Slag former for electric furnace smelting of automobile sheet steel and electric furnace smelting method

Abstract

The invention provides a slag former for electric furnace smelting of automobile sheet steel and an electric furnace smelting method, and belongs to the field of electric furnace steelmaking. The slag former is composed of the following slag systems: 50%-65% of C, 20%-40% of FetO, 8%-15% of MgO and the balance of SiO2. The slag system composition of the slag former is reasonably designed, and C can ensure that sufficient CO and CO2 are generated in the reaction and serve as a gas source of a foaming agent for rapid slag making; fetO can be used as an oxygen source for providing generated gas, so that sufficient CO and CO2 gas can be quickly generated; mgO can ensure the lasting time of the foamed slag; siO2 can be used as a raw material for adjusting the alkalinity of the foaming slag. Therefore, the slag former can promote rapid generation of foam slag of electric furnace molten scrap steel, nitrogen content increase in steel in the electric furnace process under the full scrap steel condition can be effectively reduced, product performance is improved, and high-quality steel plates are produced through the electric furnace process under the full scrap steel condition.

Description

Technical Field

[0001] The present application relates to the technical field of electric furnace steelmaking, and in particular to a slag-forming agent for electric furnace steelmaking for automobile plates and an electric furnace steelmaking method. Background Art

[0002] With global warming and the increase in CO2 emissions in the air, all countries have begun to pay attention to product CO2 emissions, and China has made a commitment to carbon peak and carbon neutrality. As the second largest emitter of industrial CO2 emissions, the steel industry is bound to reduce CO2 emissions from steel production. At the same time, with the increasing requirements of high-end customers such as BMW for reducing CO2 emissions from steel products, the production of high-grade steel grades by electric furnace process has become the most effective means to reduce CO2 emissions, especially the production of high-grade steel grades by all-scrap steel electric furnace process. The most important of these is the control of nitrogen in steel. The phenomenon that steel with high nitrogen content becomes brittle after being placed for a long time is called "aging" or "aging". The brittleness of low-carbon steel caused by nitrogen is similar to the harm of phosphorus, but the harm is more serious than phosphorus. The increase of nitrogen content in steel will deteriorate the welding performance of steel. In particular, the nitrogen element in high-grade automotive steel directly affects the deep stamping performance of automotive steel plates. Therefore, in order to ensure product performance, the nitrogen element of high-grade steel represented by automotive steel is controlled to no more than 30ppm.

[0003] Controlling the nitrogen content in the electric furnace process mainly involves reducing the nitrogen content of the raw materials, and taking measures to heat the foam slag and motor to reduce the nitrogen formed by ionization in the air. However, under the condition of full scrap steel, the tapping temperature of high-end automotive sheet steel in industrial production is higher than 1650℃. Under this condition, the control difficulty of foam slag increases, the life of foam slag decreases, and the amount of nitrogen added during the heating process increases, resulting in the current inability to achieve the production of high-end automotive sheet steel with a nitrogen content of less than 30ppm. At the same time, due to the carbon spraying to make foam slag during the electric furnace smelting process, on the one hand, carbon powder increases carbon emissions, and on the other hand, the foam slag formation time is long, and the process increases nitrogen seriously. In the past, the method of producing low-nitrogen steel in electric furnaces was to reduce the nitrogen content of raw materials by adding molten iron to reduce the nitrogen content in steel. However, with the addition of molten iron, the CO2 emissions of the product increased significantly, which could not meet the requirements of many low-carbon emission products. Another example is the use of mixed smelting of scrap steel and molten iron in the arc furnace smelting process, supplemented by full-process control technologies such as rapid slag making technology, to achieve a nitrogen content of less than 30ppm in the product. However, it is impossible to achieve a nitrogen content of less than 30ppm in steel under the condition of all scrap steel. Therefore, a slag-making agent and an electric furnace smelting method for high-end automobile plate steel in an electric furnace are urgently needed to achieve an increase in nitrogen content of less than 5ppm in the electric furnace production process under the condition of all scrap steel, and achieve a nitrogen content of less than 30ppm in steel. Summary of the invention

[0004] The present application provides a slag former for steelmaking of automotive sheets in an electric furnace and an electric furnace steelmaking method, so as to solve the following technical problems: how to reduce the nitrogen increase in steel during the electric furnace process under the condition of all scrap steel, thereby improving the performance of high-end automotive sheet steel.

[0005] In the first aspect, an embodiment of the present application provides a slag former for steelmaking of automotive sheets in an electric furnace. By mass fraction, the slag former is composed of the following slag system: C: 50% - 65%, FetO: 20% - 40%, MgO: 8% - 15%, and the balance is SiO2.

[0006] Optionally, the raw material of C is biomass charcoal, and the particle size of the biomass charcoal is 0.1 mm - 1 mm.

[0007] Optionally, the biomass charcoal meets the following performance requirements: fixed C content ≥ 80%, calorific value ≥ 4800 KCal / kg, moisture content ≤ 2%, and ash content ≤ 3%.

[0008] Optionally, by mass fraction, the raw material of FetO is composed of the following Fe oxides: Fe2O3 ≥ 90%, FeO ≤ 10%, and the particle size of the Fe oxides is 0.1 mm - 5 mm.

[0009] Optionally, the raw material of MgO is light burned dolomite, and the particle size of the light burned dolomite is 0.1 mm - 5 mm.

[0010] In the second aspect, the present application provides an electric furnace steelmaking method for automotive sheet steel, and the method includes:

[0011] Obtaining the slag former according to any one of the embodiments in the first aspect;

[0012] At the beginning of the electric furnace steelmaking, within a set time interval, part of the slag former is sprayed into a set position in the electric furnace to cover the surface of the set position with a set thickness of the slag former;

[0013] When the melting amount of the scrap steel in the electric furnace > 10%, the remaining part of the slag former is sprayed into the entire scrap steel and the steel liquid surface in the electric furnace, and the biomass charcoal is sprayed into the electric furnace until the melting of the scrap steel is completed.

[0014] Optionally, the set time interval is 1 min, and the set thickness > 1 cm.

[0015] Optionally, the set position is within a range of 50 cm centered on the electrode.

[0016] Optionally, the total mass of the added slag former is 10 kg / t steel - 15 kg / t steel.

[0017] Optionally, the basicity of the slag system for the electric furnace steelmaking is 1.5 - 2.5.

[0018] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0019] The embodiments of the present application provide a slag-making agent for smelting automobile sheet steel in an electric furnace. By reasonably designing the slag system composition of the slag-making agent, C can ensure that sufficient CO and CO2 are generated by the reaction, serving as the gas source of the foaming agent to quickly form slag; FetO can serve as the oxygen source for generating gas to ensure the rapid generation of sufficient CO and CO2 gases; MgO can ensure the duration of the foamed slag; SiO2 can be used as the raw material for adjusting the alkalinity of the foamed slag. Thus, the slag-making agent can promote the rapid formation of foamed slag for melting scrap steel in the electric furnace, effectively reduce the increase in nitrogen content in the steel during the electric furnace process under the condition of all scrap steel, improve the product performance, and realize the production of high-quality steel sheets by the electric furnace process under the condition of all scrap steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application and used together with the specification to explain the principles of the present application.

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 It is a schematic flow chart of a method for smelting automobile sheet steel in an electric furnace provided by the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0024] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0025] In addition, in the description of the specification of the present application, terms such as "comprising" and "including" mean "including but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the associated relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces). For example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as parts by weight and parts by mass represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0026] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present application can be obtained through market purchase or can be prepared by existing methods.

[0027] The present application provides a slag former for smelting automotive sheet steel in an electric furnace. By mass fraction, the slag former consists of the following slag system: C: 50% - 65%, FetO: 20% - 40%, MgO: 8% - 15%, and the balance is SiO2.

[0028] It should be noted that the specific content / content range of SiO2 can be obtained through the upper and lower limit formulas of the components, that is: the sum of the percentage contents of each component in a composition should be equal to 100%; the content ranges of several components should meet the following conditions: the upper limit value of a certain component + the lower limit values of other components ≤ 100; the lower limit value of a certain component + the upper limit values of other components ≥ 100.

[0029] The slag former provided by the embodiments of the present application can promote the rapid generation of foamed slag for melting scrap steel in an electric furnace, effectively reduce the increase in nitrogen content in steel during the electric furnace process under the condition of all scrap steel, improve product performance, and realize the production of high-quality steel plates by the electric furnace process under the condition of all scrap steel. Specifically, C can ensure that sufficient CO and CO2 are generated by the reaction, serving as the gas source of the foaming agent to quickly form slag; FetO can serve as the oxygen source for generating gas to ensure the rapid generation of sufficient CO and CO2 gases; MgO can ensure the duration of the foamed slag; SiO2 can serve as the raw material for adjusting the alkalinity of the foamed slag. Exemplarily, the mass fraction of C can be 50%, 52%, 55%, 58%, 60%, 62%, 65%, the mass fraction of FetO can be 20%, 25%, 30%, 35%, 38%, 40%, etc., and the mass fraction of MgO can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.

[0030] In some embodiments, the raw material of C is biomass carbon, and the particle size of the biomass carbon is 0.1 mm - 1 mm.

[0031] The biomass carbon is made from crop straws, trees, etc. Limiting the particle size of the biomass carbon to 0.1 mm - 1 mm helps to increase the contact area between the biomass carbon and the surrounding environment, thereby promoting the rate of chemical reactions (such as carbon oxidation). Exemplarily, the particle size of the biomass carbon can be 0.1 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1 mm, etc.

[0032] In some embodiments, the biomass carbon meets the following properties: fixed C content ≥ 80%, calorific value ≥ 4800 KCal / kg, moisture content ≤ 2%, and ash content ≤ 3%.

[0033] Limiting the fixed C content of the biochar to ≥80% can ensure that the biochar can provide sufficient carbon elements for the reaction to generate sufficient CO and CO2 gases, which is the key to the formation of foamy slag. Limiting the calorific value of the biochar to ≥4800 KCal / kg helps to maintain the stable operation of the electric furnace and improve the smelting efficiency. Limiting the moisture content of the biochar to ≤2% helps to avoid the absorption of heat when the moisture evaporates in the electric furnace, affecting the smelting temperature and efficiency. Limiting the ash content of the biochar to ≤3% helps to reduce pollutant emissions during the smelting process and improve the purity of the steel plate. Exemplarily, the fixed C content of the biochar can be 80%, 82%, 84%, 86%, 88%, 90%, etc., the calorific value can be 4800 KCal / kg, 4850 KCal / kg, 4900 KCal / kg, 4950 KCal / kg, 5000 KCal / kg, etc., the moisture content can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc., and the ash content can be 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0034] In some embodiments, the raw material of FetO, by mass fraction, consists of the following Fe oxides: Fe2O3≥90%, FeO≤10%, and the particle size of the Fe oxides is 0.1 mm to 5 mm.

[0035] A high proportion of Fe2O3 means that more oxygen atoms are available for reacting with carbon to generate CO and CO2 gases, which is a key step in the formation of foamy slag. Sufficient oxygen sources ensure rapid and stable gas generation, facilitating the slag-making process. An appropriate amount of FeO (≤10%) helps to regulate the rate of the reduction reaction, avoiding uneven gas generation or poor slag-making effects caused by too fast or too slow reduction. By controlling the content of FeO, the slag-making process can be optimized to ensure the production of high-quality foamy slag. Exemplarily, the mass fraction of Fe2O3 can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, etc., and the mass fraction of FeO can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0036] Fe oxides with a particle size in the range of 0.1 mm to 5 mm can not only ensure sufficient contact with other components in the slag-making agent but also avoid problems such as agglomeration or flying caused by being too fine. This particle size distribution helps to accelerate the rate of the oxidation-reduction reaction, ensuring that FetO can effectively provide the oxygen source required for generating CO and CO2 gases. Exemplarily, the particle size of the Fe oxides can be 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, etc.

[0037] In some embodiments, the raw material of MgO is light-burned dolomite, and the particle size of the light-burned dolomite is 0.1 mm to 5 mm.

[0038] As a raw material for MgO, the particle size of calcined dolomite in the range of 0.1 mm to 5 mm helps to form a stable and persistent foamed slag. The appropriate particle size ensures the uniform distribution of MgO in the slag former, thus enhancing the structural stability of the foamed slag. Exemplarily, the particle size of the calcined dolomite can be 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, etc.

[0039] Figure 1 The flow diagram of an electric furnace smelting method for steel used in automotive panels provided by an embodiment of the present application.

[0040] As Figure 1 shown, the present application provides an electric furnace smelting method for steel used in automotive panels, and the method includes:

[0041] S1. Obtain the slag former described in any one of the above embodiments;

[0042] S2. At the beginning of the electric furnace smelting, within a set time interval, spray part of the slag former into a set position in the electric furnace to cover the surface of the set position with a slag former having a set thickness;

[0043] In some embodiments, the set time interval is 1 min, and the set thickness > 1 cm.

[0044] In some embodiments, the set position is within 50 cm centered on the electrode.

[0045] S3. When the melting amount of scrap steel in the electric furnace > 10%, spray the remaining part of the slag former onto the entire scrap steel and molten steel surface in the electric furnace, and spray the biomass carbon into the electric furnace until the melting of the scrap steel is completed.

[0046] In some embodiments, the biomass carbon powder is the biomass carbon powder in the slag former. Pure biomass carbon powder can ensure that sufficient CO and CO2 are generated by the reaction, quickly form slag as the gas source of the foaming agent, and at the same time, pure biomass carbon powder has a zero-carbon property and can reduce carbon emissions.

[0047] In some embodiments, the total added mass of the slag former is 10 kg / t steel to 15 kg / t steel.

[0048] In the embodiments of the present application, during the electric furnace smelting process, a slag-making agent with the new component of "C + FetO + MgO" is added, and the slag system composition and components of the slag-making agent are controlled to promote the rapid formation of foamed slag for melting scrap steel in the electric furnace. At the same time, biochar is used to reduce carbon emissions, achieving an increase in nitrogen content in the electric furnace smelting process under the condition of all scrap steel ≤ 5 ppm, and achieving a breakthrough in high-quality steel grades for large electric furnace all-scrap-steel smelting. Exemplarily, the total mass of the added slag-making agent can be 10 kg / t of steel, 11 kg / t of steel, 12 kg / t of steel, 13 kg / t of steel, 14 kg / t of steel, 15 kg / t of steel, etc.

[0049] In some embodiments, the basicity of the slag system for the electric furnace smelting is 1.5 - 2.5.

[0050] The basicity is (CaO + MgO) / (SiO2 + Al2O3). In order to further reduce the nitrogen in the ionized air of the electrode from entering the molten steel, in the embodiments of the present application, the basicity of the slag system for the electric furnace smelting is limited to 1.5 - 2.5 during the smelting process. Exemplarily, the basicity of the slag system for the electric furnace smelting can be 1.5, 1.7, 1.9, 2.1, 2.4, 2.5, etc.

[0051] In some embodiments, during the electric furnace smelting process, all scrap steel is used as raw materials, and the capacity of the electric furnace is 100 t - 300 t.

[0052] In summary, the advantages of the embodiments of the present application are as follows:

[0053] (1) Promote the rapid formation of foamed slag: Through the carefully designed slag-making agent components (C, FetO, MgO, SiO2) and raw material selection (such as biomass charcoal, light-burned dolomite, etc.), the present invention can significantly promote the rapid formation of foamed slag when melting scrap steel in the electric furnace. This helps to speed up the smelting process and improve production efficiency.

[0054] (2) Reduce the nitrogen content in steel: The slag-making agent components and smelting methods in the embodiments of the present application can effectively reduce the increase in nitrogen content in steel during the electric furnace process under the condition of all scrap steel, achieving an increase in nitrogen content ≤ 5 ppm, which is crucial for the production of high-quality steel plates.

[0055] (3) Improve product performance: By optimizing the slag-making process and reducing the nitrogen content, the embodiments of the present application can significantly improve the product performance of steel for automotive panels, including key indicators such as strength, toughness, and corrosion resistance, thus meeting the production requirements of high-quality steel plates.

[0056] (4) Achieve environmentally friendly production: Using biomass charcoal as a carbon source not only provides sufficient carbon elements for the reaction to generate CO and CO2 gases, but also helps to reduce carbon emissions and achieve a green and environmentally friendly electric furnace smelting process.

[0057] (5) Improve smelting efficiency: By precisely controlling the addition amount, addition time, and position of the slag-making agent, and optimizing the parameters (such as slag basicity) during the smelting process, the embodiments of the present application can significantly improve the smelting efficiency and reduce the production cost.

[0058] (6) Strong adaptability: The slag-making agent and smelting method of the embodiments of the present application are applicable to electric furnaces with different capacities (100t - 300t), and the raw materials use all scrap steel, having wide applicability.

[0059] (7) Easy to operate and control: The smelting method of the embodiments of the present application has clear steps, is easy to operate and control, and helps to realize the automation and intelligentization of the electric furnace smelting process.

[0060] The following further elaborates the present application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0061] Example 1

[0062] An industrial experiment was carried out in an electric furnace of a certain steel plant. The capacity of the electric furnace was 100 tons, the steel grade produced was steel for automotive panels, and the nitrogen content requirement was ≤30 ppm. The control method of nitrogen content during the electric furnace smelting process was as follows:

[0063] (1) Add a new slag-making agent during the electric furnace smelting process to promote the rapid formation of foamed slag for melting scrap steel in the electric furnace. The slag system composition of the slag-making agent was: C + FetO + MgO, where the mass percentage content of C was 50%, the mass percentage content of FetO was 20%, the mass percentage content of MgO was 8%, and the remaining components of the slag-making agent were SiO2;

[0064] (2) For the above new slag-making agent, the raw material of C was biomass charcoal, the raw material of FetO was Fe oxides, including Fe2O3 and FeO, where the mass percentage content of Fe2O3 was 90%, and the raw material of MgO was light-burned dolomite;

[0065] (3) For the above new slag-making agent, the biomass charcoal was made from crop straws and trees, etc., with a fixed C content of 80%, a calorific value of 4800 KCal / kg, a water content of 2%, an ash content of 3%, and the particle size was controlled to be 0.1 - 1 mm;

[0066] (4) For the above new slag-making agent, the particle size of the Fe oxides was controlled to be 0.1 - 5 mm, and the particle size of the light-burned dolomite was controlled to be 0.1 - 5 mm;

[0067] (5) The new slag-making agent as described above is sprayed into the electric furnace at the beginning of smelting through two carbon guns. The spraying position is within a range of 50 cm centered on the electrode. It is required to cover this range completely within 1 minute, and the thickness of the slag-making agent is greater than 1 cm. When the melting amount of scrap steel in the furnace is greater than 10%, the spraying range is expanded to the entire scrap steel and molten steel surface. At the same time, other carbon guns start to spray pure biomass carbon powder until the melting of scrap steel ends;

[0068] (6) In order to further reduce the nitrogen in the ionized air of the electrode from entering the molten steel, the basicity of the new slag system during smelting is controlled as: basicity (CaO + MgO) / (SiO2 + Al2O3) = 1.5;

[0069] (7) The total amount of the slag-making agent added during the electric furnace smelting process is 10 kg / t of steel.

[0070] (8) The total amount of pure biomass carbon powder added during the electric furnace smelting process is 20 kg / t of steel.

[0071] Under the condition of all scrap steel, the nitrogen increase amount during the electric furnace smelting process is 5 ppm, and the nitrogen content in the steel is achieved to be 26 ppm.

[0072] Example 2

[0073] An industrial experiment was carried out in an electric furnace of a certain steel plant. The capacity of the electric furnace is 300 tons, and the steel grade produced is electrical steel, with the required nitrogen content of ≤30 ppm. The control method of nitrogen content during the electric furnace smelting process is as follows:

[0074] (1) During the electric furnace smelting process, a new slag-making agent is added to promote the rapid formation of foamy slag for melting scrap steel in the electric furnace. The slag system composition of the slag-making agent is: C + FetO + MgO, where the mass percentage content of C is 65%, the mass percentage content of FetO is 20%, the mass percentage content of MgO is 12%, and the remaining component of the slag-making agent is SiO2;

[0075] (2) For the new slag-making agent as described above, the raw material of C is biomass carbon, the raw material of FetO is Fe oxides, including Fe2O3 and FeO, where the mass percentage content of Fe2O3 is 95%, and the raw material of MgO is light burned dolomite;

[0076] (3) For the new slag-making agent as described above, the biomass carbon is made from crop straws, trees, etc. The fixed C content is 87%, the calorific value is 6500 KCal / kg, the moisture content is 0.5%, the ash content is 1%, and the particle size is controlled to be 0.1 - 1 mm;

[0077] (4) For the new slag-making agent as described above, the particle size of Fe oxides is controlled to be 0.1 - 5 mm, and the particle size of light burned dolomite is controlled to be 0.1 - 5 mm;

[0078] (5) The new slag-making agent as described above is sprayed into the electric furnace at the beginning of smelting through two carbon lances. The spraying position is within a range of 50 cm centered on the electrode. It is required to cover this range completely within 1 minute, and the thickness of the slag-making agent is greater than 1 cm. When the melting amount of scrap steel in the furnace is greater than 10%, the spraying range is expanded to the entire scrap steel and molten steel surface, and at the same time, other carbon lances start to spray pure biomass carbon powder until the melting of scrap steel is completed;

[0079] (6) In order to further reduce the nitrogen from the ionized air of the electrode entering the molten steel, during the smelting process, the basicity of the new slag system is controlled as: basicity (CaO + MgO) / (SiO2 + Al2O3) = 2.5;

[0080] (7) The total amount of the slag-making agent added during the electric furnace smelting process is 15 kg / t of steel.

[0081] (8) The total amount of pure biomass carbon powder added during the electric furnace smelting process is 20 kg / t of steel.

[0082] Under the condition of all scrap steel, the nitrogen increment during the electric furnace smelting process is 3 ppm, and the nitrogen content in the steel is achieved to be 25 ppm.

[0083] Comparative Example 1

[0084] An industrial experiment was carried out in an electric furnace of a certain steel plant. The capacity of the electric furnace is 100 tons, and the steel grade produced is steel for automotive panels, with the nitrogen content requirement of ≤ 30 ppm. The control method of nitrogen content during the electric furnace smelting process is as follows:

[0085] (1) During the electric furnace smelting process, a slag-making agent is added to promote the rapid formation of foamy slag for melting scrap steel. The slag system composition of the slag-making agent is: C + MgO, where the mass percentage of C is 50% and the mass percentage of MgO is 8%. The remaining components of the slag-making agent are SiO2;

[0086] (2) For the slag-making agent as described above, the raw material of C is biomass carbon, and the raw material of MgO is light-burned dolomite;

[0087] (3) For the slag-making agent as described above, the particle size of the light-burned dolomite is controlled to be 0.1 - 5 mm;

[0088] (4) For the slag-making agent as described above, it is sprayed into the electric furnace at the beginning of smelting through two carbon lances. The spraying position is within a range of 50 cm centered on the electrode. It is required to cover this range completely within 1 minute, and the thickness of the slag-making agent is greater than 1 cm. When the melting amount of scrap steel in the furnace is greater than 10%, the spraying range is expanded to the entire scrap steel and molten steel surface until the melting of scrap steel is completed;

[0089] (5) In order to further reduce the nitrogen from the ionized air of the electrode entering the molten steel, during the smelting process, the basicity of the slag system is controlled as: basicity (CaO + MgO) / (SiO2 + Al2O3) = 1.5;

[0090] (6) The total addition amount of slag formers during the electric furnace smelting process is 10 kg / t of steel.

[0091] Under the condition of using all scrap steel, the nitrogen increment during the electric furnace smelting process is 20 ppm, and the nitrogen content in the steel is 42 ppm.

[0092] Comparative Example 2

[0093] An industrial experiment was carried out in an electric furnace of a certain steel plant. The capacity of the electric furnace is 100 tons, and the steel grade produced is steel for automotive panels, with the required nitrogen content of ≤ 30 ppm. The control method of nitrogen content during the electric furnace smelting process is as follows:

[0094] (1) Slag formers are added during the electric furnace smelting process to promote the rapid formation of foamy slag for melting scrap steel in the electric furnace. The slag system composition of the slag formers is: FetO + MgO, where the mass percentage content of FetO is 20%, the mass percentage content of MgO is 8%, and the remaining components of the slag formers are SiO2;

[0095] (2) For the slag formers as described above, the raw material of FetO is Fe oxides, including Fe2O3 and FeO, where the mass percentage content of Fe2O3 is 90%, and the raw material of MgO is calcined dolomite;

[0096] (3) For the slag formers as described above, the particle size of Fe oxides is controlled to be 0.1 - 5 mm, and the particle size of calcined dolomite is controlled to be 0.1 - 5 mm;

[0097] (4) For the slag formers as described above, they are sprayed into the furnace through 2 carbon lances at the beginning of the electric furnace smelting. The spraying position is within a range of 50 cm centered on the electrode. It is required to cover this range within 1 minute, and the thickness of the slag formers is greater than 1 cm. When the melting amount of scrap steel in the furnace is greater than 10%, the spraying range is expanded to the entire scrap steel and molten steel surface until the melting of scrap steel is completed;

[0098] (5) In order to further reduce the nitrogen from the ionized air of the electrode entering the molten steel, the basicity of the slag system during the smelting process is controlled as: basicity (CaO + MgO) / (SiO2 + Al2O3) = 1.5;

[0099] (6) The total addition amount of slag formers during the electric furnace smelting process is 10 kg / t of steel.

[0100] Under the condition of using all scrap steel, the nitrogen increment during the electric furnace smelting process is 25 ppm, and the nitrogen content in the steel is 46 ppm.

[0101] Comparative Example 3

[0102] An industrial experiment was carried out in an electric furnace of a certain steel plant. The capacity of the electric furnace is 100 tons, and the steel grade produced is steel for automotive panels, with the required nitrogen content of ≤ 30 ppm. The control method of nitrogen content during the electric furnace smelting process is as follows:

[0103] (1) During the electric furnace smelting process, a slag-forming agent is added to promote the rapid formation of foamed slag for melting scrap steel in the electric furnace. The slag system composition of the slag-forming agent is: C + FetO, where the mass percentage content of C is 50%, the mass percentage content of FetO is 20%, and the remaining component of the slag-forming agent is SiO2;

[0104] (2) For the slag-forming agent as described above, the raw material of FetO is Fe oxides, including Fe2O3 and FeO, where the mass percentage content of Fe2O3 is 90%, and the raw material of C is biomass carbon;

[0105] (3) For the slag-forming agent as described above, the particle size of the Fe oxides is controlled to be 0.1 - 5 mm;

[0106] (4) For the slag-forming agent as described above, it is sprayed into the furnace through 2 carbon lances at the beginning of the electric furnace smelting. The spraying position is within a range of 50 cm centered on the electrode. It is required to cover this range within 1 minute, and the thickness of the slag-forming agent is greater than 1 cm. When the melting amount of scrap steel in the furnace is greater than 10%, the spraying range is expanded to the entire scrap steel and molten steel surface until the melting of scrap steel ends;

[0107] (5) In order to further reduce the nitrogen from the ionized air of the electrode entering the molten steel, the basicity of the slag system during the smelting process is controlled as: basicity (CaO + MgO) / (SiO2 + Al2O3) = 1.5;

[0108] (6) The total amount of the slag-forming agent added during the electric furnace smelting process is 10 kg / t.

[0109] Under the condition of all scrap steel, the nitrogen increment during the electric furnace smelting process is 15 ppm, and the nitrogen content in the steel is 37 ppm.

[0110] In addition, one or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0111] In the embodiments of the present application, by adding a slag-forming agent with a new component of "C + FetO + MgO" during the electric furnace smelting process, and controlling the slag system composition and components of the slag-forming agent, it promotes the rapid formation of foamed slag for melting scrap steel in the electric furnace. At the same time, using biochar reduces carbon emissions, achieving a nitrogen increment ≤ 5 ppm during the electric furnace smelting process under the condition of all scrap steel, and achieving a breakthrough in high-quality steel grades for large-scale electric furnace all-scrap-steel smelting.

[0112] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A slag-making agent for smelting automotive sheet steel in an electric furnace. By mass fraction, the slag-making agent is composed of the following slag system: C: 50% - 65%, FetO: 20% - 40%, MgO: 8% - 15%, the balance being SiO2.

2. The slag-forming agent according to claim 1, wherein The raw material of C is biomass charcoal, and the particle size of the biomass charcoal is 0.1 mm - 1 mm.

3. The slag-making agent according to claim 2, wherein, The biomass charcoal meets the following properties: fixed C content ≥ 80%, calorific value ≥ 4800 KCal / kg, moisture content ≤ 2%, ash content ≤ 3%.

4. The slag-forming agent according to claim 1, characterized in that, By mass fraction, the raw material of FetO consists of the following Fe oxides: Fe2O3 ≥ 90%, FeO ≤ 10%, and the particle size of the Fe oxides is 0.1 mm - 5 mm.

5. The slag-making agent according to claim 1, characterized in that, The raw material of MgO is lightly burned dolomite, and the particle size of the lightly burned dolomite is 0.1 mm - 5 mm.

6. An electric furnace smelting method for steel used in automotive sheets, the method comprising: Obtaining the slag-making agent according to any one of claims 1 - 5; At the beginning of the electric furnace smelting, within a set time interval, spraying part of the slag-making agent into a set position in the electric furnace to cover the surface of the set position with the slag-making agent having a set thickness; When the melting amount of scrap steel in the electric furnace > 10%, spraying the remaining part of the slag-making agent onto the entire scrap steel and the steel liquid surface in the electric furnace, and spraying the biomass charcoal into the electric furnace until the melting of the scrap steel ends.

7. The method according to claim 6, wherein The set time interval is 1 min, and the set thickness > 1 cm.

8. The method according to claim 6, characterized in that, The set position is within 50 cm centered on the electrode.

9. The method according to claim 6, characterized in that, The total mass of the added slag-making agent is 10 kg / t of steel - 15 kg / t of steel.

10. The method according to claim 6, wherein The basicity of the slag system in the electric furnace smelting is 1.5 - 2.5.

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