Method for preventing slag overflow in VD refining process and ultrasonic device thereof

Abstract

The invention belongs to the field of ferrous metallurgy, and particularly relates to a method for preventing slag overflow in the VD refining process and an ultrasonic device thereof. According to the method for preventing slag overflow in the VD refining process through ultrasonic waves, ultrasonic pretreatment, process dynamic regulation and control and multi-parameter linkage cooperative control are adopted, bubble vanishing in a slag layer during VD refining can be accelerated, interfacial tension can be adjusted, and the thickness fluctuation of the slag layer in the VD refining process can be stably controlled within + / -20 mm; compared with the conventional VD refining process, the treatment time can be shortened by 8-10%; and no refining slag overflow phenomenon exists, and the slag overflow risk is avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of steel metallurgy, and particularly relates to a method for preventing overflow of slag in a VD refining process and an ultrasonic device thereof. BACKGROUND

[0002] The VD refining method is a method for effectively removing gas, inclusions and other impurities in molten steel by utilizing the synergistic effect of vacuum degassing and bottom argon blowing stirring, and finally obtaining pure molten steel. The principle of vacuum degassing utilizes the characteristics that the partial pressure and solubility of gas in metal decrease with the increase of vacuum degree, so that the gas can escape from the molten steel. The bottom argon blowing stirring plays the role of adsorbing inclusions and stirring the molten steel in the process of argon gas floating, so that the vacuum degassing process can be more sufficient.

[0003] Overflow of slag in the VD refining process refers to the phenomenon that the volume of slag layer continuously increases and overflows from the ladle in the process of gas escaping from the slag layer to the vacuum environment due to the rapid increase and rapid expansion of gas bubbles in the slag layer. The main reasons for this phenomenon are: (1) the influence of steel slag. The viscosity, melting point and surface tension of the top slag of the ladle are too large, and the thickness of the slag layer is large, which will lead to poor permeability of the slag layer and blockage of the diffusion of gas phase overflow; (2) the influence of process control. For example, large change range of vacuum degree leads to too fast gas escape speed, and large argon gas flow leads to reduced stability of the slag layer; (3) equipment factors. For example, insufficient ladle headroom and insufficient vacuum pump pumping capacity. The hazards of overflow of slag are: (1) secondary oxidation of molten steel is easy to occur, and alloy composition is easy to fluctuate; (2) steel slag is easy to adhere to the inner wall of the VD furnace, vacuum pump and other equipment, leading to interruption of production; (3) increase of production cost. The current treatment methods to avoid overflow of slag mainly include: (1) increasing the headroom of the ladle, which has the disadvantage of affecting the yield of molten steel; (2) reducing the thickness of the slag layer before entering the VD, which has the disadvantage of increasing the treatment time and may need to be equipped with slag removal equipment; (3) breaking the vacuum operation and reducing the argon gas flow can improve the overflow of slag. SUMMARY

[0004] The present application aims to provide a method for preventing overflow of slag in a VD refining process, which utilizes ultrasonic waves to prevent overflow of slag in the VD refining process by adopting the synergistic control of "ultrasonic wave pretreatment + process dynamic regulation + multi-parameter linkage", which is beneficial to accelerate the extinction of gas bubbles in the slag layer and adjust the interfacial tension during VD refining, and no overflow of slag occurs, thereby avoiding the risk of overflow of slag.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] A method for preventing overflow of slag in a VD refining process, specifically comprising the following method steps:

[0007] a) Before vacuum treatment, the surface of molten steel in the ladle (1) is applied with ultrasonic waves with an initial frequency of 20-50 kHz and an ultrasonic power density of 0.5-2.0 kW / m 2 for 3-8 minutes of pretreatment;

[0008] b) During the vacuum extraction process, the ultrasonic generator (2) is started synchronously, and focused ultrasonic waves are vertically emitted into the molten steel through the immersed amplitude transformer (3), and the focal point area covers the interface between the slag layer and the molten steel in the ladle;

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

[0010] d) The thickness of the slag layer is monitored in real time through the ultrasonic echo signal, and when the thickness is >80 mm, the vacuum system (4) is linked to increase the vacuum degree to 0.3-0.8 kPa.

[0011] In the step a), the ultrasonic emission angle is 15°-30° to the axis of the ladle, and the ultrasonic frequency is dynamically adjusted according to the temperature of the molten steel, and the adjustment formula is: the ultrasonic frequency f in numerical value = 35+0.02(T-1600), wherein the unit of f is kHz, and T is the numerical value of the temperature of the molten steel, and the unit is ℃.

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

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

[0014] The ultrasonic echo signal and the infrared thermal imaging data are fused and analyzed, the risk of slag overflow is predicted through a machine learning model, and the input parameters of the model include the ultrasonic attenuation coefficient, the reflection intensity of the slag layer, and the temperature gradient distribution.

[0015] The method for preventing overflow of slag in VD refining process adopts an ultrasonic device, which comprises amplitude-reducing rods (3), an ultrasonic generator (2), an ultrasonic power controller (7), a central processing unit (8), and a sound wave shielding cover (9). A plurality of the amplitude-reducing rods (3) form a plurality of groups of liftable ultrasonic emission arrays above molten steel. The ultrasonic power controller (7) is interlocked with a vacuum system (4). The amplitude-reducing rods (3) are electrically connected with the ultrasonic generator (2) and the ultrasonic power controller (7). The ultrasonic power controller (7) is electrically connected with the central processing unit (8). The sound wave shielding cover (9) is arranged around a ladle (1).

[0016] The amplitude-reducing rod (3) adopts a double-layer water cooling structure, and a silicon nitride ceramic protection head (5) is arranged at an end of the amplitude-reducing rod (3).

[0017] Compared with the prior art, the method has the beneficial effects that:

[0018] The method for preventing overflow of slag in VD refining process by adopting the ultrasonic pretreatment, process dynamic regulation and multi-parameter linkage synergistic control has the beneficial effects that:

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

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

[0021] (3) There is no refining overflow of slag, and the risk of overflow of slag is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a structural schematic view of the device.

[0023] In the figure: 1, a ladle; 2, an ultrasonic generator; 3, an amplitude-reducing rod; 4, a vacuum system; 5, a silicon nitride ceramic protection head; 6, an ultrasonic emission array; 7, an ultrasonic power controller; 8, a central processing unit; and 9, a sound wave shielding cover. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present application clearer, the specific embodiments of the present application are further described below in combination with examples. The following examples are used to specifically describe the present application, and these examples only generally describe the present application and do not limit the present application.

[0025] Example 1

[0026] In example 1, the steel grade is hard wire steel 72A, and the ladle capacity is 100 tons.

[0027] VD furnace refining step 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 20 kHz, dynamically change the ultrasonic frequency according to the formula f = 35 + 0.02(T-1600) (where f is the frequency (kHz), T is the temperature of the molten steel (°C)), the power density is 2.0 kW / m², the duration is 3 minutes, the ultrasonic emission angle is 15° to the ladle axis.

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

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

[0031] d) 2 minutes before the end of the treatment, increase the ultrasonic frequency to 50 kHz, and simultaneously introduce argon gas (flow rate 10 NL / min).

[0032] Example 2:

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

[0034] VD furnace refining step 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 50 kHz, dynamically change the ultrasonic frequency according to the formula f = 35 + 0.02(T-1600) (where f is the frequency (kHz), T is the temperature of the molten steel (°C)), the power density is 0.5 kW / m², the duration is 8 minutes, the ultrasonic emission angle is 30° to the ladle axis.

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

[0037] c) Vacuum holding stage: dynamically adjust the ultrasonic parameters according to the slag layer thickness, when the slag layer thickness is ≤50 mm, still use continuous wave mode, frequency is set to 28 kHz; when the slag layer thickness is >50 mm, switch to pulse mode, duty cycle is 40%, peak power density is increased to 3.0 kW / m2; when the slag layer thickness exceeds 80 mm, linkage to improve the vacuum degree 0.3 kPa.

[0038] d) 3 minutes before the end of the treatment, the ultrasonic frequency is increased to 80 kHz, while argon is introduced (flow rate 5 NL / min).

[0039] Example 3:

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

[0041] The VD furnace refining step is 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 36 kHz, dynamically change the ultrasonic frequency according to the formula f=35+0.02(T-1600) (where f is the frequency (kHz), T is the steel temperature (°C)), the power density is 1.5 kW / m2, the duration is 5 minutes, and the ultrasonic emission angle is 25° to the ladle axis.

[0043] b) Vacuum extraction stage: the vacuum degree is decreased to the target value 65 Pa at a rate of 2.0 kPa / min, and the ultrasonic wave is started at the same time. Use continuous wave mode. The frequency is set to 30 kHz, and the insertion depth of the silicon nitride ceramic protection head is 1 / 4 of the total height of the molten steel.

[0044] c) Vacuum holding stage: dynamically adjust the ultrasonic parameters according to the slag layer thickness, when the slag layer thickness is ≤50 mm, still use continuous wave mode, frequency is set to 30 kHz; when the slag layer thickness is >50 mm, switch to pulse mode, duty cycle is 40%, peak power density is increased to 4.0 kW / m2; when the slag layer thickness exceeds 80 mm, linkage to improve the vacuum degree 0.5 kPa.

[0045] d) 2.5 minutes before the end of the treatment, the ultrasonic frequency is increased to 65 kHz, while argon is introduced (flow rate 8 NL / min).

[0046] Implementation effect: Examples 1-3 can respectively control the VD refining stage slag layer thickness within ±20 mm, ±18 mm, and ±15 mm, and there is no slag overflow phenomenon during the refining process. At the same time, compared with the conventional VD refining process, the refining treatment time of Examples 1-3 is shortened 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, 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. 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.

6. An ultrasonic device used in the method for preventing slag overflow in the VD refining process as described in any one of claims 1-5, characterized in that: The system includes a variable amplitude rod (3), an ultrasonic generator (2), an ultrasonic power controller (7), a central processing unit (8), and an acoustic shield (9). Multiple variable amplitude rods (3) form multiple sets of liftable ultrasonic emission arrays (6) above the molten steel. The ultrasonic power controller (7) is interlocked with the vacuum system (4). The variable amplitude rods (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).

7. The ultrasonic device used in the method for preventing slag overflow in the VD refining process according to claim 6, characterized in that: The amplitude rod (3) adopts a double-layer water-cooled structure, and its end is provided with a silicon nitride ceramic protective head (5).

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