Metallurgy method for continuous casting tundish

Abstract

The invention relates to the technical field of metallurgy, in particular to a continuous casting tundish metallurgy method which comprises the steps that refining is conducted after converter tapping, soft blowing is conducted after refining is finished, then continuous casting is conducted, and in the molten steel pouring link of the continuous casting procedure, mixed powder is sprayed into a tundish for deep deoxidation and desulfurization treatment, the mixed powder is prepared by uniformly mixing powdery CaC2 and magnesium powder. The calcium wire does not need to be fed into the molten steel in the refining link, time and equipment space are saved, and the production efficiency of steel is improved; the consumption of the mixed powder is small, the use is flexible, and a better metallurgical effect can be achieved; the cleanliness and quality of molten steel can be better improved, and introduction of new impurities is avoided; the cost is low and the potential safety hazard is low.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a continuous casting tundish metallurgical method. Background Art

[0002] In the field of metallurgy, the production of steel mainly includes ironmaking, steelmaking, continuous casting, rolling, post-processing and other steps. Among them, the continuous casting tundish metallurgy technology is a technology that uses a tundish to further treat and purify molten steel during the continuous casting process, which is an extremely important part of the iron and steel metallurgy process. Traditional tundish metallurgy technology mainly includes functions such as voltage stabilization, diversion, promoting the floating of inclusions, preventing secondary oxidation of molten steel, and reasonably adjusting the temperature of molten steel in the tundish.

[0003] In the production process of steel, after the initial smelting of the molten steel, in order to further remove impurities in the molten steel, adjust the composition of the molten steel and improve the composition and shape of inclusions, it is necessary to use equipment such as wire feeders to feed calcium wire into the molten steel of the refining equipment in the refining process. Calcium wire is a metal calcium solid cored wire. Feeding calcium wire in the refining process can transform the inclusions in the molten steel from irregular shapes to spherical or approximately spherical shapes, thereby reducing the stress concentration caused by the inclusions in the finished steel and improving the stamping and welding properties of the steel; calcium can react with impurity elements such as sulfur and oxygen in the molten steel to generate inclusions that are easy to float and remove, thereby improving the cleanliness of the molten steel and the corrosion resistance of the steel; an appropriate amount of calcium can also refine the grains and improve the comprehensive properties of the steel such as strength, toughness and plasticity.

[0004] However, in the prior art, the operation of the calcium feeding line requires precise control of the feeding speed and depth to ensure that calcium can be evenly distributed in the molten steel. The amount and timing of calcium wire addition are difficult to grasp and require a long time, which will slow down the production rhythm of steel and have an adverse impact on the continuity of steel production. The price of calcium wire and the investment and operating costs of wire feeding equipment are high, and the wire feeding equipment is large in size, making equipment scheduling more difficult, which leads to a high overall cost of the calcium feeding line. After the calcium wire feeding is completed in the refining stage, the molten steel needs to be transported and placed, during which there is a high risk of introducing new impurities. In addition, metallic calcium is an active metal that reacts violently when in contact with air and water. The storage of calcium wire and the operation of calcium feeding line have certain safety hazards. Summary of the invention

[0005] Aiming at the technical problems that calcium wire feeding in the existing refining link takes a long time, slows down the rhythm of steel production, has high overall cost, is difficult to dispatch equipment, has the risk of introducing new impurities, and has potential safety hazards in calcium wire storage and calcium wire feeding, the present invention provides a continuous casting tundish metallurgical method, which does not require calcium wire feeding into molten steel in the refining link, saves time and equipment space, and is conducive to improving the production efficiency of steel; the consumption of mixed powder is small, the use is flexible, and better metallurgical effect can be achieved; the cleanliness and quality of molten steel can be better improved, and the introduction of new impurities can be avoided; the cost is low, and the potential safety hazard is low.

[0006] The technical solution of the present invention is: A continuous casting tundish metallurgical method comprises the following steps: refining after steel is tapped from a converter, soft blowing after the refining is completed, and then continuous casting; in the molten steel pouring link of the continuous casting process, a mixed powder is sprayed into the tundish for deep deoxidation and desulfurization treatment, and the mixed powder is prepared by uniformly mixing powdered CaC2 and magnesium powder.

[0007] Furthermore, in terms of mass percentage, the Mg content in the mixed powder is 2%-5%, and the remainder is CaC2 and inevitable impurities.

[0008] The use of Mg element in the mixed powder can reduce the use of CaC2 and the amount of slag. At the same time, CaC2 can promote the nucleation and flotation of desulfurization and deoxidation products such as MgS. The mixed powder prepared by mixing the two powders in proportion can significantly improve the effect of purifying molten steel while avoiding contamination of the molten steel.

[0009] Furthermore, in the molten steel, the added amount of the mixed powder is 50-100ppm.

[0010] Furthermore, in the continuous casting process, the superheat of the first batch of molten steel in the tundish is <30°C, and the superheat of the molten steel in other batches is 15-20°C. Full protection pouring is performed during the pouring process, and a double-layer tundish covering agent is used. The amount of tundish covering agent added is 20-30kg for each casting stream and 20-40kg for the impact zone. After adding the tundish covering agent, the slag surface is covered so that no red is seen.

[0011] In the pouring process of continuous casting, the continuous casting machine usually has multiple casting strands casting at the same time. Adding 20-30kg of tundish covering agent to each individual casting strand and 20-40kg of tundish covering agent to the impact zone can ensure that the molten steel in each casting strand and the impact zone can be effectively protected and insulated, reducing heat loss and the amount of secondary oxidation of the molten steel.

[0012] Furthermore, the specific operation of spraying the mixed powder into the tundish is: preheating the powder to 500-700°C, then breaking the slag surface of the covering agent, and spraying the mixed powder into the molten steel impact zone.

[0013] Furthermore, a powder spraying device is used to preheat and spray the mixed powder. The powder spraying device includes a powder storage tank, which is connected to a powder preheating device. The powder preheating device includes a cavity, in which a heating device and a gas-powder mixing device are arranged. The powder preheating device is connected to an argon gas supply device and is connected to a spray gun through a second conveying pipeline. A flow control valve is arranged on the second conveying pipeline.

[0014] Among them, the argon supply device can provide argon and positive pressure to the powder preheating device, so that the mixed powder in the powder preheating device is transported to the spray gun through the second conveying pipe under the protection of argon, and further sprayed into the impact zone of the ladle, so as to prevent the molten steel in the impact zone from being contaminated or oxidized.

[0015] Furthermore, during the process of spraying the mixed powder into the tundish, the nozzle of the spray gun is inserted into the molten steel, and the nozzle is 100-300 mm away from the bottom of the tundish.

[0016] Furthermore, after the spraying of the mixed powder is completed, if the slag surface turns red, the tundish covering agent should be added in time to cover it until the slag surface no longer turns red, so as to prevent the molten steel from losing the protection of the tundish covering agent and being contaminated or oxidized.

[0017] The beneficial effects of the present invention are: 1. The continuous casting tundish metallurgical method provided by the present invention sprays a mixed powder of powdered CaC2 and magnesium powder into the tundish during the molten steel pouring process for deep deoxidation and desulfurization treatment. There is no need to feed calcium wire into the molten steel during the refining process. The operation difficulty is relatively low, and the process time and equipment space are significantly saved. The production rhythm of steel will not be delayed, which is conducive to improving the production efficiency of steel.

[0018] 2. The timing of adding the mixed powder to the molten steel in the present invention is during the molten steel pouring process of the continuous casting process. The node where the mixed powder is added is relatively late, which can avoid the introduction of new impurities into the molten steel due to transportation and placement after the mixed powder is added for deoxidation and desulfurization, further improve the deoxidation and desulfurization effects, improve the cleanliness of the molten steel, and then improve the quality of subsequent steel products.

[0019] 3. The present invention mixes powdered CaC2 and magnesium powder to prepare a mixed powder. The use of the mixed powder can greatly reduce the consumption of either powdered CaC2 or magnesium powder when used alone. At the same time, the ratio of the two raw materials can be adjusted according to different types of steel, and the composition of molten steel can be fine-tuned to a certain extent. It is flexible to use and can achieve better metallurgical effects.

[0020] 4. The mixed powder of the present invention is a powdery material. After the mixed powder is added to molten steel, the contact area between the mixed powder and the molten steel is large, and the reaction effect is significant. The magnesium powder can generate stable inclusions with impurity elements such as oxygen and sulfur, and the gas generated by the powdered CaC2 participating in the reaction also helps to float and remove the inclusions, which can better improve the cleanliness and quality of the molten steel.

[0021] 5. The raw material cost of the mixed powder of the present invention and the process cost of spraying the mixed powder into molten steel are low, and the economic benefit is high.

[0022] 6. The present invention does not require the use of metallic calcium, the mixed powder can be prepared immediately before use, and the potential safety hazard in storing the mixed powder raw materials and spraying the mixed powder into molten steel is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 It is a schematic diagram of the structure of the powder spraying device in Example 1.

[0025] In the figure, 1-powder storage tank, 11-first conveying pipeline, 2-powder preheating device, 21-second conveying pipeline, 22-flow control valve, 3-argon gas supply device, 4-spray gun. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0027] Example 1 A continuous casting tundish metallurgical method is used in the process of continuously casting Φ500mm round billets to produce 42CrMo alloy structural steel, the steps comprising: (1) After the converter is tapped, the molten steel is subjected to RH refining. After RH refining, calcium wire is not fed and soft blowing is performed. The soft blowing time is 11 minutes. (2) Continuous casting is performed, and the superheat of the molten steel in the tundish is controlled at 15°C. Full protection pouring is performed during the pouring process. A double-layer tundish covering agent is used. The lower layer uses a low-titanium alkaline tundish covering agent, and the upper layer uses a low-carbon tundish covering agent. The amount of tundish covering agent added is 20-30kg for each casting strand and 20-40kg for the impact zone. After adding the tundish covering agent, the slag surface is covered so that no redness appears; (3) After the covering agent is added, the mixed powder is preheated using a powder spraying device, and then the mixed powder is sprayed into the tundish using the powder spraying device for deep deoxidation and desulfurization treatment.

[0028] The powder spraying device comprises a powder storage tank 1, which is connected to a powder preheating device 2 through a first conveying pipeline 11. The powder preheating device 2 comprises a cavity, in which a heating device and an air-powder mixing device are arranged. The heating device is an electric heating wire, and the air-powder mixing device is a fluidized bed mixer. A barometer, a thermometer and an exhaust valve are arranged on the cavity. The barometer is used to measure the air pressure in the cavity, the thermometer is used to measure the temperature in the cavity, and the exhaust valve is used to adjust the air pressure in the cavity. The powder preheating device 2 is connected to the argon gas supply device 3, which is a high-pressure argon gas cylinder; the powder preheating device 2 is connected to the spray gun 4 through the second delivery pipeline 21, and the second delivery pipeline 21 is provided with a flow control valve 22; The spray gun 4 includes a spray gun body, on which a powder spray switch is provided, and the spray gun body is connected to a spray rod and a nozzle in sequence, the spray rod is 3 m long, and a scale is engraved on the spray rod; The specific operation of preheating and spraying the mixed powder using the powder spraying device is as follows: (i) adding a mixed powder into a powder storage tank 1, wherein the mixed powder is prepared by uniformly mixing powdered CaC2 and magnesium powder, wherein the Mg content in the mixed powder is 3% by mass, and the remainder is CaC2 and unavoidable impurities; (ii) conveying the mixed powder in the powder storage tank 1 to the powder preheating device 2 through the first conveying pipeline 11, turning on the heating device and the gas-powder mixing device to heat the mixed powder to 620° C., then turning on the argon gas supply device 3 to control the gas pressure in the powder preheating device to 0.4 MPa; (iii) breaking the slag surface of the tundish, and then inserting the nozzle of the spray gun 4 into the molten steel in the tundish, judging the insertion depth by the scale ruler, ensuring that the nozzle is 100-300 mm away from the bottom of the tundish, and then pressing the switch to spray the mixed powder, controlling the addition amount of the mixed powder to 80 ppm, and controlling the flow rate of the mixed powder by adjusting the flow control valve 22 to ensure that the powder spraying is completed within 2 minutes; (iv) After the spraying of the mixed powder is completed, if the slag surface is red, add the tundish covering agent in time until the slag surface no longer turns red.

[0029] After spraying mixed powder into the tundish for deep deoxidation and desulfurization treatment, the O content in the molten steel dropped from 0.018% to 0.002%, and the S content dropped from 0.021% to 0.003%, and the cleanliness of the molten steel was significantly improved.

[0030] Example 2 A continuous casting tundish metallurgical method is used in a process of continuously casting five-strand rectangular billets using a 30-ton tundish to produce 20CrMnTi carburizing steel, the steps comprising: (1) After the converter is tapped, the molten steel is subjected to RH refining. After RH refining, calcium wire is not fed and soft blowing is performed. The soft blowing time is 12 minutes. (2) Continuous casting is performed, and the superheat of the molten steel in the tundish is controlled to be 18°C. Full protection pouring is performed during the pouring process. A double-layer tundish covering agent is used. The lower layer uses a low-titanium alkaline tundish covering agent, and the upper layer uses a low-carbon tundish covering agent. The amount of tundish covering agent added is 20-30kg for each casting strand and 30-40kg for the impact zone. After adding the tundish covering agent, the slag surface is covered so that no redness appears; (3) After the covering agent is added, the mixed powder is preheated using the same powder spraying device as in Example 1, and then the mixed powder is sprayed into the tundish using the powder spraying device for deep deoxidation and desulfurization treatment.

[0031] The specific operation of preheating and spraying the mixed powder using the powder spraying device is as follows: (i) adding a mixed powder into a powder storage tank 1, wherein the mixed powder is prepared by uniformly mixing powdered CaC2 and magnesium powder, wherein the Mg content in the mixed powder is 2% by mass, and the remainder is CaC2 and unavoidable impurities; (ii) conveying the mixed powder in the powder storage tank 1 to the powder preheating device 2 through the first conveying pipeline 11, turning on the heating device and the gas-powder mixing device to heat the mixed powder to 650° C., then turning on the argon gas supply device 3 to control the gas pressure in the powder preheating device to be 0.5 MPa; (iii) breaking the slag surface of the tundish, and then inserting the nozzle of the spray gun 4 into the molten steel in the tundish, judging the insertion depth by the scale ruler, ensuring that the nozzle is 100-300 mm away from the bottom of the tundish, and then pressing the switch to spray the mixed powder, controlling the addition amount of the mixed powder to 70 ppm, and controlling the flow rate of the mixed powder by adjusting the flow control valve 22 to ensure that the powder spraying is completed within 2 minutes; (iv) After the spraying of the mixed powder is completed, if the slag surface is red, add the tundish covering agent in time until the slag surface no longer turns red.

[0032] After spraying mixed powder into the tundish for deep deoxidation and desulfurization treatment, the O content in the molten steel dropped from 0.025% to 0.003%, and the S content dropped from 0.032% to 0.004%, and the cleanliness of the molten steel was significantly improved.

[0033] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A continuous casting tundish metallurgical method, characterized in that the steps include: After the steel is tapped out of the converter, it is refined, and after the refining is completed, it is soft-blown and then continuously cast. During the molten steel pouring process of the continuous casting process, a mixed powder is sprayed into the tundish for deep deoxidation and desulfurization treatment. The mixed powder is obtained by evenly mixing powdered CaC2 and magnesium powder.

2. The continuous casting tundish metallurgical method according to claim 1, characterized in that: In terms of mass percentage, the Mg content in the mixed powder is 2%-5%, and the remainder is CaC2 and inevitable impurities.

3. The continuous casting tundish metallurgical method according to claim 1, characterized in that: In molten steel, the added amount of mixed powder is 50-100ppm.

4. The continuous casting tundish metallurgical method according to claim 1, characterized in that: In the continuous casting process, the superheat of the first batch of molten steel in the tundish is <30℃, and the superheat of molten steel in other batches is 15-20℃. Full protection pouring is carried out during the pouring process, and a double-layer tundish covering agent is used. The amount of tundish covering agent added is 20-30kg for each casting strand and 20-40kg for the impact zone. After adding the tundish covering agent, the slag surface is covered and no red is seen.

5. The continuous casting tundish metallurgical method according to claim 1, characterized in that: The specific operation of spraying the mixed powder into the tundish is: preheating the powder to 500-700°C, then breaking the slag surface of the covering agent, and spraying the mixed powder into the molten steel impact zone.

6. The continuous casting tundish metallurgical method according to claim 5, characterized in that: A powder spraying device is used to preheat and spray the mixed powder. The powder spraying device includes a powder storage tank, which is connected to a powder preheating device. The powder preheating device includes a cavity, in which a heating device and a gas-powder mixing device are arranged. The powder preheating device is connected to an argon gas supply device and is connected to a spray gun through a second delivery pipeline. A flow control valve is arranged on the second delivery pipeline.

7. The continuous casting tundish metallurgical method according to claim 6, characterized in that: During the process of spraying the mixed powder into the tundish, the nozzle of the spray gun is inserted into the molten steel, and the nozzle is 100-300mm away from the bottom of the tundish.

8. The continuous casting tundish metallurgical method according to claim 5, characterized in that: After the mixed powder spraying is completed, if the slag surface is red, add the tundish covering agent in time to cover it until the slag surface no longer turns red.

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