Decarburization and dephosphorization method for converter tapping

Abstract

The invention provides a decarburization and dephosphorization method for converter tapping, belongs to the technical field of low-carbon steel smelting in a converter smelting process, and aims to solve the problems of super peroxidation, large iron loss and furnace wall erosion caused by low carbon pulling in existing low-carbon steel smelting. According to the technical scheme, the method comprises the steps that a target steel grade endpoint carbon control interval is set, the ratio of lime to dolomite is adjusted so that the basicity of slag can reach 2.8-3.2, the circular seam flow in the later smelting period is controlled to be larger than or equal to 300 m < 3 > / h, bomb dropping is conducted in the specific carbon content interval, argon is introduced in the tapping stage by stage, stirring is conducted through residual oxygen, and deoxidation alloy and a slagging deoxidizing agent are added when 40-50 tons of steel is tapped. The method can avoid excessive oxygen blowing, reduce iron loss, stabilize slag to protect a furnace lining, inhibit rephosphorization, reduce the dosage of a deoxidizing agent and improve the smelting stability and economy of low-carbon steel.

Description

Technical Field

[0001] This invention relates to the field of low-carbon steel smelting technology in converter smelting process, specifically to a method for decarburizing and dephosphorizing steel tapped from a converter. Background Technology

[0002] This technology belongs to the field of low-carbon steel smelting in converter smelting processes, and mainly addresses the issue of carbon content control at the final stage of converter tapping. Current low-carbon steel smelting methods mostly employ a single carbon removal method or a two-stage blowing method, removing carbon in the furnace to meet process standards by "removing low carbon" (e.g., when the upper limit of carbon for a steel grade is 0.07%, the average carbon content at the final smelting stage is 0.04% to 0.05%).

[0003] However, the existing technology has obvious defects: First, the high TFe content in the slag at the end of smelting leads to a large loss of iron; second, the "low carbon" operation will make the slag too thin and the slag has strong oxidizing properties. During continuous smelting, the highly oxidizing and highly fluid slag will cause erosion and scouring of the furnace wall, which is not conducive to furnace protection and affects the service life of the converter. Summary of the Invention

[0004] The present invention aims to solve the problems mentioned in the background art by providing a method for decarburization and dephosphorization of steel tapped from a converter.

[0005] The specific technical solution is as follows:

[0006] A method for decarburizing and dephosphorizing steel tapping from a converter includes the following steps:

[0007] Step 1: Determine the endpoint carbon control range corresponding to the target steel grade in converter smelting;

[0008] Step 2: Optimize converter slag performance by adjusting the ratio of lime to dolomite to control slag alkalinity and setting the minimum lance pressing time.

[0009] Step 3: Optimize the carbon removal method at the end of the converter, control the flow rate of the annular gap in the later stage of smelting to maintain the stability of the furnace mouth flame, carry out bombing operation according to the real-time carbon content in the furnace, and dynamically calculate the amount of cold material added through the thermal model to ensure that the temperature at the end of smelting reaches the standard.

[0010] Step 4: Gas stirring is carried out during the tapping stage of the converter to decarburize the steel by reacting the residual free oxygen in the molten steel with the carbon.

[0011] Step 5: After the steel is tapped from the converter to the set tonnage, deoxidizing alloy and slag-forming deoxidizer are added to the molten steel to complete the decarburization and dephosphorization process.

[0012] This solution addresses the core issue of "super-oxidation" in existing technologies by establishing a complete process chain: "determining the endpoint carbon control range - optimizing slag properties - optimizing carbon removal methods - gas stirring decarburization - adding deoxidizer at specific stages." Determining the endpoint carbon range avoids excessive oxygen blowing at the end of smelting, reducing iron loss. Optimizing slag properties stabilizes slag viscosity and oxidizability, preventing excessively thin slag from eroding the furnace wall and achieving furnace protection. Gas stirring utilizes residual oxygen in the molten steel for decarburization, eliminating the need for additional oxygen blowing and further reducing the risk of super-oxidation. Adding deoxidizer at specific stages enables precise deoxidation on top of decarburization, reducing deoxidizer waste. The overall solution balances low-carbon control, reduced iron loss, slag stabilization, and phosphorus reversion inhibition, achieving a comprehensive performance improvement in low-carbon steel smelting.

[0013] In a preferred embodiment of the present invention, when the target steel grade in step one is XGL steel, the endpoint carbon control range is 0.055% to 0.075%. Setting a specific endpoint carbon control range for XGL steel allows the steel grade to meet low-carbon process standards while avoiding excessive oxidation caused by "excessively low carbon content" in existing technologies. By controlling the endpoint carbon within a reasonable range, there is no need for additional oxygen blowing to pursue low carbon content, while ensuring the subsequent decarburization effect under the furnace. This reduces iron loss during the smelting process of XGL steel and avoids increased slag oxidizability and decreased viscosity due to excessive oxygen blowing, reducing the risk of furnace wall erosion and stabilizing the furnace conditions during the smelting of this steel grade.

[0014] In a preferred embodiment of the present invention, when the target steel grade in step one is SWRCH6A, the endpoint carbon control range is 0.055% to 0.07%. Matching a specific endpoint carbon control range to SWRCH6A steel grade can adapt to the composition requirements of this steel grade: compared with the operation of uniformly lowering the carbon in the prior art, this range allows SWRCH6A steel grade to avoid excessive oxygen blowing at the end of smelting, reducing iron loss caused by "super peroxidation"; at the same time, a reasonable endpoint carbon content can avoid the slag from becoming too fluid due to excessive oxidation, improve the slag blocking effect, reduce phosphorus return in slag, ensure the accuracy of phosphorus content control of this steel grade, and stabilize product quality.

[0015] In a preferred embodiment of the present invention, after adjusting the ratio of lime to dolomite in step two, the slag basicity is controlled between 2.8 and 3.2, and the lance pressing time is not less than 40 seconds. By adjusting the ratio of lime to dolomite to control the slag basicity and setting a minimum lance pressing time, the problems of excessively thin slag and strong oxidizing properties in the prior art can be solved: a specific basicity range can ensure that the slag has suitable viscosity and oxidizing properties, avoiding the scouring and erosion of the furnace wall by excessively thin slag, thus achieving furnace protection; sufficient lance pressing time can allow the slag to react fully, further stabilizing the slag properties, reducing phosphorus reversion caused by slag instability, and reducing the loss of iron in the slag, thereby improving metal recovery.

[0016] In a preferred embodiment of the present invention, the flow rate of the annular gap in the later stage of smelting in step three is controlled at not less than 300 cubic meters per hour. When the carbon content in the furnace is between 0.08% and 0.12%, the bombing operation is performed. Controlling the flow rate of the annular gap in the later stage of smelting and setting a specific bombing timing can avoid the problems of unstable furnace mouth flame and excessive oxidation in the prior art: sufficient annular gap flow rate can maintain the stability of the furnace mouth flame, prevent excessive oxygen blowing caused by abnormal flame, and reduce the risk of over-oxidation; bombing within a specific carbon content range, combined with the calculation of the amount of cold material added by the thermal model, can accurately control the final carbon content and temperature, and reduce the post-blowing operation—reducing post-blowing can prevent the slag oxidation from further increasing, reduce iron loss and phosphorus return probability, and improve smelting efficiency and steel quality stability.

[0017] In a preferred embodiment of the present invention, the gas used for gas stirring in step four is argon. The argon supply is divided into two stages: the first stage is 120 seconds before tapping, with the argon flow rate controlled at 150 cubic meters per hour; the second stage is 120 seconds after tapping, with the argon flow rate controlled at 60 cubic meters per hour. This staged flow rate control of argon optimizes the decarburization effect of the molten steel and avoids disorder in the molten steel's state: the high flow rate of argon in the first 120 seconds before tapping fully stirs the molten steel, allowing the residual free oxygen in the molten steel to contact carbon evenly, improving the decarburization reaction efficiency; the subsequent low flow rate of argon maintains the stirring effect while avoiding splashing or uneven composition of the molten steel due to excessive stirring. This staged stirring can fully utilize the residual oxygen in the molten steel for decarburization, eliminating the need for additional oxygen blowing, reducing the risk of over-oxidation, reducing iron loss, and ensuring uniform composition of the molten steel, thus reducing phosphorus reversion.

[0018] In a preferred embodiment of the present invention, the tonnage in step five is set to 40 to 50 tons. When the steel output reaches this set tonnage, the deoxidizing alloy and slag-forming deoxidizer are added. Adding the deoxidizing alloy and slag-forming deoxidizer when the steel output reaches a specific tonnage can achieve a match between the timing of deoxidation and the decarburization reaction: at this tonnage, the decarburization reaction of the molten steel is basically completed. Adding the deoxidizer at this time can precisely target the remaining oxygen in the molten steel for deoxidation, avoiding adding the deoxidizer too early and affecting the decarburization reaction, or adding it too late and causing insufficient deoxidation. Precise addition timing can reduce the amount of deoxidizer used, reduce costs, and at the same time ensure the deoxidation effect, avoiding steel quality problems caused by insufficient deoxidation, and also helping to stabilize the slag state and reduce phosphorus reversion.

[0019] In a preferred embodiment of the present invention, the deoxidizing alloy comprises high-alumina ferromanganese and medium-carbon ferromanganese, and the slag-forming deoxidizer consists of 50 kg of slag-forming deoxidizer body and 200 kg of synthetic slag. The specific composition and dosage of the deoxidizing alloy and slag-forming deoxidizer can improve deoxidation efficiency and slag stability: the combination of high-alumina ferromanganese and medium-carbon ferromanganese can efficiently remove oxygen from molten steel while supplementing the alloying elements required for the steel grade, avoiding the introduction of excess impurities; the specific dosage of the slag-forming deoxidizer and synthetic slag can further optimize the slag composition, enhance the slag's phosphorus control ability, and reduce phosphorus reversion; this combination scheme can ensure deoxidation effect, improve steel purity, stabilize slag performance, reduce furnace wall erosion, and avoid waste of deoxidizer and slag-forming agent, thus controlling smelting costs.

[0020] In a preferred embodiment of the present invention, when calculating the amount of cold material added in step three using the thermal model, the reference parameters include the silicon content of molten iron, the scrap steel ratio, and the ambient temperature. Referring to the silicon content of molten iron, the scrap steel ratio, and the ambient temperature when calculating the amount of cold material added using the thermal model can improve the accuracy of the final temperature control. In existing technologies, the calculation of the amount of cold material added may ignore some key parameters, leading to deviations in the final temperature, thus requiring subsequent blowing adjustments—subsequent blowing increases slag oxidation, iron loss, and phosphorus reversion. This solution, by incorporating multiple key parameters, makes the calculation of the amount of cold material added more accurate, ensuring that the final temperature is achieved on the first attempt, reducing subsequent blowing operations, thereby avoiding problems such as over-oxidation and slag instability caused by subsequent blowing, reducing iron loss, and stabilizing furnace conditions and molten steel quality.

[0021] As a preferred embodiment of the present invention, the reaction formula for the reaction between residual free oxygen and carbon in the molten steel in step four is [C] + [O] → CO(g). This [C] + [O] → CO(g) reaction for decarburization changes the existing technology's reliance on oxygen or slag (FeO) for decarburization. This reaction does not require the introduction of additional oxygen or reliance on FeO in the slag; it directly utilizes the residual oxygen in the molten steel to react with carbon, thus avoiding "super-oxidation" at the source. This reduces iron loss caused by additional oxygen blowing and prevents the oxidizing properties of the slag from being enhanced by excessive FeO, reducing the risk of furnace wall erosion. Simultaneously, this reaction effectively consumes carbon in the molten steel, ensuring low carbon requirements, reducing post-blowing, and consequently reducing phosphorus reversion, achieving a synergistic effect of decarburization, furnace protection, and phosphorus control. This reaction can reduce the carbon content of the molten steel by more than 0.012%.

[0022] The present invention has the following beneficial effects:

[0023] 1. Reduce iron loss: By increasing the carbon content at the end point, avoid "super peroxidation" caused by excessive oxygen blowing at the end of smelting, reduce the loss of iron in the slag, and improve metal recovery.

[0024] 2. Improve furnace protection effect: Optimize slag basicity and viscosity to avoid excessively thin slag; at the same time, reduce slag oxidizability, reduce the erosion and scouring of the furnace wall by highly oxidizing and highly fluid molten slag, extend the service life of the furnace lining, and reduce furnace protection costs.

[0025] 3. Enhanced phosphorus control capability: Reduce post-blowing operations (precise control of final carbon + one-time temperature target) to avoid phosphorus return in the furnace caused by post-blowing; at the same time, the optimized slag properties improve the adsorption capacity of phosphorus, reduce phosphorus return in the slag, and ensure stable phosphorus content in molten steel.

[0026] 4. Reduce deoxidizer consumption: Decarburization by reacting residual carbon in molten steel with free oxygen can consume some of the oxygen in the molten steel, thereby reducing the amount of deoxidizer to be added later and reducing smelting costs.

[0027] 5. Stable smelting process: By controlling the carbon range at the endpoint, using thermal model temperature control, and staged argon stirring, the problems of large carbon control deviation and unstable slag performance in traditional processes are solved, improving the stability of low-carbon steel smelting and the consistency of product quality, and has industrial application value. Attached Figure Description

[0028] Figure 1 A flowchart of a method for decarburization and dephosphorization of steel tapping from a converter, provided in an embodiment of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0031] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0032] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] Reference Figure 1 The present invention provides the following three embodiments:

[0034] Example 1: Decarburization and dephosphorization of XGL steel grade in converter tapping

[0035] (1) Technical solution

[0036] 1. Endpoint carbon control: The target steel grade is clearly defined as XGL steel grade, and the endpoint carbon control range is set at 0.055% to 0.075% to avoid excessive oxygen blowing at the end of the smelting process in pursuit of low carbon.

[0037] 2. Slag performance optimization: Adjust the ratio of lime to dolomite to maintain the slag basicity (CaO / SiO2) between 2.8 and 3.2; set the lance pressing time to 45 seconds (not less than 40 seconds) to ensure that the slag reaction is complete and has suitable fluidity.

[0038] 3. Optimization of the final carbon extraction method: The flow rate of the annular gap is controlled at 320 m³ / s during the later stage of smelting. 3 / h (not less than 300m) 3 / h), maintain the flame at the furnace mouth stable; when the carbon content in the furnace is monitored to be 0.09% to 0.11% (within the range of 0.08% to 0.12%), perform the bombing operation; through the thermal model, referencing the silicon content of molten iron (0.35%), scrap steel ratio (12%) and ambient temperature (22℃), dynamically calculate the amount of cold material added to ensure that the final smelting temperature meets the standard.

[0039] 4. Gas stirring treatment: Argon gas is used for stirring, and the argon gas flow rate is controlled at 150 m³ / s 120 seconds before tapping. 3 / h, adjusted to 60m 120 seconds before tapping. 3 / h, decarburization is achieved by reacting residual free oxygen in molten steel with carbon.

[0040] 5. Addition of deoxidizer and slag-forming agent: When the steel output reaches 42 tons (in the range of 40 to 50 tons), add deoxidizing alloy (high aluminum ferromanganese + medium carbon ferromanganese) and slag-forming deoxidizer (50 kg of slag-forming deoxidizer body + 200 kg of synthetic slag) to the molten steel to complete the decarburization and dephosphorization process.

[0041] (2) Working principle

[0042] Setting the endpoint carbon control range avoids "super peroxidation" from the source: there is no need to blow oxygen in order to reduce carbon content, reducing the excessive reaction between iron and oxygen and reducing iron loss.

[0043] Controlling slag alkalinity and lance pressing time ensures that the slag reaches a stable physicochemical state: appropriate alkalinity enhances the slag's phosphorus control ability, and sufficient lance pressing time ensures uniform slag composition, avoids furnace wall erosion caused by excessively thin slag, and inhibits phosphorus reversion.

[0044] Matching the flow rate of the annular gap with the timing of bombing ensures the accuracy of carbon extraction: a stable furnace flame reflects a stable oxidation state inside the furnace, and bombing within a specific carbon content range, combined with temperature control by a thermal model, reduces the need for post-blowing operations—reducing post-blowing can prevent further enhancement of slag oxidation and reduce the risk of iron loss and phosphorus reversion.

[0045] Staged argon agitation utilizes the residual oxygen in the molten steel for decarburization: In the early stage, a large flow of argon promotes the convection of the molten steel, allowing the residual free oxygen to fully contact with carbon and undergo the [C]+[O]→CO(g) reaction; in the later stage, a small flow of argon maintains the agitation effect while avoiding splashing or compositional disorder in the molten steel, ensuring uniform decarburization.

[0046] Adding deoxidizer and slag-forming agent at specific tonnages: Adding them after the decarburization reaction is basically completed avoids adding deoxidizer too early, which would consume residual oxygen and affect decarburization. It can also accurately remove residual oxygen in the steel. At the same time, the slag-forming agent further optimizes the slag performance and consolidates the phosphorus control effect.

[0047] (3) Experimental data

[0048] Three heats of XGL steel were selected for testing, and the data are as follows:

[0049] Melting Station C One-inverted C P station entry One P Furnace pre-oxygen control Oxygen supply station 101 0.059 0.0721 0.0211 0.0201 422.3 51 103 0.0524 0.0752 0.0206 0.0195 526.3 26 105 0.0571 0.0702 0.0217 0.0244 437.2 118

[0050] (4) Technical effects

[0051] From the perspective of final carbon control: the carbon content of the first inflow is within the range set by XGL steel grade, which does not require post-blowing adjustment, avoids excessive oxidation, reduces the loss of iron in the slag, and improves metal recovery.

[0052] From the perspective of slag performance: the control of slag basicity and lance pressing time resulted in no significant increase in phosphorus content (P) at the first pour compared to the initial pour, and even a decrease in some furnaces, indicating that the slag's phosphorus control ability is stable and effectively inhibits phosphorus reversion; at the same time, the slag did not become too thin, reducing erosion of the furnace wall and extending the service life of the furnace lining.

[0053] In terms of decarburization efficiency: Argon stirring promotes the [C]+[O] reaction, effectively controlling the carbon content of molten steel. Moreover, the decarburization process does not require additional oxygen blowing, reducing energy consumption and the risk of over-oxidation.

[0054] In terms of deoxidation effect: the deoxidizing alloy and slag-forming agent added at specific times can accurately remove residual oxygen, avoid waste of deoxidizing agent, and at the same time ensure the purity of molten steel and meet the quality requirements of XGL steel grade.

[0055] Example 2: Decarburization and dephosphorization of SWRCH6A steel in converter tapping

[0056] (2) Technical solution

[0057] 1. Endpoint carbon control: The target steel grade is SWRCH6A steel, and the endpoint carbon control range is set to 0.055% to 0.07%, which is in line with the low carbon content requirements of this steel grade.

[0058] 2. Slag performance optimization: Adjust the ratio of lime to dolomite to maintain the slag alkalinity between 2.9 and 3.1; set the lance pressing time to 42 seconds to ensure a balance between slag fluidity and stability.

[0059] 3. Optimization of the final carbon extraction method: The flow rate of the annular gap in the later stage of smelting is controlled at 310 m³ / s. 3 / h, maintain a stable flame at the furnace opening; bombs are dropped when the carbon content in the furnace is 0.085% to 0.105%; the amount of cold material added is calculated by using a thermal model, referring to the silicon content of molten iron (0.38%), scrap steel ratio (14%) and ambient temperature (24℃), to ensure that the final temperature meets the standard.

[0060] 4. Gas stirring treatment: Argon gas is used for stirring, with an argon gas flow rate of 150 m³ / s for 120 seconds before tapping. 3 / h, adjusted to 60m 120 seconds before tapping. 3 / h, using residual free oxygen to achieve decarbonization.

[0061] 5. Addition of deoxidizer and slag-forming agent: When the steel output reaches 45 tons, add deoxidizing alloy (high aluminum ferromanganese + medium carbon ferromanganese) and slag-forming deoxidizer (50 kg of slag-forming deoxidizer body + 200 kg of synthetic slag).

[0062] (2) Working principle

[0063] The final carbon range of SWRCH6A steel is slightly lower than that of XGL steel, which is suitable for its strict requirements on carbon content: by precisely controlling the final carbon, it can meet the low carbon standard and avoid excessive oxidation caused by too low carbon content, thus balancing carbon control and iron loss control.

[0064] The slag basicity was finely adjusted to 2.9-3.1 to better meet the phosphorus control requirements of SWRCH6A steel: at this basicity, the slag has a stronger ability to adsorb phosphorus, while the 42-second lance pressing time ensures that the slag reaction is complete and avoids phosphorus reversion caused by local phosphorus enrichment.

[0065] Circumferential flow rate 310m 3The combination of / h and specific bombing carbon range ensures carbon extraction accuracy: a stable flame state reflects a stable oxidation rate in the furnace, the timing of bombing avoids areas with excessively low carbon content, and the reduction of back-blowing—reducing back-blowing can avoid a sudden increase in slag oxidizability and reduce iron loss and fluctuations in molten steel composition.

[0066] The core of staged argon stirring is to utilize residual oxygen for decarburization: in the early stage, high-flow stirring breaks up the stratification of the molten steel composition, allowing residual oxygen to come into uniform contact with carbon and promoting the [C]+[O] reaction; in the later stage, low-flow stirring maintains the dynamic balance of the molten steel and avoids uneven decarburization.

[0067] Adding deoxidizer when the steel output is 45 tons matches the decarburization rhythm of SWRCH6A steel: at this time, the decarburization reaction is nearing its end, and adding deoxidizer can efficiently remove residual oxygen. At the same time, the slag-forming agent optimizes the slag composition and prevents phosphorus from re-entering the molten steel.

[0068] (3) Experimental data

[0069] Three test heats of SWRCH6A steel were selected, and the data are as follows:

[0070] Melting Station C One-inverted C P station entry One P Furnace pre-oxygen control Oxygen supply station 102 0.0535 0.0792 0.0281 0.0293 473.4 88 104 0.0672 0.0746 0.0236 0.0229 467.6 50 106 0.0681 0.0671 0.0227 0.0242 532.4 56

[0071] (4) Technical effects

[0072] Regarding carbon content control: the carbon content of the first batch is basically within the range set for SWRCH6A steel grade, with only slight fluctuations in a few individual heats. No post-blowing adjustment is required to avoid iron loss due to excessive oxidation, while also meeting the low-carbon quality requirements of this steel grade.

[0073] Regarding phosphorus control effectiveness: In most heats, the phosphorus content at the first pour was not significantly higher than that at the start of the heat, indicating that the adjustment of slag basicity and lance pressing time effectively improved phosphorus control, suppressed phosphorus reversion, and ensured that the phosphorus content of molten steel met the standards.

[0074] Regarding furnace stability: the control of the flow rate in the annular gap and the timing of bomb feeding ensured a stable furnace flame, prevented abnormal oxidation, and prevented the slag from becoming too thin, thus reducing scouring of the furnace wall and ensuring stable furnace conditions for continuous smelting.

[0075] In terms of deoxidation economics: adding deoxidizers and slag-forming agents at specific times can avoid decarbonization interference caused by adding them too early, or insufficient deoxidation caused by adding them too late, thereby reducing deoxidizer consumption and lowering smelting costs.

[0076] Example 3: Decarburization and dephosphorization of converter steelmaking based on thermal model parameter optimization

[0077] (1) Technical solution

[0078] 1. Endpoint carbon control: The target steel grade is XGL steel, and the endpoint carbon control range is 0.055% to 0.075%.

[0079] 2. Slag performance optimization: Adjust the ratio of lime to dolomite, and control the slag alkalinity to 3.0-3.2; set the lance pressing time to 50 seconds to ensure a more complete slag reaction.

[0080] 3. Optimization of the final carbon extraction method: The flow rate of the annular gap in the later stage of smelting is controlled at 350m³. 3 / h, strengthen the stirring and flame stability in the furnace; when the carbon content in the furnace is 0.09% to 0.11%, bombs are dropped; through the thermal model, with key references to the silicon content of molten iron (0.40%), scrap steel ratio (16%) and ambient temperature (20℃), the amount of cold material added is accurately calculated to ensure that the final temperature reaches the standard in one go.

[0081] 4. Gas stirring treatment: Argon stirring is carried out in stages, with a flow rate of 150 m³ / s for 120 seconds before tapping. 3 / h, then adjusted to 60m 3 / h, promotes the reaction of residual oxygen with carbon.

[0082] 5. Addition of deoxidizer and slag-forming agent: When the steel output reaches 48 tons, add deoxidizing alloy (high aluminum ferromanganese + medium carbon ferromanganese) and slag-forming deoxidizer (50 kg of slag-forming deoxidizer body + 200 kg of synthetic slag).

[0083] (2) Working principle

[0084] The core is to refine the parameters of the thermal model (silicon content in molten iron, scrap steel ratio, and ambient temperature): the silicon content in molten iron affects the total heat generation in the furnace, the scrap steel ratio affects the cooling rate, and the ambient temperature affects heat loss. By combining these three factors to calculate the amount of cold material added, the deviation of the final temperature caused by too much or too little cold material can be avoided, the post-blowing adjustment can be reduced, and the risk of over-oxidation can be fundamentally reduced.

[0085] The lance pressing time is extended to 50 seconds, combined with a slag basicity of 3.0 to 3.2: the longer lance pressing time allows the slag and molten steel to react more thoroughly, improving the slag's ability to adsorb phosphorus; the higher basicity further enhances the slag's phosphorus control effect, while avoiding the slag from being too thick and affecting its fluidity.

[0086] The flow rate of the circumferential joint has been increased to 350m³. 3 / h: A larger flow rate enhances the uniformity of contact between oxygen and molten steel in the furnace, avoids excessive local oxidation, and maintains a stable flame at the furnace mouth, making it easier to accurately judge the carbon content and improve the accuracy of bomb-dropping timing.

[0087] The combination of staged argon stirring and deoxidizer at a steel output of 48 tons: high-flow stirring in the early stage ensures that residual oxygen and carbon react fully, while low-flow stirring in the later stage maintains the state of molten steel; at 48 tons, the decarburization reaction is basically completed, and the addition of deoxidizer can achieve efficient deoxidation, while slag-forming agent further consolidates the phosphorus control effect of slag and avoids phosphorus reversion caused by temperature fluctuations.

[0088] (3) Experimental data

[0089] Three test heats of XGL steel grade were selected based on thermal model parameter optimization, and the data are as follows:

[0090] Melting Station C One-inverted C P station entry One P Furnace pre-oxygen control Oxygen supply station 107 0.0648 0.0666 0.0286 0.0186 428 105 108 0.0602 0.0655 0.0207 0.0211 516.9 54 109 0.0396 0.0652 0.0226 0.0219 492.2 98

[0091] (4) Technical effects

[0092] In terms of temperature control: The thermal model references the silicon content of molten iron, the scrap steel ratio, and the ambient temperature, ensuring that the final temperature reaches the target in one go without post-blowing operations. This avoids the increased oxidizability of slag caused by post-blowing, reduces iron loss, and lowers energy consumption.

[0093] Regarding phosphorus control: The extended lance time and higher slag basicity resulted in a significant decrease in phosphorus content (P) at the bottom of some furnaces compared to the initial phosphorus content (P) at the furnace entrance. This indicates that the slag's ability to adsorb phosphorus has been enhanced, resulting in better phosphorus control and effectively suppressing phosphorus reversion, thus meeting the phosphorus content requirements for high-standard steel grades.

[0094] Regarding decarburization uniformity: Higher circumferential flow promotes in-furnace stirring, resulting in a more uniform distribution of carbon content in the molten steel. The carbon content remains stable within the set range, improving decarburization efficiency and avoiding quality fluctuations caused by excessively high or low local carbon content.

[0095] In terms of furnace lining protection: the slag has stable properties (neither too thin nor too thick), reducing erosion of the furnace wall. At the same time, there is no need for post-blowing operation, resulting in small temperature fluctuations inside the furnace, further extending the service life of the furnace lining and reducing furnace protection costs.

[0096] In summary, the converter tapping decarburization and dephosphorization method provided in this embodiment solves the core problems of traditional low-carbon steel smelting through the synergy of various steps. The specific technical effects are as follows:

[0097] 1. Reduce iron loss: By increasing the carbon content at the end point, avoid "super peroxidation" caused by excessive oxygen blowing at the end of smelting, reduce the loss of iron in the slag, and improve metal recovery.

[0098] 2. Improve furnace protection effect: Optimize slag basicity and viscosity to avoid excessively thin slag; at the same time, reduce slag oxidizability, reduce the erosion and scouring of the furnace wall by highly oxidizing and highly fluid molten slag, extend the service life of the furnace lining, and reduce furnace protection costs.

[0099] 3. Enhanced phosphorus control capability: Reduce post-blowing operations (precise control of final carbon + one-time temperature target) to avoid phosphorus return in the furnace caused by post-blowing; at the same time, the optimized slag properties improve the adsorption capacity of phosphorus, reduce phosphorus return in the slag, and ensure stable phosphorus content in molten steel.

[0100] 4. Reduce deoxidizer consumption: Decarburization by reacting residual carbon in molten steel with free oxygen can consume some of the oxygen in the molten steel, thereby reducing the amount of deoxidizer to be added later and reducing smelting costs.

[0101] 5. Stable smelting process: By controlling the carbon range at the endpoint, using thermal model temperature control, and staged argon stirring, the problems of large carbon control deviation and unstable slag performance in traditional processes are solved, improving the stability of low-carbon steel smelting and the consistency of product quality, and has industrial application value.

[0102] Working principle

[0103] The purpose of this scheme is to change the traditional "oxygen source" for decarburization—no longer relying on top-blown oxygen in the furnace or FeO in the slag for decarburization, but instead utilizing the residual free oxygen in the molten steel itself to react with carbon to achieve decarburization. The core reaction formula is [C] + [O] → CO(g). The decarburization and dephosphorization effects are ensured through multi-stage synergy. The specific principle is as follows:

[0104] 1. Endpoint carbon control principle: Increase the endpoint carbon content of the converter steel, avoid excessive oxygen blowing in the final stage of smelting in pursuit of low carbon, reduce the oxidizing properties of the slag in the furnace from the source, improve the slag viscosity, and reduce the phenomenon of "super peroxidation".

[0105] 2. Slag performance optimization principle: By adjusting the ratio of lime to dolomite to control the slag alkalinity and with sufficient lance pressing time, the slag can form a stable physicochemical state, which not only ensures that the slag has suitable fluidity, but also enhances the slag's ability to adsorb phosphorus and inhibits phosphorus reversion.

[0106] 3. Carbon extraction and temperature control principle: Controlling the flow rate of the annular gap in the later stage of smelting to maintain the stability of the furnace mouth flame and avoid local over-oxidation; dropping bombs in a specific carbon content range, and dynamically calculating the amount of cold material added by combining the silicon content of molten iron, scrap steel ratio and ambient temperature through a thermal model to ensure that the final temperature and carbon content are accurately met, reducing the need for post-blowing operations (post-blowing will aggravate the oxidation of slag, increase iron loss and phosphorus return risk).

[0107] 4. Gas stirring and deoxidation principle: Argon gas is introduced in stages during the tapping stage for stirring. In the early stage, a large flow of argon gas promotes the convection of molten steel, so that the residual free oxygen and carbon come into uniform contact, thereby improving the decarburization reaction efficiency. In the later stage, a small flow of argon gas is used to maintain the stirring effect and avoid splashing of molten steel. When the steel reaches a certain tonnage, deoxidizing alloy and slag-forming deoxidizer are added. At this time, the decarburization reaction has been basically completed, which can accurately deoxidize and further optimize the slag performance, avoiding interference with decarburization or insufficient deoxidation by the deoxidizer.

[0108] How to use

[0109] To use this solution, please follow these steps to ensure that the parameters at each stage are matched:

[0110] 1. Determine the endpoint carbon control range: Set the corresponding range according to the target steel grade. For XGL steel grade, control it at 0.055% to 0.075%, and for SWRCH6A steel grade, control it at 0.055% to 0.07%.

[0111] 2. Optimize slag properties: Adjust the ratio of lime to dolomite to maintain the slag basicity (CaO / SiO2) between 2.8 and 3.2; the lance pressing time should not be less than 40 seconds to ensure that the slag reaction is sufficient and has suitable fluidity.

[0112] 3. Optimize the final carbon extraction operation: Control the flow rate of the annular gap to no less than 300 m³ / h during the later stage of smelting. 3 / h, observe the furnace flame to ensure stability; when the carbon content in the furnace is in the range of 0.08% to 0.12%, perform the bombing operation; through the thermal model, referencing the silicon content of molten iron, scrap steel ratio and ambient temperature, dynamically calculate the amount of cold material added to ensure that the final smelting temperature meets the standard.

[0113] 4. Perform gas stirring treatment: 120 seconds before tapping, control the argon gas flow rate to 150 m³ / h. 3 / h; 120 seconds before tapping, adjust the argon flow rate to 60m³ / h. 3 / h, utilizing the reaction of residual free oxygen in molten steel with carbon to decarburize.

[0114] 5. Add deoxidizer and slag-forming agent: When the steel output reaches 40-50 tons, add deoxidizing alloy (high aluminum ferromanganese + medium carbon ferromanganese) and slag-forming deoxidizer (50 kg slag-forming deoxidizer + 200 kg synthetic slag) to the molten steel to complete the decarburization and dephosphorization process.

[0115] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for decarburization and dephosphorization of a converter tapping, characterized in that, The method comprises the following steps: Step one, determining the end-point carbon control interval corresponding to the target steel grade of converter smelting; Step two, optimizing the converter slag performance, adjusting the ratio of lime and dolomite to control the slag basicity, and setting the minimum lance pressing time; Step three, optimizing the converter end-point carbon control means, controlling the ring gap flow in the late smelting stage to maintain the stable flame at the furnace mouth, performing the bomb throwing operation according to the real-time carbon content in the furnace, and dynamically calculating the cold charge amount through the thermal model to ensure that the smelting end-point temperature meets the standard; Step four, carrying out the gas stirring treatment in the converter tapping stage, and realizing the decarburization by the reaction between the residual free oxygen and carbon in the molten steel; Step five, after the converter tapping to the set tonnage, adding the deoxidizing alloy and the slagging deoxidizer to the molten steel to complete the decarburization and dephosphorization process.

2. The method of decarburization and dephosphorization at the end of the converter tapping according to claim 1, characterized in that, When the target steel grade in step one is XGL steel grade, the end-point carbon control interval is 0.055% to 0.075%.

3. The method of decarburization and dephosphorization at the end of the converter campaign according to claim 1, characterized in that, When the target steel grade in step one is SWRCH6A steel grade, the end-point carbon control interval is 0.055% to 0.07%.

4. The method of decarburization and dephosphorization at the end of the converter campaign according to claim 1, characterized in that, After adjusting the ratio of lime and dolomite in step two, the slag basicity is controlled between 2.8 and 3.2, and the lance pressing time is not less than 40 seconds.

5. The method of decarburization and dephosphorization at the end of the converter tapping according to claim 1, characterized in that, In step three, the ring gap flow in the late smelting stage is controlled to be not less than 300 cubic meters per hour, and the bomb throwing operation is performed when the carbon content in the furnace is in the interval of 0.08% to 0.12%.

6. The method of decarburization and dephosphorization of the converter tapping according to claim 1, characterized in that, In step four, the gas used for the gas stirring treatment is argon, and the argon supply is divided into two stages, the first stage is 120 seconds before tapping, and the argon flow is controlled to be 150 cubic meters per hour; the second stage is after 120 seconds before tapping, and the argon flow is controlled to be 60 cubic meters per hour.

7. The method of decarburization and dephosphorization of the converter tapping according to claim 1, characterized in that, In step five, the set tonnage is 40 tons to 50 tons, and the deoxidizing alloy and the slagging deoxidizer are added when the tapping amount reaches the set tonnage.

8. The method of decarburization and dephosphorization at the end of the converter campaign according to claim 1 or 7, characterized in that, The deoxidizing alloy includes high-aluminum aluminum-manganese iron and medium-carbon manganese iron, and the slagging deoxidizer is composed of 50 kilograms of slagging deoxidizer body and 200 kilograms of synthetic slag.

9. The method of decarburization and dephosphorization of the converter tapping according to claim 1, characterized in that, In step three, when the thermal model calculates the cold charge amount, the reference parameters include the silicon content of molten iron, the scrap ratio and the environmental temperature.

10. The method of decarburization and dephosphorization of the converter tapping according to claim 1, characterized in that, In step four, the reaction formula of the reaction between the residual free oxygen and carbon in the molten steel is [C]+[O]→CO(g), and through the reaction, the carbon content in the molten steel can be reduced by more than 0.012%.

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