A method and storage medium for reducing W-shaped solidification segregation of slab

Abstract

The present invention provides a method and storage medium for reducing w-type solidification segregation of slabs, which is suitable for engineering applications and belongs to the field of metallurgical continuous casting technology, including: performing water distribution test on the nozzle of each secondary cooling zone, calculating the relative proportion of water at different positions in the width direction and relative to the center position under different control parameters, calculating the distribution of the surface cooling water heat transfer coefficient of each secondary cooling zone, and calculating the distribution of the comprehensive heat transfer coefficient of each secondary cooling zone based on the distribution of the cooling water heat transfer coefficient; constructing a two-dimensional heat transfer model, and loading the distribution of the comprehensive heat transfer coefficient into the two-dimensional heat transfer model as a boundary condition; taking the original process as the initial condition, and obtaining the adjustment parameter combination of each secondary cooling zone that meets the technical requirements through iterative calculation. The present invention proposes a method for reducing w-type solidification segregation of slabs suitable for engineering applications, and improves the model by using the distribution of the comprehensive heat transfer coefficient. Compared with the prior art, the error between the model prediction value and the measured value is within 3.2%, and the calculation time is reduced by 90%.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical continuous casting, and in particular relates to a method for reducing W-shaped solidification segregation of a slab and a storage medium. Background Art

[0002] After the ingot is cooled by the crystallizer, it is cooled again by water spray or aerosol spray through the nozzles inside each sector. The amount and distribution of cooling water in the secondary cooling zone significantly affect the cooling state and solidification process of the ingot, thereby affecting the quality and performance of the final slab. Due to the large width-to-thickness ratio of the slab and the large number of types and numbers of nozzles in the width direction, the cooling state of the wide surface is prone to differences, resulting in inconsistent solidification speeds in various areas of the center line of the slab, forming an uneven solidification end, such as the common W-type solidification. The uneven solidification end of the slab will weaken the effect of light reduction, resulting in severe center segregation or loose shrinkage, which will affect the quality and processing performance of the ingot.

[0003] In order to solve the problem of uneven solidification end of slab, the existing technical method is usually to adjust the model and arrangement of the nozzle in the secondary cooling zone to achieve uniform cooling of the wide surface of the slab, and conduct trial and error in combination with industrial tests, and evaluate the effectiveness of the nozzle adjustment by the central segregation of the cross section of the slab. However, in fact, the crack sensitivity of peritectic steel slabs is relatively strong. During the production of slabs, weak cooling of the corners is usually used to reduce corner cracks, but it causes the water volume of the wide surface to drop rapidly at the edge, which is the main reason for the W-shaped solidification end at the 1 / 8 to 1 / 4 position of the slab transversely. Therefore, for peritectic steel slabs, the contradiction between the reduction of water volume caused by weak cooling of the corners and the uniformity of transverse cooling of the wide surface needs to be solved urgently, and it is urgent to comprehensively consider the cooling needs of different parts; at the same time, the position of the secondary cooling zone of the nozzle adjustment in the existing technical method is unclear, and the cost of large-scale replacement is high and the effect is poor; and the use of industrial tests also has the problem of high trial and error costs, which affects the production efficiency of enterprises. Summary of the invention

[0004] To solve the above problems, the present invention provides a method and storage medium for reducing the w-type solidification segregation of slabs. A method suitable for engineering applications to reduce the w-type solidification segregation of slabs is proposed, and the distribution of the comprehensive heat transfer coefficient is used to improve the model. Compared with the prior art, the error between the model prediction value and the measured value is within 3.2%, and the calculation time is reduced by 90%.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a method for reducing W-shaped solidification segregation of slabs, which is suitable for engineering applications, comprising: performing a water volume distribution test on a nozzle of each secondary cooling zone, calculating the relative proportion of water volume at different positions in the width direction and relative to a central position under different control parameters, calculating the distribution of a surface cooling water heat exchange coefficient of each secondary cooling zone, and calculating the distribution of a comprehensive heat exchange coefficient of each secondary cooling zone based on the distribution of the cooling water heat exchange coefficient; constructing a two-dimensional heat transfer model, and loading the distribution of the comprehensive heat exchange coefficient into the two-dimensional heat transfer model as a boundary condition; taking the original process as an initial condition, obtaining an adjustment parameter combination of each secondary cooling zone that meets technical requirements through iterative calculation.

[0007] Furthermore, the comprehensive heat transfer coefficient h is calculated as follows:

[0008]

[0009] Where: h s is the cooling water heat transfer coefficient, h r is the radiation heat transfer coefficient, W is the water flow density, T W is the cooling water temperature, α is the correction coefficient, T s is the surface temperature of the casting, T 0 is the ambient temperature, ε is the blackness of the billet surface, and σ is the Boltzmann constant.

[0010] Furthermore, the control parameters include water pressure and air pressure.

[0011] Furthermore, the technical requirements include technical indicators and parameter optimization indicators, and the priority of the technical indicators is higher than that of the parameter optimization indicators; the technical indicators include: the difference between the maximum and minimum values ​​of the liquid core length at different positions in the width direction is less than a first preset value and the temperature at the corner of the straightening zone does not fall into the third brittle zone; the parameter optimization indicators include: the optimal working parameter range of the nozzle in each secondary cooling zone, the allowable working parameter range of the nozzle in each secondary cooling zone, the joint control priority of multiple secondary cooling zones is higher than the independent control of a single secondary cooling zone, and the lowest temperature at the corner of the straightening zone is at least 20°C higher than the highest temperature of the third brittle zone.

[0012] Furthermore, the simplification of the two-dimensional heat transfer model includes: the physical properties of the ingot are isotropic, one-quarter of the cross section of the slab is selected for modeling, heat transfer in the drawing direction is not considered, a two-dimensional slicing method under a moving coordinate system is used, the thermal physical properties of steel in the liquid phase, liquid-solid two-phase region and solid phase region are functions of temperature and are independent of spatial position, and the influence of crystallizer vibration on heat transfer during solidification is ignored.

[0013] Furthermore, the ratio of length to width of the cross section of the slab of the model is 5-10.

[0014] Furthermore, through iterative calculation, the adjustment parameter combination of each second cooling zone that meets the technical requirements includes: when the difference between the maximum and minimum values ​​of the liquid core length is greater than the first preset value and less than the second preset value, negative feedback adjustment is performed based on the difference between the lowest temperature entering the corner of the straightening zone and the upper limit of the third brittle zone, and the preliminary adjustment is completed when the lowest temperature at the corner of the straightening zone is greater than the upper limit of the third brittle zone. After the preliminary adjustment, the cooling intensity in the width direction of the slab is adjusted; when the difference between the maximum and minimum values ​​of the liquid core length is greater than the second preset value, feedback adjustment is performed on the cooling intensity in the width direction based on the difference between the maximum and minimum values ​​of the liquid core length. When the difference between the maximum and minimum values ​​of the liquid core length is less than the second preset value, negative feedback adjustment is performed based on the difference between the lowest temperature entering the corner of the straightening zone and the upper limit of the third brittle zone. When the lowest temperature at the corner of the straightening zone is greater than the upper limit of the third brittle zone, the preliminary adjustment is completed, and after the preliminary adjustment, the cooling intensity in the width direction of the slab is adjusted.

[0015] Furthermore, a secondary screening is performed based on the adjustment parameter combination to obtain the optimal parameter combination, and the screening priorities are as follows from high to low: the lowest temperature at the corner of the straightening zone is at least 20°C higher than the highest temperature of the third brittle zone; the optimal operating parameter range of the nozzle in each secondary cooling zone; the priority of joint control of multiple secondary cooling zones is higher than the independent control of a single secondary cooling zone; the allowable operating parameter range of the nozzle in each secondary cooling zone.

[0016] Furthermore, if the adjustment parameter combination is a non-empty set, the optimal parameter combination with a lower priority is selected for implementation; if the adjustment parameter combination is an empty set, the allowable operating parameter range of the nozzle of one or more secondary cooling zones in the arc section located upstream of the straightening zone and starting from the second secondary cooling zone in the upstream direction is adjusted, and the adjustment range is to expand the allowable operating parameter range of the nozzle by 10%.

[0017] An embodiment of the present invention further provides a computer-readable storage medium, which stores one or more programs. The one or more programs can be executed by one or more processors to implement the above-mentioned method for reducing W-type solidification segregation of slabs.

[0018] The beneficial effects brought by the technical solution provided by the embodiment of the present invention include:

[0019] (1) A method suitable for engineering applications to reduce W-type solidification segregation in slabs is proposed. The model is improved by using the distribution of the comprehensive heat transfer coefficient. Compared with the existing technology, the error between the model prediction value and the measured value is within 3.2%, and the calculation time is reduced by 90%.

[0020] (2) For peritectic steel, the W-type solidification segregation is solved, and the maximum temperature at the corner of the straightening zone is not in the third brittle zone. The prepared slab does not have the problems of segregation and cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 are the predicted value and measured value of the slab surface temperature in the embodiment of the present invention;

[0023] Figure 2 The initial water volume distribution in the width direction of the cooling zones 13-16 in Example 1 of the present invention;

[0024] Figure 3 The non-uniform solidification end under the initial secondary cooling in Example 1 of the present invention;

[0025] Figure 4 The water distribution in the width direction of the cooling zones 13-16 after optimization in Example 1 of the present invention;

[0026] Figure 5 This is the central segregation morphology of the slab in Example 1 of the present invention;

[0027] Figure 6 This is the central segregation morphology of the slab in Example 2 of the present invention;

[0028] Figure 7 This is the central segregation morphology of the slab in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] The “engineering application” is aimed at the production site, requiring timely feedback, rapid adjustment, high model accuracy, and meeting the requirements of engineering application. For example, the calculation time does not exceed 5 hours, the model accuracy is not less than 5%, and on-site discovery and on-site resolution can be achieved. The high accuracy requirements of the model require that the size of the model and the boundary conditions be more detailed, resulting in too long calculation time, measured in days, and it is impossible to achieve on-site discovery and on-site resolution. For example, the invention patent with application number CN202310894501.8 discloses a method and system for reducing the W-type solidification-segregation phenomenon of slabs, but this method does not consider the influence of nozzle arrangement on the corner cracks of peritectic steel slabs. At the same time, the actual establishment of a full-process coupling model of slab continuous casting is time-consuming and computationally expensive, and the actual application is difficult, and the method does not propose practical and effective control means.

[0031] The embodiment of the present invention provides a method for W-type solidification segregation, which is suitable for engineering applications, including:

[0032] S1 performs a water volume distribution test on the nozzles of each secondary cooling zone, calculates the relative proportion of water volume at different positions in the width direction and relative to the center position under different control parameters, calculates the distribution of the surface cooling water heat transfer coefficient of each secondary cooling zone, and calculates the distribution of the comprehensive heat transfer coefficient of each secondary cooling zone based on the distribution of the cooling water heat transfer coefficient.

[0033] The comprehensive heat transfer coefficient h is calculated as follows:

[0034]

[0035] Where: h s is the cooling water heat transfer coefficient, h r is the radiation heat transfer coefficient, W is the water flow density, T W is the cooling water temperature, α is the correction coefficient, which is 4, T s is the surface temperature of the casting, T 0 is the ambient temperature, ε is the blackness of the billet surface, which is 0.8, and σ is the Boltzmann constant, which is 5.67×10 -8 W·m -2 ·K -4 .

[0036] In order to further improve the calculation speed and reflect the actual cooling situation, the present application changes the relative proportion of the water volume at different positions in the width direction of the slab under the condition that the cooling water volume in each secondary cooling zone remains unchanged.

[0037] The control parameters include water pressure and air pressure.

[0038] The water flow density of the secondary cooling zone of the slab can be tested on site or obtained by building a platform in the laboratory. Specifically, an acrylic tube is used for measurement. The internal size of the acrylic tube needs to be designed according to the slab width. If the slab width is less than 1.0m, the size of the acrylic tube is 10×10mm 2 ; The slab width is 1.0~2.0m, and the acrylic tube size is 15×15mm 2 ; The slab width is greater than 2.0m, and the acrylic tube size is 20×20mm 2 .

[0039] It should be pointed out that the secondary cooling zone is arranged with different types of nozzles, and each secondary cooling zone can independently control the water pressure and air pressure.

[0040] S2 constructs a two-dimensional heat transfer model, and loads the distribution of the comprehensive heat transfer coefficient into the two-dimensional heat transfer model as a boundary condition.

[0041] The surface temperature and solidification state of the billet during the continuous casting process have an important influence on the billet quality, and are also the basis for indirectly determining the rationality of the continuous casting process. The main process factors affecting the thermal state and solidification process of the billet are casting temperature (superheat), billet drawing speed and cooling intensity (mainly secondary cooling intensity and distribution). The continuous casting billet moves downward from the meniscus of the molten steel in the crystallizer at a certain drawing speed, and the heat is transferred from the center of the billet to the surface of the billet. The transferred heat is affected by the basic properties of the metal and the cooling conditions of the billet boundary. Solving the mathematical model of heat transfer and solidification of the continuous casting billet can analyze the heat transfer in the continuous casting process and the temperature change law of each part of the billet at each moment in the whole process from the crystallizer to the secondary cooling zone until the air cooling after the casting machine, so as to obtain information such as cooling rate, temperature gradient, solidification rate, etc., and provide certain reference information for analyzing the solidification process of the billet and the low-temperature solid phase transformation structure. Therefore, the correct construction of the billet temperature field calculation model is crucial to ensure the reliability of the calculation results. The embodiment of the present invention uses the commercial finite element analysis software ABAQUS to establish a two-dimensional heat transfer model of the slab, and calculates the growth of the solidified slab shell (thickness) and the solidification endpoint of the slab under different continuous casting process parameters.

[0042] The simplification of the two-dimensional heat transfer model includes: the physical properties of the ingot are isotropic, one-fourth of the cross section of the slab is selected for modeling, no heat transfer is performed in the billet drawing direction, a two-dimensional slicing method under a moving coordinate system is used, the thermal physical properties of steel in the liquid phase, liquid-solid two-phase region and solid phase region are functions of temperature and are independent of spatial position, and the influence of crystallizer vibration on heat transfer during solidification is ignored.

[0043] The ratio of the length to width of the cross section of the slab of the model is 5-10. The size of the model has a certain influence on the result, and according to the model calculation method adopted by the present invention, when the ratio of the length to width of the cross section of the slab of the model is 5-10, the accuracy of the calculation result is greatly improved.

[0044] The conditions for establishing the model are:

[0045] (1) Initial conditions

[0046] The mathematical model of continuous casting slab two-dimensional solidification heat transfer takes the temperature distribution of molten steel at the meniscus of the crystallizer as the initial condition. Assuming that the temperature distribution at the meniscus of molten steel in the crystallizer is uniform, the initial temperature of the calculation domain is equal to the pouring temperature Tc when the molten steel enters the crystallizer, that is: t = 0

[0047] T t＝0 =T C

[0048] (2) Boundary conditions:

[0049] After the molten steel enters the crystallizer and forms a shell of a certain thickness at the meniscus, the solidified shell moves downward as the billet is pulled. During this movement, the billet will go through different cooling stages, so the external heat exchange conditions experienced by the billet change over time, so the boundary conditions of the billet at different positions are also different. Since the 1 / 4 model is used, the heat transfer boundary conditions of the billet are mainly divided into two parts, the internal symmetry surface of the billet and the billet surface.

[0050] The heat transfer of the ingot is symmetrical about the center, and the heat transfer boundary of the central symmetry axis can be regarded as an adiabatic boundary.

[0051] During the entire continuous casting process, the surface of the ingot is the heat exchange boundary, including crystallizer heat exchange, secondary cooling water spray heat exchange, air cooling radiation heat exchange, etc. The three heat transfer modes of conduction, convection and radiation in heat transfer all exist.

[0052] Crystallizer heat transfer:

[0053] For heat transfer in the crystallizer, the second type of boundary conditions are generally used. The instantaneous heat flux density along the casting direction is obtained by heat balance calculation, and the distribution is parabolic with time t. To obtain the instantaneous heat flux density q, the average heat flux density must first be calculated based on the flow rate of the crystallizer cooling water and the inlet and outlet water temperature difference.

[0054]

[0055] Where L is the distance from the meniscus, L m is the effective length of the crystallizer, v is the pulling speed, C w is the specific heat of cooling water, m is the cooling water flow rate, ΔT is the inlet and outlet water temperature difference, S ceff is the effective cooling area of ​​the crystallizer wall.

[0056] Heat transfer in the secondary cooling zone: Heat transfer in the secondary cooling zone takes the distribution of the comprehensive heat transfer coefficient as the boundary condition.

[0057] Calculation of thermophysical parameters of steel grades:

[0058] (1) Density

[0059] During the solidification process from liquid to solid, and when the solid phase transition occurs, the temperature drop and phase change cause the density of the internal structure to change, resulting in a change in volume. Therefore, the density of the billet is related to the steel type, temperature and internal phase structure. The following formula is usually used for calculation:

[0060] ρ L =7200

[0061] ρ SL =ρ L ·(1-f S )+ρ S ·f S

[0062] ρ S =7600

[0063] Where ρ is density, L represents liquid phase, S represents solid phase, and SL represents two-phase region; f s Solid phase ratio

[0064] (2) Thermal conductivity

[0065] The thermal conductivity of steel is related to temperature. In this model, the thermal conductivity k(T) of the solid phase of the ingot is expressed as follows:

[0066] k(T)=18.4+9.6×10 -3 ·TW / m·℃

[0067] It is worth noting that the flow of liquid steel during the casting process (such as forced convection during the casting process, natural convection caused by temperature difference or concentration difference, etc.) will have an important impact on heat transfer. This model is based on the heat transfer control equation and numerically simplifies the effects of physical phenomena such as flow and segregation on heat transfer. Therefore, the equivalent thermal conductivity is often used for the liquid phase, and its value is magnified m times that of the static molten steel thermal conductivity, that is,

[0068] k eff =m·k(T)

[0069] In this paper, m=5 is set.

[0070] For the solid-liquid two-phase region, dendrites weaken the convection movement of molten steel, so the equivalent thermal conductivity of the two-phase region should be between the solid phase and the liquid phase, using the following relationship:

[0071] k eff = k(T)·[1+(m-1)(1-f S )2 ]

[0072] (3) Specific heat and latent heat of solidification

[0073] The difficulty of heat transfer solidification calculation lies in the latent heat of solidification and the moving interface. This nonlinearity has a great influence on the calculation accuracy and convergence. By defining the equivalent specific heat C in the energy equation eff Let's consider the release of latent heat of solidification.

[0074] Specific heat of solid phase of ingot C s , Liquid phase specific heat C L And the equivalent specific heat C in the two-phase region eff Determine according to the following formula:

[0075] C S =550+9.52×10 -2 ·TJ / kg·℃

[0076] C L =842J / kg·℃

[0077]

[0078] The alloy solidification latent heat value is calculated using the internationally widely used thermodynamic software Thermo-Calc.

[0079] S3 uses the original process as the initial condition and obtains the adjustment parameter combination of each secondary cooling zone that meets the technical requirements through iterative calculation.

[0080] The technical requirements include technical indicators and parameter optimization indicators, and the priority of the technical indicators is higher than that of the parameter optimization indicators;

[0081] The technical indicators include: the difference between the maximum and minimum values ​​of the liquid core length at different positions in the width direction is less than the first preset value, and the temperature at the corner of the straightening zone does not fall into the third brittle zone. It should be pointed out that the first preset value is determined based on subsequent process requirements such as light pressing. It can be understood that the first preset value is the maximum value allowed to meet the condition that no segregation occurs in subsequent processing. The third brittle zone, that is, the third brittle temperature range, is approximately between 750-900°C. This brittle behavior is mainly related to the microstructure and composition of the material. The first preset value in the embodiment of the present invention is 20mm.

[0082] The parameter optimization indexes include: the optimal working parameter range of the nozzles in each secondary cooling zone, the allowable working parameter range of the nozzles in each secondary cooling zone, the priority of joint control of multiple secondary cooling zones is higher than the independent control of a single secondary cooling zone, and the lowest temperature of the corner of the straightening zone is at least 20°C higher than the highest temperature of the third brittle zone. It should be pointed out that the optimal working parameter range of each secondary cooling zone is the data obtained through experimental measurement to ensure the life of the nozzle and the optimal atomization effect; the allowable working parameter range of the nozzles in each secondary cooling zone is the data obtained when the nozzle can still operate even if the life of the atomizing nozzle is reduced or the atomization effect is weakened; the priority of joint control of multiple secondary cooling zones is higher than the independent control of a single secondary cooling zone to ensure that the control intensity of a certain secondary cooling zone is too high during the actual implementation process, affecting the atomization effect or life of the nozzle, and multiple secondary cooling zones are jointly controlled to prevent failures in the cooling process of a single secondary cooling zone, resulting in excessive impact on the performance of the slab and major problems in product quality.

[0083] The adjustment parameter combinations of each secondary cooling zone that meet the technical requirements obtained through iterative calculation include:

[0084] When the difference between the maximum and minimum values ​​of the liquid core length is greater than the first preset value and less than the second preset value, negative feedback adjustment is performed based on the difference between the lowest temperature entering the corner of the straightening zone and the upper limit value of the third brittle zone. The preliminary adjustment is completed when the lowest temperature at the corner of the straightening zone is greater than the upper limit value of the third brittle zone. After the preliminary adjustment, the cooling intensity in the width direction of the slab is adjusted. When the difference between the maximum and minimum values ​​of the liquid core length is greater than the second preset value, feedback adjustment is performed on the cooling intensity in the width direction based on the difference between the maximum and minimum values ​​of the liquid core length. When the difference between the maximum and minimum values ​​of the liquid core length is less than the second preset value, negative feedback adjustment is performed based on the difference between the lowest temperature entering the corner of the straightening zone and the upper limit value of the third brittle zone. The preliminary adjustment is completed when the lowest temperature at the corner of the straightening zone is greater than the upper limit value of the third brittle zone. After the preliminary adjustment, the cooling intensity in the width direction of the slab is adjusted. The second preset value is about 2-3 times the first preset value. The above method is designed in consideration of the characteristics of the liquid core length and the third brittle zone. For multi-parameter calculation, if a large number of calculations are performed to select a suitable combination of adjustment parameters, high computing power and computing time are required, which is difficult to meet engineering applications. Based on the above problem, the present invention proposes the above algorithm. When the difference between the maximum and minimum values ​​of the liquid core length is greater than the first preset value and less than the second preset value, the temperature of the straightening zone is adjusted first, and then the difference between the maximum and minimum values ​​of the liquid core length is adjusted. After the adjustment, the temperature of the straightening zone is not in the third brittle zone. On the other hand, when the difference between the maximum and minimum values ​​of the liquid core length is greater than the second preset value, the difference between the two is first controlled to be less than the second preset value, and then the method when the difference between the maximum and minimum values ​​of the liquid core length is greater than the first preset value and less than the second preset value is used for calculation. The calculation time can be greatly reduced.

[0085] Based on the adjustment parameter combination, a secondary screening is performed to obtain the optimal parameter combination. The screening priorities are as follows from high to low:

[0086] The lowest temperature at the corner of the straightening zone is at least 20°C higher than the highest temperature of the third brittle zone;

[0087] Optimal operating parameter range of nozzles in each secondary cooling zone;

[0088] The joint control of multiple secondary cooling zones has a higher priority than the independent control of a single secondary cooling zone;

[0089] The allowable operating parameter range of the nozzles in each secondary cooling zone.

[0090] If the adjustment parameter combination is a non-empty set, the optimal parameter combination with a lower priority is selected for implementation;

[0091] If the adjustment parameter combination is an empty set, the allowable operating parameter range of the nozzle of one or more secondary cooling zones is adjusted from the arc section located upstream of the straightening zone and toward the second secondary cooling zone in the upstream direction, and the adjustment range is 10% larger than the allowable operating parameter range of the nozzle. The above scheme ensures that the optimal parameter combination is screened out to avoid too many parameters, and also provides a solution to the range where the nozzle is not suitable, thereby improving the applicability of the scheme.

[0092] The present invention also provides a computer-readable storage medium, which stores one or more programs. The one or more programs can be executed by one or more processors to implement the above-mentioned method for reducing W-type solidification segregation of slabs.

[0093] The present invention uses a Danieli slab caster to verify the model, with a metallurgical length of 43.5m and a typical cross-sectional size of 1800×230mm 2 The crystallizer adopts a chamfered crystallizer with a length of 900mm, a liquid level of 100mm, and a chamfer size of 55mm / 30°. The secondary cooling section of the continuous casting machine is divided into 24 zones, of which zones 1 to 2 are the wide and narrow sides of the full roller, the cooling method is pure water cooling, and zones 3 to 24 are mist cooling. Tables 1 and 2 are the cooling parameters of the crystallizer and the secondary cooling zone, respectively.

[0094] Table 1 Crystallizer cooling parameters

[0095]

[0096] Table 2 Cooling parameters of the second cooling zone (1.3m / min)

[0097]

[0098] In order to verify the accuracy of the heat transfer solidification model, the pulling speed was measured with a calibrated Sciample CIT-G infrared temperature gun at a speed of 1.3 m / min. -1 The surface temperature of the wide surface and corner of the ingot at 16.2m, 18.3m, and 24.6m from the meniscus of the crystallizer. The comparison between the model calculation results and the measured values ​​is as follows Figure 1 The error between the predicted value and the measured value is within 3.2%, which shows that the established heat transfer solidification model has good accuracy and is suitable for subsequent analysis.

[0099] Example 1

[0100] A method for controlling local strong cooling in the secondary cooling zone of a peritectic steel slab at the end of W-shaped solidification is used for a straight arc slab continuous casting machine. The produced steel grade S590 is a typical peritectic steel with a carbon content of 0.11wt%, a casting speed of 1.2m / min, a superheat of 25°C, a cross-section of 1800mm×230mm, and a specific water volume of 0.52L / kg.

[0101] The straight arc continuous casting machine has 24 secondary cooling zones for secondary cooling. Each secondary cooling zone has an independently controlled nozzle circuit, with a total of three nozzle layouts. The cold performance test was conducted on the nozzles of each secondary cooling zone with different layouts, and the distribution of water volume in the width direction was recorded. Figure 2 This is a typical water distribution in the width direction of cooling zones 13-16.

[0102] A two-dimensional heat transfer solidification simulation model of the slab is established by computer, and the model is corrected by the surface temperature of the slab. The water distribution information of each secondary cooling zone is loaded into the model, and the end of the uneven solidification under the initial secondary cooling is calculated to be located at 1 / 8 to 1 / 4 of the width of the slab cross section, such as Figure 3 .

[0103] The cooling zone 13-16 is located before the slab straightening section. The liquid core length at different positions in the width direction of the cooling zone 13-16 is used as an input parameter, and the expected value is the liquid core length at the center of the width. According to the deviation between the input parameter and the expected value, the PID controller automatically iteratively adjusts the relative proportion of the water volume in the width direction of some fan-shaped sections of the second cooling zone. At the same time, the boundary conditions of the area are corrected and loaded into the model for calculation. The iterative solution is used to make the input parameters approach the expected value and meet the requirement that the corner temperature of the straightening zone does not fall into the third brittle zone. The final optimized water volume distribution is as follows: Figure 4 According to the above adjusted water volume distribution, the corresponding nozzle model or arrangement is selected, and the final product center segregation rating is C0.5. Figure 5 The prepared slab has no corner cracks and segregation.

[0104] Example 2

[0105] A method for controlling local strong cooling of the secondary cooling zone at the end of W-shaped solidification of a peritectic steel slab is used in a straight arc slab continuous casting machine. The produced steel grade P355 is peritectic steel with a carbon content of 0.15wt%, a casting speed of 1.3m / min, a superheat of 29°C, a cross-section of 1250mm×220mm, and a specific water volume of 0.72L / kg.

[0106] The secondary cooling of the straight arc continuous casting machine is equipped with 24 secondary cooling zones. Each secondary cooling zone has an independently controlled nozzle circuit, with a total of three nozzle arrangements. The cold performance test is carried out on the nozzles with different arrangements in each secondary cooling zone, and the distribution of water in the width direction is recorded.

[0107] A two-dimensional heat transfer solidification simulation model of the slab was established by computer and corrected by the surface temperature of the ingot. The water distribution information of each secondary cooling zone was loaded into the model, and the end of the uneven solidification under the initial secondary cooling was calculated to be located at 1 / 8 to 1 / 4 of the width of the slab cross section.

[0108] Cooling zones 9-12 are located before the slab straightening section. The liquid core lengths at different positions in the width direction of cooling zones 13-16 are used as input parameters, and the expected value is the liquid core length at the center of the width. According to the deviation between the input parameters and the expected values, the PID controller automatically and iteratively adjusts the relative proportion of water in the width direction of some fan-shaped sections of the second cooling zone. At the same time, the boundary conditions of the area are corrected and loaded into the model for calculation. The iterative solution is performed to make the input parameters approach the expected values ​​and to ensure that the corner temperature of the straightening zone does not fall into the third brittle zone. The corresponding nozzle model or layout is selected based on the above-mentioned adjusted water distribution. The final product center segregation rating is C0.5. Figure 6 , achieving control of the uneven solidification end without generating corner cracks.

[0109] Comparative Example 1

[0110] The continuous casting process was operated in the same manner as in Example 1, except that the local strong cooling method in the secondary cooling zone was not used to improve the nozzle model and arrangement. The center segregation rating of the final product was C1.5. Figure 7 .

[0111] It can be seen from the above embodiments and comparative examples that the present invention can effectively control the uneven solidification end of the slab and inhibit the center segregation of the slab through the local strong cooling method in the secondary cooling zone, while achieving weak cooling of the corners of the ingot. In addition, the simulation greatly reduces the experimental cost and labor cost, and can quickly and accurately optimize the type and layout of the nozzles in the secondary cooling zone, which is of great significance to the improvement of slab quality.

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for reducing W-type solidification segregation of slabs, suitable for engineering applications, characterized in that: include: Conduct a water volume distribution test on the nozzles of each secondary cooling zone, calculate the relative proportion of water volume at different positions in the width direction relative to the center position under different control parameters, calculate the distribution of the surface cooling water heat transfer coefficient of each secondary cooling zone, and calculate the distribution of the comprehensive heat transfer coefficient of each secondary cooling zone based on the distribution of the cooling water heat transfer coefficient; Constructing a two-dimensional heat transfer model, and loading the distribution of the comprehensive heat transfer coefficient into the two-dimensional heat transfer model as a boundary condition; Taking the original process as the initial condition, the adjustment parameter combination of each secondary cooling zone that meets the technical requirements is obtained through iterative calculation; The comprehensive heat transfer coefficient h is calculated as follows: Where: h s is the cooling water heat transfer coefficient, h r is the radiation heat transfer coefficient, W is the water flow density, T W is the cooling water temperature, α is the correction coefficient, T s is the surface temperature of the ingot, T0 is the ambient temperature, ε is the blackness of the ingot surface, and σ is the Boltzmann constant.

2. The method for reducing W-type solidification segregation of slab according to claim 1, characterized in that: The control parameters include water pressure and air pressure.

3. The method for reducing W-type solidification segregation of slab according to claim 2, characterized in that: The technical requirements include technical indicators and parameter optimization indicators, and the priority of the technical indicators is higher than that of the parameter optimization indicators; The technical indicators include: the difference between the maximum and minimum values ​​of the liquid core length at different positions in the width direction is less than a first preset value and the temperature of the corner of the straightening zone does not fall into the third brittle zone; The parameter optimization indicators include: the optimal working parameter range of the nozzles in each secondary cooling zone, the allowable working parameter range of the nozzles in each secondary cooling zone, the priority of joint control of multiple secondary cooling zones is higher than the independent control of a single secondary cooling zone, and the lowest temperature of the corner of the straightening zone is at least 20°C higher than the highest temperature of the third brittle zone.

4. The method for reducing W-type solidification segregation of slab according to any one of claims 1 to 3, characterized in that: The simplification of the two-dimensional heat transfer model includes: the physical properties of the ingot are isotropic, one quarter of the cross section of the slab is selected for modeling, heat transfer in the billet drawing direction is not considered, a two-dimensional slicing method under a moving coordinate system is used, the thermal physical properties of steel in the liquid phase, liquid-solid two-phase region and solid phase region are functions of temperature and are independent of spatial position, and the influence of crystallizer vibration on heat transfer during solidification is ignored.

5. The method for reducing W-type solidification segregation of slab according to claim 4, characterized in that: The ratio of length to width of the slab cross section of the model is 5-10.

6. The method for reducing W-type solidification segregation of slab according to claim 3, characterized in that: The adjustment parameter combinations of each secondary cooling zone that meet the technical requirements obtained through iterative calculation include: When the difference between the maximum and minimum values ​​of the liquid core length is greater than the first preset value and less than the second preset value, negative feedback adjustment is performed based on the difference between the lowest temperature at the corner of the straightening zone and the upper limit of the third brittle zone. When the lowest temperature at the corner of the straightening zone is greater than the upper limit of the third brittle zone, the preliminary adjustment is completed. After the preliminary adjustment is completed, the cooling intensity in the width direction of the slab is adjusted. When the difference between the maximum and minimum values ​​of the liquid core length is greater than the second preset value, the cooling intensity in the width direction is feedback-adjusted based on the difference between the maximum and minimum values ​​of the liquid core length. When the difference between the maximum and minimum values ​​of the liquid core length is less than the second preset value, negative feedback adjustment is performed based on the difference between the lowest temperature entering the corner of the straightening zone and the upper limit value of the third brittle zone. The preliminary adjustment is completed when the lowest temperature at the corner of the straightening zone is greater than the upper limit value of the third brittle zone. After the preliminary adjustment is completed, the cooling intensity in the width direction of the slab is adjusted.

7. The method for reducing W-type solidification segregation of slab according to claim 6, characterized in that: Based on the adjustment parameter combination, a secondary screening is performed to obtain the optimal parameter combination. The screening priorities are as follows from high to low: The lowest temperature at the corner of the straightening zone is at least 20°C higher than the highest temperature of the third brittle zone; Optimal operating parameter range of nozzles in each secondary cooling zone; The joint control of multiple secondary cooling zones has a higher priority than the independent control of a single secondary cooling zone; The allowable operating parameter range of the nozzles in each secondary cooling zone.

8. The method for reducing W-type solidification segregation of slab according to claim 7, characterized in that: If the adjustment parameter combination is a non-empty set, the optimal parameter combination with a lower priority is selected for implementation; If the adjustment parameter combination is an empty set, the allowable operating parameter range of the nozzles in one or more secondary cooling zones in the arc section located upstream of the straightening zone and starting from the second secondary cooling zone in the upstream direction is adjusted, and the adjustment range is expanded by 10% within the allowable operating parameter range of the nozzles.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores one or more programs, and the one or more programs can be executed by one or more processors to implement the method for reducing W-type solidification segregation of slabs as described in any one of claims 1-8.

Images