CN112122571B - Control method of forced cooling system for large-section continuous casting round billet solidification tail end - Google Patents
Control method of forced cooling system for large-section continuous casting round billet solidification tail end Download PDFInfo
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- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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Abstract
The invention belongs to the technical field of continuous casting in steel production, and relates to a system for performing forced cooling on the solidification tail end of a large-section continuous casting round billet and a control method, wherein the system comprises a cooling device, a cooling water supply device, a compressed air supply device and a control device; the cooling water supply device and the compressed air supply device are both connected with the cooling device, and the control device is respectively connected with the cooling device, the cooling water supply device and the compressed air supply device in a control mode. The cooling device is sequentially arranged after the continuous casting billet is straightened and before the continuous casting billet is cut along the drawing speed direction, the continuous casting round billet passes through the center of the cooling ring, the round billet solidification end region is cooled by using water spray cooling or aerial fog cooling, and the cooling region and the cooling strength are controlled by the control device. The method can establish a system for effectively cooling the continuous casting solidification tail end of the large-section round billet, can enable the surface layer and the middle layer of the casting blank to generate larger tensile stress, inhibit the tensile stress generated by the solidification of the center of the casting blank, control and eliminate the center crack of the casting blank, and improve the quality of the casting blank product.
Description
Technical Field
The invention relates to the technical field of steel continuous casting, in particular to a system for performing forced cooling on a large-section continuous casting round billet solidification tail end and a control method thereof.
Background
Continuous casting round billets are developed rapidly in recent years, and the diameter of the cross section is also developed in an expanding manner, however, with the stricter requirements of various application fields on the continuous casting diameter and the internal and external quality of the round billets, the production requirements of casting billets are higher and higher. The large-section round billet continuous casting has the characteristics of small specific surface area, large molten steel static pressure, large billet shell line shrinkage, large billet shell heat capacity, long solidification distance, small casting blank radiant heat intensity in a secondary cooling area, long liquid-phase cavity and the like, and round billet continuous casting equipment is different from plate blanks and square blanks and generally does not have a soft reduction process, so that the center of a continuous casting round billet has segregation and looseness, and central cracks are easy to generate, and the quality qualification rate and the stability of the whole product are influenced. The technology for improving the internal quality of the continuous casting round billet is very important and urgent. According to basic theory and process requirements, a strong cooling device can be arranged at the solidification tail end, so that the surface layer and the middle layer of the casting blank generate larger tensile stress, the tensile stress generated by the solidification of the center of the casting blank is inhibited, the macroscopic defects formed in the continuous casting process are reduced, and the risk and probability of the generation of center cracks are reduced, thereby improving the internal quality of the continuous casting round billet.
Disclosure of Invention
In order to solve the above problems, an object of the present invention is to provide a system for forcibly cooling a solidification end of a continuous casting round billet and a method for controlling the same, which can generate a large tensile stress in a surface layer and an intermediate layer of a cast billet, suppress a tensile stress generated by solidification of the center of the cast billet, and reduce the risk and probability of occurrence of center cracks, thereby improving the internal quality of the continuous casting round billet.
The method and the equipment comprise a plurality of cooling rings, or a plurality of pairs of cooling rings or a plurality of groups of cooling rings, wherein the specific number is determined according to the length required by the intensive cooling of the solidification tail end and the space between the straightening roll of the continuous casting billet and the cutting device. When the water spray cooling technology is adopted, the cooling rings are connected with a cooling water system, and each cooling ring can be independently used; when the gas mist cooling is adopted, two cooling rings are arranged side by side and are closely adjacent to each other to form a gas mist cooling ring pair, wherein one cooling ring is connected with a cooling water system, and the other cooling ring is connected with a compressed air system. 2-6 cooling rings or cooling ring pairs can be fixed by steel frames to form a cooling ring group. The cooling ring group is easy to be stably arranged on a continuous casting machine. The cooling ring can be made of stainless steel tube or corrosion-resistant steel, and the inner diameter of the steel tube is 5-20 mm;
the shape and diameter of the cooling ring are determined according to actual production conditions, and the shape can be circular, or regular polygons such as regular hexagon and regular octagon. The diameter of each cooling ring in the same group of cooling equipment is the same, the specific diameter of each cooling ring is determined according to the diameter of a continuous casting blank and the space in front of a cutting device of a continuous casting machine, generally is 1.5-3 times of the diameter of a continuous casting round billet, the continuous casting round billet needs to be ensured to stably pass through the center of the cooling ring, and a part of space is reserved so that a nozzle can uniformly spray water or steam to the surface of the casting blank for cooling.
The nozzles are uniformly arranged on the cooling ring, the cooling ring pair or the cooling ring group along the circumference, and the number and the arrangement interval of the nozzles are determined according to the purpose of uniformly cooling the surface layer of the casting blank, and are generally 6 to 12. Connecting the nozzles on the cooling ring with cooling water in the cooling ring, connecting the nozzles on the cooling ring pair with cooling water and gas in the cooling ring pair, and remotely controlling the cooling water supply quantity and the gas flow of each nozzle by a control device system through an electric valve;
the cooling rings, the cooling ring pairs or the cooling ring sets are sequentially arranged behind the continuous casting billet straightening roller and in front of the cutting device along the pulling speed direction, and in order to realize uniform cooling of the continuous casting billet along the pulling speed direction as far as possible, the cooling rings, the cooling ring pairs or the cooling ring sets are preferably uniformly arranged along the pulling speed direction. The continuous casting round billet passes through the center of the cooling ring, and the solidified tail region of the round billet is cooled by water spraying cooling of the cooling ring or an air mist cooling mode;
the cooling ring, the cooling ring pair or the cooling ring group can be fixed on the continuous casting equipment and can also move to adjust the position on the continuous casting equipment along the drawing speed direction. For different steel grades, the position of the solidification tail end and the length required by cooling the solidification tail end have certain difference, and whether the position of the cooling ring, the cooling ring pair or the cooling ring group needs to be moved or not can be determined according to the actual production requirement, or the nozzles on the cooling ring, the cooling ring pair or the cooling ring group at the corresponding positions are opened for cooling.
The solidification end point position of the continuous casting round billet is calculated by a control device system according to the production conditions of steel composition, continuous casting cooling strength, drawing speed, casting temperature and the like. Firstly, calculating the physical properties and thermophysical properties (density, thermal conductivity, Young/volume/shear modulus, Poisson ratio, enthalpy, specific heat, latent heat and the like) of the steel grade through the components of the steel grade; importing the calculation result into finite element numerical simulation software; establishing heat transfer models of different cooling sections (the average heat flow density of the crystallizer is calculated in the crystallizer section, the heat exchange coefficient is calculated in the foot roller second cooling section, and the radiation heat exchange coefficient is calculated in the air cooling area); substituting the production process parameters into the heat transfer model, and introducing the heat exchange conditions obtained by model calculation into finite element numerical simulation software; the heat transfer process of the large-section round billet can be simplified into a two-dimensional heat transfer process, a geometric model of the large round billet is established in finite element numerical simulation software, a round slice with the diameter consistent with that of the actual continuous casting round billet is arranged, and meshes are divided; applying load, boundary conditions, solving and post-processing to the established geometric model in finite element numerical simulation software to obtain a temperature field distribution cloud chart in the round billet continuous casting process; and the time and the position of the complete solidification of the round billet can be found out from the temperature field distribution cloud picture.
Determining the casting blank within the range of 0.5-2 m before and after the solidification end point as the solidification end point of the casting blank, opening a nozzle of a cooling ring within the range of 0.5-2 m before and after the solidification end point by using a control device system, and controlling the cooling water quantity and the gas flow through an electric valve to cool the casting blank in the interval with certain strength.
The cooling intensity of the tail end of the casting blank is controlled within the range of 0.1L/kg-0.3L/kg of specific water, and the total gas quantity of the compressed gas for aerial fog cooling is controlled within 2000-8000Nm3And h, calculating the specific cooling strength and gas pressure by a control device system according to the steel type components, the continuous casting cooling strength, the drawing speed and the casting temperature, ensuring that the tensile stress of the center of the continuous casting round billet is less than 0.3Mpa during solidification and within 1-3 minutes later, and ensuring that the tensile stress of the surface layer of the casting blank is less than 50% of the tensile strength of the steel type at the surface layer temperature of the casting blank.
The cooling intensity of the tail end of the casting blank is controlled within the range of 0.1L/kg-0.3L/kg of specific water, and the total gas quantity of the compressed gas for aerial fog cooling is controlled within 2000-8000Nm3The cooling strength of the specific solidification end was calculated by finite element numerical simulation software. On the basis of the previous model for calculating the solidification end point and calculation, firstly, setting cooling intensity with specific water volume of 0.1L/kg in a determined tail end strong cooling area for calculation, and solving and post-processing again to obtain a temperature field distribution cloud picture of the solidification end point after the tail end strong cooling is applied; selecting a solidification end point temperature field distribution cloud picture, setting thermal stress coupling analysis, applying molten steel static pressure, performing coupling analysis to solve to obtain a solidification end point casting blank stress distribution cloud picture, and reading a round blankA first principal stress at the core location and at the surface layer; setting a circulation condition, if the first main stress of a casting blank is more than 3Mpa, increasing the cooling intensity of the tail end, recalculating a solidification end point temperature field distribution cloud chart and calculating stress coupling to obtain a stress distribution cloud chart until the cooling intensity is increased to enable the first main stress of the center of the round blank to be less than 3Mpa, outputting the cooling intensity at the moment to be the minimum tail end cooling intensity, continuing to increase the cooling intensity to enable the tensile stress borne by the surface layer of the round blank to reach 50% of the tensile strength of the steel at the temperature, outputting the cooling intensity at the moment to be the maximum tail end cooling intensity, selecting the cooling intensity of the tail end in the interval from the minimum cooling intensity to the maximum cooling intensity according to the actual production condition, and enabling the maximum cooling intensity not to exceed the specific water quantity of 0.3L/kg.
According to the technical scheme, the rating of the center cracks of the large-size round billet can be obviously reduced, and the internal quality of the casting billet is improved, so that the difficulty of subsequent rolling and forging is reduced, and the yield of the product is improved.
Drawings
FIG. 1 is a schematic view of a fixed cooling ring in the equipment for forced cooling of the solidification end of a large-section continuous casting round billet.
FIG. 2 is a schematic diagram of a movable cooling ring structure in the equipment for performing forced cooling on the solidification end of the large-section continuous casting round billet.
FIG. 3 is a schematic view of a cooling ring structure in the apparatus for forced cooling of the solidification end of a large-section continuous casting round billet according to the present invention.
FIG. 4 is a schematic structural diagram of an aerosol cooling ring pair in the equipment for performing forced cooling on the solidification end of a large-section continuous casting round billet.
In the figure:
1. a steel frame, 2. a control valve; 3. a cooling device; 31. cooling water cooling rings; 32. a compressed air cooling ring; 4. continuously casting a round billet; 5. continuously casting the central axis of the round billet; 6. the continuous casting round billet is solidified at the end point; 7. and (4) a nozzle.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
The technical scheme of the invention is further explained by combining the attached drawings and specific implementation.
As shown in FIG. 1, the system for performing forced cooling on the solidification tail end of a large-section continuous casting round billet comprises a cooling device, a cooling water supply device, a compressed air supply device and a control device;
the cooling device is used for carrying out forced cooling on the solidification tail end of the continuous casting round billet through cooling water or gas mist;
the cooling water supply device is used for supplying cooling water to the cooling device;
the compressed air supply device is used for supplying compressed air for cooling to the cooling device;
the control device is used for determining a minimum cooling intensity value and a maximum cooling intensity value of the solidification tail end and controlling the cooling intensity of the tail end in a range from the minimum cooling intensity to the maximum cooling intensity by combining with the actual production condition;
the cooling device is arranged on the peripheral side of the continuous casting round billet to be cooled, the cooling water supply device and the compressed air supply device are both connected with the cooling device, and the control device is respectively in control connection with the cooling device, the cooling water supply device and the compressed air supply device.
Moving on continuous casting equipment along the direction of blank drawing, and stably passing through the center of strong cooling equipment in a strong cooling interval at the solidification tail end; the cooling device 3 fixed on the continuous casting equipment, the nozzles 7 are uniformly distributed on the cooling ring of the cooling device 3, the connecting gas circuit and the water circuit can be connected, and the gas-water ratio can be controlled by the control device. The cooling rings at different positions can be selectively opened for water cooling or steam fog cooling aiming at different steel grades, four groups of cooling rings in the middle of a certain steel grade in the drawing are obtained through calculation to be opened for cooling, 1 is a steel frame for connecting and fixing two cooling rings, and the two independent cooling rings form a cooling ring group; 6, representing the continuous casting solidification end point of the large-section round billet; and 5, a central axis of the continuous casting round billet.
The cooling device comprises a plurality of cooling rings, the cooling rings are arranged after the continuous casting billet is straightened and before the continuous casting billet is cut along the drawing speed direction, the continuous casting round billet passes through the centers of the cooling rings, and each cooling ring is provided with a control valve which is connected with the control device;
and a plurality of nozzles are arranged on the inner side wall of each cooling ring at equal intervals.
When water spray cooling is adopted, the cooling rings are arranged in a single group, two groups or a plurality of groups and are all connected with the cooling water supply device; the maximum cooling intensity is not more than 0.3L/kg of specific water.
When the air fog cooling is adopted, two adjacent cooling rings are arranged in a side-by-side adjacent mode to form an air fog cooling ring pair, the two cooling rings are communicated through a plurality of pipelines, each pipeline is provided with a nozzle, one cooling water supply device in the two cooling rings arranged in a side-by-side adjacent mode is connected, and the other cooling water supply device is connected with the compressed air supply device.
As shown in fig. 3, the shape of the cooling ring is circular, regular hexagon, regular octagon or other regular polygon, and the diameter of the cooling ring is 1.5-3 times of the diameter of the continuous casting round billet; the continuous casting round billet can smoothly pass through the cooling ring, and cooling water or vapor can be uniformly sprayed on the surface of the casting billet for cooling.
The shape of the cooling ring is circular, regular hexagon, regular octagon or other regular polygons, and the diameter of the cooling ring is 1.5-3 times of that of the continuous casting round billet;
the cooling ring is made of a stainless steel pipe or corrosion-resistant steel, and the inner diameter of the stainless steel pipe or the corrosion-resistant steel is 5-20 mm.
As shown in fig. 4, a cooling ring of air fog in the equipment for performing forced cooling on the continuous casting solidification end of a large-section round billet, 1, a cooling ring connected with a compressed air system; and 7 is a nozzle arranged on the pair of cooling rings, one side of the nozzle is connected with cooling water in the cooling rings, and the other side of the nozzle is connected with gas in the cooling rings. The cooling ring pair is formed by two cooling ring steel pipes which are compact and arranged side by side, one cooling ring supplies cooling water to the nozzle, and the other cooling ring supplies gas to the nozzle, so that the cooling ring pair nozzle continuously sprays aerial fog to the surface of the casting blank to achieve the cooling purpose.
As shown in figure 2, the movable cooling ring structure is adopted, 4 is a continuous casting round billet: moving on continuous casting equipment along a blank drawing direction, and stably penetrating through the central axis of a continuous casting round blank from the center of strong cooling equipment in a strong cooling interval at the solidification tail end; the cooling device 3 can move along the blank drawing direction, nozzles are uniformly distributed on the cooling ring, and are connected with an air passage and a water passage, and the air-water ratio can be remotely controlled by a control device. Carrying out water cooling or steam fog cooling on the movable cooling rings of different steel types to corresponding positions; 6, representing the continuous casting solidification end point of the large-section round billet;
the invention also provides a cooling control method of the system, which specifically comprises the following steps:
s1), firstly, arranging a cooling device on the continuous casting round billet to be cooled, calculating parameters of physical properties and thermophysical properties of the steel grade according to steel grade components of the continuous casting round billet to be cooled, and introducing the parameters into finite element numerical simulation software; determining a heat transfer model; calculating heat exchange conditions according to continuous casting production process parameters:
in the formula: rho is density, kg/m3(ii) a T-temperature, K; cP-heat capacity, J/kg · K;
-thermal conductivity, w/(m · K);
-latent heat of solidification;
-solid fraction.
S2) calculating heat transfer conditions according to industrial production parameters, and obtaining the average heat flow density value of the crystallizer, the heat exchange coefficient value of the cold section of the foot roller and the heat exchange coefficient value of the radiation of the air cooling area according to the heat transfer conditions;
s3), establishing a geometric model of the continuous casting round billet, solving and processing according to the applied load and boundary conditions of the established geometric model to obtain a temperature field distribution cloud chart in the continuous casting process of the continuous casting round billet to be cooled, determining the time and position of complete solidification of the continuous casting round billet to be cooled according to the temperature field distribution cloud chart, wherein the complete solidification position is a solidification end point, and determining a casting blank within a range of 0.5-2 m before and after the solidification end point as the solidification end point of the continuous casting round billet;
the S3) comprises the following specific steps:
s3.1) establishing a circular blank geometric model in finite element numerical simulation software, setting a circular sheet with the diameter consistent with that of the continuously cast circular blank actually produced and dividing a grid;
s3.2) applying load, boundary conditions, solving and post-processing to the established geometric model in finite element numerical simulation software to obtain a temperature field distribution cloud chart of the continuous casting process of the section continuous casting round billet;
s3.3) determining the time and the position of complete solidification of the cross section continuous casting round billet according to the obtained temperature field distribution cloud picture, and determining a strong and cold area of the applied tail end.
S4) obtaining a specific water quantity value of the given continuous casting cooling water at the solidification tail end in S3), calculating, solving again, performing post-treatment to obtain a temperature field distribution cloud chart of the solidification tail end after applying tail end strong cooling, finally determining a minimum tail end cooling strength value and a maximum cooling strength value of the solidification tail end, selecting the tail end cooling strength in a range from the minimum cooling strength to the maximum cooling strength according to the actual production condition, cooling, inhibiting the tensile stress generated by the solidification of the center of the casting blank, and controlling and eliminating the center crack of the casting blank.
The S1) parameters include density, thermal conductivity, young/volume/shear modulus, poisson' S ratio, enthalpy, specific heat, and latent heat.
The average heat flow density value of the crystallizer in the S2), the heat exchange coefficient value of the cold section of the foot roller II and the radiation heat exchange coefficient value of the air cooling area are respectively calculated by the following formulas:
the average heat flow density of the junction device is calculated according to the following formula:
in the formula: q is the average heat flux density of heat transfer in the crystallizer and the unit is W/m2；ρwFor the density of cooling water, unit kg/m3；CwThe specific heat capacity of cooling water of a crystallizer is expressed as unit J/(kg. K); w is coldFlow rate of cooling water, unit m3S; delta T is the temperature difference of the cooling water inlet and the cooling water outlet, and the unit K is; d is the diameter of the section of the casting blank in m; l is the length of the crystallizer section in m;
the heat exchange coefficient calculation formula adopted by the cold section of the foot roller II is as follows:
h=350w+130 （3），
in the formula: h is the heat exchange coefficient of the secondary cooling zone and the unit W/(m)2K); w is the water flow density in L/(m)2S); r is the specific water quantity of continuous casting cooling water, and the unit is L/kg; vCThe drawing speed is in m/min; s is the cross section area of the casting blank in m2(ii) a Gamma is the density of steel in kg/m3；ξnWater distribution ratio of foot roller and secondary cooling area is percent; l isnIs the length of the nth region in m;
and (3) calculating the radiation heat exchange coefficient value of the air cooling area:
wherein σ is Stefan-Boltzmann constant, 5.67X 10-8W·m-2K-4(ii) a Epsilon is the radiation heat exchange coefficient; t is the surface temperature of the casting blank, and the unit is K; t iswIs ambient room temperature in K.
The S4) comprises the following specific steps:
s4.1) obtaining a given continuous casting cooling water specific water value of a position area where the continuous casting round billet is completely solidified at S3), calculating, and solving after-treatment again to obtain a temperature field distribution cloud chart of a solidification end point after the tail end is forced to be cooled;
s4.2) obtaining a temperature field distribution cloud picture of a solidification end point after the tail end is strongly cooled according to S4.1), setting thermal stress coupling analysis, applying ferrostatic pressure, solving through the coupling analysis to obtain a solidification end point casting blank stress distribution cloud picture, reading first main stress at the central position and the surface layer of a section continuous casting round blank, if the first main stress of the casting blank is more than 3Mpa, increasing the cooling intensity of the tail end, recalculating the solidification end point temperature field distribution cloud picture and calculating through stress coupling to obtain a stress distribution cloud picture, and outputting the value that the cooling intensity is the minimum tail end cooling intensity until the first main stress at the center of the round blank is less than 3 Mpa;
and S4.3) continuously increasing the cooling strength to enable the tensile stress borne by the surface layer of the round billet to reach 50% of the tensile strength of the steel grade at the temperature, outputting the cooling strength at the moment as the maximum tail end cooling strength, and selecting the tail end cooling strength to cool in the interval from the minimum cooling strength to the maximum cooling strength according to the actual production condition, so that the tensile stress generated by the solidification of the center of the casting blank is inhibited, and the center crack of the casting blank is controlled and eliminated.
In the S4.2), the setting range of the water ratio value of the continuous casting cooling water is as follows: 0.1L/kg-0.3L/kg, the total gas amount of the compressed gas for the aerosol cooling is controlled within 2000-8000Nm3/h 。
However, in view of energy and water saving, the maximum cooling intensity should not exceed the specific water amount of 0.3L/kg.
Example 1:
a method for forced cooling of the continuous casting solidification tail end of a large-section round billet is adopted on a continuous casting production line for producing the round billet with the diameter of 600 in a certain domestic steel mill, and the cooling mode is cooling water. And a strong cooling device is arranged between 17m and 21m away from the meniscus of the crystallizer, the strong cooling device comprises fourteen cooling rings fixed on the continuous casting equipment, every two cooling rings form a cooling ring group, the interval between the two cooling rings in one cooling ring group is 0.2m, and the interval between every two cooling ring groups is 0.35 m. The cooling rings are circular with the radius of 550mm and are made of stainless steel pipes with the inner diameter of 15mm, eight nozzles are arranged on each cooling ring, the nozzles are connected with cooling water in the cooling rings, the cooling rings are connected with a cooling water system, and the cooling rings can be opened or closed remotely through a control device system and the flow of the cooling water can be controlled.
When the steel mill is used for producing high-strength medium-carbon steel AISI4130 continuous casting round billets with the diameter of 600 ℃, the drawing speed is 0.29m/min, the casting temperature is 1525 ℃, the liquidus temperature of the steel is 1500 ℃, and the solidus temperature is 1450 ℃. In the production process, the continuous casting round billet is discharged out of a crystallizer, and is cooled by air after passing through a sufficient roller section and a secondary cooling zone. The control device system calculates that the continuous casting large round billet is completely solidified at a position 18.5m away from the meniscus of the crystallizer, the surface temperature of the casting billet is 895 ℃, the central temperature is 1450 ℃, the central tensile stress is 0.36Mpa, and the risk and the probability of generating the central crack of the continuous casting large round billet are high.
Three cooling ring groups with the cooling intensity of 0.15L/kg and the specific water amount of 18-19.5 m away from the meniscus of the crystallizer are calculated and opened by a control device system, so that cooling water or vapor mist is uniformly sprayed on the surface of the casting blank. After the forced cooling is applied, the surface temperature is reduced to 750 ℃, the central tensile stress is reduced to 0.275Mpa, the central tensile stress of the casting blank is ensured to be less than 0.3Mpa within 3 minutes after the casting blank is completely solidified, and the probability and the risk of generating central cracks are greatly reduced. Meanwhile, the stress generated on the surface of the round billet under the cooling strength is calculated to be about 35Mpa which is 35 percent of the strength of the steel at 750 ℃, and surface defects such as surface cracks and the like can not occur. The AISI4130 steel produced in practice has a diameter of 600 large round billets without center cracks and surface cracks.
Example 2:
the method is characterized in that a method for carrying out forced cooling on the continuous casting solidification tail end of a large-section round billet is adopted on a continuous casting production line for producing the round billet with the diameter of 600 in a certain domestic steel mill, and the cooling mode is aerosol cooling. The strong cooling device is arranged in a 17-21 m interval from a meniscus of the crystallizer, the strong cooling device is fourteen cooling ring pairs fixed on continuous casting equipment, each cooling ring is circular with the radius of 550mm and is made of a stainless steel pipe with the inner diameter of 15mm, each cooling ring pair is formed by compactly connecting two cooling rings side by side, one cooling ring is connected with a cooling water system, the other cooling ring is connected with a compressed gas system, eight nozzles are arranged on each cooling ring pair, and the nozzles are connected with cooling water and gas in the cooling ring pairs. Every two cooling ring pairs form a cooling ring group, the interval between the two cooling ring pairs in one cooling ring group is 0.2m, the interval between every two cooling ring groups is 0.35m, and the cooling water and the gas pressure can be controlled by opening or closing each cooling ring pair through a control device system.
When the diameter of the steel grade 18CrNiMo produced by the steel mill is 600 continuous casting large round billets, the drawing speed is 0.27 m/min, the casting temperature is 1545 ℃, the liquidus temperature of the steel grade is 1510 ℃, and the solidus temperature is 1425 ℃. In the production process, the continuous casting round billet is discharged out of a crystallizer, and is cooled by air after passing through a sufficient roller section and a secondary cooling zone. The control device system calculates that the casting blank is completely solidified at a position 19.7m away from the meniscus of the crystallizer, the surface temperature of the casting blank is 915 ℃, the central temperature is 1425 ℃, the central tensile stress is 0.39Mpa, and the risk and the probability of generating the central crack of the continuous casting large round blank are high.
Calculating and starting three cooling ring groups at 19.2-20.7 m positions by a control device control system, wherein the cooling intensity is 0.18L/kg of specific water amount, and the gas pressure is 6000Nm3H is used as the reference value. After the strong cooling is applied, the surface temperature is reduced to 715 ℃, the central tensile stress is reduced to 0.283Mpa, the central tensile stress of the casting blank is ensured to be less than 0.3Mpa and lower than the tensile strength of the center of the casting blank within 3 minutes after the casting blank is completely solidified, and the probability and the risk of generating central cracks are greatly reduced. The stress generated on the surface of the round billet under the cooling strength is about 51Mpa which is 48 percent of the strength of the steel grade at 750 ℃, and surface defects such as surface cracks and the like can not occur. No central crack and surface crack are found in the actually produced 18CrNiMo steel grade with the diameter of 600 large round billets.
Example 3:
a steel mill adopts a method of forced cooling of the continuous casting solidification tail end of a large-section round billet on a production line for producing a continuous casting large round billet with the diameter of 800. A movable forced cooling device with the length of 3m is arranged on the continuous casting production line, and consists of sixteen cooling rings, and the interval between every two cooling rings is 0.18 m. The cooling ring is a regular dodecagon prepared from a stainless steel pipe with the inner diameter of 18mm, twelve nozzles are arranged on each cooling ring, the cooling rings are connected with a gas circuit and a water circuit, and the cooling rings can be opened and closed through a control device system and the proportion of cooling water and gas can be controlled.
When the WB36V steel for the high-pressure furnace is produced by the steel mill, the diameter of the continuous casting round billet is 800, the drawing speed is 0.11m/min, the casting temperature is 1530 ℃, the liquidus temperature of the steel is 1510 ℃, the solidus temperature is 1460 ℃, and the continuous casting round billet is discharged from a crystallizer in the production process and cooled by air after passing through a sufficient roller section and a secondary cooling zone. The control device system calculates that the casting blank is completely solidified at a position 26.2m away from the meniscus of the crystallizer, the surface temperature of the casting blank is 892 ℃, the central tensile stress is 0.41Mpa, and the risk and probability of central cracks generated in the continuous casting large round blank are high.
And (3) calculating the result by a control system of the control device, moving the forced cooling device to a position 25-28 m away from the meniscus of the crystallizer, and starting all cooling rings on the forced cooling device by using the control system, wherein the cooling strength is 0.16L/kg of specific water. After the strong cooling is applied, the surface temperature is reduced to 705 ℃, the central tensile stress is reduced to 0.285Mpa, the central tensile stress of the casting blank is ensured to be less than 0.3Mpa within 3 minutes after the casting blank is completely solidified, the central tensile stress is lower than the tensile strength of the center of the casting blank, and the probability and the risk of generating central cracks are greatly reduced. The calculation shows that the stress generated on the surface of the round billet under the changed cooling strength is about 39Mpa, which is 35 percent of the strength of the steel grade at 705 ℃, and surface defects such as surface cracks and the like can not occur. No central cracks and surface cracks were found in the actually produced WB36V steel round billet with a diameter of 800 mm.
In the three schemes, when the device for performing forced cooling on the large-section round billet continuous casting solidification tail end is arranged:
the device can be fixedly arranged on continuous casting equipment, and when the device is used, a part of cooling ring or a cooling ring group is opened to cool the solidification tail end of the round billet; and the round billet cooling device can also be arranged to be movable, and the round billet cooling device can be used for cooling the round billet solidification end after being moved to a position needing cooling. In the cooling process, the cooling ring switch is opened through the control device, the proportion of cooling water and gas is controlled, cooling water or vapor mist is uniformly sprayed on the surface of a casting blank, the surface temperature of the casting blank is reduced to a certain degree, the strength of the blank shell is forcibly increased, the core part of the casting blank is compacted, the thermal expansion of the blank shell can be weakened, the effect of tensile stress on the interior of the casting blank is reduced, and the probability and risk of generating central cracks are reduced.
The system for performing forced cooling on the solidification tail end of the large-section continuous casting round billet and the control method thereof provided by the embodiment of the application are described in detail above. The above description of the embodiments is only for the purpose of helping to understand the method of the present application and its core ideas; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.
As used in this specification and the appended claims, certain terms are used to refer to particular components, and various names may be used by a manufacturer of hardware to refer to a same component. This specification and claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. "substantially" means within an acceptable error range, and a person skilled in the art can solve the technical problem within a certain error range to substantially achieve the technical effect. The description which follows is a preferred embodiment of the present application, but is made for the purpose of illustrating the general principles of the application and not for the purpose of limiting the scope of the application. The protection scope of the present application shall be subject to the definitions of the appended claims.
It is also noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a good or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such good or system. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a commodity or system that includes the element.
It should be understood that the term "and/or" as used herein is merely one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.
The foregoing description shows and describes several preferred embodiments of the present application, but as aforementioned, it is to be understood that the application is not limited to the forms disclosed herein, but is not to be construed as excluding other embodiments and is capable of use in various other combinations, modifications, and environments and is capable of changes within the scope of the application as described herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the application, which is to be protected by the claims appended hereto.
Claims (8)
1. The control method of the forced cooling system for the solidification tail end of the large-section continuous casting round billet comprises a cooling device, a cooling water supply device, a compressed air supply device and a control device;
the cooling device is used for carrying out forced cooling on the solidification tail end of the continuous casting round billet through cooling water or gas mist;
the cooling water supply device is used for supplying cooling water to the cooling device;
the compressed air supply device is used for supplying compressed air for cooling to the cooling device;
the control device is used for determining a minimum terminal cooling strength value and a maximum cooling strength value of the solidification terminal and controlling the terminal cooling strength in an interval from the minimum terminal cooling strength value to the maximum cooling strength in combination with the actual production condition;
the cooling device is arranged on the peripheral side of the continuous casting round billet to be cooled, the cooling water supply device and the compressed air supply device are both connected with the cooling device, and the control device is respectively in control connection with the cooling device, the cooling water supply device and the compressed air supply device;
the cooling device comprises a plurality of cooling rings, the cooling rings are arranged after the continuous casting round billet is straightened and before the continuous casting round billet is cut along the drawing speed direction, the continuous casting round billet passes through the centers of the cooling rings, and each cooling ring is provided with a control valve which is connected with the control device;
a plurality of nozzles are arranged on the inner side wall of each cooling ring at equal intervals;
the cooling control method of the system is characterized by specifically comprising the following steps of:
s1), firstly, arranging a cooling device on the continuous casting round billet to be cooled, calculating parameters of physical properties and thermophysical properties of the steel grade according to steel grade components of the continuous casting round billet to be cooled, and introducing the parameters into finite element numerical simulation software; determining a heat transfer model; calculating heat exchange conditions according to continuous casting process parameters:
s2) calculating heat transfer conditions according to the continuous casting process parameters, and obtaining average heat flow density values of the crystallizer, the foot roller two cold sections and the air cooling area according to the heat transfer conditions;
s3), establishing a geometric model of the continuous casting round billet, arranging a round slice with the diameter consistent with that of the actually produced continuous casting round billet, and dividing a grid; according to the load and boundary conditions applied by the geometric model, solving and processing to obtain a temperature field distribution cloud picture in the continuous casting process of the round billet to be cooled, determining the time and position of complete solidification of the round billet to be cooled according to the temperature field distribution cloud picture, wherein the complete solidification position is a solidification end point, and determining the round billet to be cast as the solidification end point of the round billet in a range of 0.5-2 m before and after the solidification end point;
s4) obtaining a specific water quantity value of the given continuous casting cooling water at the solidification tail end in S3), calculating, solving again, performing post-treatment to obtain a temperature field distribution cloud chart of the solidification end point after applying tail end strong cooling, finally determining a minimum tail end cooling strength value and a maximum cooling strength value of the solidification tail end, selecting the tail end cooling strength in a range from the minimum tail end cooling strength to the maximum cooling strength according to the actual production condition, cooling, inhibiting the tensile stress generated by the solidification of the center of the continuous casting round billet, and controlling and eliminating the center crack of the continuous casting round billet.
2. The control method of claim 1, wherein the S1) parameters include density, thermal conductivity, young/volume/shear modulus, poisson' S ratio, enthalpy, specific heat, and latent heat.
3. The control method according to claim 1, wherein the average heat flow density values of the crystallizer, the second foot roll cold section and the air cooling zone in S2) are respectively obtained by the following formulas:
the average heat flow density of the junction device is calculated according to the following formula:
in the formula: q is the mean heat flow density in W/m2；ρwFor the density of cooling water, unit kg/m3；CwThe specific heat capacity of cooling water of a crystallizer is expressed as unit J/(kg. K); w is the flow rate of cooling water, unit m3S; delta T is the temperature difference of the cooling water inlet and the cooling water outlet, and the unit K is; d is the diameter of the section of the continuous casting round billet and the unit m; l is the length of the crystallizer section in m;
the heat exchange coefficient calculation formula of the average heat flux density of the cold section of the foot roller II is as follows:
q=h(T-tw) (2),
h=350w+130 （3），
in the formula: h is the heat exchange coefficient of the secondary cooling zone and the unit W/(m)2·K)；twThe temperature of cooling water in a secondary cooling area is K; w is the water flow density in L/(m)2S); r is the specific water quantity of continuous casting cooling water, and the unit is L/kg; vCThe drawing speed is in m/min; s is the cross section area of the continuous casting round billet in m2(ii) a Gamma is the density of steel in kg/m3；ξnWater distribution ratio of foot roller and secondary cooling area is percent; l isnIs the length of the nth region in m;
and (3) calculating the radiation heat exchange coefficient value of the air cooling area:
wherein σ is Stefan-Boltzmann constant, 5.67X 10-8W·m-2K-4(ii) a Epsilon is the radiation heat exchange coefficient; t is the surface temperature of the continuous casting round billet, and the unit is K; t iswIs ambient room temperature in K.
4. The control method according to claim 3, characterized in that the specific steps of S4) are as follows:
s4.1) obtaining a given continuous casting cooling water specific water value of a position area where the continuous casting round billet is completely solidified at S3), calculating the average cooling heat flux density according to a formula (2), and solving again and then processing to obtain a temperature field distribution cloud chart of a solidification end point after applying strong cooling to the tail end;
s4.2) obtaining a temperature field distribution cloud picture of a solidification end point after the solidification end point is subjected to forced cooling according to S4.1), setting thermal stress coupling analysis, applying ferrostatic pressure, solving the solidification end point continuous casting round billet stress distribution cloud picture through the coupling analysis, reading first main stress at the center position and the surface layer of a cross section continuous casting round billet, increasing the cooling intensity of the end point if the first main stress of the continuous casting round billet is more than 3Mpa, recalculating the solidification end point temperature field distribution cloud picture and calculating the stress coupling to obtain a stress distribution cloud picture until the cooling intensity is increased to enable the first main stress at the center of the round billet to be less than 3Mpa, and enabling the cooling intensity applied to the solidification end point to be the minimum end point cooling intensity at the moment;
s4.3) continuously increasing the cooling strength to enable the tensile stress on the surface layer of the continuous casting round billet to reach 50% of the tensile strength of the steel grade at the temperature, wherein the cooling strength is the maximum tail end cooling strength, and the tail end cooling strength is selected to be cooled in the interval from the minimum tail end cooling strength to the maximum cooling strength according to the actual production condition, so that the tensile stress generated by the solidification of the center of the continuous casting round billet is restrained, and the center crack of the continuous casting round billet is controlled and eliminated.
5. The control method according to claim 4, wherein in S4.2), the setting range of the ratio water amount value of the continuous casting cooling water is as follows: 0.1L/kg-0.3L/kg, gasThe total gas quantity of the fog cooling compressed gas is controlled to 2000-8000Nm3/h 。
6. The control method according to claim 1, wherein when water-jet cooling is employed, a plurality of the cooling rings are provided in a single, in groups of two or in groups of more than one, and are each connected to the cooling water supply device; the maximum cooling intensity is not more than 0.3L/kg of specific water.
7. The control method according to claim 1, characterized in that when the mist cooling is adopted, two adjacent cooling rings are arranged side by side in close proximity to form a pair of mist cooling rings, the two cooling rings are communicated through a plurality of pipelines, each pipeline is provided with a nozzle, one of the two cooling rings arranged side by side in close proximity is connected with a cooling water supply device, and the other cooling ring is connected with the compressed air supply device.
8. The control method according to claim 1, wherein the shape of the cooling ring is a circle, a regular hexagon, a regular octagon or other regular polygons, and the diameter of the cooling ring is 1.5-3 times the diameter of the continuous casting round billet;
the cooling ring is a corrosion-resistant steel pipe, and the inner diameter of the corrosion-resistant steel pipe is 5-20 mm.
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