Molten steel smelting method and steel

Abstract

The method comprises the steps that converter smelting is conducted on molten iron and waste steel in a converter, only lime is added in the converter tapping process, so that it is ensured that steel ladle slag is in an oxidizing slag state when the waste steel is added for the first time in the refining stage, and converter molten steel with the oxidizing property is obtained; lF refining is conducted on the converter molten steel, specifically, the converter molten steel is heated to be larger than or equal to 1570 DEG C in an LF furnace, waste steel is added for the first time and molten, and LF refined molten steel with molten waste steel is obtained; the temperature of the LF refined molten steel obtained by melting the scrap steel is increased to be larger than or equal to 1580 DEG C, ladle slag in the LF furnace is removed, rephosphorization in the refining process is prevented, and the LF refined molten steel obtained after slag removal is obtained; the LF refined molten steel obtained after slag removal is divided into two or more parts and placed in corresponding LF furnaces, waste steel is added for the second time for melting, and LF secondary refined molten steel is obtained; and the LF secondary refined molten steel is subjected to refining slagging treatment and component adjusting treatment, so that it is ensured that the quality of the molten steel meets the requirement, and the molten steel with the high scrap steel ratio is obtained.

Description

Technical Field

[0001] This application belongs to the field of metal smelting technology, and particularly relates to a method for smelting molten steel and steel products. Background Technology

[0002] In traditional steelmaking processes, the amount of scrap steel added to the refining furnace is limited, mainly due to insufficient ladle clearance, phosphorus reversion from refining scrap, and increased nitrogen due to long refining times. These issues restrict the amount of refining scrap steel added, making it difficult to increase the scrap steel ratio in steelmaking. Therefore, this application aims to solve the above problems through technological improvements. Summary of the Invention

[0003] This application provides a method for smelting molten steel that can significantly increase the amount of refined scrap steel added in the steelmaking process and ensure that its N and P content meets the standards.

[0004] In a first aspect, this application provides a method for smelting molten steel, comprising: smelting molten iron and scrap steel in a converter, adding only lime during the tapping process to ensure that the ladle slag is in an oxidized slag state when scrap steel is first added during the refining stage, thereby obtaining oxidized converter steel; and performing LF refining on the converter steel, comprising: heating the converter steel to ≥1570°C in an LF furnace, adding scrap steel for the first time and melting the scrap steel to obtain LF refined steel with melted scrap steel; raising the temperature of the LF refined steel with melted scrap steel to ≥1580°C and removing the ladle slag in the LF furnace to prevent phosphorus reversion during the refining process, thereby obtaining LF refined steel with slag removal; dividing the LF refined steel with slag removal into two or more portions and placing them in corresponding LF furnaces, adding scrap steel a second time for melting in each portion, thereby obtaining LF secondary refined steel; and subjecting the LF secondary refined steel to refining slag formation treatment and composition adjustment treatment to ensure that the steel quality meets the requirements and obtaining steel with a high scrap steel ratio.

[0005] According to an embodiment of the first aspect of this application, the molten iron and scrap steel in the converter are smelted in the converter, including: only lime is added to the molten steel in the converter and no deep deoxidation treatment is performed, so as to ensure that the molten steel does not increase phosphorus or can be partially dephosphorized when scrap steel is added for the first time in the refining stage, so as to obtain molten steel in the converter that does not increase phosphorus and has oxidizing properties.

[0006] According to an embodiment of the first aspect of this application, the molten iron and scrap steel in the converter are smelted in the converter, including: adding lime only to the molten steel during the tapping process of the converter, with the amount of lime added being 2 kg / ton to 4 kg / ton of molten steel, so as to ensure that the ladle slag is in the oxidized slag state when the scrap steel is added for the first time in the refining stage, so as to obtain oxidized converter molten steel.

[0007] According to an embodiment of the first aspect of this application, the composition of the lime, based on the mass percentage, needs to meet the following requirements: CaO ≥ 90%, SiO2 ≤ 1.5%, S ≤ 0.03%, loss on ignition ≤ 5%, the particle size of the lime needs to be 10 mm to 60 mm, the amount of lime exceeding the upper limit of particle size shall not exceed 10% of the batch inspection quantity, and the amount of lime exceeding the lower limit of particle size shall not exceed 12% of the batch inspection quantity.

[0008] According to an embodiment of the first aspect of this application, LF refining of converter steel further includes: in the step of heating the converter steel to ≥1570°C in the LF furnace, if slag foaming occurs in the steel in the LF furnace, aluminum blocks or modifiers are added for slag pressing treatment to suppress slag foaming.

[0009] According to an embodiment of the first aspect of this application, in the step of LF refining of converter steel, aluminum blocks are added to the LF furnace at a rate of 0.3 kg / ton to 0.6 kg / ton of steel, and / or, a modifier is added at a rate of 0.5 kg / ton to 1.2 kg / ton of steel.

[0010] According to an embodiment of the first aspect of this application, the aluminum blocks, by mass percentage, need to meet the following requirements: Al, 98.5%–99.4%; Fe, >0.50%; Ca, >0.05%; Si, 0.45%–0.6%; Mg, >0.20%; S, 0.01%–0.02%; the particle size of the aluminum blocks is 10 mm–50 mm, and the amount exceeding the upper and lower limits is less than or equal to 8% of the total batch size.

[0011] According to an embodiment of the first aspect of this application, the aluminum block, by mass percentage, needs to meet the following requirements: Al, ≥99.4%; Fe, ≤0.50%; Ca, ≤0.05%; Si, ≤0.45%; Mg, ≤0.20%; S, ≤0.01%.

[0012] According to an embodiment of the first aspect of this application, the amount of aluminum blocks exceeding the upper and lower limits is less than or equal to 5% of the total batch size.

[0013] According to an embodiment of the first aspect of this application, the modifier, by mass percentage, needs to meet the following requirements: SiO2, 5%–7%; Al, 35%–37%; Al2O3, 13%–15%; CaO, 18%–20%; MgO, >7.0%; Fe2O3, 2%–3%; S, 0.1%–0.12%; P, 0.08%–0.10%; C, 3%–5%; moisture, 0.8%–1.0%; the particle size of the modifier is 10 mm–40 mm, and the amount exceeding the upper and lower limits of the particle size is less than or equal to 8% of the total batch.

[0014] According to an embodiment of the first aspect of this application, the modifier, by mass percentage, needs to meet the following requirements: SiO2, ≤5%; Al, ≥37%; Al2O3, ≥15%; CaO, ≥20%; MgO, ≤7.0%; Fe2O3, ≤2%; S, ≤0.10%; P, ≤0.08%; C, ≤3%; and moisture, ≤0.8%.

[0015] According to the embodiments of the first aspect of this application, the amount of the modifier exceeding the upper and lower limits of particle size is less than or equal to 5% of the total batch.

[0016] According to the embodiment of the first aspect, the slag-refined LF steel is divided into two or more portions and placed in corresponding LF furnaces, and scrap steel is added to each portion for melting. This includes: pouring the slag-refined LF steel portion into an empty sub-ladle, defining the ladle from which the steel is poured as the mother ladle, and ensuring that the mother ladle and the sub-ladle are completely empty to allow for electrofusion heating after the addition of scrap steel, thereby obtaining LF secondary refined steel.

[0017] According to the embodiments of the first aspect of this application, the steel smelting method further includes: dividing two or more portions of LF secondary refined steel obtained by melting scrap steel a second time into three or more portions, and adding scrap steel a third time to each portion of LF secondary refined steel to obtain LF tertiary refined steel; subjecting the LF tertiary refined steel to refining slag formation treatment and composition adjustment treatment to ensure that the steel quality meets the requirements and to obtain steel with a high scrap steel ratio.

[0018] According to an embodiment of the first aspect of this application, LF secondary refined steel or LF tertiary refined steel is subjected to refining and slag-forming treatment and composition adjustment treatment, including: adding lime to LF secondary refined steel or LF tertiary refined steel for refining and slag-forming treatment to obtain desulfurized LF refined steel; adding an alloy to the desulfurized LF refined steel to ensure that the quality of the steel meets the requirements, thereby obtaining steel containing scrap steel.

[0019] According to the embodiments of the first aspect of this application, the alloy is selected from: ferrosilicon, high-carbon ferromanganese, ferrosilicon manganese, 40 titanium iron ball, metallic manganese, and high-carbon ferrochrome.

[0020] Secondly, this application provides a type of steel prepared according to the steelmaking method of the first aspect.

[0021] The steel smelting method and steel products of this application significantly increase the amount of scrap steel added to the refining furnace by optimizing the operation steps of adding only lime during converter tapping, adding scrap steel once during the LF refining process, and adding scrap steel twice after the furnace separation. This raises the proportion of scrap steel to over 55%, effectively utilizing scrap steel resources and achieving green development for steel plants. By controlling the refining slag to be in an oxidized slag state, promptly removing high-phosphorus ladle slag, and combining multiple ladles of molten steel, the steel smelting method of this application effectively avoids adverse factors such as phosphorus reversion and nitrogen increase during refining, ensuring stable steel quality. The steel smelting method of this application reduces the raw material cost of steelmaking by effectively utilizing scrap steel resources and optimizing the refining process. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of a steel smelting method provided in one embodiment of this application. Detailed Implementation

[0024] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0025] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0026] To address the problems of the prior art, this application provides a method for smelting molten steel. The method for smelting molten steel provided in this application will be described below. Figure 1 A schematic flowchart of a steel smelting method according to an embodiment of this application is shown.

[0027] Firstly, such as Figure 1 As shown, this application provides a method for smelting molten steel, comprising: smelting molten iron and scrap steel in a converter, adding only lime during the converter tapping process to ensure that the ladle slag is in an oxidizing slag state when the scrap steel is added for the first time in the refining stage, thereby obtaining oxidizing converter molten steel; performing LF refining on the converter molten steel, comprising: heating the converter molten steel to ≥1570℃ in an LF furnace, adding scrap steel for the first time and melting the scrap steel to obtain LF refined molten steel with melted scrap steel; raising the temperature of the LF refined molten steel with melted scrap steel to ≥1580℃ and removing the ladle slag in the LF furnace to prevent phosphorus reversion during the refining process, thereby obtaining LF refined molten steel after slag removal; dividing the LF refined molten steel after slag removal into two or more portions and placing them in corresponding LF furnaces, adding scrap steel for the second time in each portion and melting them to obtain LF secondary refined molten steel; and subjecting the LF secondary refined molten steel to refining slag formation treatment and composition adjustment treatment to ensure that the molten steel quality meets the requirements.

[0028] The steel smelting method described in this application significantly increases the amount of scrap steel added to the refining furnace by optimizing the operation steps in the converter tapping and LF refining processes, raising the proportion of scrap steel to over 55%. This effectively utilizes scrap steel resources and achieves green development for steel plants. By controlling the refining slag to be in an oxidizing slag state, promptly removing high-phosphorus ladle slag, and combining multiple ladles of molten steel, the steel smelting method of this application effectively avoids adverse factors such as phosphorus reversion and nitrogen increase during the refining process, ensuring stable steel quality. The steel smelting method of this application reduces the raw material costs of steel smelting by effectively utilizing scrap steel resources and optimizing the refining process.

[0029] The steel smelting method of this application focuses on optimizing the operation process of converter smelting and refining. The molten steel obtained from converter smelting is supplemented with an appropriate amount of lime; no slag-forming treatment is performed in the early stage of LF refining; and the slag in the ladle is removed by timely dumping. By employing a specific ladle-turning process and multiple key steps of scrap steel replenishment, the method successfully solves the problems of limited scrap steel addition, easy phosphorus increase and reversion, and unstable composition control in traditional refining processes. Furthermore, the steel smelting method of this application not only significantly increases the amount of scrap steel added but also ensures the quality and composition accuracy of the molten steel, which has significant technological innovation significance for the steel manufacturing industry and can help enterprises achieve green development.

[0030] In some embodiments, the molten iron and scrap steel in the converter are smelted in the converter, including: only lime is added to the molten steel in the converter without deep deoxidation treatment, so as to ensure that the molten steel does not increase phosphorus or can be partially dephosphorized when scrap steel is added for the first time in the refining stage, so as to obtain molten steel in the converter that does not increase phosphorus and has oxidizing properties.

[0031] The steel smelting method of this application embodiment, by adding only lime and without deep deoxidation during the converter smelting process, ensures that the molten steel does not increase phosphorus content or can undergo partial dephosphorization when scrap steel is added for the first time in the refining stage, thus creating conditions for dephosphorization treatment. It should be noted that deep deoxidation generally refers to removing the oxygen content in the molten steel to below 10 ppm. Not performing deep deoxidation means that aluminum is not added for deoxidation. This process essentially retains the oxygen in the converter molten steel, ensuring that the slag in the LF refining process is in an oxidized slag state. This oxidized slag can continue dephosphorization during the first addition and melting of scrap steel, ensuring that the scrap steel added before the sub-processing does not increase phosphorus content in the molten steel and can continue dephosphorization. This ensures that the phosphorus content in the molten steel is sufficiently low after sub-processing, thereby ensuring that the phosphorus content of the molten steel meets the target requirements after the second addition of scrap steel. It should be noted that the molten steel referred to here is a mixture containing molten iron and melted scrap steel.

[0032] In some embodiments, the smelting of molten iron and scrap steel in a converter includes: adding only lime during the converter tapping process, with the lime added at a rate of 2 kg / ton to 4 kg / ton of molten steel, to ensure that the ladle slag is in an oxidized slag state when scrap steel is first added during the refining stage, resulting in oxidized converter steel. That is, only the aforementioned amount of lime is added during the converter tapping process, without adding any alloys, to ensure that the ladle slag is in an oxidized slag state when scrap steel is first added during the refining stage, providing convenient conditions for subsequent operations. For example, only lime is added during the converter tapping process, with lime added at rates of 2.2 kg, 2.5 kg, 2.8 kg, 3 kg, 3.2 kg, 3.5 kg, 3.6 kg, 3.8 kg, and 3.9 kg per ton of molten steel, to control the refining slag to be in an oxidized slag state, utilizing the oxidized slag for dephosphorization, effectively preventing phosphorus increase in the molten steel when scrap steel is first added, and even promoting dephosphorization of the molten steel, while simultaneously preventing nitrogen increase in the molten steel under non-deoxidized conditions. It should be noted that dephosphorization must be carried out in an oxidizing atmosphere. In a reducing atmosphere, phosphorus pentoxide will be reduced to (Fe3P), meaning that a reducing atmosphere only increases phosphorus content. The dephosphorization reaction is exothermic; therefore, maintaining the oxidizing slag state and keeping the temperature stable can steer the reaction in a direction favorable to dephosphorization. Furthermore, under an oxidizing atmosphere, surface-active elements such as oxygen and sulfur in the slag and molten steel adsorb at the gas-liquid interface, occupying interfacial sites and hindering the dissociation and adsorption of N2 molecules. This prevents nitrogen from the air from entering the molten steel, thus inhibiting nitrogen absorption and reducing or preventing an increase in nitrogen content in the molten steel. Conversely, if the oxygen and sulfur content in the molten steel is low, such as after deoxidation treatment in the LF refining process, the number of active sites at the gas-liquid interface increases, leading to more significant nitrogen absorption and a substantial increase in nitrogen content.

[0033] In some embodiments, the composition of the lime, by mass percentage, needs to meet the following requirements: CaO ≥ 90%, SiO2 ≤ 1.5%, S ≤ 0.03%, loss on ignition ≤ 5%, and the particle size of the lime needs to be 10 mm to 60 mm. The amount of lime exceeding the upper limit of particle size should not exceed 10% of the batch inspection quantity, and the amount of lime exceeding the lower limit of particle size should not exceed 12% of the batch inspection quantity. Loss on ignition (LOI) is an indicator that measures the mass loss of lime after high-temperature ignition. After high-temperature ignition, CO2 gas will be released from the lime.

[0034] The steel smelting method of this application embodiment involves heating the converter steel to ≥1570°C in the LF furnace and then adding scrap steel. Before the scrap steel is fully added, no refining, slag forming and desulfurization operations are performed; only heating and stirring are carried out to promote the melting of the scrap steel.

[0035] In some embodiments, LF refining of converter steel further includes: in the step of heating the converter steel to ≥1570°C in the LF furnace, if slag foaming occurs in the molten steel of the LF furnace, aluminum blocks or modifiers are added for slag pressing treatment to suppress slag foaming.

[0036] The inventors of this application discovered during the improvement of the technical solution that excessive oxidation of molten steel, especially when the surface temperature of the molten steel is relatively high after power is supplied, causes the slag to foam. This results in the slag overflowing outside the ladle and burning the argon blowing pipe, making it impossible to effectively stir the molten steel and hindering normal production. The slag pressing treatment here, namely adding a deoxidizing alloy to remove some oxygen, prevents excessive foaming of the slag and thus avoids affecting normal production.

[0037] In some embodiments, during the LF refining step of the converter steel, aluminum blocks are added at a rate of 0.3 kg / ton to 0.6 kg / ton of molten steel. Exemplarily, aluminum blocks can be added at amounts of 0.32 kg / ton, 0.35 kg / ton, 0.38 kg / ton, 0.4 kg / ton, 0.42 kg / ton, 0.45 kg / ton, 0.48 kg / ton, 0.5 kg / ton, 0.54 kg / ton, 0.56 kg / ton, 0.58 kg / ton, and 0.59 kg / ton of molten steel.

[0038] Optionally, based on the mass percentage of the aluminum blocks, the aluminum blocks need to meet the following requirements: Al, 98.5%–99.4%; Fe, >0.50%; Ca, >0.05%; Si, 0.45%–0.6%; Mg, >0.20%; S, 0.01%–0.02%; the particle size of the aluminum blocks is 10mm–50mm, and the amount exceeding the upper and lower limits of the particle size is less than or equal to 8% of the total batch. In some embodiments, the aluminum blocks need to meet the following requirements: Al,

[0039] ≥99.4%; Fe, ≤0.50%; Ca, ≤0.05%; Si, ≤0.45%; Mg, ≤0.20%; S,

[0040] ≤0.01%. In some embodiments, the amount exceeding the upper and lower limits of particle size is less than or equal to 5% of the total batch size.

[0041] In some embodiments, during the LF refining step of the converter steel, the modifier is added to the LF furnace at a rate of 0.5 kg / ton to 1.2 kg / ton of steel.

[0042] Optionally, based on the mass percentage of the modifier, the modifier needs to meet the following requirements: SiO2, 5%–7%; Al, 35%–37%; Al2O3, 13%–15%; CaO, 18%–20%; MgO, >7.0%; Fe2O3, 2%–3%; S, 0.1%–0.12%; P, 0.08%–0.10%; C, 3%–5%; moisture, 0.8%–1.0%; the particle size of the modifier is 10 mm–40 mm, and the amount of particle size exceeding the upper and lower limits is less than or equal to 8% of the total batch size. In some embodiments, the modifier needs to meet the following requirements: SiO2, ≤5%; Al, ≥37%; Al2O3, ≥15%; CaO, ≥20%; MgO, ≤7.0%; Fe2O3, ≤2%; S, ≤0.10%; P, ≤0.08%; C, ≤3%; and moisture, ≤0.8%. In some embodiments, the amount exceeding the upper and lower limits is less than or equal to 5% of the total batch size.

[0043] The steel smelting method of this application involves adding scrap steel and melting it to obtain LF refined steel, then raising the temperature of the molten steel to ≥1580°C. At this point, the ladle slag is removed by pouring or scraping it out, thus removing the phosphorus contained in the ladle slag to prevent phosphorus reversion during subsequent refining. By pouring or scraping out the high-phosphorus oxide slag, phosphorus reversion during subsequent refining is avoided, preventing excessive phosphorus levels caused by the subsequent addition of scrap steel.

[0044] In some embodiments, the slag-refined LF steel is divided into two or more portions and placed in corresponding LF furnaces, and scrap steel is added to each portion for melting. This includes: pouring the slag-refined LF steel portion into an empty sub-ladle, defining the ladle from which the steel is poured as the mother ladle, and ensuring that the mother ladle and the sub-ladle are completely empty to allow for electrofusion heating after the addition of scrap steel, thereby obtaining secondary LF steel.

[0045] The steel smelting method of this application involves pouring the second or third ladle of molten steel, after the first addition of scrap steel and slag treatment, into an empty ladle. This process, where the steel in the ladle is divided and returned to the LF furnace, is called ladle splitting or ladle rewinding. The original ladle from which the molten steel is poured is called the mother ladle, and the empty ladle is called the daughter ladle. After the molten steel from the mother ladle is poured into the daughter ladle, sufficient space is reserved between the mother and daughter ladles to facilitate subsequent power supply and heating for electro-melting of scrap steel and refining operations. The ladle rewinding process can fully allocate the space resources of the molten steel and ladle, creating conditions for the subsequent addition of scrap steel and improving the scrap steel processing capacity of a single refining process.

[0046] The steel smelting method of this application embodiment uses an LF refining furnace as the sub-ladle, or simply an LF furnace. Scrap steel is added to both the mother ladle and the sub-ladle for melting treatment, thereby increasing the amount of scrap steel added in the refining process to obtain LF secondary refined steel.

[0047] The steel smelting method of this application embodiment, through the LF refining treatment in the above-mentioned LF furnace, uses molten steel containing melted scrap steel to remelt the scrap steel, which can effectively increase the proportion of scrap steel in the molten steel, thereby increasing the amount of refined scrap steel added in the steelmaking process more effectively and in a greener way.

[0048] In some embodiments, the steel smelting method further includes: dividing two or more portions of LF secondary refined steel obtained by melting scrap steel a second time into three or more portions, and adding scrap steel a third time to each portion of LF secondary refined steel to obtain LF tertiary refined steel; subjecting the LF tertiary refined steel to refining slag formation treatment and composition adjustment treatment to ensure that the steel quality meets the requirements and to obtain steel with a high scrap steel ratio.

[0049] Understandably, by sequentially adding and melting scrap steel to obtain molten steel containing molten scrap, it can be poured into multiple empty LF furnaces for further addition and melting of scrap steel, thereby increasing the proportion of scrap steel in the raw material molten steel. It should be noted that the multiple empty LF furnaces, which serve as sub-ladles, need to be preheated to the melting point temperature of the molten steel to prevent the molten steel from cooling and solidifying in the LF furnaces.

[0050] In some embodiments, the LF secondary refined molten steel or the LF tertiary refined molten steel is subjected to refining and slag-forming treatment and composition adjustment treatment, including: adding lime to the LF secondary refined molten steel or the LF tertiary refined molten steel for refining and slag-forming treatment to obtain desulfurized LF refined molten steel; adding an alloy to the desulfurized LF refined molten steel to ensure that the quality of the molten steel meets the requirements to obtain molten steel containing scrap steel.

[0051] The steel smelting method of this application embodiment involves adding lime / calcium oxide to LF secondary refined steel or LF tertiary refined steel for refining and slag formation treatment, and adding alloys for composition adjustment treatment, so that the quality of the molten steel meets the target requirements and molten steel containing scrap steel is obtained.

[0052] In some embodiments, the alloy is selected from one or more combinations of ferrosilicon, high-carbon ferromanganese, ferrosilicon manganese, 40 ferrotitanium spheres, metallic manganese, and high-carbon ferrochrome, by mass percentage. The composition of the alloy must meet the composition and content requirements in Tables 1 to 6 below.

[0053] Table 1 Ferrosilicon

[0054]

[0055] Table 2 High-carbon ferromanganese

[0056]

[0057]

[0058] Table 3 Silicon Manganese

[0059]

[0060] Table 4 40 Titanium Iron Balls

[0061]

[0062] Table 5 Metallic Manganese

[0063]

[0064]

[0065] Table 6 High-carbon ferrochrome

[0066]

[0067] It should be noted that after obtaining molten steel from scrap steel, different types of steel can be produced by adding different alloys. This application does not specify the composition, content, or corresponding amount of the alloy, and the amount, composition, and content can be added or adjusted as needed.

[0068] It should also be noted that, due to impurities in the added scrap steel and the raw materials added during the smelting process, such as adding lime for dephosphorization, adding lime and aluminum blocks for slag formation and deoxidation, some molten steel will be carried away when the steel slag is poured out. Therefore, the final weight of the molten steel may be less than the sum of the total weight of the molten iron and scrap steel.

[0069] The technical solution of this application will be further explained below through specific embodiments and comparative examples to demonstrate that the steel smelting method of this application can significantly increase the amount of scrap steel added to the molten steel. The following are the requirements for some of the materials used in the comparison of the comparative examples and embodiments and their available sources: Typical steel grade, model LG1500, available from Hunan Lianyuan Iron and Steel Co., Ltd.; Lime: composition and content are detailed in Table 7 below, available from Hunan Lianyuan Iron and Steel Co., Ltd.

[0070] Table 7

[0071]

[0072] Aluminum blocks: The composition and content requirements are detailed in Table 8 below. They were purchased from Shandong Shengyuan Ter Metal Technology Co., Ltd. and Hunan Lianggong Zhenxing Co., Ltd.

[0073] Table 8

[0074]

[0075] The required content of the modifier components is shown in Table 9 below; purchased from Xixia County Yaohui Metallurgical Materials Co., Ltd.

[0076] Table 9

[0077]

[0078] Slag-forming agent: The main component is lime; purchased from Hunan Lianyuan Iron and Steel Co., Ltd.

[0079] Alloys: mainly include ferrosilicon (Ordos Xijin Mining and Metallurgy Co., Ltd.), high-carbon ferromanganese (Chongqing Qianrui Manganese Industry Co., Ltd., Loudi Lianchuang Renewable Resources Co., Ltd.), ferrosilicon manganese (Tongren Wanshan Jinsheng Manganese Industry Co., Ltd., Loudi Lianchuang Renewable Resources Co., Ltd.), 40 titanium-iron balls (Jinzhou Hongming Special Alloy Co., Ltd., Jinzhou Guotai Industrial Co., Ltd., Changzhou Huanan Nonferrous Metals Co., Ltd.), metallic manganese (Hunan Bosheng Ferroalloy Co., Ltd.), and high-carbon ferrochrome (Wuhan Hengzhengrui Technology Co., Ltd., Guizhou Dingxiang Metallurgical Furnace Materials Co., Ltd.). For the specific composition of the above alloys, please refer to the general requirements in Tables 1-6.

[0080] Example 1

[0081] This embodiment provides a method for smelting molten steel, including:

[0082] The molten iron and scrap steel in the converter are smelted in the following manner: the phosphorus content of the steel from converter A is 0.009% and the oxygen content is 401 ppm; the phosphorus content of the steel from converter B is 0.0089% and the oxygen content is 421 ppm. No deep deoxidation treatment is performed on the molten steel in the converter, ensuring that the oxygen content of the molten steel in the argon station is 361 ppm in heat A and 380 ppm in heat B. This ensures that the molten steel does not increase phosphorus content or can undergo partial dephosphorization when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel that does not increase phosphorus content. Specifically, only lime is added during the converter tapping process, with lime addition amounts of 2.2 kg / ton of molten steel in heats A and 2.3 kg / ton of molten steel in heats B, respectively. This ensures that the ladle slag is in an oxidizing slag state when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel.

[0083] The process of LF refining of converter steel includes: heating the converter steel to 1570℃ in the LF furnace; if slag foaming occurs in the molten steel in the LF furnace, adding aluminum blocks at a rate of 0.49 kg / ton of molten steel for slag pressing treatment to prevent slag from overflowing from the ladle; adding 29 tons and 31 tons of scrap steel to heats A and B respectively and melting the scrap steel to obtain LF refined molten steel with melted scrap steel.

[0084] The temperature of the LF refining molten steel, which is made by melting scrap steel, is raised to 1580℃, and the ladle slag in the LF furnace is removed to prevent phosphorus reversion during the refining process, so as to obtain LF refining molten steel after slag removal.

[0085] The two bags of LF refined steel after slag removal were divided into three portions and placed in the corresponding LF furnaces. Scrap steel was then added to each portion for melting, including:

[0086] The slag-refined LF steel is poured out into an empty sub-ladle. The ladle from which the steel is poured out is defined as the mother ladle. The emptying of the mother ladle and the sub-ladle ensures that the steel can be electrofused and heated after the addition of scrap steel, thus obtaining LF secondary refined steel.

[0087] The LF secondary refining steel undergoes refining and slag formation treatment as well as composition adjustment treatment, including:

[0088] Lime is added to the LF secondary refining molten steel for refining and slag formation treatment to obtain desulfurized LF refined molten steel;

[0089] Alloys are added to the desulfurized LF refined steel to ensure that the steel quality meets the requirements.

[0090] Example 2

[0091] This embodiment provides a method for smelting molten steel, including:

[0092] The molten iron and scrap steel in the converter are smelted in the following ways: Heat D has a phosphorus content of 0.0089% and an oxygen content of 451 ppm; Heat E has a phosphorus content of 0.0086% and an oxygen content of 471 ppm. No deep deoxidation treatment is performed on the molten steel in the converter, ensuring that the oxygen content in the argon station is 401 ppm in Heat D and 422 ppm in Heat E. This ensures that the molten steel does not increase phosphorus content or can undergo partial dephosphorization when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel without phosphorus increase. Specifically, only lime is added during the converter tapping process; the lime addition amounts for Heats D and E are 2.3 kg / ton of molten steel and 2.4 kg / ton of molten steel, respectively. This ensures that the ladle slag is in an oxidizing slag state when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel.

[0093] The process of LF refining of converter steel includes: heating the converter steel to 1570℃ in the LF furnace; if slag foaming occurs in the molten steel in the LF furnace, adding aluminum blocks at a rate of 0.5 kg / ton of molten steel for slag pressing treatment to prevent slag from overflowing from the ladle; adding 31 tons and 32 tons of scrap steel to furnaces D and E respectively and melting the scrap steel to obtain LF refined molten steel with melted scrap steel.

[0094] The temperature of the LF refining molten steel, which is made by melting scrap steel, is raised to 1580℃, and the ladle slag in the LF furnace is removed to prevent phosphorus reversion during the refining process, so as to obtain LF refining molten steel after slag removal.

[0095] The two bags of LF refined steel after slag removal were divided into three portions and placed in the corresponding LF furnaces. Scrap steel was then added to each portion for melting, including:

[0096] The slag-refined LF steel is poured out into an empty sub-ladle. The ladle from which the steel is poured out is defined as the mother ladle. The emptying of the mother ladle and the sub-ladle ensures that the steel can be electrofused and heated after the addition of scrap steel, thus obtaining LF secondary refined steel.

[0097] The LF secondary refined steel is subjected to refining and slag-forming treatment and composition adjustment treatment, including: adding lime to the LF secondary refined steel for refining and slag-forming treatment to obtain desulfurized LF refined steel; adding alloys to the desulfurized LF refined steel to ensure that the steel quality meets the requirements.

[0098] Example 3

[0099] This embodiment provides a method for smelting molten steel, including:

[0100] The molten iron and scrap steel in the converter are smelted in the following ways: Heat G has a phosphorus content of 0.0087% and an oxygen content of 431 ppm; Heat H has a phosphorus content of 0.0085% and an oxygen content of 455 ppm. No deep deoxidation treatment is performed on the molten steel in the converter, ensuring that the oxygen content in the argon station is 381 ppm for Heat G and 398 ppm for Heat H. This ensures that the molten steel does not increase phosphorus content or can undergo partial dephosphorization when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel without phosphorus increase. Specifically, only lime is added during the converter tapping process; the lime addition amounts for Heat G and H are 2.4 kg / ton of molten steel and 2.5 kg / ton of molten steel, respectively. This ensures that the ladle slag is in an oxidizing slag state when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel.

[0101] The process of LF refining of converter steel includes: heating the converter steel to 1570℃ in the LF furnace; if slag foaming occurs in the molten steel in the LF furnace, adding aluminum blocks at a rate of 0.49 kg / ton of molten steel for slag pressing treatment to prevent slag from overflowing from the ladle; adding 30 tons and 32 tons of scrap steel to heats G and H respectively and melting the scrap steel to obtain LF refined molten steel with melted scrap steel.

[0102] The temperature of the LF refining molten steel, which is made by melting scrap steel, is raised to 1580℃, and the ladle slag in the LF furnace is removed to prevent phosphorus reversion during the refining process, so as to obtain LF refining molten steel after slag removal.

[0103] The two bags of LF refined steel after slag removal were divided into three portions and placed in the corresponding LF furnaces. Scrap steel was then added to each portion for melting, including:

[0104] The slag-refined LF steel is poured out into an empty sub-ladle. The ladle from which the steel is poured out is defined as the mother ladle. The emptying of the mother ladle and the sub-ladle ensures that the steel can be electrofused and heated after the addition of scrap steel, thus obtaining LF secondary refined steel.

[0105] The LF secondary refining steel undergoes refining and slag formation treatment as well as composition adjustment treatment, including:

[0106] Lime is added to the LF secondary refining molten steel for refining and slag formation treatment to obtain desulfurized LF refined molten steel;

[0107] Alloys are added to the desulfurized LF refined steel to ensure that the steel quality meets the requirements.

[0108] Example 4

[0109] This embodiment provides a method for smelting molten steel, including:

[0110] The molten iron and scrap steel in the converter are smelted in the following ways: Heat J has a phosphorus content of 0.0087% and an oxygen content of 481 ppm; Heat K has a phosphorus content of 0.0085% and an oxygen content of 491 ppm. No deep deoxidation treatment is performed on the molten steel in the converter, ensuring that the oxygen content in the argon station is 431 ppm for Heat J and 462 ppm for Heat K. This ensures that the molten steel does not increase phosphorus content or can undergo partial dephosphorization when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel without phosphorus increase. Specifically, only lime is added during the converter tapping process; the lime addition amounts for Heat J and K are 2.2 kg / ton of molten steel and 2.3 kg / ton of molten steel, respectively. This ensures that the ladle slag is in an oxidizing slag state when scrap steel is added for the first time during the refining stage, resulting in oxidizing molten steel.

[0111] The process of LF refining of converter steel includes: heating the converter steel to 1570℃ in the LF furnace; if slag foaming occurs in the molten steel in the LF furnace, adding a modifier at a dosage of 0.53 kg / ton of molten steel for slag pressing treatment to prevent slag from overflowing from the ladle; adding 30 tons and 28 tons of scrap steel to heats J and K respectively and melting them to obtain LF refined molten steel with melted scrap steel.

[0112] The temperature of the LF refining molten steel, which is made by melting scrap steel, is raised to 1580℃, and the ladle slag in the LF furnace is removed to prevent phosphorus reversion during the refining process, so as to obtain LF refining molten steel after slag removal.

[0113] The two bags of LF refined steel after slag removal were divided into three portions and placed in the corresponding LF furnaces. Scrap steel was then added to each portion for melting, including:

[0114] The slag-refined LF steel is poured out into an empty sub-ladle. The ladle from which the steel is poured out is defined as the mother ladle. The emptying of the mother ladle and the sub-ladle ensures that the steel can be electrofused and heated after the addition of scrap steel, thus obtaining LF secondary refined steel.

[0115] The LF secondary refined steel is subjected to refining and slag-forming treatment and composition adjustment treatment, including: adding lime to the LF secondary refined steel for refining and slag-forming treatment to obtain desulfurized LF refined steel; adding alloys to the desulfurized LF refined steel to ensure that the steel quality meets the requirements.

[0116] Example 5

[0117] This embodiment provides a method for smelting molten steel, including:

[0118] The molten iron and scrap steel in the converter are smelted in the converter, including: the phosphorus content of the steel from converter M is 0.0083% and the oxygen content is 511ppm, and the phosphorus content of the steel from converter N is 0.0080% and the oxygen content is 535ppm. No deep deoxidation treatment is performed on the molten steel in the converter, so that the oxygen content of the molten steel in the argon station is 465ppm in heat M and 483ppm in heat N. This ensures that the molten steel does not increase phosphorus or can undergo partial dephosphorization when scrap steel is added for the first time in the refining stage, resulting in oxidizing converter steel that does not increase phosphorus. Specifically, only lime is added during the converter tapping process, with lime addition amounts of 2.5kg / ton of molten steel in heats M and 2.6kg / ton of molten steel in heats N, respectively. This ensures that the ladle slag is in an oxidizing slag state when scrap steel is added for the first time in the refining stage, resulting in oxidizing converter steel.

[0119] The process of LF refining of converter steel includes: heating the converter steel to 1570℃ in the LF furnace; if slag foaming occurs in the molten steel in the LF furnace, adding a modifier at a dosage of 0.55 kg / ton of molten steel for slag pressing treatment to prevent slag from overflowing from the ladle; adding scrap steel and melting the scrap steel to obtain LF refined molten steel with melted scrap steel.

[0120] The temperature of the LF refining molten steel, which is made by melting scrap steel, is raised to 1580℃, and the ladle slag in the LF furnace is removed to prevent phosphorus reversion during the refining process, so as to obtain LF refining molten steel after slag removal.

[0121] The two bags of LF refined steel after slag removal were divided into three portions and placed in the corresponding LF furnaces. Scrap steel was then added to each portion for melting, including:

[0122] The slag-refined LF steel is poured out into an empty sub-ladle. The ladle from which the steel is poured out is defined as the mother ladle. The emptying of the mother ladle and the sub-ladle ensures that the steel can be electrofused and heated after the addition of scrap steel, thus obtaining LF secondary refined steel.

[0123] The LF secondary refined steel is subjected to refining and slag-forming treatment and composition adjustment treatment, including: adding lime to the LF secondary refined steel for refining and slag-forming treatment to obtain desulfurized LF refined steel; adding alloys to the desulfurized LF refined steel to ensure that the steel quality meets the requirements.

[0124] Example 6

[0125] This embodiment provides a method for smelting molten steel, including:

[0126] The molten iron and scrap steel in the converter are smelted in the converter, including: the phosphorus content of the steel from converter M is 0.0083% and the oxygen content is 511ppm, and the phosphorus content of the steel from converter N is 0.0080% and the oxygen content is 535ppm. No deep deoxidation treatment is performed on the molten steel in the converter, so that the oxygen content of the molten steel in the argon station is 465ppm in heat M and 483ppm in heat N. This ensures that the molten steel does not increase phosphorus or can undergo partial dephosphorization when scrap steel is added for the first time in the refining stage, resulting in oxidizing converter steel that does not increase phosphorus. Specifically, only lime is added during the converter tapping process, with lime addition amounts of 2.5kg / ton of molten steel in heats M and 2.65kg / ton of molten steel in heats N, respectively. This ensures that the ladle slag is in an oxidizing slag state when scrap steel is added for the first time in the refining stage, resulting in oxidizing converter steel.

[0127] The process of LF refining of converter steel includes: heating the converter steel to 1570℃ in the LF furnace; if slag foaming occurs in the molten steel in the LF furnace, adding a modifier at a dosage of 0.55 kg / ton of molten steel for slag pressing treatment to prevent slag from overflowing from the ladle; adding scrap steel and melting the scrap steel to obtain LF refined molten steel with melted scrap steel.

[0128] The temperature of the LF refining molten steel, which is made by melting scrap steel, is raised to 1580℃, and the ladle slag in the LF furnace is removed to prevent phosphorus reversion during the refining process, so as to obtain LF refining molten steel after slag removal.

[0129] The two LF refined molten steels after slag removal are added to scrap steel for melting, including: pouring part of the LF refined molten steel after slag removal into an empty sub-ladle, defining the ladle from which the molten steel is poured out as the mother ladle, and ensuring that the mother ladle and the sub-ladle are completely empty to allow for electrofusion heating after the scrap steel is added, thus obtaining LF secondary refined molten steel;

[0130] The LF secondary refined steel is subjected to refining and slag-forming treatment and composition adjustment treatment, including: adding lime to the LF secondary refined steel for refining and slag-forming treatment to obtain desulfurized LF refined steel; adding alloys to the desulfurized LF refined steel to ensure that the steel quality meets the requirements.

[0131] Comparative Example 1

[0132] This comparative example provides an existing method for smelting molten steel, comprising:

[0133] The molten steel in the converter is smelted in the converter. The phosphorus content of the steel from converter P is 0.0110% and the oxygen content is 560ppm. The phosphorus content of the steel from converter Q is 0.0112% and the oxygen content is 580ppm. During the tapping process of converter P, 300kg of ferrosilicon, 2000kg of high manganese, 201kg of aluminum blocks, 210kg of carbon powder, and 400kg of lime are added. During the tapping process of converter Q, 320kg of ferrosilicon, 2030kg of high manganese, 205kg of aluminum blocks, 212kg of carbon powder, and 405kg of lime are added.

[0134] The LF refining process for converter steel includes: heating the converter steel to 1570°C in an LF furnace, adding 30 tons of scrap steel to furnaces P and Q respectively and melting the scrap steel to obtain LF refined steel with melted scrap steel.

[0135] The temperature of the LF refining molten steel, which is made from melted scrap steel, is raised to 1580℃. In the refining process, heat P adds 1500kg of lime and 215kg of aluminum blocks to form slag and desulfurize. During the slag-forming process, 1001kg of silicon manganese is added to bring the sulfur content to 0.003% and the phosphorus content of the molten steel to 0.014%. In the refining process, heat Q adds 1405kg of lime and 225kg of aluminum blocks to form slag and desulfurize. During the slag-forming process, 1011kg of silicon manganese is added to bring the sulfur content to 0.002% and the phosphorus content of the molten steel to 0.0139%.

[0136] The desulfurized LF refined molten steel was divided into three packages from two separate packages and placed in corresponding LF furnaces. Scrap steel was added to each package for melting to obtain LF secondary refined molten steel. Each package of molten steel was then mixed with 30 tons of scrap steel. Samples of the molten steel were taken, and the phosphorus content was found to be 0.018%, 0.0179%, and 0.0182%, respectively. The phosphorus content of the molten steel exceeded the standard, forcing a change in steel grade and resulting in the failure of the repackaging process.

[0137] Comparative Example 2

[0138] This comparative example provides a method for smelting molten steel, comprising:

[0139] The molten steel in the converter is smelted in the converter. The phosphorus content of the steel from converter S is 0.0106% and the oxygen content is 590ppm. The phosphorus content of the steel from converter T is 0.0108% and the oxygen content is 601ppm. 405kg and 436kg of lime are added respectively during the tapping process of converter S and T.

[0140] The process of refining molten steel in a converter furnace by LF includes: heating the molten steel in the converter furnace to 1570°C, adding 28 tons and 30 tons of scrap steel to furnaces S and T respectively and melting the scrap steel to obtain LF refined molten steel with melted scrap steel.

[0141] The temperature of the LF refining molten steel, which is made from melted scrap steel, is raised to 1580℃. In the refining process of heat S, 1600kg of lime and 315kg of aluminum blocks are added for slag formation and desulfurization. In the slag formation process, 2001kg of silicon manganese and 985kg of high manganese are added to bring the sulfur content to 0.0028% and the phosphorus content of the molten steel to 0.0141%. In the refining process of heat T, 1505kg of lime and 335kg of aluminum blocks are added for slag formation and desulfurization. In the slag formation process, 2051kg of silicon manganese and 1085kg of high manganese are added to bring the sulfur content to 0.0025% and the phosphorus content of the molten steel to 0.0143%.

[0142] The desulfurized LF refined molten steel was divided into three portions and placed in corresponding LF furnaces. Scrap steel was added to each portion for melting to obtain LF secondary refined molten steel. Each portion of the subcontracted molten steel was then mixed with 25 tons of scrap steel. Samples of the molten steel were taken, and the phosphorus content was found to be 0.0178%, 0.0176%, and 0.0180%, respectively. The phosphorus content of the molten steel exceeded the standard, forcing a change in steel grade and resulting in the failure of the subcontracting.

[0143] Comparative Example 3

[0144] This comparative example provides a method for smelting molten steel, including: smelting molten steel in a converter, wherein the phosphorus content of the steel tapped from converter V is 0.0109% and the oxygen content is 650 ppm, and the phosphorus content of the steel tapped from converter W is 0.0108% and the oxygen content is 641 ppm; 420 kg and 430 kg of lime are added respectively during the tapping process of converters V and W.

[0145] The process of refining molten steel in a converter furnace by LF includes: heating the molten steel in the converter furnace to 1570°C, adding 33 tons and 29 tons of scrap steel respectively and melting them to obtain LF-refined molten steel with melted scrap steel.

[0146] The temperature of the LF refining molten steel, which melts scrap steel, is raised to 1580℃. During the refining process, 1600 kg of lime is added for slag formation and desulfurization. No alloy slag is added during the slag formation process. The sulfur content of the V heat is 0.026%, and the phosphorus content is 0.0091%; the sulfur content of the W heat is 0.029%, and the phosphorus content is 0.0090%.

[0147] The molten steel is not discarded as slag. Instead, it is divided into three packages from two and placed in the corresponding LF furnaces. Scrap steel is added to each package for melting to obtain LF secondary refined molten steel.

[0148] After subcontracting, heats V and W each added 30 tons of scrap steel and electrolytic scrap steel, with the molten steel temperature controlled at 1580℃. Heat V then added 320 kg of aluminum ingots, 1000 kg of lime, and 1500 kg of ferromanganese slag for desulfurization and preliminary composition adjustment; heat W then added 305 kg of aluminum ingots, 1100 kg of lime, and 1550 kg of ferromanganese slag for desulfurization and preliminary composition adjustment. After 8 minutes of slag formation and desulfurization, samples of the molten steel were taken. The sulfur content was 0.0051%, 0.0056%, and 0.0048%, respectively, and the phosphorus content was 0.0176%, 0.0174%, and 0.0179%, respectively. The phosphorus content exceeded the standard, forcing a change in steel grade, and the subcontracting failed.

[0149] It should be noted that in Examples 1-6, the molten iron and scrap steel are smelted in a converter. The scrap steel refers to the scrap steel added at one time, some of which is added to the converter before the molten iron is added, so as to use the heat of the molten iron to promote its melting. The remaining scrap steel is added in the LF refining furnace.

[0150] Referring to Table 4 below, a process comparison of the molten steel obtained from Examples 1-6 and Comparative Examples 1-3 reveals the following:

[0151] Table 4. Comparison of smelting processes between Examples 1-6 and Comparative Examples 1-3

[0152]

[0153] As shown in Table 4 above, the existing steelmaking processes using scrap steel in Comparative Examples 1-3 have low scrap steel addition amounts, low scrap steel proportions, and are prone to phosphorus and nitrogen reversion, resulting in unstable steel quality, i.e., unstable steel composition control. In contrast to Comparative Examples 1-3, the steelmaking method provided in this application, through the aforementioned technical improvements, makes it less prone to phosphorus and nitrogen reversion in the steel produced in Examples 1-6 even with the addition of higher scrap steel content. It also maintains the phosphorus content in the produced steel below 0.015 wt.% and the nitrogen content below 0.007 wt.%, enabling stable control of the steel composition. Furthermore, it significantly increases the amount of scrap steel added, raising the proportion of scrap steel in the steel to over 55%, effectively utilizing scrap steel resources and achieving green development for steel plants.

[0154] 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 process described above can be referred to the corresponding process 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 smelting molten steel, characterized in that, include: The molten iron and scrap steel in the converter are smelted in the converter. Only lime is added during the tapping process to ensure that the ladle slag is in an oxidized slag state when scrap steel is added for the first time in the refining stage, so as to obtain oxidized converter molten steel. LF refining of converter steel includes: heating the converter steel to ≥1570℃ in an LF furnace, adding scrap steel for the first time and melting the scrap steel to obtain LF refined steel with melted scrap steel; The temperature of the LF refining molten steel, which is made by melting scrap steel, is raised to ≥1580℃, and the ladle slag in the LF furnace is removed to prevent phosphorus reversion during the refining process, so as to obtain LF refining molten steel after slag removal. The slag-refined LF steel is divided into two or more portions and placed in the corresponding LF furnaces. Scrap steel is added to each portion for a second melting process to obtain secondary LF steel. The LF secondary refined molten steel undergoes refining and slag-forming treatment as well as composition adjustment treatment to ensure that the molten steel quality meets the requirements and to obtain molten steel with a high scrap steel ratio.

2. The method for smelting molten steel according to claim 1, characterized in that, The process of smelting molten iron and scrap steel in a converter includes: The molten steel in the converter is only mixed with lime and does not undergo deep deoxidation treatment to ensure that the molten steel does not increase phosphorus when scrap steel is added for the first time in the refining stage, or to allow for partial dephosphorization treatment to obtain converter molten steel that does not increase phosphorus and has oxidizing properties. Preferably, the converter smelting of molten iron and scrap steel in the converter includes: Only lime is added during the tapping process of the converter, and the amount of lime added is 2 kg / ton of molten steel to 4 kg / ton of molten steel; Preferably, the composition of the lime, based on the mass percentage of the lime, needs to meet the following requirements: CaO ≥ 90%, SiO2 ≤ 1.5%, S ≤ 0.03%, loss on ignition ≤ 5%, and the particle size of the lime needs to be 10 mm to 60 mm. The amount of lime exceeding the upper limit of particle size shall not exceed 10% of the batch inspection quantity, and the amount of lime exceeding the lower limit of particle size shall not exceed 12% of the batch inspection quantity.

3. The method for smelting molten steel according to claim 1, characterized in that, The LF refining of converter steel also includes: in the step of heating the converter steel to ≥1570℃ in the LF furnace, if slag foaming occurs in the molten steel of the LF furnace, aluminum blocks and / or modifiers are added for slag pressing treatment to suppress slag foaming.

4. The method for smelting molten steel according to claim 3, characterized in that, In the step of LF refining of molten steel in the converter, the aluminum blocks are added to the LF furnace at a rate of 0.3 kg / ton to 0.6 kg / ton of molten steel, or the modifier is added at a rate of 0.5 kg / ton to 1.2 kg / ton of molten steel.

5. The method for smelting molten steel according to claim 3 or 4, characterized in that, Based on the mass percentage of the aluminum blocks, the aluminum blocks need to meet the following requirements: Al, 98.5%–99.4%; Fe, >0.50%; Ca, >0.05%; Si, 0.45%–0.6%; Mg, >0.20%; S, 0.01%–0.02%; the particle size of the aluminum blocks is 10mm–50mm, and the amount exceeding the upper and lower limits is less than or equal to 8% of the total batch size; preferably, the aluminum blocks need to meet the following requirements: Al, ≥99.4%; Fe, ≤0.50%; Ca, ≤0.05%; Si, ≤0.45%; Mg, ≤0.20%; S, ≤0.01%; preferably, the amount exceeding the upper and lower limits is less than or equal to 5% of the total batch size; And / or, Based on the mass percentage of the modifier, the modifier needs to meet the following requirements: SiO2, 5%–7%; Al, 35%–37%; Al2O3, 13%–15%; CaO, 18%–20%; MgO, >7.0%; Fe2O3, 2%–3%; S, 0.1%–0.12%; P, 0.08%–0.10%; C, 3%–5%; moisture, 0.8%–1.0%. Preferably, the modifier needs to meet the following requirements: S The modifier has the following particle sizes: iO2, ≤5%; Al, ≥37%; Al2O3, ≥15%; CaO, ≥20%; MgO, ≤7.0%; Fe2O3, ≤2%; S, ≤0.10%; P, ≤0.08%; C, ≤3%; and moisture, ≤0.8%. The particle size of the modifier is 10mm to 40mm, and the amount exceeding the upper and lower limits is less than or equal to 8% of the total batch size. Preferably, the amount exceeding the upper and lower limits is less than or equal to 5% of the total batch size.

6. The method for smelting molten steel according to claim 1, characterized in that, The process of dividing the slag-refined LF steel into two or more portions and placing them in corresponding LF furnaces, then adding scrap steel to each portion for melting, includes: The slag-refined LF steel is poured out into an empty sub-ladle. The ladle from which the steel is poured out is defined as the mother ladle. The emptying of the mother ladle and the sub-ladle ensures that the steel can be electrofused and heated after the addition of scrap steel, thus obtaining LF secondary refined steel.

7. The method for smelting molten steel according to claim 1, characterized in that, Also includes: Divide the LF secondary refined steel obtained by adding scrap steel a second time into three or more portions, and add scrap steel a third time into each portion of LF secondary refined steel to obtain LF tertiary refined steel. The LF tertiary refining molten steel undergoes refining and slag-forming treatment as well as composition adjustment treatment to ensure that the molten steel quality meets the requirements and to obtain molten steel with a high scrap ratio.

8. The method for smelting molten steel according to claim 1 or 7, characterized in that, The refining and slag-forming treatment and composition adjustment treatment of LF secondary refined steel or LF tertiary refined steel include: Lime is added to LF secondary refining molten steel or LF tertiary refining molten steel for refining and slag formation treatment to obtain desulfurized LF refining molten steel. Alloys are added to the desulfurized LF refined steel to ensure that the quality of the steel meets the requirements, resulting in steel containing scrap steel.

9. The method for smelting molten steel according to claim 8, characterized in that, The alloy is selected from ferrosilicon, high-carbon ferromanganese, ferrosilicon manganese, 40 titanium iron balls, metallic manganese, and high-carbon ferrochrome by mass percentage.

10. A type of steel, characterized in that, Prepared by the smelting method according to any one of claims 1-9.

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