Calculation method for predicting solidification process of continuous casting billet

Abstract

The invention relates to a calculation method for predicting the solidification process of a continuous casting billet, and belongs to the technical field of continuous casting methods in the metallurgical industry. According to the technical scheme, a solidification process prediction model is established to predict changes of the temperature and the solid fraction in the casting blank solidification process; the influence of segregation on the solidification process is considered in model building, the concentration of C changes along with the thickness change of a blank shell, the initial value of a casting blank component is a tundish sampling detection value, and the end point value is a casting blank center point detection value; performing casting blank external correction, measuring the surface temperature of the casting blank, and correcting the solidification process prediction model through comparison between the temperature measurement value of the same position and calculation; multi-point correction is conducted in the casting blank, the final stirring strength is increased to enable a white bright band to appear on the cross section of the casting blank, the final stirring position and the distance from the white bright band to the edge are measured, large-rolling-reduction internal crack position measurement is conducted, and the solidification process prediction model is corrected according to the measurement result. The method has the beneficial effects that reasonable optimization of secondary cooling water distribution, tail end electromagnetic stirring and soft reduction process parameters can be accurately guided, and the internal quality of steel is improved.

Description

Technical Field

[0001] The invention relates to a calculation method for predicting a continuous casting billet solidification process, and belongs to the technical field of continuous casting methods in the metallurgical industry. Background Art

[0002] Terminal electromagnetic stirring and light reduction process are important technological means to improve the internal quality of continuous casting billets. The terminal electromagnetic stirring process changes the flow of molten steel through electromagnetic force, thereby improving component segregation and central porosity. The light reduction process applies a certain amount of reduction to the billet within a certain range to improve the porosity caused by solidification shrinkage and the segregation caused by the flow of rich elements. However, the position of the terminal electromagnetic stirring and the determination of the reduction range and reduction amount in the light reduction process are based on an accurate billet solidification model. The calculation methods of the solidification process are roughly similar, but the accuracy will vary depending on the details considered. In addition, the current correction of the solidification model is mainly through the method of billet surface temperature measurement and nail shooting test. In the absence of nail shooting equipment and low temperature detection accuracy, it is very necessary to seek other correction methods.

[0003] Patent CN114722564A discloses a method for interpreting the sulfur print of nail shooting samples to calibrate a continuous solidification model, and accurately judges the solidification position based on low-magnification samples of nail shooting tests.

[0004] Patent CN112784367A discloses a method for estimating the shell thickness of the continuous casting roller position and the solidification end of the casting machine. The solidification position is estimated by measuring the distance from the edge of the point crack on the low power of the ingot and comparing it with the shell thickness calculated by the solidification square root formula. The method for obtaining the crack position, the corresponding logic between the crack position and the shell, and the method for calculating the shell using the solidification square root formula are all too simple and not very accurate.

[0005] Patent CN116738518A discloses a numerical simulation verification method for the crack position of continuous casting light pressure. The crack position is selected as the center side while this patent is the starting side and the comparison method is different. The method of obtaining cracks is passive, while this patent is active to obtain and more obvious crack morphology.

[0006] At present, the methods in the relevant patents for verifying the solidification model are relatively simple and have limitations to varying degrees. Summary of the invention

[0007] The purpose of the present invention is to provide a calculation method for predicting the solidification process of a continuous casting billet. By establishing a solidification process prediction model that is closer to the actual condition of the billet, the temperature of the continuous casting process and the position of the two-phase zone are accurately predicted by measuring the external temperature of the billet and the multi-point position of the internal two-phase zone. This method can accurately guide the reasonable optimization of the secondary cooling water distribution, terminal electromagnetic stirring and light pressure process parameters, improve the internal quality of steel, and effectively solve the above-mentioned problems existing in the background technology.

[0008] The technical solution of the present invention is: a calculation method for predicting the solidification process of a continuous casting billet, comprising the following steps: (1) establishing a solidification process prediction model to predict the changes in temperature and solid phase ratio during the solidification process of the billet; (2) considering the influence of segregation on the solidification process in the model establishment, the concentration of C changes with the thickness of the billet shell, the initial value of the billet composition is the sampling detection value of the tundish, and the end point value is the detection value of the center point of the billet; (3) performing billet external correction, measuring the billet surface temperature, and correcting the solidification process prediction model by comparing the temperature measurement value at the same position with the calculation; (4) performing billet internal multi-point correction, measuring the internal white bright band negative segregation and the position of the internal cracks, and using the measurement results to correct the solidification process prediction model.

[0009] In the step (1), according to different algorithms, the solidification process of the ingot is divided into a crystallizer section, a foot roll section, a water cooling section, an air cooling section 1, an air cooling section 2 and a straightening section, and the heat transfer coefficient of each section is different; considering the influence of the flow of molten steel on the thermal conductivity, the thermal conductivity of the molten steel at different stages is corrected by multiplying different coefficients, the correction coefficient of the crystallizer section is 3-6, the correction coefficient of the water cooling section is 2-3, and the correction coefficient of other positions is 1-2.

[0010] In the step (2), the concentration of C varies with the thickness of the billet shell in the following manner: the composition remains unchanged within the crystallizer section, and is simplified to a linear increase to the measured value at the center of the billet at other locations.

[0011] In the step (3), the temperature of the wide and narrow surfaces of the ingot is firstly measured in the first air cooling stage, the second air cooling stage and the straightening stage respectively, and the measurement is repeated five times to take the highest value; the temperature of the ingot is measured at the moment when the oxide scale falls off in the straightening stage, and the emissivity range of the temperature measuring gun is selected to be 0.55-0.85; and the model is calibrated by comparing the temperature measurement value at the same position with the calculation value.

[0012] In the step (4), the unstirring intensity is increased to make a white bright band appear in the cross section of the ingot. The unstirring position and the distance from the white bright band to the edge are compared with the calculated distance from the position of 0.35 solid phase fraction to the edge at the same position of the ingot to further calibrate the solidification process prediction model.

[0013] In the step (4), cracks are caused to appear inside the ingot by significantly increasing the amount of reduction of one of the rolls in the light reduction section, and the solidification process prediction model is further corrected by measuring the distance from the starting position of the crack near the edge to the surface and comparing it with the calculated distance from the position to the surface when the solid phase fraction at the reduction roll position is 0.95.

[0014] The beneficial effects of the present invention are as follows: by establishing a solidification process prediction model that is closer to the actual situation of the ingot, and then accurately predicting the temperature and the position of the two-phase zone in the continuous casting process by measuring the external temperature of the ingot and the multi-point position measurement of the internal two-phase zone, it is possible to accurately guide the reasonable optimization of the secondary cooling water distribution, terminal electromagnetic stirring and light pressure process parameters, and improve the internal quality of the steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 1 is a schematic diagram of the center of the ingot at low magnification according to Example 1 of the present invention; Figure 2 1 is a schematic diagram of the center of the ingot at low magnification according to Example 2 of the present invention; Figure 3 It is a low-magnification center schematic diagram of the ingot in Example 3 of the present invention. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the invention implementation cases clearer, the technical solutions in the implementation cases of the present invention will be clearly and completely described below in conjunction with the drawings in the implementation cases. Obviously, the implementation cases described are only a small part of the implementation cases of the present invention, rather than all the implementation cases. Based on the implementation cases in the present invention, all other implementation cases obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] A calculation method for predicting the solidification process of a continuous casting billet comprises the following steps: (1) establishing a solidification process prediction model to predict changes in temperature and solid phase ratio during the solidification process of the billet; (2) considering the influence of segregation on the solidification process in the model establishment, wherein the concentration of C changes with the thickness of the billet shell, the initial value of the billet composition is the tundish sampling detection value, and the end point value is the billet center point detection value; (3) performing billet external correction, measuring the billet surface temperature, and correcting the solidification process prediction model by comparing the temperature measurement value at the same position with the calculation; (4) performing billet internal multi-point correction, measuring the internal white bright band negative segregation and the position of the internal crack, and using the measurement results to correct the solidification process prediction model.

[0018] In the step (1), according to different algorithms, the solidification process of the ingot is divided into a crystallizer section, a foot roll section, a water cooling section, an air cooling section 1, an air cooling section 2 and a straightening section, and the heat transfer coefficient of each section is different; considering the influence of the flow of molten steel on the thermal conductivity, the thermal conductivity of the molten steel at different stages is corrected by multiplying different coefficients, the correction coefficient of the crystallizer section is 3-6, the correction coefficient of the water cooling section is 2-3, and the correction coefficient of other positions is 1-2.

[0019] In the step (2), the concentration of C varies with the thickness of the billet shell in the following manner: the composition remains unchanged within the crystallizer section, and is simplified to a linear increase to the measured value at the center of the billet at other locations.

[0020] In the step (3), the temperature of the wide and narrow surfaces of the ingot is firstly measured in the first air cooling stage, the second air cooling stage and the straightening stage respectively, and the measurement is repeated five times to take the highest value; the temperature of the ingot is measured at the moment when the oxide scale falls off in the straightening stage, and the emissivity range of the temperature measuring gun is selected to be 0.55-0.85; and the model is calibrated by comparing the temperature measurement value at the same position with the calculation value.

[0021] In the step (4), the unstirring intensity is increased to make a white bright band appear in the cross section of the ingot. The unstirring position and the distance from the white bright band to the edge are compared with the calculated distance from the position of 0.35 solid phase fraction to the edge at the same position of the ingot to further calibrate the solidification process prediction model.

[0022] In the step (4), cracks are caused to appear inside the ingot by significantly increasing the amount of reduction of one of the rolls in the light reduction section, and the solidification process prediction model is further corrected by measuring the distance from the starting position of the crack near the edge to the surface and comparing it with the calculated distance from the position to the surface when the solid phase fraction at the reduction roll position is 0.95.

[0023] In practical applications, the present invention establishes a solidification process prediction model that takes into account the effect of segregation on the solidification process. The concentration of C varies with the thickness of the billet shell, the initial value is the sample detection value of the tundish, and the end value is the composition detection value of the center point of the billet. The solidification process prediction model is verified by an internal and external combined method of surface temperature, internal white bright band negative segregation and the location of internal cracks.

[0024] The continuous casting machine is an arc-shaped continuous casting machine with a cross-section range of 200mm*200mm to 410mm*530mm. The continuous casting production line is equipped with quality control equipment such as crystallizer electromagnetic stirring, solidification end electromagnetic stirring, dynamic secondary cooling water distribution, and dynamic soft pressure.

[0025] The solidification process prediction model divides the solidification process of the ingot into the crystallizer section, the foot roll section, the water cooling section, the air cooling section 1, the air cooling section 2 and the straightening section. The heat transfer coefficient of each section is different. Considering the influence of the molten steel flow on the thermal conductivity, the thermal conductivity of the molten steel at different stages is corrected by multiplying different coefficients. The correction coefficient of the crystallizer section is 3-6, the correction coefficient of the water cooling section is 2-3, and the correction coefficient of other positions is 1-2.

[0026] Billet external calibration: First, measure the temperature of the wide and narrow surfaces of the billet in the first and second air cooling stages and the straightening stage, repeat the measurement five times, and take the highest value. Measure the temperature of the billet when the iron oxide scale falls off in the straightening stage, and select the emissivity range of the temperature gun in the range of 0.55-0.85. Compare the temperature measurement value at the same position with the calculation to calibrate the solidification process prediction model.

[0027] Multi-point correction inside the ingot: by increasing the end-stirring intensity to make a white bright band appear on the cross section of the ingot, the model is further corrected by comparing the distance from the end-stirring position and the white bright band to the edge with the calculated distance from the position of the ingot with a solid phase ratio of 0.35 to the edge at the same position. By significantly increasing the pressure reduction of one of the rolls in the light pressure reduction section to make cracks appear inside the ingot, the solidification process prediction model is further corrected by measuring the distance from the starting position of the crack near the edge to the surface and comparing it with the calculated distance from the position of the pressure reduction roll with a solid phase ratio of 0.95 to the surface. Example 1

[0028] (1) A medium carbon chromium-molybdenum steel with a continuous casting billet cross-section of 200 mm × 200 mm, a liquidus temperature of 1495°C, a superheat of 25°C, and a secondary cooling water volume of 0.32 L / kg.

[0029] (2) The concentration of C in the ingot composition changes with the thickness of the ingot shell. The composition remains unchanged within the crystallizer section. From the crystallizer outlet to the end of solidification, the concentration of C increases linearly from 0.42% detected in the tundish to 0.47% measured at the center of the ingot.

[0030] (3) The calculation method of the heat flux in the crystallizer section is q=AB*(L / v)^0.5, where A is the cooling parameter related to the crystallizer, which is taken as 2680000; B can be calculated based on the average heat flux; L is the distance from the meniscus; and v is the pulling speed.

[0031] (4) The heat transfer coefficient of the second cooling section includes the convection heat transfer of the spray water, the conduction heat transfer between the rollers and the billet, and the radiation heat transfer of the billet. The heat transfer coefficients of the air cooling section and the straightening section include the conduction heat transfer between the rollers and the billet and the radiation heat transfer of the billet. The conduction heat transfer coefficient and the radiation heat transfer coefficient of each section are different according to the number and density of rollers on the four surfaces. The calculation method of each heat transfer coefficient adopts the conventional calculation method in the literature, and the heat transfer coefficient is corrected according to the subsequent correction method.

[0032] (5) The correction factor for the thermal conductivity of molten steel in the mold section is 3, the correction factor in the water cooling section is 2, and the correction factor in other locations is 1.

[0033] (6) At a distance of 8.2 m, 10.5 m, 15 m, and 17 m from the meniscus, take five temperature measurements when the scale falls off, and take the maximum values ​​of 1151°C, 1146°C, 1061°C, and 1030°C, respectively. The emissivity of the temperature gun varies with temperature and is selected in the range of 0.55-0.85.

[0034] (7) The end electromagnetic stirring current and frequency were set to 500 A and 7 Hz, respectively. The distance from the inside of the white bright band to the edge was measured by low-power observation and was 56 mm. This was compared with the calculated distance from the position with a solid phase ratio of 0.35 at the end of the stirring to the edge to further calibrate the model.

[0035] (8) The reduction amount of light reduction No. 2 was set to 10 mm, and the distance from the starting position of the crack near the edge of the ingot cross section to the surface was measured to be 53 mm. This distance was compared with the calculated position from this position to the surface when the solid phase fraction was 0.95 to further calibrate the model.

[0036] (9) The temperature values ​​at the four measurement positions and the distances from the white bright band and the internal crack to the edge were compared with the calculated values. The heat transfer coefficients of each section were modified to calibrate the model, and the optimal reduction range was obtained to be 13.1-15.6 m. The qualified rate of low-magnification center porosity of the ingot was increased from 80% to more than 95% before and after statistical process optimization. Example 2

[0037] (1) A low carbon chromium manganese steel with a continuous casting billet cross-section of 300 mm × 340 mm, a liquidus temperature of 1508 °C, a superheat of 25 °C, and a secondary cooling water volume of 0.28 L / kg.

[0038] (2) The C concentration in the ingot composition changes with the thickness of the ingot shell. The composition remains unchanged within the crystallizer section. From the crystallizer outlet to the end of solidification, the C concentration increases linearly from 0.20% detected in the tundish to 0.22% measured at the center of the ingot.

[0039] (3) The calculation method of the heat flux in the crystallizer section is q=AB*(L / v)^0.5, where A is the cooling parameter related to the crystallizer, which is taken as 2680000; B can be calculated based on the average heat flux; L is the distance from the meniscus; and v is the pulling speed.

[0040] (4) The heat transfer coefficient of the second cooling section includes the convection heat transfer of the spray water, the conduction heat transfer between the rollers and the billet, and the radiation heat transfer of the billet. The heat transfer coefficients of the air cooling section and the straightening section include the conduction heat transfer between the rollers and the billet and the radiation heat transfer of the billet. The conduction heat transfer coefficient and the radiation heat transfer coefficient of each section are different according to the number and density of rollers on the four surfaces. The calculation method of each heat transfer coefficient adopts the conventional calculation method in the literature, and the heat transfer coefficient is corrected according to the subsequent correction method.

[0041] (5) The correction factor for the thermal conductivity of molten steel in the mold section is 4, the correction factor in the water cooling section is 2.5, and the correction factor in other locations is 1.5.

[0042] (6) At the distances from the meniscus of 9.9 m, 11.2 m, 12.5 m, and 15.1 m, take five temperature measurements at the moment when the iron oxide scale falls off, and take the maximum values ​​of 1077°C, 1056°C, 1042°C, and 1007°C respectively. The emissivity of the temperature gun varies with temperature and is selected in the range of 0.55-0.85.

[0043] (7) The end electromagnetic stirring current and frequency were set to 500 A and 10 Hz, respectively. The distance from the inner side of the white bright band to the inner arc edge was measured by low-power observation and was 95 mm. This was compared with the calculated distance from the position with a solid phase ratio of 0.35 at the end stirring position to the edge to further calibrate the model.

[0044] (8) The reduction amount of light reduction No. 2 was set to 10 mm, and the distance from the starting position of the crack near the edge of the ingot cross section to the surface was measured to be 106 mm. This distance was compared with the calculated position from the position to the surface when the solid phase fraction was 0.95 to further calibrate the model.

[0045] (9) The temperature values ​​at the four measurement positions and the distances from the white bright band and the internal crack to the edge were compared with the calculated values. The heat transfer coefficients of each section were modified to calibrate the model, and the optimal reduction range was obtained to be 15.3-17.5 m. The qualified rate of low-magnification center porosity of the ingot was increased from 73% to more than 90% before and after statistical process optimization. Example 3

[0046] (1) According to a high carbon chromium steel of an embodiment of the present invention, the cross section of the continuous casting billet is 410 mm×530 mm, the liquidus temperature is 1456°C, the superheat is 25°C, and the secondary cooling water volume is 0.15 L / kg.

[0047] (2) The concentration of C in the ingot composition changes with the thickness of the ingot shell. The composition remains unchanged within the crystallizer section. From the crystallizer outlet to the end of solidification, the concentration of C increases linearly from 1.00% detected in the tundish to 1.10% measured at the center of the ingot.

[0048] (3) The calculation method of the heat flux in the crystallizer section is q=AB*(L / v)^0.5, where A is the cooling parameter related to the crystallizer, which is taken as 2680000; B can be calculated based on the average heat flux; L is the distance from the meniscus; and v is the pulling speed.

[0049] (4) The heat transfer coefficient of the second cooling section includes the convection heat transfer of the spray water, the conduction heat transfer between the rollers and the billet, and the radiation heat transfer of the billet. The heat transfer coefficients of the air cooling section and the straightening section include the conduction heat transfer between the rollers and the billet and the radiation heat transfer of the billet. The conduction heat transfer coefficient and the radiation heat transfer coefficient of each section are different according to the number and density of rollers on the four surfaces. The calculation method of each heat transfer coefficient adopts the conventional calculation method in the literature, and the heat transfer coefficient is corrected according to the subsequent correction method.

[0050] (5) The correction factor for the thermal conductivity of molten steel in the mold section is 6, the correction factor in the water cooling section is 3, and the correction factor in other locations is 2.

[0051] (6) At the distances of 18.2 m, 20.5 m, 23.5 m, and 25.5 m from the meniscus, take five temperature measurements at the moment when the iron oxide scale falls off, and take the maximum values ​​of 943°C, 930°C, 918°C, and 898°C respectively. The emissivity of the temperature gun varies with temperature and is selected in the range of 0.55-0.85.

[0052] (7) The end electromagnetic stirring current and frequency were set to 700 A and 10 Hz, respectively. The distance from the inner side of the white bright band to the inner arc edge was measured by low-power observation and was 160 mm. This was compared with the calculated distance from the position with a solid phase ratio of 0.35 at the end stirring position to the edge to further calibrate the model.

[0053] (8) The reduction amount of light reduction No. 2 was set to 10 mm, and the distance from the starting position of the crack near the edge of the ingot cross section to the surface was measured to be 142 mm. This distance was compared with the calculated position from this position to the surface when the solid phase fraction was 0.95 to further calibrate the model.

[0054] (9) The temperature values ​​at the four measurement positions and the distances from the white bright band and the internal crack to the edge were compared with the calculated values. The heat transfer coefficient of each section was modified to calibrate the model, and the optimal reduction range was obtained to be 18.9-26.6 m. Before and after statistical process optimization, the qualified rate of low-magnification central porosity of the ingot was increased from 70% to more than 90%.

[0055] The present invention establishes a solidification model that is closer to the actual ingot, and then accurately predicts the temperature and position of the two-phase zone during continuous casting by measuring the external temperature of the ingot and the multi-point position of the internal two-phase zone. It can accurately guide the rational optimization of the process parameters of secondary cooling water distribution, terminal electromagnetic stirring and soft pressure reduction, and improve the internal quality of steel.

Claims

1. A calculation method for predicting the solidification process of continuous casting billet, characterized in that The method comprises the following steps: (1) establishing a solidification process prediction model to predict the changes in temperature and solid phase ratio during the solidification process of the ingot; (2) considering the influence of segregation on the solidification process in the model establishment, the concentration of C changes with the thickness of the ingot shell, the initial value of the ingot composition is the sampling detection value of the tundish, and the end point value is the detection value of the center point of the ingot; (3) performing an external correction of the ingot, measuring the surface temperature of the ingot, and correcting the solidification process prediction model by comparing the temperature measurement value at the same position with the calculation; (4) performing a multi-point correction inside the ingot, measuring the negative segregation of the white bright band inside and the position of the internal cracks, and using the measurement results to correct the solidification process prediction model.

2. The calculation method for predicting the solidification process of a continuous casting billet according to claim 1, characterized in that: In the step (1), according to different algorithms, the solidification process of the ingot is divided into a crystallizer section, a foot roll section, a water cooling section, an air cooling section 1, an air cooling section 2 and a straightening section, and the heat transfer coefficient of each section is different; considering the influence of the flow of molten steel on the thermal conductivity, the thermal conductivity of the molten steel at different stages is corrected by multiplying different coefficients, the correction coefficient of the crystallizer section is 3-6, the correction coefficient of the water cooling section is 2-3, and the correction coefficient of other positions is 1-2.

3. The calculation method for predicting the solidification process of a continuous casting billet according to claim 1, characterized in that: In the step (2), the concentration of C varies with the thickness of the billet shell in the following manner: the composition remains unchanged within the crystallizer section, and is simplified to a linear increase to the measured value at the center of the billet at other locations.

4. The calculation method for predicting the solidification process of a continuous casting billet according to claim 2, characterized in that: In the step (3), the temperature of the wide and narrow surfaces of the ingot is firstly measured in the first air cooling stage, the second air cooling stage and the straightening stage respectively, and the measurement is repeated five times to take the highest value; the temperature of the ingot is measured at the moment when the oxide scale falls off in the straightening stage, and the emissivity range of the temperature measuring gun is selected to be 0.55-0.85; and the model is calibrated by comparing the temperature measurement value at the same position with the calculation value.

5. The calculation method for predicting the solidification process of a continuous casting billet according to claim 1, characterized in that: In the step (4), the unstirring intensity is increased to make a white bright band appear in the cross section of the ingot. The unstirring position and the distance from the white bright band to the edge are compared with the calculated distance from the position of 0.35 solid phase fraction to the edge at the same position of the ingot to further calibrate the solidification process prediction model.

6. The calculation method for predicting the solidification process of a continuous casting billet according to claim 1, characterized in that: In the step (4), cracks are caused to appear inside the ingot by significantly increasing the amount of reduction of one of the rolls in the light reduction section, and the solidification process prediction model is further corrected by measuring the distance from the starting position of the crack near the edge to the surface and comparing it with the calculated distance from the position to the surface when the solid phase fraction at the reduction roll position is 0.95.

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