A method for synergistic control of sulfide and oxide inclusions in steel

Abstract

This invention provides a method for synergistically controlling sulfide and oxide inclusions in steel, belonging to the field of metallurgy. The method includes: pre-treating molten iron with desulfurization and slag removal to obtain desulfurized molten iron; smelting the desulfurized molten iron in a converter to obtain converter steel; refining the converter steel using LF refining, and performing alloying and slag deoxidation treatment during the LF refining process to obtain first refined steel; refining the first refined steel using RH refining, and controlling the following parameters of the RH refining process: calcium wire feed rate, calcium wire feed speed, soft blowing flow rate, and soft blowing time to obtain second refined steel; casting the second refined steel, and performing ladle side blowing during the casting process to obtain a cast billet. By moving the alloying operation to the LF refining process, controlling the parameters of the RH refining process, and performing ladle side blowing with inert gas in the later stages of casting, the quantity and size of sulfide and oxide inclusions in the steel are synergistically controlled.

Description

Technical Field

[0001] This application relates to the field of steelmaking technology, and in particular to a method for synergistically controlling sulfide and oxide inclusions in steel. Background Technology

[0002] Inclusion control in steel has always been a key research topic in the iron and steel metallurgy field, especially the control of non-metallic inclusions. In recent years, with the increasing demands for high-quality steel production, inclusion control has become increasingly critical. Based on composition, inclusions are generally classified into sulfide inclusions (Type A), alumina inclusions (Type B), silicate inclusions (Type C), spherical oxide inclusions (Type D), and single-particle spherical inclusions (Type Ds). Each type of inclusion has an adverse effect on steel quality, such as easily leading to stress concentration and fracture.

[0003] For most steel grades, sulfide inclusions and oxide inclusions have always been difficult to control. To control sulfide inclusions in steel, besides controlling the sulfur content in raw materials and performing KR pretreatment and LF desulfurization, calcium treatment (calcium feeding) is commonly used to modify sulfides, primarily converting the more harmful MnS inclusions into CaS inclusions. For oxide inclusions in steel, Al-based or Si-Mn-based deoxidizers are mainly used for deoxidation. Furthermore, for hot-rolled steel grades, calcium treatment is generally used to modify high-melting-point Al2O3 inclusions into low-melting-point Ca-Al-O inclusions to prevent nozzle blockage. Calcium treatment during the refining process is a common method for controlling sulfide and oxide inclusions. Most steel mill practices show that when the calcium feed amount is low, MnS inclusions cannot be effectively controlled, while when the calcium feed amount is high, Al2O3 inclusions are modified into large-sized Ca-Al-O inclusions (>20μm), which is detrimental to improving steel quality. To address this issue, some steel mills have developed precise calcium treatment models, but the application results have been unsatisfactory. Therefore, there is an urgent need to develop a method that can synergistically control sulfide and oxide inclusions in steel. Summary of the Invention

[0004] This application provides a method for synergistically controlling sulfide and oxide inclusions in steel to solve the following technical problem: how to synergistically control the quantity and size of sulfide and oxide inclusions in steel.

[0005] This application provides a method for synergistically controlling sulfide and oxide inclusions in steel, the method comprising:

[0006] The molten iron is pretreated for desulfurization and slag is removed to obtain desulfurized molten iron;

[0007] The desulfurized molten iron is then smelted in a converter to obtain converter steel.

[0008] The converter steel is subjected to LF refining, and alloying and slag deoxidation are carried out during the LF refining process to obtain the first refined steel.

[0009] The first refined molten steel is subjected to RH refining, and the following parameters of the RH refining are controlled: calcium wire feed rate, calcium wire feed speed, soft blowing flow rate and soft blowing time to obtain the second refined molten steel.

[0010] The second refined steel is cast, and side blowing of the ladle is performed during the casting process to obtain a billet.

[0011] Optionally, the value of the calcium wire feeding rate satisfies the following relationship:

[0012] V = 2 + (d 实测 -d min ) / (d max -d min )

[0013] In the formula, V represents the numerical value of the calcium wire feeding speed, in m / s; d 实测 d max d min These represent the actual thickness, maximum thickness, and minimum thickness values ​​in the ladle top slag thickness detection, all in mm.

[0014] Optionally, the soft blowing time is 6 to 8 minutes, and the soft blowing flow rate satisfies the following relationship:

[0015] L = 0.5 + (d 实测 -d min ) / 100

[0016] In the formula, L represents the numerical value of the soft blowing flow rate, with units of NL / (min·t steel); d 实测 d min These represent the actual thickness value and the minimum thickness value in the ladle top slag thickness detection, respectively, both in mm.

[0017] Optionally, the actual thickness value in the ladle top slag thickness detection is 50mm to 120mm.

[0018] Optionally, the side blowing of the ladle during the casting process includes:

[0019] During the later stage of casting, when the ladle is filled to 1 / 4, ladle side blowing is performed. After the ladle slag detection system alarms, the ladle side blowing is stopped. The ladle side blowing uses inert gas, and the flow rate of the inert gas is 1.5NL / (min·t steel) to 2.0NL / (min·t steel).

[0020] Optionally, the raw material for the slag deoxidation treatment is aluminum granules, and the amount of aluminum granules added is 0.6 kg / t steel to 0.7 kg / t steel, and the aluminum granules are added in batches of 2 to 3 batches.

[0021] Optionally, the number of times the slag is removed is ≥2, the total time for removing the slag is ≤10min, and the area of ​​the shiny surface of the slag is ≥95%.

[0022] Optionally, the temperature of the molten iron is >1330℃, and the [S] content in the molten iron is ≤0.06% by mass fraction; the oxygen activity of the converter steel is ≤0.045%.

[0023] Optionally, the ladle used to receive the molten iron is an online turnover ladle with an age of ≥5 years.

[0024] Optionally, the number density of MnS inclusions and Ca-Al-O system inclusions in the cast billet is ≤0.30 inclusions / mm. 2 The size of the MnS inclusions is ≤6μm, and the size of the Ca-Al-O inclusions is ≤20μm.

[0025] The technical solutions provided in this application have the following advantages compared with the prior art:

[0026] This application provides a method for synergistically controlling sulfide and oxide inclusions in steel, comprising: pre-treating molten iron with desulfurization and slag removal to obtain desulfurized molten iron; smelting the desulfurized molten iron in a converter to obtain converter steel; refining the converter steel using LF refining, and performing alloying and slag deoxidation treatment during the LF refining process to obtain first refined steel; refining the first refined steel using RH refining, and controlling the following parameters of the RH refining: calcium wire feed rate, calcium wire feed speed, soft blowing flow rate, and soft blowing time to obtain second refined steel; casting the second refined steel, and performing ladle side blowing during the casting process to obtain a billet. By moving alloying operations such as Ti adjustment to LF refining, the problem of increased sulfur content in the alloy is solved. By controlling the calcium wire feed rate, feed speed, and soft blowing flow rate during RH refining, the formation and removal of large-size Ca-Al-O inclusions are controlled while ensuring sufficient modification of MnS inclusions. Furthermore, by using inert gas to side-blow the ladle during the later stages of casting, vortex formation can be controlled, resolving the problem of excessive inclusions in the steel caused by slag entrapment. These measures collectively control the quantity and size of sulfide and oxide inclusions in the steel. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A schematic flowchart illustrating a method for synergistically controlling sulfide and oxide inclusions in steel, provided in an embodiment of this application;

[0030] Figure 2 A front view of a ladle side-blowing structure provided in an embodiment of this application;

[0031] Figure 3 This is a top view of a ladle side-blowing structure provided in an embodiment of this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0034] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0036] Figure 1 This is a flowchart illustrating a method for synergistically controlling sulfide and oxide inclusions in steel, as provided in an embodiment of this application.

[0037] Please see Figure 1 This application provides a method for synergistically controlling sulfide and oxide inclusions in steel, the method comprising:

[0038] S1. Desulfurize the molten iron and remove the slag to obtain desulfurized molten iron;

[0039] In some embodiments, the temperature of the molten iron is >1330°C, and the [S] content in the molten iron is ≤0.06% by mass fraction.

[0040] The positive effects of controlling the molten iron temperature to >1330℃ and the [S] content to ≤0.06%: Thermodynamics of molten iron desulfurization shows that the higher the temperature, the higher the desulfurization rate. Controlling the molten iron temperature to >1330℃ ensures the desulfurization effect and controls the [S] content of the molten iron entering the furnace after KR pretreatment to be relatively low, reducing the deS load on the converter and refining processes. For example, the molten iron temperature can be 1330℃, 1335℃, 1340℃, 1345℃, 1350℃, etc., and the [S] content can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, etc.

[0041] In some embodiments, the number of times the slag is removed is ≥2, the total time for removing the slag is ≤10 minutes, and the area of ​​the shiny surface of the slag is ≥95%.

[0042] The positive effects of controlling the number of slag removals to ≥2 times, the total slag removal time to ≤10 minutes, and the bright surface area of ​​the slag removal to ≥95% are as follows: Controlling the number of slag removals after KR pretreatment can achieve the goal of lower [S] content in the molten iron entering the furnace after KR pretreatment, reducing the desulfurization load in the converter and refining. Controlling the slag removal time aims to ensure efficient connection between the KR pretreatment process and the converter process, avoiding excessive temperature loss in the molten iron; controlling the bright surface area of ​​the slag removal to ≥95% can effectively reduce the amount of desulfurization slag entering the converter, reducing the subsequent desulfurization load. For example, the total slag removal time can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc., and the bright surface area of ​​the slag removal can be 95%, 96%, 97%, 98%, etc.

[0043] In some implementations, the slag is removed twice.

[0044] In some embodiments, the ladle that holds the molten iron is an online turnover ladle with an age of ≥5 years.

[0045] It should be noted that "ladle age" refers to the number of times the ladle has been used online between two consecutive maintenance periods. This can be understood as follows: after a ladle is put back into service following maintenance, if it has been used 5 times, its age is considered to be 5. The positive effects of controlling the age of the ladle to be an online turnover ladle ≥ 5 years are as follows: New ladles with an age < 5 years generally have not yet reached heat storage saturation in their walls and bottom refractory materials. Using such ladles to hold molten iron will cause a significant temperature drop in the molten iron, which is detrimental to desulfurization. At the same time, non-online turnover ladles with an age ≥ 5 years also have the same problems. For example, the ladle in question can be an online turnover ladle with an age of 5, 6, 7, or 8 years.

[0046] S2. The desulfurized molten iron is smelted in a converter to obtain converter steel;

[0047] In some embodiments, the oxygen activity of the converter steel is ≤0.045%.

[0048] The positive effects of controlling the oxygen activity of molten steel in a converter to ≤0.045% include: controlling the oxygen content in the molten steel at a low level helps control the formation of oxide inclusions. For example, the oxygen activity of molten steel in a converter can be 0.020%, 0.025%, 0.030%, 0.035%, 0.040%, 0.045%, etc.

[0049] S3. The converter steel is subjected to LF refining, and alloying and slag deoxidation are carried out during the LF refining process to obtain the first refined steel.

[0050] In some embodiments, the raw material for the slag deoxidation treatment is aluminum granules, and the amount of aluminum granules added is 0.6 kg / t steel to 0.7 kg / t steel, and the aluminum granules are added in batches of 2 to 3 batches.

[0051] Depending on the steel composition requirements, alloying agents need to be added during the refining process. These alloys typically contain a certain amount of sulfur (S). If alloying is carried out during the RH refining process, the S introduced by the alloy is difficult to remove and will be inherited into the cast billet. Moving the alloying operation to LF refining allows for effective removal of the introduced S through the desulfurization function of LF refining. Simultaneously, LF refining produces reducing slag, which does not affect the recovery rate of alloying elements. The same principle applies to using aluminum granules for deoxidation in LF refining. For example, the amount of aluminum granules added can be 0.6 kg / t steel, 0.62 kg / t steel, 0.64 kg / t steel, 0.66 kg / t steel, 0.68 kg / t steel, 0.7 kg / t steel, etc., and the aluminum granules can be added to the slag surface in two or three batches.

[0052] S4. The first refined molten steel is subjected to RH refining, and the following parameters of the RH refining are controlled: calcium wire feed rate, calcium wire feed speed, soft blowing flow rate and soft blowing time, to obtain the second refined molten steel.

[0053] In some implementations, the amount of calcium wire fed into the RH refining process depends primarily on the composition of the molten steel. The amount of calcium wire fed is adjusted based on the [Mn] and [S] content in the molten steel; the higher the [Mn] and [S] content in the molten steel, the greater the amount of calcium wire fed.

[0054] In some embodiments, the numerical value of the calcium wire feeding rate satisfies the following relationship:

[0055] V = 2 + (d 实测 -d min ) / (d max -d min )

[0056] In the formula, V represents the numerical value of the calcium wire feeding speed, in m / s; d 实测 d max d min These represent the actual thickness, maximum thickness, and minimum thickness values ​​in the ladle top slag thickness detection, all in mm.

[0057] In some embodiments, the value of the calcium wire feeding rate is taken to one decimal place.

[0058] The feeding of calcium wire inevitably causes fluctuations in the molten steel surface. The faster the feeding speed, the greater the surface fluctuations. When the ladle slag is thick, surface fluctuations are less likely to expose the molten steel, allowing for a faster feeding speed. Conversely, when the ladle slag is thin, surface fluctuations easily expose the molten steel, requiring a lower feeding speed. Dynamically adjusting the calcium wire feeding speed based on the ladle slag thickness can prevent secondary oxidation caused by exposed molten steel due to surface fluctuations, while also ensuring calcium feeding efficiency. It should be noted that the actual thickness value measured in the ladle slag thickness detection is within the range of the minimum and maximum thickness values. For example, if the actual thickness is 80 mm, and the minimum and maximum thicknesses are 50 mm and 120 mm respectively, then substituting these values ​​into the above formula yields a calcium wire feeding speed of 2.4 m / s.

[0059] In some embodiments, the soft blowing time is 6 to 8 minutes, and the soft blowing flow rate satisfies the following relationship:

[0060] L = 0.5 + (d 实测 -d min ) / 100

[0061] In the formula, L represents the numerical value of the soft blowing flow rate, with units of NL / (min·t steel); d 实测 d min These represent the actual thickness value and the minimum thickness value in the ladle top slag thickness detection, respectively, both in mm.

[0062] After the calcium feeding line is completed, soft blowing can increase the diffusion rate of Ca in the molten steel and accelerate the removal of inclusions. The soft blowing time is usually controlled between 6 and 8 minutes to achieve the above effects without affecting the efficient connection between the refining and continuous casting processes. When the ladle slag is thin, even a low soft blowing flow rate can cause the liquid surface to be exposed, leading to secondary oxidation. When the ladle slag is thick, soft blowing is less likely to cause liquid surface exposure, and the soft blowing flow rate can be appropriately increased to maximize its function of promoting Ca diffusion and accelerating the removal of inclusions. Therefore, dynamically adjusting the soft blowing flow rate according to the thickness of the ladle slag is of practical significance. It should be noted that the actual thickness value in the ladle slag thickness detection must be greater than or equal to the minimum thickness value. For example, the soft blowing time can be 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes, 8 minutes, etc. For example, if the actual thickness is 80 mm and the minimum thickness is 50 mm, substituting into the above relationship, the calculated soft blowing flow rate is 0.8 NL / (min·t steel).

[0063] In some embodiments, the actual thickness value in the ladle top slag thickness detection is 50mm to 120mm.

[0064] When the top ash of the ladle is thin, even a low calcium wire feed rate can cause the molten steel surface to be exposed, affecting calcium feeding efficiency. Conversely, when the top ash is thick, the ash has a significant impact on the quality of the molten steel; therefore, the thickness of the top ash needs to be controlled. It should be noted that the controlled actual thickness range is 50mm to 120mm, meaning the maximum thickness can be 120mm and the minimum thickness can be 50mm. For example, the actual thickness can be 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, etc.

[0065] S5. The second refined molten steel is cast, and side blowing of the ladle is performed during the casting process to obtain a billet.

[0066] In some embodiments, the side blowing of the ladle during the casting process includes:

[0067] During the later stage of casting, when the ladle is filled to 1 / 4, ladle side blowing is performed. After the ladle slag detection system alarms, the ladle side blowing is stopped. The ladle side blowing uses inert gas, and the flow rate of the inert gas is 1.5NL / (min·t steel) to 2.0NL / (min·t steel).

[0068] Figure 2 A front view of a ladle side-blowing structure provided in an embodiment of this application;

[0069] Figure 3 This is a top view of a ladle side-blowing structure provided in an embodiment of this application.

[0070] Please refer to the schematic diagram of the ladle side-blowing structure. Figure 2 and 3 In the later stages of casting, the molten steel in the ladle exhibits significant vortex phenomena, easily leading to slag entrainment. To prevent excessive inclusions caused by slag entrainment during this phase, steel retention in the ladle is typically used for control, but this reduces metal yield and is not conducive to cost reduction and efficiency improvement. This application addresses this issue by using side-blowing inert gas when the ladle is 1 / 4 full during the later stages of casting. The side-blowing flow rate can be controlled, and the generated airflow interferes with vortex formation, thereby avoiding excessive inclusions in the steel caused by slag entrainment. For example, the inert gas flow rate can be 1.5 NL / (min·t steel), 1.6 NL / (min·t steel), 1.7 NL / (min·t steel), 1.8 NL / (min·t steel), 1.9 NL / (min·t steel), 2.0 NL / (min·t steel), etc.

[0071] In some embodiments, the number density of MnS inclusions and Ca-Al-O inclusions in the cast billet is ≤0.30 inclusions / mm². 2The size of the MnS inclusions is ≤6μm, and the size of the Ca-Al-O inclusions is ≤20μm.

[0072] This application reduces the desulfurization load in subsequent refining by controlling the [S] content, temperature, and slag removal degree after KR desulfurization; it addresses the issue of increased sulfur content in alloys by moving alloying operations such as Ti adjustment to LF refining; it controls the calcium wire feed rate, feed speed, and soft blowing flow rate during RH refining to ensure sufficient modification of MnS inclusions while controlling the formation and removal of large-size Ca-Al-O inclusions; and it uses side-blowing inert gas in the ladle during the later stages of casting to control vortex formation and solve the problem of excessive inclusions in steel caused by slag entrapment. For example, the number density of both MnS and Ca-Al-O inclusions in the billet can be 0.25 inclusions / mm². 2 0.26 pieces / mm 2 0.27 pieces / mm 2 0.28 pieces / mm 2 0.30 pieces / mm 2 The size of the MnS inclusions can be 4.00 μm, 4.50 μm, 5.00 μm, 5.50 μm, 6.00 μm, etc., and the size of the Ca-Al-O system inclusions can be 13.00 μm, 14.00 μm, 15.00 μm, 16.00 μm, 18.00 μm, 20.00 μm, etc.

[0073] It should be noted that the inclusion control method provided in this application is mainly applicable to medium and high carbon steel with a C content ≥ 0.25%.

[0074] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0075] This application provides a method for synergistically controlling sulfide and oxide inclusions in steel, comprising the following steps:

[0076] S11. The molten iron is subjected to desulfurization pretreatment and slag removal to obtain desulfurized molten iron; the slag removal is performed twice.

[0077] S12. The desulfurized molten iron is smelted in a converter to obtain converter steel;

[0078] S13. The converter steel is subjected to LF refining, and alloying and slag deoxidation are carried out during the LF refining process to obtain the first refined steel. The raw material for slag deoxidation is aluminum particles, which are added to the slag surface in 2 to 3 batches.

[0079] S14. The first refined molten steel is subjected to RH refining, and the following parameters of the RH refining are controlled: calcium wire feed rate, calcium wire feed speed, soft blowing flow rate and soft blowing time, to obtain the second refined molten steel; the maximum thickness of the ladle top slag and the minimum thickness of the ladle top slag are controlled at 120mm and 50mm respectively, and the thickness of the ladle top slag is ≥50mm and ≤120mm;

[0080] S15. The second refined molten steel is cast, and ladle side blowing is performed during the casting process to obtain a billet. The process parameters of the method for synergistically controlling the inclusion of sulfides and oxides in the steel are shown in Table 1.

[0081] Table 1. Process parameters for the method of synergistic control of sulfide and oxide inclusions in steel

[0082]

[0083] The application effect of the method described in this invention is characterized by the quantity density and size of MnS and Ca-Al-O system inclusions in the billet. The results of the examples and comparative examples are shown in Table 2.

[0084] Table 2 Comparison of the number density and size of MnS and Ca-Al-O inclusions in the cast billets of the examples and comparative examples.

[0085]

[0086]

[0087] As shown in Table 2, the number density of MnS inclusions and Ca-Al-O system inclusions in the billet of this application embodiment is controlled at 0.30 inclusions / mm. 2 Within the specified range, the quality control requirements are met. The maximum sizes of MnS inclusions and Ca-Al-O inclusions are controlled within 6 μm and 20 μm, respectively, meeting the quality control requirements. In Comparative Example 1, side blowing was not performed, resulting in the Ca-Al-O inclusion quantity density and maximum size not meeting the quality control requirements. In Comparative Example 2, the calcium wire feed amount was small and the feed rate was fast, resulting in the MnS and Ca-Al-O inclusion quantity densities and the maximum size of MnS inclusions not meeting the quality control requirements. In Comparative Example 3, the soft blowing flow rate was large, resulting in the Ca-Al-O inclusion quantity density and maximum size not meeting the quality control requirements. In Comparative Example 4, the hot metal composition and temperature before KR pretreatment, the bright surface area after slag removal, and the oxygen activity at the converter endpoint were not controlled according to the described method, resulting in the Ca-Al-O inclusion quantity density and the maximum size of MnS inclusions not meeting the quality control requirements.

[0088] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for synergistically controlling sulfide and oxide inclusions in steel, characterized in that, The method includes: The molten iron is pretreated for desulfurization and slag is removed to obtain desulfurized molten iron; The desulfurized molten iron is then smelted in a converter to obtain converter steel. The converter steel is subjected to LF refining, and alloying and slag deoxidation are carried out during the LF refining process to obtain the first refined steel. The first refined molten steel is subjected to RH refining, and the following parameters of the RH refining are controlled: calcium wire feed rate, calcium wire feed speed, soft blowing flow rate and soft blowing time to obtain the second refined molten steel. The second refined steel is cast, and side blowing of the ladle is performed during the casting process to obtain a billet; The value of the calcium wire feeding rate satisfies the following relationship: V=2+(d 实测 -d min ) / (d max -d min ) In the formula, V represents the numerical value of the calcium wire feeding speed, in m / s; d 实测 d max d min These represent the actual thickness, maximum thickness, and minimum thickness values ​​in the ladle top slag thickness detection, all in mm. The soft blowing time is 6 to 8 minutes, and the soft blowing flow rate satisfies the following relationship: L=0.5+(d 实测 -d min ) / 100 In the formula, L represents the numerical value of the soft blowing flow rate, with units of NL / (min·t steel); d 实测 d min These represent the actual thickness and minimum thickness value of the ladle top slag thickness during the thickness detection, both in mm; During the casting process, ladle side blowing is performed, including: During the later stage of casting, when the ladle is filled to 1 / 4, ladle side blowing is performed. After the ladle slag detection system alarms, the ladle side blowing is stopped. The ladle side blowing uses inert gas, and the flow rate of the inert gas is 1.5NL / (min·t steel)~2.0NL / (min·t steel). The bright surface area of ​​the slag removal is ≥95%, the temperature of the molten iron is >1330℃, and the [S] content in the molten iron is ≤0.06% by mass fraction; the oxygen activity of the converter steel is ≤0.045%.

2. The method according to claim 1, characterized in that, The actual thickness value in the ladle top slag thickness detection is 50mm~120mm.

3. The method according to claim 1, characterized in that, The raw material for the slag deoxidation treatment is aluminum granules, and the amount of aluminum granules added is 0.6 kg / t steel to 0.7 kg / t steel. The aluminum granules are added in batches of 2 to 3 batches.

4. The method according to claim 1, characterized in that, The number of times the slag is removed is ≥2 times, and the total time for removing the slag is ≤10 minutes.

5. The method according to claim 1, characterized in that, The ladle used to receive the molten iron is an online turnover ladle with an age of ≥5 years.

6. The method according to claim 1, characterized in that, The number density of MnS inclusions and Ca-Al-O series inclusions in the cast billet is ≤0.30 inclusions / mm². 2 The size of the MnS inclusions is ≤6μm, and the size of the Ca-Al-O inclusions is ≤20μm.

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