Compact billet continuous casting process suitable for cable steel making

Abstract

The present application relates to a kind of billet continuous casting processes suitable for cable steel smelting, comprising the following steps: 1) using quartz quality protection sleeve, ladle working layer refractory, ladle covering agent, stopper and submerged entry nozzle material are all used micro-carbon material;2) using crystallizer electromagnetic stirring process, control the center magnetic induction intensity of copper tube after crystallizer is 450±50GS;3) ladle roasting is ≥3.5h, ensure that package wall temperature is ≥1100℃, ladle is filled with argon before and during pouring process;4) low carbon steel protecting slag is used for pouring operation, after liquid level is stable and turns into liquid level automatic control, start to replace and use carbon-free protecting slag;5) the inner diameter of water gap is expanded to 35-45mm;6) when the net weight of molten steel in ladle is 5-7 tons, close ladle slide;7) control the superheat of molten steel in ladle, no less than 20℃;after crystallizer liquid level is stable, according to high speed and constant speed pouring mode operation, the present application is suitable for cable steel smelting billet continuous casting process, which can improve the production quality and production efficiency of cable steel.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy, and more specifically, to a continuous casting process for small billets suitable for smelting cable steel. Background Technology

[0002] Cable steel can be used as electronic lead wires, coaxial cables, shielded copper-clad stranded wires, headphone cables, enameled wires, etc. Due to conductivity and drawing requirements (minimum drawing diameter of 0.05mm), cable steel has extremely strict requirements for its molten steel composition. A certain high-grade cable steel has the following composition requirements: C≤0.0018%, Si≤0.020%, Mn≤0.050%, P≤0.015%, S≤0.005%, Alt≤0.010%, N≤0.0030%.

[0003] Cable steel requires extremely low carbon content. Besides ensuring the steelmaking process guarantees the correct carbon content in the molten steel, the continuous casting process can also easily lead to excessive carbon content. Furthermore, poor protective casting can also cause excessive nitrogen (N) content in the steel.

[0004] Due to the low carbon, low manganese, and low silicon characteristics of cable steel, the oxygen content in the steel is usually high, and subcutaneous bubbles are prone to appear in the billet, which will seriously affect its drawing performance. High-grade cable steel requires strict control of the occurrence of subcutaneous bubbles in the billet.

[0005] The oxygen content in cable steel is controlled by the aluminum content. However, casting aluminum-containing steel in small square billets (side length ≤ 200mm) is prone to nodule formation, which can lead to production interruptions. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a small billet continuous casting process suitable for cable steel smelting, which can improve the production quality and efficiency of cable steel.

[0007] The technical solution adopted by this invention to solve its technical problem is: to construct a small billet continuous casting process suitable for cable steel smelting, including the following steps:

[0008] 1) Quartz protective sleeves are used, and the refractory material of the working layer of the tundish, the tundish covering agent, the stopper rod and the submerged nozzle material are all made of micro-carbon material;

[0009] 2) The crystallizer electromagnetic stirring process is adopted to control the center magnetic induction intensity of the copper tube with crystallizer to be 450±50GS;

[0010] 3) The intermediate ladle is baked for ≥3.5h to ensure the ladle wall temperature is ≥1100℃. Argon gas is used to purge the intermediate ladle before pouring and during the pouring process.

[0011] 4) Low-carbon steel protective slag is used during the initial pouring operation. After the liquid level stabilizes and the liquid level is switched to automatic control, carbon-free protective slag is used instead.

[0012] 5) In response to the characteristics of cable steel nodules, the overall submersible nozzle was optimized by increasing the inner diameter of the nozzle to 35-45mm, so that alumina inclusions would not accumulate and adhere to the inner wall of the nozzle.

[0013] 6) When the net weight of molten steel in the ladle is 5-7 tons, close the ladle slide to prevent slag from entering the tundish and contaminating the molten steel; at the same time, strictly control the ladle changing time to not exceed 150 seconds to control slag entrapment and steel oxidation caused by unsteady casting during continuous casting.

[0014] 7) Control the superheat of the molten steel in the tundish to be no less than 20°C; after the start of casting is completed and the liquid level in the crystallizer is stable, operate according to the high casting speed and constant casting speed steel casting mode.

[0015] According to the above scheme, in step 1), the C content of the stopper rod is ≤2.9%, the C content of the refractory material in the working layer of the intermediate ladle is ≤0.8%, the C content of the submerged nozzle is ≤9%, and the C content of the intermediate ladle covering agent is ≤0.5%.

[0016] According to the above scheme, in step 7), the superheat of the molten steel in the ladle of the first casting furnace is controlled at a target of 30-50℃, and the superheat of the molten steel in the ladle of the consecutive casting furnaces is controlled at a target of 20-40℃.

[0017] According to the above scheme, in step 7), the casting speed is controlled according to the actual production rhythm of steelmaking on site and the casting machine capacity. The casting speed of a 150-170 cubic cross-section casting machine is not less than 2.4 m / min, and the casting speed of a 180-200 cubic cross-section casting machine is not less than 1.6 m / min.

[0018] The continuous casting process for small square billets applicable to cable steel smelting, as described in this invention, has the following beneficial effects:

[0019] 1. The raw materials for the refractory materials of the tundish working layer, the tundish covering agent, the stopper rod and the submerged nozzle are all made of low-carbon materials to minimize the carbonization effect of the refractory materials on the molten steel.

[0020] 2. The magnetic induction intensity at the center of the copper tube with crystallizer should be controlled at 450±50GS. If the magnetic induction intensity is too low, the stirring effect will be insignificant. If the magnetic induction intensity is too high, the steel flow in the crystallizer will be disturbed too much, which will cause the immersion nozzle to erode too quickly and easily lead to leakage.

[0021] 3. The conventional low-carbon steel protective slag is used during the initial casting operation. After the liquid level stabilizes and the liquid level is switched to automatic control, carbon-free protective slag is used. This mode can not only effectively improve the problem of subcutaneous bubbles in ultra-low carbon steel, but also effectively reduce the carbon increase of protective slag in the continuous casting process.

[0022] 4. In response to the characteristics of cable steel nodules, the overall submersible nozzle was optimized by increasing the inner diameter of the nozzle, so that alumina inclusions would not accumulate and adhere to the inner wall of the nozzle.

[0023] 5. This invention reduces the need for speed adjustment during the casting process, especially the speed reduction operation, which can effectively improve the nodule formation in small square billet aluminum steel casting. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0025] Figure 1 This is a diagram of a conventional small square billet integral submerged sprue structure;

[0026] Figure 2 This is a diagram of the optimized integral immersion gate structure for small square billets according to the present invention. Detailed Implementation

[0027] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] In the absence of abnormalities such as diversion, the steelmaking process must ensure that the T[O] content in the molten steel in the continuous casting ladle is ≤100ppm and that other components are qualified.

[0029] The continuous casting process for small square billets applicable to cable steel smelting of the present invention includes the following steps:

[0030] 1) Use quartz protective sleeves and replace them with new ones for each furnace. Do not use more corrosion-resistant aluminum-carbon protective sleeves. The protective sleeves should be protected by conventional argon sealing.

[0031] 2) The raw materials for the refractory materials of the tundish working layer, the tundish covering agent, the stopper rod, and the submerged entry nozzle are all made of low-carbon materials to minimize the carbon increase effect of the refractory materials on the molten steel. The [C] content of the stopper rod is ≤2.9%, the [C] content of the refractory material of the tundish working layer is ≤0.8%, the [C] content of the submerged entry nozzle is ≤9%, and the [C] content of the tundish covering agent is ≤0.5%.

[0032] 3) The crystallizer electromagnetic stirring process is adopted to improve the gas overflow of molten steel in the crystallizer and reduce the formation of subsurface bubbles in the billet. By adjusting the working current and frequency of the electromagnetic stirring, the magnetic induction intensity at the center of the copper tube of the crystallizer is controlled to be 450±50GS. If the magnetic induction intensity is too low, the stirring effect will be insignificant; if the magnetic induction intensity is too high, the steel flow in the crystallizer will be disturbed too much, which will cause the submerged nozzle to erode too quickly and easily lead to leakage.

[0033] 4) Baking of the intermediate ladle for ≥3.5h to ensure the ladle wall temperature ≥1100℃. Argon gas is purged into the intermediate ladle before and during the pouring process (if there is an argon blowing device with a ladle cover, open the argon gas; if there is no argon blowing device with a ladle cover, connect one end of the hose to the argon gas pipe and the other end to the steel pipe, insert the steel pipe into the intermediate ladle for manual argon blowing).

[0034] 5) Conventional low-carbon steel protective slag is used during the initial casting operation. Once the liquid level stabilizes and automatic level control is implemented, carbon-free protective slag should be used instead. Carbon-free protective slag does not contain carbonaceous materials such as graphite and carbon black; it is a powdery slag. If carbon-free protective slag is used during initial casting, the unstable liquid level in the crystallizer and the large amount of protective slag added will result in more dust in the crystallizer. On-site operation will not be able to clearly see the liquid level in the crystallizer, making it easy for steel leakage to occur during initial casting. Therefore, carbon-free protective slag should be used only after the liquid level in the crystallizer stabilizes and automatic level control is implemented.

[0035] Because cable steel has a high [O] content, it easily reacts with carbonaceous materials in the protective slag to form CO or CO2 gas, leading to subcutaneous bubbles in the cast billet. Using carbon-free protective slag can effectively avoid the above problems, thus effectively improving the subcutaneous bubble problem in ultra-low carbon steel, and also effectively reducing the carbon increase of the protective slag in the continuous casting process.

[0036] C(s) = [C]

[0037] [C] + [O] = CO (g)

[0038] [C] + 2[O] = CO2 (g)

[0039] Table 1 shows the physicochemical properties of the carbon-free protective slag used in the smelting of cable steel from small square billets:

[0040] Table 1. Physicochemical properties of carbon-free protective slag in the smelting of cable steel from small square billets.

[0041]

[0042] 6) During the final stage of casting, slag and steel flow into the tundish, which seriously affects the quality of the molten steel. Therefore, when the net weight of the molten steel in the ladle is about 5-7 tons, the ladle slide should be closed to prevent slag from entering the tundish and contaminating the molten steel.

[0043] Once the molten steel in the ladle has been poured out, the time for changing the ladle must be strictly controlled to not exceed 150 seconds. If the time for changing the ladle is too long, the liquid level will drop too much, and the flushing process after the molten steel is connected to the next ladle can easily lead to slag buildup and oxidation of the molten steel, contaminating the molten steel.

[0044] 7) Since cable steel does not strongly corrode the sprue, the main problem in producing cable steel from small billets is nodule formation. Furthermore, the number of consecutive castings per ladle for cable steel produced on small billet casting machines in China is generally low (usually less than 8 heats). Therefore, the wall thickness of conventional submerged entry nozzles can be reduced, while the diameter of the nozzle's inner hole can be increased. Figure 1 The standard ≤28mm has been expanded to Figure 2 The diameter is 35-45mm. With the optimized nozzle, the taper of the inner hole is reduced, which makes it less likely for alumina inclusions to accumulate and adhere to the inner wall of the nozzle. At the same time, because the diameter of the inner hole of the nozzle is significantly enlarged, even if there is a small amount of adhesion, it will not affect the normal control of the casting flow.

[0045] 8) Superheat and Casting Speed ​​Control: The target superheat of the molten steel in the ladle during the initial casting furnace is 30-50℃, and the target superheat of the molten steel in the ladle during consecutive casting furnaces is 20-40℃. The superheat of the molten steel should not be lower than 20℃, otherwise it will reduce the fluidity of the molten steel and aggravate the occurrence of nodule formation. After the initial casting is completed and the liquid level in the crystallizer stabilizes, steel casting should be carried out at high and constant casting speeds (the casting speed should be controlled according to the actual production rhythm of steelmaking on site and the casting machine capacity, but should not be too low; for example, the casting speed of a 150-170 square section casting machine should not be lower than 2.4 m / min, and the casting speed of a 180-200 square section casting machine should not be lower than 1.6 m / min). Reducing the casting speed adjustment during the casting process, especially the speed reduction operation, can effectively improve the nodule formation of aluminum steel cast from small square billets.

[0046] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A continuous casting process for small square billets suitable for smelting cable steel, characterized in that, Includes the following steps: (1) Quartz protective sleeves are used, and the refractory material of the working layer of the tundish, the tundish covering agent, the stopper rod and the submerged nozzle material are all made of micro-carbon material; (2) The electromagnetic stirring process of the crystallizer is adopted to control the central magnetic induction intensity of the copper tube with crystallizer to be 450±50GS; (3) The intermediate ladle is baked for ≥3.5h to ensure that the ladle wall temperature is ≥1100℃. Argon gas is filled into the intermediate ladle before pouring and during the pouring process. (4) Low-carbon steel protective slag is used during the initial pouring operation. After the liquid level stabilizes and automatic liquid level control is implemented, carbon-free protective slag is used instead. The carbon-free protective slag includes the following components, expressed as a percentage by mass: SiO2 35~40%, CaO 25~30%, Al2O3 10~13%, MgO≤5%, F- 4~6%, Na2O+K2O 6~9%, TC 1~3%, H2O≤0.5%; (5) In view of the characteristics of cable steel nodules, the overall submersible nozzle is optimized by increasing the inner diameter of the nozzle to 35-45mm, so that alumina inclusions are not easy to accumulate and adhere on the inner wall of the nozzle. (6) When the net weight of molten steel in the ladle is 5-7 tons, close the ladle slide to prevent slag from entering the tundish and contaminating the molten steel; at the same time, strictly control the ladle replacement time to not exceed 150s to control slag entrapment and molten steel oxidation caused by unsteady casting during continuous casting. (7) Control the superheat of the molten steel in the tundish to be no less than 20°C; after the start of casting is completed and the liquid level in the crystallizer is stable, operate according to the high casting speed and constant casting speed casting mode. In step 1), the C content of the stopper rod is ≤2.9%, the C content of the refractory material in the working layer of the tundish is ≤0.8%, the C content of the submerged nozzle is ≤9%, and the C content of the tundish covering agent is ≤0.5%. In step 7), the superheat of the molten steel in the ladle of the first casting furnace is controlled at a target of 30-50°C, and the superheat of the molten steel in the ladle of the consecutive casting furnaces is controlled at a target of 20-40°C. In step 7), the casting speed is controlled according to the actual production rhythm of steelmaking on site and the casting machine capacity. The casting speed of a 150-170 cubic cross-section casting machine is not less than 2.4 m / min, and the casting speed of a 180-200 cubic cross-section casting machine is not less than 1.6 m / min.

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