Method for adding scrap steel to molten iron in a blast furnace and method for producing steel

Abstract

This application provides a method for adding scrap steel to blast furnace molten iron and a method for preparing steel, comprising the following steps: adding blast furnace molten iron to a ladle, and then placing the ladle at the power supply and heating station of an LF furnace; adding scrap steel to the ladle in multiple batches; wherein, after each batch of scrap steel is added to the ladle, power supply and heating are performed to melt the scrap steel, and then the mixed melt in the ladle is heated to T1, and the next batch of scrap steel is added; after the last batch of scrap steel is added to the ladle, power supply and heating are continued to melt the last batch of scrap steel, and the mixed melt in the ladle is heated to T2 to obtain molten scrap steel; T1 is greater than or equal to 1400℃, and T2 is greater than or equal to 1380℃; after the first batch of scrap steel is added to the ladle and before the first power supply and heating, a slagging agent is added under the condition of bottom blowing of the ladle to form foamy slag, wherein the binary basicity of the slagging agent is ≥3, and the mass content of iron oxide in the slagging agent is <1%.

Description

Technical Field

[0001] This application belongs to the field of steel preparation technology, and in particular relates to a method for adding scrap steel to molten iron in a blast furnace and a method for preparing steel. Background Technology

[0002] As a recyclable resource, scrap steel has high economic, environmental and social benefits. Increasing the scrap steel ratio and reducing the consumption of molten iron not only saves energy and reduces emissions, but also effectively solves the problems of insufficient molten iron resources and surplus scrap steel resources.

[0003] Traditionally, adding scrap steel to the converter can increase the scrap ratio. However, once the scrap ratio in the converter is increased to a certain extent, it will disrupt the converter's heat balance, causing problems such as difficulty in melting scrap steel, increased end-point overblowing and make-up blowing rates, enhanced slag oxidation, severe erosion of furnace lining bricks, and increased steel material consumption. Therefore, it is necessary to find additional ways to add scrap steel to reduce the unit consumption of molten iron. Summary of the Invention

[0004] In view of this, this application provides a method for adding scrap steel to blast furnace molten iron, which can effectively melt scrap steel, increase the scrap steel ratio, and cause less corrosion to the furnace equipment. The molten scrap steel obtained by this method is of good quality after being smelted and refined in a converter. Furthermore, a method for preparing steel is also provided.

[0005] In a first aspect, this application provides a method for adding scrap steel to blast furnace molten iron, comprising the following steps: adding blast furnace molten iron to a ladle, and then placing the ladle at the power supply and heating station of an LF furnace; adding scrap steel to the ladle in multiple batches; wherein, after each batch of scrap steel is added to the ladle, power supply and heating are performed to melt the scrap steel, and then the mixed melt in the ladle is heated to T1, and the next batch of scrap steel is added; after the last batch of scrap steel is added to the ladle, power supply and heating are continued to melt the last batch of scrap steel, and the mixed melt in the ladle is heated to T2 to obtain molten scrap steel; T1 is greater than or equal to 1400℃, and T2 is greater than or equal to 1380℃; after the first batch of scrap steel is added to the ladle and before the first power supply and heating, a slagging agent is added under the condition of bottom blowing of the ladle to form foamy slag, wherein the binary basicity of the slagging agent is ≥3, and the mass content of iron oxide in the slagging agent is <1%.

[0006] According to an embodiment of the first aspect of this application, the slag-forming agent is selected from one or more of the following: recovered continuous casting residue, refined slag fragments, and foaming agents.

[0007] According to an embodiment of the first aspect of this application, based on the nominal capacity of the ladle, the amount of slag-forming agent added is 2 kg / t-10 kg / t; and / or, the thickness of the foam slag is 20-100 mm.

[0008] According to an embodiment of the first aspect of this application, during the foaming slag process, the air blowing flow rate at the bottom of the ladle is 200NL / min-600NL / min.

[0009] According to an embodiment of the first aspect of this application, the method satisfies at least one of the following conditions:

[0010] (1) Scrap steel is added to the ladle in at least three batches, and the air flow rate at the bottom of the ladle is 400NL / min-1000NL / min during each intermediate and final batch of scrap steel addition.

[0011] (2) The gas used for blowing is an inert gas; preferably, the gas is argon.

[0012] According to an embodiment of the first aspect of this application, scrap steel is added to a ladle in three batches. The specific steps include: adding the first batch of scrap steel to an empty molten iron ladle, then transporting it to a blast furnace to receive molten iron, then transferring the molten iron and the first batch of scrap steel to a ladle, and then placing the ladle at the power supply and heating station of the LF furnace; performing an initial power supply and heating to melt the first batch of scrap steel to obtain a first mixed melt, and heating the first mixed melt to T3; T3 is greater than or equal to 1420°C; adding the second batch of scrap steel, continuing to supply power and heat to melt the second batch of scrap steel to obtain a second mixed melt, and heating the second mixed melt to T4; T4 is greater than or equal to 1420°C; adding the third batch of scrap steel, supplying power and heating again to melt the third batch of scrap steel to obtain a third mixed melt, and heating the third mixed melt to T2.

[0013] According to the embodiments of the first aspect of this application, based on the nominal capacity of the ladle, the method satisfies at least one of the following conditions: (1) the amount of scrap steel added in the first batch is 0 kg / t-60 kg / t; (2) the amount of molten iron added to the blast furnace is 600-900 kg / t; (3) the amount of scrap steel added in the second batch is 30 kg / t-60 kg / t; (4) the amount of scrap steel added in the third batch is 0-50 kg / t.

[0014] According to an embodiment of the first aspect of this application, the first batch of scrap steel, by mass percentage, comprises the following components: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%;

[0015] The second batch of scrap steel includes the following composition: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%;

[0016] The third batch of scrap steel contains the following components: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%.

[0017] According to the embodiment of the first aspect of this application, the first batch of scrap steel, the second batch of scrap steel and the third batch of scrap steel are each preheated to 500°C-1000°C independently before being added to the ladle.

[0018] Secondly, embodiments of this application provide a method for preparing steel, comprising the following steps: providing blast furnace molten iron; adding scrap steel to the blast furnace molten iron according to the method of the first aspect to obtain molten scrap steel; subjecting the molten scrap steel to converter roughing and LF refining in sequence to obtain refined steel; and performing forming treatment on the steel.

[0019] This application improves the physical heat of molten iron by adding scrap steel in stages and multiple times, and by increasing the temperature through power supply. This ensures that the scrap steel added to the molten iron can melt and mix quickly and evenly. It improves the physicochemical conditions for desulfurization and converter low iron consumption under conditions of strong slag layer oxidation and excessively low temperature after adding scrap steel to the ladle. It solves the problems of large slag removal losses and inadequate desulfurization caused by excessively low temperature. It also solves the problems of converter smelting difficulties, steel quality fluctuations, and environmental protection and high costs caused by converter reheating due to insufficient heat in converter smelting. It increases the amount of scrap steel added, reduces the unit iron consumption, reduces carbon emissions from scrap steel, improves desulfurization efficiency, and has little impact on steel quality, thereby achieving the goal of increasing steel production and economic benefits. Detailed Implementation

[0020] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0021] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0025] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0026] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0027] Unless otherwise specified, this application uses conventional testing methods or testing methods recommended by the instrument.

[0028] Research has shown that adding scrap steel to molten steel through ladle refining processes (such as LF furnaces) can also increase the scrap steel ratio. However, this method has the following technical bottlenecks: First, the addition of scrap steel causes a significant drop in the temperature of the molten steel, which has an adverse effect on the fluidity of the molten steel and the desulfurization, deoxidation and alloying effects of the refining process; Second, the larger the amount of scrap steel added, the longer the melting time, which will aggravate the corrosion of the ladle refractory materials and reduce the service life of the ladle. Moreover, practice has shown that when the amount of scrap steel added in the ladle refining process reaches 150 kg / t, the iron consumption per unit can be reduced by 10%-15%, but at the same time, the following problems are brought about: (1) the nitrogen content of the molten steel increases by 0.0003%-0.0005%, and the total oxygen and hydrogen content rise simultaneously; (2) the number of oxide inclusions in the steel increases, and the rating of B, D and Ds inclusions increases; (3) the power consumption per ton of steel, electrode and ladle refractory material consumption increase significantly. These negative effects prevent the process from being applied to steel grades with strict composition requirements (such as [C]≤0.05%, [Si]≤0.03%, [P]≤0.008%, [N]≤0.005%), especially for ultra-low carbon steel grades where the addition of scrap steel in the post-converter process is strictly limited.

[0029] Currently, scrap steel is generally added during the ladle refining process. However, while adding scrap steel during refining can improve scrap steel yield, it also presents several problems: Firstly, adding scrap steel to molten steel causes a significant temperature drop, affecting the fluidity of the molten steel and the refining processes of desulfurization, deoxidation, and alloying. Secondly, the larger the amount of scrap steel added, the longer the melting time, leading to greater erosion of the ladle refractory materials and affecting the ladle's lifespan. Increasing the amount of scrap steel added during the refining process to 150 kg / t can reduce the iron consumption per unit volume by 10%-15%. However, for every 50 kg / t increase in scrap steel added during the refining process, the nitrogen mass fraction of the molten steel increases by 0.0003%-0.0005%, and the total oxygen and hydrogen mass fractions also rise simultaneously; the number of oxide inclusions in the steel and the rating of B, D, and Ds inclusions increase; and the power consumption per ton of steel, electrode and ladle refractory material consumption increase significantly. Therefore, some steel grades with strict requirements on steel composition and inclusions ([C]≤0.05%, [Si]≤0.03%, [P]≤0.008%, [N]≤0.005%, etc.) cannot have scrap steel added during LF furnace refining. In particular, scrap steel cannot be added in the processes after the converter for ultra-low carbon steel grades, resulting in higher iron consumption per unit.

[0030] Currently, scrap steel is added to empty ladles (such as torpedo ladles) after molten iron is poured into the blast furnace. The scrap steel is preheated using residual heat from the empty ladle or a scrap steel baking device. Through heat exchange and carburizing melting of the molten iron after it enters the blast furnace, the scrap steel melts in the molten iron. This technology is widely used, but it significantly reduces the temperature of the molten iron entering the converter, which to some extent affects the operation and control of the KR (Kiln Reduction) and converter. Patent CN115449592B, a method for efficient heating of molten scrap steel in an LF furnace, only involves heating the molten iron in the blast furnace before adding scrap steel. It uses converter slag for slag formation, but the converter's high oxidizing properties make it difficult to create foamed slag, easily leading to rapid erosion of the slag line in the ladle. This method has some drawbacks in practical application.

[0031] In view of the above problems, this application provides a method for adding scrap steel to blast furnace molten iron, which can effectively melt scrap steel, increase the scrap steel ratio, and cause less corrosion to the furnace equipment. The molten scrap steel obtained by this method is of good quality after being smelted and refined in a converter. Furthermore, a method for preparing steel is also provided.

[0032] In a first aspect, this application provides a method for adding scrap steel to molten iron in a blast furnace, comprising the following steps:

[0033] The molten iron from the blast furnace is added into the ladle, and then the ladle is placed in the power supply and heating position of the LF furnace.

[0034] Scrap steel is added to a ladle in multiple batches. After each batch of scrap steel is added to the ladle, electricity is supplied to heat the ladle and melt it. The temperature of the mixed melt in the ladle is then raised to T1 before the next batch of scrap steel is added. After the last batch of scrap steel is added to the ladle, electricity is supplied to heat the ladle and melt it. The temperature of the mixed melt in the ladle is then raised to T2 to obtain molten scrap steel. T1 is greater than or equal to 1400℃, and T2 is greater than or equal to 1380℃.

[0035] After the first batch of scrap steel is added to the ladle and before the first power supply and heating, a slagging agent is added to create foamy slag under the condition of blowing air at the bottom of the ladle. The binary basicity of the slagging agent is ≥3 and the mass content of iron oxide in the slagging agent is <1%.

[0036] This application embodiment effectively increases the amount of scrap steel added to blast furnace molten iron by adding scrap steel in multiple batches and coordinating with power supply to raise the temperature. This breaks through the limitation of scrap steel addition in traditional methods and helps to further reduce the unit consumption of molten iron.

[0037] Each time scrap steel is added, electricity is supplied to raise the temperature, and the mixed melt is heated to a suitable temperature before the next batch of scrap steel is added. This avoids the problem of excessive reduction in the physical heat of the molten iron caused by adding a large amount of scrap steel at once, ensuring the stability of the molten iron temperature, which is beneficial to the subsequent KR and converter operation and control.

[0038] Reasonable scrap steel addition methods and temperature control make the heat of molten iron entering the converter more balanced, reduce the impact of scrap steel addition on the converter's heat balance, and reduce the probability of problems such as difficulty in melting scrap steel in the converter, increased end-point overblowing rate, and increased supplementary blowing rate.

[0039] The method in this application embodiment controls the composition and timing of the slag-forming agent to create foamed slag under bottom air blowing conditions in the ladle. This reduces the contact between molten steel and air, lowers the content of gases such as nitrogen, oxygen, and hydrogen, as well as inclusions in the molten steel, and can meet the production requirements of high-grade steel with strict requirements on the composition and inclusions of molten steel, effectively reducing the iron consumption per unit of high-grade steel.

[0040] For example, the temperature of T1 is 1400℃, 1410℃, 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃ or a range of any two of the above values.

[0041] For example, the temperature of T2 is 1380℃, 1390℃, 1400℃, 1410℃, 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃ or a range of any two of the above values.

[0042] In some embodiments, the slag-forming agent is selected from one or more of the following: recovered continuous casting residue, refined slag fragments, and foaming agents.

[0043] For example, the foaming agent is a CaO-Na2CO3 based foaming agent.

[0044] Recycled continuous casting slag and refining slag fragments are secondary resources in the steel production process. Using them as components of slag-forming agents not only achieves resource recycling and reduces production costs, but also makes full use of their residual effective components. Continuous casting slag and refining slag fragments contain a certain amount of alkaline oxides, which help increase the binary basicity of the slag-forming agent, meeting the basicity requirements for foam slag formation. This allows the foam slag to better protect the molten steel and reduce the intrusion of gases and inclusions.

[0045] Foaming agents can promote the formation and stabilization of foamed slag under conditions of air blowing at the bottom of the ladle. Foamed slag has a large specific surface area and good covering properties, forming a stable foam layer on the surface of molten steel, effectively isolating the molten steel from contact with air. On the one hand, it reduces the dissolution of gases such as nitrogen and oxygen from the air into the molten steel, lowering the nitrogen and oxygen mass fraction in the steel; on the other hand, it hinders the floating and discharge of inclusions, while also preventing the mixing of external inclusions. This is of great significance for meeting the stringent requirements of high-grade steel for steel composition and inclusions.

[0046] In practical applications, the type and ratio of slagging agents can be flexibly selected according to specific production needs and steel grade characteristics. For example, for high-grade steel grades with extremely strict requirements on nitrogen content, the proportion of foaming agent can be appropriately increased to enhance the isolation effect of foamed slag. For production scenarios that prioritize cost-effectiveness, the proportion of recycled continuous casting residue and refining slag fragments can be increased to reduce raw material costs while ensuring slagging effect. By rationally combining the components of slagging agents, the technical step of blowing air at the bottom of the ladle to create foamed slag can be further optimized. This, combined with technical features such as adding scrap steel in multiple batches and powering up the temperature, can better achieve technical effects such as increasing the amount of scrap steel added, stabilizing the physical heat of molten iron, balancing the heat of the converter, and being suitable for the production of high-grade steel grades.

[0047] In some embodiments, the amount of slag-forming agent added is 2 kg / t to 10 kg / t, based on the nominal capacity of the ladle.

[0048] In some embodiments, the thickness of the foam residue is 20-100 mm.

[0049] Based on the nominal capacity of the ladle, the addition amount of slag-forming agent is 2 kg / t-10 kg / t. When the addition amount is at a lower level, such as 2 kg / t-4 kg / t, it is suitable for the production of ordinary steel grades where the requirements for molten steel quality are relatively less stringent and production efficiency and cost control are prioritized. In this case, an appropriate amount of slag-forming agent can basically meet the needs for creating foamed slag, reducing the cost of slag-forming agent use and processing time while ensuring a certain level of molten steel protection. For high-grade steel grades, especially products with strict requirements for inclusion and gas content, the addition amount of slag-forming agent is usually chosen at a higher level, such as 6 kg / t-10 kg / t. More slag-forming agent can generate a thicker and more stable foamed slag layer, enhancing the protective effect on the molten steel and ensuring that the composition and quality of the molten steel meet high standards.

[0050] For example, the amount of slag-forming agent added is 2 kg / t, 3 kg / t, 4 kg / t, 5 kg / t, 6 kg / t, 7 kg / t, 8 kg / t, 10 kg / t, or any range of two of the above values.

[0051] The thickness of the foamed slag is 20-100mm. When the thickness of the foamed slag is within the above range, the foamed slag has a good protective effect on the molten steel, covering the surface of the molten steel, reducing radiation and convective heat loss, improving heat utilization efficiency, reducing energy consumption, inhibiting radiation damage to the furnace lining by the electric arc, and extending the service life of refractory materials; buffering gas impact, stabilizing the fluctuation of the electric arc and molten pool, facilitating process control, and the foamed slag can isolate air and prevent secondary oxidation of the molten steel.

[0052] For example, the thickness of the foam residue is 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm or any range of two of the above values.

[0053] By rationally controlling the amount of slag-forming agent added and the thickness of the foamed slag, and through the synergistic effect of technical features such as the selection of slag-forming agent components, bottom blowing of the ladle to create foamed slag, and multiple batches of scrap steel added and power supply heating, the process of adding scrap steel to blast furnace molten iron in the LF furnace through power supply heating can be further optimized. This can better achieve technical effects such as increasing the amount of scrap steel added, stabilizing the physical heat of molten iron, balancing the heat of the converter, and being suitable for the production of high-grade steel.

[0054] In some embodiments, during the foaming slag formation process, the air blowing flow rate at the bottom of the ladle is 200NL / min-600NL / min.

[0055] Within the aforementioned flow rate range, the blowing air effectively promotes the full reaction between the slagging agent and the molten steel, accelerating the formation and stabilization of foamed slag. Stable and high-performance foamed slag can form a dense protective barrier on the surface of the molten steel, significantly reducing the contact area and time between the molten steel and air, and substantially reducing the absorption of gases such as nitrogen and oxygen from the molten steel. This effectively controls the gas content of the molten steel, meeting the stringent purity requirements of high-grade steels.

[0056] Meanwhile, a reasonable air flow rate can cause moderate flow in the molten steel, achieving effective stirring and promoting uniform mixing of various components. This avoids component segregation, ensures uniform distribution of alloying elements in the molten steel, and improves the quality stability of the steel. Furthermore, the flow of molten steel accelerates heat transfer, making the temperature field of the molten steel more uniform and creating favorable thermodynamic conditions for the rapid and uniform melting of scrap steel.

[0057] Furthermore, the stirring effect generated by an appropriate air flow rate can significantly increase the contact opportunities between scrap steel and high-temperature molten steel, enhancing the heat and mass transfer processes between them. This helps to accelerate the melting rate of scrap steel, improve the melting efficiency of scrap steel in molten steel, and thus achieve a higher scrap steel addition amount while ensuring the quality of molten steel, effectively reducing the unit consumption of molten iron.

[0058] For example, the air flow rate at the bottom of the ladle is 200NL / min, 250NL / min, 300NL / min, 350NL / min, 400NL / min, 450NL / min, 500NL / min, 550NL / min, 600NL / min, or a range of any two of the above values.

[0059] In some embodiments, scrap steel is added to the ladle in at least three batches, with the air flow rate at the bottom of the ladle being 400 NL / min to 1000 NL / min independently during each intermediate and final batch of scrap steel addition.

[0060] In some embodiments, the gas being blown is an inert gas; preferably, the gas is argon.

[0061] For example, during the process of adding scrap steel in each intermediate and final batch, the air flow rate at the bottom of the ladle is independently 400NL / min, 450NL / min, 500NL / min, 600NL / min, 700NL / min, 800NL / min, 900NL / min, 1000NL / min or any combination of two of the above values.

[0062] In the process of adding scrap steel to the LF furnace after the blast furnace molten iron is heated by electricity, in order to further optimize the smelting effect, scrap steel is added to the ladle in at least three batches.

[0063] When adding scrap steel in at least three batches, with the middle and final batches added, the bottom air flow rate of the ladle should be controlled between 400 NL / min and 1000 NL / min. During the scrap steel addition process, this flow rate range generates strong gas agitation, effectively accelerating the melting process of the scrap steel. The strong flow of molten steel promotes full contact between the scrap steel and the high-temperature molten iron, significantly increasing heat and mass transfer efficiency, allowing the scrap steel to melt quickly and uniformly, thereby improving the melting efficiency of the scrap steel in the molten steel. Especially when adding scrap steel in the middle and final batches, as the amount of material in the ladle increases and the reaction complexity rises, the strong agitation helps to break down local temperature and composition differences, ensuring complete melting of the scrap steel while maintaining the uniformity of the molten steel's composition and temperature, laying a good foundation for subsequent smelting processes.

[0064] The aforementioned air flow rate range also helps to enhance the performance of the foamed slag. During the scrap steel addition process, a larger air flow rate promotes a more complete reaction between the slag-forming agent and the molten steel, allowing the foamed slag to form quickly and maintain a good expansion state, resulting in a thicker and more uniformly covered foamed slag layer. This high-quality foamed slag layer effectively isolates the air, greatly reducing the gas exchange between the molten steel and the outside environment during scrap steel addition, significantly reducing the intake of impurity gases such as nitrogen and oxygen in the molten steel, and meeting the stringent requirements for the purity of molten steel for high-grade steel. At the same time, the good coverage of the foamed slag also reduces heat loss from the surface of the molten steel, stabilizes the steel temperature, and ensures the stability of the smelting process.

[0065] Choosing inert gases, especially argon, as the blowing gas further improves the quality and stability of the smelting process. Argon, as an inert gas, is chemically stable, does not react with molten steel, and does not introduce additional impurities, ensuring the purity of the steel composition. During the addition of scrap steel, the blowing of argon allows for precise control of the molten steel's flow, avoiding potential changes in steel composition or adverse reactions that might occur with other reactive gases. Simultaneously, the bubbles formed by argon in the molten steel effectively carry inclusions to the surface, where they are adsorbed by the foam slag, thus purifying the steel and reducing inclusion content. This allows for the production of high-grade steel with strict requirements regarding inclusion content.

[0066] Furthermore, using a blowing flow rate of 400 NL / min-1000 NL / min, combined with inert argon gas, when adding scrap steel in the middle and final batches can significantly improve smelting efficiency. Rapid scrap melting and effective steel mixing reduce overall smelting time and increase equipment utilization. Simultaneously, stable steel quality and a low scrap rate lower production costs, enhancing the process's economic benefits and market competitiveness. In actual production, the blowing flow rate can be flexibly adjusted within this range based on specific scrap steel addition amounts and steel grade requirements, using argon gas as the blowing gas to achieve efficient and high-quality smelting under different operating conditions, meeting diverse production needs.

[0067] In some embodiments, scrap steel is added to the ladle in three batches. The specific steps include: adding the first batch of scrap steel to an empty ladle, then transporting it to the blast furnace to receive blast furnace hot metal, then transferring the blast furnace hot metal and the first batch of scrap steel to the ladle, and then placing the ladle at the power supply and heating station of the LF furnace; performing the first power supply and heating to melt the first batch of scrap steel to obtain a first mixed melt, and heating the first mixed melt to T3; T3 is greater than or equal to 1420°C; adding the second batch of scrap steel, continuing to power supply and heating to melt the second batch of scrap steel to obtain a second mixed melt, and heating the second mixed melt to T4; T4 is greater than or equal to 1420°C; adding the third batch of scrap steel, powering and heating again to melt the third batch of scrap steel to obtain a third mixed melt, and heating the third mixed melt to T2.

[0068] In the process system where blast furnace hot metal is heated by electricity in the LF furnace and scrap steel is added, in order to achieve efficient utilization of scrap steel and precise control of molten steel quality, the embodiments of this application adopt a three-batch method to add scrap steel to the ladle. The specific process steps are as follows:

[0069] First, the first batch of scrap steel is added to an empty ladle. Choosing an empty ladle as the container for this first batch of scrap steel allows for preliminary preheating using the residual heat of the ladle itself. This not only reduces energy consumption for melting the scrap steel during subsequent smelting but also mitigates the negative impact of the scrap steel addition on the molten iron temperature. After adding the first batch of scrap steel, the empty ladle is transported to the blast furnace to receive the high-temperature molten iron produced by the blast furnace. During the blast furnace molten iron injection process, the high-temperature molten iron and the preheated first batch of scrap steel immediately exchange heat. The scrap steel begins to slowly melt under the heat transfer of the high-temperature molten iron, while the temperature of the molten iron itself decreases moderately due to the heat absorption of the scrap steel, forming a relatively mild heat balance process. This pre-mixing method avoids the drastic temperature fluctuations that might occur when a large amount of scrap steel is added to the ladle at once, creating favorable conditions for stable smelting in the subsequent process. Subsequently, the blast furnace molten iron mixed with the first batch of scrap steel is transferred to a ladle, which is then placed in the power-on heating position of the LF furnace.

[0070] Next, the initial power-on heating operation is performed. The LF furnace transfers energy to the material in the ladle through electrode heating, causing the first batch of scrap steel to completely melt. During this process, the heating process is strictly controlled so that the first batch of scrap steel melts to form the first mixed melt, which is then heated to T3, and T3 is greater than or equal to 1420℃. The T3 temperature ensures the complete melting of the first batch of scrap steel and provides a suitable temperature base for the addition of subsequent batches. A higher temperature maintains good fluidity in the molten steel, facilitating the integration of subsequent scrap steel and homogenizing the steel composition. If the temperature is too low, it will lead to difficulties in melting subsequent scrap steel, prolonging smelting time and increasing energy consumption; if the temperature is too high, it may cause excessive oxidation of the molten steel, affecting its quality.

[0071] After the first batch of scrap steel has completely melted and reached the target temperature T3, the second batch of scrap steel is added. At this point, the ladle already contains a first mixed melt at a high temperature with good fluidity. Upon addition of the second batch of scrap steel, it quickly comes into contact with the first mixed melt and melts rapidly under the high-temperature environment and continuous power supply from the LF furnace. Power continues to be supplied to the ladle to further heat the material, ensuring the second batch of scrap steel completely melts to form a second mixed melt. This second mixed melt is then heated to T4, which is greater than or equal to 1420℃. This temperature stage ensures the complete melting of the second batch of scrap steel while maintaining the uniformity of steel composition and temperature. During the heating process, the air flow rate at the bottom of the ladle can be adjusted within a reasonable range according to actual conditions. Through gas stirring, the second batch of scrap steel is promoted to fully integrate with the first mixed melt, accelerating the heat and mass transfer process, ensuring uniform distribution of steel composition, and avoiding localized compositional differences.

[0072] Finally, the last batch of scrap steel is added, and power is supplied again to raise the temperature. After the first two batches of scrap steel were added and heated, a mixed system with a certain temperature and composition had formed inside the ladle. Upon the addition of the last batch of scrap steel, it rapidly melted under the continuous heating of the LF furnace and the agitation of the gas at the bottom of the ladle, resulting in the third mixed melt. By precisely controlling the power supply and heating time, the temperature of the third mixed melt reached T2. During this process, stable temperature control and effective gas agitation ensured the complete melting of the last batch of scrap steel, while also further homogenizing the composition of the molten steel, ensuring that the final molten scrap steel met the requirements for subsequent smelting and product quality.

[0073] For example, T3 is 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃ or a range of any two of the above values.

[0074] For example, T4 is 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃ or a range of any two of the above values.

[0075] This application employs a three-batch scrap steel addition method, combined with temperature control and air flow rate adjustment, to avoid the heat imbalance and melting difficulties caused by adding a large amount of scrap steel at once, effectively improving the melting efficiency and utilization rate of scrap steel. Each batch of scrap steel is heated to a specific temperature after addition, ensuring that the molten steel maintains good fluidity and thermal state at each stage, which is beneficial for subsequent scrap steel addition and melting, and also facilitates precise control of the molten steel composition. The reasonable air flow rate combined with the batch heating operation enhances steel mixing, promotes the full integration of scrap steel and molten steel, accelerates the floating and removal of inclusions, improves the purity of the molten steel, meets the production requirements of high-grade steel, and achieves a highly efficient and high-quality steel smelting process.

[0076] In some embodiments, the amount of scrap steel added in the first batch is 0-60 kg / t, based on the nominal capacity of the ladle.

[0077] The first batch of scrap steel is pre-added to the empty molten iron ladle. This addition range is set to consider both the heat balance during the smelting process and the preheating requirements of the scrap steel. Adding an appropriate amount of the first batch of scrap steel allows for effective preheating using the residual heat of the empty ladle, reducing energy consumption for subsequent heating in the LF furnace. It also ensures adequate heat exchange with the high-temperature molten iron during blast furnace pouring, preventing a sudden drop in molten iron temperature due to excessive scrap steel, which could affect subsequent scrap melting efficiency and molten steel quality. Simultaneously, this addition range ensures that the first batch of scrap steel is preliminarily mixed with the molten iron before being transferred to the ladle, creating favorable conditions for further processing in the LF furnace. This reduces molten iron consumption per unit area while maintaining stable operation of the smelting process.

[0078] For example, the amount of scrap steel added in the first batch is 0 kg / t, 5 kg / t, 10 kg / t, 15 kg / t, 20 kg / t, 25 kg / t, 30 kg / t, 35 kg / t, 40 kg / t, 45 kg / t, 50 kg / t, 55 kg / t, 60 kg / t, or any range of two of the above values.

[0079] In some embodiments, the amount of molten iron added to the blast furnace is 600-900 kg / t, based on the nominal capacity of the ladle.

[0080] As a fundamental raw material for smelting, the appropriate amount of blast furnace hot metal added provides sufficient heat and reaction space for the melting of scrap steel, ensuring a proper ratio between the hot metal and scrap. This range of addition not only helps optimize resource utilization and increase the proportion of scrap steel in the mixture, further reducing the consumption of hot metal per unit weight, but also meets the hot metal content requirements for different steel grades. In actual production, the amount of blast furnace hot metal added can be flexibly adjusted within this range according to specific production plans, scrap steel quality, and equipment conditions to ensure that the entire smelting process is efficient and stable, producing steel that meets quality standards.

[0081] For example, the amount of molten iron added to the blast furnace is 600 kg / t, 620 kg / t, 650 kg / t, 680 kg / t, 700 kg / t, 720 kg / t, 750 kg / t, 780 kg / t, 800 kg / t, 820 kg / t, 850 kg / t, 880 kg / t, 900 kg / t, or any range of two of the above values.

[0082] In some embodiments, the amount of scrap steel added in the second batch is 30 kg / t to 60 kg / t, based on the nominal capacity of the ladle.

[0083] The second batch of scrap steel is added after the first batch has completely melted and the first mixed melt has reached a suitable temperature. This range of addition amounts allows for a further increase in the total amount of scrap steel added, while ensuring steel quality and smelting stability. Within this range, the second batch of scrap steel can melt rapidly in the high-temperature and highly fluid environment of the first mixed melt, fully integrating with the molten steel to achieve a uniform distribution of composition and temperature. By rationally controlling the power supply of the LF furnace and the bottom air flow rate of the ladle, the full melting of the second batch of scrap steel can be ensured, meeting the stringent requirements of different steel grades for steel composition and properties. This improves economic efficiency while guaranteeing a smooth smelting process.

[0084] For example, the amount of scrap steel added in the second batch is 30 kg / t, 35 kg / t, 40 kg / t, 45 kg / t, 50 kg / t, 55 kg / t, 60 kg / t, or any range of two of the above values.

[0085] In some embodiments, the amount of scrap steel added in the third batch is 0-50 kg / t, based on the nominal capacity of the ladle.

[0086] The addition of the final batch of scrap steel plays a crucial role in the final quality of the molten steel and the smelting effect. Adding the final batch within this range allows for rapid melting under the heating and gas stirring of the LF furnace, achieving the final adjustment and homogenization of the steel composition. By rationally controlling the amount of the final batch of scrap steel added, combined with the addition of the first two batches and the heating operation, efficient utilization of scrap steel can be achieved, producing high-quality molten steel to meet diverse market demands, while ensuring an efficient and stable smelting process and improving overall production efficiency.

[0087] For example, the amount of scrap steel added in the third batch is 0 kg / t, 5 kg / t, 10 kg / t, 15 kg / t, 20 kg / t, 25 kg / t, 30 kg / t, 35 kg / t, 40 kg / t, 45 kg / t, 50 kg / t, or any range of two of the above values.

[0088] In some embodiments, the first batch of scrap steel comprises the following components by mass percentage: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%.

[0089] In some embodiments, the second batch of scrap steel comprises the following components: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%.

[0090] In some embodiments, and in the third batch of scrap steel, the composition includes: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%.

[0091] In some embodiments, the sources of the second batch of scrap steel include rebar pellets, hot-rolled trimmed steel, cold-rolled trimmed steel wire, purchased recycled profiles, and scattered waste.

[0092] In some embodiments, the sources of the third batch of scrap steel include rebar pellets, hot-rolled trimmed steel, cold-rolled trimmed wire, purchased recycled profiles, and scattered waste.

[0093] In some embodiments, the second and third batches of scrap steel come from the same source, and the operations of adding scrap steel and supplying electricity for heating are the same.

[0094] The second and third batches of scrap steel can also come from different sources.

[0095] In some embodiments, scrap steel with a length ≤200mm and a thickness ≤30mm is selected.

[0096] In some embodiments, the first batch, the second batch, and the third batch of scrap steel are each preheated independently to 500°C-1000°C before being added to the ladle.

[0097] For example, the preheating temperature of the first batch of scrap steel is 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C or a range of any two of the above values.

[0098] For example, the preheating temperature of the second batch of scrap steel is 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃ or a range of any two of the above values.

[0099] For example, the preheating temperature of the third batch of scrap steel is 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃ or a range of any two of the above values.

[0100] The preheating temperatures for the first, second, and third batches of scrap steel can be the same or different.

[0101] When scrap steel is preheated to 500℃-1000℃, its inherent heat energy can rapidly exchange heat with the molten iron and the mixed melt within the ladle after being added. Compared to unpreheated scrap steel, preheated scrap steel significantly shortens the melting time in the ladle, accelerates the melting process, and substantially improves smelting efficiency. During the LF furnace's power supply and heating process, preheating the scrap steel reduces the energy consumption required to raise its temperature to the melting point, lowers the LF furnace's electrical energy consumption, effectively saves production costs, and improves energy utilization efficiency.

[0102] Furthermore, a reasonable preheating temperature can reduce the negative impact of adding scrap steel on the temperature of molten steel. When scrap steel is added to the ladle, it will not excessively absorb heat from the molten steel due to excessively low temperatures, avoiding a significant temperature drop in the molten steel. This helps maintain a stable molten steel temperature, creating favorable conditions for precise control and homogenization of the steel composition. A stable molten steel temperature can also reduce steel quality problems caused by temperature fluctuations, such as increased inclusions and uneven composition, improving the purity and quality stability of the molten steel and better meeting the stringent quality requirements of high-grade steel.

[0103] Preheating each batch of scrap steel independently allows for flexible adjustment of the preheating temperature based on the process requirements and the state of the molten steel at the time of addition. For example, preheating the first batch of scrap steel before adding it to the empty ladle enhances its heat exchange with the blast furnace molten steel. The second and third batches of scrap steel, already at a certain temperature within the LF furnace, can be more quickly and fully integrated with the molten steel through appropriate preheating, achieving a more uniform distribution of composition and temperature. Simultaneously, the preheating process can remove impurities adhering to the surface of the scrap steel to some extent, reducing the risk of impurities entering the molten steel and further ensuring steel quality.

[0104] By preheating the first, second, and third batches of scrap steel to 500℃-1000℃ before adding them to the ladle, and coordinating this process with other steps such as adding multiple batches of scrap steel, powering up the LF furnace, and blowing air into the bottom of the ladle to create foamy slag, the entire process of adding scrap steel to blast furnace hot iron can be significantly optimized, achieving the goal of efficient, energy-saving, and high-quality steel smelting.

[0105] Secondly, embodiments of this application provide a method for preparing steel, comprising the following steps: providing blast furnace molten iron; adding scrap steel to the blast furnace molten iron according to the method of the first aspect to obtain molten scrap steel; subjecting the molten scrap steel to converter roughing and LF refining in sequence to obtain refined steel; and performing forming treatment on the steel.

[0106] In the steel preparation method described in this application, scrap steel is added to the molten iron in stages and multiple times. Electric heating increases the physical heat of the molten iron, ensuring that the added scrap steel melts and mixes quickly. This improves the physicochemical conditions for desulfurization and converter low iron consumption under conditions of strong slag layer oxidation and excessively low temperature after adding scrap steel to the ladle. It solves the problems of large slag removal losses and inadequate desulfurization caused by excessively low temperatures. It also addresses the difficulties in converter smelting due to insufficient heat, fluctuations in molten steel quality, and the environmental and high cost issues associated with converter reheating. Increasing the amount of scrap steel added reduces the unit consumption of molten iron, decreases carbon emissions from scrap steel, improves desulfurization efficiency, and minimizes the impact on molten steel quality, thereby achieving the goal of increasing steel production and economic benefits.

[0107] Example

[0108] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0109] Example 1

[0110] A method for adding scrap steel to molten iron in a blast furnace, using a 100t converter to smelt ultra-low carbon steel grade galvanized substrate DX52D, the specific steps are as follows:

[0111] (1) 3000 kg of hot-rolled scrap steel is added to an empty 100t capacity ladle using a steel grabber. The scrap steel is preheated to 500°C using a pure oxygen scrap steel preheating system. The ladle is then covered and transported to the blast furnace to receive 80t of molten iron. After being transported back to the steel plant, the molten iron is transferred to a 100t capacity ladle with a spout. The ladle is then hoisted and transported to the LF furnace power supply and heating station.

[0112] (2) Connect the bottom blowing argon system and control the bottom blowing flow rate to 300 NL / min, maintaining slight fluctuation of the liquid level. Add 1 t of recovered continuous casting residue to the ladle to create foam slag; wherein, the basicity of the continuous casting residue is 3.8 and the mass content of iron oxide is 0.48%.

[0113] (3) The power supply and heating conditions are as follows: In the early stage, the voltage on one side of the No. 7 gear is 23357V and the current on the other side is 385.3A, the voltage on both sides is 327V and the current on both sides is 41240A for preheating and arc initiation. The arc length is controlled to avoid the electric arc directly acting on the refractory material of the ladle slag line, and to promote the slag formation and foaming process of the top slag. After the arc pressure is stabilized, the high-level gear 2-3 voltage is used for heating, with a voltage of 25000V and a current of 412.4A on one side, and a voltage of 373V and a current of 38700A on both sides. High current power supply is used to ensure the stability of the top slag submerged arc, increase the heating intensity and heating rate of the molten iron, and shorten the heating time. During the heating process, the argon bottom blowing gas flow rate (400NL / min-600NL / min) is dynamically adjusted to ensure the stability of the arc flow and arc pressure during the heating process. The power supply is used to heat up to 1420℃.

[0114] (4) Add a second batch of scrap steel at a temperature of 800℃ to the molten iron in the ladle. The amount of the second batch of scrap steel added is 5000kg, the addition rate is 1000kg / min, and the flow rate of bottom blowing argon is 600NL / min. The sources of the second batch of scrap steel include rebar pellets, hot-rolled trimmed material, cold-rolled trimmed wire, purchased recycled profiles, and scattered waste.

[0115] (5) Confirm the power supply and heating conditions. In the early stage, use the No. 7 gear with a voltage of 23357V on one side and a current of 385.3A on the other side, and a voltage of 327V on the other side and a current of 41240A on the other side to preheat the arc and control the arc length to avoid the electric arc directly acting on the refractory material of the ladle slag line, and promote the slag formation and foaming process of the top slag. After the arc pressure is stable, use the high-level gear 2-3 voltage for heating, with a side voltage of 25000V and a current of 412.4A on one side, and a voltage of 373V on the other side and a current of 38700A on the other side. Under the condition of ensuring the stability of the top slag submerged arc, increase the heating intensity and heating rate of the molten iron, shorten the heating time, and dynamically adjust the argon bottom blowing flow during the heating process to ensure the stability of the arc flow and arc pressure during the heating process. When the power supply heats up to 1400℃, it can be powered up in 2-3 times to reduce the time of each power supply, adjust the subsequent operation in time, reduce ladle erosion, and save time.

[0116] (6) Add the third batch of scrap steel at a temperature of 600℃ to the molten iron in the ladle. The amount of the third batch of scrap steel added is 5000kg, the addition rate is 1000kg / min, the flow rate of bottom blowing argon is 600NL / min, and the sources of the third batch of scrap steel include rebar pellets, hot-rolled trimmed material, cold-rolled trimmed wire, purchased recycled profiles, and scattered waste.

[0117] (7) Heat the molten metal in the ladle to 1380°C, then lift the ladle out and enter the KR desulfurization station for desulfurization. This completes the LF furnace heating process for a ladle of molten iron and scrap steel.

[0118] Through the implementation of the above steps, the blast furnace can produce 80 tons of iron, which can reach 93 tons after adding scrap steel for melting. The heating rate of the molten iron in the LF furnace can reach 4-6℃ / min. The binary basicity of the top slag of the molten iron before and after the LF furnace heating process increases from 0.8 to 2.0. Under the relatively short production cycle of the LF furnace, the average temperature of the molten scrap steel entering the furnace increases from 1300℃ to 1380℃, achieving efficient and rapid heating of the molten iron in the LF furnace. The amount of scrap steel added reaches more than 100kg, and the iron consumption per unit is reduced from 911.7kg / t to 784.3kg / t, a reduction of 127.4kg / t. This achieves the comprehensive goals of rapid scrap steel melting, low heating cost, and high iron temperature entering the converter, helping steelmaking units reduce iron consumption per unit and reduce carbon emissions.

[0119] Example 2

[0120] A method for adding scrap steel to blast furnace molten iron, using LG510L steel grade smelted in a 100t converter with [N] ≤ 0.0050%, where scrap steel cannot be added during the refining process to reduce nitrogen gain, necessitating a shorter refining time. The specific steps are as follows:

[0121] (1) 5000 kg of the first bulk scrap steel is added to a 100t empty molten iron ladle using a steel grabber. The scrap steel is preheated to above 500°C using a pure oxygen scrap steel preheating system. The ladle is covered and transported to the blast furnace to receive 65t of molten iron. After being transported back to the steelmaking plant, the molten iron is transferred to a 100t ladle with a ladle spout, and then hoisted and transported to the LF furnace power supply and heating station.

[0122] (2) Connect the bottom blowing argon system, with a bottom blowing flow rate of 300 NL / min, keep the liquid surface slightly moving, add 800 kg of cold refining slag fragments to make foam slag, and the alkalinity of the refining slag fragments is 3.5;

[0123] (3) The power supply and heating conditions are as follows: In the early stage, the voltage on one side of the No. 7 gear is 23357V and the current on the other side is 385.3A, the voltage on both sides is 327V and the current on both sides is 41240A for preheating and arc initiation. The arc length is controlled to avoid the electric arc directly acting on the refractory material of the ladle slag line, and to promote the slag formation and foaming process of the top slag. After the arc pressure is stable, the high-level gear 2-3 voltage is used for heating, with a side voltage of 25000V and a current on one side of 412.4A, and a voltage on both sides of 373V and a current on both sides of 38700A. High current power supply is used to ensure the stability of the top slag submerged arc, increase the heating intensity and heating rate of the molten iron, shorten the heating time, and dynamically adjust the argon bottom blowing flow rate during the heating process to ensure the stability of the arc flow and arc pressure during the heating process. The power supply and heating to 1420℃ can be done in two stages.

[0124] (4) A second batch of baked scrap steel was added to the molten iron. The amount of the second batch of scrap steel added was 4500 kg. The temperature of the baked scrap steel entering the molten iron was 800℃, the addition rate of the second batch of scrap steel was 1000 kg / min, the flow rate of bottom-blown argon gas was 600 NL / min, and the sources of the second batch of scrap steel included rebar granules, hot-rolled trimmed material, cold-rolled trimmed wire, purchased recycled profiles, and scattered waste.

[0125] (5) Confirm the power supply and heating conditions. In the early stage, use the No. 7 gear with a voltage of 23357V on one side and a current of 385.3A on the other side, a voltage of 327V on the other side and a current of 41240A on the other side to preheat the arc and control the arc length to avoid the electric arc directly acting on the refractory material of the ladle slag line and promote the top slag slagging and foaming process. After the arc pressure is stable, use the high-level gear 2-3 voltage for heating, with a side voltage of 25000V and a current of 412.4A on one side, a voltage of 373V on the other side and a current of 38700A on the other side. Under the condition of ensuring the stability of the top slag submerged arc, increase the heating intensity and heating rate of the molten iron and shorten the heating time. During the heating process, dynamically adjust the argon bottom blowing gas flow rate to ensure the stability of the arc flow and arc pressure during the heating process. When the power supply heats up to 1400℃, it can be powered up in two stages to reduce the time of each power supply, adjust the subsequent operation in time, reduce ladle erosion, and save time.

[0126] (6) Add the third batch of scrap steel, with a steel addition amount of 4500 kg. The temperature of the baked scrap steel entering the molten iron is 520℃, the addition rate of the third batch of scrap steel is 1000 kg / min, the flow rate of bottom-blown argon is 600 NL / min, and the sources of the third batch of scrap steel include rebar granules, hot-rolled trimmed material, cold-rolled trimmed wire, purchased recycled profiles, and scattered waste.

[0127] (7) Heat the molten iron to above 1380°C, then hoist the molten iron into the converter for smelting. Complete the LF furnace heating process for a ladle of molten iron and scrap steel.

[0128] Through the implementation of the above steps, this type of steel grade that cannot be refined scrap steel in the LF furnace after the converter can achieve a blast furnace output of 65t of iron, which can reach 79t after adding scrap steel for melting. The heating rate of molten iron in the LF furnace can reach 4-5℃ / min. The binary basicity of the top slag of molten iron before and after the LF furnace heating process increases from 0.8 to 2.0. Under the condition of a short production cycle of the LF furnace, the average temperature of the molten scrap steel entering the converter furnace increases from 1280℃ to 1380℃, realizing efficient and rapid heating of molten iron in the LF furnace. The amount of scrap steel added reaches more than 100kg, and the iron consumption per unit is reduced from 831.5kg / t to 684.2kg / t, a reduction of 147.3kg / t. This achieves the comprehensive goals of rapid scrap steel melting, low heating cost, high iron temperature entering the converter furnace, rapid processing in subsequent processes, and no impact on the quality of molten steel, helping steelmaking units reduce iron consumption per unit and reduce carbon emissions.

[0129] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A method for adding scrap steel to molten iron in a blast furnace, characterized in that, Includes the following steps: Molten iron from the blast furnace is added to a ladle, and then the ladle is placed in the power supply and heating position of the LF furnace. Scrap steel is added to the ladle in multiple batches; after each batch of scrap steel is added to the ladle, electricity is supplied to heat the ladle and melt the scrap steel, then the temperature of the mixed melt in the ladle is raised to T1, and the next batch of scrap steel is added; after the last batch of scrap steel is added to the ladle, electricity is supplied to heat the ladle and melt the last batch of scrap steel, and the temperature of the mixed melt in the ladle is raised to T2, to obtain molten scrap steel; T1 is greater than or equal to 1400°C, and T2 is greater than or equal to 1380°C; After the first batch of scrap steel is added to the ladle and before the first power supply and heating, a slag-forming agent is added to form foam slag under the condition of blowing air at the bottom of the ladle. The binary basicity of the slag-forming agent is ≥3 and the mass content of iron oxide in the slag-forming agent is <1%.

2. The method according to claim 1, characterized in that, The slag-forming agent is selected from one or more of the following: recovered continuous casting residue, refined slag fragments, and foaming agents.

3. The method according to claim 1, characterized in that, Based on the nominal capacity of the ladle, the amount of slag-forming agent added is 2kg / t-10kg / t; and / or, the thickness of the foam slag is 20-100mm.

4. The method according to any one of claims 1 to 3, characterized in that, During the foaming process, the air flow rate at the bottom of the ladle is 200NL / min-600NL / min.

5. The method according to any one of claims 1 to 3, characterized in that, The method satisfies at least one of the following conditions: (1) The scrap steel is added to the ladle in at least three batches, and during each intermediate and final batch of adding the scrap steel, the air flow rate at the bottom of the ladle is independently 400NL / min-1000NL / min; (2) The gas being blown is an inert gas.

6. The method according to claim 5, characterized in that, The gas is argon.

7. The method according to claim 5, characterized in that, The scrap steel is added to the ladle in three batches, specifically including the following steps: The first batch of scrap steel is added to the empty molten iron ladle and then transported to the blast furnace to receive the molten iron. The molten iron and the first batch of scrap steel are then transferred to the ladle and placed in the power supply and heating station of the LF furnace. The first batch of scrap steel is melted by the initial power supply and heating to obtain a first mixed melt, and the first mixed melt is heated to T3; wherein T3 is greater than or equal to 1420°C. A second batch of scrap steel is added, and power is continued to be supplied to raise the temperature, so that the second batch of scrap steel melts to obtain a second mixed melt, and the temperature of the second mixed melt is raised to T4; wherein T4 is greater than or equal to 1420°C; A third batch of scrap steel is added, and power is supplied again to raise the temperature, causing the third batch of scrap steel to melt and obtain a third mixed melt, and the temperature of the third mixed melt reaches T2.

8. The method according to claim 7, characterized in that, Based on the nominal capacity of the ladle, the method satisfies at least one of the following conditions: (1) The amount of scrap steel added in the first batch is 0 kg / t to 60 kg / t; (2) The amount of molten iron added to the blast furnace is 600-900 kg / t; (3) The amount of scrap steel added in the second batch is 30kg / t-60kg / t; (4) The amount of the third batch of scrap steel added is 0-50 kg / t.

9. The method according to claim 7, characterized in that, Based on mass percentage, the first batch of scrap steel comprises the following components: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%. The second batch of scrap steel comprises the following components: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%. The third batch of scrap steel contains the following components: Fe ≥ 80%, P ≤ 0.050%, S ≤ 0.050%, Cu ≤ 0.3%, Cr ≤ 0.3%, Ni ≤ 0.3%, and the remaining elements are impurities ≤ 0.1%.

10. The method according to claim 7, characterized in that, The first batch, the second batch, and the third batch of scrap steel are each preheated independently to 500℃-1000℃ before being added to the empty molten iron ladle or the steel ladle.

11. A method for preparing steel, characterized in that, Includes the following steps: Provide molten iron for blast furnaces; According to any one of claims 1-10, scrap steel is added to molten blast furnace iron to obtain molten scrap steel. The molten scrap steel is subjected to converter roughing and LF refining in sequence to obtain refined steel. The molten steel is then subjected to a forming process.