Method for improving castability of direct aluminum deoxidation continuous casting

Abstract

The method comprises the working procedures of molten iron pretreatment, converter treatment, argon blowing and continuous casting, and specifically comprises the steps that a KR method is adopted for conducting desulfurization and slagging-off on molten iron, and the sulfur content of the molten iron is controlled to be lower than 0.05%; charging the desulfurized molten iron into a furnace for smelting, blowing in a top-bottom combined blowing converter, and controlling blowing end point components and carbon temperature through a sublance system; converter smelting tapping is carried out, slag washing materials and top slag lime are added for slagging, and aluminum blocks are added for primary deoxidation; recycling hot casting residues in an argon station, carrying out strong blowing and slag adjustment in an argon blowing station, carrying out slag adjustment by using a composite deoxidizer, a covering agent and aluminum powder, and carrying out calcium and aluminum wire feeding treatment after slag adjustment; and carrying out continuous casting protective pouring. Compared with the prior art, under the condition of no LF refining, the continuous casting state is stable, inclusions are well controlled, the number of continuous casting furnaces under the aluminum deoxidation process condition is increased, the problem of flocculation at a continuous casting nozzle of steel for aluminum deoxidation is solved, and the molten steel flowability is improved.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking production, and in particular to a method for improving the castability of direct aluminum deoxidation continuous casting. Background Art

[0002] Aluminum is a strong deoxidizing element that can effectively reduce the oxygen content in steel and improve the cleanliness of molten steel. At the same time, aluminum is an important alloying element. A certain amount of aluminum in steel can refine the grains, improve the strength and toughness of the steel, promote the nitriding layer, and improve oxidation resistance.

[0003] When the aluminum content in steel is greater than 0.01%, the dissolved oxygen in the steel is very low, which can ensure that the inclusion content in the steel is at a low level. However, for continuous casting aluminum killed steel, the deoxidation product is a high melting point substance. The high melting point of A1 2 O 3 After the floccules gather on the inner wall of the nozzle and the bowl, the molten steel shows poor fluidity. In order to ensure the stability of the crystallizer liquid level, the stopper rod position shows an upward trend. At the same time, the floccules are affected by the long-term scouring of the molten steel and the scouring of the stopper rod with argon, and the floccules fall irregularly. During the falling process of the inclusions, the flow of molten steel in the nozzle increases instantly, the crystallizer liquid level rises, and the stopper rod position suddenly drops to ensure the stability of the crystallizer liquid level, which leads to liquid level fluctuations.

[0004] The traditional aluminum deoxidation process mainly controls the liquid level fluctuation from two aspects: 1) increasing the final carbon content, limiting the soft blowing time, and reducing the deoxidation process A1 2 O 3 The amount of production increases, and the top slag produces A1 in the deoxidation and secondary oxidation process 2 O 3 1) In the continuous casting process, by properly adjusting the argon gas in the stopper rod, the possibility of inclusions adhering to the inner wall of the nozzle and the bowl can be reduced. However, the above two control measures cannot fundamentally solve the problem of A1. 2 O 3 Flocculation, continuous casting castability is limited.

[0005] The traditional process adopts converter → LF refining → continuous casting to realize the calcium treatment process and stabilize the continuous casting pouring liquid level. However, the traditional converter → continuous casting straight-up process is difficult to achieve stable calcium treatment and cannot completely solve the problem of continuous casting nozzle flocculent flow and the liquid level fluctuation caused by nozzle flocculent flow. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for improving the castability of direct-on aluminum deoxidation continuous casting, which achieves stable continuous casting pouring state and good control of inclusions without LF refining, increases the number of continuous casting furnaces under aluminum deoxidation process conditions, solves the problem of flocculation in the continuous casting nozzle of steel for aluminum deoxidation, and improves the fluidity of molten steel.

[0007] To achieve this technical purpose, the present invention adopts the following scheme:

[0008] A method for improving the castability of direct aluminum deoxidation continuous casting, comprising the steps of molten iron pretreatment → converter → argon blowing → continuous casting, specifically comprising the following steps:

[0009] S1. Use KR method (Kambara Reactor) to desulfurize and slag the molten iron to control the sulfur content of the molten iron to less than 0.05%;

[0010] S2, after desulfurization, the molten iron is charged into the furnace for smelting, and the top and bottom combined blowing converter is used for blowing, and the blowing end composition and carbon temperature are controlled by the auxiliary gun system;

[0011] S3, smelting steel in converter, adding slag washing material and top slag lime to make slag, adding aluminum block for primary deoxidation;

[0012] S4, the argon station hot pouring residual slag recovery, argon blowing station strong blowing slag adjustment, composite deoxidizer, covering agent and aluminum powder are used for slag adjustment, and calcium aluminum wire feeding is carried out after slag adjustment;

[0013] S5. Continuous casting protection pouring.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention adds slag washing material and top slag lime to wash slag during the steel-making process, and adopts an aluminum block centralized deoxidation process to achieve accelerated collision and floating of deoxidation products. At the same time, the steel-making process is thoroughly deoxidized, and the oxidation of the ladle slag is relatively low, which is beneficial to desulfurization during the steel-making process. The ladle hot casting residual slag is recovered to accelerate the ladle slag forming speed. The argon blowing station adds a composite deoxidizer to assist in slag surface oxygen removal, and at the same time increases the thickness of the ladle slag layer. Aluminum powder and large argon gas are used to stir the deep slag surface oxygen, reduce the oxidation of the ladle top slag, and use calcium aluminum wire for treatment to reduce the splashing effect of molten steel, reduce the secondary oxidation of molten steel, and stabilize the calcium yield. The present invention achieves stable continuous casting pouring state and good control of inclusions without LF refining, and realizes an increase in the number of continuous casting and continuous pouring furnaces under aluminum deoxidation process conditions, solves the flocculent flow problem of continuous casting water inlet for aluminum deoxidation steel, and improves the fluidity of molten steel.

[0016] Furthermore, the slag basicity is 3.5-4.0, the steel tapping temperature is 1620-1650° C., and the final carbon content is 0.05%-0.07%.

[0017] Furthermore, in step S3, argon is turned on in advance in the ladle before steel tapping to achieve argon replacement in the ladle, and carbon powder is used for pre-deoxidation during the steel tapping process.

[0018] Furthermore, in step S3, 700kg-900kg / furnace of top slag lime, 200kg / furnace of slag washing material, 290kg-350kg / furnace of aluminum blocks are added, and after the aluminum blocks are deoxidized, Als≥0.02% is added into the station.

[0019] Through the above settings, sufficient deoxidation can be achieved, which is beneficial to accelerate the slag formation speed, reduce the oxidizability of the ladle slag, stabilize the calcium recovery rate, and utilize the steel slag washing process to accelerate the floating of alumina inclusions in the primary deoxidation product, while achieving the desulfurization effect of steel slag washing.

[0020] Furthermore, in step S4, the ladle car drives out of the argon blowing station to recover the residual slag from the previous ladle hot pouring. After the hot slag is recovered, the ladle car drives back to the argon blowing station for strong blowing and slag adjustment treatment, and a composite deoxidizer is added to assist in slag surface oxygen removal, and then aluminum powder and large argon gas are added for strong stirring to deeply remove the slag surface oxygen, and then a covering agent is added.

[0021] Furthermore, in step S4, after the calcium aluminum wire is fed, it is also required to undergo soft argon blowing treatment for no less than 6 minutes. The soft blowing is based on the slight creeping of the molten steel and the exposed surface of the molten steel not exceeding 100 mm, so as to stabilize the calcium wire yield.

[0022] Furthermore, in step S4, the calcium aluminum wire is vertically fed into the ladle at a wire feeding speed of 2 to 4 m / s. The wire feeding time is the same as the soft argon blowing time. The argon flow rate is controlled to ensure that the exposed diameter of the steel sheet does not exceed 100 mm.

[0023] Furthermore, in step S4, the main components of the ladle slag include: SiO 2 : 2.5~6%, CaO: 45~50%, MgO: 6.5~9.5%, Al 2 O 3 : 25-32%, TFe: 0.7-1.0%, MnO: 0.14-0.24%, R: 10-18, where R = CaO / SiO 2 .

[0024] Furthermore, in step S5, the tundish cover is argon blown, and the tundish covering agent is added in time during the argon blowing process, and the slag layer thickness is controlled to be 30-60 mm; the long shroud of the ladle adopts a sealing ring and argon blowing to protect the pouring throughout the process, and the argon gas in the long shroud is controlled at 100L / min.

[0025] Furthermore, the covering agent is a carbon-free, low-silicon, high-alkalinity covering agent.

[0026] It should be noted that the substance contents in the present invention are all by mass. DETAILED DESCRIPTION

[0027] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific implementation methods, but the present invention is not limited thereto.

[0028] The present invention provides a method for improving the castability of direct aluminum deoxidation continuous casting, comprising the steps of molten iron pretreatment → converter → argon blowing → continuous casting, and specifically comprising the following steps:

[0029] S1. When the sulfur content of molten iron in blast furnace is 0.05% or above, KR method (Kambara Reactor) is used to desulfurize and slag the molten iron, and the sulfur content of the molten iron charged to the furnace is controlled to be lower than 0.05%. Under the premise of fully utilizing the desulfurization capacity of the converter, it is beneficial to control the sulfur content of the final molten steel.

[0030] S2. After desulfurization, the molten iron is charged into the furnace for smelting, and the top and bottom combined blowing converter is used for blowing, that is, the top and bottom combined blowing converter steelmaking method, in which oxygen is blown from the converter top and different gases are blown into the bottom of the converter for blowing. The addition of converter slag is controlled to ensure that the slag basicity is 3.5-4.0, and the desulfurization and dephosphorization capacity of the converter smelting process is improved; at the same time, the blowing end point composition and carbon temperature are controlled through the auxiliary gun and the secondary equipment system to ensure that the end point composition and temperature are both hit, and the steel tapping temperature is controlled to be 1620-1650℃, the end point carbon content is 0.05%-0.07%, and the end point oxygen content is reduced.

[0031] S3. Open the ladle argon in advance before tapping to achieve argon replacement in the ladle and reduce the air in the ladle. Use carbon powder for pre-deoxidation in the tapping process to further reduce the oxygen content of the molten steel and reduce aluminum deoxidation products.

[0032] During the steel-making process, slag washing material and top slag lime are added to form slag. 700kg-900kg of top slag lime is added per furnace, and 200kg of slag washing material is added per furnace to accelerate slag formation. After that, aluminum blocks are added for one-time deoxidation. 290kg-350kg of aluminum blocks are added per furnace, which is conducive to the collision and floating of deoxidation products. The slag washing process is used to improve the inclusion removal effect and reduce the oxidizability of the ladle slag. After deoxidation, Als entering the argon station is ≥0.02%.

[0033] S4, the argon station hot pouring residual slag recovery, argon blowing station strong blowing slag adjustment, composite deoxidizer, covering agent and aluminum powder are used for slag adjustment, and calcium aluminum wire feeding is carried out after slag adjustment;

[0034] Specifically, the molten steel leaves the argon blowing station to recover the residual slag from the previous ladle hot pouring. Recovering the residual slag from hot pouring can speed up the modification of the top slag of the ladle and increase the thickness of the slag layer of the ladle. After the hot slag is recovered, the ladle car returns to the argon blowing station. After the molten steel arrives at the argon blowing station, it is subjected to strong blowing and slag adjustment. After temperature measurement and sampling at the station, aluminum powder, composite deoxidizer and other large argon gas are added for argon blowing and stirring to accelerate slag formation. Specifically, a composite deoxidizer is added to assist in slag surface oxygen removal and increase the thickness of the ladle slag layer. Then, aluminum powder and large argon gas are added for strong stirring to deeply remove the slag surface oxygen. The argon gas stirring is used to quickly form slag to obtain a slag with low oxidation and suitable components, and then a covering agent is added.

[0035] After strong blowing for 2 to 3 minutes, visually observe that there are no aluminum stars on the slag surface and then adjust the argon blowing intensity. The exposed diameter of the molten steel surface is 100 to 300 mm. Dip the slag in the slag to observe its color. The slag is grayish white. If no unsatisfactory slag sample is found, continue to add aluminum powder to adjust the slag until the slag color meets the requirements.

[0036] The temperature at the station is high and the furnace needs to be temperature adjusted. The temperature is adjusted after adding the slag adjusting agent. If the composition of the ladle sample does not meet the requirements of the steel grade, it should be adjusted immediately. After the composition is adjusted, soft blowing is performed for 2 to 3 minutes, and calcium aluminum wire feeding is performed. The calcium aluminum wire is fed vertically into the ladle to avoid the wire feeding position being above the argon blowing hole, ensuring a stable calcium recovery rate. The calcium aluminum wire feeding speed is controlled at 2 to 4 m / s. Soft blowing is used as the basis when feeding the calcium aluminum wire. After feeding the calcium aluminum wire, the argon flow rate is adjusted for soft blowing to ensure that the exposed diameter of the molten steel surface does not exceed 100 mm. Soft blowing must be performed for at least 6 minutes before leaving the station. The composition of the ladle slag is shown in Table 1. Among them, R = CaO / SiO 2 .

[0037] Table 1 Ladle slag composition control

[0038] <![CDATA[SiO 2 ]]> CaO MgO <![CDATA[Al 2 THE 3 ]]> TFe MnO R 2.5～6％ 45～50％ 6.5～9.5％ 25～32％ 0.7～1.0％ 0.14～0.24％ 10～18

[0039] S5, continuous casting protective pouring. Blow argon in the impact zone and the tundish cover to achieve a low-oxidizing atmosphere in the tundish and improve the stability of continuous casting. During the argon blowing process, add the tundish covering agent in time to reduce the exposure of the molten steel surface. The covering agent is a carbon-free, low-silicon, high-alkalinity covering agent, and the slag layer thickness is controlled at 30-60mm; the long water nozzle of the large ladle uses a sealing ring and argon blowing to protect the pouring throughout the process to reduce nitrogen absorption caused by exposed molten steel, and the argon gas in the long water nozzle is controlled at 100L / min. The tundish uses a breathable upper water nozzle to prevent accumulation near the upper water nozzle of the tundish. Argon is turned on between the stopper rod and the plate to reduce air entry. At the same time, the argon gas of the stopper rod is controlled to reduce the accumulation of inclusions at the head of the stopper rod.

[0040] The invention solves the problem of flocculation in the nozzle of direct aluminum-killed steel continuous casting, realizes continuous casting of more than 50 furnaces, and completely improves the problem of liquid level fluctuation caused by flocculation in the tundish nozzle or the immersion nozzle.

[0041] Finally, it should be noted that the above are only preferred embodiments of the present invention. Of course, those skilled in the art can make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and their equivalent technologies, they should be considered to be within the scope of protection of the present invention.

Claims

1. A method for improving the castability of direct aluminum deoxidation continuous casting, comprising the steps of molten iron pretreatment → converter → argon blowing → continuous casting, characterized in that: The specific steps include: S1. Use KR method to desulfurize and slag the molten iron to control the sulfur content of the molten iron to less than 0.05%; S2, after desulfurization, the molten iron is charged into the furnace for smelting, and the top and bottom combined blowing converter is used for blowing, and the blowing end composition and carbon temperature are controlled by the auxiliary gun system; S3, smelting steel in converter, adding slag washing material and top slag lime to make slag, adding aluminum block for primary deoxidation; S4, the argon station hot pouring residual slag recovery, argon blowing station strong blowing slag adjustment, composite deoxidizer, covering agent and aluminum powder are used for slag adjustment, and calcium aluminum wire feeding is carried out after slag adjustment; S5. Continuous casting protection pouring.

2. The method for improving the castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: The slag basicity is 3.5~4.0, the steel-making temperature is 1620~1650℃, and the final carbon content is 0.05%~0.07%.

3. The method for improving the castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: In step S3, argon is turned on in advance in the ladle before steel is tapped to achieve argon replacement in the ladle, and carbon powder is used for pre-deoxidation during the steel tapping process.

4. The method for improving the castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: In step S3, 700kg-900kg of top slag lime is added per furnace, 200kg of slag washing material is added per furnace, and 290kg-350kg of aluminum blocks are added per furnace. After the aluminum blocks are deoxidized, Als≥0.02% is added into the station.

5. The method for improving the castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: In step S4, the ladle car drives out of the argon blowing station to recover the residual slag from the previous ladle hot pouring. After the hot slag is recovered, the ladle car drives back to the argon blowing station for strong blowing and slag adjustment treatment, and a composite deoxidizer is added to assist in slag surface oxygen removal. Then, aluminum powder and large argon gas are added for strong stirring to deeply remove the slag surface oxygen, and then a covering agent is added.

6. The method for improving the castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: In step S4, after the calcium-feeding aluminum wire treatment, it is also required to undergo soft argon blowing treatment, and the soft argon blowing treatment is not less than 6 minutes.

7. The method for improving the castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: In step S4, the calcium aluminum wire is vertically fed into the ladle at a wire feeding speed of 2-4 m / s. The wire feeding time is the same as the soft argon blowing time. The argon flow rate is controlled to ensure that the exposed diameter of the steel sheet does not exceed 100 mm.

8. The method for improving castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: In step S4, the main components of the ladle slag include: SiO2: 2.5~6%, CaO: 45~50%, MgO: 6.5~9.5%, Al2O3: 25~32%, TFe: 0.7~1.0%, MnO: 0.14~0.24%, and R: 10~18.

9. The method for improving castability of direct aluminum deoxidation continuous casting according to claim 1, characterized in that: In step S5, argon is blown into the tundish cover, and the tundish covering agent is added in time during the blowing process, and the thickness of the slag layer is controlled to be 30-60 mm; the long shroud of the ladle adopts a sealing ring and argon blowing to protect the pouring throughout the process, and the argon gas in the long shroud is controlled at 100 L / min.

10. The method for improving castability of direct aluminum deoxidation continuous casting according to claim 9, characterized in that: The covering agent is a carbon-free, low-silicon, high-alkalinity covering agent.