A method for controlling inclusions in the smelting of a sulfur-containing controlled-aluminum steel

Abstract

The application discloses a kind of inclusions control method of sulfur-containing aluminum control steel smelting, including S1, electric furnace tapping: aluminum block, alloy, lime, refining slag are sequentially added;S2, LF refining: control refining end point target slag system is: basicity R: 2~3.5, Al2O3: 7%~13%, TFe≤0.5%;S3, VD vacuum refining: molten steel is to station after blowing nitrogen gas and increasing nitrogen, after breaking vacuum, argon gas is blown and stirred, and after breaking vacuum, the feeding sequence of wire is silicon nitride wire, calcium wire, aluminum wire, titanium wire and sulfur wire;S4, large square billet continuous casting.The application has the advantages of effectively reducing the number of high melting point inclusions, improving the purity of molten steel, realizing multi-furnace continuous casting of molten steel, improving production efficiency and stably improving product quality.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a method for controlling inclusions in the smelting of sulfur-containing aluminum steel. Background Technology

[0002] Currently, non-quenched and tempered steel has become one of the fastest-growing steel grades in the automotive steel sector. Among them, sulfur-containing aluminum-controlled steel is a representative steel grade that was applied earlier and has a larger usage volume, and is widely used in the manufacture of key load-bearing parts and structural components such as connecting rods, crankshafts, steering knuckle shafts, drive shafts, and front axles. However, MnS inclusions in steel have good plasticity and lower hardness than the steel matrix. When subjected to rolling force during rolling, they elongate along the rolling direction, becoming long strips, which easily leads to a deterioration in the transverse mechanical properties of the steel. There are many ways to control MnS inclusions. Generally, adjusting the slag system, wire feeding, and controlling the oxygen content can all play a certain role in the morphology and distribution of sulfides.

[0003] However, conventional deoxidation processes struggle to control the oxygen content of molten steel while maintaining the sulfur content. Adding iron sulfide to increase the sulfur content further raises the oxygen level in the molten steel, significantly increasing the difficulty of deoxidation control. Insufficient deoxidation leads to substandard purity of the molten steel, while excessive deoxidation causes an excessive reduction in sulfur content, failing to meet composition requirements.

[0004] In sulfur-containing aluminum-controlled steel, sulfur can effectively improve the machinability of the steel, while aluminum acts as the main deoxidizer to refine the steel grains. However, in the existing production process, there has always been a difficult technical contradiction to resolve in the control of the composition and inclusions of this type of steel: on the one hand, when the aluminum content is high, the deoxidation reaction will generate a large number of hard inclusions of Al2O3, which will not only affect the mechanical properties of the steel, but also easily cause blockage of the gate during the casting process; on the other hand, in order to ensure the machinability, it is necessary to maintain a high sulfur content in the molten steel. However, the desulfurization reaction follows the thermodynamic law [S]+(CaO)=(CaS)+[O]. Under low oxygen potential conditions, the desulfurization reaction proceeds in the forward direction, and it is difficult to stably control the sulfur content of the molten steel within the target range. On the other hand, to ensure the sulfur content, it is necessary to maintain an appropriate oxygen potential, which will increase the difficulty of controlling the deoxidation process.

[0005] In addition, when there are high levels of sulfur, calcium, and aluminum in the molten steel, a large number of high-melting-point inclusions such as calcium aluminates and CaS are easily generated. These inclusions have high melting points and are not easy to float and remove. During continuous casting, they are very easy to adhere to the inner wall of the nozzle and form nodules, causing blockage of the continuous casting nozzle. This directly leads to the inability to cast multiple furnaces in a continuous process, which not only reduces production efficiency and disrupts the production rhythm, but also significantly increases production costs and seriously affects the quality stability of the final product. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of high inclusion content, incompatibility between high sulfur content and deoxidation, and low purity of molten steel in the production of sulfur-containing aluminum-controlled steel. It provides a method for controlling inclusions in the smelting of sulfur-containing aluminum-controlled steel, which effectively reduces the number of high-melting-point inclusions, improves the purity of molten steel, enables continuous casting of molten steel in multiple furnaces, and improves production efficiency while steadily improving product quality.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for controlling inclusions in the smelting of sulfur-containing aluminum-controlled steel includes electric arc furnace tapping, LF refining, VD vacuum refining, and continuous casting of large billets. This method optimizes the deoxidation and wire feeding processes, primarily focusing on the deoxidation, slag-forming, calcium treatment, and sulfur-enhancing processes. By controlling the slag system of the sulfur-containing aluminum-controlled steel, the methods control the Ca, S, and O content in the molten steel, reducing the amount of high-melting-point inclusions such as calcium aluminates and CaS. Furthermore, by controlling the sulfur content in the molten steel, the methods control the morphology and distribution of MnS inclusions, improving the purity of the molten steel.

[0008] The electric furnace tapping process includes: When tapping steel from the electric furnace, aluminum blocks are added first for deoxidation to ensure a certain recovery rate of easily oxidized elements. Then, alloys are added for steelmaking. After the alloys are added, lime and refining slag are added for slag formation. The ladle is then moved to the LF position, ready for refining.

[0009] The LF refining process includes: Argon stirring is applied to the LF furnace. After 5 minutes of power supply, sample 1 is taken for analysis. The target temperature is 30°C above the liquidus. Depending on the slag viscosity or sulfur content, up to 50 kg of quicklime is added. Initial desulfurization is appropriate, but the sulfur content should not be reduced too much. Then, with the electrodes powered, 60-80 kg of silicon carbide deoxidizer is added for slag surface deoxidation. The LF furnace maintains a reducing atmosphere to ensure white slag refining. After 10 minutes of power supply, nitrogen stirring is switched to. During the mid-refining stage, the nitrogen flow rate is maintained at 300-400 L / min. Strong arc and high flow rate stirring facilitate the removal of inclusions. After sample 2, a slag sample is taken. If the slag is white, 140-18 kg of quicklime can be added after power supply. At 0 kg of ferrous sulfide, the oxygen content of the molten steel increases. It is not advisable to add silicon carbide immediately for deoxidation to avoid the generation of a large amount of gas by ferrous sulfide and silicon carbide under the action of electric arc, which would cause the molten steel to splash. Therefore, after adding ferrous sulfide, an appropriate amount of ferrosilicon powder can be added for deoxidation. In the subsequent refining process, silicon carbide should be added in small batches, with a total addition of ≥120 kg, to continuously carry out diffusion deoxidation and reduce slag basicity. The target slag system at the end of the refining process should be controlled as follows: basicity R: 2~3.5, Al2O3: 7%~13%, TFe≤0.5%.

[0010] In the above-mentioned LF refining process, it is required that Al ≥ 0.035% in LF refining sample 1. If the aluminum content does not meet 0.035%, aluminum wire should be added to bring it up to 0.035%~0.040%. The composition requirements of S before entering the vacuum are 0.028%~0.030% and the composition requirements of Al are 0.020%~0.040%.

[0011] The VD vacuum refining process includes: After the molten steel leaves the LF station, it undergoes vacuum treatment. Nitrogen is added upon arrival at the station, and argon is blown to stir after the vacuum is broken. The process VD vacuum degree is ≤67Pa, and the vacuum holding time is ≥15min. When feeding silicon nitride wire, N is adjusted to the target value of 175ppm. After the VD vacuum is broken, the wire feeding sequence is as follows: silicon nitride wire, calcium wire, aluminum wire, titanium wire, sulfur wire, and tellurium wire (first furnace).

[0012] Furthermore, during the VD process, the length of the calcium feeding line is 30~40m, and after calcium treatment, static stirring is performed, with the static stirring time controlled to be greater than or equal to 15min.

[0013] Furthermore, before supplementing the sulfur line during the VD process, the static stirring time is controlled to be greater than 15 minutes, and the sulfur content is adjusted to the target value of 0.026%.

[0014] Furthermore, the length of the silicon nitride feeding wire during the VD process is 300m.

[0015] Furthermore, after the sulfur content of the first furnace is adjusted during the VD process, a 55m tellurium wire is fed. No tellurium is added for the second furnace, and the static stirring time is greater than 5 minutes after the tellurium wire is fed.

[0016] In addition, the continuous casting process of the large billet includes: the continuous casting temperature of the sulfur-containing aluminum steel is 1555~1565℃ for the first furnace and 1535~1545℃ for the continuous casting furnace.

[0017] The design principle of this invention is as follows: As a surface-active element, sulfur (S) exhibits the highest activity at the interface, decreasing towards the interior of the molten steel. Therefore, it provides activity near the interface. Since a higher S content in the molten steel results in lower interfacial tension, S can be considered a beneficial element for promoting the removal of inclusions from the molten steel. However, excessively high S content can lead to the formation of CaS inclusions in the steel. The wetting angle between CaS inclusions and molten steel is less than 90°, making them difficult to remove during gas stirring. Therefore, this invention controls the S content of LF sample 2 to approximately 100 ppm in the early stage, which promotes the removal of inclusions in the circulating molten steel without excessively increasing the formation of CaS inclusions in the steel.

[0018] Compared with the prior art, the advantages of the technical solution of the present invention are as follows: (1) Significant effect of inclusion control: This invention optimizes the entire process of deoxidation, slag making, calcium treatment and sulfur increase, and precisely controls the slag system composition of sulfur-containing aluminum-controlled steel, so as to achieve stable control of the contents of the three key elements Ca, S and O in the molten steel, effectively reducing the amount of high melting point harmful inclusions such as calcium aluminate and CaS; at the same time, by precisely controlling the sulfur content of the molten steel, the morphology and distribution of MnS inclusions are actively controlled, thereby reducing the adverse effects of inclusions on steel quality from the source. (2) The purity of molten steel is greatly improved: After the process optimization of the present invention, the deoxidation problem of the oxygen level of molten steel increased after the addition of iron sulfide to high sulfur steel is specifically solved, the secondary oxidation and inclusion generation caused by excessive oxygen content are reduced, the overall purity of molten steel is significantly improved, and the cleanliness of molten steel meets the production requirements of high-quality sulfur-containing aluminum-controlled steel. (3) Improved stability of continuous casting production: This invention improves the pourability of molten steel, eliminates the phenomenon of high melting point inclusions clogging the nozzle and affecting the smooth pouring process, successfully realizes multi-furnace continuous casting of sulfur-containing aluminum-controlled steel, reduces abnormal working conditions such as unplanned stop-casting and slow-down casting, and improves the continuity and stability of continuous casting production. (4) Outstanding economic benefits: The refining method of the present invention is adapted to the existing steelmaking production process, without the need for additional large-scale equipment investment. At the same time, it reduces the scrap rate of inclusions and reduces the process loss of continuous casting process, resulting in a decrease in overall production cost and an increase in production efficiency. It has high production applicability and economic benefits. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the processing sequence of the wire feeding during the VD vacuum treatment in Embodiment 1 of the present invention. Detailed Implementation Example 1

[0020] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a method for controlling inclusions in the smelting of sulfur-containing aluminum steel. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0021] A method for controlling inclusions in the smelting of sulfur-containing aluminum-controlled steel, employing the EAF-LF-VD-CC process, wherein the composition and mass percentage of the sulfur-containing aluminum-controlled steel include: C: 0.37%~0.39%, Si: 0.68%~0.74%, Mn: 1.38%~1.46%, P: 0.000%~0.020%, S: 0.024%~0 .035%, Alt: 0.013%~0.025%, V: 0.11%~0.13%, Ti: 0.010%~0.020%, N: 165ppm~200ppm.

[0022] Within the above range, the target composition values ​​are: C: 0.38%, Si: 0.70%, Mn: 1.42%, P: 0.000%, S: 0.026%, Alt: 0.017%, V: 0.12%, Ti: 0.015%, N: 175ppm.

[0023] The specific steps are as follows: (1) When tapping steel from an electric furnace, aluminum blocks are added first for deoxidation, followed by the addition of alloys for steelmaking. After the alloys are added, lime and refining slag are added for slag formation. (2) LF process: Argon is blown into the LF station for stirring, and the argon flow rate is maintained at 250L / min. After 5 minutes of power supply, sample 1 is taken for analysis. The target temperature is 30℃ above the liquidus. According to the slag viscosity or sulfur content, up to 50kg of active lime is added for appropriate desulfurization in the early stage. Then, under the electrode power supply state, 60~80kg of silicon carbide deoxidizer is added for slag surface deoxidation to maintain white slag refining. After 10 minutes of power supply, nitrogen stirring is switched. The nitrogen flow rate during the refining process is 300~400L / min. After sample 2 is taken, the slag sample is dipped. After observing that it is white slag, 140~180kg of iron sulfide is added, and an appropriate amount of ferrosilicon powder is added for deoxidation. In the subsequent refining process, silicon carbide should be added in small batches, with a total addition of ≥120kg, and diffusion deoxidation is continuously carried out to reduce the slag basicity. The target slag system at the refining endpoint is controlled as follows: basicity R: 2~3.5, Al2O3: 7%~13%, TFe≤0.5%.

[0024] (3) VD treatment: After the molten steel arrives at the station, nitrogen gas is introduced for nitrogen enrichment, and vacuuming begins. After the vacuum is broken, argon gas is switched, and samples are taken for analysis, such as... Figure 1 As shown, the composition of calcium, aluminum, sulfur, and nitrogen is adjusted by feeding wire. A 300m silicon nitride wire is fed in, adjusting N to the target value of 175ppm; a 30-40m calcium wire is fed in, and aluminum wire is added to adjust Al to 0.013%-0.025%; titanium wire is fed in to adjust Ti to 0.010%-0.020%; after stirring for 15 minutes, sulfur wire is fed in to adjust S to 0.024%-0.035%; after the sulfur content of the first batch is adjusted, 55m tellurium wire is fed in. No Te is added in the second batch, and the stirring time after feeding the tellurium wire is greater than 5 minutes. (4) Continuous casting: The composition and temperature of the vacuum furnace are adjusted to be qualified, and after the static stirring is completed, the ladle is hoisted to the large billet casting table for continuous casting protection to prevent secondary oxidation.

[0025] This embodiment provides a refining method for sulfur-containing aluminum-controlled steel, characterized in that: S1: The first batch of steel is tapped from the electric furnace after slag blocking. Before tapping, 1 kg / t of aluminum blocks is added for deoxidation. After tapping, 450 kg of lime and 600 kg of refining slag are added.

[0026] S2: After the LF arrives at the station, the electrode is lowered and electroslag is fed. Sample 1 is taken for analysis after 5 minutes of power supply. Nitrogen gas is purged for 10 minutes at a flow rate of 450 L / min. Sample 1 has an Al content of 0.037%. No aluminum wire was fed. The Al content before entering the vacuum was 0.024%. No aluminum was added later.

[0027] S3: In the initial stage of electrolytic slag formation, 50 kg of lime and 60 kg of high-purity silicon carbide were added for slag surface deoxidation. During the refining process, appropriate desulfurization was performed without increasing sulfur content. Subsequently, two more batches of silicon carbide, 30 kg each, were added for diffusion deoxidation. After 15 minutes of refining, the slag turned white and remained so throughout the process. The sulfur content of Sample 1 was 0.009%. After Sample 2 was taken, 160 kg of iron sulfide was added, and the sulfur content before vacuuming was 0.028%.

[0028] S4: After entering VD, nitrogen gas is used to evacuate the vacuum. After venting, a nitrogen sample is taken. 300m silicon nitride wire and 40m calcium wire are fed in. After sampling, the mixture is stirred for 20 minutes. The Al content is 0.0375%. No aluminum is added. 50m titanium wire is fed in. The mixture is stirred for 15 minutes again. 40m sulfur wire is added. After stirring for 7 minutes, a sample is taken for testing. The S content is 0.0244%.

[0029] S5: After adjusting VD to S, feed 55m of tellurium wire, stir statically for 7 minutes, measure the molten steel temperature as 1568℃, and then continuously cast the large square billet.

[0030] After refining using the methods described in the above embodiments, the final target slag composition and percentages are as follows: CaO: 46.72%, SiO2: 16.28%, MgO: 8.86%, Al2O3: 11.56%, TFe: 0.432%, and alkalinity R: 2.87. Example 2

[0031] This embodiment provides a refining method for sulfur-containing aluminum-controlled steel, characterized in that: S1: The second electric furnace taps steel with slag blocked. Before tapping, 0.8 kg / t aluminum blocks are added for deoxidation. After tapping, 400 kg of lime and 550 kg of refining slag are added. S2: After the LF arrives at the station, the electrode is lowered and electroslag is fed. Sample 1 is taken for analysis after 5 minutes of power supply. Nitrogen gas is purged for 10 minutes at a flow rate of 430 L / min. The Al content of sample 1 is 0.0245%. 70 m of aluminum wire was fed. The Al content before entering the vacuum was 0.0223%, and no aluminum was added later.

[0032] S3: In the initial stage of electrolytic slag formation, 60 kg of high-purity silicon carbide was added for surface deoxidation. During refining, appropriate desulfurization was performed without increasing sulfur content. Subsequently, two more batches of silicon carbide, 30 kg each, were added for diffusion deoxidation. After 15 minutes of refining, the slag turned white and remained so throughout the process. The sulfur content of Sample 1 was 0.012%. After Sample 2 was completed, 160 kg of iron sulfide was added, and the sulfur content before vacuuming was 0.0262%.

[0033] S4: After entering VD, nitrogen gas is used to evacuate the vacuum. After venting, a nitrogen sample is taken. 300m silicon nitride wire and 30m calcium wire are fed in. After sampling, the mixture is stirred for 15 minutes. The Al content is 0.0156%. 20m aluminum is added. 50m titanium wire is fed in. The mixture is stirred for another 15 minutes. 30m sulfur wire is added. After stirring for 7 minutes, a sample is taken for testing. The S content is 0.0263%.

[0034] S5: After adjusting VD to S, feed 55m of tellurium wire, stir statically for 7 minutes, measure the molten steel temperature as 1538℃, and then continuously cast the large square billet.

[0035] After refining using the methods described in the above embodiments, the final target slag composition and percentages are as follows: CaO: 50.89%, SiO2: 21.47%, MgO: 7.42%, Al2O3: 9.27%, TFe: 0.379%, and alkalinity R: 2.37.

[0036] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for controlling inclusions in the smelting of sulfur-containing aluminum-controlled steel, comprising electric arc furnace tapping, LF refining, VD vacuum refining, and continuous casting of large billets, characterized in that: S1, Electric furnace tapping: Aluminum blocks are added first for deoxidation during electric furnace tapping, followed by the addition of alloys for alloying during tapping. After the alloys are added, lime and refining slag are added for slag formation. S2, LF Refining: S21: LF is brought in and stirred with argon. After 5 minutes of power supply, a sample is taken for analysis. The target temperature is 30 ℃ above the liquidus. Depending on the slag viscosity or sulfur content, up to 50 kg of active lime is added. S22: Then, under the electrode energizing state, add 60~80kg of silicon carbide deoxidizer to deoxidize the slag surface. The LF furnace is in a reducing atmosphere to maintain white slag refining. S23: After 10 minutes of power supply, switch to nitrogen stirring. During the refining process, maintain the nitrogen flow rate at 300~400L / min and use strong electric arc and high flow rate stirring. S24: After sampling two, retain the slag sample. If the slag is white, add 140~180kg of iron sulfide and an appropriate amount of ferrosilicon powder for deoxidation after power supply. S25: In subsequent refining processes, silicon carbide should be added in small batches, with a total addition of ≥120kg. The target slag system at the refining endpoint should be controlled as follows: basicity R: 2~3.5, Al2O3: 7%~13%, TFe≤0.5%; S3, VD vacuum refining: After the molten steel arrives at the station, nitrogen is added by blowing nitrogen gas, and after the vacuum is broken, argon gas is blown for stirring; the VD vacuum degree is ≤67Pa, and the vacuum holding time is ≥15min; when feeding silicon nitride wire, the N is adjusted to the target value of 175ppm; after the VD vacuum is broken, the wire feeding sequence is as follows: silicon nitride wire, calcium wire, aluminum wire, titanium wire, sulfur wire, tellurium wire (first furnace). S4, large billet continuous casting: the continuous casting temperature of sulfur-containing aluminum steel is 1555~1565℃ for the first furnace and 1535~1545℃ for the continuous casting furnace.

2. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1, characterized in that: In step S1, if it is the first batch of electric furnace slag blocking and tapping, 1 kg / t of aluminum blocks are added first for deoxidation, and 450 kg of lime and 600 kg of refining slag are added after tapping; if it is the second batch of electric furnace slag blocking and tapping, 0.8 kg / t of aluminum blocks are added first for deoxidation, and 400 kg of lime and 550 kg of refining slag are added after tapping.

3. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S21, LF is introduced to blow argon for stirring, and the argon flow rate is maintained at 250 L / min.

4. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S21, it is required that Al ≥ 0.035% in LF refined sample 1. If the aluminum content does not meet 0.035%, aluminum wire is added to bring the content to 0.035%~0.040%. The composition requirements of S before entering the vacuum are 0.028%~0.030% and the Al content requirements are 0.020%~0.040%.

5. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S3, the length of the silicon nitride feeding wire is 300m, and N is adjusted to the target value of 175ppm.

6. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S3, the length of the calcium feeding line is 30~40m. After calcium treatment, the calcium is stirred statically for ≥15min.

7. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S3, the aluminum wire is replenished and the Al is adjusted to 0.013%~0.025%, with a target value of 0.017%.

8. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S3, the titanium wire is fed in and the Ti is adjusted to 0.010%~0.020%, with a target value of 0.015%.

9. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S3, before feeding the sulfur line, the static stirring time is controlled to be greater than 15 minutes, and the composition of S is adjusted to 0.024%~0.035%, with a target value of 0.026%.

10. The method for controlling inclusions in the smelting of sulfur-containing aluminum steel according to claim 1 or 2, characterized in that: In step S3, after the sulfur content of the first furnace is adjusted, 55m of tellurium wire is fed. No tellurium is added for the second furnace. After the tellurium wire is fed, the static stirring time is greater than 5min.

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