Method for reducing transition ladle overflow in thin-strip high-carbon steel continuous casting process

Abstract

The invention belongs to the field of thin-strip continuous casting, and relates to a method for reducing transition ladle overflow in the thin-strip high-carbon steel continuous casting process. In the chemical components of the molten steel, C is not less than 0.48%, Al is not more than 0.0020%, and Ca is not less than 0.0020%; the free oxygen content of the primary smelting molten steel before VD vacuum treatment is greater than or equal to 600ppm, and the Al content after VD vacuum treatment is less than or equal to 0.0020%; after the refined molten steel is subjected to LF refining treatment, Ca is greater than or equal to 0.0015%, the free oxygen content is greater than or equal to 60ppm, and Al is less than or equal to 0.0020 The alkalinity R of LF refining final slag is 2.0-2.5, and the content of Al2O3 is smaller than or equal to 3%; in the chemical components of the tundish molten steel, C is not less than 0.48%, Al is not more than 0.0020%, Ca is not less than 0.0010%, and the content of free oxygen is not less than 40ppm; the temperature of a tundish is 1620 + / -10 DEG C; the weight of the transition bag is 100-550 kg; and the pulling speed is 20-55m / min. By optimizing the steelmaking process, adjusting the refining slag system, adjusting the chemical components of the molten steel, adjusting the temperature of the tundish and controlling the tundish operation and the pulling speed when the weight of the transition ladle is increased, the overflow occurrence rate of the transition ladle is effectively reduced when the high-carbon steel is produced by adopting the double-roller thin-strip cast-rolling technology.

Description

Technical Field

[0001] The present invention belongs to the field of thin slab continuous casting, and relates to a method for reducing the overflow of the tundish during the continuous casting of high-carbon thin slabs. Background Art

[0002] The thin slab continuous casting technology is a new type of thin strip steel production process. During the molten steel casting process, the molten steel flows from the ladle through the tundish to the tundish, and is distributed from the tundish to the core nozzle and the twin-roll melt pool. The melt pool is surrounded by a pair of reversely rotating casting rolls and side seals. The molten steel is directly cooled and solidified into a strip on the surface of the casting roll. Compared with the traditional hot rolling process, it has the advantages of simple production process, low energy consumption, and low product cost. However, there are still certain bottlenecks in this technology at present. The main problem is that the overflow rate of the tundish is relatively high during the continuous casting of high-carbon steel. The high-carbon steel molten steel cannot smoothly pass through the tundish and be distributed to the core nozzle and the melt pool, resulting in the inability to continuously produce high-carbon thin slabs.

[0003] Starting from the purpose of reducing the overflow of the tundish during the continuous casting of high-carbon thin slabs, the present invention increases the free oxygen content in the molten steel, controls the tundish temperature, reduces the Al content in the molten steel, modifies the type of Al2O3 inclusions, and reduces the deposition and nodulation rate of inclusions at the distribution nozzle of the tundish, thereby improving the fluidity of the high-carbon steel molten steel and solving the problems of tundish overflow and the inability to continuously produce high-carbon thin slabs. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technologies, the purpose of the present invention is to provide a method for reducing the overflow of the tundish during the continuous casting of high-carbon thin slabs, so as to realize the continuous production of high-carbon thin slabs.

[0005] The technical solution for achieving the purpose of the present invention is as follows:

[0006] The embodiment of the present invention discloses a method for reducing the overflow of the tundish during the continuous casting of high-carbon thin slabs, specifically:

[0007] (1) The free oxygen content in the primary molten steel is ≥600 ppm. The free oxygen in the primary molten steel can effectively reduce the Al content in the molten steel during the subsequent smelting process. The free oxygen content in the primary molten steel ≥600 ppm is an important guarantee for reducing the Al content in the molten steel; the free oxygen content in the tundish molten steel is ≥40 ppm, and the higher the free oxygen content in the tundish, the better the fluidity of the molten steel and the more stable the liquid level of the molten steel in the transfer ladle; due to the composition system of high-carbon steel, it is extremely difficult to have a high free oxygen content in the molten steel. In order to make the free oxygen content in the tundish molten steel ≥40 ppm in the present invention, the free oxygen content of the primary molten steel and the refined molten steel is controlled to ensure the free oxygen content of the molten steel in the tundish. However, considering the difficulty of maintaining a high free oxygen content in the molten steel under the high-carbon composition system, generally, the free oxygen content in the tundish molten steel is ≥40 ppm, and preferably the free oxygen content in the tundish molten steel is ≥60 ppm.

[0008] (2) In the chemical composition of the molten steel at the end of LF refining, Ca ≥ 0.0015%; Wire feeding operation is carried out at the LF refining station, which can modify the inclusions of the Al2O3 system to make them have a lower melting point and weaken the deposition and nodulation of Al2O3 inclusion particles on the inner wall of the tundish nozzle; the reaction among Al2O3, Ca and oxygen in the molten steel is a dynamic equilibrium process. Because the normal casting time per furnace of thin strip high-carbon steel is long (>100 min), a certain amount of Ca element is required in the molten steel, and preferably Ca ≥ 0.0020%.

[0009] (3) The molten steel flows into the molten pool through the tundish and the transfer ladle. The tundish molten steel temperature is controlled at 1620 ± 10 °C; the higher the molten steel temperature, the better the fluidity of the molten steel. In order to avoid the overflow of cold steel nodules at the tundish nozzle in the present invention, the tundish molten steel temperature ≥ 1610 °C. However, too high a molten steel temperature will directly affect the solidification heat load of the molten steel on the surface of the casting roll and the production cost. Therefore, the tundish molten steel temperature generally does not exceed 1630 °C, and preferably the tundish molten steel temperature is 1620 ± 5 °C.

[0010] (4) Control the weight of the molten steel in the transfer ladle to be 100 - 550 kg and the liquid level of the transfer ladle to be 100 - 550 mm. After the molten steel flows from the tundish into the transfer ladle, it must accumulate to a certain weight in the transfer ladle to form a relatively stable liquid level in the transfer ladle, so as to ensure stable casting. However, due to the properties and quality of high-carbon steel molten steel, nodulation and blockage occur at the tundish nozzle of the transfer ladle, which will cause the weight and liquid level of the transfer ladle to continuously rise, resulting in the overflow of the transfer ladle and unplanned stoppage of casting. Therefore, the weight and liquid level of the molten steel in the transfer ladle should not be too high. Considering comprehensively, the present invention controls the weight of the transfer ladle to be 100 - 550 kg and the liquid level of the transfer ladle to be 100 - 550 mm, and preferably the molten steel volume in the transfer ladle is 300 - 500 kg and the liquid level of the transfer ladle is 300 - 500 mm.

[0011] (5) Carry out tundish oxygen supplementation. The composition design of high-carbon steel causes the free oxygen in the tundish molten steel to be continuously consumed during casting, resulting in a continuous decrease in the free oxygen content in the tundish. As the free oxygen content in the molten steel decreases, it will cause an increase in the weight and liquid level of the transition ladle and a tendency for the transition ladle to overflow. Generally, when the weight of the transition ladle > 500 kg, tundish oxygen supplementation is required. Preferably, each time the tundish is supplemented with 3 - 5 m 3 .

[0012] According to the method for reducing the overflow of the transition ladle in the continuous casting process of thin-strip high-carbon steel described above, the occurrence rate of the overflow of the transition ladle in the continuous casting process of thin-strip high-carbon steel can be made not higher than 1.0%.

[0013] The present invention specifically adopts the following technical solutions:

[0014] According to the first aspect of the present invention, a method for reducing the overflow of the transition ladle in the continuous casting process of thin-strip high-carbon steel is proposed. The method includes the following steps:

[0015] (1) The primary steelmaking furnace obtains primary molten steel with a free oxygen content ≥ 600 ppm; the balance is Fe, C, and inevitable residual elements and impurities;

[0016] (2) The primary molten steel with a free oxygen content ≥ 600 ppm is subjected to vacuum treatment in a VD vacuum furnace for more than 25 minutes, and molten steel with Al ≤ 0.0020% is obtained by vacuum treatment;

[0017] (3) The molten steel subjected to VD vacuum treatment is subjected to LF refining treatment. After LF refining treatment, the molten steel has C ≥ 0.48%, Ca ≥ 0.0015%, a free oxygen content ≥ 60 ppm, and Al ≤ 0.0020%; the basicity R of the final slag of LF refining is controlled to be: 2.0 - 2.5, and the Al2O3 content is controlled to be ≤ 3%;

[0018] (4) Control the chemical composition of the tundish molten steel:

[0019] C ≥ 0.48%, Al ≤ 0.0020%, Ca ≥ 0.0010%, and the free oxygen content ≥ 40 ppm;

[0020] The tundish temperature is controlled to be 1620 ± 10 °C;

[0021] (5) The molten steel flows into the molten pool through the tundish and the transition ladle. The weight of the transition ladle is controlled to be 100 - 550 kg, and the liquid level of the transition ladle is controlled to be 100 - 550 mm by using the casting speed and the opening degree of the tundish slide plate;

[0022] (6) Control the casting speed to be 20 - 55 m / min.

[0023] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (2), the high vacuum pressure is controlled to P ≤ 67 Pa.

[0024] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (2), the high vacuum time is controlled to be ≥ 15 min.

[0025] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (3), the lime added per ton of steel is controlled to be 6 - 8 kg, and the fluorite is controlled to be 2 - 3 kg.

[0026] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (3), the tapping temperature of the LF refining is controlled to be 1675 ± 5 °C.

[0027] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (3), the oxygen supplementation per ton of steel is controlled to be 0.75 - 1.0 m 3 。

[0028] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (3), the feeding of calcium wire is controlled to be ≥ 1 m / t.

[0029] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (5), the opening degree of the tundish slide plate is controlled to be 50 - 70%.

[0030] According to the method for reducing the overflow of the tundish in the continuous casting process of thin-strip high-carbon steel of the present invention, preferably, in the step (5), when the weight of the tundish > 500 kg, oxygen supplementation of the tundish is carried out, 3 - 5 m each time 3 。

[0031] According to the second aspect of the present invention, a high-carbon steel is provided. The overflow of the tundish in the production process of the high-carbon steel is controlled by the foregoing method, and the overflow incidence rate of the tundish is less than 1.0%.

[0032] Beneficial technical effects

[0033] Compared with the prior art, the technical concept and corresponding technical solutions of the present invention can at least obtain the following beneficial technical effects:

[0034] By the method of the present invention, the liquid level of the tundish in the continuous casting process of thin-strip high-carbon steel can be stabilized, the overflow phenomenon of the tundish in the continuous casting process of thin-strip high-carbon steel can be greatly avoided, the problem that thin-strip high-carbon steel cannot be continuously cast in multiple furnaces due to the overflow of the tundish is solved, the production continuity of thin-strip high-carbon steel is improved, and the production cost is reduced. Brief Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention and do not limit the present invention.

[0036] Figure 1 It is a schematic diagram of typical curves of the molten steel volume and the tundish liquid level in the tundish during the overflow phenomenon in the twin-roll thin strip continuous casting process of high-carbon steel.

[0037] Figure 2 It is a schematic diagram of typical curves of the molten steel volume and the tundish liquid level in the tundish when no overflow phenomenon occurs during the twin-roll thin strip continuous casting process of high-carbon steel. Detailed Embodiments

[0038] In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0039] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains.

[0040] The following are the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0041] To illustrate the effects of the free oxygen content, Al element content, Ca element content, and tundish molten steel temperature in the tundish on the tundish molten steel weight and overflow situation, the specific comparative examples and examples are shown in Table 1 below:

[0042] Table 1 Key elements, temperature in the tundish, and tundish overflow situation in comparative examples and examples

[0043]

[0044] It can be seen from the data in Table 1 that:

[0045] (1) Analyzing the data of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, it can be seen that when the free oxygen content in the molten steel in the tundish is relatively low (<30 ppm), the overflow ratio of the transition ladle in the twin-roll strip casting production line is relatively high; by increasing the Ca content in the molten steel, the accumulation of molten steel in the transition ladle can be alleviated, but the amount of molten steel in the transition ladle is still relatively large, the liquid level is relatively high, and overflow is likely to occur.

[0046] (2) Analyzing the data of Example 1, Example 2, Example 3 and Example 4, it can be seen that increasing the free oxygen content in the molten steel in the tundish can solve the overflow problem of the transition ladle in the twin-roll strip casting production line, and by increasing the Ca content in the molten steel, the fluidity of the molten steel and the liquid level of the transition ladle can be further improved.

[0047] (3) The above comparative examples and examples illustrate that the method according to the present invention can greatly avoid the overflow phenomenon of the transition ladle during the casting of high-carbon thin strips. Moreover, with the increase of the free oxygen content in the molten steel, the decrease of the Al content, and the guarantee of the Ca content and the molten steel temperature, the fluidity of the molten steel in the transition ladle is improved, and the amount and liquid level of the molten steel in the transition ladle are reduced.

[0048] The above are only specific embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process, characterized in that: The method comprises the following steps: (1) A primary molten steel having a free oxygen content of ≥ 600 ppm is obtained in a primary smelting furnace; the remainder is Fe, C and unavoidable residual elements and impurities; (2) The primary molten steel with a free oxygen content of ≥600 ppm is subjected to vacuum treatment in a VD vacuum furnace for more than 25 minutes to obtain molten steel with Al ≤0.0020% by vacuum treatment; (3) The molten steel after VD vacuum treatment is subjected to LF refining treatment, wherein the molten steel after LF refining treatment has C ≥ 0.48%, Ca ≥ 0.0015%, free oxygen content ≥ 60 ppm, and Al ≤ 0.0020%; the basicity R of the final slag of LF refining is controlled to be: 2.0-2.5, and the Al2O3 content is controlled to be ≤ 3%; (4) Control the chemical composition of molten steel in the tundish: C ≥ 0.48%, Al ≤ 0.0020%, Ca ≥ 0.0010%, free oxygen content ≥ 40ppm; The temperature of the tundish is controlled at 1620±10℃; (5) The molten steel flows into the molten pool through the tundish and transition ladle. The weight of the transition ladle is controlled to be 100-550 kg and the liquid level of the transition ladle is controlled to be 100-550 mm by using the pulling speed and the opening of the tundish slide plate. (6) Control the pulling speed to 20-55 m / min.

2. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to claim 1, characterized in that: In the step (2), the high vacuum pressure is controlled to be P≤67Pa.

3. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to claim 1, characterized in that: In the step (2), the high vacuum time is controlled to be ≥15 min.

4. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to claim 1, characterized in that: In the step (3), the amount of lime added per ton of steel is controlled to be 6-8 kg, and the amount of fluorite added is controlled to be 2-3 kg.

5. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to claim 1, characterized in that: In the step (3), the LF refining steelmaking temperature is controlled to be 1675±5°C.

6. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to claim 1, characterized in that: In the step (3), oxygen supplementation is controlled to be 0.75-1.0 m / ton of steel. 3 .

7. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to claim 1, characterized in that: In the step (3), the calcium wire feeding is controlled to be ≥1m / t.

8. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to claim 1, characterized in that: In the step (5), the opening of the tundish slide plate is controlled to be 50-70%.

9. The method for reducing overflow of a transition ladle in a thin strip high carbon steel continuous casting process according to any one of claims 1 to 8, characterized in that: In the step (5), when the weight of the transition bag is greater than 500 kg, oxygen is added to the intermediate bag for 3 to 5 minutes each time. 3 .

10. A high carbon steel, characterized in that: The production process of the high carbon steel adopts the method according to any one of claims 1 to 9 to control the overflow of the transition ladle, wherein the overflow occurrence rate of the transition ladle is less than 1.0%.

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