CN113695539B - Method for determining cooling liquid flux of crystallizer for high titanium steel - Google Patents
Method for determining cooling liquid flux of crystallizer for high titanium steel Download PDFInfo
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- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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Abstract
The invention discloses a method for determining the flux of cooling liquid of a crystallizer for high titanium steel, which comprises the following steps: s10: measuring the casting temperature range of the high titanium steel and the surface cooling rate of the high titanium steel in the crystallizer; s20: substituting the minimum value in the high titanium steel casting temperature range, the throwing speed and the heat flux density into a preset casting blank model to obtain the blank shell thickness and the surface average cooling rate of the high titanium steel in the crystallizer; s30: comparing the surface cooling rate obtained in step S10 with the surface average cooling rate obtained in step S20; s40: if the surface cooling rate obtained in the step S10 is smaller than the surface average cooling rate obtained in the step S20, comparing the blank shell thickness obtained in the step S20 with a preset blank shell thickness; s50: if the thickness of the blank shell obtained in the step S20 is larger than the preset thickness of the blank shell, extracting the heat flux density corresponding to the thickness of the blank shell obtained in the step S20; the crystallizer coolant flux is calculated from the heat flux density determined in step S50. The method of the invention optimizes the design of the cooling system of the crystallizer for the high titanium steel.
Description
Technical Field
The invention belongs to the technical field of high titanium steel continuous casting, and particularly relates to a method for determining the cooling liquid flux of a crystallizer of high titanium steel.
Background
Ferrous materials are one of the most commonly used materials at present and play an irreplaceable role in the manufacture of important equipment. The abrasion of the steel material has a great influence on life and production. Particularly in the mining industry, because the working environment of the mining industry is severe, the mining machinery is often greatly abraded in the working process, the service life of mechanical equipment is greatly shortened, the industrial production cost is increased, unnecessary production loss is caused, meanwhile, the equipment maintenance time is increased, and the production efficiency is reduced.
The high titanium steel is an important raw material for manufacturing wear-resistant equipment, and the Ti element is added into the steel to effectively refine grains and play a role in precipitation strengthening. When the Ti content is more than or equal to 0.2 percent, a large amount of micron-level and nano-level titanides are separated out from the matrix, so that the wear resistance of the steel can be obviously improved, the wear loss in the matrix is reduced, and the strength and the service performance of the steel are greatly improved.
Compared with the traditional die casting, the continuous casting process has great advantages, and has been widely accepted in the metallurgical industry by virtue of the characteristics of simple flow, high production efficiency, high metal yield, environmental friendliness and the like. However, in the continuous casting of high titanium steel, the cooling system of the crystallizer is difficult to make as the titanium content in the steel grade increases. If the casting temperature is not proper, the large-size liquated TiN is easily precipitated by enrichment in the liquid phase, and the size of the liquated TiN can even reach tens of microns. The large-size liquated TiN is easy to gather at a water gap to further cause the water gap to be blocked, so that the smooth running of the casting process is threatened, the improvement of the performance of steel products is seriously limited, alloy elements are wasted, and the alloying effect of the alloy elements is influenced. In addition, large-size TiC (the major axis is larger than 15 microns) is easy to precipitate in the cooling and solidifying process of the high-titanium steel, the large-size TiC precipitates are easy to aggregate at the position of a grain boundary, the performance of the high-titanium steel is greatly damaged, and the crack risk in the continuous casting process is increased.
With the increasing attention paid to high titanium steel, research on the precipitation of titanium compounds of the high titanium steel is continuously progressing. The strain induced precipitation process analysis of the titanium compound of the high titanium steel indicates that Ti has an obvious strain induced precipitation process within the temperature range of 600-1000 ℃, and the precipitated phase size is smaller as the temperature is lower. At high cooling rates, the size of the TiN inclusions precipitated in the edge region was significantly smaller than the inclusion size in the center region. However, the prior art does not relate to the relationship between the size and the quantity of liquated titanides and the superheat degree and the cooling speed of the high-titanium steel in the solidification process, and does not relate to the precipitation rule of the Ti compounds of the high-titanium steel in the continuous casting crystallizer.
The prior art provides a casting method for effectively improving the blockage of a high titanium steel casting nozzle. In the method, the continuous casting of the high titanium steel is realized by strengthening the protection mechanism of the tundish, adopting a low drawing speed, high superheat casting, a secondary cooling zone forced cooling system and applying a method of dynamic soft pressing of a solidification tail end, and the problem of water gap blockage is effectively avoided. However, the method does not specifically consider the relationship between the precipitation of the titanium compound and the casting temperature and the cooling speed, only points out that the risk of steel leakage is reduced by improving the superheat degree and enhancing the heat flux density, does not have the mechanism of making, checking and optimizing a cooling system, neglects the calculation of the cooling system of the crystallizer, and cannot make an accurate cooling system of the crystallizer.
The field practical experience shows that the problems of large-size liquated TiN water plugging and large-size TiC educt damaging the performance of the high titanium steel often occur in the continuous casting process of the high titanium steel. Researches show that proper high-superheat-degree and high-cooling-rate casting is required to be selected in the continuous casting process of high-titanium steel so as to improve the solid solubility of titanium element and reduce the precipitation of high-temperature titanides. However, the casting superheat degree of the high titanium steel is improved, and simultaneously, the risk of steel leakage is greatly increased, and the design of the cooling system of the crystallizer of the high titanium steel becomes a difficult problem.
The crystallizer cooling system of the high titanium steel is more and needs crystallizer cooling liquid flux as a measurement standard.
Therefore, in view of the above-mentioned drawbacks of the prior art, there is still a need for a method for designing a cooling system of a high titanium steel continuous casting mold and a method for determining a flux of a high titanium steel mold coolant.
Disclosure of Invention
In order to solve the technical problem, the embodiment of the invention provides a method for determining the cooling liquid flux of a crystallizer of high titanium steel.
The embodiment of the invention discloses a method for determining the flux of a cooling liquid of a crystallizer of high titanium steel, which comprises the following steps:
step S10: measuring the casting temperature range of the high titanium steel and the surface cooling rate of the high titanium steel in the crystallizer;
step S20: substituting the minimum value in the high titanium steel casting temperature range, the throwing speed and the heat flux density into a preset casting blank model to obtain the blank shell thickness and the surface average cooling rate of the high titanium steel in the crystallizer;
step S30: comparing the surface cooling rate obtained in step S10 with the surface average cooling rate obtained in step S20;
step S40: if the surface cooling rate obtained in the step S10 is smaller than the surface average cooling rate obtained in the step S20, comparing the blank shell thickness obtained in the step S20 with a preset blank shell thickness;
step S50: if the thickness of the blank shell obtained in the step S20 is larger than the preset thickness of the blank shell, extracting the heat flux density corresponding to the thickness of the blank shell obtained in the step S20;
step S60: the crystallizer coolant flux is calculated from the heat flux density determined in step S50.
Further, the step S10 includes:
step S11: heating the high titanium steel sample to be fully melted, then preserving heat, and cooling and quenching the high titanium steel sample; analyzing the quenched high titanium steel sample, and finding out that the quenching temperature range corresponding to the high titanium steel sample without TiN precipitates with micron-sized grain sizes is the casting temperature range of the high titanium steel;
step S12: heating the high titanium steel sample to be completely melted, respectively selecting different cooling rates within the interval of 0.4-7.5 ℃/s to cool the high titanium steel sample to be below 1200 ℃, finding out the cooling rate corresponding to the sample with the average length of the major axis of TiC being less than 10 micrometers, and selecting the cooling rate as the surface cooling rate of the high titanium steel in the crystallizer.
Further, the step of establishing a preset casting blank model comprises the following steps:
determining a geometric model of the casting blank according to the size of a two-dimensional slice of the casting blank produced by the high-titanium steel continuous casting machine, and meshing the geometric model; the cutting mode of the two-dimensional slice of the casting blank is cutting in a direction vertical to the drawing direction;
and establishing the casting blank model according to the liquidus, solidus, density, heat conductivity coefficient and specific heat of the continuously cast high-titanium steel as material parameters.
Further, in the step S20, the range of the selected value of the blank drawing speed is 0.5 to 1.2m/min; the selected value range of the heat flow density is 100～1000kJ/(m 2 /s)。
Further, in the comparison step of step S30: if the surface cooling rate obtained in step S10 is greater than the average surface cooling rate obtained in step S20, the process returns to step S20, and after the casting speed and/or the heat flux density substituted into the preset casting blank model is increased, the process continues from step S20 to step S30.
Further, in the comparing step of step S40: and if the thickness of the shell obtained in the step S20 is smaller than the preset shell thickness, returning to the step S20, reducing the blank drawing speed and/or the heat flux density substituted into the preset casting blank model, and continuing to perform the steps S20 to S30.
Further, the thickness of the shell is preset to be 13mm.
Further, the step S60 includes:
the calculation of the crystallizer cooling liquid flux is carried out by the following formula:
in the above formula, m represents the mass of the cooling liquid flowing through the crystallizer in unit time, kg/s;
C w Represents the specific heat of the coolant;
T 1 denotes the initial temperature of the coolant, DEG C;
T 2 denotes the coolant end temperature, ° c;
Further, in step S11: dividing high titanium steel samples to be produced into a plurality of groups, heating to more than 1640 ℃, preserving heat for 10-30 min after the high titanium steel samples are fully melted, cooling the high titanium steel samples to 1550-1640 ℃ at a cooling speed of 5-20 ℃/min respectively, and then quenching.
Further, in step S12: dividing a high titanium steel sample into a plurality of parts, and grinding and polishing the parts; heating the high titanium steel sample to 1550 ℃, and preserving the heat for 3-10 min to completely melt the high titanium steel sample.
The invention has the following beneficial technical effects:
the method for determining the flux of the cooling liquid of the high-titanium steel crystallizer determines the selection range of the casting parameters of the high-titanium steel through a pre-experiment, considers the factors such as temperature, cooling rate, throwing speed, heat flux density and the like in the continuous casting process through a preset casting blank model, judges and selects proper heat flux density through the thickness of a blank shell and the cooling rate, further calculates the flux of the cooling liquid of the crystallizer, and provides a vital parameter for the design of a cooling system of the high-titanium steel crystallizer, namely the flux of the cooling liquid of the crystallizer.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other embodiments can be obtained according to the drawings without creative efforts;
FIG. 1 is the observed morphology of TiN inclusions;
FIG. 2 is a flow chart of a method for determining the cooling liquid flux of the crystallizer for high titanium steel according to an embodiment of the invention;
FIG. 3 is a schematic view of the cooling rate extraction position and the shell thickness of an embodiment of the present invention;
FIG. 4 is a view showing the observation results of TiN precipitates at different temperatures measured by a quenching experiment in example 1 of the present invention;
FIG. 5 is an image of the TiC precipitate size and shape observed in the high temperature confocal experiment in example 1 of the present invention, which is observed at a cooling rate of 0.4 ℃/s.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following embodiments of the present invention are described in further detail with reference to the accompanying drawings.
The method for determining the crystallizer cooling liquid flux of the high titanium steel as shown in figure 2 comprises the following steps:
1) Step S10: and measuring the casting temperature range of the high titanium steel and the surface cooling rate of the high titanium steel in the crystallizer.
The step S10 includes:
step S11: heating the high titanium steel sample to be fully melted, then preserving heat, and cooling and quenching the high titanium steel sample; and analyzing the quenched high titanium steel sample, and finding out that the temperature interval after cooling corresponding to the high titanium steel sample without TiN precipitates with micron-sized grain sizes is within the high titanium steel casting temperature range.
In order to avoid the problem of nozzle nodulation caused by large-size TiN precipitates, the sizes of the TiN precipitates at different casting temperatures are observed through experiments, and a proper high titanium steel casting temperature selection range is determined.
Specifically, high titanium steel samples to be produced are divided into a plurality of groups, the groups are placed into a magnesia crucible, the temperature is increased to more than 1640 ℃, and after the steel samples are fully melted, the temperature is kept for 10-30 min. The sample is cooled to 1550-1640 ℃ at a cooling rate of 5-20 ℃/min.
Taking a quartz tube and an aurilave, plugging one side of the quartz tube by using an air blowing port of the aurilave, inserting the other side of the quartz tube into the molten steel, sucking a small amount of the molten steel, quickly putting the molten steel into cold water for quenching, and taking the quartz tube out after the quenching is finished.
And (3) grinding and polishing the quenched sample, monitoring and analyzing the sample by using an SEM (Scanning Electron Microscope) and an EDS (Energy Dispersive Spectrometer), and observing whether the sample is pure in large-size liquated TiN (the large-size liquated TiN is defined as micron-size liquated TiN). Wherein, the quenching temperature interval consisting of the quenching temperatures corresponding to the plurality of samples without large-size TiN precipitates is an available continuous casting temperature interval, and the high titanium steel casting temperature range is designed according to the quenching temperature interval. The morphology of large size liquated TiN is shown in fig. 1.
Step S12: heating the high titanium steel sample to be completely melted, respectively selecting different cooling rates within the interval of 0.4-7.5 ℃/s to cool the high titanium steel sample to be below 1200 ℃, finding out the cooling rate corresponding to the sample with the average length of the major axis of TiC being less than 10 micrometers, and selecting the minimum value of the cooling rates as the surface cooling rate of the high titanium steel in the crystallizer.
In order to avoid that a large amount of large-size TiC is precipitated on the surface of a casting blank when the high-titanium steel is cooled in the crystallizer so as to greatly increase the risk of surface cracks, the proper surface cooling rate of the high-titanium steel in the crystallizer is determined through experiments.
Dividing a high titanium steel sample to be continuously cast into a plurality of parts, grinding and polishing the sample, and keeping the measured surface of the sample smooth. Putting the sample into an alumina crucible, heating the sample to 1550 ℃, and preserving the temperature for 3-10 min to completely melt the sample. Selecting different cooling speeds within the interval of 0.4-7.5 ℃/s respectively to cool the sample to below 1200 ℃. The coagulation of the samples was observed in situ using a high temperature confocal apparatus, for example model VL2000DX-SVF17 SP. If the average length of the long axis of the observed TiC is less than 10 microns, the minimum value of the corresponding cooling rates of the samples can be selected in the crystallizer for cooling so as to effectively control the precipitation size of the TiC.
2) Step S20: and substituting the minimum value in the high titanium steel casting temperature range, the throwing speed and the heat flux density into a preset casting blank model to obtain the blank shell thickness and the surface average cooling rate of the high titanium steel in the crystallizer.
Establishing a preset casting blank model to calculate the thickness of a blank shell:
determining a geometric model of the casting blank according to the size of a two-dimensional slice of the casting blank produced by the high-titanium steel continuous casting machine, and meshing the geometric model; the cutting mode of the two-dimensional slice of the casting blank is cutting in a direction perpendicular to the drawing direction. The liquidus, solidus, density, thermal conductivity and specific heat of the continuously cast high titanium steel are applied as material parameters to the established casting blank model. Selecting the minimum value within the casting temperature range of the high titanium steel obtained in the step S10 as the initial casting temperature condition of the model;
0.5-1.2 m/min is selected as the blank drawing speed, and 100-1000 kJ/(m) is selected 2 And/s) as heat flux density, and operating the model to ensure that the temperature of the center of the wide surface is about 1050 ℃ when the casting blank is discharged from the crystallizer. The position of the center of the broad surface of the cast slab when exiting the mold is shown in fig. 3.
And extracting the temperature distribution of the model after the model is taken out of the crystallizer from the model operation result, and taking the shortest length of the solidus temperature from the surface of the wide surface as the thickness of the blank shell. And extracting the temperature average cooling speed at a position 3mm away from the surface of the wide surface as the surface average cooling speed of the high titanium steel in the crystallizer.
3) Step S30: comparing the surface cooling rate obtained in step S10 with the surface average cooling rate obtained in step S20;
step S40: if the surface cooling rate obtained in the step S10 is smaller than the surface average cooling rate obtained in the step S20, comparing the blank shell thickness obtained in the step S20 with a preset blank shell thickness;
step S50: if the thickness of the blank shell obtained in the step S20 is larger than the preset thickness of the blank shell, extracting the heat flux density corresponding to the thickness of the blank shell obtained in the step S20;
further, the surface cooling rate obtained in step S10 and the surface average cooling rate obtained in step S20 are compared in step S30. In another case (step S70), if the surface cooling rate obtained in step S10 is greater than the average surface cooling rate obtained in step S20, returning to step S20, increasing the casting speed and the heat flux density substituted into the predetermined casting blank model, and continuing from step S20 to step S30;
in addition, in step S40, if the surface cooling rate obtained in step S10 is smaller than the surface average cooling rate obtained in step S20, the shell thickness obtained in step S20 is compared with a preset shell thickness. In another case (step S80), if the shell thickness obtained in step S20 is smaller than the preset shell thickness, the process returns to step S20, and after the blank drawing speed and the heat flux density substituted into the preset casting blank model are reduced, the process continues from step S20 to step S30.
The above process is to evaluate and correct the scheme according to the model extraction result.
Comparing the surface average cooling rate extracted from the model result with the surface cooling rate obtained in the step S10, and evaluating the shell thickness extracted from the model result, wherein the three conditions can be divided into:
(1) This is possible if the extracted surface average cooling rate is greater than the surface cooling rate obtained in step S10 and the extracted shell thickness is greater than 13 mm;
(2) If the extracted surface average cooling rate is less than the surface cooling rate obtained in the step S10, increasing the blank drawing speed, increasing the heat flow density, re-operating the model, extracting the result, and re-performing the comparison in the step S30;
(3) If the extracted surface average cooling rate is greater than the surface cooling rate obtained in step S10 but the extracted shell thickness is less than 13mm, the pulling rate is reduced, the model is re-run, the extraction results are extracted, and the comparison in step S30 is re-performed.
4) Step S60: the crystallizer cooling fluid flux is calculated from the heat flux density determined in step S50.
The heat flux density in the feasible scheme obtained in step S50 is inversely extrapolated to the crystallizer water flux.
And extracting the heat flux density of the crystallizer corresponding to the two-dimensional slice model at each moment according to the obtained feasible model heat flux density, and integrating the effective area of the crystallizer by using the heat flux density at each moment to obtain the heat flux of the crystallizer at each moment. The calculation of the heat flux density crystallizer water flux is further performed by the following formula:
in the above formula, m represents the mass of the cooling liquid flowing through the crystallizer in unit time, kg/s;
C w Represents the specific heat of the coolant;
T 1 denotes the initial temperature of the coolant, DEG C;
T 2 denotes the coolant end temperature, ° c;
Preferably, the cooling liquid is water, C w The specific heat of water is 4.2X 10 3 J/(kg·℃)。
In the above step, the method for adjusting the heat flux density in step S20 is: if the temperature of the center of the wide surface is higher than 1070 ℃ when the wide surface is taken out of the crystallizer, the heat flow density is increased; and if the temperature of the center of the broad surface is less than 1030 ℃ when the broad surface is taken out of the crystallizer, reducing the heat flow density.
In model operation, the selected blank drawing speed and the selected heat flux density are adjusted along with the operation result of the model until the constraint conditions of the cooling speed and the blank shell thickness are met.
In order to ensure that the temperature of the center of the wide surface is about 1050 ℃ when the casting blank in the step S20 is discharged from the crystallizer, the blank drawing speed is increased when the heat flux density is increased in the steps S70 and S80; the heat flux density will be reduced simultaneously as the withdrawal speed is reduced.
The present invention will be described in further detail with reference to specific examples.
Example 1
The cooling system of the continuous casting crystallizer is established by the method by taking the continuous casting process of a certain high titanium steel plate blank with the section of 1200mm multiplied by 200mm in a certain steel mill as an object.
The quenching experiment is carried out on the high-temperature molten high-titanium steel liquid to obtain a proper casting temperature, and the specific experiment steps are as follows:
(1) cutting the high titanium steel into cylindrical rods with the diameter of 3cm and the height of 4cm, putting the cylindrical rods into a magnesium oxide crucible with the diameter of 4cm, heating to 1640 ℃ at 10 ℃/min, preserving the heat for 30min after the steel sample is fully melted, and then cooling to 1590 ℃, 1610 ℃, 1630 ℃ and 1640 ℃ at 8 ℃/min.
(2) And (3) plugging one side of the quartz tube by using an aurilave, inserting the other side of the quartz tube into the molten steel, sucking a small amount of the molten steel, quickly putting the molten steel into ice water for quenching, and taking out the sample after the sample is completely cooled.
(3) And (3) grinding and polishing the quenched sample, and detecting and analyzing by using an SEM (scanning Electron microscope), an EDS (electronic data System) and other instruments to see whether micron-sized liquated TiN exists in the sample.
The results obtained for quenched samples of high titanium steel at different temperatures are shown in fig. 4. Almost no large-size liquid-separated TiN appears in a substrate at 1640 ℃, and individual large-size TiN appears in the substrate at 1630 ℃ along with the reduction of the quenching temperature, so that the small number of large-size TiN proves that the large-size TiN begins to be separated out from the molten steel at 1630 ℃, and the majority of large-size TiN is between 5 and 8 mu m. At the quenching temperature of 1610 ℃, the size of TiN is increased, the size of most TiN is between 5 and 10 mu m, and at the quenching temperature of 1590 ℃, a certain ultra-large size TiN is generated in the matrix, and the size can reach tens of microns, so that the superheat degree is improved to a certain extent, the solubility of titanium and nitrogen elements can be improved, and the precipitation amount of large size TiN is reduced. At 0.37Ti and 50ppmN, the casting temperature is raised at least to more than 1590 ℃.
The test pieces were cooled at different cooling rates, and the size of TiC precipitates was observed at different cooling rates to obtain a suitable cooling rate. The specific experimental steps are as follows:
and carrying out in-situ observation experiments on the high titanium steel at different cooling speeds by adopting high-temperature confocal equipment with the model number of VL2000DX-SVF17 SP. And dividing the high titanium steel sample to be continuously cast into 5 parts, grinding and polishing the high titanium steel sample, and keeping the measured surface smooth. Putting the sample into an alumina crucible, heating the sample to 1550 ℃ at the speed of 5 ℃/s, preserving the heat for 5min, and cooling the sample to 1000 ℃ at the cooling zone speeds of 0.4 ℃/s, 2.5 ℃/s and 5 ℃/s respectively after the sample is completely melted. To avoid oxidation of the sample, the experiment was performed under vacuum. In-situ observation experiments are carried out by a high-temperature confocal device at different cooling speeds, and the observed TiC precipitates are shown in figure 5.
It was observed that as the cooling rate increased, the size of TiC precipitates decreased. When the cooling rate reaches 5 ℃/s, the precipitation amount of TiC is low, and the size can be reduced to below 10 mu m. Therefore, 5 ℃/s can be set as the minimum rate of lowering the surface temperature of the cast slab.
Establishing a high-titanium steel casting blank heat transfer model by using MSC.MARC software, and carrying out grid division. The liquidus, solidus, density, thermal conductivity and specific heat of the continuously cast high titanium steel are applied as material parameters to the established casting blank model.
Assigning the model with 1590 deg.C calculated in the above steps as initial condition, selecting initial pull rate of 1.1m/min, and setting average heat flux density in crystallizer to 971.10 kJ/(m) 2 S) as boundary condition, the model was run, in which case the temperature in the center of the broad face at the time the strand exited the crystallizer was 1038 ℃.
After the model operation is finished, extracting the temperature average cooling rate at the position 3mm away from the surface of the wide surface, and obtaining that the average cooling rate is 7.55 ℃/s and is greater than the minimum cooling rate (5 ℃/s) obtained in the early-stage experiment. And extracting the thickness of the blank shell to obtain the blank shell with the thickness of 11.58mm which is 13mm smaller than the minimum required blank shell thickness, so that the pulling speed is reduced, and the simulation calculation is carried out again.
The pulling speed is reduced to 1.0m/min, and the average heat flux density in the crystallizer is set to be 924.34 kJ/(m) 2 /s) as boundary condition, the model was run, in which case the temperature in the center of the broad face at the time the strand exited the crystallizer was 1043 ℃. After the model operation is finished, extracting the temperature average cooling speed at the position 3mm away from the surface of the wide surface to obtain that the average cooling speed is 6.95 ℃/s and is greater than the minimum cooling speed (5 ℃/s) obtained by the experiment. And extracting the thickness of the blank shell to obtain the blank shell with the thickness of 13.28mm which is 13mm larger than the minimum required blank shell thickness, so the scheme can be used for designing the cooling system of the crystallizer of the steel grade, and the heat flux density 924.34 kJ/(m) set before extraction 2 /s)。
The heat flow density in the above model (924.34 kJ/(m) was used 2 Is calculated per second)) to obtain the water flux of 3697.39L/min in unit time.
Example 2:
this example uses the same steel type as example 1, so the experiments for measuring the minimum casting temperature and the minimum cooling rate, which were 1590 ℃ for the minimum casting temperature and 5 ℃/s for the minimum cooling rate, were not repeated.
Since the structure of the mold and the size of the cast slab are completely the same as those in example 1, the established model and the thermal physical properties are completely the same as those in example 1.
Selecting the initial drawing speed to be 0.7m/min, and setting the average heat flux density in the crystallizer to be 766.64 kJ/(m) 2 /s) as boundary condition, the model was run, in which case the temperature in the center of the broad face at the time the strand exited the crystallizer was 1045 ℃.
After the model operation is finished, extracting the temperature average cooling speed at the position 3mm away from the surface of the wide surface, and obtaining that the average cooling speed is 4.94 ℃/s and is less than the minimum cooling speed (5 ℃/s) obtained by the experiment, so that the heat flow density is increased, and the simulation calculation is carried out again.
Setting the average heat flux density in the crystallizer to be 835.59 kJ/(m) 2 And/s) as boundary conditions, and the drawing speed must be increased to ensure that the central temperature of the wide surface of the casting blank is about 1050 ℃ when the casting blank is discharged from the crystallizer. The drawing speed is adjusted to obtain the drawing speed of 0.8m/min, and the central temperature of the broad face is 1036 ℃ when the broad face is taken out of the crystallizer.
After the model operation is finished, extracting the temperature average cooling speed at the position 3mm away from the surface of the wide surface, and obtaining that the average cooling speed is 5.62 ℃/s and is greater than the minimum cooling speed (5 ℃/s) obtained by the experiment. Then extracting the thickness of the blank shell to obtain the blank shell with the thickness of 14.19mm which is 13mm larger than the minimum required blank shell thickness, so the scheme can be used for carrying out the design of the cooling system of the crystallizer of the steel grade, and the heat flux density 835.59 kJ/(m) arranged before extraction 2 /s)。
The heat flow density in the above model (835.59 kJ/(m) was used 2 /s)) to obtain the water flux of 3342.36L/min in unit time.
Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, of embodiments of the invention is limited to these examples; within the idea of an embodiment of the invention, also technical features in the above embodiment or in different embodiments may be combined and there are many other variations of the different aspects of the embodiments of the invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, substitutions, improvements, and the like that may be made without departing from the spirit and principles of the embodiments of the present invention are intended to be included within the scope of the embodiments of the present invention.
Claims (9)
1. A method for determining the crystallizer coolant flux of high titanium steel, comprising:
step S10: measuring the casting temperature range of the high titanium steel and the surface cooling rate of the high titanium steel in the crystallizer;
step S20: substituting the minimum value in the high titanium steel casting temperature range, the throwing speed and the heat flow density into a preset casting blank model to obtain the blank shell thickness and the surface average cooling rate of the high titanium steel in the crystallizer;
step S30: comparing the surface cooling rate obtained in step S10 with the surface average cooling rate obtained in step S20;
step S40: if the surface cooling rate obtained in the step S10 is smaller than the surface average cooling rate obtained in the step S20, comparing the blank shell thickness obtained in the step S20 with a preset blank shell thickness;
step S50: if the thickness of the blank shell obtained in the step S20 is larger than the preset thickness of the blank shell, extracting the heat flux density corresponding to the thickness of the blank shell obtained in the step S20;
step S60: calculating the flux of the cooling liquid of the crystallizer according to the heat flux density determined in the step S50;
wherein the step S10 includes:
step S11: heating the high titanium steel sample to be fully melted, then preserving heat, and cooling and quenching the high titanium steel sample; analyzing the quenched high titanium steel sample, and finding out that the quenching temperature range corresponding to the high titanium steel sample without TiN precipitates with micron-sized grain sizes is within the high titanium steel casting temperature range;
step S12: heating the high titanium steel sample to be completely melted, respectively selecting different cooling rates within the interval of 0.4-7.5 ℃/s to cool the high titanium steel sample to be below 1200 ℃, finding out the cooling rate corresponding to the sample with the average length of the major axis of TiC being less than 10 micrometers, and selecting the cooling rate as the surface cooling rate of the high titanium steel in the crystallizer.
2. The method for determining the cooling liquid flux of the crystallizer for high titanium steel according to claim 1, wherein the step of establishing the preset casting blank model comprises the following steps:
determining a geometric model of the casting blank according to the size of a two-dimensional slice of the casting blank produced by the high-titanium steel continuous casting machine, and meshing the geometric model; the cutting mode of the two-dimensional slice of the casting blank is cutting in a direction vertical to the drawing direction;
and establishing the casting blank model according to the liquidus, solidus, density, heat conductivity coefficient and specific heat of the continuously cast high-titanium steel as material parameters.
3. The method for determining the flux of the cooling liquid of the crystallizer for high titanium steel according to claim 1, wherein in the step S20, the selected value of the throwing speed is in the range of 0.5-1.2 m/min; the selected value range of the heat flow density is 100-1000 kJ/(m) 2 /s)。
4. Method for determining the crystallizer coolant flux of high titanium steels according to claim 3, characterized in that in the comparison step of step S30: if the surface cooling rate obtained in step S10 is greater than the average surface cooling rate obtained in step S20, the process returns to step S20, and after the casting speed and/or the heat flux density substituted into the preset casting blank model is increased, the process continues from step S20 to step S30.
5. Method for determining the crystallizer coolant flux of high titanium steels according to claim 3, characterized in that in the comparison step of step S40: and if the thickness of the shell obtained in the step S20 is smaller than the preset shell thickness, returning to the step S20, reducing the blank drawing speed and/or the heat flux density substituted into the preset casting blank model, and continuing to perform the steps S20 to S30.
6. The method for determining the crystallizer coolant flux of high titanium steel according to claim 4, wherein the predetermined billet shell thickness is 13mm.
7. The method for determining the crystallizer coolant flux of high titanium steel according to claim 1, wherein said step S60 comprises:
the calculation of the crystallizer cooling liquid flux is carried out by the following formula:
in the above formula, m represents the mass of the cooling liquid flowing through the crystallizer in unit time, kg/s;
C w Represents the specific heat of the coolant;
T 1 denotes the initial temperature of the coolant, DEG C;
T 2 denotes the coolant end temperature, ° c;
8. Method for determining the crystallizer coolant flux of high titanium steels according to claim 1, characterized in that in step S11: dividing high titanium steel samples to be produced into a plurality of groups, heating to more than 1640 ℃, preserving heat for 10-30 min after the high titanium steel samples are fully melted, cooling the high titanium steel samples to 1550-1640 ℃ at a cooling speed of 5-20 ℃/min respectively, and then quenching.
9. Method for determining the crystallizer coolant flux of high titanium steels according to claim 1, characterized in that in step S12: dividing a high titanium steel sample into a plurality of parts, and grinding and polishing the parts; heating the high titanium steel sample to 1550 ℃, and preserving the heat for 3-10 min to completely melt the high titanium steel sample.
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| JP5505086B2 (en) * | 2010-05-26 | 2014-05-28 | 新日鐵住金株式会社 | Method, apparatus and program for estimating state in mold in continuous casting |
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