Production process and application of low-carbon low-silicon steel

Abstract

The application discloses a production process and application of low-carbon low-silicon steel and belongs to the technical field of steel metallurgy. The production process comprises the steps of initial smelting by an electric furnace, LF refining, VD vacuum refining, continuous casting pouring, and cutting waste by an open pouring furnace, wherein the raw material dosage, adding mode and adding node of each step are controlled, production process fluctuation can be greatly reduced, technical problems such as continuous casting nodulation and liquid level fluctuation are solved, safe production is realized, and the quality of the low-carbon low-silicon steel is improved. Through the production process, the low-carbon low-silicon steel is produced, and the composition of the low-carbon low-silicon steel is as follows in percentage by mass: carbon content is [0.03%, 0.06%], silicon content is [0.02%, 0.08%], manganese content is [0.25%, 0.35%], phosphorus content is less than or equal to 0.030%, sulfur content is less than or equal to 0.025%, and aluminum content is [0.015%, 0.040%].

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and specifically relates to a production process and application of low-carbon and low-silicon steel. Background Technology

[0002] Low-carbon and low-silicon steel generally refers to carbon steel with a carbon and silicon content of less than 0.10%. Due to its low carbon and low silicon characteristics, the molten steel has a high oxygen activity during the smelting process. Aluminum is generally used for deoxidation, so the aluminum content in the steel is generally required to be between 0.020% and 0.040%. This results in a large number of high-melting-point Al-O inclusions, which are prone to secondary oxidation during continuous casting, and can easily cause production and quality accidents such as casting nodules and liquid surface fluctuations.

[0003] In current related technologies, the use of strong deoxidizers such as aluminum and titanium can easily generate low-melting-point Ca-Si-Al-O inclusions. These inclusions have low melting points, good wettability with molten steel, are not easy to float, and are difficult to be adsorbed and removed by slag. Summary of the Invention

[0004] This invention addresses the characteristics of low-carbon and low-silicon steel continuous casting process, which is prone to fluctuations and has poor castability. It rationally designs the entire production process, significantly reduces production process fluctuations, solves the technical problems of continuous casting nodules and liquid level fluctuations, achieves safe production, and improves the quality of low-carbon and low-silicon steel.

[0005] According to one aspect of the present invention, a production process for low-carbon, low-silicon steel is provided, comprising the following steps:

[0006] (1) Electric furnace primary refining: After the steel is tapped from the front furnace, there are 30wt to 40wt% of molten steel remaining in the furnace. When the total mass of scrap steel and molten iron is set to 100 parts by mass, 15 to 25 parts by mass of scrap steel are continuously added into the furnace, and 75 to 85 parts by mass of molten iron are continuously added into the furnace. The oxygen lance is then turned on for blowing.

[0007] The electric furnace is an eccentric furnace. When 30 to 40 parts by weight of steel are tapped from the bottom of the eccentric furnace, 0.18 to 0.2 parts by weight of pure aluminum blocks are added at once for pre-deoxidation, and then additives are added in sequence.

[0008] (2) LF refining: The molten steel in the electric furnace enters the refining furnace, and the slag is heated by energizing. After the slag surface melts, 50m to 100m of aluminum wire is fed in. The mass percentage of each component in the final slag is as follows: CaO: 50%-55%, SiO2: 3%-6%, MgO: 4%-8%, Al2O3: 25%-35%, FeO: 0.1%-0.4%;

[0009] Take an initial sample of molten steel, feed aluminum wire according to the aluminum content in the initial sample, adjust the aluminum composition to 0.04wt%-0.05wt%, and refine until the aluminum content of the tapped steel is 0.30wt%-0.40wt%.

[0010] (3) VD vacuum refining: The molten steel refined by LF enters the VD furnace and is evacuated to a vacuum state of ≤67Pa. After vacuum pressure holding, the vacuum is broken and the aluminum content is analyzed. Aluminum wire is added to the furnace to 0.15wt%-0.40wt% according to the aluminum content. After adding aluminum wire, argon gas is blown softly for several minutes, and then 150-200 meters of pure calcium wire is fed in.

[0011] (4) Continuous casting: The ladle is protected by a long nozzle sleeve and an integral immersion nozzle in the tundish. Before casting in the tundish, argon is purged to remove air. After casting in the ladle, alkaline covering agent is added to the tundish, followed by heat-insulating covering agent.

[0012] After the middle buns are baked, start pouring. After pouring from the middle buns immersion nozzle for 3-5 minutes, when the liquid level in the middle buns is stable, manually flush the stopper rod 2-3 times.

[0013] (5) Cutting waste in the casting furnace, wherein the length of the waste cut in the casting furnace is 4.5m to 6m.

[0014] Optionally, in step (1), the continuous addition of 15 to 25 parts by weight of scrap steel into the furnace specifically means adding 15 to 25 parts by weight of scrap steel into the furnace at a rate of 1.0 to 1.5 tons / minute.

[0015] Optionally, in step (1), the simultaneous addition of 75 to 85 parts by weight of molten iron into the furnace specifically means: simultaneously adding 75 to 85 parts by weight of molten iron into the furnace at a rate of 3 to 5 tons per minute.

[0016] Optionally, in step (1), the additive comprises metallic manganese, ferrosilicon and slag; the slag is composed of lime and pre-melted slag, and the mass ratio of lime to pre-melted slag is 7:2.

[0017] Optionally, the composition of the pre-melted slag is: CaO: 40wt%-50wt%, SiO2: 5wt%-7wt%, Al2O3: 45wt%-55wt%, and water: 0-0.5wt%.

[0018] Optionally, in step (2), after feeding in 50m to 100m of aluminum wire, the following steps are also included: adding an appropriate amount of quicklime to make the refining slag appear as smooth white slag.

[0019] Optionally, in step (3), the vacuum pressure holding specifically involves: maintaining pressure for 5 to 8 minutes with a soft blowing of argon gas at a flow rate of 50 NL / min.

[0020] Optionally, in step (3), the step of supplementing aluminum wire to 0.15wt%-0.40wt% according to the aluminum content specifically means: supplementing aluminum wire to 0.25% according to the aluminum content.

[0021] Optionally, in step (4), the alkaline covering agent in the intermediate package comprises: CaO: 45wt%-55wt%, 0 <SiO2≤8wt%,0<MgO≤8wt%,0<TiO2≤0.8wt%,0<FeO≤1.0wt%,30wt%≤Al2O3≤40wt%。

[0022] Optionally, in step (4), the heat-insulating covering agent is carbonized rice husk ash, wherein the fixed carbon content is ≥35wt%.

[0023] On the other hand, an application of a production process for low-carbon, low-silicon steel is provided for producing low-carbon, low-silicon steel, wherein the components of the low-carbon, low-silicon steel are as follows by mass percentage: carbon content: [0.03%, 0.06%], silicon content: [0.02%, 0.08%], manganese content: [0.25%, 0.35%], phosphorus content ≤0.030%, sulfur content ≤0.025%, and aluminum content: [0.015%, 0.040%].

[0024] This invention rationally designs the entire production process: electric furnace primary refining, LF refining, VD vacuum refining, continuous casting, and furnace opening and scrap removal. It controls the raw material usage ratios, timing, and methods at each step, significantly reducing production process fluctuations and solving the technical problems of continuous casting nodules and liquid level fluctuations. This achieves safe production and improves the quality of low-carbon, low-silicon steel. Through the low-carbon, low-silicon steel production process provided by this invention, the components of the obtained low-carbon, low-silicon steel, by mass percentage, are: carbon content: [0.03%, 0.06%], silicon content: [0.02%, 0.08%], manganese content: [0.25%, 0.35%], phosphorus content ≤0.030%, sulfur content ≤0.025%, and aluminum content: [0.015%, 0.040%]. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the production process of low-carbon, low-silicon steel, which is an exemplary embodiment of the present invention. Detailed Implementation

[0026] This invention is not limited to the following specific embodiments. Those skilled in the art can implement this invention using other specific embodiments based on the content disclosed herein. Any simple changes or modifications made to the design structure and concept of this invention fall within the protection scope of this invention.

[0027] Unless otherwise defined, the technical or scientific terms used in this specification and claims shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0028] The heat-insulating covering agent involved in the specific embodiments of the present invention is carbonized rice husk ash. The product after rice husk is burned generally has a fixed carbon content of 30%-60%. The carbonized rice husk ash used in the specific embodiments of the present invention has a fixed carbon content of ≥35%.

[0029] For details on the production process of low-carbon, low-silicon steel according to specific embodiments of the present invention, please refer to [link / reference needed]. Figure 1 This includes the following steps:

[0030] (1) Electric furnace primary smelting: After the steel is tapped from the furnace, there is 30wt to 40wt% molten steel remaining in the furnace. When the total mass of scrap steel and molten iron is set to 100 parts by mass, 15 to 25 parts by mass of scrap steel are continuously added into the furnace at a rate of 1.0 to 1.5 tons / minute. At the same time, 75 to 85 parts by mass of molten iron are continuously added into the furnace at a rate of 3 to 5 tons / minute. The oxygen lance is turned on for blowing. The advantage of this method is that the scrap steel and molten iron are not added into the furnace all at once, but are added continuously at a certain rate, which avoids the furnace boiling accident caused by severe over-oxidation of molten steel during the smelting process.

[0031] The electric furnace is an eccentric furnace, which effectively avoids excessive slag discharge. When 30-40 parts by weight of steel are tapped from the bottom of the eccentric furnace, 0.18-0.2 parts by weight of pure aluminum blocks are added at once for pre-deoxidation. Then, additives containing metallic manganese, ferrosilicon, and slag are added in sequence, in the conventional amounts used in this field. The aluminum blocks are added all at once during the steel tapping process. The advantage of this method is that the deoxidation mainly produces clustered Al-O inclusions, which are easily floated and adsorbed by the slag during subsequent smelting and are easy to remove. If the aluminum blocks are added together with or after the ferrosilicon alloys, low-melting-point Ca-Si-Al-O inclusions are easily formed. These inclusions have low melting points, good wettability with molten steel, are not easy to float, and are difficult to be adsorbed and removed by the slag.

[0032] (2) LF Refining: Molten steel from the electric furnace enters the refining furnace, where electricity is applied to melt the slag and raise the temperature. After the slag surface melts, 50m-100m of aluminum wire is fed in for deep deoxidation. This process avoids the use of carbon- or silicon-containing deoxidizing materials and aluminum particle slag surface deoxidation, thus preventing the rapid saturation of Al2O3 in the refining slag and the incomplete removal of Al2O3 inclusions in the aluminum deoxidation products. During the refining process, a small amount of lime can be added to adjust the slag, ensuring that the refining slag has a smooth, white surface. The mass percentages of the components in the final slag after refining are: CaO: 50%-55%, SiO2: 3%-6%, MgO: 4%-8%, Al2O3: 25%-35%, FeO: 0.1%-0.4%.

[0033] Take an initial sample of molten steel, feed aluminum wire according to the aluminum content in the initial sample, adjust the aluminum composition to 0.04wt%-0.05wt%, and refine until the aluminum content of the tapped steel is 0.30wt%-0.40wt%.

[0034] (3) VD vacuum refining: The molten steel refined by LF enters the VD furnace and is evacuated to a vacuum state of ≤67Pa. After vacuum pressure holding, the aluminum content is sampled and analyzed. Aluminum wire is added to 0.15wt%-0.40wt%, generally 0.25wt%, to meet the steel composition design requirements. After adding aluminum wire, argon gas is blown softly for several minutes, and then 150-200 meters of pure calcium wire is added. The purpose of adding calcium wire is to modify the high melting point Al-O inclusions produced by aluminum deoxidation to generate low melting point Ca-Al-O inclusions. The low melting point inclusions will not cause the sprue to form nodules and the liquid surface to fluctuate during continuous casting.

[0035] (4) Continuous casting: The tundish is protected by a long nozzle sleeve in the ladle and an integral submerged nozzle in the tundish. Before casting in the tundish, argon is purged to remove air. After casting in the ladle, an alkaline covering agent is added to the tundish. The composition of the covering agent is preferably CaO: 45%-55%, SiO2≤8%, MgO≤8%, TiO2≤0.8%, FeO≤1.0% by mass percentage. Generally, the alkalinity CaO / SiO2 is greater than 8. The reason is that as casting in the tundish continues, the adsorbed inclusions and the inevitable slag entering the tundish from the ladle will continuously reduce the alkalinity of the tundish slag, thus affecting the adsorption capacity of the tundish slag for inclusions in the later stage of production.

[0036] Adding an insulating covering agent, such as carbonized rice husk ash (preferably with fixed carbon (FCd) ≥35% and moisture ≤4%), can effectively prevent slag surface crusting. It provides insulation, anti-oxidation, and adsorption of inclusions floating in the molten steel during continuous casting. However, a lower content of this component can lead to hardening of the slag layer in the tundish, reducing its ability to adsorb inclusions from the molten steel.

[0037] After the tundish is baked, casting begins. The tundish baking time is 3-6 hours, and the temperature is 1100-1300℃. Because this steel grade is low in carbon and silicon and has a high aluminum content, some secondary oxidation will inevitably occur during the first casting in the tundish. Therefore, after the tundish liquid level stabilizes 3-5 minutes after the tundish submersible nozzle starts casting, the stopper rod is manually flushed 2-3 times. At this time, the ladle has just started casting and the tundish flow field is not yet stable. This can prevent nodules from accumulating between the submersible nozzle bowl and the stopper rod tip, and avoid fluctuations in the liquid level of the casting furnace.

[0038] (5) Waste removal during furnace opening: The waste removal length of the continuous casting head billet during furnace opening is 4.5m to 6m, ensuring that the continuous casting billet in the punching section is completely removed. In the specific embodiment of the present invention, the punching operation is performed 3-5 minutes after the immersion nozzle of the tundish is opened. At this time, the area between the plug tip and the nozzle bowl of the tundish is relatively clean, without a large amount of flocculated material. Punching at this time can prevent the flocculated material between the plug tip and the nozzle bowl from accumulating and growing, which is a measure to prevent the flocculated material from causing nozzle nodules.

[0039] In a specific embodiment of the present invention, in step (1), the slag material is composed of lime and pre-melted slag, and the mass ratio of lime to pre-melted slag is 7:2. This allows for rapid slag formation, reduces the difficulty of early-stage refining operations, and facilitates the rapid absorption of oxides generated during the steel tapping process.

[0040] In a specific embodiment of the present invention, the composition of the pre-melted slag is: CaO: 40wt%-50wt%, SiO2: 5wt%-7wt%, Al2O3: 45wt%-55wt%, and water: 0-0.5wt%. Thus, the low melting point allows for rapid melting, and its composition is similar to that of the final slag, which is beneficial for adsorbing floating inclusions.

[0041] In some other specific embodiments, after feeding in 50m to 100m of aluminum wire in step (2), an appropriate amount of quicklime is added to make the refining slag appear as a smooth white slag.

[0042] In a specific embodiment of the present invention, the step of supplementing aluminum wire to 0.15wt%-0.40wt% according to the aluminum content specifically means: supplementing aluminum wire to 0.25% according to the aluminum content. The aluminum content is adjusted according to the steel composition requirements, and the aluminum loss in subsequent operations is fully considered. After the adjustment is completed, no further aluminum supplementation is required.

[0043] The components of the low-carbon, low-silicon steel in the specific embodiments of the present invention are as follows by mass percentage: carbon content: [0.03%, 0.06%], silicon content: [0.02%, 0.08%], manganese content: [0.25%, 0.35%], phosphorus content ≤0.030%, sulfur content ≤0.025%, aluminum content: [0.015%, 0.040%], with no nodules and high quality.

[0044] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A production process for low-carbon, low-silicon steel, characterized in that, Includes the following steps: (1) Electric furnace primary refining: After the steel is tapped from the front furnace, there are 30wt% to 40wt% of molten steel remaining in the furnace. When the total mass of scrap steel and molten iron is set to 100 parts by mass, 15 to 25 parts by mass of scrap steel are continuously added into the furnace, and 75 to 85 parts by mass of molten iron are continuously added into the furnace. The oxygen lance is turned on for blowing. The electric furnace is an eccentric furnace. When 30-40 parts by weight of steel are tapped from the bottom of the eccentric furnace, 0.18-0.2 parts by weight of pure aluminum blocks are added at once for pre-deoxidation. Then, metallic manganese, ferrosilicon, and slag are added in sequence. The slag consists of quicklime and pre-melted slag, with a quicklime to pre-melted slag mass ratio of 7:

2. The pre-melted slag is composed of: CaO: 40wt%-50wt%, SiO2: 5wt%-7wt%, Al2O3: 45wt%-55wt%, and water: 0-0.5wt%. (2) LF refining: The molten steel in the electric furnace enters the refining furnace, and the slag is heated by energizing. After the slag surface melts, 50m to 100m of aluminum wire is fed in. The mass percentage of each component in the final slag is as follows: CaO: 50% to 55%, SiO2: 3% to 6%, MgO: 4% to 8%, Al2O3: 25% to 35%, FeO: 0.1% to 0.4%; the sum of the above components is 100%. Take an initial sample of molten steel, feed aluminum wire according to the aluminum content in the initial sample, adjust the aluminum content to 0.04wt% to 0.05wt%, and refine until the aluminum content of the tapped steel is 0.30wt% to 0.40wt%. (3) VD vacuum refining: The molten steel refined by LF enters the VD furnace and is evacuated to a vacuum state of ≤67Pa. After vacuum pressure holding, the vacuum is broken and the aluminum content is sampled and analyzed. Aluminum wire is added according to the aluminum content until the aluminum content is 0.15wt%-0.40wt%. After adding aluminum wire, argon gas is blown softly for several minutes, and then 150-200 meters of pure calcium wire is fed in. (4) Continuous casting: Casting is performed using a long nozzle sleeve on the ladle and an integrally submerged nozzle protection system on the tundish. Before casting begins on the tundish, argon is purged to remove air. After casting begins on the ladle, an alkaline covering agent is added to the tundish, followed by an insulating covering agent. The alkaline covering agent includes: CaO: 45wt%-55wt%, 0 <SiO2≤8wt%;0<MgO≤8wt%,0<TiO2≤0.8wt%,0<FeO≤1.0wt%,30wt%≤Al2O3≤40wt%; After the middle slab is baked, start pouring. After pouring from the middle slab immersion nozzle for 3-5 minutes, when the liquid level in the middle slab is stable, manually flush the stopper rod 2-3 times. (5) Cutting waste in the casting furnace, wherein the length of the waste cut in the casting furnace is 4.5m to 6m.

2. The production process for low-carbon, low-silicon steel according to claim 1, characterized in that, In step (1), the continuous addition of 15 to 25 parts by weight of scrap steel into the furnace specifically means adding 15 to 25 parts by weight of scrap steel into the furnace at a rate of 1.0 to 1.5 tons per minute.

3. The production process for low-carbon, low-silicon steel according to claim 1, characterized in that, In step (1), the simultaneous addition of 75 to 85 parts by mass of molten iron into the furnace specifically means: simultaneously adding 75 to 85 parts by mass of molten iron into the furnace at a rate of 3 to 5 tons per minute.

4. The production process for low-carbon, low-silicon steel according to claim 1, characterized in that, In step (2), after feeding in 50m to 100m of aluminum wire, the following steps are also included: adding an appropriate amount of quicklime to make the refining slag appear as smooth white slag.

5. The production process for low-carbon, low-silicon steel according to claim 1, characterized in that, In step (3), the vacuum pressure holding specifically involves: maintaining pressure for 5 to 8 minutes with a soft blowing of argon gas at a flow rate of 50 NL / min.

6. The production process for low-carbon, low-silicon steel according to claim 1, characterized in that, In step (3), the step of supplementing aluminum wire to 0.15wt%-0.40wt% according to the aluminum content specifically means: supplementing aluminum wire to 0.25% according to the aluminum content.

7. An application of a production process for low-carbon, low-silicon steel according to any one of claims 1 to 6, used for producing low-carbon, low-silicon steel, characterized in that, The components of the low-carbon, low-silicon steel, by mass percentage, are as follows: carbon content: 0.03%–0.06%, silicon content: 0.02%–0.08%, manganese content: 0.25%–0.35%, phosphorus content ≤0.030%, sulfur content ≤0.025%, and aluminum content: 0.015%–0.040%.

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