A method for continuous casting of high-purity electrode flat steel YTO

Abstract

This invention discloses a continuous casting production method for high-purity electrode flat steel YTO. The electrode flat steel YTO is mainly used as the cathode of the electrolytic cell in the electrolytic aluminum industry. It has extremely high requirements for the control of the composition C, Si, Mn, P and inclusions, which increases the difficulty of smelting the product. By optimizing the continuous casting process, the content of P, S and inclusions in the molten steel is controlled at a low level, which improves the cleanliness of the electrode flat steel, ensures the quality of the cast billet, increases the yield of the product, and reduces the production cost.

Description

Technical Field

[0001] This invention relates to the field of steelmaking technology in iron and steel metallurgy, and in particular to a continuous casting production method for high-purity electrode flat steel YTO. Background Technology

[0002] The successful development of electrode flat steel meets the needs of different customers in the market. It can be designed and produced according to the special needs of customers to realize customized services. It can achieve multi-specification, multiple length, single length, and through-seam deep processing and cutting delivery, directly providing aluminum plants with finished electrolytic cathode rods, reducing the processing and logistics costs of aluminum plants, and significantly shortening the processing cycle, providing convenient services for major domestic and foreign electrolytic aluminum enterprises. Summary of the Invention

[0003] The purpose of this invention is to provide a method for continuous casting of high-purity electrode flat steel YT0. Through process optimization of converter, LF furnace, RH furnace and casting machine processes, the cleanliness of electrode flat steel billet is improved, the composition of molten steel is stably controlled, and the stable control of product performance is guaranteed, laying the foundation for the stable production of electrode flat steel.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for continuous casting of high-purity electrode flat steel YTO, with the following process path: KR desulfurization—converter—LF furnace—RH furnace—casting machine; wherein:

[0006] The molten iron must undergo KR desulfurization treatment, requiring the sulfur content of the molten iron entering the converter to be ≤0.003%, and the desulfurization slag removal area to be greater than 95%;

[0007] The converter's final temperature is controlled at ≥1600℃, and the final oxygen content is controlled at less than 900ppm. Normal turnover ladles must be used, and top slag modifiers are added to the top slag during converter tapping for top slag modification.

[0008] The purpose of adding quicklime and modifiers to the LF furnace for heating and smelting is to reduce the content of P and Mn in the molten steel, provide a suitable temperature for the RH furnace, reduce the oxygen blowing volume of the RH furnace, and increase the cleanliness of the molten steel.

[0009] The RH furnace undergoes deep decarburization treatment, with the oxygen content at the decarburization endpoint controlled below 350 ppm. After decarburization, aluminum particles are added for deoxidation and the composition of molten steel is adjusted to ensure that the pure degassing time of molten steel is more than 7 minutes. After repressurization, a modifier is added for top slag modification.

[0010] The casting machine adopts constant casting speed control, with a casting speed range of 1.0-1.3m / min. The casting superheat is controlled between 30-40℃, and protective casting is carried out throughout the continuous casting process.

[0011] Furthermore, the converter charge is controlled at 280-288 tons.

[0012] Furthermore, the amount of quicklime added during the LF refining process is 620-680 kg.

[0013] Furthermore, the amount of modifier added during the LF refining process is 500-1100 kg.

[0014] Furthermore, the RH furnace undergoes vacuum decarburization treatment, with the oxygen content at the carbon endpoint controlled at 250-317 ppm.

[0015] Furthermore, the casting machine speed is 1.2 m / min, the casting superheat is controlled between 31-37℃, and protective pouring is carried out throughout the continuous casting process.

[0016] Furthermore, the inclusion detection was completed: the inclusions D and Ds were found to be within level 1.0, and the results of the detection of the remaining inclusions were all level 0.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] (1) The temperature control in the converter smelting process is relatively low, the amount of lime added is increased, the P and Mn content in the molten steel is controlled within a low range, and the over-oxidation of the converter during tapping is prevented, thus improving the cleanliness of the molten steel.

[0019] (2) The YTO process path for electrode flat steel adds the LF furnace process. The purpose of heating and smelting in the LF furnace is to reduce the content of P and Mn in the molten steel, provide a suitable temperature for the RH furnace, reduce the oxygen blowing amount in the RH furnace, and increase the cleanliness of the molten steel.

[0020] (3) After the vacuum decarburization of the RH furnace is completed, the oxygen content at the end of the decarburization is controlled within 350ppm. Due to the low control of the end oxygen content, the aluminum content required for deoxidation is reduced, the Al2O3 inclusions formed in the steel are reduced, and the cleanliness of the molten steel is improved.

[0021] (4) Continuous casting adopts protective casting to prevent secondary oxidation of molten steel.

[0022] This invention provides a widely applicable continuous casting method for YTO electrode flat steel, producing electrode flat steel with extremely high cleanliness. Through process optimization in the converter, LF furnace, RH furnace, and casting machine stages, this invention improves the cleanliness of the electrode flat steel billet, stably controls the steel composition, and ensures stable product performance control, laying the foundation for stable production of electrode flat steel. The product quality has been recognized by users, enhancing the market competitiveness of this specialty product. Detailed Implementation

[0023] The following embodiments are used to specifically illustrate the content of the present invention. These embodiments are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0024] Comparative Example 1:

[0025] In the early stages of production, the oxygen content at the converter's endpoint was controlled to be below 1200ppm, resulting in a relatively high oxygen content at the RH endpoint of around 500ppm. This led to a large number and size of inclusions in the product, which seriously affected the quality of the cast billet. The specific process conditions in the early stages of production are as follows.

[0026] Process route: KR desulfurization—converter—LF furnace—RH furnace—casting machine.

[0027] The finished YT0 steel requires a sulfur content of ≤0.009%. The KR desulfurization process adopts deep desulfurization operation. The amount of desulfurizing agent added during the KR desulfurization process is 1.8 to 2.7 tons, the stirring time is greater than 19 minutes, the slag removal is carried out twice per heat of steel casting, and the slag removal rate is greater than 95%, to ensure that the sulfur content of the molten iron entering the furnace meets the requirements (the sulfur content of the molten iron entering the furnace is required to be ≤0.0010%). The KR desulfurization process and the amount of desulfurizing agent added are shown in Table 1.

[0028] Table 1. KR desulfurization process and desulfurizing agent dosage

[0029]

[0030] The molten iron produced in this batch has a Si content of 0.32-0.47%, a relatively high P content of 0.139-0.150%, a manganese content of 0.43-0.51% (the finished product requires a manganese content of less than 0.10%), a sulfur content of 0.001%, and a temperature of over 1337℃, meeting the requirements for molten iron entering the furnace (as shown in Table 2).

[0031] Table 2. Molten iron condition before KR desulfurization treatment

[0032]

[0033] The converter charge for this casting process was controlled at 286-295 tons, and all scrap steel fed into the furnace was added from steel mill self-produced scrap steel to meet the low sulfur control requirements for scrap steel. To control and stabilize the process temperature during converter smelting, quicklime, dolomite, iron briquettes, etc., were added to the converter. The amounts of iron-containing materials and slag added are shown in Table 3.

[0034] Table 3. Amount of iron-containing materials and slag added (t)

[0035]

[0036] The final temperature of the converter in this casting was controlled at 1615-1642℃, and the oxygen content at the final point of the converter was controlled at above 950ppm. The oxygen content at the final point of the converter was too high, and the converter was severely over-oxidized. When the steel was tapped from the converter, lime and modifiers were added to modify the top slag. The temperature drop at the final point of the converter tapping was controlled as shown in Table 4.

[0037] Table 4. Converter end-point control of tapping temperature drop

[0038]

[0039] The manganese content at the final stage of the converter was controlled to be less than 0.08%, and the phosphorus content at the final tapping was less than 0.013%. The final tapping composition of the converter is shown in Table 5.

[0040] Table 5. Steel composition at the final tapping point of the converter (%)

[0041] Serial Number C Mn P S 1# 0.019 0.08 0.009 0.006 2# 0.021 0.07 0.012 0.006 3# 0.022 0.07 0.013 0.005 4# 0.020 0.08 0.014 0.006 5# 0.018 0.07 0.008 0.005

[0042] The converter tapping process does not involve deoxidation, but quicklime and modifiers are added during the LF treatment. To improve dephosphorization efficiency and submerged arc heating during the LF refining process, approximately 500 kg of quicklime and 600 kg of modifiers are added. During LF heating, the slag and molten steel are oxidizing, and P and Mn are further oxidized, producing oxides that enter the slag and reduce the P and Mn content in the molten steel. The steel composition during the LF treatment is shown in Table 6.

[0043] Table 6. Steel composition (%) during LF processing

[0044] Serial Number Process Mn P S 1# LF off-position 0.020 0.003 0.006 2# LF off-position 0.017 0.003 0.006 3# LF off-position 0.020 0.002 0.005 4# LF off-position 0.04 0.003 0.005 5# LF off-position 0.018 0.002 0.006

[0045] The RH vacuum treatment process is stable. The RH furnace performs vacuum decarburization, and the oxygen content at the carbon endpoint is controlled between 450 and 531 ppm. After decarburization, aluminum particles are added for deoxidation, with a relatively large amount of deoxidized aluminum added, ranging from 180 to 212 kg. After the RH deoxidation alloying is completed, the pure degassing time is ensured to be within 5 minutes. The composition of the RH molten steel meets the design requirements (see Table 7).

[0046] Table 7. Composition of RH-exposed molten steel (%)

[0047]

[0048] The casting machine adopts constant casting speed control, with a casting speed of 1.3 m / min. The casting superheat is controlled between 22 and 33°C. Protective casting is carried out throughout the continuous casting process, and the composition of the tundish meets the design requirements (see Table 8).

[0049] Table 8 lists the chemical composition (%)

[0050] Serial Number C Si Mn P S Al Superheat (°C) 1# 0.0020 0.000 0.045 0.006 0.006 0.020 22 2# 0.003 0.010 0.045 0.003 0.006 0.022 29 3# 0.001 0.000 0.046 0.006 0.006 0.021 31 4# 0.003 0.010 0.045 0.004 0.006 0.018 33 5# 0.0020 0.000 0.046 0.003 0.006 0.019 31

[0051] Inclusion detection was completed. The results showed that inclusions of type D and type Ds were within grade 1.0, while inclusions of type B were grade 0.5 to 1.0. The presence of inclusions of type B affects the quality of molten steel (as shown in Table 9).

[0052] Table 9. Inspection results of inclusions (%)

[0053]

[0054] Example 1:

[0055] Through process optimization, the oxygen content at the converter endpoint was reduced to within 900 ppm and the oxygen content at the RH vacuum decarburization endpoint was reduced to within 350 ppm, thereby improving the cleanliness of the molten steel and enhancing the quality of the cast billet.

[0056] Process route: KR desulfurization—converter—LF furnace—RH furnace—casting machine.

[0057] The finished YT0 steel requires a sulfur content of ≤0.009%. The KR desulfurization process adopts deep desulfurization operation. The amount of desulfurizing agent added during the KR desulfurization process is 0.8 to 1.8 tons, the stirring time is greater than 15 minutes, the slag removal is carried out twice per heat of steel casting, and the slag removal rate is greater than 95%, to ensure that the sulfur content of the molten iron entering the furnace meets the requirements (the sulfur content of the molten iron entering the furnace is required to be ≤0.0010%). The KR desulfurization process and the amount of desulfurizing agent added are shown in Table 10.

[0058] Table 10 KR Desulfurization Process and Desulfurizing Agent Dosage

[0059]

[0060] The molten iron produced in this batch has a Si content of 0.36-0.47%, a relatively high P content of 0.139-0.150%, a manganese content of 0.46-0.50% (the finished product requires a manganese content of less than 0.10%), a sulfur content of 0.001%, and a temperature of over 1342℃, meeting the requirements for molten iron entering the furnace (as shown in Table 11).

[0061] Table 11. Conditions of molten iron before KR desulfurization treatment

[0062]

[0063] The converter charge for this casting process was controlled at 280-288 tons, with all scrap steel added from the steel rolling mill itself to meet the low-sulfur control requirements. To control and stabilize the process temperature and maximize dephosphorization and demanganese removal from the slag, the consumption of slag and iron-containing materials was relatively large. The amounts of quicklime, dolomite, and iron pellets used were 24-30 tons. By increasing the amount of slag, the total amount of MnO and P2O5 in the slag was increased, ultimately maximizing dephosphorization and demanganese removal. The amounts of iron-containing materials and slag added are shown in Table 12.

[0064] Table 12. Amount of iron-containing materials and slag added (t)

[0065]

[0066] The converter's final temperature for this casting was controlled at 1601–1619℃. By controlling the low temperature at the final stage, the converter effectively reduced the residual manganese content. The manganese content supplied by the converter for LF refining was less than 0.04%, meeting the control requirement (less than 0.10%). The oxygen content at the final stage of this casting was controlled at 600–900 ppm. Since dephosphorization in the LF refining process requires high oxidizing properties, the oxygen content at the final stage of the converter needs to be controlled slightly higher to ensure the dephosphorization rate in the LF refining process. The temperature drop at the tapping stage of the converter is shown in Table 13.

[0067] Table 13 Converter End-Point Control of Steel Tap Temperature Drop

[0068]

[0069] The converter's final composition control is good and meets the requirements for converter final control. The converter avoids manganese return during the process by controlling the low temperature and high oxidizing properties of the slag. The control of the final low temperature, large slag volume, and high oxidizing slag eliminates manganese return in the later stage of smelting. Finally, the manganese content at the converter final is stably controlled at less than 0.08%, and the phosphorus content at the final tap steel is less than 0.010%. The composition of the final tap steel is shown in Table 14.

[0070] Table 14. Steel composition at the final tapping point of the converter (%)

[0071] Serial Number C Mn P S 6# 0.035 0.06 0.010 0.005 7# 0.037 0.08 0.009 0.003 8# 0.043 0.08 0.011 0.006 9# 0.040 0.06 0.006 0.005 10# 0.045 0.07 0.007 0.006

[0072] The converter tapping process does not involve deoxidation, but quicklime and modifiers are added during the LF treatment. To improve dephosphorization efficiency and submerged arc heating during the LF refining process, approximately 650 kg of quicklime and 500–1100 kg of modifiers are added. During LF heating, the slag and molten steel are oxidizing, and P and Mn are further oxidized, producing oxides that enter the slag and reduce the P and Mn content in the molten steel. The steel composition during the LF treatment is shown in Table 15.

[0073] Table 15 Steel composition (%) during LF processing

[0074]

[0075] The RH vacuum treatment process is stable, and the in-situ oxygen content meets the decarburization requirements. The RH furnace is used for vacuum decarburization treatment, and the oxygen content at the carbon endpoint is controlled between 250 and 317 ppm. After decarburization, 102-126 kg of aluminum particles are added for deoxidation. After the RH deoxidation alloying is completed, the pure degassing time is ensured to be more than 7 minutes. Extending the pure degassing time and reducing the oxygen content at the decarburization endpoint ensures the cleanliness of the molten steel. The composition of the RH out-of-situ molten steel meets the design requirements (see Table 16).

[0076] Table 16. Composition of RH-exposed molten steel (%)

[0077]

[0078] The casting machine adopts constant casting speed control, with a casting speed of 1.2 m / min. The casting superheat is controlled between 31 and 37°C. Protective casting is carried out throughout the continuous casting process, and the composition of the tundish meets the design requirements (see Table 17).

[0079] Table 17 lists the chemical composition (%)

[0080]

[0081]

[0082] Inclusion testing was completed. The results showed that inclusions of type D and type Ds were within level 1.0, while inclusions of type B and the rest were all at level 0. This indicates that reducing the oxygen content at the converter endpoint, reducing the oxygen content at the RH decarburization endpoint, and extending the pure degassing time ensured the cleanliness of the molten steel and met the design requirements (as shown in Table 18).

[0083] Table 18. Inspection results of inclusions (%)

[0084]

[0085] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-cleanliness electrode flat steel YT0 steelmaking continuous casting production method, characterized in that, Process route: KR desulphurization - converter - LF furnace - RH furnace - caster; wherein: The molten iron needs to be treated by KR desulphurization, and the requirement is that the sulphur content of the molten iron entering the converter is ≤0.003%, and the desulphurization slag cleaning area is greater than 95%; The converter endpoint temperature is controlled at ≥1600℃, and the endpoint oxygen content is controlled within 900ppm, a normal turnaround ladle must be used, and top slag modification agent is added during converter tapping for top slag modification; White lime and modification agent are added in the LF furnace for heating and smelting, the purpose is to reduce the P and Mn content in the molten steel, to provide suitable temperature for the RH furnace, to reduce the oxygen blowing amount of the RH furnace, and to increase the cleanliness of the molten steel; wherein the white lime addition amount during the LF refining process is 620-680kg; the modification agent addition amount during the LF refining process is 500-1100kg; The RH furnace performs deep decarburization treatment, and the decarburization endpoint oxygen content is controlled within 350ppm, after the decarburization is completed, aluminum particles are added for deoxidization and adjustment of the molten steel composition, to ensure that the pure degassing time of the molten steel is more than 7min, and after the re-pressurization, modification agent is added for top slag modification; The caster uses constant speed control, the casting speed range is 1.0-1.3m / min, the caster casting superheat is controlled between 30-40℃, and the whole continuous casting process is protected casting.

2. The high-cleanliness electrode flat steel YT0 steelmaking continuous casting production method according to claim 1, characterized in that, The converter charging amount is controlled at 280-288 tons.

3. The high-cleanliness electrode flat steel YT0 steelmaking continuous casting production method according to claim 1, characterized in that, The RH furnace performs vacuum decarburization treatment, and the carbon endpoint oxygen content is controlled at 250-317ppm.

4. The high-cleanliness electrode flat steel YT0 steelmaking continuous casting production method according to claim 1, characterized in that, The caster casting speed is 1.2m / min, the caster casting superheat is controlled between 31-37℃, and the whole continuous casting process is protected casting.

5. The high-cleanliness electrode flat steel YT0 steelmaking continuous casting production method according to claim 1, characterized in that, Complete inclusion detection: after inspection, the inclusions D and Ds are within 1.0 level, and the rest of the inclusion detection results are 0 level.

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