A method for purifying molten steel in a tundish based on the synergistic effect of ultrasonic zoning

Abstract

This invention belongs to the field of continuous casting technology in iron and steel metallurgy, and specifically relates to a method for purifying molten steel in a tundish based on the synergistic effect of ultrasonic zoning. Frequency-divided ultrasonic control is applied in the impact zone and the casting zone. In the impact zone, large inclusions are broken up through low-frequency cavitation effects, while the turbulent kinetic energy of the molten steel is reduced, thus decreasing the slag entrainment rate. In the casting zone, high-frequency acoustic flow effects suppress air intake at the inlet, preventing oxidation of the molten steel and reducing component segregation. By employing the coupling effect of argon microbubbles with the ultrasonic field, the removal efficiency of inclusions through bubble adsorption and flotation is improved. A composite lining encapsulates the probe, enhancing its resistance to corrosion and thermal shock, resulting in a long probe lifespan.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting technology in iron and steel metallurgy, and specifically relates to a method for purifying molten steel in a tundish based on the synergistic effect of ultrasonic partitioning. Background Technology

[0002] In continuous casting, the tundish is the final purification container before the molten steel solidifies, and its cleanliness directly affects the quality of the cast billet. Traditional technologies mainly optimize the cleanliness of the molten steel in the tundish through the following methods: (1) Physical interception method: using slag walls, filters and other devices to intercept inclusions. Its disadvantage is that it is difficult to remove small (10~50μm) inclusions and it is easy to cause flow field turbulence; (2) Inert gas blowing method: blowing argon gas through permeable bricks to promote the floating of inclusions. However, larger bubbles (>2mm) are easy to cause secondary oxidation of molten steel and the adsorption efficiency for small particle inclusions is insufficient; (3) Tundish structure optimization: by designing the shape of the tundish, such as using a deep melting pool and a reasonable length-to-width ratio, the flow state of the molten steel is improved, the residence time of the molten steel in the tundish is extended, and the floating and removal of inclusions is promoted. (4) Ultrasonic Purification Method: Existing technologies mostly apply ultrasonic waves to the bottom of the tundish or inside the stopper rod, which has the following drawbacks: 1. Single action area: Differentiated ultrasonic parameters are not designed for different metallurgical reaction areas (such as the impact zone and the casting zone) in the tundish, resulting in an inability to simultaneously suppress turbulence and homogenize the composition; 2. Short equipment lifespan: Ultrasonic probes are easily corroded in the high-temperature molten steel environment, and traditional magnesium linings cannot provide effective protection. Therefore, there is an urgent need to develop an efficient tundish molten steel purification method that, by synergistically considering the flow field characteristics of the impact zone and the casting zone, can achieve efficient removal of micron-level inclusions, prevent slag entrapment in the turbulent zone and air intake in the injection port area, while ensuring the durability of the probe.

[0003] Chinese patent CN102145380A, entitled "A Method for Cleaning Molten Steel in a Continuous Casting Tundish," proposes a method that uses bottom-blowing gas and the shearing force of ultrasound to break bubbles into microbubbles, ultimately achieving degassing and removing micro-non-metallic inclusions. Chinese patent CN103252459A, entitled "A Method for Improving the Cleanliness of Molten Steel and Refining Grain Size through Ultrasound," proposes integrating ultrasound and argon blowing functions into the tundish stopper rod to improve molten steel cleanliness. However, both patents have a single area of ​​action, failing to suppress slag entrapment and secondary oxidation in the inlet area, effectively preventing dead zones in the flow field, especially in the casting zone, and ensuring effective removal of micron-level inclusions. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a tundish molten steel purification method based on the synergistic effect of ultrasonic partitioning, which solves the problems of low removal efficiency of micro-inclusions, poor adaptability of ultrasound in different metallurgical reaction zones within the tundish, and insufficient durability of ultrasonic probes under high-temperature environments.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for purifying molten steel in a ladle based on the synergistic effect of ultrasonic partitioning, specifically including the following methods:

[0007] 1) An ultrasonic system (4) is installed on the side wall of the impact zone (2) and the casting zone (3) of the tundish (1), wherein: the impact zone (2) is located within 0.5 to 1.5 m below the steel inlet axis; the casting zone (3) is located within 0.3 to 0.8 m near the injection port axis;

[0008] 2) An ultrasonic system (4) is used to apply an ultrasonic wave to the molten steel with a frequency of 80–220 kHz and a power density of 200–500 W / cm². 2 Ultrasound;

[0009] 3) Intermittent ultrasonic treatment is used, with a working cycle of 30-60 seconds and an interval of 10-20 seconds;

[0010] 4) Simultaneously blow argon gas into the intermediate package (1), with the blowing position located 300-500 mm below the ultrasonic generating system (4).

[0011] In step 2), the ultrasonic frequency of the impact zone (2) is 80-150kHz, and the ultrasonic frequency of the casting zone (3) is 160-220kHz.

[0012] The ultrasonic system (4) includes an ultrasonic generator (5), a waveguide (6) and a probe (7), wherein the transmitting end of the waveguide (5) is embedded with a magnesium oxide-silicon carbide-based composite liner (8).

[0013] The magnesium oxide-silicon carbide-based composite liner (8) is composed of the following components by weight percentage: MgO: 50%–75%, SiC: 15%–30%, Al2O3: 3%–12%, ZrO2: 2%–8%, binder: 5%–10%.

[0014] In the impact zone (2), the ultrasonic emission direction is at an angle of 15° to 70° with the direction of molten steel flow, and in the casting zone (3), the ultrasonic emission direction is at an angle of 75° to 90° with the axis of the injection port.

[0015] Argon gas is blown into the intermediate liner (1) through the porous permeable brick (9) to generate microbubbles, with a gas flow rate of 8-15 L / min.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] (1) By implementing frequency-division ultrasonic control in the impact zone and the casting zone. In the impact zone, large-sized inclusions can be broken by low-frequency cavitation effect, while reducing the turbulent kinetic energy of the molten steel and thus reducing the slag entrainment rate. In the casting zone, the high-frequency acoustic flow effect can suppress air intake at the injection port, prevent oxidation of the molten steel, and reduce the segregation of molten steel components.

[0018] (2) By using the coupling effect of argon microbubbles and ultrasonic sound field, the removal efficiency of bubble adsorption and floating removal of impurities can be improved.

[0019] (3) The composite liner wrapping of the probe improves the ultrasonic probe’s resistance to corrosion and thermal shock, resulting in a longer probe lifespan. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the installation structure of the ultrasonic device of the present invention.

[0021] In the diagram: 1. Tundish; 2. Impact zone; 3. Casting zone; 4. Ultrasonic system; 5. Ultrasonic generator; 6. Waveguide rod; 7. Probe; 8. Magnesium oxide-silicon carbide based composite lining; 9. Porous permeable brick. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0023] Example 1:

[0024] Example 1 describes a method for purifying molten steel in a tundish using low-carbon steel of grade M3A33. The composition of the molten steel before entering the tundish is: C: 0.002%; Si: 0.01%; Mn: 0.13%; P: 0.008%; S: 0.008%; Als: 0.035%; N: 0.002%; Ti: 0.075%, with the remainder being iron. Specific parameter settings and procedures are as follows: the probe position in the impact zone is horizontal to the upper part of impact zone 2 (0.5m below the molten steel inlet axis), and the probe position in the casting zone is horizontal to the upper part of casting zone 3 (0.3m above the injection port axis). Simultaneously, ultrasonic and argon gas are activated when the molten steel enters tundish 1. The ultrasonic frequency in impact zone 2 is 80kHz, and the power density is 200W / cm³. 2The angle between the ultrasonic wave emission direction and the molten steel flow direction is 15°. The ultrasonic frequency in casting zone 3 is 220kHz, and the power density is 500W / cm³. 2 The ultrasonic wave emission direction forms a 90° angle with the injection port axis. The ultrasonic working cycle for both impact zone 2 and casting zone 3 is 30 seconds, with an interval of 20 seconds. Argon gas is blown 300 mm below the ultrasonic wave generation system at a flow rate of 8 L / min. The magnesium oxide-silicon carbide-based composite lining used in Example 1 consists of MgO: 50%, SiC: 30%, Al₂O₃: 12%, ZrO₂: 2%, and binder: 6%.

[0025] Example 2:

[0026] Example 2 describes a method for purifying molten steel in a tundish for medium carbon steel grade S30C. The composition of the molten steel before entering the tundish is: C: 0.29%; Si: 0.15%; Mn: 0.9%; P: 0.009%; S: 0.012%; Als: 0.028%, with the remainder being iron. Specific parameter settings and procedures are as follows: the probe position in the impact zone is horizontal to the upper part of impact zone 2 (1.5m below the molten steel inlet axis), and the probe position in the casting zone is horizontal to the upper part of casting zone 3 (0.8m above the injection port axis). Simultaneously, ultrasonic and argon gas are activated when the molten steel enters the tundish. The ultrasonic frequency in impact zone 2 is 150kHz, and the power density is 500W / cm³. 2 The ultrasonic wave emission direction is at a 70° angle to the molten steel flow direction. The ultrasonic frequency in casting zone 3 is 160kHz, and the power density is 200W / cm³. 2 The ultrasonic wave emission direction forms a 75° angle with the injection port axis. The ultrasonic working cycle for both impact zone 2 and casting zone 3 is 60 seconds, with an interval of 10 seconds. Argon gas is blown in at a position 500 mm below the ultrasonic wave generation system, with a gas flow rate of 15 L / min. The magnesium oxide-silicon carbide-based composite lining used in Example 1 has the following composition: MgO: 64%, SiC: 15%, Al₂O₃: 3%, ZrO₂: 8%, and binder: 10%.

[0027] Example 3:

[0028] Example 3 describes a method for purifying molten steel in a tundish for high-carbon alloy steel grade 105CrSi5. The composition of the molten steel before entering the tundish is: C: 0.95%; Si: 1.45%; Mn: 0.45%; P: 0.012%; S: 0.006%; Cr: 1.15%; Als: 0.027%, with the remainder being iron. Specific parameter settings and procedures are as follows: the probe position in the impact zone is horizontal to the upper part of impact zone 2 (1.1m below the steel inlet axis), and the probe position in the casting zone is horizontal to the upper part of casting zone 3 (0.6m above the injection port axis). Simultaneously, ultrasonic and argon gas are activated when the molten steel enters tundish 1. The ultrasonic frequency in impact zone 2 is 110kHz, and the power density is 260W / cm³. 2 The ultrasonic wave emission direction is at a 45° angle to the molten steel flow direction. The ultrasonic frequency in casting zone 3 is 190kHz, and the power density is 300W / cm³. 2 The ultrasonic wave emission direction forms an 85° angle with the injection port axis. The ultrasonic working cycle for both impact zone 2 and casting zone 3 is 45 seconds, with an interval of 15 seconds. Argon gas is blown in at a position 400 mm below the ultrasonic wave generation system, with a gas flow rate of 11 L / min. The magnesium oxide-silicon carbide-based composite lining used in Example 1 has the following composition: MgO: 75%, SiC: 15%, Al₂O₃: 3%, ZrO₂: 2%, and binder: 5%.

[0029] Example 4:

[0030] Example 4 describes a method for purifying molten steel in the tundish of bearing steel grade GCr15. The composition of the molten steel before entering the tundish is: C: 1.02%; Si: 0.25%; Mn: 0.35%; P: 0.013%; S: 0.006%; Cr: 1.50%; Als: 0.019%, with the remainder being iron. Specific parameter settings and procedures are as follows: the probe position in the impact zone is horizontal to the upper part of impact zone 2 (0.8m below the molten steel inlet axis), and the probe position in the casting zone is horizontal to the upper part of casting zone 3 (0.5m above the injection port axis). Simultaneously, ultrasonic and argon gas are activated when the molten steel enters tundish 1. The ultrasonic frequency in impact zone 2 is 90kHz, and the power density is 320W / cm³. 2 The angle between the ultrasonic wave emission direction and the molten steel flow direction is 55°. The ultrasonic frequency in casting zone 3 is 210kHz, and the power density is 360W / cm³. 2 The ultrasonic wave emission direction forms an 80° angle with the injection port axis. The ultrasonic working cycle for both impact zone 2 and casting zone 3 is 50 seconds, with an interval of 18 seconds. Argon gas is blown at a position 450 mm below the ultrasonic wave generation system, with a gas flow rate of 13 L / min. The magnesium oxide-silicon carbide-based composite lining used in Example 1 has the following composition: MgO: 60%, SiC: 20%, Al₂O₃: 10%, ZrO₂: 4%, and binder: 6%.

[0031] Comparative example:

[0032] The comparative example is the purification method of molten steel in the tundish of low carbon steel grade M3A33. The difference is that no ultrasonic waves were applied during the casting process. The conventional process of casting was used only, which involves controlling the molten steel level and flow rate, using a slag-blocking device and a covering agent. These processes were all used in Examples 1-4, and the process parameters were basically the same.

[0033] Samplings were taken from the middle section of the cross-section of the billets after treatment in Examples 1-4, and the test indicators included TO, N, H, and the mathematical statistics of inclusions. TO, N, and H were detected using an ICP composition analyzer, and the mathematical statistics of inclusions were performed using an ASPEX inclusion analyzer and Image-pro-plus software. The statistical results are shown in Table 1 below. As can be seen from the data in Table 1, compared with the comparative examples, the TO, N, and H contents detected in the samples of Examples 1-4 were significantly lower. This indicates that the present invention effectively improves the problem of high TO, N, and H content caused by air intake at the sprue, preventing secondary oxidation of the molten steel. This also avoids the problem of [O] reacting with Al, Si, Mn, etc., to form oxide inclusions, leading to an increase in inclusions. Furthermore, the samples in Examples 1-4 of this invention exhibited lower inclusion density and a higher proportion of inclusions with diameters (d≤5μm). The low inclusion density indicates that this invention is extremely effective in achieving the flotation and removal of inclusions from molten steel in the tundish. The higher proportion of inclusions with diameters (d≤5μm) demonstrates that this invention can efficiently remove inclusions with diameters (d>5μm), simultaneously removing both small and large inclusions, resulting in fewer and smaller inclusions remaining in the steel. Additionally, there was no slag entrapment in the molten steel within the tundish, and the temperature was uniform and stable.

[0034] Table 1

[0035]

Claims

1. A method for purifying molten steel in a ladle based on the synergistic effect of ultrasonic zoning, characterized in that, Specifically, the methods include the following: 1) An ultrasonic system (4) is installed on the side wall of the impact zone (2) and the casting zone (3) of the tundish (1), wherein: the impact zone (2) is located within 0.5 to 1.5 m below the steel inlet axis; the casting zone (3) is located within 0.3 to 0.8 m near the injection port axis; 2) An ultrasonic system (4) is used to apply an ultrasonic wave to the molten steel with a frequency of 80–220 kHz and a power density of 200–500 W / cm². 2 Ultrasound; 3) Intermittent ultrasonic treatment is used, with a working cycle of 30-60 seconds and an interval of 10-20 seconds; 4) Simultaneously blow argon gas into the intermediate package (1), with the blowing position located 300-500 mm below the ultrasonic generating system (4); In step 2), the ultrasonic frequency of the impact zone (2) is 80-150kHz, and the ultrasonic frequency of the casting zone (3) is 160-220kHz.

2. The method for purifying molten steel in a tundish based on the synergistic effect of ultrasonic zoning as described in claim 1, characterized in that: The ultrasonic system (4) includes an ultrasonic generator (5), a waveguide (6) and a probe (7), wherein the transmitting end of the waveguide (5) is embedded with a magnesium oxide-silicon carbide-based composite liner (8).

3. The method for purifying molten steel in a tundish based on the synergistic effect of ultrasonic zoning as described in claim 2, characterized in that: The magnesium oxide-silicon carbide-based composite liner (8) is composed of the following components by weight percentage: MgO: 50%–75%, SiC: 15%–30%, Al2O3: 3%–12%, ZrO2: 2%–8%, binder: 5%–10%.

4. The method for purifying molten steel in a tundish based on the synergistic effect of ultrasonic zoning as described in claim 1, characterized in that: In the impact zone (2), the ultrasonic emission direction is at an angle of 15° to 70° with the direction of molten steel flow, and in the casting zone (3), the ultrasonic emission direction is at an angle of 75° to 90° with the axis of the injection port.

5. The method for purifying molten steel in a tundish based on the synergistic effect of ultrasonic zoning as described in claim 1, characterized in that: Argon gas is blown into the intermediate liner (1) through the porous permeable brick (9) to generate microbubbles, with a gas flow rate of 8-15 L / min.

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