Vacuum denitrification method for molten steel

Abstract

The invention provides a vacuum denitrification method for molten steel, and belongs to the field of steelmaking. The method comprises the steps that molten steel is fed into a refining station and then subjected to vacuum treatment, and the molten steel enters a vacuum chamber to be circulated; in the process from the beginning of the vacuum refining denitrification to the time t1, carrying out first bottom blowing of CO2 gas on the molten steel entering the vacuum chamber for circulation, and carrying out first blowing of carbon powder by taking CO2 as carrier gas; in the time process of vacuum refining denitrification from t1 to t2, second bottom blowing of CO2 gas is carried out on the molten steel entering the vacuum chamber for circulation, and second injection of carbon powder is carried out with CO2 as carrier gas; and in the process from t2 to the end of vacuum refining denitrification, argon bottom blowing is carried out on the molten steel entering the vacuum chamber for circulation, so that vacuum refining denitrification is carried out. CO2 is used as carrier gas, carbon powder is blown and immersed into molten steel, CO2 and carbon powder react under the high-temperature condition of the molten steel to generate CO bubbles, and the CO bubbles have a remarkable promoting effect on molten steel denitrification, so that the denitrification efficiency is improved.

Description

Technical Field

[0001] The present application relates to the technical field of steelmaking, and in particular to a method for vacuum denitrification of molten steel. Background Art

[0002] In the steelmaking and refining process, vacuum refining is usually used to remove gas components in the molten steel, such as nitrogen and hydrogen. The removal efficiency of hydrogen under vacuum conditions is relatively fast and can quickly reach below 0.0002%, but the removal efficiency of nitrogen is relatively low, especially when the nitrogen content is ≤0.005%. Even if the vacuum treatment time is extended, it is difficult to effectively remove nitrogen from the molten steel. In recent years, due to the demand for low-carbon technology, the electric furnace steelmaking process has developed rapidly, but the nitrogen content of the molten steel after electric furnace smelting is significantly higher than that of the converter process. Therefore, how to quickly and efficiently remove nitrogen in the vacuum refining process has become a hot topic.

[0003] In order to improve the denitrification effect in the vacuum refining process, conventional processes have carried out research from the aspects of strengthening the stirring of molten steel, increasing the nitrogen capacity of refining slag and reducing the content of elements affecting denitrification in molten steel. Although the denitrification efficiency is improved under conditions of high nitrogen content, after the nitrogen content of molten steel drops to 0.005%, the denitrification efficiency is extremely low and it is difficult to denitrify the molten steel. Summary of the invention

[0004] The present application provides a method for vacuum denitrification of molten steel to solve the following technical problem: how to improve the denitrification efficiency of vacuum denitrification of molten steel.

[0005] The present application provides a method for vacuum denitrification of molten steel, the method comprising:

[0006] The molten steel is sent to a refining station and then subjected to vacuum treatment, so that the molten steel enters a vacuum chamber for circulation;

[0007] During the process of vacuum refining and denitrification from the beginning to time t1, the molten steel entering the vacuum chamber for circulation is subjected to a first bottom blowing of CO2 gas, and a first carbon powder spraying is performed using CO2 as a carrier gas;

[0008] During the time from t1 to t2 of vacuum refining and denitrification, the molten steel entering the vacuum chamber for circulation is subjected to a second bottom blowing of CO2 gas, and a second carbon powder injection is performed using CO2 as a carrier gas; wherein the CO2 flow rate of the first bottom blowing CO2 gas is greater than the CO2 flow rate of the second bottom blowing CO2 gas, and the carbon powder injection rate of the first carbon powder injection is greater than the carbon powder injection rate of the second carbon powder injection; and

[0009] During the process of vacuum refining and denitrification from t2 to the end, argon is blown from the bottom of the molten steel circulating in the vacuum chamber to carry out vacuum refining and denitrification.

[0010] Optionally, t1 is 4 minutes and t2 is 7 minutes.

[0011] Optionally, the CO2 flow rate of the first bottom-blown CO2 gas is 500Nl / min to 600Nl / min.

[0012] Optionally, the CO2 flow rate of the second bottom-blown CO2 gas is 300Nl / min to 500Nl / min.

[0013] Optionally, the first carbon powder blowing rate is 15kg / min to 25kg / min.

[0014] Optionally, the second carbon powder blowing rate is 10kg / min to 15kg / min.

[0015] Optionally, the total amount of CO2 blown by the first bottom-blown CO2 gas and the second bottom-blown CO2 gas satisfies the following relationship:

[0016] Q CO2 =1570447.2×(w[%N] 初始 -w[%N] 目标 ) / 44×22.4

[0017] Where, QCO2 is the total amount of carbon dioxide blowing, the unit is Nl; w[%N] 初始 The initial nitrogen content at the refining station, in %; w[%N] 目标 It is the target nitrogen content at the end of refining, in %.

[0018] Optionally, the total amount of carbon powder sprayed by the first sprayed carbon powder and the second sprayed carbon powder satisfies the following relationship:

[0019] m c =28285.4×(w[%N] 初始 -w[%N] 目标 )

[0020] In the formula, m c is the total amount of carbon powder sprayed, in kg; w[%N] 初始 The initial nitrogen content at the refining station, in %; w[%N] 目标 It is the target nitrogen content at the end of refining, in %.

[0021] Optionally, while the vacuum treatment is being carried out, pre-bottom blowing of argon is performed to prevent clogging; the argon flow rate of the pre-bottom blowing of argon is 30NL / min to 50NL / min.

[0022] Optionally, when the refining station is an RH refining station, the gas is sprayed through a blowing element on the lower side of the RH vacuum chamber;

[0023] When the refining station is a VD refining station, the gas is sprayed through the VD ladle annular gap bottom blowing element.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The embodiment of the present application provides a method for vacuum denitrification of molten steel. During the vacuum refining process of molten steel, CO2 is used as a carrier gas, and carbon powder is sprayed and immersed into the interior of the molten steel. The weak oxidizing property of CO2 gas is utilized, and CO2 and carbon powder react under high temperature conditions of the molten steel to generate CO bubbles. The CO bubbles have a significant promoting effect on the denitrification of the molten steel, thereby improving the denitrification efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the description, are used to explain the principles of the present application.

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 A schematic flow chart of a method for vacuum denitrification of molten steel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0030] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0031] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one-to-one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0033] Figure 1 A schematic flow chart of a method for vacuum denitrification of molten steel provided in an embodiment of the present application.

[0034] like Figure 1 As shown, the embodiment of the present application provides a method for vacuum denitrification of molten steel, the method comprising:

[0035] S1, sending the molten steel to a refining station, and then performing vacuum treatment, so that the molten steel enters a vacuum chamber for circulation;

[0036] In some embodiments, while the vacuum treatment is being performed, pre-bottom blowing of argon is performed to prevent clogging; the argon flow rate of the pre-bottom blowing of argon is 30 NL / min to 50 NL / min.

[0037] While the vacuum treatment is being carried out, pre-bottom blowing of argon is carried out, and the argon flow rate is set to 30NL / min to 50NL / min. Pre-bottom blowing of argon can prevent the blockage of the bottom blowing element and ensure the smooth progress of the subsequent bottom blowing of gas. At the same time, the stirring effect of argon also contributes to the homogenization of the molten steel and the denitrification reaction. Exemplarily, the argon flow rate of the pre-bottom blowing of argon can be 30NL / min, 35NL / min, 38NL / min, 40NL / min, 45NL / min, 50NL / min, etc.

[0038] In some embodiments, when the refining station is an RH refining station, gas is blown through a blowing element on the lower side of the RH vacuum chamber;

[0039] When the refining station is a VD refining station, the gas is sprayed through the VD ladle annular gap bottom blowing element.

[0040] Before the steel liquid is vacuum treated, 6 to 8 blowing elements with a diameter of 10 mm to 30 mm are distributed from the lower side of the RH vacuum chamber at the connection position of the two immersion pipes; or 2 to 3 bottom blowing elements are evenly distributed on the 1 / 2 circle of the bottom radius of the ladle in the VD furnace.

[0041] S2, during the process of vacuum refining and denitrification from the beginning to time t1, the molten steel entering the vacuum chamber for circulation is subjected to a first bottom blowing of CO2 gas, and a first carbon powder spraying is performed using CO2 as a carrier gas;

[0042] S3, during the time from t1 to t2 of vacuum refining and denitrification, the molten steel entering the vacuum chamber for circulation is subjected to a second bottom blowing of CO2 gas, and a second carbon powder injection is performed using CO2 as a carrier gas; wherein the CO2 flow rate of the first bottom blowing CO2 gas is greater than the CO2 flow rate of the second bottom blowing CO2 gas, and the carbon powder injection rate of the first carbon powder injection is greater than the carbon powder injection rate of the second carbon powder injection; and

[0043] In some embodiments, t1 is 4 min and t2 is 7 min.

[0044] In some embodiments, the CO2 flow rate of the first bottom-blown CO2 gas is 500Nl / min to 600Nl / min.

[0045] During the first bottom blowing CO2 gas stage, the CO2 flow rate is set to 500Nl / min~600Nl / min. At this stage, the molten steel has just started to enter the vacuum chamber circulation, and the nitrogen content is high. Strong stirring and reaction are required to quickly reduce the nitrogen content. A higher CO2 flow rate can produce more CO bubbles. These bubbles not only increase the stirring intensity of the molten steel, but also help to break the active atomic interface barrier on the surface of the molten steel and promote the denitrification reaction. At the same time, CO2 reacts with carbon in the molten steel to generate CO. This reaction is endothermic and helps to control the temperature of the molten steel. Exemplarily, the CO2 flow rate of the first bottom blowing CO2 gas is 500Nl / min, 520Nl / min, 540Nl / min, 560Nl / min, 580Nl / min, 600Nl / min, etc.

[0046] In some embodiments, the CO2 flow rate of the second bottom-blown CO2 gas is 300Nl / min to 500Nl / min.

[0047] During the second bottom blowing CO2 gas stage, the CO2 flow rate is set to 300Nl / min to 500Nl / min. As vacuum refining proceeds, the nitrogen content in the molten steel gradually decreases. At this time, if a high CO2 flow rate is maintained, the reaction may be too intense, which is not conducive to the homogenization of the molten steel composition and the further improvement of the denitrification efficiency. Therefore, appropriately reducing the CO2 flow rate can maintain a stable denitrification rate while avoiding excessive disturbance to the molten steel. Exemplarily, the CO2 flow rate of the second bottom blowing CO2 gas is 300Nl / min, 350Nl / min, 380Nl / min, 400Nl / min, 450Nl / min, 500Nl / min, etc.

[0048] In some embodiments, the carbon powder blowing rate of the first carbon powder blowing is 15 kg / min to 25 kg / min.

[0049] In the first carbon powder injection stage, the carbon powder injection rate is set to 15kg / min to 25kg / min. The nitrogen content in the molten steel is relatively high at this stage, and a large amount of carbon powder is required to provide sufficient carbon source to react with CO2 to generate CO bubbles, thereby promoting the denitrification reaction. A higher carbon powder injection rate can ensure that there is enough carbon in the molten steel to participate in the reaction, and it also helps to increase the stirring intensity of the molten steel. Exemplarily, the carbon powder injection rate of the first carbon powder injection is 15kg / min, 17kg / min, 19kg / min, 20kg / min, 22kg / min, 24kg / min, 25kg / min, etc.

[0050] In some embodiments, the second carbon powder blowing rate is 10 kg / min to 15 kg / min.

[0051] In the second carbon powder injection stage, the carbon powder injection rate is set to 10kg / min to 15kg / min. As vacuum refining proceeds, the nitrogen content in the molten steel gradually decreases. At this time, if a high carbon powder injection rate is maintained, the carbon content in the molten steel may be too high, which is not conducive to subsequent processing. Therefore, appropriately reducing the carbon powder injection rate can maintain a stable denitrification rate while avoiding excessive accumulation of carbon content in the molten steel. Exemplarily, the carbon powder injection rate of the second carbon powder injection can be 10kg / min, 11kg / min, 12kg / min, 13kg / min, 14kg / min, 15kg / min, etc.

[0052] In some embodiments, the total amount of CO2 blowing of the first bottom blowing CO2 gas and the second bottom blowing CO2 gas satisfies the following relationship:

[0053]

[0054] In the formula, is the total amount of carbon dioxide blowing, the unit is Nl; w[%N] 初始 The initial nitrogen content at the refining station, in %; w[%N] 目标 It is the target nitrogen content at the end of refining, in %.

[0055] In some embodiments, the total amount of the first sprayed carbon powder and the second sprayed carbon powder meets the following relationship:

[0056] m C =28285.4×(w[%N] 初始 -w[%N] 目标 )

[0057] In the formula, m c is the total amount of carbon powder sprayed, in kg; w[%N] 初始 The initial nitrogen content at the refining station, in %; w[%N] 目标 It is the target nitrogen content at the end of refining, in %.

[0058] S4. Vacuum refining and denitrification During the process from t2 to the end, argon is blown from the bottom of the molten steel circulating in the vacuum chamber to perform vacuum refining and denitrification.

[0059] From the 7th minute to the end of denitrification, argon is used instead of CO2 for bottom blowing. At this time, the nitrogen content in the molten steel is relatively low, the carbon content is also relatively low, and the carbon-oxygen reaction is weakened. At this time, the stirring effect of argon bubbles is mainly used to remove the remaining nitrogen. Argon is an inert gas that does not react chemically with the elements in the molten steel, so it can be used as a carrier gas for denitrification. Through the stirring effect of argon bubbles, the nitrogen content in the molten steel can be further reduced to achieve the refining goal.

[0060] In some embodiments, after denitrification is completed, the vacuum can be broken for non-decarburized steels, and argon gas is continuously blown into the blowing element at a flow rate of 20 NL / min to 50 NL / min to prevent the blowing element from being blocked. Vacuum decarburization can be continued for decarburized steels.

[0061] In summary, the steel liquid vacuum denitrification method provided in the embodiment of the present application has the following advantages:

[0062] (1) Efficient denitrification: CO2 is used as a carrier gas to react with carbon powder to generate a large number of small CO bubbles, which greatly promote the stirring of the molten steel and the denitrification reaction. At the same time, by adjusting the CO2 flow rate and carbon powder injection rate in stages, the denitrification process is precisely controlled, and the denitrification efficiency is improved by 30% to 50%. The nitrogen content can be stably controlled below 0.003%, meeting the production requirements of high-quality steel.

[0063] (2) Flexible process: Applicable to RH refining station and VD refining station, gas injection is achieved through different bottom blowing elements, which enhances the adaptability and flexibility of the process. The total amount of CO2 blowing and carbon powder injection can be flexibly adjusted according to the initial nitrogen content and target nitrogen content of the molten steel to meet the production requirements of different steel grades.

[0064] (3) Equipment protection: During vacuum treatment, pre-bottom blowing of argon is performed to prevent clogging of the bottom blowing components, thus ensuring the smooth progress of subsequent bottom blowing of gas. After denitrification, for non-decarburized steel grades, argon is continued to be blown to prevent clogging of the blowing components, thus extending the service life of the equipment.

[0065] (4) Temperature control: The reaction of CO2 with carbon in the molten steel to produce CO is an endothermic reaction, which helps control the temperature of the molten steel and reduces the need for additional cooling.

[0066] (5) Cost saving: By precisely controlling the CO2 flow rate and carbon powder injection rate, waste is avoided and production costs are reduced. At the same time, argon, as an inert gas, will not chemically react with the elements in the molten steel and can be used as a carrier gas for denitrification, further reducing costs.

[0067] (6) Environmental protection and energy saving: This method reduces the pollutant emissions that may be generated in traditional denitrification processes and meets environmental protection requirements. By efficiently utilizing CO2 and carbon powder, it achieves maximum utilization of resources and meets the concept of energy conservation and emission reduction.

[0068] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0069] Embodiment 1:

[0070] The steel product smelted in this embodiment has a nitrogen content of ≤0.003% low-carbon aluminum-killed steel, the ladle capacity is 220t, and the actual molten steel volume is 218t. After the molten steel enters the VD refining station, the initial nitrogen content at the station is 0.0074%.

[0071] The ladle car is driven to the vacuum treatment position, the ladle is lifted, the immersion tube is inserted into the molten steel, and the vacuum pumping system and circulating gas are turned on at the same time. At the same time, the 6 blowing elements on the bottom side of the vacuum chamber keep blowing argon, with a total flow rate of 50NL / min.

[0072] After the molten steel enters the VD vacuum chamber and starts to circulate, CO2 gas is blown in from the two blowing elements at the bottom of the ladle, and the CO2 flow rate is controlled to be 500Nl / min. At the same time, carbon powder is sprayed with CO2 as the carrier gas, and the carbon powder spraying rate is controlled to be 15kg / min.

[0073] From 4 minutes to 7 minutes, CO2 gas is continuously blown in from the blowing element at the bottom of the ladle, and the CO2 flow rate is controlled at 300Nl / min. At the same time, carbon powder is sprayed with CO2 as the carrier gas, and the carbon powder spraying rate is controlled at 10kg / min.

[0074] The total CO2 injection volume is calculated by the formula to be 3598Nl, and the total carbon powder injection volume is 128kg.

[0075] From 7 minutes to the end of denitrification, argon was used to replace CO2, the flow rate was maintained at 500Nl / min, and the carbon powder was stopped;

[0076] After denitrification, since this steel grade is non-decarburized, the vacuum is directly broken, and argon is continuously blown into the blowing element at a flow rate of 50NL / min to prevent the blowing element from being blocked. The nitrogen content in the molten steel after vacuum refining is 0.0026%, and the denitrification efficiency is 64.9%.

[0077] Embodiment 2:

[0078] The steel product smelted in this embodiment has a nitrogen content of ≤0.002% ultra-low carbon steel, the ladle capacity is 220t, and the actual molten steel volume is 221t. After the molten steel enters the RH refining station, the initial nitrogen content at the station is 0.0067%.

[0079] The ladle car is driven to the vacuum treatment position, the ladle is lifted, the immersion tube is inserted into the molten steel, and the vacuum pumping system and circulating gas are turned on at the same time. At the same time, the 6 blowing elements on the bottom side of the vacuum chamber keep blowing argon, with a total flow rate of 50NL / min.

[0080] After the molten steel enters the RH vacuum chamber and starts to circulate, CO2 gas is blown in from the 6 blowing elements on the lower side of the RH vacuum chamber, and the CO2 flow rate is controlled to be 500Nl / min. At the same time, carbon powder is sprayed with CO2 as the carrier gas, and the carbon powder spraying rate is controlled to be 15kg / min.

[0081] From 4 minutes to 7 minutes, CO2 gas was continuously blown in from the blowing element on the lower side of the RH vacuum chamber, and the CO2 flow rate was controlled to be 300Nl / min. At the same time, carbon powder was sprayed using CO2 as a carrier gas, and the carbon powder spraying rate was controlled to be 10kg / min.

[0082] The total CO2 injection volume is calculated by the formula to be 3758Nl, and the total carbon powder injection volume is 123kg.

[0083] From 7 minutes to the end of denitrification, argon was used to replace CO2, the flow rate was maintained at 500Nl / min, and the carbon powder was stopped;

[0084] After denitrification, since this steel grade is decarburized steel, argon gas is continuously blown into the blowing element at a flow rate of 50NL / min to prevent the blowing element from being blocked. The air is then broken after RH decarburization, deoxidation and alloying are completed. The nitrogen content in the molten steel after vacuum refining is 0.0018%, and the denitrification efficiency is 73.1%.

[0085] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0086] In the embodiment of the present application, CO2 is used as a carrier gas in the vacuum denitrification process, and carbon powder is sprayed and immersed into the interior of the molten steel through the bottom blowing element on the lower side of the RH vacuum chamber or the bottom blowing element of the VD refining ladle. CO2 and carbon powder react under the high temperature conditions of the molten steel to generate a large number of small CO bubbles, and the CO bubbles are used to promote the denitrification of the molten steel. During the RH or VD vacuum refining process of the molten steel, carbon powder is blown into the molten steel through the blowing element on the lower side of the RH vacuum chamber or the annular bottom blowing element of the VD ladle with CO2 as a carrier gas. The weak oxidizing property of CO2 gas is utilized, and CO bubbles are generated by reaction with carbon powder, and CO bubbles have a significant promoting effect on the denitrification of the molten steel.

[0087] In the embodiment of the present application, a large number of CO bubbles are generated inside the molten steel through the CO2+C=2CO reaction, which has a significant promoting effect on the denitrification of the molten steel, and the denitrification efficiency is improved by 30% to 50%, and the nitrogen content can be stably controlled below 0.003%.

[0088] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for vacuum denitrification of molten steel, the method comprising: The molten steel is sent to a refining station and then subjected to vacuum treatment, so that the molten steel enters a vacuum chamber for circulation; During the process of vacuum refining and denitrification from the beginning to time t1, the molten steel entering the vacuum chamber for circulation is subjected to a first bottom blowing of CO2 gas, and a first carbon powder spraying is performed using CO2 as a carrier gas; During the time from t1 to t2 of vacuum refining and denitrification, the molten steel entering the vacuum chamber for circulation is subjected to a second bottom blowing of CO2 gas, and a second carbon powder injection is performed using CO2 as a carrier gas; wherein the CO2 flow rate of the first bottom blowing CO2 gas is greater than the CO2 flow rate of the second bottom blowing CO2 gas, and the carbon powder injection rate of the first carbon powder injection is greater than the carbon powder injection rate of the second carbon powder injection; as well as During the process of vacuum refining and denitrification from t2 to the end, argon is blown from the bottom of the molten steel circulating in the vacuum chamber to carry out vacuum refining and denitrification.

2. The method according to claim 1, characterized in that t1 is 4min and t2 is 7min.

3. The method according to claim 1, characterized in that The CO2 flow rate of the first bottom-blown CO2 gas is 500Nl / min to 600Nl / min.

4. The method according to claim 1, characterized in that: The CO2 flow rate of the second bottom-blown CO2 gas is 300Nl / min to 500Nl / min.

5. The method according to claim 1, characterized in that The carbon powder spraying rate of the first carbon powder spraying is 15kg / min to 25kg / min.

6. The method according to claim 1, characterized in that The second carbon powder spraying rate is 10kg / min to 15kg / min.

7. The method according to claim 1, characterized in that The total amount of CO2 blowing of the first bottom blowing CO2 gas and the second bottom blowing CO2 gas satisfies the following relationship: Q CO2 =1570447.2×(w[%N] 初始 -w[%N] 目标 ) / 44×22.4 Where QCO2 is the total amount of carbon dioxide blowing, in Nl; w[%N] 初始 The initial nitrogen content at the refining station, in %; w[%N] 目标 It is the target nitrogen content at the end of refining, in %.

8. The method according to claim 1, characterized in that The total amount of carbon powder sprayed by the first sprayed carbon powder and the second sprayed carbon powder satisfies the following relationship: m c =28285.4×(w[%N] 初始 -w[%N] 目标 ) In the formula, m c is the total amount of carbon powder sprayed, in kg; w[%N] 初始 The initial nitrogen content at the refining station, in %; w[%N] 目标 It is the target nitrogen content at the end of refining, in %.

9. The method according to claim 1, characterized in that: While the vacuum treatment is being carried out, pre-bottom blowing of argon is carried out to prevent clogging; the argon flow rate of the pre-bottom blowing of argon is 30NL / min to 50NL / min.

10. The method according to claim 1, characterized in that When the refining station is an RH refining station, the gas is sprayed through the blowing element on the lower side of the RH vacuum chamber; When the refining station is a VD refining station, the gas is sprayed through the VD ladle annular gap bottom blowing element.

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