A preparation method for improving cleanliness of plain carbon steel

Abstract

The present application belongs to the field of converter steelmaking system, and relates to a preparation method for improving the cleanliness of plain carbon steel, comprising the following steps: after the tapping of the previous furnace is completed, a soft slag stopping plug is added into the tapping hole; during the tapping process, top slag lime, calcium carbide, fluorite, strong deoxidizer, aluminum block, ferrosilicon and ferromanganese-silicon alloy are added into the ladle according to the end-point carbon and oxygen content of the molten steel; then, special aluminum-calcium-based pressure balls are added into the ladle, and after the tapping of the converter is completed, the ladle is opened into the argon blowing station; through an automatic soft blowing control model, the bottom blowing flow and time of the ladle are solidified and adjusted, and finally the ladle is organized to leave the station. Through the addition of the soft slag stopping plug and lime, aluminum block and special aluminum-calcium-based pressure balls before the tapping, the slag composition of the ladle reaches a certain range requirement, the argon gas is circularly stirred through the automatic module of the ladle, and the floating inclusions are adsorbed, so as to reduce the inclusion content and achieve the purpose of improving the cleanliness of the molten steel.

Description

Technical Field

[0001] This invention belongs to the field of converter steelmaking systems and relates to a method for improving the cleanliness of plain carbon steel. Background Technology

[0002] The conventional deoxidation and alloying process in converter smelting is as follows: After tapping from the furnace, a strong deoxidizer is added to the ladle—the required ferroalloy for the smelting steel grade is added—slag is blocked before tapping—after tapping, the ladle enters the argon station and is purged with argon for six minutes—the ladle is then lifted out of the argon station and hoisted to the continuous casting machine. During smelting, a large amount of molten ladle slag is generated in the furnace. All the slag floats on the surface of the molten steel. However, many impurities in the slag that are harmful to the composition of the molten steel are still unstable and may re-dissolve into the molten steel, becoming impurities in the steel. This leads to deviations in the steel composition and ultimately has an adverse effect on the quality of the steel.

[0003] Since the vast majority of the top slag in steel ladles comes from the final slag of the converter, controlling the amount of slag carried over during converter tapping is one of the most effective measures to reduce top slag volume. Various methods for controlling the amount of slag carried over during tapping have been developed both domestically and internationally, such as the slag-blocking ball method, slag-blocking plug method, slag-blocking material method, slag-avoiding hood method, electromagnetic slag-blocking method, sliding plate method, pneumatic slag-blocking method, slag-blocking rod method, slag pot slag-blocking method, and taphole air-blowing interference eddy current method. Many successful experiences in reducing the amount of slag carried over during the tapping process have been accumulated, which can be summarized as follows:

[0004] (1) Improve the efficiency of slag-blocking equipment and methods, such as improving and perfecting the slag-blocking body in terms of materials and structure;

[0005] (2) Prepare good process slag and control the converter terminal slag so that the terminal ladle slag has a certain degree of alkalinity, oxidizing properties and high viscosity;

[0006] (3) Strengthen the maintenance and management of the steel tapping outlet. For steel tapping outlets that are too large, timely maintenance of the bushings or replacement of the entire outlet is required to ensure that the steel tapping outlet meets the requirements.

[0007] However, the existing process involves a large number of inclusions and large particles, which affects the overall quality of the steel. Summary of the Invention

[0008] This invention provides a method for improving the cleanliness of carbon steel to solve the problems of traditional processes. Its feature is that by adjusting the range of ladle slag system and using argon blowing solidification mode, the purity of molten steel is ultimately improved.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for improving the cleanliness of plain carbon steel includes the following steps:

[0011] S1. After the previous furnace is tapped, a soft slag-blocking plug is added into the tapping port during the upward rocking process.

[0012] S2. After blowing is completed, the ladle is turned over and the steel is tapped. During the tapping process, top slag lime is added from the high-level silo into the ladle to control the slag basicity of the ladle at 1.5-2.0.

[0013] S3. After seeing the steel flow, add 20-40 kg of calcium carbide, and 20 seconds later add 10-30 kg of fluorite.

[0014] S4. Add a strong deoxidizer 10 seconds after step S3. Add 0.17-0.42 kg / t of aluminum blocks according to the carbon and oxygen content at the end of the molten steel.

[0015] S5. Add ferrosilicon and ferrosilicon manganese alloys required for steelmaking;

[0016] S6. Add specially made aluminum-calcium based briquettes into the ladle to control the Al2O3 content of the ladle slag to 10-15%; reduce the TFe content in the ladle to less than 1%.

[0017] S7. After the converter tapping is completed, the molten steel ladle is moved into the argon blowing station;

[0018] S8. Through the automatic soft blowing control device, the bottom blowing flow rate and time of the ladle are fixed and adjusted. During the strong blowing stage, the bottom blowing flow rate is set to 800NL / min and the strong blowing time is 3min. After 3min, it automatically switches to the soft blowing stage, the bottom blowing flow rate is automatically switched to 100NL / min and the soft blowing time is 6min.

[0019] S9. When the slag from the ladle changes from black to a glassy light brown, the ladle is removed from the station and transported to the continuous casting machine by overhead crane.

[0020] As a preferred technical solution, the weight of quicklime in S2 is 100 kg; when the quicklime addition is 100 kg, the composition of ladle slag is: TFe: 2.54%, SiO2: 26.19%, CaO: 40.74%, MgO: 8.59%, Al2O3: 8.35%, MnO: 3.31%, FeO: 3.27%, with the balance being unavoidable impurities; the basicity R is: 1.56.

[0021] As a preferred technical solution, the relationship between the endpoint carbon and oxygen levels and the amount of aluminum added in S4 is as follows: when the endpoint carbon is 0.04% and the oxygen level is 700ppm, the amount of aluminum added is 0.42Kg / t of molten steel; when the endpoint carbon is 0.10% and the oxygen level is 280ppm, the amount of aluminum added is 0.17Kg / t of molten steel.

[0022] As a preferred technical solution, the composition of the specially made aluminum-calcium based spheres in S6, calculated by mass percentage, is Al: 43-47%, Al2O3: 16-26%, CaO: 22-35%, SiO2: 1-2%, H2O: ≤1%.

[0023] As a preferred technical solution, the amount of specially made aluminum-calcium based briquettes added in S6 is 20-50 kg; when the amount of specially made aluminum-calcium based briquettes added is 20-50 kg, the content of ladle slag sample is: TFe: 0.72-0.81%, SiO2: 23.44-27.76%, CaO: 44.22-44.50%, MgO: 8.06-8.47%, Al2O3: 10.11-11.26%, MnO: 2.78-3.59%, FeO: 0.92-1.04%, with the balance being unavoidable impurities; the basicity R is: 1.60-1.89.

[0024] As a preferred technical solution, the inlet temperature in S7 is controlled above 1598℃.

[0025] As a preferred technical solution, the ladle slag composition is as follows: TFe: 0.81-0.98%, SiO2: 26.17-27.76%, CaO: 43.9-44.50%, MgO: 8.47-9.68%, Al2O3: 10.24-10.77%, MnO: 2.99-3.19%, FeO: 1.04-1.26%, with the balance being unavoidable impurities; the basicity R is 1.60-1.68.

[0026] As a preferred technical solution, the inclusions obtained by using this process are grade 1.5-2.0 and have a length of less than 191.67 μm.

[0027] The advantages and positive effects of this invention are:

[0028] This invention effectively controls the initial slag discharge by adding a soft slag-blocking plug before tapping, reducing the amount of slag in the ladle and improving the purity of the molten steel. During tapping, 100 kg of top slag quicklime is added to the ladle to facilitate the fluidity of the ladle slag and aid in the purification of the molten steel. After the steel flow is observed, calcium carbide, fluorite, and a strong deoxidizer are added sequentially. Depending on the carbon and oxygen content at the end of the molten steel, 0.17-0.52 kg / t of aluminum blocks are added, followed by the addition of ferrosilicon and ferromanganese alloy. Then, 20-50 kg of specially made aluminum-calcium based pressure balls are added to the ladle to control the Al2O3 content of the ladle slag at 10%-15%, improving the fluidity of the slag and reducing its oxidizing properties. This achieves the purpose of purifying the molten steel and improves the overall ladle slag's ability to adsorb inclusions. After tapping, the ladle is moved to the argon blowing station. Through an automatic soft blowing control model, the bottom blowing flow rate and time of the ladle are adjusted to ensure that inclusions in the steel float evenly to the reducing slag. Finally, the ladle exits the station. Practice has shown that when the new process is implemented, the quantity and grade of Class C silicate inclusions are reduced, thereby improving the purity of molten steel. Attached image description:

[0029] Figure 1 This is a schematic diagram showing the amount of slag discharged from the ladle when using a hard slag-blocking plug in this invention;

[0030] Figure 2 This is a schematic diagram showing the amount of slag discharged from the ladle when using a soft slag-blocking plug in this invention;

[0031] Figure 3 This is a schematic diagram of an automatic soft-blow control device;

[0032] Figure 4 This is the energy spectrum of silicate composite inclusions in sample 1 of the original process;

[0033] Figure 5 This is the energy spectrum of silicate composite inclusions in sample 2 of the original process;

[0034] Figure 6 This is the energy spectrum of silicate composite inclusions in sample 1 of the new process;

[0035] Figure 7 This is the energy spectrum of silicate composite inclusions in sample 2 of the new process.

[0036] Among them: 1. Steel slag; 2. Molten steel; 3. Steel outlet; 4. Steel ladle; 5-1. First ball valve; 5-2. First ball valve; 6-1. First solenoid valve; 6-2. Second solenoid valve; 7-1. First mass flow controller; 7-2. Second mass flow controller; 8-1. First timer; 8-2. Second timer; 9. Pipeline No. 1; 10. Pipeline No. 2. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention provides a method for improving the cleanliness of plain carbon steel, which mainly includes the following steps:

[0039] S1. After the previous furnace is finished tapping, add a soft slag-blocking plug into the tapping port during the upward rocking process.

[0040] The soft slag-blocking plug adopts the slag-blocking plug structure in patent CN212955203U. For example... Figure 1 As shown, the original process used a hardened slag-blocking plug that had been baked dry. It was cone-shaped, had a small contact area with the tapping spout, and poor resistance to the static pressure of molten steel. It could not adequately block the initial slag discharge, resulting in a significant amount of slag 1 being poured into the ladle 4 through the tapping spout 3 during tapping. For example... Figure 2 As shown, the new process uses a soft slag-blocking plug, which is cylindrical in shape and sealed in a plastic bag to retain some moisture. This allows it to heat up and expand inside the taphole, increasing the contact area with the taphole and greatly enhancing its resistance to static pressure of molten steel. This effectively controls the slag discharge in the early stage, reduces the amount of slag discharge from the ladle, and improves the purity of the molten steel.

[0041] Furthermore, the relationship between the weight of ladle residue and the residue composition of hard and soft slag plugs is shown in the following table:

[0042]

[0043] S2. After the blowing process is completed, the ladle is turned over and the steel is tapped. During the tapping process, top slag lime is added from the high-level silo into the ladle to control the slag basicity of the ladle at 1.5-2.0.

[0044] Preferably, the weight of quicklime is 100 kg. Comparative analysis using varying amounts of quicklime (100-300 kg) revealed that excessive addition prevented complete dissolution and hindered slag formation, impeding the fluidity of the ladle slag. Since desulfurization is not required, and only adsorption of impurities and purification of the molten steel by the ladle slag is needed, 100 kg of quicklime was chosen. The relationship between the amount of quicklime added and the composition of the ladle slag is shown in the table below.

[0045]

[0046] S3. After the steel flow is observed, add 20-40 kg of calcium carbide, followed by 10-30 kg of fluorite after 20 seconds. Calcium carbide is used to remove harmful elements such as sulfur and phosphorus from the molten steel, and to adjust the composition and temperature of the steel, thereby improving its quality. Fluorite acts as a flux and desulfurizer. The fluorine produced after the decomposition of fluorite reacts with sulfides in the steel to generate gas. As the gas is released, sulfur is removed, purifying the molten steel.

[0047] S4. Ten seconds after step S3, add a strong deoxidizer. Depending on the final carbon and oxygen levels in the molten steel, add 0.17-0.42 kg / t of aluminum blocks. The relationship between the final carbon and oxygen levels in the molten steel and the amount of aluminum blocks added is shown in the table below:

[0048]

[0049] S5. Add ferrosilicon and ferrosilicon manganese alloys required for steelmaking. Ferrosilicon and ferrosilicon manganese alloys act as deoxidizers to remove excess oxygen from molten steel, thereby obtaining qualified steel billets; they can also be used as alloying agents to adjust the chemical composition of steel; and they can also act as reducing agents.

[0050] S6. Adding specially made aluminum-calcium based briquettes into the ladle controls the Al2O3 content of the ladle slag to 10-15%, improving the slag fluidity and reducing its oxidizing properties. The TFe content in the ladle is reduced to less than 1%, which fully demonstrates that a reducing atmosphere is formed in the ladle, achieving the purpose of purifying the molten steel and improving the overall ladle slag's ability to adsorb inclusions.

[0051] The preferred composition of the specially made aluminum-calcium based pressure ball is shown in the table below:

[0052] content(%) 43-47 16-26 28-35 1-2 ≤1

[0053] Further preferred, the amount of specially formulated aluminum-calcium based briquettes added is 20-50 kg. The relationship between the amount of specially formulated aluminum-calcium based briquettes added and the content of slag in the ladle sample is shown in the table below:

[0054]

[0055] S7. After the converter tapping is completed, the molten steel ladle is moved into the argon blowing station. The temperature entering the station is controlled above 1598℃.

[0056] S8. Using an automatic soft-blow control model, the bottom blowing flow rate and time of the ladle are fixed and adjusted. During the strong blowing stage, the bottom blowing flow rate is set to 800 NL / min, the strong blowing time is 3 minutes, and the fluctuation range of the molten steel surface diameter is controlled at around 800 mm. After 3 minutes, it automatically switches to the soft blowing stage, the bottom blowing flow rate automatically switches to 100 NL / min, the soft blowing time is 6 minutes, and the fluctuation range of the molten steel surface diameter is controlled at around 100 mm.

[0057] like Figure 3As shown, the automatic soft blowing device is existing technology; its specific structure is described in [reference needed]. Figure 3 This will not be elaborated upon here.

[0058] By comparing different bottom blowing flow rates in the ladle, it was found that flow rates exceeding 800 NL / min caused the molten steel to rise into the air due to excessively high gas velocity, resulting in secondary oxygen absorption by the molten steel and an increase in the number of inclusions. Therefore, flow rates of 800 NL / min and 100 NL / min were selected for comparison. Strong blowing at 800 NL / min can meet the requirements for forming a reducing atmosphere in the ladle, while soft blowing at 100 NL / min can ensure that inclusions in the steel float evenly to the reducing slag.

[0059] S9. When the slag from the ladle changes from black to a glassy light brown, the ladle is removed from the station and transported to the continuous casting machine by overhead crane.

[0060] Metallographic analysis of molten steel rolled into strips using different processes yielded the following results: Figure 4-5 As shown, during the original process, a total of 4215 inclusions were detected, including 1652 silicate composite inclusions with nitride cores, the longest being approximately 705.05 μm; Figure 6-7 As shown, during the implementation of the new process, a total of 1900 inclusions were inspected, including 1551 silicate composite inclusions with nitride cores, the longest being approximately 191.67 μm. Practice has proven that this invention can control the composition of ladle slag to a certain range, reduce inclusion content, and thus improve the purity of molten steel.

[0061] The effects of the original and new processes on type C silicate inclusions are shown in the table below:

[0062]

[0063] After all process steps were completed, the ladle slag composition was measured inside the ladle. The effects of the two operating methods on the ladle slag composition are shown in the table below:

[0064]

[0065] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for improving the cleanliness of plain carbon steel, characterized in that: Includes the following steps: S1. After the previous furnace is tapped, a soft slag-blocking plug is added into the tapping opening during the upward shaking of the furnace. The soft slag-blocking plug is cylindrical and sealed with a plastic bag to retain some moisture, so that it heats up and expands in the tapping opening. S2. After blowing is completed, the ladle is turned over and the steel is tapped. During the tapping process, top slag lime is added from the high-level silo into the ladle to control the slag basicity of the ladle at 1.5-2.

0. S3. After seeing the steel flow, add 20-40 kg of calcium carbide, and 20 seconds later add 10-30 kg of fluorite. S4. Add a strong deoxidizer 10 seconds after step S3. Add 0.17-0.42 kg / t of aluminum blocks according to the carbon and oxygen content at the end of the molten steel. S5. Add ferrosilicon and ferrosilicon manganese alloys required for steelmaking; S6. Add specially made aluminum-calcium based briquettes into the ladle to control the Al2O3 content of the ladle slag to 10-15%; reduce the TFe content in the ladle to below 1%; the composition of the specially made aluminum-calcium based briquettes is Al: 43-47%, Al2O3: 16-26%, CaO: 28-35%, SiO2: 1-2%, H2O: ≤1%; the amount of specially made aluminum-calcium based briquettes added is 20-50 kg; when the amount of specially made aluminum-calcium based briquettes added is 20 kg... At a weight of 50 kg, the ladle slag composition is as follows: TFe: 0.72-0.81%, SiO2: 23.44-27.76%, CaO: 44.22-44.50%, MgO: 8.06-8.47%, Al2O3: 10.11-11.26%, MnO: 2.78-3.59%, FeO: 0.92-1.04%, with the balance being unavoidable impurities; the basicity R is 1.60-1.

89. S7. After the converter tapping is completed, the molten steel ladle is moved into the argon blowing station; S8. Through the automatic soft blowing control device, the bottom blowing flow rate and time of the ladle are fixed and adjusted. The bottom blowing flow rate during the strong blowing stage is set to 800NL / min and the strong blowing time is 3min. After 3 minutes, it will automatically switch to the soft blowing stage, with the bottom blowing flow rate automatically set to 100 NL / min and the soft blowing time being 6 minutes. S9. When the slag from the ladle changes from black to a glassy light brown, the ladle is removed from the station and transported to the continuous casting machine by overhead crane. The inclusions obtained using this process are grade 1.5-2.0 and have a length of less than 191.67 μm.

2. The preparation method for improving the cleanliness of plain carbon steel as described in claim 1, characterized in that: The weight of quicklime in S2 is 100 kg; when the quicklime content is 100 kg, the ladle slag composition is: TFe: 2.54%, SiO2: 26.19%, CaO: 40.74%, MgO: 8.59%, Al2O3: 8.35%, MnO: 3.31%, FeO: 3.27%; alkalinity R: 1.

56.

3. The preparation method for improving the cleanliness of plain carbon steel as described in claim 1, characterized in that: The relationship between the final carbon and oxygen levels and the amount of aluminum added in S4 is as follows: when the final carbon level is 0.04% and the oxygen level is 700ppm, the amount of aluminum added is 0.42Kg / t of molten steel; when the final carbon level is 0.10% and the oxygen level is 280ppm, the amount of aluminum added is 0.17Kg / t of molten steel.

4. The preparation method for improving the cleanliness of plain carbon steel as described in claim 1, characterized in that: The inlet temperature of S7 is controlled above 1598℃.

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