RH furnace deep decarburization modular technology and smelting method

Abstract

The application discloses a RH furnace deep decarburization modular technology and a smelting method, and belongs to the technical field of smelting. The smelting method is mainly used for producing EDDQ and SEDDQ similar high-grade IF steel, and smelting steps include: S1, decarburization pretreatment; S2, super deep decarburization; and S3, decarburization post-treatment. The application adopts up-draught pipes and down-draught pipes to alternately circulate, and adds a decarburization accelerator to accelerate the floating of inclusions and the decarburization. The smelting method improves the decarburization efficiency, reduces the carbon content to an extremely low level, simultaneously uses an existing condition to generate micro-bubbles to significantly improve the purity of the molten steel, and provides solid technical support for the production and quality guarantee of high-grade IF steel.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a modular technology and smelting method for deep decarburization of an RH furnace. Background Technology

[0002] With the rapid development of industries such as automobiles and home appliances, the demand for ultra-low carbon deep-drawing steel, represented by DC04 and DC06, is constantly increasing. Deep-drawing steel has good formability and performance uniformity. It is a gapless deep-drawing steel with very low carbon content and the addition of alloying stabilizing elements. It is mainly used in automobiles, home appliances, and electrical components, and has good market prospects and product benefits.

[0003] Ultra-low carbon steel products require extremely low carbon content, making deep decarburization a crucial stage in the process, while the decarburization rate becomes the limiting factor. Many steel mills add RH vacuum smelting equipment based on later product demands. Due to the slender and tall ladle design, the diameter is relatively small, limiting the expansion of the RH furnace immersion tube diameter; that is, the cross-sectional area of ​​the riser pipe cannot be further increased, thus making it difficult to increase the molten steel circulation flow rate Q. Furthermore, when the carbon content drops to 20 ppm, decarburization stagnates, and increasing the circulation flow rate at this point does not significantly improve decarburization. To obtain extremely low carbon content (less than 10 ppm), most methods increase the volumetric mass transfer coefficient and improve the reaction area of ​​the decarburization interface, thereby increasing decarburization efficiency. We simultaneously produce high-grade IF steel (fuel tanks and oil pans, etc.) of EDDQ (Extra Deep Drawing Quality) and SEDDQ (Super Extra Deep Drawing Quality). According to the requirements of steel rolling technology, when the carbon content is greater than 13ppm, only high-temperature annealing can be used, and when the carbon content is less than 13ppm, low-temperature annealing can be used, thereby improving the efficiency of cold rolling production.

[0004] Therefore, from the perspectives of reducing steel rolling costs, achieving breakthroughs in process technology, and improving product quality, it is particularly important to carry out technological development based on existing equipment; thus, it is especially urgent to research and develop a deep decarburization smelting technology and its application method in an RH furnace. Summary of the Invention

[0005] To address the aforementioned limitations of existing technologies, the present invention aims to provide a modular technology and smelting method for deep decarburization in an RH furnace. Based on the fundamental thermodynamic and kinetic principles of deep decarburization, this invention analyzes each reaction stage of deep decarburization, studies and formulates corresponding decarburization smelting modes and favorable decarburization conditions, and utilizes a combination of the heterogeneous nucleation mechanism of iron oxide in the decarburization promoter and the expansion of the reaction interface area by calcium carbonate to further overcome the carbon-oxygen reaction limitation in the ultra-low carbon region. Simultaneously, the microbubbles generated by the impregnation tube and downcomer accelerate the flotation and removal of inclusions. This method can significantly improve the efficiency of deep decarburization in an RH furnace and the smelting of extremely low carbon materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a modular smelting method for deep decarburization in an RH furnace for high-grade IF steel, comprising the following steps: S1 Decarburization Pretreatment: Oxygen-containing molten steel is pre-treated for decarburization in the RH furnace. The oxygen content at the furnace entrance is 450-550ppm. The smelting method is Mode 2. S2 Ultra-Deep Decarburization Treatment: After the decarburization pretreatment is completed, smelting is carried out in an RH furnace, alternating between Mode 1 and Mode 2; at the same time, decarburization accelerator is added at a rate of 1.0-1.2 kg / ton of molten steel in 3-4 batches for ultra-deep decarburization treatment. S3 decarburization post-treatment: After the deep decarburization treatment is completed, deoxidation alloying is carried out, and the smelting method adopts alternating mode 2 and mode 3; Modes 1 through 3 are as follows: Mode 1: The gas flow rates in the riser and downcomer of the RH furnace are the same, with a flow rate of Q1 Nm. 3 / h, and the flow rate is controlled at 90%~100% of the maximum flow rate; among them, the vacuum tank immersion tube of the RH furnace is divided into rising tube and falling tube. When molten steel flows into the immersion tube, it is the rising tube, and when molten steel flows out, it is the falling tube. Mode 2: The gas flow rate in the riser of the RH furnace is Q1, and the gas flow rate in the downcomer is Q1. (0.2-0.25); Mode 3: The riser pipe of the RH furnace becomes a downcomer pipe, and the downcomer pipe becomes a riser pipe. The gas flow rate blown into the riser pipe is Q1 Nm. 3 / h, the downcomer gas flow rate is Q1 (0.2-0.25) Nm 3 / h.

[0007] Furthermore, after the S1 decarburization pretreatment, the carbon content of the molten steel is <50ppm.

[0008] Furthermore, during the S2 ultra-deep decarburization process, the circulation time for each cycle in Mode 1 is 20-30 seconds, and the circulation time for each cycle in Mode 2 is 1-1.5 minutes. Mode 1 and Mode 2 are alternated in a cycle for a total of 3 cycles.

[0009] Furthermore, after the S2 ultra-deep decarburization treatment, the carbon content of the molten steel is <13ppm.

[0010] Furthermore, during the S3 decarbonization post-treatment, the circulation time for each cycle in Mode 2 is 5-7 minutes, and the circulation time for each cycle in Mode 3 is 5-7 minutes; Mode 2 and Mode 3 are alternated in a cycle, and the cycle is repeated once.

[0011] Furthermore, the number of air blowing pipes in both the riser and the faller is 12-16, and the pipe diameter is 3-3.5mm.

[0012] Furthermore, the gas source for the riser and downcomer is nitrogen or argon. Argon is used during smelting and nitrogen is used during non-smelting processes, and the inlet pressure is 0.8-1.2 MPa.

[0013] Furthermore, the decarbonization accelerator comprises the following components: 40-45 parts iron oxide, 45-50 parts calcium carbonate, 1-3 parts silicon dioxide, and 5-10 parts carbon-free binder; the particle size of the decarbonization accelerator is 10-30 mm, wherein the total content of impurities phosphorus and sulfur is <0.1 wt%, and the carbon-free binder used is a cellulose binder.

[0014] Furthermore, the vacuum level inside the vacuum chamber of the RH furnace should not exceed 67 Pa.

[0015] A second aspect of the present invention provides the application of the RH furnace deep decarburization modular smelting method in the smelting of ultra-low carbon steel, wherein the ultra-low carbon steel is ultra-deep drawing grade or ultra-ultra-deep drawing grade.

[0016] The beneficial effects of this invention are: This invention is applied to the ultra-low carbon smelting of molten steel in an RH furnace. It analyzes the entire reaction process of deep decarburization, optimizing the process by employing different circulation modes and decarburization mechanisms at multiple stages of decarburization. Firstly, this invention uses air blowing pipes arranged in both the immersion tube riser and downcomer, defined as riser and downcomer pipes distinguished by air blowing flow rate. This design facilitates rapid switching between circulation modes. Deep decarburization is treated using a two-pipe, dual-air blowing mode, increasing the reaction interface area and dynamic conditions of the molten steel in the vacuum tank, which is beneficial for the carbon-oxygen reaction. After deoxidation and alloying... The use of asymmetrical flow rates in the riser and downcomer for circulation facilitates the formation of microbubbles in the low-flow-rate gas in the downcomer under high-speed steel flow, which is beneficial for the removal of inclusions in the later stages. At the same time, the interchange of the functions of the riser and downcomer in this stage is equally important. It can strongly stir the areas in the ladle that were originally less fluid. The dead zone at the bottom of the riser side is now strongly scourned. The flow pattern in the area that was originally on the downcomer side has also changed. This greatly promotes the mixing and homogenization of the molten steel in the entire ladle, which is particularly beneficial for achieving the ultimate uniformity of composition and temperature in the final stage of refining. Secondly, this invention employs a decarburization accelerator consisting of a mixture of iron oxide and calcium carbonate in a certain proportion in the deep decarburization zone, further enhancing the carbon-oxygen reaction in the extremely low carbon zone. The iron oxide component, when added to the molten steel, not only forms an oxygen source for the carbon reaction but also acts as a heterogeneous nucleation agent, reducing the resistance to the carbon-oxygen reaction. In addition, the addition of the calcium carbonate component rapidly decomposes in the high-temperature molten steel environment to form a large amount of carbon dioxide gas, thereby reducing the static pressure of the molten steel and the partial pressure of the gas phase formed by the carbon-oxygen reaction, which plays a better role in the decarburization reaction. This invention features a rationally designed decarburization process in the smelting zone, emphasizing modular and intelligent implementation of parameters. The impregnation tube circulation mode is configured with three modes, each with pre-defined circulation flow parameters that can be fine-tuned during the smelting process. The circulation mode settings facilitate pre-setting the mode's operating cycle at different decarburization stages and optimizing the mode's operating time under varying entry conditions. Furthermore, the multiple circulation modes creatively propose an asymmetric blowing smelting mode with dual impregnation tubes, breaking existing limitations. The accumulation and superposition of large amounts of data facilitates the advancement of intelligent models. This production method lays a solid foundation for the intelligent modularization and iterative upgrading of deep decarburization in the RH furnace process, effectively promoting long-term stable improvement in product quality and extreme cost control. Similarly, ultra-low carbon and extremely low carbon control provide the necessary technical conditions for low-cost rolling in subsequent processes, thus realizing an integrated cost reduction channel for steel rolling. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the smelting model structure of the present invention; wherein, 1 is a vacuum tank, 1-a is a vacuum tank feeding chute, 1-b is a vacuum tank immersion tube; and 2 is a steel ladle. Detailed Implementation

[0018] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0020] The RH furnace has multiple preset parameter modes (including specific gas source and gas flow rate) for easy switching during use. Details are as follows: Mode S1: The gas flow rate is the same in both the riser and downcomer.

[0021] Mode S2: When the gas flow rate in the riser is Q1, the gas flow rate in the downcomer is Q1. (0.2-0.25).

[0022] Mode S3: The riser becomes a downcomer, and the downcomer becomes a riser. When the gas flow rate in the riser is Q1, the gas flow rate in the downcomer is Q1. (0.2-0.25).

[0023] The test materials used in the embodiments of this invention, unless otherwise specified, are all conventional test materials in the art and can be purchased through commercial channels. The carbonless adhesive used in this invention is a cellulose adhesive.

[0024] Example 1: Deep Decarburization Module Smelting Method in RH Furnace A 120-ton RH furnace was used to smelt ultra-low carbon deep-drawing steel of grade "DC04-N". The vacuum tank impregnation tube had an inner diameter of 240 cm and a Q1max circulation flow rate of 120 Nm³. 3 The vacuum system employs a 5-stage steam jet pump, with a minimum vacuum level of 20 Pa in the vacuum tank. Argon or nitrogen is used as the gas source; argon is used during smelting, and nitrogen is used during non-smelting. The inlet pressure is controlled between 0.8-1.2 MPa. The RH furnace vacuum tank impregnation pipe consists of riser and downcomer pipes, each with 12 blowing pipes of 3 mm diameter. When molten steel flows into the impregnation pipe (suction), it acts as the riser pipe; when molten steel flows out (expulsion), it acts as the downcomer pipe. A deoxidizer accelerator is added at 1 kg / ton of steel, with an actual molten steel volume of 120 tons. The decarburization accelerator composition is as follows: 43% iron oxide, 48% calcium carbonate, 2% silicon dioxide, and 7% carbon-free binder. After mixing the above inorganic materials, they are pressed into spheres with a resin-based carbon-free binder, resulting in a particle size of 10-30 mm.

[0025] The RH furnace operation process is as follows: S1: Decarbonization pretreatment At 0 min of circulation, the temperature and oxygen content at the inlet were measured: 1622℃, oxygen content 496ppm. Smelting mode 2 was selected, with a gas flow rate of 110 Nm³ / h rising pipe. 3 / h, the downcomer gas flow rate is Q1 0.2 = 110 0.2 = 22 Nm 3 / h.

[0026] S2: Ultra-deep decarburization treatment After 10 minutes of circulation, temperature and oxygen content were measured: the temperature was 1602℃, and the oxygen content was 360ppm. Sample 1 was taken for carbon content analysis, and the measured carbon content was 48ppm. The smelting process automatically switched between Mode 1 and Mode 2, as shown in Table 1; Mode 1 was selected first, with a gas flow rate of 110Nm³ in the riser. 3 / h, the downcomer blow-in gas flow rate is 110 Nm 3 / h. A total of 120 kg of decarbonization accelerator was added, divided into 3 batches, with 40 kg added at the beginning of each Mode 1.

[0027] Table 1 Ultra-deep decarburization treatment modes S3: Post-decarbonization treatment After 16 minutes of circulation, temperature and oxygen content were measured: the temperature was 1593℃ and the oxygen content was 403ppm.

[0028] Add 120 kg of aluminum granules for deoxidation and alloying. Switch between smelting selection modes 2 and 3. The switching method is shown in Table 2.

[0029] After 19 minutes of circulation, the aluminum content was determined by temperature measurement: the temperature was 1605℃ and the aluminum content was 0.023%.

[0030] Temperature was measured at 1600℃ after 26 minutes of circulation; two samples were taken for carbon content analysis. The sample was then repressurized before exiting the station.

[0031] Table 2 Post-decarbonization treatment modes Using the method described in this embodiment, the carbon content at the smelting endpoint was measured to be 8 ppm, the decarburization time was 16 min, and the total oxygen content of the rolled material was 12 ppm. The smelting process met the product technical requirements (endpoint carbon less than 13 ppm), achieving a good smelting effect.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that, in the post-decarburization treatment at S3, only mode 2 is used for 10 minutes, without switching to mode 3.

[0033] Using this comparative method, the carbon content at the smelting endpoint was measured to be 13 ppm, the decarburization time was 16 min, and the total oxygen content of the rolled product was 18 ppm, which is higher than that of Example 1.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that in the S2 ultra-deep decarburization process, only Mode 2 is used for 6 minutes, without switching to Mode 1, and no decarburization accelerator is added.

[0035] Using this comparative method, the carbon content at the smelting endpoint was measured to be 25 ppm, the decarburization time was 16 min, and the total oxygen content of the rolled product was 19 ppm. The smelting process did not meet the technical requirement that the carbon content at the product endpoint be less than 13 ppm.

[0036] In summary, this invention enables the smelting of products with extremely low carbon content in RH furnaces. This technology not only achieves ultra-low carbon content but also demonstrates excellent metallurgical effects in terms of decarburization efficiency and steel purity. From the unique innovation of the smelting mode to the development of decarburization accelerators, and the microbubbles generated by the asymmetric blowing volume in the later stages of smelting, which accelerate the flotation of inclusions and decarburization, this invention significantly promotes the rapid advancement of the carbon-oxygen reaction in a vacuum environment. This invention integrates technologies such as the heterogeneous nucleation carbon-oxygen reaction mechanism, the expansion of the carbon-oxygen reaction interface area, the reduction of static pressure and phase partial pressure in the carbon-oxygen reaction, and the generation of microbubbles in high-temperature molten steel. It solves the problem of stable and efficient production of high-end IF steel under the limitations of RH furnace equipment, and also provides steel companies with broad design ideas and multiple options for future equipment technology upgrades. The controlled production of extremely low carbon content provides reliable technical support for low-cost smelting on the rolling side, enabling a two-way expansion of cost reduction space in integrated steel rolling, and creating excellent and solid technical support for the development and improvement of enterprise product quality.

[0037] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A modular RH furnace deep decarburization smelting method for high-grade IF steel, characterized in that, Includes the following steps: S1 Decarburization Pretreatment: Oxygen-containing molten steel is pre-treated for decarburization in the RH furnace. The oxygen content at the furnace entrance is 450-550ppm. The smelting method is Mode 2. S2 Ultra-Deep Decarburization Treatment: After the decarburization pretreatment is completed, smelting is carried out in an RH furnace, alternating between Mode 1 and Mode 2; at the same time, decarburization accelerator is added at a rate of 1.0-1.2 kg / ton of molten steel in 3-4 batches for ultra-deep decarburization treatment. S3 decarburization post-treatment: After the deep decarburization treatment is completed, deoxidation alloying is carried out, and the smelting method adopts alternating mode 2 and mode 3; Modes 1 through 3 are as follows: Mode 1: The gas flow rates in the riser and downcomer of the RH furnace are the same, with a flow rate of Q1 Nm. 3 / h, and the flow rate is controlled at 90%~100% of the maximum flow rate; among them, the vacuum tank immersion tube of the RH furnace is divided into rising tube and falling tube. When molten steel flows into the immersion tube, it is the rising tube, and when molten steel flows out, it is the falling tube. Mode 2: The gas flow rate in the riser of the RH furnace is Q1, and the gas flow rate in the downcomer is Q1. (0.2-0.25); Mode 3: The riser pipe of the RH furnace becomes a downcomer pipe, and the downcomer pipe becomes a riser pipe. The gas flow rate blown into the riser pipe is Q1 Nm. 3 / h, the downcomer gas flow rate is Q1 (0.2-0.25) Nm 3 / h.

2. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, After the S1 decarburization pretreatment, the carbon content of the molten steel is <50ppm.

3. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, During the S2 ultra-deep decarburization process, the circulation time for each cycle in Mode 1 is 20-30 seconds, and the circulation time for each cycle in Mode 2 is 1-1.5 minutes. Mode 1 and Mode 2 are alternated in a cycle for a total of 3 cycles.

4. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, After the S2 ultra-deep decarburization treatment, the carbon content of the molten steel is <13ppm.

5. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, During the S3 decarbonization post-treatment, the circulation time for each cycle is 5-7 minutes for Mode 2 and 5-7 minutes for each cycle for Mode 3; Mode 2 and Mode 3 are alternated in a cycle, and the cycle is repeated once.

6. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, The number of air blowing pipes in both the riser and the downcomer is 12-16, and the pipe diameter is 3-3.5mm.

7. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, The gas source for the riser and downcomer is nitrogen or argon. Argon is used during smelting and nitrogen is used during non-smelting. The inlet pressure is 0.8-1.2 MPa.

8. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, The decarbonization accelerator comprises the following components: 40-45 parts iron oxide, 45-50 parts calcium carbonate, 1-3 parts silicon dioxide, and 5-10 parts carbon-free binder; the particle size of the decarbonization accelerator is 10-30 mm, wherein the total content of impurities phosphorus and sulfur is <0.1 wt%, and the carbon-free binder used is a cellulose binder.

9. The modular smelting method for deep decarburization in an RH furnace for high-grade IF steel according to claim 1, characterized in that, The vacuum level in the vacuum chamber of the RH furnace shall not exceed 67 Pa.

10. The application of the RH furnace deep decarburization modular smelting method according to any one of claims 1-9 in the smelting of ultra-low carbon steel, characterized in that, The ultra-low carbon steel mentioned is of the ultra-deep drawing grade or ultra-ultra-deep drawing grade.

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