Large scrap ratio converter slagging process and application thereof

Abstract

The invention discloses a large scrap ratio converter slagging process and application thereof. The technology is suitable for converter steelmaking with the scrap steel ratio being 15%-30% and sequentially comprises the following steps that S1, pretreatment is conducted, specifically, slag is completely poured after slag splashing converter protection is completed, and a solid carbonaceous heat generating agent in linear proportional relation with the scrap steel ratio is added into an empty converter; s2, loading, wherein waste steel and molten iron are sequentially loaded on the heat generating agent; s3, blowing and slagging control: starting oxygen blowing smelting, controlling the lance position and oxygen flow of an oxygen lance in different stages of the total oxygen supply amount according to the smelting model, and adding slagging flux in at least four batches; and S4, terminal operation. According to the method, by optimizing the adding position and time of the heat generating agent, the batch adding strategy of the flux and the cooperation with the oxygen supply system, the problems of insufficient heat, difficult slagging, serious furnace mouth slagging and the like of converter smelting under the condition of a large scrap steel ratio are effectively solved, the stability of the blowing process and the accurate control of the end point are realized, and the utilization efficiency of scrap steel resources is improved.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to a high scrap steel ratio converter slag-making process and its application. Background Technology

[0002] With the continuous growth of my country's steel reserves, social scrap steel resources are becoming increasingly abundant. Industry forecasts indicate that the total amount of usable scrap steel resources in China will reach 240-270 million tons in 2025, and further increase to 290-360 million tons by 2030. The recycling of scrap steel resources is of great strategic significance for reducing dependence on imported iron ore and ensuring national iron resource security, and its economic and environmental benefits are becoming increasingly prominent.

[0003] Currently, my country's steel production still primarily relies on long-process converter steelmaking. In this process, the heat required for smelting mainly comes from the physical and chemical heat of the molten iron itself. Therefore, traditional converter operation typically requires a high iron-to-metal ratio, generally maintained above 85%, meaning the scrap steel addition ratio is limited to below 15%. When attempting to increase the scrap steel ratio in the converter (e.g., to 15%-30%), the material and heat balance of the entire smelting system undergoes a fundamental change, leading to a series of severe technical challenges, including: Severe heat deficiency: The high heat absorption during scrap steel melting results in a low molten pool temperature and deterioration of smelting thermodynamic conditions; Difficulty in slag formation: Under low-temperature conditions, the slag-forming flux is difficult to melt quickly, resulting in high slag viscosity and poor fluidity, affecting metallurgical reaction efficiency; Severe slag formation at the furnace mouth: An unreasonable slag formation and oxygen supply system can easily cause flux to be splashed to the furnace mouth by the gas flow and solidify, severely impacting equipment operation and maintenance. Shortened oxygen supply time and difficulties in slag formation and dephosphorization: Due to the reduced iron-to-metal ratio, the carbon content introduced by the molten iron decreases, resulting in a shorter overall oxygen supply time and a shorter slag-to-steel reaction time. Under low-temperature and low-carbon conditions, slag formation and dephosphorization become more challenging. Using iron oxide-based slag-forming materials is problematic because the FeO reaction is endothermic, leading to insufficient heat reduction during smelting and exacerbating steel over-oxidation and furnace lining maintenance difficulties. Adding fluorite slag-forming increases over-oxidation in molten steel due to the high scrap ratio, intensifying furnace erosion. Furthermore, fluorite is a scarce and expensive resource, unsuitable for large-scale use. Conventional slag-forming materials are unsuitable under high scrap ratio conditions; "steelmaking is slag making," and the slag-forming process is the core of converter smelting.

[0004] However, existing traditional slag-forming processes suitable for high iron-to-water ratios cannot solve the core contradictions of insufficient heat, furnace mouth slagging, and slag formation difficulties when dealing with high scrap steel ratios, severely restricting the efficient and large-scale utilization of scrap steel resources. Therefore, there is an urgent need to develop a new converter slag-forming process suitable for high scrap steel ratios (15%-30%). Summary of the Invention

[0005] Aiming at solving the core contradiction in the above-mentioned common technologies that cannot solve the problems of insufficient heat, slagging at the furnace mouth and difficult slag formation under the condition of a large scrap ratio, the present invention provides a slag-making process for a converter with a large scrap ratio. The process is applicable to converter steelmaking with a scrap ratio of 15% to 30% and includes the following sequential steps: S1. Pretreatment: After the slag splashing in the previous smelting cycle is completed, all the residual slag in the furnace is poured out, and then a predetermined amount of solid carbonaceous heating agent is added into the empty furnace; S2. Charging: Scrap and hot metal are charged above the solid carbonaceous heating agent; S3. Blowing and slag formation control: Start oxygen blowing smelting. According to the preset smelting model, at different stages of the total oxygen supply, control the lance position and oxygen flow rate of the oxygen lance, and add slag-making fluxes into the furnace in four batches; S4. Endpoint operation: After reaching the blowing endpoint, steelmaking and alloying are carried out.

[0006] Further, in the step S1, the solid carbonaceous heating agent includes self-produced dry coke breeze from the steel plant, and the screened coke breeze with a particle size of 3 - 40 mm; The addition amount of the solid carbonaceous heating agent and the scrap ratio satisfy the following linear relationship: When R = 15%, W = 0; when R = 30%, W = 1000; when 15% < R < 30%, W is calculated and determined according to the linear ratio between the two points; where W is the solid carbonaceous heating agent, with the unit of kg / 110t (scrap + hot metal); R is the scrap ratio, with the unit of %.

[0007] Further, the slag-making flux includes calcium-containing flux and calcium-magnesium composite flux, and the mass ratio of the calcium-containing flux to the calcium-magnesium composite flux is 1 - 2:1; In the step S3, the slag-making flux is added in four batches, and the addition timing and ratio of each batch are as follows: The first batch: After the blowing ignition is normal, add a part accounting for one-third of the total addition amount of the calcium-containing flux and the calcium-magnesium composite flux respectively; The second batch: When the total oxygen supply reaches 25%, add a part accounting for one-third of the total addition amount of the calcium-containing flux and the calcium-magnesium composite flux respectively. When adding in this batch, first add the calcium-magnesium composite flux, and then add the calcium-containing flux; The third batch: When the total oxygen supply reaches 40%, add the remaining calcium-magnesium composite flux; The fourth batch: When the total oxygen supply reaches 60%, add the remaining calcium-containing flux.

[0008] Further, in the step S3, the control of the lance position and oxygen flow rate of the oxygen lance is specifically as follows: In the stage of 0 to 15% of the total oxygen supply, control the oxygen flow rate to be the first flow rate, and the lance position gradually decreases from the initial height; After the total oxygen supply exceeds 15%, the oxygen flow rate is increased to the second flow rate until the blowing end point, and the gun position is lowered to the pressure gun height at the end point; wherein, the second flow rate is higher than the first flow rate; the first flow rate is 19000-21000 M³ / h, and the second flow rate is 24000-26000 M³ / h; Furthermore, the initial height is 1.6-1.7m, and the gun position is reduced to 1.4-1.6m when the total oxygen supply is 10%-15%; When the total oxygen supply is >15% and <60%, the oxygen supply gun position is 1.4-1.5m. When the total oxygen supply is 60%-92%, the gun position should be controlled at 1.6-1.8m; When the total oxygen supply is greater than 92% and less than or equal to 100%, the gun position is controlled at the final gun pressure height, which is 1.0-1.2m.

[0009] Furthermore, the mass ratio of the calcium-containing flux to the calcium-magnesium composite flux is 1.55-1.7:1.

[0010] Furthermore, the calcium-containing flux includes lime, and the calcium-magnesium composite flux includes lightly calcined dolomite; the lime contains ≥90% CaO, the lightly calcined dolomite contains 40-60% CaO and 30-40% MgO, and the remainder is unavoidable impurities.

[0011] Furthermore, after charging in step S2 and before blowing in step S3, after confirming the amount of coke added based on the scrap steel ratio, 75% ferrosilicon is added to the converter for auxiliary heating based on the heat balance model calculation.

[0012] Furthermore, in step S4, the final carbon content of the molten steel at the blowing endpoint is 0.04%-0.06%, the final oxygen content is 400-500ppm, the final temperature is 1610-1625℃, and the final phosphorus content is ≤0.02%.

[0013] This invention provides an application of the high scrap ratio converter slag-making process described above in converter smelting.

[0014] Compared with the prior art, the present invention has at least the following advantages: This invention provides a converter slagging process under high scrap steel ratio conditions. By following the sequence specified in steps S1 (pretreatment) and S2 (charging) of "first adding a solid carbonaceous exothermic agent to the empty furnace bottom, then charging scrap steel and molten iron on top," a physical structure is constructed where the exothermic agent is covered by the metal material. At high temperatures, the solid carbonaceous exothermic agent forms a carbon gradient with the molten scrap steel, promoting carburization and facilitating rapid melting of the scrap steel, while simultaneously improving the carbon combustion rate and thermal efficiency. This is beneficial for the exothermic agent to react within the molten pool or at the interface during the initial blowing stage, providing a foundation for fundamentally alleviating the insufficient specific heat of high scrap steel, thereby reducing the resulting splashing, short steel-slag reaction time, and furnace mouth slagging problems.

[0015] Step S3 of this invention requires "adding slag-forming flux into the furnace in at least four batches." This "small batch, multiple batches" addition mode aims to avoid poor slag formation and re-drying problems caused by the concentrated addition of a large amount of cold material in the early stage of low temperature. It also helps to reduce the amount of material added at one time, reduce the risk of flux being directly impacted by high-speed oxygen flow and carried to the furnace mouth, and make the addition of flux adapt to the temperature rise process of the molten pool, thus providing a basic process framework for promoting rapid and uniform slag formation.

[0016] Step S3 also requires "controlling the position and flow rate of the oxygen lance at different stages of the total oxygen supply" and combining it with batch feeding. This establishes the control principle of dynamically matching the oxygen supply system with the smelting process and feeding rhythm, creating a prerequisite for stable blowing, suppressing splashing, and thus reducing furnace mouth slagging.

[0017] In summary, this invention, through its core process structure of "bottom-laying heating agent → top-loading metal material → segmented oxygen supply and batch feeding," systematically addresses the challenges posed by a high scrap steel ratio from three levels: heat transfer, material addition, and process control, thus forming the basis for subsequent specific optimizations. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the actual production process of slagging at the converter mouth in Comparative Example 1 of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0022] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0023] This invention provides a slag-forming process for converters with a high scrap ratio. The process is applicable to converter steelmaking with a scrap ratio of 15% to 30%, and includes the following sequential steps: S1. Pretreatment: After the slag splashing of the previous smelting cycle is completed, all the residual slag in the furnace is poured out, and then a predetermined amount of solid carbonaceous exothermic agent is added into the empty furnace.

[0024] This invention controls the scrap ratio in converter steelmaking to 15% to 30%. With the increasing stockpile of steel in my country, future scrap resources will be abundant. The total amount of usable scrap resources in my country's steel industry will reach 240-270 million tons in 2025 and 290-360 million tons in 2030. In the future, domestic scrap resources will become increasingly abundant, and the cost-effectiveness of scrap resources compared to iron ore will become increasingly prominent. The increase in scrap resources can reduce my country's dependence on imported iron ore and ensure the security of ferrous resources. However, currently, the domestic steelmaking industry mainly uses long-process converter steelmaking, which primarily uses molten iron to provide heat for blowing. Generally, converter steelmaking requires an iron-to-iron ratio of over 85%, meaning a scrap ratio of less than 15%.

[0025] However, existing conventional processes face catastrophic challenges in terms of heat and slag formation systems, manifesting as severe heat shortages, extreme difficulty in slag formation, loss of control at the endpoint, and a sharp increase in equipment wear and tear, significantly increasing the process difficulty. This new process, through systematic innovation, successfully achieves stable and efficient smelting within this challenging range, greatly enhancing the economic and environmental benefits of scrap steel resources.

[0026] In the present invention, in step S1, the solid carbonaceous heating agent includes coke breeze. In some embodiments, the coke breeze can be dry quenched coke produced by a steel plant, and the coke breeze with a particle size of 3 - 40 mm obtained by screening.

[0027] The functions of the carbonaceous heating agent in the present invention include: supplementing the problem of reduced carbon content caused by the reduction of molten iron, extending the oxygen supply time, and having a low heat supplement cost at the same time.

[0028] In some embodiments of the present invention, the addition amount of the solid carbonaceous heating agent and the scrap ratio satisfy the following linear relationship: when R = {15}\%, W = 0; when R = {30}\%, W = 1000; when {15}\% < R < {30}\%, W is calculated and determined according to the linear ratio between the two points; where, W is the solid carbonaceous heating agent, with the unit kg / 110t (scrap + molten iron); R is the scrap ratio, with the unit \%.

[0029] This linear relationship is determined based on a large number of heat balance calculations and experimental verifications, and can accurately match the basic heat and the steel slag reaction time requirements under different scrap ratios, providing a stable and predictable benchmark for subsequent dynamic heat compensation, and avoiding insufficient or wasted heat supply.

[0030] S2. Charging: Above the solid carbonaceous heating agent, scrap and molten iron are charged.

[0031] In the present invention, adding coke breeze to the bottom of the scrap is mainly to form a carbon gradient with the molten scrap at high temperature, promote carburization of the scrap, which is beneficial to the rapid melting of the scrap, and at the same time increase the combustion rate of carbon in the coke breeze and improve the thermal efficiency.

[0032] In comparison, in the conventional technology, the coke breeze is mostly added after ignition at the start of blowing, which will cause the coke to be夹杂 in the slag layer and cannot be fully melted into the molten steel, and the heat generated by combustion is directly discharged by the furnace gas and not absorbed by the molten steel, resulting in the heat not conforming to the model calculation, serious over-oxygenation of the molten steel, and furnace lining erosion.

[0033] In some embodiments, after the charging in step S2 and before the blowing in step S3, ferrosilicon is further added into the furnace for auxiliary heating according to the heat balance model. Among them, the heat balance model refers to a mathematical model established based on the principles of material balance and heat balance. This model comprehensively considers all heat income and expenditure items such as the physical heat, chemical heat, element oxidation heat release of molten iron and scrap, furnace body heat dissipation, and slag material melting heat absorption, and calculates the theoretical heat demand and predicted heat gap during the blowing process in real time. <000?152>The method of adding auxiliary heating to ferrosilicon involves precisely adding ferrosilicon based on the real-time heat gap calculated by the model. The silicon element in the ferrosilicon rapidly oxidizes and releases a large amount of heat in the early stage of blowing, which can quickly and directly compensate for the insufficient dynamic heat caused by the increase in the scrap steel ratio. This ensures that the temperature of the molten pool always follows the preset ideal heating curve, laying a solid temperature foundation for stable slag formation and endpoint control.

[0035] S3. Blowing and Slag Formation Control: When oxygen blowing smelting begins, according to the preset smelting model, the position of the oxygen lance and the oxygen flow rate are controlled at different stages of the total oxygen supply, and slag-forming flux is added to the furnace in four batches.

[0036] In this invention, the slag-forming flux includes a calcium-containing flux and a calcium-magnesium composite flux, wherein the mass ratio of the calcium-containing flux to the calcium-magnesium composite flux is 1-2:1; in step S3, the slag-forming flux is added in four batches, and the timing and proportion of each batch are as follows: First batch: After the blowing and ignition are normal, add one-third of the total amount of the calcium-containing flux and the calcium-magnesium composite flux respectively. The second batch: When the total oxygen supply reaches 25%, add one-third of the total amount of calcium-containing flux and calcium-magnesium composite flux respectively. In this batch, the calcium-magnesium composite flux is added first, followed by the calcium-containing flux. The third batch: When the total oxygen supply reaches 40%, add the remaining calcium-magnesium composite flux; Fourth batch: When the total oxygen supply reaches 60%, add the remaining calcium-containing flux.

[0037] This invention utilizes a four-batch slag-forming flux method, enabling the flux melting process to precisely match the phased temperature rise and chemical reaction requirements (such as the oxidation of silicon, manganese, and phosphorus) of the molten pool. This "small batch, multiple batches" approach effectively avoids slag "drying" and clumping caused by adding a large amount of cold material in the early stage of low temperature, as well as the problem of inhibiting the temperature rise of the molten pool due to adding too much flux at once, thus creating conditions for maintaining good slag fluidity and reactivity throughout the process.

[0038] This invention strictly limits the order in which the second batch of calcium-containing flux and calcium-magnesium composite flux are added. This ensures that in the early to mid-stages, when the molten pool temperature has risen significantly, the carbon-oxygen reaction becomes active, and foamy slag may be generated, the calcium-magnesium composite flux (such as lightly calcined dolomite) added preferentially can quickly participate in slag formation, which is beneficial for early slag formation, stabilizing furnace conditions, and suppressing splashing. If lime is added first, a dense layer of high-melting-point dicalcium silicate easily forms on the surface of its particles, hindering its own dissolution and exacerbating the risk of splashing. This order is crucial for ensuring stable blowing in the mid-stages.

[0039] In this invention, step S3 specifically involves controlling the position of the oxygen lance and the oxygen flow rate as follows: During the 0 to 15% total oxygen supply phase, the oxygen flow rate is controlled at the first flow rate, and the gun position is gradually lowered from the initial height. After the total oxygen supply exceeds 15%, the oxygen flow rate is increased to the second flow rate until the blowing end point, and the gun position is lowered to the pressure gun height before the end point; wherein, the second flow rate is higher than the first flow rate.

[0040] In some embodiments, the first flow rate is 19,000-21,000 m³ / h, and the second flow rate is 24,000-26,000 m³ / h.

[0041] In some embodiments, the initial height is 1.6-1.7m, and the gun position is reduced to 1.4-1.6m when the total oxygen supply is 10%-15%; When the total oxygen supply is >15% and <60%, the oxygen supply gun position is 1.4-1.5m. When the total oxygen supply is 60%-92%, the gun position should be controlled at 1.6-1.8m; When the total oxygen supply is greater than 92% and less than or equal to 100%, the gun position is controlled at the final gun pressure height, which is 1.0-1.2m.

[0042] This invention achieves deep coordination between the blowing process, slag formation, and temperature regime by controlling the oxygen lance position and oxygen flow rate. Using a lower flow rate and higher lance position in the early stages facilitates stable ignition, promotes initial slag formation, and reduces excessive cooling and splashing of the molten pool. Increasing the flow rate and adjusting the lance position in the middle and later stages enhances molten pool agitation, accelerates the reaction, and adapts to the rising physical state of the molten pool. Lowering the lance position to the final lance height before the endpoint enhances agitation in the lower part of the molten pool, homogenizes composition and temperature, and achieves precise endpoint control.

[0043] In some embodiments, the mass ratio of the calcium-containing flux to the calcium-magnesium composite flux is 1.55-1.7:1. This ratio range was determined through extensive process experiments and metallurgical mechanism analysis, aiming to achieve optimal synergy between CaO and MgO in the slag. At this ratio, the two work together to easily form a low-melting-point calcium-magnesium silicate phase, which not only significantly accelerates the flux dissolution and slag formation rate, promoting rapid slag formation in the early and middle stages, but also effectively suppresses splashing caused by the formation of a high-melting-point coating layer on the lime surface. Simultaneously, it facilitates the formation of slag that protects the furnace lining and reduces slagging problems at the furnace mouth caused by splashing.

[0044] In some embodiments, the calcium-containing flux includes lime, and the calcium-magnesium composite flux includes lightly calcined dolomite; the lime contains ≥90% CaO, the lightly calcined dolomite contains 40-60% CaO and 30-40% MgO, and the remainder is unavoidable impurities.

[0045] This invention controls the calcium-magnesium composite flux to be a magnesium-calcium composite light-calcined dolomite, enabling CaO and MgO in the slag to work synergistically. The CaO•MgO phase contained in the light-calcined dolomite itself has a significantly lower melting point than pure CaO and pure MgO, and at steelmaking temperatures, it reacts with SiO2 to form a low-melting-point calcium-magnesium silicate liquid phase. This greatly promotes the rapid dissolution of CaO and MgO in the slag, avoiding the formation of high-melting-point 2CaO·SiO2 or 2MgO·SiO2 coating layers, thereby achieving rapid slag formation in the early and middle stages, effectively controlling splashing, and providing good protection for the furnace lining.

[0046] S4. End-point operation: After reaching the blowing endpoint, steel is tapped and alloyed.

[0047] In some embodiments of the present invention, in step S4, the final carbon content of the molten steel at the blowing endpoint is 0.04%-0.06%, the final oxygen content is 400-500 ppm, the final temperature is 1610-1625℃, and the final phosphorus content is ≤0.02%. This set of endpoint parameters is a comprehensive reflection of the successful resolution of the contradiction between heat and slag formation under a high scrap ratio and the achievement of precise control throughout the entire process. The stable endpoint temperature ensures the fluidity of the molten steel and meets the requirements of subsequent processes; the low and controllable carbon-oxygen product indicates that the molten steel has a low degree of over-oxidation, a high metal recovery rate, and that the dephosphorization task has been successfully completed. These excellent endpoint indicators collectively verify that the process of the present invention can stably produce high-quality low-carbon molten steel while increasing the scrap ratio.

[0048] The present invention also provides an application of the high scrap ratio converter slag-forming process described above in converter smelting of low carbon steel or ultra-low carbon steel.

[0049] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided: Example 1 S1. (Furnace production, total charge 110t, including 80.3t of molten iron and 29.7t of scrap steel, scrap steel ratio 27%; 900kg of coke and 72kg of ferrosilicon added) Pretreatment: After the slag splashing in the previous furnace is completed, pour out all the slag. After pouring out the slag, shake the converter upright and add the set amount of coke.

[0050] S2. Add scrap steel and molten iron to the loading.

[0051] S3. (Oxygen supply calculated based on the model is 4500m³) 3 The amount of calcium-containing flux (lime) added is 1812 kg, and the amount of calcium-magnesium composite flux (lightly calcined dolomite) added is 1155 kg. The calcium-containing flux is lime with a CaO content of 91%, and the calcium-magnesium composite flux is lightly calcined dolomite: CaO 51%, MgO 38%, with the remainder being unavoidable impurities. Smelting and slag formation control: When oxygen blowing smelting begins, according to the preset smelting model, the position of the oxygen lance and the oxygen flow rate are controlled at different stages of the total oxygen supply. Slag-forming flux is added into the furnace in four batches. 72 kg of ferrosilicon is added after the blowing and ignition are normal.

[0052] Oxygen lance position control: 10% before blowing (0-450m) 3 The oxygen supply process involves a gun position of 1.65m. 10-15% (450-675m) 3 The oxygen supply gun position should be adjusted between 1.5 and 1.6 meters. Total oxygen supply >15% and <60% (greater than 675m) 3 and <2700m 3 In this case, the oxygen supply gun position should be adjusted between 1.4 and 1.5 meters. Oxygen supply is 60%-92% (2700m) 3 -4140m 3 The gun position was 1.75m. Oxygen supply > 92% (greater than 4140m) 3 The gun position is 1.1m until the oxygen blowing ends.

[0053] Oxygen flow control: During the period of 0% to 15% of the total oxygen supply, control the oxygen flow at the first flow rate, and the second flow rate at 20,000 m³ / h. 3 / h control; after the total oxygen supply exceeds 15%, increase the oxygen flow rate to the second flow rate until the blowing end, the first flow rate is 25000M. 3 / h.

[0054] Slag-forming flux addition control: First batch: After the blowing and ignition are normal, add one-third of the total amount of the calcium-containing flux and the calcium-magnesium composite flux, namely 604 kg of lime and 386 kg of lightly calcined dolomite.

[0055] The second batch: when the total oxygen supply reaches 25% (1125m). 3 When adding the calcium-containing flux and the calcium-magnesium composite flux, add one-third of the total amount of each of the two fluxes, namely 386 kg of lightly calcined dolomite and 604 kg of lime; and when adding the flux in this batch, add the lightly calcined dolomite first and then add the lime.

[0056] The third batch: when the total oxygen supply reaches 40% (1800m) 3 Add the remaining calcium-magnesium composite flux; that is, 386 kg of lightly calcined dolomite.

[0057] Fourth batch: When the total oxygen supply reaches 60% (2700m) 3 Add the remaining calcium-containing flux, i.e., 604 kg of lime.

[0058] S4. Endpoint Operation: After reaching the blowing endpoint, proceed with tapping and alloying. The endpoint lance position is 1.1m, and the TSO test results show carbon 0.05%, oxygen 450ppm, T 1620℃, and P 0.012%.

[0059] Example 2 S1. (Furnace production, total charge 110t, including 79.2t molten iron, 30.8t scrap steel, scrap steel ratio 28%; 933kg coke and 80kg ferrosilicon added) Pretreatment: After the slag splashing in the previous furnace is completed, pour out all the slag. After pouring out the slag, shake the converter upright and add the set amount of coke.

[0060] S2. Add scrap steel and molten iron to the loading.

[0061] S3. (Oxygen supply calculated based on the model is 4600m³) 3 The amount of calcium-containing flux (lime) added is 1812 kg, and the amount of calcium-magnesium composite flux (lightly calcined dolomite) added is 1155 kg. The calcium-containing flux is lime with a CaO content of 91%, and the calcium-magnesium composite flux is lightly calcined dolomite: CaO 51%, MgO 38%, with the remainder being unavoidable impurities. Smelting and Slag Formation Control: Oxygen blowing smelting begins. Based on a pre-set smelting model, the position and flow rate of the oxygen lance are controlled at different stages of total oxygen supply. Slag-forming flux is added to the furnace in four batches. 80 kg of ferrosilicon is added after normal ignition.

[0062] Oxygen lance position control: 10% before blowing (0-460m) 3 The oxygen supply process involves a gun position of 1.65m. Total oxygen supply is 10-15% (460-690m) 3 In this case, the gun position should be adjusted between 1.5 and 1.6 meters. When the total oxygen supply is >15% and <60% (greater than 690m) 3 And less than 2760m 3 The oxygen supply gun position should be adjusted between 1.4 and 1.5 meters. Under the condition of oxygen supply of 60%-92% (2760m) 3 -4232m 3 (The gun position is 1.75m). Oxygen supply > 92% (greater than 4232m) 3 The gun position is 1.1m, and oxygen blowing continues until it ends.

[0063] Oxygen flow control: During the period of 0% to 15% of the total oxygen supply, control the oxygen flow at the first flow rate, and the second flow rate at 20,000 m³ / h. 3 / h control; after the total oxygen supply exceeds 15%, increase the oxygen flow rate to the second flow rate until the blowing end, the first flow rate is 25000M. 3 / h.

[0064] Slag-forming solvent addition control: First batch: After the blowing and ignition are normal, add one-third of the total amount of the calcium-containing flux and the calcium-magnesium composite flux, namely 604 kg of lime and 385 kg of lightly calcined dolomite.

[0065] Second batch: When the total oxygen supply reaches 25% (1150m) 3 Add one-third of the total amount of the calcium-containing flux and the calcium-magnesium composite flux, namely 385 kg of lightly calcined dolomite and 604 kg of lime; and when adding them to this batch, add the lightly calcined dolomite first and then the lime.

[0066] The third batch: when the total oxygen supply reaches 40% (1840m). 3 When adding the remaining calcium-magnesium composite flux, i.e., lightly calcined dolomite 385kg.

[0067] Fourth batch: When the total oxygen supply reaches 60% (2760m) 3 Add the remaining calcium-containing flux, i.e., 604 kg of lime.

[0068] S4. Endpoint Operation: After reaching the blowing endpoint, proceed with tapping and alloying. The endpoint lance position is 1.1m, and the TSO test results show carbon 0.055%, oxygen 420ppm, T 1620℃, and P 0.015%.

[0069] Comparative Example 1 Compared to Example 2, the other conditions remain unchanged in this comparative example, except for the preprocessing step in step S1.

[0070] S1. (Furnace production, total charge 110t, including 79.2t molten iron, 30.8t scrap steel, scrap steel ratio 28%, 80kg ferrosilicon, and 933kg coke added) Pre-treatment: After the slag splashing in the previous furnace is completed, pour out all the slag.

[0071] S2. Add scrap steel and molten iron to the loading.

[0072] S3. (Oxygen supply calculated based on the model is 4600m³) 3 The amount of calcium-containing flux (lime) added is 1812 kg, and the amount of calcium-magnesium composite flux (lightly calcined dolomite) added is 1155 kg. (The calcium-containing flux is lime, with a CaO content of 91%, and the calcium-magnesium composite flux is lightly calcined dolomite, with a CaO content of 51% and MgO content of 38%). Smelting and slag formation control: When oxygen blowing smelting begins, according to the preset smelting model, the position of the oxygen lance and the oxygen flow rate are controlled at different stages of the total oxygen supply. Slag-forming flux is added to the furnace in three batches. 80 kg of ferrosilicon is added after the blowing and ignition are normal.

[0073] Oxygen gun position control: 10% before starting the purge (0-460m) 3 The oxygen supply process involves a gun position of 1.65m. Total oxygen supply is 10-15% (460-690m) 3 In this case, the gun position should be adjusted between 1.5 and 1.6 meters. Total oxygen supply >15% (greater than 690m) 3 When the oxygen supply rate is <60%, the oxygen supply gun position should be adjusted between 1.4-1.5m. Under the condition of oxygen supply of 60%-92% (greater than 2760m) 3 (The gun position is 1.75m). Oxygen supply > 92% (greater than 4232m) 3 The gun position is 1.1m, and oxygen blowing continues until it ends.

[0074] Oxygen flow control: During the period of 0% to 15% of the total oxygen supply, control the oxygen flow at the first flow rate, and the second flow rate at 20,000 m³ / h. 3 / h control; after the total oxygen supply exceeds 15%, increase the oxygen flow rate to the second flow rate until the blowing end, the first flow rate is 25000M. 3 / h.

[0075] Slag-forming solvent addition control: First batch: After the blowing and ignition are normal, add coke (i.e., add it on top of the molten iron and scrap steel) and add one-third of the total amount of the calcium-containing flux and the calcium-magnesium composite flux, namely 604 kg of lime and 385 kg of lightly calcined dolomite.

[0076] Second batch: When the total oxygen supply reaches 25% (1150m) 3 Add one-third of the total amount of the calcium-containing flux and the calcium-magnesium composite flux, namely 385 kg of lightly calcined dolomite and 604 kg of lime; and when adding them to this batch, add the lightly calcined dolomite first and then the lime.

[0077] The third batch: when the total oxygen supply reaches 40% (1840m). 3 When adding the remaining calcium-magnesium composite flux, i.e., lightly calcined dolomite 385kg.

[0078] Fourth batch: When the total oxygen supply reaches 60% (2760m) 3 Add the remaining calcium-containing flux, i.e., 604 kg of lime.

[0079] When the oxygen supply reaches 92%, the flame at the furnace opening is not obvious.

[0080] S4. Endpoint Operation: After reaching the blowing endpoint, tapping and alloying are performed. The endpoint lance position is 1.1m. TSO testing shows carbon 0.031%, oxygen 800ppm, T 1600℃, and P 0.011%. During tapping, unmelted scrap steel was found. After re-blowing, the molten steel was over-oxidized, leading to severe furnace lining erosion over long-term production. See [link / details]. Figure 1 .

[0081] Comparative Example 2 Compared to Example 1, the other conditions remain unchanged in this comparative example, except for the adjustment of the slag-forming flux addition control method in step S3.

[0082] S1. (Furnace production, total charge 110t, including 80.3t of molten iron and 29.7t of scrap steel, scrap steel ratio 27%; 900kg of coke and 72kg of ferrosilicon added) Pretreatment: After the slag splashing in the previous furnace is completed, pour out all the slag. After pouring out the slag, shake the converter upright and add the set amount of coke.

[0083] S2. Add scrap steel and molten iron to the loading.

[0084] S3. (Oxygen supply calculated based on the model is 4500m³) 3 (The amount of calcium-containing flux added is 1814 kg of lime, and the amount of calcium-magnesium composite flux added is 1158 kg of lightly calcined dolomite. The calcium-containing flux is lime, with a CaO content of 91%, and the calcium-magnesium composite flux is lightly calcined dolomite, with a CaO content of 51% and MgO content of 38%) Smelting and Slag Formation Control: Oxygen blowing smelting begins. Based on a pre-set smelting model, the position and flow rate of the oxygen lance are controlled at different stages of total oxygen supply. Slag-forming flux is added to the furnace in two batches. 72 kg of ferrosilicon is added after normal ignition and initial blowing.

[0085] Oxygen lance position control: 10% before blowing (0-450m) 3 The oxygen supply process involves a gun position of 1.65m. 10-15% (450-675m) 3 The oxygen supply gun position should be adjusted between 1.5 and 1.6 meters. Total oxygen supply >15% and <60% (greater than 675m) 3 In this case, the oxygen supply gun position should be adjusted between 1.4 and 1.5 meters. Oxygen supply is 60%-92% (greater than 2700m). 3 The gun position was 1.75m. Oxygen supply > 92% (greater than 4140m) 3 The gun position is 1.1m until the oxygen blowing ends.

[0086] Oxygen flow control: During the period of 0% to 15% of the total oxygen supply, control the oxygen flow at the first flow rate, and the second flow rate at 20,000 m³ / h. 3 / h control; after the total oxygen supply exceeds 15%, increase the oxygen flow rate to the second flow rate until the blowing end, the first flow rate is 25000M. 3 / h.

[0087] Slag-forming flux addition control: First batch: After the blowing and ignition are normal, add 1210 kg of lime and 772 kg of lightly burned dolomite.

[0088] The second batch: When the total oxygen supply reached 25%, 386 kg of lightly calcined dolomite and 604 kg of lime were added. The lime was added first, followed by the lightly calcined dolomite, which caused severe splashing.

[0089] S4. Endpoint Operation: After reaching the blowing endpoint, tapping and alloying are performed. At the endpoint, the lance position is 1.1m. When oxygen supply reaches 93%, the furnace mouth flame is not obvious. At the endpoint, the TSO test shows carbon 0.035%, oxygen 500ppm, T1615℃, and P 0.041%. Re-blowing and dephosphorization are performed. The molten steel is over-oxidized, and long-term operation has resulted in severe furnace lining erosion and furnace mouth slagging.

[0090] Comparative Example 3 Compared to Example 1, the other conditions remain unchanged in this comparative example, except that the oxygen lance position control method and oxygen flow control method in step S3 are adjusted.

[0091] S1. (Furnace production, total charge 110t, including 80.3t of molten iron and 29.7t of scrap steel, scrap steel ratio 27%; 900kg of coke and 72kg of ferrosilicon added) Pretreatment: After the slag splashing in the previous furnace is completed, pour out all the slag. After pouring out the slag, shake the converter upright and add the set amount of coke.

[0092] S2. Add scrap steel and molten iron to the loading.

[0093] S3. (Oxygen supply calculated based on the model is 4500m³) 3 The amount of calcium-containing flux (lime) added is 1812 kg, and the amount of calcium-magnesium composite flux (lightly calcined dolomite) added is 1155 kg. (The calcium-containing flux is lime, with a CaO content of 91%, and the calcium-magnesium composite flux is lightly calcined dolomite, with a CaO content of 51% and MgO content of 38%). Smelting and Slag Formation Control: Oxygen blowing smelting begins. Based on a pre-set smelting model, the position and flow rate of the oxygen lance are controlled at different stages of total oxygen supply. Slag-forming flux is added to the furnace in two batches. 72 kg of ferrosilicon is added after normal ignition and initial blowing.

[0094] Oxygen lance position control: 10% before blowing (0-450m)3 The oxygen supply process involves a gun position of 1.45m. 10-15% (450-675m) 3 The oxygen supply gun position should be adjusted between 1.5 and 1.6 meters. Total oxygen supply >15% and <60% (>675m) 3 and <2700m 3 In this case, the oxygen supply gun position should be adjusted between 1.4 and 1.5 meters. Oxygen supply is 60%-92% (2700m) 3 -4140m 3 The gun position was 1.75m. Oxygen supply > 92% (greater than 4140m) 3 The gun position is 1.1m until the oxygen blowing ends.

[0095] Oxygen flow control: During the 0-15% total oxygen supply phase, control the oxygen flow at the first flow rate, and the second flow rate at 25000 m³ / h. 3 / h control; after the total oxygen supply exceeds 15%, increase the oxygen flow rate to the second flow rate until the blowing end, the first flow rate is 25000M. 3 / h.

[0096] Oxygen supply greater than 15% (675m) 3 Adjust the first batch: After the blowing and ignition are normal, add one-third of the total amount of the calcium-containing flux and the calcium-magnesium composite flux, namely 604 kg of lime and 386 kg of lightly calcined dolomite.

[0097] The second batch: when the total oxygen supply reaches 25% (1125m). 3 When adding the calcium-containing flux and the calcium-magnesium composite flux, add one-third of the total amount of each of the two fluxes, namely 386 kg of lightly calcined dolomite and 604 kg of lime; and when adding the flux in this batch, add the lightly calcined dolomite first and then add the lime.

[0098] The third batch: when the total oxygen supply reaches 40% (1800m) 3 Add the remaining calcium-magnesium composite flux; that is, lightly calcined dolomite 386 kg. Splashing occurs.

[0099] Fourth batch: When the total oxygen supply reaches 60% (2700m) 3 Add the remaining calcium-containing flux, i.e., 604 kg of lime.

[0100] S4. Endpoint Operation: After reaching the blowing endpoint, steel is tapped and alloyed. Endpoint lance position: 1.1m. TSO test results: carbon 0.05%, oxygen 460ppm, T 1610℃, P 0.035%. Slag formation and dephosphorization are poor; long-term operation leads to severe furnace lining erosion and furnace mouth slagging.

[0101] Comparative analysis Equipment maintenance issues: Inappropriate slag formation and temperature regimes can easily lead to accelerated furnace lining erosion and severe slag buildup at the furnace mouth, affecting smooth production and furnace lifespan. Compared with Comparative Examples 1 and 2, Example 1 showed good slag formation, minimal error in oxygen supply and model, normal carbon-oxygen product in the final molten steel, and complete melting of scrap steel. The main reasons are as follows.

[0102] Firstly, in Examples 1 and 2 of this invention, the coke is added to the bottom of the scrap steel primarily to form a carbon gradient with the molten scrap steel at high temperatures, promoting carburization and facilitating rapid melting of the scrap steel. Simultaneously, it increases the combustion rate of carbon in the coke, thereby improving thermal efficiency. However, in Comparative Example 1, the coke is added after ignition. The coke is trapped in the slag layer and cannot fully melt into the molten steel. The heat generated during combustion is directly discharged by the furnace gas and not absorbed by the molten steel, resulting in a discrepancy between the heat output and the model calculations. This leads to severe over-oxygenation in the molten steel and erosion of the furnace lining.

[0103] Secondly, in Examples 1 and 2, the flux was added evenly in small batches, while in Comparative Example 2, the flux continued the high iron-to-water ratio process, and the flux was added in the early stage. Due to the low temperature of the molten pool under the high scrap steel ratio process, it was not conducive to the early slag formation. The concentrated addition caused the slag to dry out. Combined with the high oxygen flow rate in the early stage in Comparative Example 2, the blowing at this time formed splashing slag. The flux was splashed to the furnace mouth by oxygen, causing slag formation at the furnace mouth, reducing lime utilization, and resulting in poor slag formation and dephosphorization effects.

[0104] In Comparative Example 2, adding lime before the lightly calcined dolomite during the second batch of flux addition caused splashing. When the second batch was added, the molten pool temperature had already risen significantly, at which point the carbon-oxygen reaction began to form foamy slag. Adding lightly calcined dolomite first facilitated slag formation. Adding lime alone promoted the formation of dicalcium silicate coatings on the surface of the lime particles, hindering lime dissolution. Similarly, the addition of pure MgO resulted in the formation of a high-melting-point mesophase, 2MgO·SiO2, which could not dissolve in time. When CaO and MgO are used in combination, such as lightly calcined dolomite (CaO 51%, MgO 38%), the reaction with SiO2 produces a low-melting-point Ca and Mg silicate phase, which is liquid at steelmaking temperatures. This promotes the rapid dissolution of CaO and MgO in the slag, facilitating rapid slag formation in the early and middle stages and controlling splashing. Furthermore, the melting point of CaO•MgO is 2300℃, lower than that of CaO (2600℃) and MgO (2800℃), which also increases the dissolution rate of CaO and MgO.

[0105] In Comparative Example 3, the oxygen flow rate reached 25000 M.3 / h, greater than 21000M 3 / h, lance position control 1.45m, greater than 1.6m, early control of oxygen flow rate is too large, lance position is too low, the added flux material actually has slag splashing effect under strong blowing, the added flux in the furnace is splashed onto the furnace mouth, the flux utilization rate is reduced, the dephosphorization effect is worse, and the slag formation effect is poor.

[0106] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A slag-forming process for a converter with a high scrap ratio, the process being applicable to converter steelmaking with a scrap ratio of 15% to 30%, characterized in that, It includes the following sequential steps: S1. Pretreatment: After the slag splashing in the previous smelting cycle ends, all the residual slag in the furnace is poured out, and then a predetermined amount of solid carbonaceous heating agent is added into the empty furnace. S2. Charging: Scrap steel and hot metal are charged above the solid carbonaceous heating agent. S3. Blowing and slag formation control: Oxygen blowing smelting is started. According to the preset smelting model, at different stages of the total oxygen supply, the lance position and oxygen flow rate of the oxygen lance are controlled, and slag-making fluxes are added into the furnace in four batches. S4. Endpoint operation: After reaching the blowing endpoint, steelmaking and alloying are carried out.

2. The high scrap ratio converter slagging process according to claim 1, characterized in that, In the step S1, the solid carbonaceous heating agent includes coke breeze. The addition amount of the solid carbonaceous heating agent and the scrap ratio satisfy the following linear relationship: When R = 15%, W = 0; when R = 30%, W = 1000; when 15% < R < 30%, W is calculated and determined according to the linear ratio between the two points; where, W is the solid carbonaceous heating agent, unit kg / 110t (scrap steel + hot metal); R is the scrap ratio, unit %.

3. The high scrap ratio converter slag-forming process according to claim 1, characterized in that, The slag-making flux includes calcium-containing flux and calcium-magnesium composite flux, and the mass ratio of the calcium-containing flux to the calcium-magnesium composite flux is 1 - 2:

1. In the step S3, the slag-making flux is added in four batches, and the addition timing and ratio of each batch are as follows: The first batch: After the blowing ignition is normal, add a part accounting for one-third of the total addition amount of the calcium-containing flux and the calcium-magnesium composite flux respectively. The second batch: When the total oxygen supply reaches 25%, add a part accounting for one-third of the total addition amount of the calcium-containing flux and the calcium-magnesium composite flux respectively. And when adding in this batch, first add the calcium-magnesium composite flux, and then add the calcium-containing flux. The third batch: When the total oxygen supply reaches 40%, add the remaining calcium-magnesium composite flux. The fourth batch: When the total oxygen supply reaches 60%, add the remaining calcium-containing flux.

4. The high scrap ratio converter slagging process according to claim 3, characterized in that, In the step S3, the specific control of the lance position and oxygen flow rate of the oxygen lance is as follows: In the stage of 0 to 15% of the total oxygen supply, control the oxygen flow rate to be the first flow rate, and the lance position gradually decreases from the initial height. After the total oxygen supply exceeds 15%, increase the oxygen flow rate to the second flow rate until the blowing endpoint, and lower the lance position to the endpoint pressing height at the endpoint; where, the second flow rate is higher than the first flow rate.

5. The high scrap ratio converter slag-forming process according to claim 4, characterized in that, The first flow rate is 19000 - 21000 M³ / h, and the second flow rate is 24000 - 26000 M³ / h. The initial height is from 1.6 to 1.7m, and the lance position drops to 1.4 - 1.6m when the total oxygen supply is 10% - 15%.

6. The high scrap ratio converter slag-forming process according to claim 3, characterized in that, In the case where the total oxygen supply > 15% and < 60%, the lance position for oxygen supply is 1.4 - 1.5m. In the case where the total oxygen supply is 60% - 92%, the lance position is controlled at 1.6 - 1.8m. In the case where the total oxygen supply is greater than 92% and ≤ 100%, the lance position is controlled at the endpoint pressing height, and the endpoint pressing height is 1.0 - 1.2m. The mass ratio of the calcium-containing flux to the calcium-magnesium composite flux is 1.55 - 1.7:

1.

7. The high scrap ratio converter slagging process according to claim 6, characterized in that, The calcium-containing flux includes lime, and the calcium-magnesium composite flux includes lightly calcined dolomite; the lime contains ≥90% CaO, the lightly calcined dolomite contains 40-60% CaO and 30-40% MgO, and the remainder is unavoidable impurities.

8. The high scrap ratio converter slag-forming process according to claim 1, characterized in that, After the charging in step S2 and before the blowing in step S3, ferrosilicon is added to the converter for auxiliary heating according to the calculation of the heat balance model.

9. The high scrap ratio converter slagging process according to any one of claims 1-8, characterized in that, In step S4, the final carbon content of the molten steel at the blowing endpoint is 0.04%-0.06%, the final oxygen content is 400-500ppm, the final temperature is 1610-1625℃, and the final phosphorus content is ≤0.02%.

10. The application of a high scrap ratio converter slag-forming process as described in any one of claims 1-9 in converter smelting.

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