CN111761039A - Longitudinal crack control process for wide slab - Google Patents
Longitudinal crack control process for wide slab Download PDFInfo
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- CN111761039A CN111761039A CN201910257036.0A CN201910257036A CN111761039A CN 111761039 A CN111761039 A CN 111761039A CN 201910257036 A CN201910257036 A CN 201910257036A CN 111761039 A CN111761039 A CN 111761039A
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- crystallizer
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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
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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
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/111—Treating the molten metal by using protecting powders
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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
- B22D11/165—Controlling or regulating processes or operations for the supply of casting powder
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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
- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
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- Engineering & Computer Science (AREA)
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Abstract
The invention discloses a longitudinal crack control process for a wide slab, which relates to the technical field of continuous casting processes, and is characterized in that the manganese-sulfur ratio is improved by reducing the mass fraction of sulfur, manganese and sulfur are combined to generate manganese sulfide, and the manganese sulfide is a plastic inclusion and can effectively reduce the crack sensitivity; the high-alkalinity casting powder has lower heat conductivity and higher crystallization rate, and can effectively make up for the surface crack defect of a casting blank caused by peritectic reaction; the cooling intensity of the crystallizer is properly reduced, so that the non-uniformity of cooling can be effectively relieved, and a relatively uniform blank shell is obtained; the overall taper of the crystallizer is set in a proper interval, so that the serious abrasion of the blank shell and the copper plate caused by overlarge overall taper is avoided, the condition that the gap between the primary blank shell and the copper plate is enlarged caused by undersize taper is also avoided, the primary blank shell is not effectively supported, the two side surfaces of a casting blank are bulged, and the occurrence rate of longitudinal cracks can be greatly reduced by the arrangement.
Description
Technical Field
The invention relates to the technical field of continuous casting processes, in particular to a longitudinal crack control process for a wide slab.
Background
The longitudinal cracks of the continuous casting slabs are main defects influencing the yield of a casting machine and the yield of casting blanks, seriously cause steel leakage or casting blank scrap, influence the operation rate and the metal yield of the casting machine, and disturb the production plan while increasing the production cost.
No. 1 wide slab continuous casting machine of the first south steel plant adopts the austenite-steel union technology, and the problem of surface longitudinal cracks is difficult to solve since the production is put into production. The wide slab blank produced by the casting machine has a larger section, the width is 3250mm, the thickness is 150mm, the wide slab blank is one of the widest continuous casting machines put into production in the world at present, and the width-thickness ratio of the wide slab blank reaches 21.7. Compare with conventional slab, super wide slab width-thickness ratio is big, has increased continuous casting billet surface quality control's the degree of difficulty, and the concrete expression does: because the flow field in the crystallizer is not uniform, the transverse temperature difference of the blank shell is large, the heat flow distribution is not uniform, and the slab has larger tensile stress along the horizontal direction of the wide edge in the solidification process, which is increased along with the increase of the width of the casting blank, so that the slab is easier to generate surface longitudinal cracks compared with the common slab; the temperature distribution deviation of the crystallizer in the width direction of the liquid level is large, the uniformity of a slag film is poor, the quality control difficulty is large, and the requirement on the adaptability of the casting powder is strict; the uniformity of water distribution in the width direction of the secondary cooling system has great influence on the cross section quality of the casting blank.
The production of such a wide slab is more likely to cause the occurrence of longitudinal cracks.
Disclosure of Invention
The invention aims to solve the technical problem that longitudinal cracks are more easily generated during production due to the fact that the width and the thickness of a wide plate blank are high.
In order to solve the technical problem, the invention provides a longitudinal crack control process for a wide slab, which comprises the following steps:
in the continuous casting process, steel grade with the manganese-sulfur ratio of 30-35 when the carbon content is within the range of 0.10-0.16% is adopted;
adopting covering slag with alkalinity within the range of 1.19-1.31;
controlling the cooling intensity of the wide surface of the crystallizer at 5100-;
the total taper of the crystallizer is set to be 1.05-1.10%/m.
The technical effects are as follows: because the sulfur and the iron can form ferrous sulfide, the ferrous sulfide and the iron can form low melting point (985 ℃) hot brittle eutectic and are separated out at a crystal boundary, the higher the mass fraction of the sulfur is, the smaller the stress borne by the formed blank shell is, the blank shell with high mass fraction of the sulfur is easy to form cracks under the actions of thermal stress, friction force, ferrostatic pressure and the like, the manganese-sulfur ratio is improved by reducing the mass fraction of the sulfur, and because the manganese is combined with the sulfur to generate manganese sulfide, the manganese sulfide is a plastic inclusion, and the sensitivity of the cracks can be effectively reduced; the steel grade with the carbon mass fraction of 0.10-0.16% belongs to medium carbon steel, so that the casting powder with higher alkalinity is adopted, and the casting powder with high alkalinity has lower heat conductivity and higher crystallization rate, so that the defect of casting blank surface cracks caused by peritectic reaction can be effectively compensated; the cooling intensity of the crystallizer is properly reduced, so that the non-uniformity of cooling can be effectively relieved, and a relatively uniform blank shell is obtained; the overall taper of the crystallizer is too large, the blank shell and the copper plate are seriously abraded, the blank drawing resistance is large, transverse cracks are easily generated on the surface of the casting blank, the taper is too small, the gap between the primary blank shell and the copper plate is enlarged in a denaturation mode, heat is not transferred disadvantageously, the primary blank shell cannot be effectively supported, two side faces of the casting blank are bulged, the liquid molten steel at the center part has drawing force, longitudinal cracks are generated in the middle area of the surface of the casting blank, the overall taper is enabled to be in a proper interval due to the arrangement of the overall taper value of the crystallizer, the two adverse conditions are not easily generated, and the occurrence rate of longitudinal cracks can be greatly reduced through the arrangement.
The technical scheme of the invention is further defined as follows: the melting point of the covering slag is set to be 30-50 ℃ lower than the melting points of the conventional slab and the thick slab.
Furthermore, the water inlet temperature of the crystallizer is set to be 31-39 ℃, and the water flow speed in the crystallizer is set to be 6-8 m/s.
The invention has the beneficial effects that:
(1) according to the invention, because the width and thickness of the wide plate continuous casting machine are larger, the surface area of the upper opening of the crystallizer is smaller than that of a conventional plate blank and a thick plate blank, so that the phenomenon of bridging of the protective slag is easy to occur near the submerged nozzle on the liquid level of the crystallizer, and the poor melting of the protective slag can be caused, and the melting point of the protective slag is set to be 30-50 ℃ lower than that of the conventional plate blank and the thick plate blank, so that the situation can be effectively avoided, and the wide plate continuous casting machine is more suitable for on-site;
(2) in the invention, when the crystallizer is cooled too weakly, the thickness of the blank shell is reduced, after the blank shell is taken out of the crystallizer, the blank shell is difficult to resist the static pressure of molten steel, so that the blank shell bulges in the gap of the roller, the liquid level of the crystallizer periodically fluctuates, the slag discharging uniformity of the protective slag is influenced, and finally, the longitudinal cracks on the surface of the plate blank can be generated, and the cooling strength in the crystallizer can be reduced by setting the water inlet temperature, the water flow speed and the water inlet and outlet temperature difference of the crystallizer, so that the stress can be fully released, and the possibility of cracks can be greatly reduced.
Detailed Description
Example 1: the process for controlling the longitudinal cracks of the wide plate blank provided by the embodiment comprises the following steps:
in the continuous casting process, steel grade with the manganese-sulfur ratio of 30 when the carbon content fraction is within the range of 0.10-0.16% is adopted;
adopting covering slag with alkalinity within 1.19, wherein the melting point of the covering slag is set to be 30 ℃ lower than that of the conventional slab and the thick slab;
controlling the cooling intensity of the wide surface of the crystallizer to be 5100L/min and the cooling intensity of the narrow surface to be 250L/min, setting the water inlet temperature of the crystallizer to be 31 ℃, and setting the water flow rate in the crystallizer to be 6 m/s;
the overall taper of the crystallizer was set to 1.05%/m.
Example 2: the process for controlling the longitudinal cracks of the wide plate blank provided by the embodiment comprises the following steps:
in the continuous casting process, steel grade with the manganese-sulfur ratio of 33 when the carbon content fraction is within the range of 0.10-0.16% is adopted;
adopting covering slag with alkalinity within 1.26, wherein the melting point of the covering slag is 40 ℃ lower than that of the conventional slab and the thick slab;
controlling the cooling intensity of the wide surface of the crystallizer to 5200L/min and the cooling intensity of the narrow surface to 300L/min, setting the water inlet temperature of the crystallizer to 35 ℃, and setting the water flow rate in the crystallizer to 7 m/s;
the overall taper of the crystallizer was set to 1.10%/m.
Example 3: the process for controlling the longitudinal cracks of the wide plate blank provided by the embodiment comprises the following steps:
in the continuous casting process, steel grade with the manganese-sulfur ratio of 35 when the carbon content fraction is within the range of 0.10-0.16% is adopted;
adopting covering slag with alkalinity within 1.31, wherein the melting point of the covering slag is set to be 50 ℃ lower than that of the conventional slab and the thick slab;
controlling the cooling intensity of the wide surface of the crystallizer to be 5300L/min and the cooling intensity of the narrow surface to be 350L/min, setting the water inlet temperature of the crystallizer to be 39 ℃, and setting the water flow rate in the crystallizer to be 8 m/s;
the overall taper of the crystallizer was set to 1.10%/m.
Comparative example: wide plate blanks produced by a moving steel making branch plant.
The performance comparison experiments of the examples 1 to 3 and the comparative example are carried out, the performances are determined according to the national standard, the experimental conditions and other experimental materials are the same, and the test results are shown in the table 1:
| test items | Example 1 | Example 2 | Example 3 | Comparative example |
| Temperature difference/DEG C of inlet and outlet water of crystallizer | 7.1 | 7.8 | 8.4 | 9.1 |
| Fluctuation/mm of liquid level | ±4.7 | ±4.8 | ±4.9 | ±5.3 |
| Incidence of longitudinal cracking | 0.40％ | 0.47％ | 0.53％ | 1.05％ |
| Wide plate rate of change | 0.31％ | 0.42％ | 0.49％ | 0.78％ |
TABLE 1
As can be seen from Table 1, compared with the comparative example, the wide plate blank produced by the invention has the advantages of smaller temperature difference of the inlet and outlet water of the crystallizer, smaller fluctuation range of the liquid level, lower longitudinal crack incidence rate and lower wide plate improvement rate.
Because the sulfur and the iron can form ferrous sulfide, the ferrous sulfide and the iron can form low melting point (985 ℃) hot brittle eutectic and are separated out at a crystal boundary, the higher the mass fraction of the sulfur is, the smaller the stress borne by the formed blank shell is, the blank shell with high mass fraction of the sulfur is easy to form cracks under the actions of thermal stress, friction force, ferrostatic pressure and the like, the manganese-sulfur ratio is improved by reducing the mass fraction of the sulfur, and because the manganese is combined with the sulfur to generate manganese sulfide, the manganese sulfide is a plastic inclusion, and the sensitivity of the cracks can be effectively reduced; the steel grade with the carbon mass fraction of 0.10-0.16% belongs to medium carbon steel, so that the casting powder with higher alkalinity is adopted, and the casting powder with high alkalinity has lower heat conductivity and higher crystallization rate, so that the defect of casting blank surface cracks caused by peritectic reaction can be effectively compensated; the cooling intensity of the crystallizer is properly reduced, so that the non-uniformity of cooling can be effectively relieved, and a relatively uniform blank shell is obtained; the overall taper of the crystallizer is too large, the blank shell and the copper plate are seriously abraded, the blank drawing resistance is large, transverse cracks are easily generated on the surface of the casting blank, the taper is too small, the gap between the primary blank shell and the copper plate is enlarged in a denaturation mode, heat is not transferred disadvantageously, the primary blank shell cannot be effectively supported, two side faces of the casting blank are bulged, the liquid molten steel at the center part has drawing force, longitudinal cracks are generated in the middle area of the surface of the casting blank, the overall taper is enabled to be in a proper interval due to the arrangement of the overall taper value of the crystallizer, the two adverse conditions are not easily generated, and the occurrence rate of longitudinal cracks can be greatly reduced through the arrangement.
Because the wide and thick ratio of the wide plate continuous casting machine is large, the surface area of the upper opening of the crystallizer is smaller than that of the conventional plate blank and the thick plate blank, so that the phenomenon of bridging of the covering slag easily occurs near the submerged nozzle of the liquid level of the crystallizer, the covering slag is not melted well, the melting point of the covering slag is set to be 30-50 ℃ lower than that of the conventional plate blank and the thick plate blank, the situation can be effectively avoided, and the wide plate continuous casting machine is more suitable for on-site production conditions.
When the crystallizer is cooled too weakly, the thickness of the blank shell is reduced, after the blank shell is taken out of the crystallizer, the blank shell is difficult to resist the static pressure of molten steel, so that the blank shell expands in the gap between rollers, the liquid level of the crystallizer periodically fluctuates, the slag discharging uniformity of the covering slag is influenced, and finally longitudinal cracks on the surface of a plate blank can be generated, and the cooling strength in the crystallizer can be reduced by setting the water inlet temperature, the water flow speed and the water inlet and outlet temperature difference of the crystallizer, so that the stress can be fully released, and the possibility of cracks can be greatly reduced.
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (3)
1. A longitudinal crack control process for a wide slab is characterized by comprising the following steps: the method comprises the following steps:
in the continuous casting process, steel grades with the manganese-sulfur ratio of 30-35 when the carbon content fraction is within the range of 0.10-0.16% are adopted;
adopting covering slag with alkalinity within the range of 1.19-1.31;
controlling the cooling intensity of the wide surface of the crystallizer at 5100-;
the total taper of the crystallizer is set to be 1.05-1.10%/m.
2. The wide slab longitudinal crack control process of claim 1, wherein: the melting point of the covering slag is set to be 30-50 ℃ lower than the melting points of the conventional slab and the thick slab.
3. The wide slab longitudinal crack control process of claim 1, wherein: the water inlet temperature of the crystallizer is set to be 31-39 ℃, and the water flow speed in the crystallizer is set to be 6-8 m/s.
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| CN201910257036.0A CN111761039A (en) | 2019-04-01 | 2019-04-01 | Longitudinal crack control process for wide slab |
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| CN201910257036.0A CN111761039A (en) | 2019-04-01 | 2019-04-01 | Longitudinal crack control process for wide slab |
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Cited By (3)
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| CN112247089A (en) * | 2020-11-05 | 2021-01-22 | 山东钢铁集团日照有限公司 | Method for reducing longitudinal cracks of ultra-wide plate blank continuous casting blank |
| CN112893793A (en) * | 2021-01-19 | 2021-06-04 | 南京钢铁股份有限公司 | Method for controlling corner cracks of wide and thick plate arc-shaped continuous casting billet |
| CN113664173A (en) * | 2021-07-05 | 2021-11-19 | 包头钢铁（集团）有限责任公司 | Control method for longitudinal crack defect of high-strength steel of wide and thick plate blank |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112247089A (en) * | 2020-11-05 | 2021-01-22 | 山东钢铁集团日照有限公司 | Method for reducing longitudinal cracks of ultra-wide plate blank continuous casting blank |
| CN112893793A (en) * | 2021-01-19 | 2021-06-04 | 南京钢铁股份有限公司 | Method for controlling corner cracks of wide and thick plate arc-shaped continuous casting billet |
| CN113664173A (en) * | 2021-07-05 | 2021-11-19 | 包头钢铁（集团）有限责任公司 | Control method for longitudinal crack defect of high-strength steel of wide and thick plate blank |
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Application publication date: 20201013 |