Method for smelting ultra-low carbon steel through establishment of RH process decarburization platform

Abstract

The invention discloses a method for smelting ultra-low carbon steel through establishment of an RH process decarburization platform. The method comprises the steps of desulfurization, converter-RH vacuum refining, molten iron desulfurization and slagging-off, and control of the sulfur content of molten iron entering a furnace. Carrying out converter non-sedative tapping, and carrying out modification treatment on the slag after tapping; in the RH refining process, natural decarburization is taken as a main part, forced decarburization is taken as an auxiliary part, after decarburization is finished, deoxidation alloying and pure circulation inclusion removal are carried out, and the smelting target of ultra-low carbon is achieved. According to the method, RH vacuum decarburization serves as the center, the converter procedure provides crude steel meeting the requirement, an ultra-low carbon steel decarburization platform is established, efficient and stable decarburization of the ultra-low carbon steel RH vacuum treatment procedure is achieved, and the carbon content of molten steel obtained after RH decarburization can be stably controlled to be smaller than or equal to 10 ppm. According to the method, the RH vacuum decarburization efficiency can be effectively improved, it is guaranteed that the carbon content of molten steel is controlled to a low level, and the product performance and stability of ultra-low carbon steel are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for smelting ultra-low carbon steel by establishing a decarburization platform through an RH process. Background Art

[0002] Ultra-low carbon steel usually refers to steel with a carbon content of less than 0.01%. Its typical representative steel is IF steel. The ultra-low carbon steel currently developed includes: ultra-low carbon high-strength IF steel, hot-dip galvanized IF steel and ultra-low carbon electrical steel. It is a symbol of a country's automotive steel production level. The key to ultra-low carbon production is the control of carbon content. If the carbon content of ultra-low carbon steel can be stably controlled at ≤20ppm, the ultra-low carbon steel has the following advantages: ① excellent deep drawing performance and electromagnetic properties; ② no aging; ③ excellent processing formability; ④ high strain.

[0003] When smelting ultra-low carbon steel, the process is generally as follows: desulfurization-converter-RH vacuum refining, molten iron desulfurization and slag removal, and sulfur content of molten iron entering the furnace is controlled; non-quiet steelmaking in the converter, and slag modification after steelmaking; the RH refining process is mainly natural decarburization, supplemented by forced decarburization, and after decarburization, multiple process steps such as deoxidation alloying and pure circulation to remove inclusions are carried out to achieve the ultra-low carbon smelting goal. Among them, RH vacuum refining is the key to smelting ultra-low carbon decarburization. The vacuum decarburization effect directly affects the carbon content of ultra-low carbon steel at the end. For this reason, we have invented a method for smelting ultra-low carbon steel through the RH process decarburization platform based on industrial production practice. This method is centered on RH vacuum decarburization, and the converter process provides crude steel that meets the requirements. An ultra-low carbon steel decarburization platform is established, and the ultra-low carbon steel RH vacuum treatment process is realized. Efficient and stable decarburization, the carbon content of molten steel after RH decarburization can be stably controlled at ≤10ppm. This invention can effectively improve the efficiency of RH vacuum decarburization, ensure that the carbon content of molten steel is controlled at a low level, and greatly improve the product performance and stability of ultra-low carbon steel. Summary of the invention

[0004] The purpose of the present invention is to provide a method for smelting ultra-low carbon steel through an RH process decarburization platform, which is specifically applied to the smelting of ultra-low carbon steel by RH vacuum refining in various steel mills. The invention can effectively improve the RH decarburization efficiency and ensure that the carbon content after decarburization in the RH process is ≤10ppm, thereby greatly improving the product performance and stability of ultra-low carbon steel.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for smelting ultra-low carbon steel by using a RH process decarburization platform, comprising:

[0007] 1) KR desulfurized hot metal pretreatment steps: after pretreatment, [S] in the hot metal should be ≤ 0.003%, the hot metal temperature should be ≮1300℃, and pneumatic double slag removal should be adopted to ensure that the hot metal mirror surface rate is ≥ 95%;

[0008] 2) Converter smelting steps: the ratio of pre-treated molten iron and clean scrap steel is 5:1-7:1, the temperature of molten iron entering the furnace is ≥1300℃, the S content in the molten iron is ≤0.003%, and active lime and high-silicon dolomite must be added during the blowing process to ensure the slag basicity; top and bottom composite blowing and bottom blowing are carried out with argon blowing throughout the process, sampling, temperature measurement and oxygen determination are carried out after the converter is carbonized, [C] is controlled at 0.025-0.055%, the temperature is controlled at 1680-1705℃, the oxygen content is controlled at 700-950ppm, and [S] ≤0.003%; in principle, the carbon temperature is guaranteed to be hit once, and the spot blowing is not more than once; during the steel tapping process, the steel outlet does not disperse and the steel tapping time is ≮5 minutes, and slag is strictly prohibited. During the steel tapping process, slag washing is carried out to ensure that the inclusions are fully gathered and floated, and the purity of the molten steel is improved. The terminal temperature of the molten steel shall comply with the current operating standards;

[0009] The target of RH molten steel for converter is: [C]: 0.025%~0.055%, [O]: (500~750)×10 -6 , T = 1615 ~ 1635 ℃;

[0010] 3) RH refining step: The temperature of the molten steel at the RH station is 1615-1635℃, and the minimum vacuum degree must reach below 266Pa after evacuation for ≯4 minutes, and the vacuum degree fluctuation rebound during the vacuum treatment is ≤100Pa. Based on the monitoring and analysis of the flue gas CO data, the RH end point CO and decarburization relationship curve is determined, and the RH decarburization end point is determined by the CO change. During the process, the circulating argon flow rate is adjusted to ensure sufficient circulation of the molten steel and decarburization as quickly as possible to ensure the decarburization effect, so that the carbon content in the molten steel is ≤10ppm at 15min; use a micro-carbon high-purity alloy for deoxidation and alloying, control the alloy carbon increase to ≯5ppm, the pure degassing time after alloying is ≥5 minutes, the molten steel is left to stand for ≥5 minutes before steel is added, and the molten steel targets when leaving the position are: [C]≤15ppm, [H]≤1.2ppm, [O]≤15ppm, [N]≤20ppm;

[0011] 4) Casting machine steps: Use special protective slag for ultra-low carbon steel and carbon-free tundish covering agent, seal the water nozzle during continuous casting, and protect the tundish pouring to ensure that the carbon and nitrogen addition amounts are ≯5ppm.

[0012] Furthermore, in step 2), the steel-tapping time needs to be strictly controlled and should be greater than 5 minutes. At the same time, the steel flow cannot be dispersed during steel-tapping. At the same time, the slag-blocking effect of the converter is improved and slag is strictly prohibited. Good conditions need to be created for the modification of the ladle top slag.

[0013] Furthermore, in step 2), the converter dry dust removal gas analyzer is used to analyze the converter end point flue gas CO change data curve, determine the converter end point CO and C relationship curve, determine the converter end point C content through the CO change, and achieve precise carbon pulling at the converter end point; through the use of this technology, the converter end point carbon content of ultra-low carbon steel is accurately controlled at 0.025-0.055%.

[0014] Furthermore, in step 2), slag is added at 1 / 3 of the steel tapping process and is completed at 2 / 3. The argon volume is controlled at 1500N l / m 3 The remaining 1 / 3 is controlled by a small flow rate of 200-300N l / m 3 , until the steel is tapped, the stirring of argon is always guaranteed to promote slag formation and the completion of top slag modification. During the steel tapping process, slag washing operation is performed to add active lime and part of the slag-removing agent into the ladle. The amount of lime added is 2-3.5kg / t steel, and the amount of slag-removing agent added is 1-1.5kg / t steel. After the steel is tapped, about 100kg of aluminum iron powder is added to the surface of the molten steel in the ladle.

[0015] Furthermore, oxygen blowing is not recommended in step 3). If oxygen blowing is required, it should be performed when the vacuum degree reaches 10 kPa. Generally, oxygen blowing is completed when the vacuum degree reaches between 6 and 10 kPa.

[0016] Furthermore, according to the oxygen blowing flow rate of 2000Nm 3 / h, oxygen blowing 10m 3 Add 27-30 ppm of oxygen to the steel for estimation.

[0017] Furthermore, the carbon content of molten steel after RH decarburization can be stably controlled at ≤10ppm.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] According to the characteristics of the ultra-low carbon steel smelting process, the present invention has successfully developed a method for smelting ultra-low carbon steel through the RH process decarburization platform based on the precise control of the CO at the converter end point and the RH vacuum refining rapid decarburization technology. That is, through the precise control of the CO at the converter end point to create good steel-passing conditions for the RH, the RH adopts low vacuum and high circulation flow to rapidly decarburize, and at the same time controls the deoxidation and alloying processes to increase carbon, thus establishing an ultra-low carbon steel production mode with rapid decarburization in the RH process. At the same time, the casting machine strictly protects the pouring, and uses carbon-free covering agents and other methods to ensure that the carbon and nitrogen addition amounts are ≯5ppm. By using a method for smelting ultra-low carbon steel through the RH process decarburization platform, it is achieved in industrial production that the molten steel [C] of ultra-low carbon steel after RH decarburization is ≤10ppm, the molten steel [C] when the RH is out of position is ≤15ppm, and the molten steel [C] is ≤20ppm when the casting machine pouring is completed.

[0020] In summary, a method for smelting ultra-low carbon steel by establishing a decarburization platform through the RH process can realize the industrial production of ultra-low carbon steel, and its carbon content can be stably controlled at ≤20ppm, fully meeting the requirements of the ultra-low carbon steel market and customers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings.

[0022] Figure 1 This is the converter flue gas composition change curve. DETAILED DESCRIPTION

[0023] A technical solution for establishing a method for smelting ultra-low carbon steel through a RH process decarburization platform is:

[0024] 1) KR desulfurized iron pretreatment steps: After pretreatment, [S] in the iron is required to be ≤0.003%, the iron temperature is ≮1300℃, and pneumatic double slag removal is used to ensure that the iron mirror surface rate is ≥95%.

[0025] 2) Converter smelting steps: The ratio of pre-treated molten iron and clean scrap steel is 5:1-7:1, the temperature of molten iron entering the furnace is ≥1300℃, the S content in the molten iron is ≤0.003%, and active lime and high-silicon dolomite must be added during the blowing process to ensure the slag basicity; top and bottom composite blowing and bottom blowing are operated with argon blowing throughout the process, sampling, temperature measurement, and oxygen determination after the converter is carbonized, [C] is controlled at 0.025-0.055%, the temperature is controlled at 1680-1705℃, the oxygen content is controlled at 700-950ppm, and [S] ≤0.003%. In principle, the carbon temperature is guaranteed to be hit once, and the spot blowing is not more than once. During the steel-making process, the steel-making outlet does not disperse and the steel-making time is ≮5 minutes. It is strictly forbidden to slag. During the steel-making process, slag washing is performed to ensure that the inclusions are fully gathered and floated, and the purity of the molten steel is improved. The terminal temperature of the molten steel shall comply with the current operating standards.

[0026] The target of RH molten steel for converter is: [C]: 0.025%~0.055%, [O]: (500~750)×10 -6 , T=1615~1635℃.

[0027] 3) RH refining step: The temperature of RH molten steel is 1615~1635℃, and the minimum vacuum degree must reach below 266Pa after evacuation for ≯4 minutes, and the vacuum degree fluctuation rebound is ≤100Pa during vacuum treatment. Based on the monitoring and analysis of flue gas CO data, the RH end point CO and decarburization relationship curve is determined, and the RH decarburization end point is determined by the CO change. During the process, the circulation argon flow rate is adjusted to ensure sufficient circulation of the molten steel and decarburization as quickly as possible to ensure the decarburization effect, so that the carbon content in the molten steel is ≤10ppm at 15min. Use micro-carbon high-purity alloys such as micro-carbon aluminum iron / high-purity silicon steel for deoxidation and alloying, control the carbon increase of the alloy to ≯5ppm, the pure degassing time after alloying is ≥5 minutes, and the molten steel is left to stand for ≥5 minutes before steel is added. The molten steel targets when leaving the position are: [C]≤15ppm, [H]≤1.2ppm, [O]≤15ppm, [N]≤20ppm.

[0028] After the RH process, the molten steel finally fully meets the composition requirements of ultra-low carbon steel as shown in Table 1:

[0029] Table 1 Requirements for ultra-low carbon molten steel composition

[0030] element C S O N H Require <15ppm <30ppm <15ppm <20ppm <1.2ppm

[0031] 4) Casting machine steps: Use special protective slag for ultra-low carbon steel and carbon-free tundish covering agent, seal the water nozzle during continuous casting, and protect the tundish pouring to ensure that the carbon and nitrogen addition amounts are ≯5ppm.

[0032] Furthermore, in step 2), the steel-tapping time needs to be strictly controlled and should be greater than 5 minutes. At the same time, the steel flow cannot be dispersed during steel-tapping. At the same time, the slag-blocking effect of the converter is improved and slag is strictly prohibited. Good conditions need to be created for the modification of the ladle top slag.

[0033] Furthermore, in step 2), the converter dry dust removal gas analyzer is used to analyze the converter end flue gas CO change data curve, determine the converter end CO and C relationship curve, determine the converter end C content by CO change, and achieve accurate carbon extraction at the converter end. By using this technology, the converter end carbon content of ultra-low carbon steel can be accurately controlled at 0.025-0.055%. See details. Figure 1 :

[0034] Furthermore, in step 2), slag is added at 1 / 3 of the steel tapping process and is completed at 2 / 3. The argon volume is controlled at 1500N l / m 3 The remaining 1 / 3 is controlled by a small flow rate of 200-300N l / m 3Until the steel is tapped, the stirring of argon is always ensured to promote slag formation and the completion of top slag modification. During the steel tapping process, slag washing operation is performed to add active lime and part of the slag-removing agent into the ladle (the composition of the slag-removing agent is shown in Table 2). The amount of lime added is 2-3.5 kg / t steel, and the amount of slag-removing agent added is 1-1.5 kg / t steel. After the steel is tapped, about 100 kg of aluminum iron powder is added to the surface of the molten steel in the ladle (the composition of the aluminum iron powder is shown in Table 3).

[0035] Table 2: Composition of slag-removing agent Unit: wt%

[0036] CaO Mg0 <![CDATA[SiO 2 ]]> <![CDATA[CaF 2 ]]> <![CDATA[Al 2 THE 3 ]]> <![CDATA[H 2 The]]> <![CDATA[Fe 2 THE 3 ]]> C ≥30 ≤1.5 ≤10 2-4 ≥50 ≤0.6 ≤1.5 ≤0.10

[0037] Table 3: Aluminum iron powder composition Unit: wt%

[0038] Al C P S 44-49 ≤0.10 ≤0.03 ≤0.03

[0039] Furthermore, oxygen blowing is not recommended in step 3). If oxygen blowing is required, it can be performed when the vacuum degree reaches 10 kPa. Generally, oxygen blowing is completed when the vacuum degree reaches between 6 and 10 kPa; oxygen blowing flow rate is 2000 Nm 3 / h, oxygen blowing 10m 3 , we can add 27 to 30 ppm of oxygen in the steel for estimation.

[0040] Furthermore, in step 3), a standardized operation specification was established to realize the establishment of an efficient decarbonization platform for the RH process, as shown in Table 4:

[0041] Table 4 Standardized operation specifications for efficient decarburization in RH process

[0042]

[0043] The present invention will be further described below in conjunction with the embodiments.

[0044] A method for smelting ultra-low carbon steel is established through a RH process decarburization platform, wherein the KR desulfurization process controls the sulfur content of molten iron entering the converter to ≯0.003%; the converter process realizes accurate carbon pulling of the converter through the real-time change of CO, controls the end point [C] to 0.025-0.055%, controls the temperature to 1680-1705°C, controls the oxygen content to 700-950ppm, and provides good molten steel conditions for the RH process through slag washing; the RH adopts an ultra-low carbon steel production mode of low vacuum and high circulation flow rate rapid decarburization, controlled deoxidation and alloying and other process carbonization, so that the molten steel [C] after RH decarburization is ≤10ppm, and the molten steel [C] is ≤15ppm when the RH is out of position; ultra-low carbon steel special protective slag and carbon-free tundish covering agent are used, the continuous casting nozzle is well sealed, the tundish is protected and poured, and the carbon and nitrogen addition amounts are ensured to be ≯5ppm, and the molten steel [C] is ≤20ppm when the casting machine pouring is completed.

[0045] According to the present invention, a method for smelting ultra-low carbon steel by using a RH process decarburization platform is as follows:

[0046] KR desulfurization step → converter smelting step → RH vacuum refining step → continuous casting step. Specifically:

[0047] KR desulfurization steps: The molten iron must undergo KR molten iron pretreatment. After the treatment, the [S] in the molten iron is ≯0.003%, the molten iron temperature is ≮1300℃, and it must undergo two slag removals. The molten iron mirror surface rate is ≥95%.

[0048] Converter smelting steps: the ratio of pre-treated molten iron and clean scrap steel is 5:1-7:1, the temperature of molten iron entering the furnace is ≥1300℃, the S content in the molten iron is ≤0.003%, and active lime and high-silicon dolomite must be added during the blowing process to ensure the slag basicity; top and bottom composite blowing and bottom blowing are operated with argon blowing throughout the process, sampling, temperature measurement, and oxygen determination after the converter is carbonized, [C] is controlled at 0.025-0.055%, the temperature is controlled at 1680-1705℃, the oxygen content is controlled at 700-950ppm, and [S] ≤0.003%. In principle, the carbon temperature is guaranteed to be hit once, and the spot blowing is not more than once. During the steel-making process, the steel outlet does not disperse and the steel-making time is ≮5 minutes. It is strictly forbidden to slag. During the steel-making process, slag washing is performed to ensure that the inclusions are fully gathered and floated, and the purity of the molten steel is improved. The terminal temperature of the molten steel shall comply with the current operating standards. The target of RH molten steel supplied by the converter is: [C]: 0.025% to 0.055%, [O]: (500 to 750)×10-6, T=1615 to 1635°C. The specific production example is shown in Table 5.

[0049] Table 5 Desulfurization and converter production examples

[0050]

[0051]

[0052] RH refining steps: The temperature of the molten steel at the RH station is 1610-1635℃. It is required that the minimum vacuum degree must reach below 266Pa after evacuation for ≯4 minutes, and the vacuum degree fluctuation rebound during the vacuum treatment must be ≤100Pa. The RH decarburization endpoint is determined by the change of CO. During the vacuum process, the flow rate of circulating argon gas is adjusted to ensure sufficient circulation of the molten steel and decarburization as quickly as possible to ensure the decarburization effect, so that the carbon content in the molten steel is ≤10ppm after 15 minutes. Use micro-carbon high-purity alloys such as micro-carbon aluminum iron / high-purity silicon steel for deoxidation and alloying, control the carbon increase of the alloy to ≯5ppm, the pure degassing time after alloying is ≥5 minutes, and the molten steel is left to stand for ≥5 minutes before steel is added. The molten steel targets when leaving the position are: [C]≤15ppm, [H]≤1.2ppm, [O]≤15ppm, [N]≤20ppm. See Table 6 for specific examples of step production.

[0053] Table 6 RH vacuum refining production example

[0054]

[0055]

[0056] Continuous casting steps: Use special protective slag for ultra-low carbon steel and carbon-free tundish covering agent to protect the casting throughout the process, and ensure that the carbon and nitrogen addition amounts are ≯5ppm. Close the ladle water inlet 30 seconds before the ladle slag detection alarm to prevent the ladle from slag, and the dynamic secondary cooling water distribution parameters are calculated by computer. The specific examples of step production are shown in Table 7.

[0057] Table 7 Casting machine production example

[0058]

[0059] Specific implementation results:

[0060] A method for smelting ultra-low carbon steel by establishing a decarburization platform in the RH process can achieve in industrial production that the molten steel [C] is ≤10ppm after RH decarburization of ultra-low carbon steel, the molten steel [C] is ≤15ppm when RH is off, and the molten steel [C] is ≤20ppm when the casting machine is finished. A method for smelting ultra-low carbon steel by establishing a decarburization platform in the RH process can achieve industrial production of ultra-low carbon steel, and its carbon content can be stably controlled at ≤20ppm, fully meeting the requirements of the ultra-low carbon steel market and customers.

[0061] The present invention is applicable to steel mills in the process of smelting ultra-low carbon steel, and the process generally adopts: desulfurization-converter-RH vacuum refining, molten iron desulfurization and slag removal, and control of the sulfur content of the molten iron entering the furnace; non-quiet steel tapping of the converter, and slag modification after steel tapping; the RH refining process is mainly natural decarburization, supplemented by forced decarburization, and multiple process steps such as deoxidation alloying and pure cycle removal of inclusions after decarburization are completed to achieve the ultra-low carbon smelting goal. Among them, RH vacuum refining is the key to smelting ultra-low carbon decarburization, and the vacuum decarburization effect directly affects the carbon content of the ultra-low carbon steel terminal. For this reason, we have invented a method for smelting ultra-low carbon steel through the RH process decarburization platform based on industrial production practice. The method is centered on RH vacuum decarburization, and the converter process provides crude steel that meets the requirements as a match. An ultra-low carbon steel decarburization platform is established, and the efficient and stable decarburization of the ultra-low carbon steel RH vacuum treatment process is achieved. The carbon content of the molten steel after RH decarburization can be stably controlled at ≤10ppm. This invention can effectively improve the efficiency of RH vacuum decarburization, ensure that the carbon content of molten steel is controlled at a low level, and greatly improve the product performance and stability of ultra-low carbon steel.

[0062] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for smelting ultra-low carbon steel by establishing a decarburization platform through an RH process, characterized in that: include: 1) KR desulfurized hot metal pretreatment steps: after pretreatment, [S] in the hot metal should be ≤ 0.003%, the hot metal temperature should be ≮1300℃, and pneumatic double slag removal should be adopted to ensure that the hot metal mirror surface rate is ≥ 95%; 2) Converter smelting steps: the ratio of pre-treated molten iron and clean scrap steel is 5:1-7:1, the temperature of molten iron entering the furnace is ≥1300℃, the S content in the molten iron is ≤0.003%, and active lime and high-silicon dolomite must be added during the blowing process to ensure the slag basicity; top and bottom composite blowing and bottom blowing are carried out with argon blowing throughout the process, sampling, temperature measurement and oxygen determination are carried out after the converter is carbonized, [C] is controlled at 0.025-0.055%, the temperature is controlled at 1680-1705℃, the oxygen content is controlled at 700-950ppm, and [S] ≤0.003%; in principle, the carbon temperature is guaranteed to be hit once, and the spot blowing is not more than once; during the steel tapping process, the steel outlet does not disperse and the steel tapping time is ≮5 minutes, and slag is strictly prohibited. During the steel tapping process, slag washing is carried out to ensure that the inclusions are fully gathered and floated, and the purity of the molten steel is improved. The terminal temperature of the molten steel shall comply with the current operating standards; The target of RH molten steel for converter is: [C]: 0.025%~0.055%, [O]: (500~750)×10 -6 , T = 1615 ~ 1635 ℃; 3) RH refining step: The temperature of the molten steel at the RH station is 1615-1635℃, and the minimum vacuum degree must reach below 266Pa after evacuation for ≯4 minutes, and the vacuum degree fluctuation rebound during the vacuum treatment is ≤100Pa. Based on the monitoring and analysis of the flue gas CO data, the RH end point CO and decarburization relationship curve is determined, and the RH decarburization end point is determined by the CO change. During the process, the circulating argon flow rate is adjusted to ensure sufficient circulation of the molten steel and decarburization as quickly as possible to ensure the decarburization effect, so that the carbon content in the molten steel is ≤10ppm at 15min; use a micro-carbon high-purity alloy for deoxidation and alloying, control the alloy carbon increase to ≯5ppm, the pure degassing time after alloying is ≥5 minutes, the molten steel is left to stand for ≥5 minutes before steel is added, and the molten steel targets when leaving the position are: [C]≤15ppm, [H]≤1.2ppm, [O]≤15ppm, [N]≤20ppm; 4) Casting machine steps: Use special protective slag for ultra-low carbon steel and carbon-free tundish covering agent, seal the nozzle during continuous casting, and protect the tundish casting to ensure the amount of carbon and nitrogen increase.

2. The method for smelting ultra-low carbon steel by establishing a decarburization platform through the RH process according to claim 1, characterized in that: In step 2), the steel-tapping time needs to be strictly controlled and should be greater than 5 minutes. At the same time, the steel flow cannot be dispersed during steel-tapping. At the same time, the slag-blocking effect of the converter is improved and slag is strictly prohibited. Good conditions need to be created for the modification of the ladle top slag.

3. The method for smelting ultra-low carbon steel by establishing a decarburization platform through the RH process according to claim 1, characterized in that: In step 2), the converter dry dust removal gas analyzer is used to analyze the converter end point flue gas CO change data curve, determine the converter end point CO and C relationship curve, determine the converter end point C content through the CO change, and achieve precise carbon pulling at the converter end point; through the use of this technology, the converter end point carbon content of ultra-low carbon steel is accurately controlled at 0.025-0.055%.

4. The method for smelting ultra-low carbon steel by establishing a decarburization platform through the RH process according to claim 1, characterized in that: Step 2) Add slag at 1 / 3 of the steel tapping process and complete at 2 / 3. Ensure that the argon volume is controlled at 1500Nl / m 3 The remaining 1 / 3 is controlled by a small flow rate of 200-300Nl / m 3 , until the steel is tapped, the stirring of argon is always guaranteed to promote slag formation and the completion of top slag modification. During the steel tapping process, slag washing operation is performed to add active lime and part of the slag-removing agent into the ladle. The amount of lime added is 2-3.5kg / t steel, and the amount of slag-removing agent added is 1-1.5kg / t steel. After the steel is tapped, about 100kg of aluminum iron powder is added to the surface of the molten steel in the ladle.

5. The method for smelting ultra-low carbon steel by establishing a decarburization platform through the RH process according to claim 1, characterized in that: In step 3), oxygen blowing is not recommended. If oxygen blowing is required, it should be performed when the vacuum degree reaches 10 kPa. Generally, oxygen blowing is completed when the vacuum degree reaches between 6 and 10 kPa.

6. The method for smelting ultra-low carbon steel by establishing a decarburization platform through the RH process according to claim 5, characterized in that: According to the oxygen blowing flow rate 2000Nm 3 / h, oxygen blowing 10m 3 Add 27-30 ppm of oxygen to the steel for estimation.

7. The method for smelting ultra-low carbon steel by establishing a decarburization platform through the RH process according to claim 1, characterized in that: After RH decarburization, the carbon content of molten steel can be stably controlled at ≤10ppm.

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