can easily generate microcracks at the bottom of deeper depressions, which are difficult to detect with the naked eye. Therefore, the occurrence of these depressions poses a hidden danger to efficient and smooth continuous casting production and also brings significant quality risks to coil rolling.
[0003] CN202410829556.5 - A method for detecting and tracking surface depressions of a cast billet. This method utilizes the deviation between the length of the cast billet and the length of the surface curve to perform online detection of surface depressions on hot-cast billets. It provides a good method for dynamically adjusting the process to improve the defects of surface depressions in cast billets, but it does not consider the impact of the degree of surface depression at a single location on the quality of the cast billet.
[0004] CN202211374799.1 - A method for controlling surface depression defects in continuously cast slabs mentions various factors that affect the occurrence of surface depressions in slabs, and uses improvements to continuous casting process parameters to mitigate or reduce the occurrence of surface depressions in slabs, but does not provide a quantitative evaluation of the degree of surface depressions in slabs.
[0005] CN202011153370.0 - A portable testing device and method for the surface quality of continuously cast billets, mainly describing the testing method and device for cracks on the surface of billets, without involving the quantification and evaluation of surface depressions of the billets.
[0006] Currently, most literature analyzes the causes of surface depressions in peritectic steel billets and formulates continuous casting process measures to mitigate them. However, no quantitative evaluation has been made regarding the rapid quantification of surface depressions in production, or the impact of the size of a single depression on the surface quality of the billet. Summary of the Invention
[0007] The technical problem to be solved by the present invention is to provide a rapid and accurate quantitative evaluation method for surface depressions of peritectic steel billets.
[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps: 1) Calculate the depression area S of the surface depression using the area method;
[0009] 2) Measure the depth L of the depression on the surface of the cast billet;
[0010] 3) Calculate the indentation index R using the following formula (2);
[0011] R = S × L × δ (2;
[0012] In the formula: R is the depression index; S is the depression area (mm). 2 L is the depth of the depression, in mm; δ is the depression coefficient, ranging from 0.020 to 0.200.
[0013] 4) The depression index R is used as a quantitative indicator of the depression on the surface of peritectic steel billet.
[0014] Further, in step 1), the surface depression contour is approximated as an ellipse, and the area S of the surface depression is calculated using the following formula (1);
[0015] S = π × a × b (1);
[0016] In the formula: S is the area of the depression, mm 2 π is the mathematical constant pi; a is the major semi-axis of the ellipse, mm; b is the minor semi-axis of the ellipse, mm.
[0017] Furthermore, the measurement process for the major and minor semi-axes of the ellipse of the surface depression contour is as follows: the longest distance of the depression is directly measured using a length measuring tool, and half of the longest distance segment is taken as the major semi-axe of the ellipse; a perpendicular line is drawn through the midpoint of the above-mentioned long distance segment, and intersects the edge of the depression at two points, and the longer segment of the perpendicular line is taken as the minor semi-axe of the ellipse.
[0018] Furthermore, in step 2), the depth of the depression on the surface of the billet is measured several times, and the maximum value is taken as the depression depth L.
[0019] Furthermore, in step 1), the depression area S is divided into the following four levels: S > 3500 is level I, 2000 < S ≤ 3500 is level II, 1000 < S ≤ 2000 is level III, and S ≤ 1000 is level IV; in step 2), the depression depth is divided into the following three levels: 5 ≤ L < 7 is level A, 3 ≤ L < 5 is level B, and 1 ≤ L < 3 is level C.
[0020] Furthermore, in step 3), the value of the depression coefficient δ is determined based on the level of the depression area S and the depression depth L:
[0021] For Level I+A, δ is 0.200; for Level II+A, δ is 0.150; for Level III+A, δ is 0.100; for Level IV+A, δ is 0.060.
[0022] For Level I + B, δ is 0.120; for Level II + B, δ is 0.090; for Level III + B, δ is 0.050; for Level IV + B, δ is 0.030.
[0023] For Level I+C, δ is 0.080; for Level II+C, δ is 0.060; for Level III+C, δ is 0.040; and for Level IV+C, δ is 0.020.
[0024] The beneficial effects of adopting the above technical solution are as follows: This invention, combined with the causes of surface depressions in crack-sensitive steel billets, summarizes and analyzes the depression morphology, comprehensively considers factors such as depression area, depression depth, and the impact of depressions on billet quality, and obtains a quantitative formula for billet surface depressions; it can be directly applied to the quantification of irregular depression shapes in actual billets, and the quantitative formula can be used for direct calculation, realizing convenient quantification of surface depression defects in billets, quickly evaluating the degree of impact of depressions on billet quality, and the obtained quantitative evaluation results can be used to guide production decisions, improving production efficiency by approximately 95% or more.
[0025] This invention utilizes only a measuring tape and depth gauge for measurement, making it simple and easy to operate. It allows for targeted quantitative evaluation of individual depressions, avoiding inaccurate evaluations caused by the accumulation of numerous minor depressions on the billet surface. Different degrees of depression are quantified, graded, and their impact on billet quality is evaluated. Attached Figure Description
[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0027] Figure 1 This is a photograph of the actual morphology of the surface depressions on the cast billet;
[0028] Figure 2 This is a schematic diagram illustrating the equivalent calculation of the surface depression of the billet using the area of an ellipse;
[0029] Figure 3 This is a schematic diagram of the process for measuring surface depressions on the cast billet as described in Example 1;
[0030] Figure 4 This is a schematic diagram of the process for measuring surface depressions on the cast billet as described in Example 2;
[0031] Figure 5 This is a schematic diagram of the process for measuring surface depressions on the cast billet as described in Example 3;
[0032] Figure 6 This is a schematic diagram of the process for measuring surface depressions on the billet as described in Example 4;
[0033] Figure 7 This is a schematic diagram of the process for measuring surface depressions on the cast billet as described in Example 5;
[0034] Figure 8 This is a schematic diagram of the process for measuring surface depressions on the cast billet as described in Example 6;
[0035] Figure 9 This is a schematic diagram of the process for measuring surface depressions on the cast billet as described in Example 7. Detailed Implementation
[0036] During the solidification process of peritectic steel in the continuous casting mold, indentations occur on the surface of the billet due to the inherent solidification characteristics of the steel and poor heat transfer conditions. This method, based on accumulated observations of the indentation profiles and analysis of their causes, finds that both transverse and longitudinal indentations can be approximated by ellipses. The formation process of the indentations reveals that stress concentration at the indentation points, combined with deep vibration marks, easily leads to crack formation in deeper indentations. Therefore, considering the impact of indentation depth on billet quality, an indentation index is developed by classifying depth into different levels to quantitatively evaluate the surface indentations of the billet.
[0037] This quantitative evaluation method for surface depressions in granulated steel billets combines an approximate area method with depth, and makes corrections based on different areas and depths. It further calculates the depression index and evaluates the severity of surface depressions in the billet, including the following steps:
[0038] 1) Calculate the area S of the depression using the area method: Figure 1 As shown, the surface depressions on a typical cast billet are irregularly shaped, making it difficult to accurately describe their size using conventional area formulas. Observing the shape of the depressions on the cast billet surface, we find that they are approximately elliptical. Therefore, we quantify the size of the depressions by directly measuring the key dimensions of their contours.
[0039] The measurement process is as follows: Figure 2 As shown, use a ruler to measure the position of the longest depression, and mark the two positions as Q and P respectively. The longest distance line segment is denoted as QP, and the midpoint of the line segment is marked as O. Then, draw perpendicular lines from the midpoint O of the line segment QP to both sides. The perpendicular lines intersect the edge of the depression at two points. The intersection point of the longer perpendicular line is marked as M, and the intersection point of the shorter perpendicular line is marked as N. Draw an ellipse through the three points Q, P and M, and measure it on the surface of the billet using a ruler. The length of QO is a and the length of MO is b. Calculate the depression area S using the following formula (1).
[0040] S = π × a × b (1);
[0041] In the formula: S is the area of the concave depression, i.e., the area of the ellipse, in mm. 2 π is the mathematical constant pi; a is the major semi-axis of the ellipse, mm; b is the minor semi-axis of the ellipse, mm.
[0042] Based on the calculated indentation area S, the indentation area S is divided into the following four levels: Level I, S > 3500; Level II, 2000 < S ≤ 3500; Level III, 1000 < S ≤ 2000; Level IV, S ≤ 1000.
[0043] 2) Measure the depression depth L of the billet: Use a depth measuring instrument to detect the depth of the depression on the surface of the billet. Measure several times, preferably three or more times, and take the largest value as the depression depth, denoted as L. According to the size of the depression depth L, the depression depth is divided into the following three levels: Level A, 5≤L<7; Level B, 3≤L<5; Level C, 1≤L<3.
[0044] 3) Calculate the indentation index R: The indentation index R is calculated using the following formula (2);
[0045] R = S × L × δ (2;
[0046] In the formula: R is the depression index; S is the depression area (mm). 2 L is the indentation depth in mm; δ is the indentation coefficient, ranging from 0.020 to 0.200. δ is an exponential coefficient that generates different values based on the magnitudes of S and L. The value of δ is determined according to Table 1 below.
[0047] Table 1: Relationship between the grade of depression area and depression depth and the depression coefficient
[0048] A 0.200 0.150 0.100 0.060 B 0.120 0.090 0.050 0.030 C 0.080 0.060 0.040 0.020
[0049] .
[0050] 4) The indentation index R serves as a quantitative indicator of surface indentation, used to quantitatively evaluate the surface indentation of peritectic steel billets. By recording data from 1080 peritectic steel billets produced in 100 casting cycles, the relationship between billet indentation-induced coil defects and the billet surface indentation index was analyzed: when the indentation index R is less than 1000, surface defects caused by billet indentation are almost nonexistent in the coil; when the indentation index exceeds 1000 and gradually increases, the probability of surface defects appearing in the corresponding coil is positively correlated. Thus, during the production of peritectic steel billets, a surface grinding plan can be formulated based on the magnitude of the indentation index R. Billets with an indentation index R less than 1000 do not require surface cleaning, while billets with an indentation index R ≥ 1000 require surface cleaning, thereby reducing waste from all billet cleaning and improving the billet grinding rate by approximately 95%.
[0051] Example 1: The quantitative evaluation of surface depressions in DP780 duplex steel billets is used as an example for illustration.
[0052] The measurement process is as follows Figure 3 As shown, QP is 55mm and MO is 12mm. The depression area S is calculated to be 1036.2mm² using formula (1). 2The surface depressions of the billet were classified as Grade III. The depths of the depressions on the surface of the billet were measured using a depth measuring instrument, and the results were 2.09 mm, 2.09 mm, 2.12 mm, 1.99 mm, 2.17 mm, and 2.00 mm, respectively. The depression depth L was 2.17 mm, which is classified as Grade C. According to the depression area and depression depth grades, Table 1 shows that δ is 0.040. The depression index R is calculated to be 89.94 according to formula (2).
[0053] If the resulting indentation index R is less than 1000, it is determined that the coil will not suffer from surface defects caused by indentation in the cast billet, and surface cleaning of the cast billet is unnecessary. No surface defects were observed in the rolled coils during subsequent production.
[0054] Example 2: The quantitative evaluation of surface depressions on DP980 duplex steel billets is used as an example for illustration.
[0055] The measurement process is as follows Figure 4 As shown, QP is 50mm and MO is 19mm. The depression area S is calculated to be 1491.5mm² using formula (1). 2 The surface depressions of the billet were classified as Grade III. The depths of the depressions on the surface of the billet were measured using a depth measuring instrument, and were 1.64 mm, 1.71 mm, 1.71 mm, 1.80 mm, 1.57 mm, and 1.83 mm, respectively. The depression depth L was 1.83 mm, which is classified as Grade C. According to the depression area and depression depth grades, Table 1 shows that δ is 0.040. The depression index R is calculated to be 109.18 according to formula (2).
[0056] If the resulting indentation index R is less than 1000, it is determined that the coil will not suffer from surface defects caused by indentation in the cast billet, and surface cleaning of the cast billet is unnecessary. No surface defects were observed in the rolled coils during subsequent production.
[0057] Example 3: The quantitative evaluation of surface depressions on a 590 grade wheel steel billet is used as an example.
[0058] The measurement process is as follows Figure 5 As shown, QP is 40mm and MO is 10mm. The depression area S is calculated to be 628mm² using formula (1). 2 The surface depressions of the billet were classified as Grade IV. The depths of the depressions on the surface of the billet were measured five times using a depth measuring instrument, and were 1.35 mm, 1.36 mm, 1.42 mm, 1.29 mm, and 1.42 mm respectively. Therefore, the depression depth L was 1.42 mm, classifying it as Grade C. Based on the depression area and depth grades, Table 1 shows that δ is 0.020. According to formula (2), the depression index R is calculated to be 17.84.
[0059] If the resulting indentation index R is less than 1000, it is determined that the coil will not suffer from surface defects caused by indentation in the cast billet, and surface cleaning of the cast billet is unnecessary. No surface defects were observed in the rolled coils during subsequent production.
[0060] Example 4: The quantitative evaluation of surface depressions on weathering steel billets is illustrated as an example.
[0061] The measurement process is as follows Figure 6 As shown, QP is 50mm and MO is 15mm. The depression area S is calculated to be 1177.5mm² using formula (1). 2 The surface depressions of the billet were measured using a depth measuring instrument, and the depths were 1.71 mm, 1.84 mm, 1.94 mm, and 1.93 mm, respectively. The depression depth L was 1.94 mm, which is classified as Grade C. Based on the depression area and depression depth grades, the δ value is 0.040 as shown in Table 1. The depression index R is calculated to be 91.37 according to formula (2).
[0062] If the resulting indentation index R is less than 1000, it is determined that the coil will not suffer from surface defects caused by indentation in the cast billet, and surface cleaning of the cast billet is unnecessary. No surface defects were observed in the rolled coils during subsequent production.
[0063] Example 5: The quantitative evaluation of surface depressions on grade 510 beam steel billets is used as an example for illustration.
[0064] The measurement process is as follows Figure 7 As shown, QP is 88mm and MO is 30mm. The depression area S is calculated to be 4144.8mm² using formula (1). 2 The surface depressions of the billet were measured using a depth measuring instrument, and the depths were 3.99 mm, 4.02 mm, 3.70 mm, 3.98 mm, 4.00 mm, and 3.93 mm, respectively. The depression depth L was 4.02 mm, which is classified as Grade B. Based on the depression area and depression depth grades, Table 1 shows that δ is 0.120. According to formula (2), the depression index R is calculated to be 1999.45.
[0065] If the resulting indentation index R is greater than 1000, it is determined that the coil is highly likely to have surface defects caused by indentation in the cast billet. In subsequent production, some 510 beam steel cast billets were surface-cleaned, while others were not. A comparison revealed that, with the same indentation index, the coils rolled from the cast billets that were not surface-cleaned exhibited surface defects.
[0066] Example 6: The quantitative evaluation of surface depressions on grade 600 steel billets is used as an example.
[0067] The measurement process is as follows Figure 8As shown, QP is 100mm and MO is 20mm. The depression area S is calculated to be 3140.0mm² using formula (1). 2 The surface depressions of the billet were measured seven times using a depth measuring instrument. The results were 1.89 mm, 2.03 mm, 1.97 mm, 1.83 mm, 2.07 mm, 1.86 mm, and 1.75 mm, respectively. The depression depth L was 2.07 mm, which is classified as Grade C. Based on the depression area and depression depth grades, Table 1 shows that δ is 0.060. According to formula (2), the depression index R is calculated to be 389.99.
[0068] If the resulting indentation index R is less than 1000, it is determined that the coil will not suffer from surface defects caused by indentation in the cast billet, and surface cleaning of the cast billet is unnecessary. No surface defects were observed in the rolled coils during subsequent production.
[0069] Example 7: The quantitative evaluation of surface depressions on a 590 grade automotive structural steel billet is used as an example.
[0070] The measurement process is as follows Figure 9 As shown, QP is 88mm and MO is 15mm. The depression area S is calculated to be 2072.4mm² using formula (1). 2 The surface depressions of the billet were measured five times using a depth measuring instrument. The results were 5.06 mm, 5.10 mm, 5.09 mm, 5.08 mm, and 5.08 mm, respectively. The depression depth L was 5.10 mm, which is classified as Grade A. Based on the depression area and depression depth grades, Table 1 shows that δ is 0.150. According to formula (2), the depression index R is calculated to be 1585.39.
[0071] If the resulting indentation index R is greater than 1000, it is determined that the coil is highly likely to have surface defects caused by indentation in the cast billet. In subsequent production, some 590 grade automotive structural steel cast billets were surface-cleaned, while others were not. A comparison revealed that, with the same indentation index, the coils rolled from the cast billets that were not surface-cleaned exhibited surface defects.
Claims
1. A method for quantitatively evaluating surface depressions in peritectic steel billets, characterized in that, Includes the following steps: 1) Calculate the depression area S of the surface depression using the area method; 2) Measure the depth L of the depression on the surface of the cast billet; 3) Calculate the indentation index R using the following formula (2); R = S × L × δ (2; In the formula: R is the depression index; S is the depression area (mm). 2 L is the depth of the depression, in mm; δ is the depression coefficient, ranging from 0.020 to 0.
200. 4) The depression index R is used as a quantitative indicator of the depression on the surface of peritectic steel billet.
2. The method for quantitatively evaluating surface depressions of peritectic steel billets according to claim 1, characterized in that: In step 1), the surface depression contour is approximated as an ellipse, and the area S of the surface depression is calculated using the following formula (1). S = π × a × b (1); In the formula: S is the area of the depression, mm 2 π is the mathematical constant pi; a is the major semi-axis of the ellipse, in mm; b is the minor semi-axis of the ellipse, in mm.
3. The method for quantitatively evaluating surface depressions of peritectic steel billets according to claim 2, characterized in that, The measurement process of the major and minor semi-axis of the ellipse of the surface depression contour is as follows: the longest distance of the depression is directly measured using a length measuring tool, and half of the longest distance line segment is taken as the major semi-axis of the ellipse; a perpendicular line is drawn through the midpoint of the above long distance line segment, and intersects the edge of the depression at two points, and the longer line segment of the perpendicular line is taken as the minor semi-axis of the ellipse.
4. The method for quantitatively evaluating surface depressions of peritectic steel billets according to claim 1, characterized in that: In step 2), the depth of the depression on the surface of the billet is measured several times, and the maximum value is taken as the depression depth L.
5. A method for quantitatively evaluating surface depressions of peritectic steel billets according to any one of claims 1-4, characterized in that: In step 1), the depression area S is divided into the following four levels: S > 3500 is level I, 2000 < S ≤ 3500 is level II, 1000 < S ≤ 2000 is level III, and S ≤ 1000 is level IV; In step 2), the depression depth is divided into the following three levels: 5 ≤ L < 7 is level A, 3 ≤ L < 5 is level B, and 1 ≤ L < 3 is level C.
6. The method for quantitatively evaluating surface depressions of peritectic steel billets according to claim 5, characterized in that, In step 3), the value of the depression coefficient δ is determined based on the level of the depression area S and the depression depth L: For grade I+A, δ is taken as 0.200; For Level II+A, δ is 0.150; for Level III+A, δ is 0.100; for Level IV+A, δ is 0.
060. For Level I + B, δ is 0.120; for Level II + B, δ is 0.090; for Level III + B, δ is 0.050; for Level IV + B, δ is 0.
030. For Level I+C, δ is 0.080; for Level II+C, δ is 0.060; for Level III+C, δ is 0.040; and for Level IV+C, δ is 0.020.