Large-section vertical continuous casting cleanliness control method

Abstract

The invention discloses a large-section vertical continuous casting cleanliness control method, which comprises the following control processes: 1) adopting a large-section vertical continuous casting machine, and ensuring that the floating time of inclusions in the solidification process of molten steel is 70-82 minutes; (2) when the first ladle of continuous casting is started and the tundish molten steel is in the range of 5-27 tons, slag absorbing agents are added into an impact area and a casting area at the same time; 100-300 kg of a slag absorbing agent is added into the impact area, and 300-500 kg of a slag absorbing agent is added into the casting area; (3) a modulating wave crystallizer electromagnetic stirring technology is adopted, the electromagnetic stirring current parameter ranges from 150 A to 600 A, and the frequency ranges from 1.0 HZ to 1.5 HZ; and 4) adopting a four-hole SEN immersion depth of 90-130mm. According to the method, secondary oxidation of molten steel in a continuous casting starting process can be effectively reduced, adhesion and aggregation of inclusions at a casting blank dendritic crystal solidification front edge are reduced, the inclusions are dispersed and distributed in the steel grade, and the final grades of the inclusions are as follows: the fineness A is less than or equal to 1.0 grade, the thickness A is less than or equal to 0.5 grade, the fineness B is less than or equal to 1.0 grade, the thickness B is less than or equal to 0.5 grade, the fineness C is less than or equal to 0.5 grade, the thickness C is less than or equal to 0.5 grade, the fineness D is less than or equal to 1.0 grade, and the thickness D is less than or equal to 0.5 grade.

Description

Technical Field

[0001] The invention relates to a continuous casting method, in particular to a large-section vertical continuous casting cleanliness control method. Background Art

[0002] With the continuous development of the steel industry, especially in the field of special steel, many manufacturers have higher and higher requirements for the quality of steel raw materials. Improving the purity of molten steel is one of the important means to improve the quality of steel. In order to further improve the purity of molten steel, domestic and foreign steel companies have added secondary refining and vacuum degassing after steel is tapped from the converter or electric furnace. However, as a continuous casting process from molten steel solidification to continuous casting, it is also a difficult problem for most steel companies to ensure that the refined molten steel reduces secondary oxidation, further promotes the floating of inclusions in the steel, and reduces the attachment and aggregation of inclusions at the solidification front of the dendrite of the ingot, so that the inclusions are dispersed in the steel grade. Therefore, it is particularly important to invent a continuous casting cleanliness control method. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for controlling the cleanliness of large-section vertical continuous casting.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: (1) Use a large-section vertical continuous casting machine to ensure that the time for inclusions to float up during the solidification process of molten steel is 70 to 82 minutes; (2) When the first ladle of continuous casting is started, when the molten steel in the tundish is in the range of 5 to 27 tons, slag absorbing agent is added to the impact zone and the casting zone at the same time; 100 to 300 kg of slag absorbing agent is added to the impact zone, and 300 to 500 kg of slag absorbing agent is added to the casting zone; (3) Adopting modulated wave crystallizer electromagnetic stirring technology, the electromagnetic stirring current parameters are 150~600A and the frequency is 1.0~1.5HZ; (4) Use 4-hole SEN with an immersion depth of 90 to 130 mm.

[0005] Furthermore, in the control process (1), the pulling speed control range is 0.28 to 0.38 m / min. Furthermore, in the control process (1), the liquid core length is controlled within the range of 24.5 to 27.5 m.

[0006] Furthermore, in the control process (1), the casting section of the large-section vertical continuous casting machine is 460 mm×610 mm.

[0007] The beneficial effects of the above technical scheme are as follows: the present invention utilizes a vertical continuous casting machine to make inclusions float vertically in the unsolidified molten steel of the ingot, thereby avoiding inclusion enrichment at the 1 / 4 radius of the ingot; adopts a slag agent addition method of early slag formation and late machine start-up to ensure that a slag film is formed on the molten steel interface in the early stage of the first package start-up, isolating the molten steel from the air, and reducing the secondary oxidation of the molten steel; by controlling the process parameters of the casting machine, the length of the ingot liquid core is controlled to 24.5 to 27.5 m, ensuring that the time for inclusions to float during the solidification of the molten steel is 70 to 82 minutes; using modulated wave electromagnetic stirring, the refined molten steel reduces the attachment and aggregation of inclusions at the solidification front of the ingot dendrite, so that the inclusions are dispersed in the steel grade; a 4-hole SEN immersion depth of 90 to 130 mm is adopted to ensure a reasonable flow field in the crystallizer, while preventing slag rolling during the casting process in the crystallizer, ensuring the activity of the meniscus, and promoting the floating of inclusions.

[0008] The present invention can effectively reduce the secondary oxidation of molten steel during the continuous casting startup process, further promote the floating of inclusions in the steel, reduce the attachment and aggregation of inclusions at the solidification front of the dendrite of the casting billet, and make the inclusions dispersedly distributed in the steel grade. The final inclusion level reaches A fine ≤1.0 level, A coarse ≤0.5 level, B fine ≤1.0 level, B coarse ≤0.5 level, C fine ≤0.5 level, C coarse ≤0.5 level, D fine ≤1.0 level, D coarse ≤0.5 level, meeting the use requirements of high-purity special steel. DETAILED DESCRIPTION

[0009] The present invention is further described in detail below in conjunction with specific implementation modes.

[0010] The large-section vertical continuous casting cleanliness control method includes the following control processes: (1) A large-section vertical continuous casting machine is used, with a casting section of 460 mm × 610 mm; the casting speed control range is 0.28 to 0.38 m / min, and the liquid core length is controlled at 24.5 to 27.5 m to ensure that the time for inclusions to float up during the solidification process of the molten steel is 70 to 82 minutes; (2) A slag agent adding method of early slag formation and late start-up is adopted. When the first batch of continuous casting is started, when the molten steel in the tundish is in the range of 5 to 27 tons, a slag absorbent is added to the impact zone and the casting zone at the same time. The impact zone is added with 100 to 300 kg of slag absorbent, and the casting zone is added with 300 to 500 kg of slag absorbent. This ensures that a slag film is formed on the molten steel interface in the early stage of the first batch of start-up, isolates the molten steel from the air, reduces the secondary oxidation of the molten steel, and improves the cleanliness of the molten steel. No slag absorbent is added to the continuous casting furnace, and 80 to 120 kg of thermal insulation covering agent is added to each furnace to ensure that the impact zone and the casting zone maintain a black liquid level.

[0011] On the basis of the traditional crystallizer electromagnetic stirring sinusoidal current, by modulating the sinusoidal current and amplitude, the ordinary current generates harmonic oscillations of different frequencies, so that the stirring force changes from a specific direction to a fixed direction and diffuses to the surroundings at the same time. The electromagnetic stirring current parameters are 150-600A and the frequency is 1.0-1.5HZ, so that the inclusions are dispersed in the molten steel and the inclusions are reduced. The tundish water inlet adopts a 4-hole water inlet, and the steel holes of the water inlet are facing the four sides of the crystallizer. During the casting process, the height of the tundish is controlled to ensure that the immersion depth of SEN and the molten steel in the crystallizer is 90-130mm, so that the molten steel above the meniscus in the crystallizer has good activity, which prevents slag rolling during the casting process in the crystallizer and promotes the floating of inclusions.

[0012] Embodiments 1-9: This large-section vertical continuous casting cleanliness control method uses the following specific process.

[0013] (1) This method adopts the above control method. The specific process parameters such as continuous casting speed, slag absorber addition amount, electromagnetic stirring, SEN immersion depth, etc. are shown in Table 1; Table 1: Process parameters of continuous casting production process

[0014] In Table 1, the amount of slag absorbent added is the amount added in the impact zone + the amount added in the casting zone. For example, in Example 1, the amount added in the impact zone is 100 kg and the amount added in the casting zone is 300 kg.

[0015] (2) The inclusion test results obtained in each embodiment are shown in Table 2; Table 2: Inclusion test results of each example (grade)

[0016] It can be seen from Table 2 that the levels of inclusions in the steel obtained by this method are A fine ≤ 1.0, A coarse ≤ 0.5, B fine ≤ 1.0, B coarse ≤ 0.5, C fine ≤ 0.5, C coarse ≤ 0.5, D fine ≤ 1.0, D coarse ≤ 0.5, which meet the use requirements of high-purity special steel.

Claims

1. A large-section vertical continuous casting cleanliness control method, characterized in that: The following control processes are included: (1) Use a large-section vertical continuous casting machine to ensure that the time for inclusions to float up during the solidification process of molten steel is 70 to 82 minutes; (2) When the first ladle of continuous casting is started, when the molten steel in the tundish is in the range of 5 to 27 tons, slag absorbing agent is added to the impact zone and the casting zone at the same time; 100 to 300 kg of slag absorbing agent is added to the impact zone, and 300 to 500 kg of slag absorbing agent is added to the casting zone; (3) Adopting modulated wave crystallizer electromagnetic stirring technology, the electromagnetic stirring current parameters are 150~600A and the frequency is 1.0~1.5HZ; (4) Use 4-hole SEN with an immersion depth of 90 to 130 mm.

2. A large-section vertical continuous casting cleanliness control method according to claim 1, characterized in that: The control process (1) has a drawing speed control range of 0.28 to 0.38 m / min.

3. A large-section vertical continuous casting cleanliness control method according to claim 1, characterized in that: In the control process (1), the liquid core length is controlled within the range of 24.5 to 27.5 m.

4. A large-section vertical continuous casting cleanliness control method according to claim 1, 2 or 3, characterized in that: In the control process (1), the casting section of the large-section vertical continuous casting machine is 460 mm×610 mm.

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