A continuous casting process for producing Nb-containing low-alloy steel thick slabs in an electric furnace.

Abstract

This invention discloses a continuous casting process for producing Nb-containing low-alloy steel thick slabs in an electric furnace, belonging to the field of metallurgical engineering technology. The process includes an electric furnace primary refining step, an LF refining step, a VD vacuum degassing step, a continuous casting step, and a straightening step. The continuous casting step includes: casting molten steel to form a thick slab; the formed thick slab, immediately after leaving the crystallizer, enters the foot roll section; the thick slab undergoes zoned cooling in a secondary cooling zone. This invention effectively reduces surface transverse cracks in Nb-containing low-alloy steel thick slabs through synergistic technologies such as end-to-end low-nitrogen pure smelting, pre-aluminum followed by niobium deoxidation and inclusion modification, crystallizer parameter control, zoned cooling in the secondary cooling zone, and precision control of the continuous casting equipment. This eliminates the need for surface finishing of the slab surface and allows it to be directly fed into the rolling furnace, significantly improving the hot delivery efficiency of the slab.

Description

Technical Field

[0001] This invention relates to the field of metallurgical engineering technology, specifically to a continuous casting production process for producing Nb-containing low alloy steel thick slabs in an electric furnace. Background Technology

[0002] Low-alloy steels, especially those containing 0.025-0.035% Nb, are highly susceptible to transverse cracks on the surface of continuously cast slabs. The main reasons include: The large straightening strain in the continuous casting of extra-thick slabs exacerbates the tendency for surface cracking. The steel produced by electric furnaces has a higher nitrogen content; Low-alloy steel requires Al ≥ 0.020%, but steels containing Al are more prone to straightening cracks.

[0003] Based on this, the present invention designs a continuous casting production process for producing Nb-containing low alloy steel thick slabs in an electric furnace to solve the above problems. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a continuous casting process for producing Nb-containing low-alloy steel slabs in an electric furnace.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A continuous casting process for producing Nb-containing low-alloy steel thick slabs in an electric furnace includes the following steps: I. Electric furnace primary refining process: Using scrap steel and molten iron as raw materials, when the furnace charge is fully melted and the temperature reaches 1500-1550°C, high-intensity oxygen supply decarburization is carried out using the furnace wall bundled oxygen lance and the furnace door carbon oxygen lance, and denitrification is driven by dense CO bubbles; then the steel is tapped. II. LF Refining Process: First, gray slag is made. Then, after the dissolved oxygen is <10ppm, pure aluminum wire is fed in. After the dissolved oxygen is <5ppm, niobium iron is added. After temperature adjustment, CaSi wire is fed in for inclusion modification treatment. Finally, by covering and soft blowing argon, the total nitrogen content of the molten steel is controlled to <60ppm at the refining endpoint. III. VD Vacuum Degassing Process: The ladle is hoisted from the LF refining furnace to the VD station, ensuring that the ladle clearance is not less than 800mm; the ladle is evacuated to a working pressure <67Pa, and held at this vacuum level for at least 18 minutes, during which the bottom-blown argon flow rate is controlled at 80-100L / min; at the VD endpoint, the total oxygen content of the molten steel is controlled to be <15ppm and the total nitrogen content to be <40ppm. IV. Continuous casting process, including: (4.1) The molten steel is hoisted to the turret of the continuous casting ladle and is ready to start casting; the molten steel flows from the ladle to the tundish and is conveyed by a long nozzle, and then the molten steel flows from the tundish into the crystallizer and is conveyed by an immersion nozzle. (4.2) Molten steel is cast into a thick slab in the crystallizer; (4.3) The formed thick slab just leaves the crystallizer and enters the foot roller section; (4.4) The thick slab undergoes zoned cooling in the secondary cooling section: Side section: Cooling water is controlled separately. Zone 1 water flow rate is 80-100L / min, Zone 2 water flow rate is 10-20L / min, and Zone 3 and above use protection water flow rate of 5-10L / min. Central area: Zones 1-4 use a safe water flow rate of 70-120L / min; Zone 5 and above use a weak water flow rate of 20-60L / min. V. Straightening process.

[0006] Furthermore, in step one, scrap steel with a total content of As, Sn, Pb, Sb and Bi of <0.05% is selected as raw material, and 25-30% of molten iron is added into the furnace.

[0007] Furthermore, in step one, the oxygen pressure of both the furnace wall cluster oxygen lance and the furnace door carbon-oxygen lance is controlled at 0.6-0.8 MPa, and the total oxygen supply flow rate is 4500-5500 Nm³. 3 / h; Automatic secondary lance is used for endpoint monitoring, endpoint carbon is controlled at C0.08-0.11%, and tapping temperature is controlled at 1600-1620°C.

[0008] Furthermore, more than 50 tons of steel are left in the furnace to prevent oxidized slag from entering the ladle. When the steel output reaches 1 / 4 of the ladle's capacity, 0.4-0.6 kg / t of high-purity aluminum blocks are added to the ladle for deoxidation, along with 0.5-1.0 kg / t of silicon-aluminum-barium-calcium composite deoxidizer. When the steel output reaches 1 / 2, 4-5 kg / t of pre-melted high-calcium pre-melted slag and 2-3 kg / t of lime are added. Throughout the tapping process, the double permeable bricks at the bottom of the ladle are kept open for argon blowing protection, with the flow rate controlled at 35-45 L / min.

[0009] Furthermore, in step two, after the ladle arrives at the LF refining station, 2-3 kg / t of active lime and 0.2-0.5 kg / t of silicon carbide are immediately added to the LF refining furnace, along with bottom-blown argon gas for stirring, until the slag color turns grayish-white; the FeO+MnO content in the slag is controlled to be <1.0%.

[0010] Furthermore, in step two, after determining that the dissolved oxygen is <10ppm, feed in 0.5-1.2m / t of pure aluminum wire, adjust the dissolved aluminum to 0.025-0.040%, and stir with argon for 3-5 minutes; after determining that the dissolved oxygen is <5ppm, add FeNb70 to ensure that Nb is 0.025-0.035%, and stir with argon for 3-5 minutes; adjust the temperature of the molten steel to 1590-1610°C, feed in 0.8-1.2m / t of CaSi wire at a speed of 2.5-3.5m / s; after feeding the CaSi wire, immediately cover the container, switch the bottom blowing argon flow rate to a soft blowing mode of 20-40L / min, and let it stand for 6-8 minutes.

[0011] Furthermore, in step three, the ladle is bottom-blown with argon through double permeable bricks. The argon pipeline of the double permeable bricks at the bottom of the ladle is connected, and the gas supply test is started to confirm that the gas is emitted evenly from both permeable bricks and forms a strong bidirectional convection on the surface of the molten steel.

[0012] Furthermore, in step three, after vacuum treatment, argon gas is introduced into the vacuum chamber to restore the pressure inside the chamber to atmospheric pressure; the bottom blowing argon gas flow rate is switched to a soft blowing mode of 20-40 L / min for 8-10 min.

[0013] Furthermore, in step four, the superheat of the molten steel in the tundish is strictly controlled at 15-25℃; Controlling crystallizer operating parameters: For thick slabs, the casting speed is stably controlled at 0.50 m / min; the heat flux density of the wide and narrow faces of the crystallizer is stably controlled at 0.8-1.0 MW / m. 2 The crystallizer adopts a non-sinusoidal vibration mode with an amplitude of 6-8 mm, a frequency of 65-85 cpm, and a skew factor controlled at 20-30%. It also includes the precision control of continuous casting equipment: the online arc connection accuracy between section 0 and section 1 is strictly controlled within ±0.3mm; the accuracy of all roll gaps in the fan-shaped section is controlled within ±0.5mm; and the shrinkage per meter of the roll gap in section 0 is set to 1.0-1.5mm / m.

[0014] Compared with the prior art, the beneficial effects of this invention are as follows: This invention effectively reduces the surface transverse cracks of Nb-containing low alloy steel slabs by using synergistic technologies such as low-nitrogen pure smelting throughout the entire process, aluminum-niobium deoxidation and inclusion modification, crystallizer parameter control, zoned cooling in the secondary cooling zone, and precision control of continuous casting equipment. This eliminates the need for finishing of the slab surface quality and allows it to be directly fed into the rolling heating furnace, significantly improving the hot delivery efficiency of the slab. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0016] Example 1: A continuous casting process for producing Nb-containing low-alloy steel thick slabs in an electric furnace, comprising the following steps: I. Electric Furnace (EAF) Primary Refining Process (1.1) Select scrap steel with a total content of As, Sn, Pb, Sb and Bi < 0.05% as raw material and add it to the electric furnace; (1.2) Add 25% molten iron to the furnace; (1.3) When the furnace charge is completely melted and the molten steel temperature reaches 1500°C, the furnace wall bundled oxygen lance and the furnace door carbon-oxygen lance are turned on. The oxygen pressure of both the furnace wall bundled oxygen lance and the furnace door carbon-oxygen lance is controlled at 0.6MPa, and the total oxygen supply flow rate is 4500Nm³. 3 / h; Nitrogen in molten steel is removed by dense CO bubbles generated by high-flow-rate decarburization reaction through high-intensity oxygen supply; endpoint monitoring is carried out by automatic auxiliary gun (TCO), the endpoint carbon is controlled at C0.08-0.11%, and the tapping temperature is controlled at 1610°C. (1.4) Tapping: Leave more than 50t of steel in the furnace to prevent oxidized slag from entering the ladle; when the tapping amount reaches 1 / 4 of the ladle's capacity, add 0.4kg / t of high-purity aluminum blocks to the ladle for deoxidation, and simultaneously add 1.0kg / t of silicon-aluminum-barium-calcium composite deoxidizer; when the tapping amount reaches 1 / 2, add 4kg / t of pre-melted high-calcium pre-melted slag (CaO-Al2O3 system, CaO>50%) and 3kg / t of lime. Throughout the tapping process, the double permeable bricks at the bottom of the ladle are kept open for weak argon blowing protection, with the flow rate controlled at 35L / min.

[0017] II. LF Refining Process (2.1) After the steel ladle arrives at the LF refining station, 2 kg / t of active lime and 0.5 kg / t of silicon carbide (SiC) are immediately added to the LF refining furnace, along with bottom-blown argon gas (150 L / min) and stirring, until the slag color turns grayish-white. The FeO+MnO content in the slag is controlled to be <1.0%.

[0018] (2.2) After determining that the dissolved oxygen is <10ppm, feed in 0.5m / t of pure aluminum wire, adjust the acid to dissolve aluminum to 0.040%, and stir with argon (150L / min) for 5min.

[0019] (2.3) After determining that the dissolved oxygen is <5ppm, add FeNb70 to ensure that Nb is 0.025%, and stir for 3min while blowing argon (200L / min).

[0020] (2.4) Adjust the temperature of molten steel to 1590°C, feed CaSi wire at a speed of 1.2m / t and 2.5m / s.

[0021] (2.5) After the CaSi line is finished, immediately cover it and switch the bottom blowing argon flow rate to a soft blowing mode of 20L / min. Let it stand for 8 minutes. Control the total nitrogen content of the molten steel to <60ppm at the refining endpoint.

[0022] III. VD Vacuum Degassing Process (3.1) The ladle is hoisted from the LF refining furnace to the VD station. First, the clear air of the ladle is measured to ensure that it is not less than 800 mm. The ladle adopts bottom blowing argon with double permeable bricks. The double permeable brick argon pipeline at the bottom of the ladle is connected and the gas supply test is started to confirm that the gas output of the two permeable bricks is uniform and a strong bidirectional convection is formed on the surface of the molten steel to ensure that there are no dead corners in the circulation of molten steel during vacuum treatment. (3.2) Secure the vacuum cover to the ladle, evacuate to the working pressure of 66 Pa, and maintain the pressure at this vacuum level for 18 min. During the pressure maintenance process, control the bottom blowing argon flow rate at 80 L / min. (3.3) After vacuum treatment, argon gas is introduced into the vacuum tank to restore the pressure in the tank to normal pressure; the bottom blowing argon gas flow rate is switched to soft blowing mode of 20L / min for 10min; the VD endpoint control of the total oxygen content of molten steel is <15ppm and the total nitrogen content is <40ppm.

[0023] IV. Continuous Casting (CC) Process (4.1) The molten steel is hoisted to the turret of the continuous casting ladle and is ready to start casting; the molten steel flows from the ladle to the tundish and is conveyed by a long nozzle, and then the molten steel flows from the tundish into the crystallizer and is conveyed by an immersion nozzle. The superheat of molten steel in the tundish is strictly controlled between 15-25℃; the entire process from the ladle to the tundish and from the tundish to the crystallizer is protected by argon gas to prevent secondary nitrogen absorption. (4.2) Molten steel is cast into a thick slab in the crystallizer; Controlling crystallizer operating parameters: For 460mm extra-thick slabs, the casting speed should be stably controlled at 0.50m / min, and large fluctuations are prohibited; the heat flux density of the wide and narrow faces of the crystallizer should be stably controlled at 0.8-1.0MW / m². 2 To ensure uniform growth of the initial billet shell; the crystallizer adopts a non-sinusoidal vibration mode with an amplitude of 6mm, a frequency of 85cpm, and a skew factor (waveform constant) of 20%.

[0024] (4.3) The formed thick slab just leaves the crystallizer and enters the foot roller section; (4.4) To ensure that the surface and corner temperatures of the 460mm thick slab remain above 920℃ when it enters the straightening machine (avoiding the brittle zone), the slab undergoes zoned cooling in the secondary cooling zone: The second cooling zone is divided into 11 cooling zones. For the edges (corners): cooling water is controlled separately, with zone 1 at 80L / min, zone 2 at 20L / min, and zones 3-11 using a protective water flow of 5L / min. For the middle section: zones 1-4 use a safe water flow (e.g., zone 1 120L / min, zones 2-3 80L / min, zone 4 90L / min), and zones 5-11 use a weak cooling water flow (e.g., zones 5-6 40L / min, zones 7-9 50L / min, zones 10-11 20L / min) to increase the straightening temperature at the slab corners. The surface temperature of the corner of the slab at the entrance of the straightening zone is ≥920℃, the center temperature of the wide face of the slab at the entrance of the straightening zone is ≥920℃, and the temperature difference between the corner and the center is ≤30℃.

[0025] (4.5) Precision control of continuous casting equipment: The online arc connection accuracy between segment 0 and segment 1 is strictly controlled within ±0.3mm to eliminate the additional mechanical bending stress caused by arc connection misalignment to the thick blank shell.

[0026] All roll gaps in the fan-shaped section are controlled within ±0.5mm to prevent bulging deformation of the billet caused by roll gap deviations, thereby reducing the cumulative strain before straightening.

[0027] The 0-segment roll gap adopts a large shrinkage design. Based on the solid phase shrinkage characteristics of 460mm steel, the shrinkage per meter of the 0-segment is set to 1.0mm / m.

[0028] V. Straightening Process After meeting the temperature requirements (corners and center ≥920℃, temperature difference ≤30℃), the thick slab enters the straightening machine to achieve straightening of the entire high plasticity zone.

[0029] When this entire process is implemented, 460mm thick Nb-containing low alloy steel slabs produced by electric furnaces can achieve straightening throughout the high plasticity zone, with a surface transverse crack incidence rate of 0.36%.

[0030] Example 2: A continuous casting process for producing Nb-containing low-alloy steel thick slabs in an electric furnace, comprising the following steps: I. Electric Furnace (EAF) Primary Refining Process (1.1) Select scrap steel with a total content of As, Sn, Pb, Sb and Bi < 0.05% as raw material and add it to the electric furnace; (1.2) Add 28% molten iron to the furnace; (1.3) When the furnace charge is completely melted and the molten steel temperature reaches 1550°C, the furnace wall bundled oxygen lance and the furnace door carbon-oxygen lance are turned on. The oxygen pressure of both the furnace wall bundled oxygen lance and the furnace door carbon-oxygen lance is controlled at 0.8MPa, and the total oxygen supply flow rate is 5500Nm³. 3 / h; Nitrogen in molten steel is removed by dense CO bubbles generated by high-flow-rate decarburization reaction through high-intensity oxygen supply; endpoint monitoring is carried out by automatic auxiliary gun (TCO), the endpoint carbon is controlled at C0.08-0.11%, and the tapping temperature is controlled at 1620°C. (1.4) Tapping: Leave more than 50t of steel in the furnace to prevent electric furnace oxidizer slag from entering the ladle; when the tapping amount reaches 1 / 4 of the ladle's capacity, add 0.6kg / t of high-purity aluminum blocks to the ladle for deoxidation, and simultaneously add 0.5kg / t of silicon-aluminum-barium-calcium composite deoxidizer; when the tapping amount reaches 1 / 2, add 5kg / t of pre-melted high-calcium pre-melted slag (CaO-Al2O3 system, CaO>50%) and 2kg / t of lime. Throughout the tapping process, the double permeable bricks at the bottom of the ladle are kept open for weak argon blowing protection, with the flow rate controlled at 45L / min.

[0031] II. LF Refining Process (2.1) After the steel ladle arrives at the LF refining station, 3 kg / t of active lime and 0.2 kg / t of silicon carbide (SiC) are immediately added to the LF refining furnace, along with bottom-blown argon gas (200 L / min) and stirring, until the slag color turns grayish-white. The FeO+MnO content in the slag is controlled to be <1.0%.

[0032] (2.2) After determining that the dissolved oxygen is <10ppm, feed in 1.2m / t of pure aluminum wire, adjust the acid to dissolve the aluminum to 0.025%, and stir for 3min by blowing argon (200L / min).

[0033] (2.3) After determining that the dissolved oxygen is <5ppm, add FeNb70 to ensure that Nb is 0.035%, and stir with argon (150L / min) for 5min.

[0034] (2.4) Adjust the temperature of molten steel to 1610°C, feed CaSi wire at a speed of 3.5 m / s at a rate of 0.8 m / t.

[0035] (2.5) After the CaSi line is finished, immediately cover it and switch the bottom blowing argon flow rate to a soft blowing mode of 40L / min. Let it stand for 6 minutes. Control the total nitrogen content of the molten steel to <60ppm at the refining endpoint.

[0036] III. VD Vacuum Degassing Process (3.1) The ladle is hoisted from the LF refining furnace to the VD station. First, the clear air of the ladle is measured to ensure that it is not less than 800 mm. The ladle adopts bottom blowing argon with double permeable bricks. The double permeable brick argon pipeline at the bottom of the ladle is connected and the gas supply test is started to confirm that the gas output of the two permeable bricks is uniform and a strong bidirectional convection is formed on the surface of the molten steel to ensure that there are no dead corners in the circulation of molten steel during vacuum treatment. (3.2) Secure the vacuum cover to the ladle, evacuate to the working pressure of 65Pa, and maintain the pressure at this vacuum level for 20 minutes. During the pressure maintenance process, control the bottom blowing argon flow rate at 100L / min. (3.3) After vacuum treatment, argon gas is introduced into the vacuum tank to restore the pressure in the tank to normal pressure; the bottom blowing argon gas flow rate is switched to soft blowing mode of 40L / min for 8min; the VD endpoint control of the total oxygen content of molten steel is <15ppm and the total nitrogen content is <40ppm.

[0037] IV. Continuous Casting (CC) Process (4.1) The molten steel is hoisted to the turret of the continuous casting ladle and is ready to start casting; the molten steel flows from the ladle to the tundish and is conveyed by a long nozzle, and then the molten steel flows from the tundish into the crystallizer and is conveyed by an immersion nozzle. The superheat of molten steel in the tundish is strictly controlled between 15-25℃; the entire process from the ladle to the tundish and from the tundish to the crystallizer is protected by argon gas to prevent secondary nitrogen absorption. (4.2) Molten steel is cast into a thick slab in the crystallizer; Controlling crystallizer operating parameters: For 460mm extra-thick slabs, the casting speed should be stably controlled at 0.50m / min, and large fluctuations are prohibited; the heat flux density of the wide and narrow faces of the crystallizer should be stably controlled at 0.8-1.0MW / m². 2 To ensure uniform growth of the initial billet shell; the crystallizer adopts a non-sinusoidal vibration mode with an amplitude of 8mm, a frequency of 65cpm, and a skew factor (waveform constant) of 30%.

[0038] (4.3) The formed thick slab just leaves the crystallizer and enters the foot roller section; (4.4) To ensure that the surface and corner temperatures of the 460mm thick slab remain above 920℃ when it enters the straightening machine (avoiding the brittle zone), the slab undergoes zoned cooling in the secondary cooling zone: The second cooling zone is divided into 11 cooling zones. For the edges (corners): cooling water is controlled separately, with zone 1 at 100L / min, zone 2 at 10L / min, and zones 3-11 using a protective water flow of 10L / min. For the middle: zones 1-4 use a safe water flow (e.g., zone 1 at 100L / min, zones 2-3 at 100L / min, zone 4 at 70L / min), and zones 5-11 use a weak cooling water flow (e.g., zones 5-6 at 60L / min, zones 7-9 at 30L / min, zones 10-11 at 40L / min) to increase the straightening temperature at the corners of the slab. The surface temperature of the corner of the slab at the entrance of the straightening zone is ≥920℃, the center temperature of the wide face of the slab at the entrance of the straightening zone is ≥920℃, and the temperature difference between the corner and the center is ≤30℃.

[0039] (4.5) Precision control of continuous casting equipment: The online arc connection accuracy between segment 0 and segment 1 is strictly controlled within ±0.3mm to eliminate the additional mechanical bending stress caused by arc connection misalignment to the thick blank shell.

[0040] All roll gaps in the fan-shaped section are controlled within ±0.5mm to prevent bulging deformation of the billet caused by roll gap deviations, thereby reducing the cumulative strain before straightening.

[0041] The 0-segment roll gap adopts a large shrinkage design. Based on the solid phase shrinkage characteristics of 460mm steel, the shrinkage per meter of the 0-segment is set to 1.5mm / m.

[0042] V. Straightening Process After meeting the temperature requirements (corners and center ≥920℃, temperature difference ≤30℃), the thick slab enters the straightening machine to achieve straightening of the entire high plasticity zone.

[0043] When this entire process is implemented, 460mm thick Nb-containing low alloy steel slabs produced by electric furnaces can achieve straightening throughout the high plasticity zone, with a surface transverse crack incidence rate of 0.25%.

[0044] Example 3: A continuous casting process for producing Nb-containing low-alloy steel thick slabs in an electric furnace, comprising the following steps: I. Electric Furnace (EAF) Primary Refining Process (1.1) Select scrap steel with a total content of As, Sn, Pb, Sb and Bi < 0.05% as raw material and add it to the electric furnace; (1.2) Add 30% molten iron into the furnace; (1.3) When the furnace charge is completely melted and the molten steel temperature reaches 1520°C, the furnace wall bundled oxygen lance and the furnace door carbon-oxygen lance are turned on. The oxygen pressure of both the furnace wall bundled oxygen lance and the furnace door carbon-oxygen lance is controlled at 0.7MPa, and the total oxygen supply flow rate is 5000Nm³. 3 / h; Nitrogen in molten steel is removed by dense CO bubbles generated by high-flow-rate decarburization reaction through high-intensity oxygen supply; endpoint monitoring is carried out by automatic auxiliary gun (TCO), the endpoint carbon is controlled at C0.08-0.11%, and the tapping temperature is controlled at 1600°C. (1.4) Tapping: Leave more than 50t of steel in the furnace to prevent oxidized slag from entering the ladle; when the tapping amount reaches 1 / 4 of the ladle's capacity, add 0.5kg / t of high-purity aluminum blocks to the ladle for deoxidation, and simultaneously add 0.6kg / t of silicon-aluminum-barium-calcium composite deoxidizer; when the tapping amount reaches 1 / 2, add 4.3kg / t of pre-melted high-calcium pre-melted slag (CaO-Al2O3 system, CaO>50%) and 2.2kg / t of lime. Throughout the tapping process, the double permeable bricks at the bottom of the ladle are kept open for weak argon blowing protection, with the flow rate controlled at 40L / min.

[0045] II. LF Refining Process (2.1) After the steel ladle arrives at the LF refining station, 2.3 kg / t of active lime and 0.3 kg / t of silicon carbide (SiC) are immediately added to the LF refining furnace, along with bottom-blown argon gas (180 L / min) and stirring, until the slag color turns grayish-white. The FeO+MnO content in the slag is controlled to be <1.0%.

[0046] (2.2) After determining that the dissolved oxygen is <10ppm, feed in 1.0m / t of pure aluminum wire, adjust the acid to dissolve aluminum to 0.030%, and stir for 4min by blowing argon (180L / min).

[0047] (2.3) After determining that the dissolved oxygen is <5ppm, add FeNb70 to ensure that Nb is 0.030%, and blow argon (180L / min) and stir for 4min.

[0048] (2.4) Adjust the temperature of molten steel to 1600°C, feed CaSi wire at a rate of 1.0 m / t and a speed of 3.0 m / s.

[0049] (2.5) After the CaSi line is finished, immediately cover it and switch the bottom blowing argon flow rate to a soft blowing mode of 30L / min. Let it stand for 7 minutes. Control the total nitrogen content of the molten steel to <60ppm at the refining endpoint.

[0050] III. VD Vacuum Degassing Process (3.1) The ladle is hoisted from the LF refining furnace to the VD station. First, the clear air of the ladle is measured to ensure that it is not less than 800 mm. The ladle adopts bottom blowing argon with double permeable bricks. The double permeable brick argon pipeline at the bottom of the ladle is connected and the gas supply test is started to confirm that the gas output of the two permeable bricks is uniform and a strong bidirectional convection is formed on the surface of the molten steel to ensure that there are no dead corners in the circulation of molten steel during vacuum treatment. (3.2) Secure the vacuum cover to the ladle, evacuate to the working pressure of 65 Pa, and maintain the pressure at this vacuum level for 22 min. During the pressure maintenance process, control the bottom blowing argon flow rate at 90 L / min. (3.3) After vacuum treatment, argon gas is introduced into the vacuum tank to restore the pressure in the tank to normal pressure; the bottom blowing argon gas flow rate is switched to soft blowing mode of 30L / min for 9min; the VD endpoint control of the total oxygen content of molten steel is <15ppm and the total nitrogen content is <40ppm.

[0051] IV. Continuous Casting (CC) Process (4.1) The molten steel is hoisted to the turret of the continuous casting ladle and is ready to start casting; the molten steel flows from the ladle to the tundish and is conveyed by a long nozzle, and then the molten steel flows from the tundish into the crystallizer and is conveyed by an immersion nozzle. The superheat of molten steel in the tundish is strictly controlled between 15-25℃; the entire process from the ladle to the tundish and from the tundish to the crystallizer is protected by argon gas to prevent secondary nitrogen absorption. (4.2) Molten steel is cast into a thick slab in the crystallizer; Controlling crystallizer operating parameters: For 460mm extra-thick slabs, the casting speed should be stably controlled at 0.50m / min, and large fluctuations are prohibited; the heat flux density of the wide and narrow faces of the crystallizer should be stably controlled at 0.8-1.0MW / m². 2 To ensure uniform growth of the initial billet shell; the crystallizer adopts a non-sinusoidal vibration mode with an amplitude of 7mm, a frequency of 72cpm, and a skew factor (waveform constant) of 25%.

[0052] (4.3) The formed thick slab just leaves the crystallizer and enters the foot roller section; (4.4) To ensure that the surface and corner temperatures of the 460mm thick slab remain above 920℃ when it enters the straightening machine (avoiding the brittle zone), the slab undergoes zoned cooling in the secondary cooling zone: The second cooling zone is divided into 11 cooling zones. For the edges (corners): cooling water is controlled separately, with zone 1 at 90L / min, zone 2 at 15L / min, and zones 3-11 using a protective water flow of 7L / min. For the middle section: zones 1-4 use a safe water flow (e.g., zone 1 at 110L / min, zones 2-3 at 90L / min, zone 4 at 80L / min), and zones 5-11 use a weak cooling water flow (e.g., zones 5-6 at 50L / min, zones 7-9 at 40L / min, and zones 10-11 at 30L / min) to increase the straightening temperature at the slab corners. The surface temperature of the corner of the slab at the entrance of the straightening zone is ≥920℃, the center temperature of the wide face of the slab at the entrance of the straightening zone is ≥920℃, and the temperature difference between the corner and the center is ≤30℃.

[0053] (4.5) Precision control of continuous casting equipment: The online arc connection accuracy between segment 0 and segment 1 is strictly controlled within ±0.3mm to eliminate the additional mechanical bending stress caused by arc connection misalignment to the thick blank shell.

[0054] All roll gaps in the fan-shaped section are controlled within ±0.5mm to prevent bulging deformation of the billet caused by roll gap deviations, thereby reducing the cumulative strain before straightening.

[0055] The 0-segment roll gap adopts a large shrinkage design. Based on the solid phase shrinkage characteristics of 460mm steel, the shrinkage per meter of the 0-segment is set to 1.2mm / m.

[0056] V. Straightening Process After meeting the temperature requirements (corners and center ≥920℃, temperature difference ≤30℃), the thick slab enters the straightening machine to achieve straightening of the entire high plasticity zone.

[0057] When this entire process is implemented, 460mm thick Nb-containing low alloy steel slabs produced by electric furnaces can achieve straightening throughout the high plasticity zone, with a surface transverse crack incidence rate of 0.4%.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A continuous casting process for producing Nb-containing low-alloy steel thick slabs in an electric furnace, characterized in that, Includes the following steps: I. Electric furnace primary refining process: Using scrap steel and molten iron as raw materials, when the furnace charge is fully melted and the temperature reaches 1500-1550°C, high-intensity oxygen supply decarburization is carried out using the furnace wall bundled oxygen lance and the furnace door carbon oxygen lance, and denitrification is driven by dense CO bubbles; then the steel is tapped. II. LF Refining Process: First, gray slag is made. Then, after the dissolved oxygen is <10ppm, pure aluminum wire is fed in. After the dissolved oxygen is <5ppm, niobium iron is added. After temperature adjustment, CaSi wire is fed in for inclusion modification treatment. Finally, by covering and soft blowing argon, the total nitrogen content of the molten steel is controlled to <60ppm at the refining endpoint. III. VD Vacuum Degassing Process: The ladle is hoisted from the LF refining furnace to the VD station, ensuring that the ladle clearance is not less than 800mm; the ladle is evacuated to a working pressure <67Pa, and held at this vacuum level for at least 18 minutes, during which the bottom-blown argon flow rate is controlled at 80-100L / min; at the VD endpoint, the total oxygen content of the molten steel is controlled to be <15ppm and the total nitrogen content to be <40ppm. IV. Continuous casting process, including: Molten steel is hoisted to the turret of the continuous casting ladle, ready to begin casting; molten steel flows from the ladle to the tundish, conveyed by a long nozzle, and then flows from the tundish into the crystallizer, conveyed by a submerged entry nozzle. Molten steel is poured and cast in a crystallizer to form a thick slab. The formed thick slab has just left the crystallizer and entered the foot roller section; The thick slab undergoes zoned cooling in the secondary cooling section: Side section: Cooling water is controlled separately. Zone 1 water flow rate is 80-100L / min, Zone 2 water flow rate is 10-20L / min, and Zone 3 and above use protection water flow rate of 5-10L / min. Central area: Zones 1-4 use a safe water flow rate of 70-120L / min; Zone 5 and above use a weak water flow rate of 20-60L / min. V. Straightening process.

2. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, In step one, scrap steel with a total content of As, Sn, Pb, Sb and Bi of <0.05% is selected as raw material, and 25-30% of molten iron is added into the furnace.

3. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, In step one, the oxygen pressure of the oxygen lance in the wall cluster and the oxygen lance in the door is controlled at 0.6-0.8 MPa, and the total oxygen supply flow is 4500-5500 Nm 3 / h; the end point is monitored by using an automatic sub-lance, the end point carbon is controlled at C0.08-0.11%, and the tapping temperature is controlled at 1600-1620 °C.

4. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, Steel is left inside the furnace to prevent oxidized slag from entering the ladle. When the steel output reaches 1 / 4 of the ladle's capacity, 0.4-0.6 kg / t of high-purity aluminum blocks are added to the ladle for deoxidation, along with 0.5-1.0 kg / t of silicon-aluminum-barium-calcium composite deoxidizer. When the steel output reaches 1 / 2, 4-5 kg / t of pre-melted high-calcium pre-melted slag and 2-3 kg / t of lime are added. Throughout the tapping process, the double permeable bricks at the bottom of the ladle are kept open for argon blowing protection, with the flow rate controlled at 35-45 L / min.

5. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, In step two, after the steel ladle arrives at the LF refining station, 2-3 kg / t of active lime and 0.2-0.5 kg / t of silicon carbide are immediately added to the LF refining furnace, and stirred with bottom-blown argon gas until the slag color turns grayish-white; the FeO+MnO content in the slag is controlled to be less than 1.0%.

6. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, In step two, after determining that the dissolved oxygen is <10ppm, feed in 0.5-1.2m / t of pure aluminum wire, adjust the dissolved aluminum to 0.025-0.040%, and stir with argon for 3-5 minutes; after determining that the dissolved oxygen is <5ppm, add FeNb70 to ensure that Nb is 0.025-0.035%, and stir with argon for 3-5 minutes; adjust the temperature of the molten steel to 1590-1610°C, feed in 0.8-1.2m / t of CaSi wire at a speed of 2.5-3.5m / s; after feeding the CaSi wire, immediately cover the tank, switch the bottom blowing argon flow rate to a soft blowing mode of 20-40L / min, and let it stand for 6-8 minutes.

7. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, In step three, the ladle is argon-blown from the bottom using double permeable bricks. The argon pipeline of the double permeable bricks at the bottom of the ladle is connected, and the gas supply test is started to confirm that the gas output from both permeable bricks is uniform and that a strong bidirectional convection is formed on the surface of the molten steel.

8. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, In step three, after vacuum treatment, argon gas is introduced into the vacuum chamber to restore the pressure inside the chamber to atmospheric pressure; the bottom blowing argon gas flow rate is switched to a soft blowing mode of 20-40 L / min for 8-10 min.

9. The continuous casting production process for producing Nb-containing low-alloy steel thick slabs in an electric furnace according to claim 1, characterized in that, In step four, the superheat of the molten steel in the tundish is strictly controlled between 15-25℃; Controlling crystallizer operating parameters: For thick slabs, the casting speed is stably controlled at 0.50 m / min; the heat flux density of the wide and narrow faces of the crystallizer is stably controlled at 0.8-1.0 MW / m. 2 The crystallizer adopts a non-sinusoidal vibration mode with an amplitude of 6-8 mm, a frequency of 65-85 cpm, and a skew factor controlled at 20-30%. It also includes precision control of continuous casting equipment: the online arc connection accuracy between section 0 and section 1 is controlled within ±0.3mm; the accuracy of all roll gaps in the fan-shaped section is controlled within ±0.5mm; and the shrinkage per meter of the roll gap in section 0 is set to 1.0-1.5mm / m.