CN114082913B - Control method for improving center carbon segregation of hypereutectoid steel produced by small square billet section - Google Patents

Control method for improving center carbon segregation of hypereutectoid steel produced by small square billet section Download PDF

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CN114082913B
CN114082913B CN202111349469.2A CN202111349469A CN114082913B CN 114082913 B CN114082913 B CN 114082913B CN 202111349469 A CN202111349469 A CN 202111349469A CN 114082913 B CN114082913 B CN 114082913B
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temperature
carbon segregation
tundish
pouring
section
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CN114082913A (en
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赵晓敏
吕刚
王刚
惠治国
卜向东
白月琴
杨鲁明
宋振东
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Baotou Iron and Steel Group Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/18—Controlling or regulating processes or operations for pouring
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
    • B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Continuous Casting (AREA)

Abstract

The invention discloses a control method for improving the center carbon segregation of hypereutectoid steel produced by a small square billet section, wherein the center carbon segregation of the small square billet section is caused by the flowing of molten steel which is not solidified at the final stage of casting blank solidification, and in order to prevent the center carbon segregation, the casting process of a casting blank is mainly controlled, so that an equiaxial crystal area at the center of the casting blank is expanded as much as possible. According to the theoretical analysis of casting blank solidification and solute sorting crystallization, the influence of the superheat degree, secondary cooling strength, pulling speed and the tail end electromagnetic stirring position on the central carbon segregation of the casting blank is large, so that proper and matched measures must be selected for controlling the central carbon segregation of the 150mm multiplied by 150mm small square blank section of the steel ladle, and the purpose of controlling the central carbon segregation is really achieved. After sampling, a chemical method is adopted for inspection, and compared with smelting components, the center carbon segregation index is found to be between 0.94 and 1.05, and the center segregation is obviously improved.

Description

Control method for improving center carbon segregation of hypereutectoid steel produced by small square billet section
Technical Field
The invention relates to the technical field of smelting, in particular to a control method for improving the central carbon segregation of hypereutectoid steel produced by a small square billet section.
Background
The SWRH82B belongs to hypereutectoid steel, has the carbon content of more than 0.77 percent, is a main raw material of a prestressed wire or a steel strand with high strength, high toughness and low relaxation, and is mainly applied to important construction projects such as viaducts, large-span bridges, high-rise buildings, dams, nuclear power stations, tunnels and the like. The requirements of wire rod manufacturers on their raw materials are very strict. The ladle steel has the history of producing the SWRH82B hypereutectoid steel for many years, and the SWRH82B hypereutectoid steel gradually changes from adopting a large billet section to adopting a small billet section for production along with the intense competition of the steel industry. The section of a small square billet of the clad steel is mainly 150mm multiplied by 150mm, the most failure modes at the initial trial production stage are mainly pen-point-shaped fractures, and the analysis of the existence of a reticular secondary cementite in the core part tissue of the fracture is caused by relatively low cooling speed of a wire rod and higher central carbon segregation, so that the central carbon segregation of a casting blank and the cooling speed before phase change during rolling are strictly controlled in the smelting production process in order to inhibit the precipitation of the secondary cementite during production, thereby reducing the quality complaint frequently caused by the pen-point-shaped fractures of downstream metal product users and improving the quality of stable SWRH 82B.
Disclosure of Invention
The invention aims to provide a control method for improving the center carbon segregation of hypereutectoid steel produced on a small square billet section, which aims to improve the center carbon segregation of SWRH82B hypereutectoid steel produced on a small square billet section of 150mm multiplied by 150mm, thereby reducing the quality complaints of downstream metal product users caused by frequent pencil point-shaped fracture and improving the quality of stable SWRH 82B.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention relates to a control method for improving the center carbon segregation of hypereutectoid steel produced by a small square billet section, which comprises the following steps of:
the water quantity of the crystallizer is controlled at 120m 3 H, current: 200A, frequency: 3.5Hz;
the foot roller of the zero section of the secondary cooling water system and the output rollers of the other secondary cooling sections always work normally, and the specific water amount is as follows: 0.70L/Kg; the distribution ratio is as follows: and (3) region I: and (2) zone II: zone III: zone iv =45%:27%:17%:11 percent;
the gas spray nozzles and the water spray nozzles of each section are smooth for sure, so that the uniform cooling of each surface of the casting blank is ensured;
end electromagnetic stirring current: 260A, frequency: 7Hz;
baking tundish at a temperature of more than 1000 deg.C, using submerged nozzle and ladle long nozzle after baking in advance, and more than 600 deg.C; the ladle long nozzle is cast under the protection of argon seal; six lower water gaps of the tundish must be aligned and centered with the upper openings of the crystallizer; the ladle long nozzle adopts argon seal protection pouring, the argon flow is controlled, and the ladle does not expose the tapping liquid surface; pouring the ladle: after the middle package is aligned, the big package is used as a heat preservation agent; the slag is not added too early so as to avoid slag mixing and recarburization; the liquid level of the tundish is required to be free from red leakage in the pouring process; pouring the tundish, wherein the pouring can be carried out when the tundish liquid level reaches 400 mm; starting the pull speed to be 0.6-0.7m/min; controlling the pulling speed of the rest furnaces to be 1.9m/min +/-0.1 m/min; the liquid level of the tundish cannot be lower than 800mm during normal casting; slag is produced in the ladle nozzle steel flow, and the ladle nozzle steel flow is immediately closed; the pouring liquid level of the tundish is not less than 250mm;
the head billet cutting of the casting blank is more than 5m, and the tail billet cutting is more than 3m; when the steel ladle in each working procedure is off-line in the production process, the off-station temperature can be properly increased according to the condition of the steel ladle and other abnormal conditions, the continuous casting billet can be sent in a red mode or slowly cooled, the continuous casting billet is required to be placed in a special slow cooling pit or a special slow cooling area in a workshop during slow cooling, the temperature of the casting billet is more than or equal to 450 ℃ when the casting billet enters the slow cooling area, and the slow cooling time is more than or equal to 36 hours.
Furthermore, the number of times of using the crystallizer is controlled within 50 to 200 times.
Furthermore, the coating on the inner wall of the crystallizer does not fall off.
Further, measuring the temperature of the tundish: the casting was started for 5 minutes and the temperature was measured every 10 minutes thereafter.
Further, the heating section temperature: 970-1020 ℃, temperature of soaking section: 1150-1200 ℃, heating temperature to ensure that the initial rolling temperature can be properly adjusted; keeping the temperature for 2-3 h, and then rolling at the rolling temperature of 970 +/-20 ℃ at the rolling speed of 10-110 m/s; the Ac1 temperature is 716 ℃ measured according to CCT curve, the water quantity of the water tank is controlled before and after spinning, the temperature is below Ac1, the precipitation of secondary reticular cementite is restrained, and the center carbon segregation can be improved.
Compared with the prior art, the invention has the beneficial technical effects that:
taking the cross section of a casting blank for carrying out casting blank segregation test, taking points on the casting blank according to the shapes of cross and diagonal lines, carrying out test by a chemical method after sampling, and carrying out relative comparison with smelting components to find that the central carbon segregation index is between 0.94 and 1.05 and the central segregation is obviously improved.
Drawings
The invention is further illustrated in the following description with reference to the drawings.
FIG. 1 is a schematic diagram of points on a casting blank according to the shapes of a cross and a diagonal;
FIG. 2 is a diagram showing the results of chemical examination and relative comparison with the melting composition.
Detailed Description
A control method for improving the center carbon segregation of hypereutectoid steel of a small square billet section aims to improve the center carbon segregation of SWRH82B hypereutectoid steel produced by a small square billet section of 150mm multiplied by 150mm, thereby reducing quality complaints of downstream metal product users due to frequent pencil point-shaped fractures and improving the quality of stable SWRH 82B. At present, SWRH82B hypereutectoid steel is the most widely 1860 MPa-grade steel strand, a phi 12.5 mm-14 mm SWRH82B series wire rod is mainly used as a raw material, the SWRH82B hypereutectoid steel with the wire rod specification larger than 14mm cannot be produced by smelting a 150mm multiplied by 150mm small square billet section, and the wire rod generally comprises the following chemical components: 0.79-0.86%, si:0.15% -0.35%, mn: 0.60-0.90%, P is less than or equal to 0.030%, S is less than or equal to 0.030%, V: 0.01-0.03%, cr:0.15 to 0.35 percent. The central carbon segregation of the section of the 150mm x 150mm small square billet is caused by the flowing of liquid steel which is not solidified at the final stage of the solidification of the casting billet, and in order to prevent the central carbon segregation, the casting process of the casting billet is mainly controlled, so that the equiaxial crystal area of the center of the casting billet is enlarged as much as possible. According to the analysis of casting blank solidification and solute sorting crystallization theory, the influence of superheat degree, secondary cooling strength, pulling speed and tail end electromagnetic stirring position on the central carbon segregation of the casting blank is large, so that proper and matched measures must be selected for controlling the central carbon segregation of the 150mm multiplied by 150mm small square billet section of the steel ladle, and the purpose of controlling the central carbon segregation is really achieved.
The secondary cooling strength is too weak or too strong, which can cause serious central carbon segregation, and for small-section casting blanks, the strong cooling can increase the thickness of a chilling layer to accelerate the generation of columnar crystals to form interparticle crystals, thereby reducing the central carbon segregation. The casting must be carried out at a relatively high pulling speed in cooperation with the pulling speed to form a thick billet shell, so that steel leakage or bulging of a casting blank is avoided. The superheat degree is selected to be lower temperature as much as possible, but the superheat degree cannot be too low, so that the problem of casting stop and flocculation death is prevented.
The chemical composition of the SWRH82B hypereutectoid steel in this example is shown in table 1. The process route is as follows: pretreatment of molten iron, converter, refining and continuous casting. The key point is that the continuous casting process is controlled, the using times of the crystallizer is controlled within 50 to 200 times, and the coating on the inner wall of the crystallizer is not allowed to fall off. The water quantity of the crystallizer is controlled at 120m 3 H, current: 200A, frequency: 3.5Hz. The foot roller of the zero section of the secondary cooling water system and the output rollers of the other secondary cooling sections always work normally, and the specific water amount (L/Kg): 0.70; the distribution ratio is as follows: and (3) region I: and (II) zone: zone III: zone iv =45%:27%:17%: and 11 percent. The gas spray nozzles and the water nozzles of all the sections are smooth, so that the uniform cooling of all the surfaces of the casting blank is ensured. End electromagnetic stirring current: 260A, frequency: 7Hz. The middle ladle baking temperature is more than 1000 ℃, the immersion water gap, the big ladle long water gap are used after being baked in advance, and the temperature is more than 600 ℃. And the ladle long nozzle is cast under the protection of argon seal. Six lower nozzles (submerged nozzles) of the tundish must be aligned and centered with the upper opening of the crystallizer. The ladle long nozzle adopts argon seal protection pouring, and the argon flow is controlled, so that the ladle does not expose the tapping liquid surface. Pouring the ladle: after the middle package is aligned, the big package is used as a heat preservation agent. The slag is not added too early so as to avoid slag mixing and recarburization. The tundish liquid surface is required to be free from red leakage (particularly in an impact area) in the pouring process. Pouring the tundish, and pouring when the tundish liquid level reaches 400 mm. The pull speed is started to be 0.6-0.7m/min. The pulling speed of the rest furnaces is controlled to be 1.9m/min +/-0.1 m/min. Measuring the temperature of the tundish: pouring for 5 minutes and measuring the temperature once. After which the temperature was measured every 10 minutes. The liquidus temperature of SWRH82B hypereutectoid steel is 1463 ℃ and the value exceeding the solidification temperature is 20-30 ℃. The liquid level of the tundish cannot be lower than 800mm during normal pouring. And (4) slag is produced in the ladle nozzle steel flow, and the ladle nozzle steel flow is immediately closed. The pouring liquid level of the tundish is not less than 250mm. Casting blankThe head blank is cut to be more than 5m, and the tail blank is cut to be more than 3m. When the steel ladle in each procedure is off-line in the production process, the off-station temperature (less than or equal to 20 ℃) can be properly increased according to the condition of the steel ladle and other abnormal conditions, the continuous casting billet can be conveyed in a red mode or slowly cooled, the continuous casting billet is required to be placed in a special slow cooling pit or a special slow cooling area in a workshop during slow cooling, the casting billet temperature is greater than or equal to 450 ℃ when the continuous casting billet enters the slow cooling area, and the slow cooling time is greater than or equal to 36 hours.
Taking the cross section of a casting blank to carry out casting blank segregation test, taking points on the casting blank according to the shapes of cross and diagonal lines, as shown in figure 1, carrying out test by a chemical method after sampling, and carrying out relative comparison with smelting components, wherein the result is shown in figure 2, the center carbon segregation index is between 0.94 and 1.05, and the center segregation is obviously improved.
Temperature of the heating section: 970-1020 ℃, temperature of soaking section: 1150-1200 deg.C, and heating to ensure proper adjustment of initial rolling temperature. Keeping the temperature for 2-3 h, and then rolling at the initial rolling temperature of 970 +/-20 ℃ at the rolling speed of 10-110 m/s. The Ac1 temperature is 716 ℃ measured according to CCT curve, the water quantity of the water tank is controlled before and after spinning, the temperature is below Ac1, the precipitation of secondary reticular cementite is restrained, and the center carbon segregation can be improved.
TABLE 1 chemical composition/% of SWRH82B hypereutectoid steel
Specific examples C Si Mn P S Cr V
Specific example 1 0.82 0.24 0.68 0.011 0.002 0.19 0.012
Specific example 2 0.84 0.26 0.70 0.009 0.003 0.20 0.015
Specific example 3 0.82 0.28 0.71 0.008 0.005 0.19 0.013
Specific example 4 0.81 0.29 0.73 0.011 0.003 0.20 0.014
Specific example 5 0.83 0.23 0.69 0.007 0.004 0.21 0.012
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims (4)

1. A control method for improving the center carbon segregation of hypereutectoid steel produced by a small square billet section is characterized by comprising the following steps of:
the water quantity of the crystallizer is controlled at 120m 3 H, current: 200A, frequency: 3.5Hz;
the foot roller of the zero section of the second cooling water system and the output rollers of the other second cooling sections are always in normal operation, and the specific water quantity is as follows: 0.70L/Kg; the distribution ratio is as follows: and (3) region I: and (2) zone II: zone III: zone iv =45%:27%:17%:11 percent;
the gas spray nozzles and the water spray nozzles of all the sections are smooth for sure, so that all the surfaces of the casting blank are uniformly cooled;
end electromagnetic stirring current: 260A, frequency: 7Hz;
baking tundish at a temperature of more than 1000 deg.C, using submerged nozzle and ladle long nozzle after baking in advance, and more than 600 deg.C; the ladle long nozzle is cast under the protection of argon seal; six water outlets of the tundish are necessarily aligned and centered with the upper opening of the crystallizer; the ladle long nozzle adopts argon seal protection pouring, the argon flow is controlled, and the ladle does not expose the tapping liquid surface; pouring the ladle: after the middle package is aligned, the big package is used as a heat preservation agent; the slag is not added too early so as to avoid slag mixing and recarburization; the liquid level of the tundish is required to be free from red leakage in the pouring process; pouring the tundish, wherein the pouring can be carried out when the tundish liquid level reaches 400 mm; starting the pull speed is 0.6-0.7m/min; controlling the pulling speed of the rest furnaces to be 1.9m/min +/-0.1 m/min; the liquid level of the tundish cannot be lower than 800mm during normal pouring; the ladle nozzle steel flows with slag and is immediately closed; the pouring liquid level of the tundish is not less than 250mm;
the head billet cutting of the casting blank is more than 5m, and the tail billet cutting is more than 3m; when the steel ladles in all working procedures are off-line in the production process, the off-station temperature is properly increased according to the conditions of the steel ladles, the continuous casting billets are subjected to red conveying or slow cooling, the continuous casting billets are required to be placed in a special slow cooling area in a workshop during slow cooling, the temperature of the casting billets is more than or equal to 450 ℃ when the continuous casting billets enter the slow cooling area, and the slow cooling time is more than or equal to 36 hours;
temperature of the heating section: 970-1020 ℃, temperature of soaking section: 1150-1200 deg.C, heating to ensure proper adjustment of initial rolling temperature; keeping the temperature for 2-3 h, and then rolling at the rolling temperature of 970 +/-20 ℃ at the rolling speed of 10-110 m/s; the Ac1 temperature is 716 ℃ measured according to CCT curve, the water quantity of the water tank is controlled before and after spinning, the temperature is below Ac1, the precipitation of secondary reticular cementite is restrained, and the center carbon segregation is improved.
2. The method for controlling the center carbon segregation in hypereutectoid steel production from small billet sections according to claim 1, wherein the number of times of using the crystallizer is controlled within a range of 50 to 200 times.
3. The method for controlling the center carbon segregation in hypereutectoid steel for improving the production of small billet sections as set forth in claim 1, wherein the coating on the inner wall of the crystallizer does not fall off.
4. The method for controlling the center carbon segregation of hypereutectoid steel produced by improving the billet section according to claim 1, wherein the tundish temperature is measured by: the casting was started for 5 minutes and the temperature was measured every 10 minutes thereafter.
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CN115323109B (en) * 2022-07-14 2024-01-30 包头钢铁（集团）有限责任公司 Control method for continuous casting center cracks of steel billets for large-specification and high-niobium-content steel bars

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CN104498805A (en) * 2014-12-29 2015-04-08 首钢总公司 Production method of high-carbon low-nitrogen steel for strand wires
CN106735025A (en) * 2017-02-09 2017-05-31 首钢总公司 A kind of control method of prestress steel continuous small-billet casting center segregation
CN107142417A (en) * 2017-07-07 2017-09-08 中天钢铁集团有限公司 A kind of file carbon, C steel wire rod and preparation method thereof
CN111283156A (en) * 2020-03-23 2020-06-16 江苏利淮钢铁有限公司 Method for reducing segregation in casting process of continuous casting square billet for gear
CN112410650A (en) * 2020-10-30 2021-02-26 建龙北满特殊钢有限责任公司 Control method for improving low-power quality and segregation index of high-carbon chromium bearing steel

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02151354A (en) * 1988-12-02 1990-06-11 Nippon Steel Corp Method for improving segregation in continuously cast slab
CN104498805A (en) * 2014-12-29 2015-04-08 首钢总公司 Production method of high-carbon low-nitrogen steel for strand wires
CN106735025A (en) * 2017-02-09 2017-05-31 首钢总公司 A kind of control method of prestress steel continuous small-billet casting center segregation
CN107142417A (en) * 2017-07-07 2017-09-08 中天钢铁集团有限公司 A kind of file carbon, C steel wire rod and preparation method thereof
CN111283156A (en) * 2020-03-23 2020-06-16 江苏利淮钢铁有限公司 Method for reducing segregation in casting process of continuous casting square billet for gear
CN112410650A (en) * 2020-10-30 2021-02-26 建龙北满特殊钢有限责任公司 Control method for improving low-power quality and segregation index of high-carbon chromium bearing steel

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