Low-carbon steel production process adopting converter-VD tank-LF furnace-continuous casting method

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a converter-VD tank-LF furnace-continuous casting method low-carbon steel production process, and relates to molten steel converter primary smelting, VD refining, LF refining and continuous casting production, by optimizing a converter loading system and slagging, and controlling the lance position and oxygen supply in the process, the converter end point carbon content is controlled within 0.05%, the end point temperature is higher than 1630 DEG C, and the converter end point carbon content is controlled within 0.05%; after the molten steel is discharged to a steel ladle, residual oxygen in the molten steel reacts with carbon in the molten steel in a low-vacuum environment to be decarbonized to below 0.01%, the molten steel subjected to VD residual oxygen decarburization is lifted to an LF furnace to be heated and refined, low-carbon alloy is used for alloying the molten steel in the process, the molten steel is lifted to continuous casting steel after being refined, a low-carbon covering agent and low-carbon covering slag are used for continuous casting, and the low-carbon covering agent and the low-carbon covering slag are used for continuous casting. And the recarburization amount in the LF refining and continuous casting process is controlled within 0.04%, the final steel billet carbon content is lower than 0.05%, low-carbon steel production through a converter-VD tank-LF furnace-continuous casting method is completed, the production process is high in operability and low in implementation cost, the whole production rhythm is not affected, and high-efficiency low-cost stable production of low-carbon steel can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a converter-VD tank-LF furnace-continuous casting method for producing low-carbon steel. Background Art

[0002] With the development of science and technology and construction, the demand for steel types is increasing. Among them, there is a huge demand for low-carbon steel in the fields of energy, automobiles, home appliances, etc. Usually, the converter can only remove the carbon of molten steel to 0.04%, and further decarburization requires the help of refining equipment. Generally, RH furnace vacuum cycle decarburization is used to produce low-carbon steel, but many steel mills are not equipped with RH furnaces, but with VD refining furnaces. Traditional VD furnaces are used to remove hydrogen and nitrogen from molten steel, but cannot produce low-carbon steel.

[0003] In view of this, the present application aims to provide a converter-VD tank-LF furnace-continuous casting low-carbon steel production process to better solve the above-mentioned technical problems. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a converter-VD tank-LF furnace-continuous casting low-carbon steel production process, which achieves the purpose of decarburization by reactivating the reaction between oxygen-enriched and carbon in molten steel under vacuum, thereby meeting the production needs of smelting low-carbon steel.

[0005] The technical solution adopted by the present invention is:

[0006] A converter-VD tank-LF furnace-continuous casting method low carbon steel production process comprises the following steps:

[0007] S1. The raw materials of converter are molten iron, scrap steel and pig iron;

[0008] S2. The amount of slag remaining in the converter from the previous furnace before charging is less than one third, and then the converter is slag-forming;

[0009] S3. Converter endpoint measurement of carbon, oxygen, phosphorus content and molten steel temperature in molten steel;

[0010] S4. Put the qualified molten steel from the converter into the spare ladle. Before putting the steel, ensure that the ladle temperature is greater than 800℃, the ladle is clean and free of debris, the ladle bottom blowing system is normal, and no alloy materials are added during the steel putting process, and no slag is added;

[0011] S5. The molten steel in step S4 is hoisted to a VD tank, connected to argon gas, and vacuumed after temperature measurement. The process is bottom blowing. When the vacuum degree in the VD tank is lower than 100Pa, the vacuum is released, the temperature is measured, and sampling is performed. The residual oxygen in the molten steel reacts with the carbon in the molten steel in a low vacuum environment to decarbonize to less than 0.01%;

[0012] S6. The molten steel in step S5 is hoisted to the LF furnace for refining, the submerged arc operation of the refining process is controlled, a small amount of argon bottom blowing is used during the power transmission process, the molten steel on the slag surface is not exposed, the power transmission is stopped during the large stirring, and the electrode is lifted to 1 meter above the molten steel surface, the refining process uses a low-carbon alloy for alloying treatment, and aluminum wire, aluminum particles, and ferrosilicon powder are used to deoxidize the molten steel. The carbon increase during the entire LF refining process is less than 0.03%. After LF refining, the total carbon content of the molten steel is not higher than 0.04%;

[0013] S7. Measure the temperature and composition of the molten steel in step S6. After meeting the requirements of the steel grade, lift it to the continuous casting and pour steel. Use low-carbon covering agent in the continuous casting tundish and low-carbon protective slag in the crystallizer. The final carbon content of the continuous casting billet is less than 0.05%, completing the production of low-carbon steel by converter-VD tank-LF furnace-continuous casting method.

[0014] Furthermore, in step S1, the proportion of pig iron is not higher than 8%.

[0015] Furthermore, in step S2, the converter uses lime, light-burned dolomite and sintered ore to make slag, and the total slag amount is less than 50 kg / t steel.

[0016] Furthermore, in step S3, the carbon content in the molten steel measured at the converter endpoint is less than 0.06%, the oxygen content is greater than 500 ppm, the phosphorus content is internally controlled for the composite steel grade, and the molten steel temperature is greater than 1630°C.

[0017] Furthermore, in step S5, the bottom blowing flow rate is 60-200m 3 / h, and ensure that the liquid level in the ladle does not rise to prevent burning of the equipment; the vacuum time is 6-10 minutes.

[0018] Furthermore, in step S6, refined arc slag, lime and fluorite are used to make foamed slag.

[0019] The beneficial effects of the present invention are as follows:

[0020] The production process provided by the present invention involves the production of molten steel converter primary refining, VD refining, LF refining and continuous casting. By optimizing the converter charging system and slag making, controlling the process gun position and oxygen supply, the converter terminal carbon content is controlled within 0.05%, the terminal temperature is greater than 1630°C, and no alloy material is added to the converter during the steel tapping process. After the molten steel is discharged from the ladle, it is first hoisted to the VD tank for vacuuming, and the residual oxygen in the molten steel is used to react with the carbon in the molten steel in a low vacuum environment to decarbonize to less than 0.01%. The molten steel after VD residual oxygen decarbonization is hoisted to the LF furnace for heating and refining. The process uses low-carbon alloy to alloy the molten steel. Chemical treatment, use aluminum wire, aluminum particles, and ferrosilicon powder to deoxidize the molten steel, control the argon blowing intensity of the ladle bottom during LF refining, control carbon increase during submerged arc refining to make foam slag, and hoist the molten steel for continuous casting after refining. Use low-carbon covering agent and low-carbon protective slag in continuous casting to control the carbon increase amount in LF refining and continuous casting processes within 0.04%, and the carbon content of the final steel billet is less than 0.05%, completing the production of low-carbon steel by converter-VD tank-LF furnace-continuous casting. This production process has strong operability, low implementation cost, does not affect the entire production rhythm, and plays a positive role in the efficient, low-cost and stable production of low-carbon steel in the steelmaking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow chart in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively by way of examples, and preferred embodiments of the present invention are given below. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. Any other implementation schemes obtained by modifying or equivalently replacing the technical scheme of the present invention without creative results are within the protection scope of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0024] The numerical values ​​disclosed in the embodiments of the present invention are approximate values, not definite values. When the error or experimental conditions permit, all values ​​within the error range may be included without being limited to the specific numerical values ​​disclosed in the embodiments of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] Example

[0027] This embodiment provides a converter-VD tank-LF furnace-continuous casting method for producing low-carbon steel, comprising the following steps:

[0028] S1. The raw materials of the converter are molten iron + scrap steel + pig iron, of which the proportion of pig iron is not higher than 6%, the proportion of scrap steel is 10%, and the proportion of molten iron is 84%;

[0029] S2. The slag left in the converter before charging is half of the slag left in the previous furnace. The converter uses lime (28kg / t), light-burned dolomite (10kg / t), and sintered ore (6kg / t) to make slag and control the process temperature. The total slag volume is 44kg / t steel;

[0030] S3. The carbon, oxygen, phosphorus content and temperature of the molten steel are measured by a secondary gun or other detection equipment at the end of the converter, wherein the carbon content is 0.046%, the oxygen content is 625ppm, the phosphorus content is 0.018%, and the molten steel temperature is 1650°C;

[0031] S4. The molten steel in step S3 is placed from the converter to the spare ladle. The ladle temperature is 900°C before the steel is released. The ladle is clean and free of matter. The ladle bottom blowing system is normal. No alloy, deoxidizer or other materials are added during the steel release process. No slag is added. The temperature of the molten steel to the argon blowing station is 1616°C.

[0032] S5. Lift the molten steel in step S4 to the VD tank, connect the argon belt to blow argon gas from the bottom, measure the temperature at 1608°C, evacuate, and the bottom blowing flow rate during the process is 60-200m 3 / h, total vacuum degree of 80Pa for 8 minutes, release the vacuum, measure the temperature at 1560℃, take samples, the carbon content in the molten steel is 0.004%;

[0033] S6. The molten steel in step S5 is hoisted to LF refining. Refining uses 2kg / t of refined submerged arc slag, 5kg / t of lime, and 1.8kg / t of fluorite to make foamed slag. Submerged arc operation is performed. A small amount of argon bottom blowing is used during the power transmission process. The molten steel on the slag surface is not exposed. 15kg / t of silicon manganese alloy is added during the power transmission process for alloying. 1.2kg / t of aluminum particles and 1kg / t of ferrosilicon powder are used for diffusion deoxidation. The power transmission is stopped after 10 minutes, and the electrode is lifted to 1 meter above the steel liquid level. Deep deoxidation and desulfurization are carried out by strong stirring for 2 minutes. Sampling is taken after LF refining. The carbon content of the molten steel is not higher than 0.032%.

[0034] S3. The molten steel in step 6 is added with a covering agent and hoisted to the continuous casting steel casting, a low-carbon covering agent is used in the continuous casting tundish, and a low-carbon protective slag is used in the crystallizer.

[0035] According to the test, the carbon content of the continuous casting billet of this embodiment is 0.038%, which meets the requirement of less than 0.05%.

[0036] In summary, the production method of low-carbon steel billets provided by the present application, through the analysis of the carbon content in the molten steel smelting process, the carbon in the molten steel comes from molten iron, scrap steel and pig iron, the carbon in the molten iron is relatively easy to remove, and the melting of iron blocks requires time and temperature, so it is not suitable to add too much. The converter decarburization must ensure sufficient oxygen blowing, the slag volume cannot be large, and the bottom blowing of the converter must have sufficient strength. Even so, the converter can only remove the carbon in the molten steel to 0.04%. Further removal requires more time and cost, and the effect is minimal. The present application utilizes the equilibrium relationship between carbon and oxygen in a vacuum state, and vacuum treatment of the molten steel can easily remove the carbon in the molten steel to below 0.01%, and the molten steel after decarburization is guaranteed to have little or no carbon increase, and in the refining process, the carbon increase of the alloy material and the refining electrode must be controlled, and the continuous casting process focuses on controlling the carbon increase of the covering agent and protective slag that are directly in contact with the molten steel, and the carbon increase in the LF and continuous casting process is controlled to be below 0.03%, and the final carbon content of the steel billet is below 0.05%. This method is highly operational, has low implementation cost, does not affect the entire production rhythm, and plays a positive role in the efficient, low-cost and stable production of low-carbon steel in the steelmaking process.

[0037] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A converter-VD tank-LF furnace-continuous casting low carbon steel production process, characterized in that: The steps include: S1. The raw materials of converter are molten iron, scrap steel and pig iron; S2. The amount of slag remaining in the converter from the previous furnace before charging is less than one third, and then the converter is slag-forming; S3. Converter endpoint measurement of carbon, oxygen, phosphorus content and molten steel temperature in molten steel; S4. Put the qualified molten steel from the converter into the spare ladle. Before putting the steel, ensure that the ladle temperature is greater than 800℃, the ladle is clean and free of debris, the ladle bottom blowing system is normal, and no alloy materials are added during the steel putting process, and no slag is added; S5. The molten steel in step S4 is hoisted to a VD tank, connected to argon gas, and vacuumed after temperature measurement. The process is bottom blowing. When the vacuum degree in the VD tank is lower than 100Pa, the vacuum is released, the temperature is measured, and sampling is performed. The residual oxygen in the molten steel reacts with the carbon in the molten steel in a low vacuum environment to decarbonize to less than 0.01%; S6. The molten steel in step S5 is hoisted to the LF furnace for refining, the submerged arc operation of the refining process is controlled, a small amount of argon bottom blowing is used during the power transmission process, the molten steel on the slag surface is not exposed, the power transmission is stopped during the large stirring, and the electrode is lifted to 1 meter above the molten steel surface, the refining process uses a low-carbon alloy for alloying treatment, and aluminum wire, aluminum particles, and ferrosilicon powder are used to deoxidize the molten steel. The carbon increase during the entire LF refining process is less than 0.03%. After LF refining, the total carbon content of the molten steel is not higher than 0.04%; S7. Measure the temperature and composition of the molten steel in step S6. After meeting the requirements of the steel grade, lift it to the continuous casting and pour steel. Use low-carbon covering agent in the continuous casting tundish and low-carbon protective slag in the crystallizer. The final carbon content of the continuous casting billet is less than 0.05%, completing the production of low-carbon steel by converter-VD tank-LF furnace-continuous casting method.

2. The converter-VD tank-LF furnace-continuous casting low carbon steel production process according to claim 1 is characterized in that: In step S1, the pig iron ratio is not higher than 8%.

3. The converter-VD tank-LF furnace-continuous casting low carbon steel production process according to claim 1 is characterized in that: In step S2, the converter uses lime, light-burned dolomite and sintered ore to make slag, and the total slag amount is less than 50kg / t steel.

4. The converter-VD tank-LF furnace-continuous casting low carbon steel production process according to claim 1, characterized in that: In step S3, the carbon content in the molten steel measured at the converter endpoint is less than 0.06%, the oxygen content is greater than 500 ppm, the phosphorus content is internally controlled for the composite steel grade, and the molten steel temperature is greater than 1630°C.

5. The converter-VD tank-LF furnace-continuous casting low carbon steel production process according to claim 1, characterized in that: In step S5, the bottom blowing flow rate is 60-200m 3 / h, and ensure that the liquid level in the ladle does not rise to prevent burning of the equipment; the vacuum time is 6-10 minutes.

6. The converter-VD tank-LF furnace-continuous casting low carbon steel production process according to claim 1, characterized in that: In step S6, refined arc slag, lime and fluorite are used to make foamed slag.

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