Method for removing inclusions in low-carbon low-silicon steel

Abstract

The invention belongs to the technical field of low-carbon low-silicon steel smelting, and particularly relates to a method for removing inclusions in low-carbon low-silicon steel. The method comprises the steps of converter smelting, LF furnace refining and ultrasonic treatment. The standing bottom argon blowing time of LF furnace refining is 8-15 min, and the ultrasonic treatment is 1-5 min after argon blowing of LF furnace refining is started, and the ultrasonic action time is 2-8 min; the power of the ultrasonic waves is 600-1000 w, and the frequency of the ultrasonic waves is 30-40 kHz; the low-carbon low-silicon steel comprises the following chemical components in percentage by weight: 0.03%-0.06% of C, less than or equal to 0.03% of Si, 0.15%-0.25% of Mn, less than or equal to 0.020% of P, less than or equal to 0.015% of S and 0.015%-0.045% of Als. According to the method, bottom argon blowing is carried out firstly, then ultrasonic waves with specific power and frequency are emitted to be combined with argon, and small-size inclusions in the molten steel are effectively removed.

Description

Technical Field

[0001] The present invention belongs to the technical field of smelting of low-carbon and low-silicon steel, and particularly relates to a method for removing inclusions in low-carbon and low-silicon steel. Background Art

[0002] In the smelting process, inclusion control is a crucial task, and the control of inclusions has a serious impact on the performance of the final product. Effective control of inclusions is of great significance for improving product quality and production efficiency. Compared with most steel grades, the number of large-sized inclusions generated during the refining process of low-carbon and low-silicon steel is relatively small. One reason is that the amount of gas such as carbon monoxide generated by the carbon-oxygen reaction is relatively small, and the probability of generating large-sized inclusions due to secondary oxidation caused by the carbon-oxygen reaction is reduced. The other reason is that silicon is a strong deoxidizing element. The silicon content in low-carbon and low-silicon steel is low, and its deoxidizing ability is relatively weak. During the refining process, a large amount of deoxidation products will not accumulate due to a large amount of deoxidation reaction of silicon to form large-sized inclusions. Currently, bottom blowing argon during the ladle furnace (LF) refining is a method beneficial for removing large-sized inclusions, but the remaining small-sized inclusions are difficult to deeply remove. Considering the inclusion size characteristics of low-carbon and low-silicon steel, a method for removing inclusions in low-carbon and low-silicon steel needs to be designed. Summary of the Invention

[0003] In order to effectively remove inclusions in low-carbon and low-silicon steel, the present invention provides a new method for removing inclusions.

[0004] To achieve the above invention object, the present invention adopts the following technical solutions:

[0005] The present invention provides a method for removing inclusions in low-carbon and low-silicon steel, and the steps of the method include: converter smelting, LF furnace refining, and ultrasonic treatment;

[0006] The ladle furnace (LF) refining has a static bottom blowing argon time of 8 - 15 min, an argon blowing flow rate of 400 - 900 l / min, and an argon blowing pressure of 0.4 - 0.6 MPa;

[0007] The ultrasonic treatment is carried out 1 - 5 min after the start of argon blowing in the LF furnace refining, and the ultrasonic wave acts for 2 - 8 min; the ultrasonic power is 600 - 1000 w, and the ultrasonic frequency is 30 - 40 kHz;

[0008] The chemical composition of the low-carbon and low-silicon steel by weight percentage includes: C: 0.03% - 0.06%, Si: ≤0.03%, Mn: 0.15% - 0.25%, P: ≤0.020%, S: ≤0.015%, Als: 0.015% - 0.045%.

[0009] In the above technical solution, further, the converter smelting is as follows: Alloy addition per ton of steel: 0.5 - 0.8 kg / t of high-carbon ferromanganese, 0.5 - 1.4 kg / t of aluminum pellets; Auxiliary addition per ton of steel: 25 - 40 kg / t of lime, 12 - 26 kg / t of dolomite; Tapping temperature is 1640 - 1680 °C, final carbon-pulling time ≥ 15 s, final carbon is 0.02 - 0.06%, oxygen-fixing aluminum wire addition is 1 - 3 kg / t, oxygen content is 400 - 600 ppm; It is transported to the argon station for argon blowing for 3 - 5 min.

[0010] In the above technical solution, further, the LF furnace refining is as follows: The arrival temperature of the LF furnace is 1580 - 1620 °C; The air permeability of the ladle is tested upon arrival; According to the oxygen-fixing value upon entering the station, the quantity of aluminum wire is supplemented, and the wire-feeding speed is 3 - 8 m / s; A large current of 18000 - 27000 A is used to raise the temperature and melt the slag; Alloy supplementation: Lime addition is 2 - 3.5 kg / t, aluminum pellets are 1 - 3.5 kg / t; Calming argon blowing.

[0011] In the above technical solution, further, the bottom of the ladle used in the LF furnace refining is connected to an argon steel pipe, the argon steel pipe is connected to an argon gas tank, one side of the argon steel pipe is provided with an ultrasonic transducer connected to the argon steel pipe, and the ultrasonic transducer is connected to an ultrasonic emission controller.

[0012] In the above technical solution, further, at least two porous plugs are provided at the bottom of the ladle to connect the argon steel pipe.

[0013] In the above technical solution, further, after argon blowing at the bottom of the ladle for 1 - 5 min, the ultrasonic emission controller is turned on, and the ultrasonic wave acts on the argon steel pipe for 2 - 8 minutes.

[0014] In the above technical solution, further, the ultrasonic transducer is a high-temperature resistant ceramic transducer.

[0015] Compared with the prior art, the beneficial effects of the present invention:

[0016] In view of the characteristics of inclusions in low-carbon and low-silicon steel, argon is first blown from the bottom to quickly remove large-sized inclusions in the molten steel. Then, ultrasonic waves with a specific power and frequency are emitted in combination with argon to remove small-sized inclusions in the molten steel, ensuring the purity of the molten steel. When using ultrasonic treatment, acoustic pressure waves are formed and propagated in the liquid. When the acoustic pressure waves reach the bubbles, intense oscillations and vortex effects are generated. When the amplitude of the acoustic pressure exceeds the limit that the surface tension of the bubbles can withstand, the surface of the bubbles will rupture. The high energy of the ultrasonic waves destroys the film structure on the surface of the bubbles, thereby decomposing large bubbles into many small bubbles. Small bubbles are beneficial for the removal of small-sized inclusions by adhesion. The smaller the size of the small bubbles, the better the adhesion of inclusions. By combining ultrasonic waves with bottom blowing of argon, large bubbles are broken up into small bubbles, effectively controlling the bubble size, and thus effectively removing small-sized inclusions.

[0017] The original structure of the ladle does not need to be modified in the present invention. Ultrasonic waves are directly applied to the argon steel pipe to disperse large bubbles in the molten steel into small bubbles, achieving the removal of small-sized inclusions. The ultrasonic transducer uses a high-temperature-resistant ceramic transducer, which is suitable for high-temperature and high-pressure industrial environments, and its temperature resistance can be as high as over 1000 °C. Brief Description of the Drawings

[0018] Figure 1 Schematic diagram of the structure of bottom blowing argon in the ladle. Detailed Embodiments

[0019] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0020] Example 1: LF refining and bottom blowing argon for ladle

[0021] Chemical composition: C: 0.04%, Si: 0.020%, Mn: 0.15%, P: 0.010%, S: 0.005%, Als: 0.020%.

[0022] Converter smelting: Alloy addition per ton of steel: High-carbon ferromanganese 0.7 kg / t, aluminum pellets 1.1 kg / t. Auxiliary material addition per ton of steel: Lime 30 kg / t, dolomite 20 kg / t. Tapping temperature 1650 °C, final tapping carbon time 17 s, final carbon 0.05%, oxygen content 450 ppm after feeding aluminum wire for oxygen determination at 1.5 kg / t. Transferred to the argon station for argon blowing for 5 min.

[0023] LF Furnace Refining: The temperature of the LF furnace when it arrives at the station is 1590°C. The air permeability of the ladle is tested when it arrives at the station, and the oxygen content is determined after blowing argon for 4 minutes. The amount of aluminum wire is supplemented according to the oxygen content determined when entering the station, and the feeding speed of the wire is 5.3 m / s to reach the target value at one time. A large current of 21000 A is used to raise the temperature and melt the slag. Alloy addition: The addition amount of lime is 3 kg / t, which is added in 3 batches with an interval of about 1 minute between batches. The addition amount of aluminum pellets is 2.7 kg / t. The time for starting the calming argon blowing is maintained for 15 minutes, the argon blowing flow rate is 800 l / min, and the argon blowing pressure is 0.6 MPa.

[0024] Ultrasonic Treatment: Two minutes after the bottom argon blowing of the ladle starts, the ultrasonic wave emission controller is turned on. The ultrasonic wave directly acts inside the argon gas steel pipe for about 7 minutes to break and float out the large bubbles.

[0025] As Figure 1 shown, the bottom of the ladle 1 is connected to the argon gas steel pipe 2, and the argon gas steel pipe 2 is connected to the argon gas cylinder 4. One side of the argon gas steel pipe 2 is provided with a high-temperature resistant ceramic ultrasonic transducer 5 connected to the argon gas steel pipe 2. The ultrasonic transducer 5 is connected to the ultrasonic wave emission controller 7. The argon gas cylinder and the argon gas steel pipe are connected by a pipeline, and a gas flow control valve 3 is set on the pipeline. The ultrasonic wave acts inside the argon gas steel pipe to break up the large bubbles in the molten steel to form small bubbles and float out. The small-sized inclusions are adsorbed on the small bubbles and removed together.

[0026] Using ultrasonic waves to act on the bubbles, the large bubbles are broken into small bubbles about 6 mm in size. The small bubbles adhere to the inclusions and promote the floating of the inclusions. To ensure that the large bubbles are broken into small bubbles, the ultrasonic wave emission parameters should be set before using the ultrasonic wave emitter. The ultrasonic power is 750 w, and the frequency is set to 35 kHz.

[0027] Samples are taken before and after the LF refining calming bottom argon blowing. According to the non-metallic inclusion inspection standard, the number of inclusions of different sizes within 12 mm 2 is inspected and counted. See Table 1. The refined sample -1 before process optimization is the process without the ultrasonic treatment step. The refined sample -1, refined sample -2, and refined sample -3 after process optimization are the processes with the above ultrasonic treatment steps. Three samples are taken. It can be seen from the results in Table 1 that after the ultrasonic wave acts on the bottom argon blowing, the number of inclusions is significantly reduced.

[0028] Table 1

[0029]

[0030] Example 2: LF Refining Calming Bottom Argon Blowing

[0031] Chemical Composition: C: 0.045%, Si: 0.015%, Mn: 0.23%, P: 0.015%, S: 0.010%, Als: 0.025%.

[0032] Converter smelting: alloy addition per ton of steel: high carbon ferromanganese 0.6kg / t, aluminum particles 1.1kg / t. Auxiliary materials addition per ton of steel: lime 35kg / t, dolomite 15kg / t. Steel tapping temperature 1660℃, final carbon pulling time 21s, final carbon 0.06%, fixed oxygen feeding aluminum wire 2kg / t, oxygen content 500ppm. Transport to argon station for argon blowing for 5min.

[0033] LF furnace refining: LF furnace arrival temperature is 1600℃. Test the ladle permeability at the station, and perform oxygen determination after blowing argon for 5 minutes. Add the amount of aluminum wire according to the oxygen value at the station, and feed the wire at a speed of 5.8m / s to reach the target value at one time. Use a large current of 22000A to heat and melt the slag. Add alloy: lime addition amount is 3kg / t, added in 3 batches, with a batch interval of about 1min. Aluminum particles are 3kg / t. Start the argon blowing time for calming, and keep it for 12min.

[0034] Use ultrasonic waves to act on bubbles, breaking up large bubbles into small bubbles of about 6 mm. Small bubbles adhere to inclusions and promote the floating of inclusions. To ensure that large bubbles are broken into small bubbles, the argon flow rate is 700l / min and the argon pressure is 0.6MPa. Before using the ultrasonic transmitter, the ultrasonic emission parameters should be set first. The ultrasonic power is 950w and the frequency is set to 30kHz. Install the high-temperature resistant ceramic transducer at the argon steel pipe. 2 minutes after the argon blowing starts at the bottom of the ladle, turn on the ultrasonic transmitter and let the ultrasonic wave act for about 7 minutes to break the large bubbles and float out. The structure is as follows Figure 1 shown.

[0035] Take the samples before and after LF refining, calming and bottom blowing argon, and inspect and count the 12mm 2 As shown in Table 2, the number of inclusions of different sizes in the steel is significantly reduced after the ultrasonic treatment step. The refined sample 1 before process optimization is the process without ultrasonic treatment step, the refined sample 1 after process optimization, the refined sample 2 after process optimization, and the refined sample 3 after process optimization are the processes with the above ultrasonic treatment step. The results in Table 2 show that the number of inclusions is significantly reduced after the ultrasonic treatment and bottom blowing of argon.

[0036] Table 2

[0037]

[0038] Example 3: LF refining sedation bottom blowing argon

[0039] Chemical composition: C: 0.03%, Si: 0.015%, Mn: 0.25%, P: 0.010%, S: 0.008%, Als: 0.025%.

[0040] Converter smelting: Alloy addition per ton of steel: 0.7 kg / t of high-carbon ferromanganese, 1.2 kg / t of aluminum pellets. Auxiliary addition per ton of steel: 33 kg / t of lime, 17 kg / t of dolomite. Tapping temperature is 1640 °C, final carbon-pulling time is 20 s, final carbon content is 0.04%, 1.8 kg / t of oxygen-fixing aluminum wire is fed, and oxygen content is 470 ppm. It is transported to the argon station for argon blowing for 4 min.

[0041] LF furnace refining: The arrival temperature at the LF furnace is 1580 °C. The air permeability of the ladle is tested upon arrival, and oxygen is determined after 5 min of argon blowing. The amount of aluminum wire is supplemented according to the oxygen-determination value upon entering the station, and the wire-feeding speed is 5.5 m / s to reach the target value at one time. A large current of 22,000 A is used to raise the temperature and melt the slag. Alloy supplementation: The addition amount of lime is 2.5 kg / t, added in 2 batches with an interval of about 1 min between batches. 3 kg / t of aluminum pellets. The starting time of calm argon blowing is maintained for 15 min.

[0042] Use ultrasonic waves to act on the bubbles, break the large bubbles into small bubbles about 6 mm in size, and the small bubbles adhere to the inclusions to promote the floating of the inclusions. To ensure that the large bubbles are broken into small bubbles, the argon blowing flow rate is 800 l / min, and the argon blowing pressure is 0.5 MPa. The ultrasonic transmitter should be set with ultrasonic emission parameters before use. The ultrasonic power is 800 w, and the frequency is set to 40 kHz. The high-temperature-resistant ceramic transducer is installed at the argon steel pipe. After 2 minutes of bottom argon blowing in the ladle, the ultrasonic transmitter is turned on, and the ultrasonic waves act for about 7 minutes to break and float the large bubbles. The structure is as Figure 1 shown.

[0043] Samples are taken before and after LF refining with calm bottom argon blowing. According to the non-metallic inclusion inspection standard, the number of inclusions of different sizes within 12 mm 2 is inspected and counted. See Table 3. The refined sample -1 before process optimization is the process without the ultrasonic treatment step. The refined sample -1, refined sample -2, and refined sample -3 after process optimization are the processes with the above ultrasonic treatment step. Three samples are taken. It can be seen from the results in Table 3 that after the ultrasonic wave acts on the bottom argon blowing, the number of inclusions is significantly reduced.

[0044] Table 3

[0045]

[0046] Comparative example 1:

[0047] The difference from Example 1 is that ultrasonic treatment is carried out simultaneously when calm argon blowing starts. The ultrasonic waves directly act inside the argon steel pipe, and the argon and ultrasonic waves act together for 13 minutes. The ultrasonic power is 750 w, and the frequency is set to 35 kHz.

[0048] Samples before and after LF refining and calming with bottom argon blowing were taken. According to the non-metallic inclusion inspection standard, the number of inclusions of different sizes within 12mm was inspected and counted. 2 As shown in Table 4, the refined sample - 1 before process optimization is the process without the ultrasonic treatment step, and the refined sample - 1, refined sample - 2, and refined sample - 3 after process optimization are the processes with the above ultrasonic treatment step. Three samples were taken. From the results in Table 4, it can be seen that compared with Example 1, performing ultrasonic treatment simultaneously at the beginning of argon blowing is not conducive to the removal of large-sized inclusions.

[0049] Table 4

[0050]

[0051] Comparative Example 2

[0052] The difference from Example 2 is that the ultrasonic power is 400w and the frequency is set to 15kHz.

[0053] Samples before and after LF refining and calming with bottom argon blowing were taken. According to the non-metallic inclusion inspection standard, the number of inclusions of different sizes within 12mm was inspected and counted. 2 As shown in Table 4, the refined sample - 1 before process optimization is the process without the ultrasonic treatment step, and the refined sample - 1, refined sample - 2, and refined sample - 3 after process optimization are the processes with the above ultrasonic treatment step. Three samples were taken. From the results in Table 4, it can be seen that compared with Example 2, the set ultrasonic power and frequency are not within the specified range, and the removal effect on small-sized inclusions is not obvious.

[0054] Table 5

[0055]

[0056] The above has described the examples of the present invention in detail in combination with the embodiments. However, the present invention is not limited to the above examples. Within the knowledge scope of those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention, and they should also be regarded as the protection scope of the present invention.

Claims

1. A method for removing inclusions in low-carbon and low-silicon steel, characterized in that, The steps of the method include: converter smelting, LF furnace refining, and ultrasonic treatment; During the LF furnace refining, the argon bottom blowing time for calming is 8 - 15 min, the argon blowing flow rate is 400 - 900 l / min, and the argon blowing pressure is 0.4 - 0.6 MPa; The ultrasonic treatment is carried out 1 - 5 min after the start of argon blowing in the LF furnace refining, and the ultrasonic action lasts for 2 - 8 min; the ultrasonic power is 600 - 1000 w, and the ultrasonic frequency is 30 - 40 kHz; The chemical composition of the low - carbon low - silicon steel by weight percentage includes: C: 0.03% - 0.06%, Si: ≤0.03%, Mn: 0.15% - 0.25%, P: ≤0.020%, S: ≤0.015%, Als: 0.015% - 0.045%.

2. The method for removing inclusions in low-carbon low-silicon steel according to claim 1, characterized in that, The converter smelting is as follows: the addition amount of alloy per ton of steel: high - carbon ferromanganese 0.5 - 0.8 kg / t, aluminum pellets 0.5 - 1.4 kg / t; the addition amount of auxiliary materials per ton of steel: lime 25 - 40 kg / t, dolomite 12 - 26 kg / t; the tapping temperature is 1640 - 1680 °C, the end - point carbon - pulling time ≥15 s, the end - point carbon is 0.02 - 0.06%, the oxygen - fixing aluminum wire feeding amount is 1 - 3 kg / t, the oxygen content is 400 - 600 ppm; it is transported to the argon station for argon blowing for 3 - 5 min.

3. The method for removing inclusions in low-carbon and low-silicon steel according to claim 1, characterized in that The LF furnace refining is as follows: the temperature of the LF furnace when arriving at the station is 1580 - 1620 °C; the air permeability of the ladle for the incoming test steel is measured; the amount of aluminum wire is supplemented according to the incoming oxygen - fixing value, and the wire - feeding speed is 3 - 8 m / s; a large current of 18000 - 27000 A is used for heating and slag melting; alloy supplementation: the addition amount of lime is 2 - 3.5 kg / t, and the addition amount of aluminum pellets is 1 - 3.5 kg / t; calming argon blowing.

4. The method for removing inclusions in low-carbon and low-silicon steel according to claim 1, characterized in that In the LF furnace refining, an argon gas steel pipe is connected to the bottom of the ladle, the argon gas steel pipe is connected to an argon gas tank, and a side of the argon gas steel pipe is provided with an ultrasonic transducer connected to the argon gas steel pipe, and the ultrasonic transducer is connected to an ultrasonic emission controller.

5. The method for removing inclusions in low-carbon low-silicon steel according to claim 4, characterized in that, At least two porous plugs are provided at the bottom of the ladle to connect the argon gas steel pipe.

6. The method for removing inclusions in low-carbon low-silicon steel according to claim 4, characterized in that, After argon blowing at the bottom of the ladle for 1 - 5 min, the ultrasonic emission controller is turned on, and the ultrasonic wave acts on the argon gas steel pipe for 2 - 8 minutes.

7. The method for removing inclusions in low-carbon and low-silicon steel according to claim 4, characterized in that, The ultrasonic transducer is a high - temperature - resistant ceramic transducer.

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