A method for preventing slag overflow in VD refining process and its ultrasonic device

Abstract

This invention belongs to the field of iron and steel metallurgy, and specifically relates to a method and ultrasonic device for preventing slag overflow during VD refining. This invention proposes a method for preventing slag overflow during VD refining by employing a synergistic control approach of "ultrasonic pretreatment + dynamic process control + multi-parameter linkage." This method is beneficial for accelerating the elimination of bubbles in the slag layer and regulating interfacial tension during VD refining, and can stably control the slag layer thickness fluctuation within ±20mm during the VD refining process; it can shorten the processing time by 8% to 10% compared to conventional VD refining processes; and it eliminates the phenomenon of refining slag overflow, avoiding the risk of slag overflow.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy, and specifically relates to a method for preventing slag overflow during VD refining and its ultrasonic device. Background Technology

[0002] The Vacuum Degassing (VD) refining method utilizes the synergistic effect of two key principles—vacuum degassing and bottom-blowing argon stirring—to effectively remove impurities such as gases and inclusions from molten steel, ultimately obtaining pure molten steel. Vacuum degassing leverages the characteristic that the partial pressure and solubility of gases in metals decrease with increasing vacuum, allowing gases to escape from the molten steel. Bottom-blowing argon stirring utilizes the adsorption of inclusions and agitation of the molten steel during the argon gas's upward movement, ensuring a more thorough vacuum degassing process.

[0003] Slag overflow during VD refining refers to the phenomenon where, as gas escapes through the slag layer into the vacuum environment, bubbles in the slag layer rapidly increase and expand, causing the slag layer volume to continuously increase and overflow from the ladle. The main reasons for this phenomenon are: (1) the influence of steel slag. High viscosity, high melting point, excessive surface tension, and large slag layer thickness of the top slag of the ladle all lead to poor permeability of the slag layer, hindering the gas phase overflow and diffusion; (2) the influence of process control. For example, large changes in vacuum level lead to excessively fast gas escape rate, and large argon flow rate leads to reduced slag layer stability; (3) equipment factors. For example, insufficient net height of the ladle and insufficient pumping capacity of the vacuum pump. The hazards of slag overflow are: (1) molten steel is prone to secondary oxidation, and alloy composition is prone to fluctuation; (2) steel slag is prone to adhere to the inner wall of the VD furnace, vacuum pumps, and other equipment, leading to production interruption; (3) increased production costs. The main methods to avoid slag overflow are: (1) increasing the net height of the ladle, which has the disadvantage of affecting the steel production; (2) reducing the thickness of the slag layer before entering VD, which has the disadvantage of increasing the processing time and possibly requiring slag removal equipment; (3) breaking the air and reducing the argon flow rate can improve the slag overflow phenomenon. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preventing slag overflow during the VD refining process. By adopting a collaborative control approach of "ultrasonic pretreatment + dynamic process control + multi-parameter linkage", a method for preventing slag overflow during the VD refining process using ultrasound is proposed. This method is beneficial for accelerating the elimination of bubbles in the slag layer and adjusting the interfacial tension during VD refining, eliminating the phenomenon of refining slag overflow and avoiding the risk of slag overflow.

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

[0006] A method for preventing slag overflow during VD refining specifically includes the following steps:

[0007] a) Before vacuum treatment, apply ultrasonic waves with an initial frequency of 20–50 kHz to the surface of the molten steel inside the ladle (1), with an ultrasonic power density of 0.5–2.0 kW / m². 2 Continue pretreatment for 3–8 minutes;

[0008] b) During the vacuuming process, the ultrasonic generator (2) is started simultaneously, and focused ultrasonic waves are emitted vertically into the molten steel through the immersion-type amplitude transformer (3). The focal area covers the interface between the slag layer and the molten steel in the ladle.

[0009] c) During the vacuum holding stage, the ultrasonic parameters are dynamically adjusted according to the slag layer thickness: when the slag layer thickness is ≤50mm, the continuous wave mode is adopted with a frequency of 30kHz±2kHz; when the slag layer thickness is >50mm, the pulse mode is switched to a duty cycle of 20%~40%, and the peak power density is increased to 3.0~5.0kW / m².

[0010] d) Monitor the slag layer thickness in real time using ultrasonic echo signals. When the thickness is >80mm, link the vacuum system (4) to increase the vacuum level to 0.3~0.8kPa.

[0011] In step a), the ultrasonic emission angle is at an angle of 15° to 30° with the ladle axis, and the ultrasonic frequency is dynamically adjusted with the change of molten steel temperature. The adjustment formula is: ultrasonic frequency f = 35 + 0.02(T - 1600), where f is in kHz and T is the molten steel temperature in °C.

[0012] In step b), the amplitude rod (3) is inserted into the molten steel to a depth of 1 / 10 to 1 / 8 of the total height of the molten steel.

[0013] It also includes a slag layer crushing and strengthening step: 2 to 3 minutes before the end of vacuum treatment, the ultrasonic frequency is increased to 50 to 80 kHz, and argon gas with a flow rate of 5 to 10 NL / min is introduced into the bottom of the ladle.

[0014] The ultrasonic echo signal is fused with infrared thermal imaging data for analysis. A machine learning model is used to predict the risk of slag overflow. The model input parameters include ultrasonic attenuation coefficient, slag layer reflection intensity, and temperature gradient distribution.

[0015] An ultrasonic device used in a method to prevent slag overflow during VD refining includes an amplitude transformer (3), an ultrasonic generator (2), an ultrasonic power controller (7), a central processing unit (8), and an acoustic shield (9). Multiple amplitude transformers (3) form multiple sets of liftable ultrasonic emission arrays above the molten steel. The ultrasonic power controller (7) is interlocked with a vacuum system (4). The amplitude transformers (3) are electrically connected to the ultrasonic generator (2) and the ultrasonic power controller (7). The ultrasonic power controller (7) is electrically connected to the central processing unit (8). The acoustic shield (9) is arranged around the ladle (1).

[0016] The amplitude rod (3) adopts a double-layer water-cooled structure, and its end is provided with a silicon nitride ceramic protective head (5).

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] This invention proposes a method for preventing slag overflow in the VD refining process by employing a synergistic control approach combining ultrasonic pretreatment, dynamic process control, and multi-parameter linkage. This method is beneficial for accelerating the elimination of air bubbles in the slag layer and regulating interfacial tension during VD refining, and has the following advantages:

[0019] (1) The slag layer thickness fluctuation during the VD refining process can be stably controlled within ±20mm;

[0020] (2) The processing time can be shortened by 8% to 10% compared with the conventional VD refining process;

[0021] (3) There is no refining slag overflow, thus avoiding the risk of slag overflow. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the device of the present invention.

[0023] In the diagram: 1. Steel ladle; 2. Ultrasonic generator; 3. Amplitude bar; 4. Vacuum system; 5. Silicon nitride ceramic protective head; 6. Ultrasonic transmitting array; 7. Ultrasonic power controller; 8. Central processing unit; 9. Acoustic shield. Detailed Implementation

[0024] 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.

[0025] Example 1:

[0026] The steel grade described in Example 1 is hard wire steel 72A, and the ladle capacity is 100 tons.

[0027] The VD furnace refining steps are as follows:

[0028] a) Pour the molten steel with a certain amount of slag into the VD refining tank. Before vacuum treatment, start ultrasonic pretreatment: set the initial ultrasonic frequency to 20kHz, the ultrasonic frequency dynamically changes according to the formula f=35+0.02(T-1600) (where f is the frequency (kHz) and T is the temperature of the molten steel (°C)), the power density is 2.0kW / m², the duration is 3 minutes, and the ultrasonic emission angle is at a 15° angle with the ladle axis.

[0029] b) Vacuuming stage: The vacuum level decreases to the target value of 65 Pa at a rate of 1.5 kPa / min, and ultrasonic waves are started simultaneously in continuous wave mode. The frequency is set to 32 kHz, and the insertion depth of the silicon nitride ceramic protective head is 1 / 4 of the total height of the molten steel.

[0030] c) Vacuum holding stage: The ultrasonic parameters are dynamically adjusted according to the slag layer thickness. When the slag layer thickness is ≤50mm, the continuous wave mode is still used and the frequency is set to 32kHz. When the slag layer thickness is >50mm, the pulse mode is switched to, the duty cycle is 20%, and the peak power density is increased to 5.0kW / m². When the slag layer thickness exceeds 80mm, the vacuum degree is increased by 0.8kPa.

[0031] d) Two minutes before the end of the treatment, increase the ultrasonic frequency to 50kHz and simultaneously introduce argon gas (flow rate 10NL / min).

[0032] Example 2:

[0033] The steel used in Example 2 is bearing steel Gr15, and the ladle capacity is 120 tons.

[0034] The VD furnace refining steps are as follows:

[0035] a) Pour the molten steel with a certain amount of slag into the VD refining tank. Before vacuum treatment, start ultrasonic pretreatment: set the initial ultrasonic frequency to 50kHz, the ultrasonic frequency dynamically changes according to the formula f=35+0.02(T-1600) (where f is the frequency (kHz) and T is the temperature of the molten steel (°C)), the power density is 0.5kW / m², the duration is 8 minutes, and the ultrasonic emission angle is at a 30° angle with the ladle axis.

[0036] b) Vacuuming stage: The vacuum level decreases to the target value of 65 Pa at a rate of 1.8 kPa / min, and ultrasonic waves are started simultaneously in continuous wave mode. The frequency is set to 35 kHz, and the insertion depth of the silicon nitride ceramic protective head is 1 / 3 of the total height of the molten steel.

[0037] c) Vacuum holding stage: The ultrasonic parameters are dynamically adjusted according to the slag layer thickness. When the slag layer thickness is ≤50mm, the continuous wave mode is still used and the frequency is set to 28kHz. When the slag layer thickness is >50mm, the pulse mode is switched to, the duty cycle is 40%, and the peak power density is increased to 3.0kW / m². When the slag layer thickness exceeds 80mm, the vacuum degree is increased by 0.3kPa.

[0038] d) Three minutes before the end of the treatment, increase the ultrasonic frequency to 80kHz and simultaneously introduce argon gas (flow rate 5NL / min).

[0039] Example 3:

[0040] The steel used in Example 3 is spring steel 60Si2Mn, and the ladle capacity is 100 tons.

[0041] The VD furnace refining steps are as follows:

[0042] a) Pour the molten steel with a certain amount of slag into the VD refining tank. Before vacuum treatment, start ultrasonic pretreatment: set the initial ultrasonic frequency to 36kHz, the ultrasonic frequency dynamically changes according to the formula f=35+0.02(T-1600) (where f is the frequency (kHz) and T is the temperature of the molten steel (°C)), the power density is 1.5kW / m², the duration is 5 minutes, and the ultrasonic emission angle is at a 25° angle with the ladle axis.

[0043] b) Vacuuming stage: The vacuum level decreases to the target value of 65 Pa at a rate of 2.0 kPa / min, and ultrasonic waves are started simultaneously in continuous wave mode. The frequency is set to 30 kHz, and the insertion depth of the silicon nitride ceramic protective head is 1 / 4 of the total height of the molten steel.

[0044] c) Vacuum holding stage: The ultrasonic parameters are dynamically adjusted according to the slag layer thickness. When the slag layer thickness is ≤50mm, the continuous wave mode is still used and the frequency is set to 30kHz. When the slag layer thickness is >50mm, the pulse mode is switched to, the duty cycle is 40%, and the peak power density is increased to 4.0kW / m². When the slag layer thickness exceeds 80mm, the vacuum degree is increased by 0.5kPa.

[0045] d) 2.5 minutes before the end of the treatment, increase the ultrasonic frequency to 65kHz and simultaneously introduce argon gas (flow rate 8NL / min).

[0046] Implementation Results: Examples 1-3 can control the slag layer thickness fluctuation during VD refining within ±20mm, ±18mm, and ±15mm respectively, with no slag overflow during the refining process. Furthermore, compared to conventional VD refining processes, the refining time in Examples 1-3 is reduced by 8%-10%.

Claims

1. A method for preventing slag overflow during VD refining, characterized in that, Specifically, the methods and steps include the following: a) Before vacuum treatment, apply ultrasonic waves with an initial frequency of 20–50 kHz to the surface of the molten steel inside the ladle (1), with an ultrasonic power density of 0.5–2.0 kW / m². 2 Continue pretreatment for 3–8 minutes; b) During the vacuuming process, the ultrasonic generator (2) is started simultaneously, and focused ultrasonic waves are emitted vertically into the molten steel through the immersion-type amplitude transformer (3). The focal area covers the interface between the slag layer and the molten steel in the ladle. c) During the vacuum holding stage, the ultrasonic parameters are dynamically adjusted according to the slag layer thickness: when the slag layer thickness is ≤50mm, continuous wave mode is used with a frequency of 30kHz±2kHz; when the slag layer thickness is >50mm, pulse mode is switched to with a duty cycle of 20%~40% and the peak power density is increased to 3.0~5.0kW / m 2 ; d) Monitor the slag layer thickness in real time using ultrasonic echo signals. When the thickness is >80mm, link the vacuum system (4) to increase the vacuum level to 0.3~0.8kPa.

2. The method for preventing slag overflow during VD refining according to claim 1, characterized in that: In step a), the ultrasonic emission angle is at an angle of 15° to 30° with the ladle axis, and the ultrasonic frequency is dynamically adjusted with the change of molten steel temperature. The adjustment formula is: ultrasonic frequency f = 35 + 0.02(T - 1600), where f is in kHz and T is the molten steel temperature in °C.

3. The method for preventing slag overflow during VD refining according to claim 1, characterized in that: In step b), the amplitude rod (3) is inserted into the molten steel to a depth of 1 / 10 to 1 / 8 of the total height of the molten steel.

4. The method for preventing slag overflow during VD refining according to claim 1, characterized in that: It also includes a slag layer crushing and strengthening step: 2 to 3 minutes before the end of vacuum treatment, the ultrasonic frequency is increased to 50 to 80 kHz, and argon gas with a flow rate of 5 to 10 NL / min is introduced into the bottom of the ladle.

5. The method for preventing slag overflow during VD refining according to claim 1, characterized in that: The ultrasonic echo signal is fused with infrared thermal imaging data for analysis. A machine learning model is used to predict the risk of slag overflow. The model input parameters include ultrasonic attenuation coefficient, slag layer reflection intensity, and temperature gradient distribution.

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