System and method for preventing surface layer recarburization of continuous casting high-pulling-speed casting blank and steel plate

Abstract

The invention belongs to the technical field of ferrous metallurgy steelmaking, and particularly relates to a system and method for preventing surface recarburization of a continuous casting high-pulling-speed casting blank and a steel plate. Comprising an amplitude difference control module, a liquid slag layer adjusting module and a casting powder adding module. The amplitude difference control module is used for controlling the liquid level fluctuation amplitude difference of the crystallizer to be within a preset value; the liquid slag layer adjusting module is used for adjusting the thickness of a liquid slag layer in the casting powder to reach a set value; the covering slag adding module is used for adding covering slag to the edge of the crystallizer. According to the method, the liquid level fluctuation amplitude difference of the crystallizer and the thickness of the liquid slag layer are controlled within a certain range, meanwhile, the slag adding mode of the casting powder in the production process is reasonably adjusted, and therefore the problem that molten steel makes contact with a carbon-rich layer on the top of the liquid slag layer is effectively solved, and the production cost is reduced on the premise that continuous casting high-pulling-speed production is not affected. And recarburization on the surface layer of the casting blank can be prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy and steelmaking, and in particular relates to a system, a method and a steel plate for preventing carbon increase on the surface of a continuous casting high-drawing speed billet. Background Art

[0002] Steel is smelted from iron ore. It is an alloy composed of iron (Fe), carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S) and other small amounts of elements (Cr, V, etc.), also known as iron-carbon alloy. Among them, carbon is a hardening element that helps increase the strength of steel. According to the carbon content, steel can be divided into low-carbon steel, medium-carbon steel and high-carbon steel. Low-carbon steel, especially ultra-low-carbon steel (W(C) <0.06%), has a low carbon content. When it comes into contact with materials with high carbon content under high temperature during continuous casting, the carbon in the material will quickly penetrate into the steel, causing carbon increase.

[0003] Continuous casting is the process of cooling the smelted molten steel into billets through a crystallizer. The molten steel forms a billet shell in the crystallizer, and the upper layer is covered with protective slag. The liquid slag flows into the space between the billet shell and the wall of the crystallizer to play a lubricating role. The crystallizer protective slag is a metallurgical auxiliary material with CaO, SiO2, Al2O3 and alkaline oxides as the main components. Its main function is to lubricate and keep warm. The protective slag contains a certain amount of carbon, usually around 1.0%-10.0%. After the protective slag is added to the surface of the molten steel in the tundish, the carbon will burn at high temperature to form liquid slag, and there will be a carbon-rich layer with a higher carbon content on the upper layer of the liquid slag. Its structure is as follows: Figure 2 As shown in the figure, after the protective slag enters the crystallizer and contacts with the high-temperature molten steel, it is in a dynamic equilibrium process of continuous melting and consumption. The carbon in the powder slag will continue to burn at high temperature and enter the molten slag layer after melting. The layer with the highest carbon content is the carbon-rich layer on the top of the liquid slag layer, reaching more than 20%. The carbon content of the liquid slag layer itself is only about 0.2%. Figure 2 It can be seen that the carbon content of the carbon-rich layer is much higher than that of the slag itself.

[0004] High drawing speed is an important technical development direction for efficient continuous casting production. In high-drawing speed continuous casting production, the liquid level in the crystallizer fluctuates greatly. The billet shell contacts the carbon-rich layer on the top of the protective slag liquid slag layer, and even rolls the powder slag into the steel. This is the main reason for carbon increase in the billet shell. The carbon content on the surface of the billet increases, which has a great impact on the billet structure and will further lead to product quality problems.

[0005] At present, the prevention of carbon increase on the surface of the ingot is usually solved by significantly reducing the carbon content of the mold slag, or even using carbon-free mold slag, or reducing the continuous casting speed. However, there are the following problems: (1) Carbon is an important component of the mold slag. A significant reduction in the carbon content may cause the mold slag to melt too quickly, resulting in defects such as slag curling in the ingot; (2) Reducing the casting speed can ensure a stable liquid level, reduce the contact between the ingot shell and the carbon-rich layer or the powder slag layer, and prevent carbon increase in the ingot shell. However, after the casting speed is reduced, the ingot production efficiency is reduced and cannot meet the requirements of high casting speed production. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of the prior art that carbon increase on the surface of the ingot is prevented by reducing the carbon content or reducing the drawing speed during the continuous casting production process, thereby causing slag rolling on the ingot or leading to low production efficiency, and thus propose a system, method and steel plate for preventing carbon increase on the surface of the ingot during continuous casting and high drawing speed. The method of the present invention controls the crystallizer liquid level fluctuation amplitude difference and the thickness of the liquid slag layer within a certain range, and at the same time reasonably adjusts the slag adding method of the protective slag during the production process, thereby effectively solving the problem of contact between the molten steel and the carbon-rich layer on the top of the liquid slag layer, and can prevent carbon increase on the surface of the ingot without affecting the continuous casting and high drawing speed production.

[0007] The first aspect of the present invention proposes a system for preventing carbon increase on the surface of continuous casting high-speed ingots, the system comprising: an amplitude difference control module, a liquid slag layer adjustment module and a protective slag adding module; the amplitude difference control module is used to control the amplitude difference of the crystallizer liquid level fluctuation within a preset value; the liquid slag layer adjustment module is used to adjust the liquid slag layer thickness in the protective slag to a set value; the protective slag adding module is used to add protective slag to the edge of the crystallizer.

[0008] Preferably, the specific method for controlling the crystallizer liquid level fluctuation amplitude difference within a preset value is: placing the electromagnetic braking device at the outlet of the submerged water inlet, setting the electromagnetic braking intensity according to the casting machine pulling speed or the stopper rod opening, so that the crystallizer liquid level fluctuation amplitude difference is controlled within the preset value.

[0009] Preferably, the specific method for setting the electromagnetic braking strength according to the casting machine pulling speed is: under the same cross-section condition, the electromagnetic braking strength = A*casting machine pulling speed, wherein A is a constant.

[0010] Preferably, the specific method for setting the electromagnetic braking strength according to the stopper rod opening is: electromagnetic braking strength = K*(stopper rod opening) 2 , where K is an empirical constant.

[0011] Preferably, the specific method for adjusting the thickness of the liquid slag layer in the protective slag to reach a set value is: by lowering the melting point of the protective slag and increasing the melting rate of the protective slag, so that the thickness of the liquid slag layer in the protective slag reaches a set value; the specific method for increasing the melting rate of the protective slag is: reducing the basicity and Al2O3 content of the protective slag.

[0012] Preferably, the liquid slag layer adjustment module also includes reducing the carbon content in the protective slag. In the liquid slag layer adjustment module, the melting point of the protective slag is 1050-1150°C, the basicity of the protective slag is 0.85-0.90, the Al2O3 content is 2.0-4.0%, the carbon content is 1.0-4.0%, and the melting speed of the protective slag is 18-22s.

[0013] Preferably, the protective slag adding module also includes adding protective slag to the middle of the crystallizer; based on the total weight of the protective slag as 100 weight %, 70-80 weight % of the protective slag is added to the edge of the crystallizer, and 20-30 weight % of the protective slag is added to the middle of the crystallizer.

[0014] The second aspect of the present invention proposes a method for preventing carbon increase on the surface of continuous casting high-speed ingots in the above-mentioned system, which includes: controlling the difference in the fluctuation amplitude of the liquid level in the crystallizer within a preset value; adjusting the thickness of the liquid slag layer in the protective slag to reach a set value; and adding protective slag to the edge of the crystallizer.

[0015] Preferably, the crystallizer liquid level fluctuation amplitude difference is controlled to be ≤5mm; and the thickness of the liquid slag layer in the protective slag is adjusted to 15-20mm.

[0016] The third aspect of the present invention provides a steel plate produced according to the above-mentioned method for preventing carbon increase on the surface of a continuous casting high-drawing speed ingot.

[0017] The system, method and steel plate for preventing carbon increase on the surface of continuous casting high-speed casting slabs according to the present invention have at least the following beneficial effects:

[0018] (1) In the present invention, the crystallizer liquid level fluctuation amplitude difference and the liquid slag layer thickness are controlled within a certain range, and the slag adding method of the protective slag in the production process is reasonably adjusted, thereby effectively solving the problem of the contact between the molten steel and the carbon-rich layer on the top of the liquid slag layer. Under the premise of not affecting the high-speed continuous casting production, the primary billet shell is effectively prevented from contacting the carbon-rich layer on the top of the liquid slag layer, and the occurrence of carbon increase on the surface of the billet is suppressed. At the same time, the generation of defects such as billet slag curling caused by significantly reducing the carbon content of the protective slag is avoided;

[0019] (2) In the present invention, by using electromagnetic braking during the continuous casting process, the impact strength of the molten steel stream flowing out of the water inlet on the narrow surface of the crystallizer can be significantly reduced, thereby reducing the fluctuation amplitude of the liquid level and making it closer to the set value;

[0020] (3) Under the preferred conditions, by reasonably reducing the basicity, Al2O3 content and carbon content of the protective slag, and lowering the melting point of the protective slag within a certain range, the thickness of the liquid slag layer can reach the set value, while reducing the probability and amount of carburization when the carbon-rich layer contacts the molten steel, thereby effectively reducing the possibility of carbon increase on the surface of the ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A structural block diagram of a system for preventing carbon increase on the surface of a continuous casting high-speed casting slab according to the present invention;

[0022] Figure 2 This is a layered structure diagram of the mold slag after it enters the crystallizer and melts;

[0023] Figure 3 It is a structural diagram of the narrow side edge portion (narrow edge) and the middle portion of the present invention;

[0024] Figure 4 This is a scanning electron microscope image of the surface structure of the ingot prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0026] Low carbon steel, especially ultra-low carbon steel (W(C)<0.06%), has a low carbon content. When it contacts with a material with a high carbon content under high temperature in continuous casting, the carbon in the material will quickly penetrate into the steel, causing carbon increase. Therefore, the present invention prevents the primary billet shell from contacting with the carbon-rich layer on the top of the liquid slag layer, thereby inhibiting the occurrence of carbon increase on the surface of the billet.

[0027] The first aspect of the present invention provides a system for preventing carbon increase on the surface of a continuous casting high-speed casting billet, such as Figure 1 As shown, the system includes: an amplitude difference control module, a liquid slag layer adjustment module and a protective slag adding module; the amplitude difference control module is used to control the crystallizer liquid level fluctuation amplitude difference within a preset value; the liquid slag layer adjustment module is used to adjust the liquid slag layer thickness in the protective slag to reach a set value; the protective slag adding module is used to add protective slag to the edge of the crystallizer.

[0028] In a specific embodiment of the system described in the present invention, a specific method for controlling the difference in amplitude of the crystallizer liquid level fluctuation within a preset value is as follows: placing an electromagnetic braking device at the outlet of the submerged water inlet, specifically, taking the outlet of the submerged water inlet as the center line, and the outlet in this article is the range within 250 mm along the center line along the crystallizer wall, and then setting the electromagnetic braking intensity according to the casting machine pulling speed or the stopper rod opening, thereby ensuring that the flow rate of the outlet stream is uniformly stable within a certain range, so that the difference in amplitude of the crystallizer liquid level fluctuation is controlled within a preset value.

[0029] In a specific implementation of the system of the present invention, a specific method for setting the electromagnetic braking strength according to the casting machine pulling speed is: under the same cross-section condition, electromagnetic braking strength = A*casting machine pulling speed, wherein A is a constant.

[0030] In a specific embodiment of the system of the present invention, the specific method for setting the electromagnetic braking strength according to the stopper rod opening is: electromagnetic braking strength = K*(stopper rod opening) 2 , where K is an empirical constant.

[0031] Since different types of steel have different melting temperatures, ranging from 1400-1530°C, the higher the melting temperature of the steel, the melting temperature of the protective slag can be appropriately increased, and the lower the melting temperature of the steel, the lower the melting temperature of the protective slag should be. In a specific implementation of the system of the present invention, the specific method for adjusting the thickness of the liquid slag layer in the protective slag to reach a set value is: according to the type of steel being cast, the protective slag components are redesigned. On the basis of its normal slag properties, the present invention reduces the melting point of the protective slag and increases the melting rate of the protective slag, which is conducive to forming a thicker liquid slag layer, so that the thickness of the liquid slag layer in the protective slag reaches the set value.

[0032] Specifically, on the basis of normal mold slag performance, the specific method for increasing the melting speed of the mold slag is: reducing the basicity and Al2O3 content of the mold slag, thereby increasing the thickness of the liquid slag layer.

[0033] In a specific embodiment of the system of the present invention, the liquid slag layer adjustment module also includes reducing the carbon content in the protective slag. Appropriately reducing the carbon content is a method for effectively reducing the carbon content of the "carbon-rich layer", thereby reducing the probability and amount of carburization when the "carbon-rich layer" comes into contact with molten steel.

[0034] In this article, the normal slag melting point is 1120-1220°C, the basicity is 0.9-1.0, the Al2O3 content is 3.0-5.0%, the carbon content is 2.0-5.0%, and the melting speed is 25s. In a preferred embodiment of the system of the present invention, in the liquid slag layer adjustment module, the melting point of the protective slag is 1050-1150°C, the basicity of the protective slag is 0.85-0.90, the Al2O3 content is 2.0-4.0%, the carbon content is 1.0-4.0%, and the melting speed of the protective slag is 18-22s.

[0035] In the preferred embodiment of the system of the present invention, the principle of "adding at the edge and adding appropriately in the middle" is strictly implemented, and the protective slag adding module also includes adding protective slag in the middle of the crystallizer; based on the total weight of the protective slag as 100 weight%, 70-80 weight% of the protective slag is added to the edge of the crystallizer, and 20-30 weight% of the protective slag is added to the middle of the crystallizer. In this article, the edge of the crystallizer (i.e., the narrow side edge of the crystallizer) generally refers to the position 5-10mm away from the edge of the crystallizer, and the middle is around the submerged water nozzle, such as Figure 3 shown.

[0036] The second aspect of the present invention proposes a method for preventing carbon increase on the surface of continuous casting high-speed ingots in the above-mentioned system, which includes: controlling the difference in the fluctuation amplitude of the liquid level in the crystallizer within a preset value; adjusting the thickness of the liquid slag layer in the protective slag to reach a set value; and adding protective slag to the edge of the crystallizer.

[0037] In a specific implementation of the method of the present invention, by measuring the positions of the peaks and troughs under different process conditions, the best control level is currently 5mm. Therefore, the crystallizer liquid level fluctuation amplitude difference is controlled to be ≤5mm. When the crystallizer liquid level fluctuation amplitude difference is ≤5mm, the steel liquid level in the entire crystallizer is in a stable state, which is conducive to a more stable slag layer on the steel liquid, preventing the steel liquid from contacting the "carbon-rich layer" on the top of the liquid slag layer, thereby inhibiting the occurrence of carbon increase on the surface of the ingot.

[0038] In a specific implementation manner of the method described in the present invention, the thickness of the liquid slag layer in actual production is greater than the maximum value of the normal production liquid level fluctuation of 10mm (±5mm) + the maximum value of the difference between the peak and the trough of 5mm, and the sum of the two is ≥15mm. The increase in the thickness of the liquid slag layer means that the distance between the molten steel and the "carbon-rich layer" at the top of the liquid slag layer is greater, thereby preventing the molten steel from contacting the "carbon-rich layer" at the top of the liquid slag layer, avoiding the carbon increase phenomenon; in a preferred implementation manner of the method described in the present invention, the thickness of the liquid slag layer in the protective slag is adjusted to 15-20mm.

[0039] The third aspect of the present invention provides a steel plate produced according to the above-mentioned method for preventing carbon increase on the surface of a continuous casting high-drawing speed ingot.

[0040] The experimental methods or test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0041] Example 1

[0042] The production process of continuous casting ultra-low carbon steel (carbon content 0.03%) with thin slabs with a cross section of 1250*70mm is as follows:

[0043] The electromagnetic brake device is placed at the outlet of the submerged water inlet (25 cm from the outlet of the submerged water inlet along the wall of the crystallizer), the continuous casting speed is 5 m / min, the electromagnetic brake intensity is 280 A, and the liquid level amplitude difference is controlled to 4 mm;

[0044] The melting point of the protective slag is 980°C, the basicity of the protective slag is 0.85, the Al2O3 content in the protective slag is 2.0%, the melting speed of the protective slag is 18s, and the thickness of the liquid slag layer reaches 16mm;

[0045] Based on the total weight of the mold slag being 100 weight %, 70 weight % of the mold slag is added to the edge of the crystallizer, and 30 weight % of the mold slag is added to the middle of the crystallizer;

[0046] The carbon increase on the surface of the ingot disappeared, and after the process was stably applied, the uneven structure of the ingot after hot rolling basically disappeared. After rolling and pickling, there were no stripe defects on the surface, meeting the product quality requirements.

[0047] Example 2

[0048] The production process of continuous casting ultra-low carbon steel (carbon content 0.04%) with thin slabs with a cross section of 1250*70mm is as follows:

[0049] The electromagnetic brake device is placed at the outlet of the submerged water nozzle (25 cm from the outlet of the submerged water nozzle along the wall of the crystallizer), the continuous casting speed is 5 m / min, the electromagnetic brake intensity is 300 A, and the liquid surface amplitude difference is controlled to be 5 mm;

[0050] The melting point of the protective slag is 1050°C, the basicity of the protective slag is 0.90, the Al2O3 content in the protective slag is 3.0%, the melting speed of the protective slag is 20s, and the thickness of the liquid slag layer reaches 18mm;

[0051] Based on the total weight of the mold slag being 100 weight %, 60 weight % of the mold slag is added to the edge of the crystallizer, and 40 weight % of the mold slag is added to the middle of the crystallizer;

[0052] The carbon increase on the surface of the ingot disappeared, and after the process was stably applied, the uneven structure of the ingot after hot rolling basically disappeared. After rolling and pickling, there were no stripe defects on the surface, meeting the product quality requirements.

[0053] Example 3

[0054] The production process of continuous casting ultra-low carbon steel (carbon content 0.05%) with thin slabs with a cross section of 1250*70mm is as follows:

[0055] The electromagnetic brake device is placed at the outlet of the submerged water inlet (25 cm from the outlet of the submerged water inlet along the wall of the crystallizer), the continuous casting speed is 5 m / min, the electromagnetic brake intensity is 280 A, and the liquid surface amplitude difference is controlled to be 5 mm;

[0056] The melting point of the protective slag is 1150°C, the basicity of the protective slag is 0.90, the Al2O3 content in the protective slag is 4.0%, the melting speed of the protective slag is 22s, and the thickness of the liquid slag layer reaches 20mm;

[0057] Based on the total weight of the mold slag being 100 weight %, 50 weight % of the mold slag is added to the edge of the crystallizer, and 50 weight % of the mold slag is added to the middle of the crystallizer;

[0058] The carbon increase on the surface of the ingot disappeared, and after the process was stably applied, the uneven structure of the ingot after hot rolling basically disappeared. After rolling and pickling, there were no stripe defects on the surface, meeting the product quality requirements.

[0059] Comparative Example 1

[0060] The method of Example 1 was followed, except that the liquid level amplitude difference was controlled to be 11 mm, the thickness of the liquid slag layer in the protective slag was adjusted to be 10 mm, and the surface layer of the prepared ingot was observed under a scanning electron microscope. The results are as follows: Figure 4 As shown, from Figure 4 It can be seen that the carbon content in the surface layer of the ingot increases.

[0061] According to the results of Examples 1-3 and Comparative Example 1, it can be seen that the method of the present invention is used to control the crystallizer liquid level fluctuation amplitude difference and the liquid slag layer thickness within a certain range, and at the same time, the slag adding method of the protective slag during the production process is reasonably adjusted, thereby effectively solving the problem of contact between the molten steel and the carbon-rich layer on the top of the liquid slag layer. Under the premise of not affecting the continuous casting high-speed production, the primary billet shell is effectively prevented from contacting the carbon-rich layer on the top of the liquid slag layer, and the occurrence of carbon increase on the surface of the billet is suppressed. At the same time, the generation of defects such as billet slag curling caused by a significant reduction in the carbon content of the protective slag is avoided.

[0062] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A system for preventing carbon increase on the surface of a continuous casting high-speed casting billet, characterized in that: The system comprises: an amplitude difference control module, a liquid slag layer adjustment module and a protective slag adding module; The amplitude difference control module is used to control the crystallizer liquid level fluctuation amplitude difference within a preset value; The liquid slag layer adjustment module is used to adjust the thickness of the liquid slag layer in the protective slag to reach a set value; The protective slag adding module is used to add protective slag to the edge of the crystallizer.

2. The system for preventing carbon increase on the surface of continuous casting high-speed casting billet according to claim 1 is characterized in that: The specific method for controlling the crystallizer liquid level fluctuation amplitude difference within the preset value is: placing the electromagnetic brake device at the outlet of the immersed water inlet, setting the electromagnetic brake intensity according to the casting machine pulling speed or the stopper rod opening, so that the crystallizer liquid level fluctuation amplitude difference is controlled within the preset value.

3. The system for preventing carbon increase on the surface of continuous casting high-speed casting billet according to claim 2, characterized in that: The specific method for setting the electromagnetic braking strength according to the casting machine pulling speed is: under the same cross-section condition, the electromagnetic braking strength = A*casting machine pulling speed, where A is a constant.

4. The system for preventing carbon increase on the surface of continuous casting high-speed casting billet according to claim 2, characterized in that: The specific method for setting the electromagnetic braking strength according to the stopper rod opening is: electromagnetic braking strength = K*(stopper rod opening) 2 , where K is an empirical constant.

5. The system for preventing carbon increase on the surface of continuous casting high-speed casting billet according to claim 1, characterized in that: The specific method of adjusting the thickness of the liquid slag layer in the protective slag to reach the set value is: by lowering the melting point of the protective slag and increasing the melting speed of the protective slag, the thickness of the liquid slag layer in the protective slag reaches the set value; The specific method for increasing the melting speed of the protective slag is to reduce the basicity and Al2O3 content of the protective slag.

6. The system for preventing carbon increase on the surface of continuous casting high-speed casting billet according to claim 5, characterized in that: The liquid slag layer adjustment module also includes reducing the carbon content in the protective slag. In the liquid slag layer adjustment module, the melting point of the protective slag is 1050-1150°C, the basicity of the protective slag is 0.85-0.90, the Al2O3 content is 2.0-4.0%, the carbon content is 1.0-4.0%, and the melting speed of the protective slag is 18-22s.

7. The system for preventing carbon increase on the surface of continuous casting high-speed casting billet according to claim 1, characterized in that: The protective slag adding module further comprises adding protective slag in the middle of the crystallizer; Based on the total weight of the protective slag being 100 weight %, 70-80 weight % of the protective slag is added to the edge of the crystallizer, and 20-30 weight % of the protective slag is added to the middle of the crystallizer.

8. A method for preventing carbon increase on the surface of a continuous casting high-speed casting billet based on the system according to any one of claims 1 to 7, characterized in that: It includes: Control the crystallizer liquid level fluctuation amplitude difference within the preset value; adjust the liquid slag layer thickness in the protective slag to reach the set value; Add protective slag to the edge of the crystallizer.

9. The method for preventing carbon increase on the surface of a continuous casting high-speed casting billet according to claim 8, characterized in that: Control the crystallizer liquid level fluctuation amplitude difference ≤5mm; Adjust the thickness of the liquid slag layer in the protective slag to 15-20mm.

10. A steel plate produced according to the method for preventing carbon increase on the surface of a continuous casting high-drawing speed ingot according to claim 8 or 9.

Images