A method for smelting ultra-clean Cr-Ni-Mo-V steel liquid using CO2-Ar

Abstract

The invention discloses a method for smelting ultra-clean Cr-Ni-Mo-V steel liquid using CO2-Ar, and belongs to the technical field of steelmaking process. A medium-frequency furnace smelting system is used in the smelting process, including four stages: an early melting stage, a mid-term mixed bottom blowing stage, a mid-term feeding bottom blowing stage, and a late feeding bottom blowing stage. The present invention is applicable to the process of smelting high-alloy special steel in a 10kg-50t medium-frequency furnace; CO2-Ar is used as a bottom blowing stirring gas, and alloy smelting is added to the molten pool in the order of alloy element content and oxidation property strength. According to the different alloy element contents in the molten steel predicted by the computer and control system, the mixing ratio and flow rate of the bottom blowing CO2-Ar are adjusted in real time, and a large number of CO bubbles are generated by the reaction of CO2 with the carbon element in the molten steel, so as to strengthen the stirring of the molten pool, make the composition and temperature of the molten steel more uniform, shorten the smelting time, avoid alloy element burnout, and improve the alloy yield.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking process, and specifically relates to a method for smelting ultra-clean Cr-Ni-Mo-V series steel liquid by utilizing CO2-Ar. Background Art

[0002] Medium frequency furnace (medium frequency induction furnace) is a furnace with an operating frequency between 50 and 2000Hz, which is widely used in the melting of nonferrous metals and ferrous metals, and is suitable for the smelting of high-alloy special steel. The electromagnetic stirring generated by itself is the use of induction heating of metals. The large current after AC-DC-AC conversion of the medium frequency power supply generates a strong magnetic field through the induction coil, and thus generates a strong electromagnetic force. The molten metal is stirred by the electromagnetic force.

[0003] However, compared with gas stirring, the electromagnetic stirring speed of the medium frequency furnace itself is slow, and the effect of uniform molten steel is poor, which eventually causes fluctuations in the quality of the molten steel and leads to reduced product quality. The traditional way to enhance the stirring of molten steel in the medium frequency furnace is to increase the electromagnetic stirring power. However, this method will increase the erosion of the crucible by the molten steel, shorten the service life of the crucible by melting, and increase the smelting cost.

[0004] In order to solve the problem of poor stirring effect of molten steel, many researchers have proposed measures such as increasing bottom blowing gas stirring. However, no one has yet proposed a feasible plan for achieving the dual goals of ensuring high alloy yield and enhancing molten steel stirring during the smelting of ultra-pure Cr-Ni-Mo-V molten steel in a medium frequency furnace.

[0005] Patent CN108728607A introduces a LF furnace dynamic bottom blowing CO2-Ar refining method and device, the main feature of which is to use CO2-Ar mixed gas to achieve desulfurization and denitrification of molten steel. However, in the traditional LF refining process, alloy elements are added after the molten steel is deoxidized. Therefore, the use of CO2 in the LF refining process is not suitable for smelting high-alloy steel, especially ultra-clean Cr-Ni-Mo-V steel.

[0006] Patent CN112322839A introduces a method of degassing by blowing argon at the bottom of a medium frequency furnace. The main feature is that a bottom blowing device is installed at the bottom of the medium frequency furnace to blow Ar into the molten steel to remove harmful gas elements such as nitrogen and hydrogen in the molten steel. However, since Ar is an inert gas and does not react with the molten steel, CO2 can react with carbon in the molten steel to generate twice the volume of CO. Therefore, compared with bottom blowing Ar, bottom blowing CO2 has a better stirring effect, and the generation of more bubbles is more conducive to denitrification and dehydrogenation of the molten steel. In addition, Ar blowing will greatly increase the cost of bottom blowing gas.

[0007] Patent CN116657046A introduces a Cr-Ni-Mo-V martensitic heat-resistant steel and its manufacturing method, which is mainly characterized by using VIM+VAR double vacuum smelting and casting into ingots, which can produce CrNiMoV steel with higher purity, but because its stirring method is electromagnetic stirring, its stirring effect is far less than additional bottom blowing gas stirring. In addition, the production efficiency of this method is lower than that of conventional casting.

[0008] To this end, we proposed a method of adding bottom blowing CO2-Ar gas in a medium frequency furnace to smelt ultra-clean Cr-Ni-Mo-V steel liquid. Summary of the invention

[0009] Aiming at the problem that the electromagnetic stirring effect generated by the existing medium frequency furnace is poor when smelting Cr-Ni-Mo-V molten steel, increasing the electromagnetic stirring power causes the erosion of the crucible by the molten steel to increase, thus damaging the life of the crucible, the present invention provides a method for smelting ultra-clean Cr-Ni-Mo-V molten steel by using CO2-Ar. During the smelting process in the medium frequency furnace, CO2 and Ar are used as bottom blowing media in the medium frequency furnace, and the bottom blowing flow rates of CO2 and Ar are adjusted in time periods according to the target molten steel composition requirements. While ensuring a high alloy yield of alloy elements in the molten steel, the molten pool stirring is enhanced and the molten steel composition is uniform. In addition, CO2 is used to replace part of Ar for bottom blowing, which reduces Ar consumption and reduces smelting costs.

[0010] In order to achieve the above object, the technical solution of the present invention is:

[0011] The purpose of the present invention is to provide a method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar. The smelting process adopts a medium frequency furnace smelting system, including four stages: an early melting stage, a mid-term mixing bottom blowing stage, a mid-term feeding bottom blowing stage, and a late feeding bottom blowing stage.

[0012] According to the raw material composition ratio of the molten steel, iron, ferromolybdenum, ferronickel and 35wt% of carbon powder are added in sequence in the early melting stage, and the intermediate frequency furnace smelting system is controlled to set the bottom blowing Ar flow rate based on the molten steel composition, and the temperature is raised to 1600℃ until the molten steel components are completely melted;

[0013] In the mid-term mixing and bottom blowing stirring stage, the bottom blowing gas mixing ratio and the injection flow rate are adjusted in real time according to the carbon content [%C] in the molten steel and the carbon content [%C] in the molten steel measured by the smelting system;

[0014] In the mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 40wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time;

[0015] In the later stage of feeding and bottom blowing, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 25wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time;

[0016] When the target carbon content [%C] is 0.48-0.55, the smelting system is controlled to measure the content of each element in the molten steel to reach the expected target value, and the smelting of ultra-clean Cr-Ni-Mo-V molten steel is completed.

[0017] Furthermore, in terms of mass percentage, the composition ratio of the ultra-clean Cr-Ni-Mo-V steel liquid is:

[0018] [%C]=0.48~0.55; [%Cr]=4.90~5.40; [%Ni]=0.30~0.50; [%Mo]=0.30~0.50; [%V]=0.10~0.20; [%Mn]=0.20~0.50; [%Si]=0.30~0.55; [%B], [%Nb], [%Zr], [%Co] trace elements are all ≤0.020, and the rest is pure iron.

[0019] Furthermore, it is characterized in that, according to the data of the analysis of the flue gas composition generated by the smelting system during the smelting process, the decarburization amount and carbon content of the molten steel composition in the smelting process are calculated, and then the molten steel composition is predicted, wherein the calculation method of the decarburization amount is: The carbon content is calculated as: Where Δm c is the decarburization amount, unit is g; M c is the molar mass of carbon element, unit is g / mol; 0.06 is the standard gas conversion coefficient; Q 气体 M is the gas flow rate of the mixed gas, unit: NL / (min·t); 钢液 is the mass of molten steel, unit: t; β co is the CO gas content obtained by online gas analyzer, unit: %; M co is the molar volume of CO gas, take 22.4L / mol; [%C] 初始 is the initial carbon content of the molten steel; [%C] 当前 It is the current real-time carbon content of molten steel.

[0020] Further, the smelting process is as follows:

[0021] Weigh the raw material composition ratio of molten steel;

[0022] In the early melting stage, the furnace gas composition and concentration are measured by the smelting system, and the data information is uploaded to the control system. Iron, ferromolybdenum, ferronickel and 35wt% carbon powder are added to the furnace in sequence, and the intermediate frequency furnace smelting system is controlled to control the bottom blowing Ar flow rate based on the steel liquid composition, and the temperature is raised to 1600℃ until the steel liquid composition is completely melted;

[0023] In the mid-term mixed bottom blowing stirring stage, the carbon content [%C] in the molten steel is measured by the smelting system to adjust the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 12-15NL / (min·t), and the CO2 gas accounts for 60-80% of the bottom blowing mixed gas.

[0024] In the mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 40wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 15-18NL / (min·t), and the CO2 gas accounts for 40-80% of the bottom blowing mixed gas;

[0025] In the later feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 25wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 18-20NL / (min·t), and the CO2 gas accounts for 50-80% or 0 in the bottom blowing mixed gas;

[0026] When the target carbon content [%C] is 0.48-0.55, the smelting system is controlled to determine that the content of each element in the molten steel reaches the expected target value, completing the smelting of ultra-clean Cr-Ni-Mo-V molten steel.

[0027] Furthermore, in the early melting stage, the bottom blowing flow rate of Ar is 3 to 5 NL / (min·t).

[0028] Furthermore, in the mid-term mixing and bottom blowing stirring stage, the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time. The specific steps are as follows:

[0029] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12-15NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0030] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12~15NL / (min·t), and the CO2 gas accounts for 70% of the bottom-blown mixed gas;

[0031] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 12~15NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas.

[0032] Furthermore, in the mid-term feeding and bottom blowing stage, the carbon content [%C] in the molten steel measured by the monitoring system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time. The specific steps are as follows:

[0033] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15-18NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0034] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15~18NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0035] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 15~18NL / (min·t), and the CO2 gas accounts for 40% of the bottom-blown mixed gas.

[0036] Furthermore, in the later stage of feeding and bottom blowing, the carbon content [%C] in the molten steel measured by the monitoring system is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time; the specific steps are as follows:

[0037] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18-20NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0038] When 0.55≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18~20NL / (min·t), and the CO2 gas accounts for 50% of the bottom-blown mixed gas;

[0039] When [%C]<0.55, the bottom blowing gas flow rate is 18~20NL / (min·t), and the bottom blowing gas is pure Ar blowing.

[0040] Furthermore, during the smelting process, the medium frequency furnace smelting system used includes a computer and control system, an online gas analyzer, a smoke filter, a medium frequency furnace, a flow controller, a CO2 gas cylinder and an Ar gas cylinder; a bottom blowing nozzle is provided at the bottom of the medium frequency furnace, and the bottom blowing nozzle is connected to the flow controller through a gas pipeline, and the CO2 gas cylinder and the Ar gas cylinder are connected to the flow controller through an air intake pipeline respectively, and the flow controller is connected to the computer and control system, and a gas flow pipe is provided at the upper end of the medium frequency furnace, and the gas flow pipe is connected to the smoke filter, and the smoke filter is connected to the online gas analyzer, and the online gas analyzer is connected to the computer and control system.

[0041] Furthermore, during the smelting process, the online gas analyzer is used to analyze the gas composition and concentration of the furnace gas in real time, and transmit its data to the computer and control system. The computer and control system are used to predict the change of carbon content in the molten steel based on the gas composition and concentration and bottom blowing gas flow in the medium frequency furnace, and control the gas mixing ratio and blowing flow of the flow controller according to the change of carbon content in the molten steel; the medium frequency furnace is used to smelt alloys.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention is applicable to the process of smelting ultra-pure Cr-Ni-Mo-V series molten steel in a 10kg-50t medium frequency furnace. The present invention can strengthen the stirring of the molten steel, make the composition and temperature of the molten steel more uniform, and at the same time, ensure the recovery rate of alloy elements in the molten steel, further improve the quality of the molten steel, and realize the effective utilization of CO2 greenhouse gas in the medium frequency furnace smelting process. At the same time, the addition of gas stirring shortens the smelting cycle and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a connection diagram of the medium frequency furnace smelting system of the present invention;

[0045] Description of reference numerals:

[0046] 1. Computer and control system, 2. Online gas analyzer, 3. Smoke filter, 4. Medium frequency furnace, 5. Flow controller, 6. CO2 gas cylinder, 7. Ar gas cylinder. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0049] The present invention provides a method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar. The smelting process adopts a medium frequency furnace smelting system, which includes four stages: an early melting stage, a mid-term mixing bottom blowing and stirring stage, a mid-term feeding bottom blowing stage, and a late feeding bottom blowing stage.

[0050] According to the raw material composition ratio of the molten steel, iron, ferromolybdenum, ferronickel and 35wt% of carbon powder are added in sequence in the early melting stage, and the intermediate frequency furnace smelting system is controlled to set the bottom blowing Ar flow rate based on the molten steel composition, and the temperature is raised to 1600℃ until the molten steel components are completely melted;

[0051] In the mid-term mixing and bottom blowing stirring stage, the bottom blowing gas mixing ratio and the injection flow rate are adjusted in real time according to the carbon content [%C] in the molten steel and the carbon content [%C] in the molten steel measured by the smelting system;

[0052] In the mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 40wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time;

[0053] In the later stage of feeding and bottom blowing, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 25wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time;

[0054] When the target carbon content [%C] is 0.48-0.55, the smelting system is controlled to measure the content of each element in the molten steel to reach the expected target value, and the smelting of ultra-clean Cr-Ni-Mo-V molten steel is completed.

[0055] The present invention is applicable to the process of smelting high-alloy special steel in a 10kg-50t medium frequency furnace. CO2-Ar is used as a bottom blowing stirring gas, and alloy smelting is added to the molten pool in the order of alloy element content and oxidation property strength. According to the different alloy element contents in the molten steel predicted by the computer and the control system, the mixing ratio and flow rate of the bottom blowing CO2-Ar are adjusted in real time. A large number of CO bubbles are generated by the reaction of CO2 with the carbon element in the molten steel to achieve enhanced molten pool stirring. The present invention can strengthen the stirring of the molten steel, make the composition and temperature of the molten steel more uniform, and at the same time, ensure the recovery rate of the alloy elements in the molten steel, further improve the quality of the molten steel, and realize the effective use of CO2 greenhouse gas in the smelting process of the medium frequency furnace. At the same time, the addition of gas stirring shortens the smelting cycle, makes the composition and temperature of the molten steel more uniform, shortens the smelting time, avoids the burning of alloy elements, improves the alloy recovery rate, and improves production efficiency.

[0056] In some specific embodiments, the composition ratio of the ultra-clean Cr-Ni-Mo-V steel liquid is as follows, calculated by mass percentage:

[0057] [%C]=0.48~0.55; [%Cr]=4.90~5.40; [%Ni]=0.30~0.50; [%Mo]=0.30~0.50; [%V]=0.10~0.20; [%Mn]=0.20~0.50; [%Si]=0.30~0.55; [%B], [%Nb], [%Zr], [%Co] trace elements are all ≤0.020, and the rest is pure iron.

[0058] In some specific embodiments, according to the smelting process, the smelting system generates flue gas composition analysis data, the flue gas generated in the medium frequency furnace is filtered and captured into the gas analyzer to analyze its composition, and the data is transmitted to the computer and control system, and the content of C, Cr, Ni, Mo, V, Mn, and Si elements in the molten steel is determined by the computer molten steel composition real-time monitoring system; the decarburization amount and carbon content of the molten steel composition in the smelting process are calculated, and then the molten steel composition is predicted, wherein the calculation method of the decarburization amount is:

[0059]

[0060] The carbon content is calculated as:

[0061]

[0062] Where Δm c is the decarburization amount, unit is g; M c is the molar mass of carbon element, unit is g / mol; 0.06 is the standard gas conversion coefficient; Q 气体 M is the gas flow rate of the mixed gas, unit: NL / (min·t); 钢液is the mass of molten steel, unit: t; β co is the CO gas content obtained by online gas analyzer, unit: %; M co is the molar volume of CO gas, take 22.4L / mol; [%C] 初始 is the initial carbon content of the molten steel; [%C] 当前 It is the current real-time carbon content of molten steel.

[0063] In some specific embodiments, the smelting process is as follows:

[0064] Determine the specific mass of each raw material according to the volume of the medium frequency furnace, weigh the raw material composition ratio of the molten steel, and calculate it by mass percentage as follows: ferromolybdenum 0.50-1.00%, carbon powder 2.95-3.25%, ferronickel 0.50-2.50%, ferrochromium 6.50-9.80%, ferromanganese 0.23-0.83%, ferrosilicon 0.40-0.78%, ferrovanadium 0.12-0.50%, boron, niobium, zirconium, cobalt and other pure material trace elements are all ≤0.020, and the rest are industrial pure iron;

[0065] In the early melting stage, the furnace gas composition and concentration are measured by the smelting system, and the data information is uploaded to the control system. Iron, ferromolybdenum, ferronickel and 35wt% of carbon powder are added to the furnace in sequence, and the bottom blowing gas is set to pure Ar blowing. The intermediate frequency furnace smelting system is controlled to blow the bottom Ar flow rate based on the steel liquid composition, and the bottom blowing flow rate of Ar is 3-5NL / (min·t). The temperature is raised to 1600°C until the steel liquid composition is completely melted;

[0066] In the mid-term mixed bottom blowing stirring stage, after the temperature reaches 1600°C and the raw materials are completely melted, the carbon content [%C] in the molten steel is measured by the smelting system to adjust the bottom blowing gas mixing ratio and the injection flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 12-15NL / (min·t), and the CO2 gas accounts for 60-80% of the bottom blowing mixed gas. The specific bottom blowing steps of CO2 and Ar are as follows:

[0067] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12-15NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0068] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12~15NL / (min·t), and the CO2 gas accounts for 70% of the bottom-blown mixed gas;

[0069] When [%C] < 0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 12-15 NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0070] In the mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 40wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 15-18NL / (min·t), and the CO2 gas accounts for 40-80% of the bottom blowing mixed gas; the specific bottom blowing steps of CO2 and Ar are as follows:

[0071] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15-18NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0072] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15~18NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0073] When [%C] < 0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 15-18 NL / (min·t), and the CO2 gas accounts for 40% of the bottom-blown mixed gas;

[0074] In the later stage of feeding and bottom blowing, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 25wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 18-20NL / (min·t), and the CO2 gas accounts for 50-80% or 0 in the bottom blowing mixed gas; the specific bottom blowing steps of CO2 and Ar are as follows:

[0075] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18-20NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0076] When 0.55≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18~20NL / (min·t), and the CO2 gas accounts for 50% of the bottom-blown mixed gas;

[0077] When [%C]<0.55, the bottom blowing gas flow rate is 18~20NL / (min·t), and the bottom blowing gas is pure Ar blowing;

[0078] When the target carbon content [%C] is 0.48-0.55, that is, the medium frequency furnace smelting system shows that the molten steel [%C] = 0.48-0.55, the bottom blowing CO2-Ar mixed gas decarburization enhanced molten steel stirring task is completed, the smelting system is controlled to determine that the content of each element in the molten steel reaches the expected target value, the medium frequency furnace smelting system is closed, the gas supply is stopped, and the smelting of ultra-clean Cr-Ni-Mo-V molten steel is completed.

[0079] During the smelting process, the medium frequency furnace smelting system used includes a computer and control system 1, an online gas analyzer 2, a smoke filter 3, a medium frequency furnace 4, a flow controller 5, a CO2 gas cylinder 6 and an Ar gas cylinder 7; a bottom blowing nozzle is provided at the bottom of the medium frequency furnace 4, and the bottom blowing nozzle is connected to the flow controller 5 through a gas transmission pipeline, and the CO2 gas cylinder 6 and the Ar gas cylinder 7 are respectively connected to the flow controller 5 through an air intake pipeline, and the flow controller 5 is connected to the computer and control system 1, and a gas flow pipe is provided at the upper end of the medium frequency furnace 4, and the gas flow pipe is connected to the smoke filter 3, and the smoke filter 3 is connected to the online gas analyzer 2, and the online gas analyzer 2 is connected to the computer and control system 1.

[0080] During the smelting process, the online gas analyzer 2 is used to analyze the gas composition and concentration of the furnace gas in real time, and transmit its data to the computer and control system 1. The computer and control system 1 is used to predict the change of carbon content in the molten steel based on the gas composition and concentration and the bottom blowing gas flow rate in the medium frequency furnace 4, and control the gas mixing ratio and injection flow rate of the flow controller 5 according to the change of carbon content in the molten steel; the medium frequency furnace 4 is used to smelt alloys; the computer and control system 1 is connected to the online gas analyzer 2 and the flow controller 5 through signal transmission wires, respectively. The online gas analyzer 2 is used to analyze the gas composition and concentration of the furnace gas in real time, and transmit its data to the computer and control system. The computer and control system 1 uses the furnace gas composition data, the initial alloy content data of the molten steel, and the bottom blowing gas flow rate data to calculate and predict the change of carbon content in the molten steel, and sends instructions to the flow controller 5 to adjust the mixing ratio and injection flow rate of CO2 and Ar according to the change of carbon content in the molten steel. The upper end of the medium frequency furnace 4 is provided with a furnace cover, and the gas flow pipe penetrates the furnace cover and the penetrating part is located in the medium frequency furnace 4. The furnace gas of the medium frequency furnace 4 is transported to the smoke filter 3 through the gas flow pipe, and then transported to the online gas analyzer 2 after being filtered by the smoke filter 3. The CO2 gas cylinder 6 and the Ar gas cylinder 7 are respectively connected to the flow controller 5 through an air intake pipe. The CO2 gas cylinder 6 and the Ar gas cylinder 7 are provided with a flow valve and a pressure valve for separate control. After the gas in the CO2 gas cylinder 6 and the Ar gas cylinder 7 are collected to the flow controller 5 through the air intake pipe, they enter the medium frequency furnace 4 through the bottom blowing nozzle, thereby enhancing the stirring of the molten steel, improving the smelting dynamics conditions, uniformizing the composition of the molten steel, improving the quality of the molten steel, and ensuring the final steel alloy yield. A bottom blowing gas control valve is also provided on the bottom blowing nozzle to control the flow of the gas in the bottom blowing nozzle.

[0081] The invention is further described below through specific examples.

[0082] Example 1

[0083] A method for smelting ultra-clean Cr-Ni-Mo-V steel liquid using CO2-Ar, comprising the following steps: a medium frequency furnace smelting system is used during the smelting process, including four stages: an early melting stage, a mid-term mixing bottom blowing stirring stage, a mid-term feeding bottom blowing stage, and a late feeding bottom blowing stage;

[0084] S1. Determine the specific mass of each raw material according to the volume of the medium frequency furnace, weigh the raw material composition ratio of the molten steel, and calculate it in mass percentage: Determine the specific mass of each raw material according to the 50kg melting capacity of the medium frequency furnace and the mass percentage of each raw material: 29kg of industrial pure iron, 270g of ferromolybdenum (containing 50% molybdenum), 1000g of carbon powder, 225g of ferronickel (containing 60% nickel), 2500g of ferrochrome (containing 70% chromium), 210g of ferromanganese (containing 80% manganese), 220g of ferrosilicon (containing 75% silicon), 125g of ferrovanadium (containing 80% vanadium), 7g each of pure trace elements such as boron, niobium, zirconium, and cobalt;

[0085] S2, in the early melting stage, the gas composition and concentration of the furnace gas are measured by an online gas analyzer 2, and the data information is uploaded to the computer and control system 1, iron, ferromolybdenum, ferronickel and 350g of carbon powder are added to the furnace in sequence, the bottom blowing gas is set to pure Ar blowing, the intermediate frequency furnace smelting system is controlled to blow Ar flow rate based on the molten steel composition, the bottom blowing flow rate of Ar is 4NL / (min·t), and the temperature is raised to 1600°C until the molten steel composition is completely melted;

[0086] S3, mid-term mixing bottom blowing stirring stage, after the temperature reaches 1600°C and the raw materials are completely melted, the carbon content [%C] in the molten steel is measured by the computer and control system 1 to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0087] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0088] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 13NL / (min·t), and the CO2 gas accounts for 70% of the bottom-blown mixed gas;

[0089] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 12NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0090] S4, mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 400g of carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the computer and control system 1 is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0091] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 17NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0092] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 16NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0093] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 15NL / (min·t), and the CO2 gas accounts for 40% of the bottom-blown mixed gas;

[0094] S5, in the later stage of feeding and bottom blowing, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 250g of carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the computer and control system 1 is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0095] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 20NL / (min·t), and the CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0096] When 0.55≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 19NL / (min·t), and the CO2 gas accounts for 50% of the bottom-blown mixed gas;

[0097] When [%C]<0.55, the bottom blowing gas flow rate is 18NL / (min·t), and the bottom blowing gas is pure Ar blowing;

[0098] S6. When the computer and control system 1 displays that [%C] of the molten steel is 0.52, the bottom blowing CO2-Ar mixed gas decarburization enhancement and molten steel stirring task is completed, the smelting system is controlled to determine that the content of each element in the molten steel reaches the expected target value, the medium frequency furnace smelting system is closed, the gas supply is stopped, and the smelting of the ultra-clean Cr-Ni-Mo-V series molten steel is completed; after the smelting is completed, the component ratio of the ultra-clean Cr-Ni-Mo-V series molten steel is, calculated by mass percentage: [%C]=0.52; [%Cr]=5.10; [%Ni]=0.40; [%Mo]=0.35; [%V]=0.18; [%Mn]=0.38; [%Si]=0.50; and trace elements such as [%P], [%S], [%Pb], [%Bi], [%Sb], [%Sn], and [%As] are all ≤0.020.

[0099] By adopting the present invention, the total oxygen content of the steel liquid at the smelting end point of the 50kg medium frequency induction furnace is ≤4ppm, the nitrogen content can be controlled within 5-15ppm, the hydrogen content can be controlled within 1.0ppm, and the temperature and composition of the steel liquid are uniform, the product quality is improved, and the smelting of ultra-pure Cr-Ni-Mo-V series steel liquid is realized.

[0100] Example 2

[0101] A method for smelting ultra-clean Cr-Ni-Mo-V steel liquid using CO2-Ar, comprising the following steps: a medium frequency furnace smelting system is used during the smelting process, including four stages: an early melting stage, a mid-term mixing bottom blowing stirring stage, a mid-term feeding bottom blowing stage, and a late feeding bottom blowing stage;

[0102] S1. Determine the specific mass of each raw material according to the volume of the medium frequency furnace, weigh the raw material composition ratio of the molten steel, and calculate it in mass percentage: Determine the specific mass of each raw material according to the 10kg melting capacity of the medium frequency furnace and the mass percentage of each raw material: 6kg of industrial pure iron, 45g of ferromolybdenum (containing 60% molybdenum), 200g of carbon powder, 45g of ferronickel (containing 60% nickel), 467g of ferrochrome (containing 75% chromium), 45g of ferromanganese (containing 75% manganese), 37g of ferrosilicon (containing 90% silicon), 25g of ferrovanadium (containing 80% vanadium), 1.4g each of pure trace elements such as boron, niobium, zirconium, and cobalt;

[0103] S2, in the early melting stage, the gas composition and concentration of the furnace gas are measured by an online gas analyzer 2, and the data information is uploaded to the computer and control system 1, iron, ferromolybdenum, ferronickel and 70g of carbon powder are added to the furnace in sequence, the bottom blowing gas is set to pure Ar blowing, the intermediate frequency furnace smelting system is controlled to blow Ar flow rate based on the steel liquid composition, the bottom blowing flow rate of Ar is 3NL / (min·t), and the temperature is raised to 1600°C until the steel liquid composition is completely melted;

[0104] S3, mid-term mixing bottom blowing stirring stage, after the temperature reaches 1600°C and the raw materials are completely melted, the carbon content [%C] in the molten steel is measured by the computer and control system 1 to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0105] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0106] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12NL / (min·t), and the CO2 gas accounts for 70% of the bottom-blown mixed gas;

[0107] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 12NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0108] S4, mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 80g of carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the computer and control system 1 is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0109] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0110] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0111] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 15NL / (min·t), and the CO2 gas accounts for 40% of the bottom-blown mixed gas;

[0112] S5, in the later stage of feeding and bottom blowing, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 50g of carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the computer and control system 1 is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0113] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0114] When 0.55≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18NL / (min·t), and the CO2 gas accounts for 50% of the bottom-blown mixed gas;

[0115] When [%C]<0.55, the bottom blowing gas flow rate is 18NL / (min·t), and the bottom blowing gas is pure Ar blowing;

[0116] S6. When the computer and control system 1 displays that [%C] of the molten steel is 0.50, the bottom blowing CO2-Ar mixed gas decarburization enhancement and molten steel stirring task is completed, the smelting system is controlled to determine that the content of each element in the molten steel reaches the expected target value, the medium frequency furnace smelting system is closed, the gas supply is stopped, and the smelting of the ultra-clean Cr-Ni-Mo-V series molten steel is completed; after the smelting is completed, the component ratio of the ultra-clean Cr-Ni-Mo-V series molten steel is, calculated by mass percentage: [%C]=0.50; [%Cr]=5.10; [%Ni]=0.40; [%Mo]=0.35; [%V]=0.18; [%Mn]=0.38; [%Si]=0.50; and trace elements such as [%P], [%S], [%Pb], [%Bi], [%Sb], [%Sn], and [%As] are all ≤0.020.

[0117] By adopting the present invention, the total oxygen content of the steel liquid at the end point of smelting in the 10kg medium frequency induction furnace is ≤3ppm, the nitrogen content can be controlled within 5-13ppm, the hydrogen content can be controlled within 1.1ppm, and the temperature and composition of the steel liquid are uniform, the product quality is improved, and the smelting of ultra-pure Cr-Ni-Mo-V series steel liquid is realized.

[0118] Example 3

[0119] A method for smelting ultra-clean Cr-Ni-Mo-V steel liquid using CO2-Ar, comprising the following steps: a medium frequency furnace smelting system is used during the smelting process, including four stages: an early melting stage, a mid-term mixing bottom blowing stirring stage, a mid-term feeding bottom blowing stage, and a late feeding bottom blowing stage;

[0120] S1. Determine the specific mass of each raw material according to the volume of the medium frequency furnace, weigh the raw material composition ratio of the molten steel, and calculate it in mass percentage: Determine the specific mass of each raw material according to the 150kg melting capacity of the medium frequency furnace and the mass percentage of each raw material: 90kg of industrial pure iron, 735g of ferromolybdenum (containing 55% molybdenum), 3kg of carbon powder, 623g of ferronickel (containing 65% nickel), 7kg of ferrochrome (containing 70% chromium), 672g of ferromanganese (containing 75% manganese), 619g of ferrosilicon (containing 80% silicon), 400g of ferrovanadium (containing 75% vanadium), 20g each of pure trace elements such as boron, niobium, zirconium, and cobalt;

[0121] S2, in the early melting stage, the gas composition and concentration of the furnace gas are measured by an online gas analyzer 2, and the data information is uploaded to the computer and control system 1, iron, ferromolybdenum, ferronickel and 1050g of carbon powder are added to the furnace in sequence, the bottom blowing gas is set to pure Ar blowing, the intermediate frequency furnace smelting system is controlled to blow Ar flow rate based on the steel liquid composition, the bottom blowing flow rate of Ar is 5NL / (min·t), and the temperature is raised to 1600°C until the steel liquid composition is completely melted;

[0122] S3, mid-term mixing bottom blowing stirring stage, after the temperature reaches 1600°C and the raw materials are completely melted, the carbon content [%C] in the molten steel is measured by the computer and control system 1 to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0123] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0124] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15NL / (min·t), and the CO2 gas accounts for 70% of the bottom-blown mixed gas;

[0125] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 14NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0126] S4, mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 1200g of carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the computer and control system 1 is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0127] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0128] When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas;

[0129] When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 16NL / (min·t), and the CO2 gas accounts for 40% of the bottom-blown mixed gas;

[0130] S5, in the later stage of feeding and bottom blowing, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 750g of carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the computer and control system 1 is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The specific bottom blowing steps of CO2 and Ar are as follows:

[0131] When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 20NL / (min·t), and the CO2 gas accounts for 80% of the bottom-blown mixed gas;

[0132] When 0.55≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 20NL / (min·t), and the CO2 gas accounts for 50% of the bottom-blown mixed gas;

[0133] When [%C]<0.55, the bottom blowing gas flow rate is 19NL / (min·t), and the bottom blowing gas is pure Ar blowing;

[0134] S6. When the computer and control system 1 displays that [%C] of the molten steel is 0.50, the bottom blowing CO2-Ar mixed gas decarburization enhancement and molten steel stirring task is completed, the smelting system is controlled to determine that the content of each element in the molten steel reaches the expected target value, the medium frequency furnace smelting system is closed, the gas supply is stopped, and the smelting of the ultra-clean Cr-Ni-Mo-V series molten steel is completed; after the smelting is completed, the component ratio of the ultra-clean Cr-Ni-Mo-V series molten steel is, calculated by mass percentage: [%C]=0.50; [%Cr]=5.10; [%Ni]=0.40; [%Mo]=0.35; [%V]=0.18; [%Mn]=0.38; [%Si]=0.50; and trace elements such as [%P], [%S], [%Pb], [%Bi], [%Sb], [%Sn], and [%As] are all ≤0.020.

[0135] By adopting the present invention, the total oxygen content of the steel liquid at the 150kg medium frequency induction furnace smelting end point is ≤4ppm, the nitrogen content can be controlled within 5-15ppm, the hydrogen content can be controlled within 1.1ppm, and the temperature and composition of the steel liquid are uniform, the product quality is improved, and the smelting of ultra-pure Cr-Ni-Mo-V series steel liquid is realized.

[0136] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0137] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for smelting ultra-clean Cr-Ni-Mo-V steel liquid using CO2-Ar, characterized in that: The smelting process uses a medium frequency furnace smelting system, which includes four stages: early melting stage, mid-term mixing bottom blowing stage, mid-term feeding bottom blowing stage, and late feeding bottom blowing stage. According to the raw material composition ratio of the molten steel, iron, ferromolybdenum, ferronickel and 35wt% of carbon powder are added in sequence in the early melting stage, and the intermediate frequency furnace smelting system is controlled to set the bottom blowing Ar flow rate based on the molten steel composition, and the temperature is raised to 1600℃ until the molten steel components are completely melted; In the mid-term mixing and bottom blowing stirring stage, the bottom blowing gas mixing ratio and the injection flow rate are adjusted in real time according to the carbon content [%C] in the molten steel and the carbon content [%C] in the molten steel measured by the smelting system; In the mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 40wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time; In the later stage of feeding and bottom blowing, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 25wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the injection flow rate in real time; When the target carbon content [%C] is 0.48-0.55, the smelting system is controlled to measure the content of each element in the molten steel to reach the expected target value, and the smelting of ultra-clean Cr-Ni-Mo-V molten steel is completed.

2. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid using CO2-Ar according to claim 1, characterized in that: Calculated by mass percentage, the composition ratio of ultra-clean Cr-Ni-Mo-V molten steel is: [%C]=0.48~0.55; [%Cr]=4.90~5.40; [%Ni]=0.30~0.50; [%Mo]=0.30~0.50; [%V]=0.10~0.20; [%Mn]=0.20~0.50; [%Si]=0.30~0.55; [%B], [%Nb], [%Zr], [%Co] trace elements are all ≤0.020, and the rest is pure iron.

3. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar according to claim 1, characterized in that: According to the data of the flue gas composition analysis generated by the smelting system during the smelting process, the decarburization amount and carbon content of the molten steel composition in the smelting process are calculated, and then the molten steel composition is predicted. The calculation method of the decarburization amount is: The carbon content is calculated as: Where Δm c is the decarburization amount, unit is g; M c is the molar mass of carbon element, unit is g / mol; 0.06 is the standard gas conversion coefficient; Q 气体 M is the gas flow rate of the mixed gas, unit: NL / (min·t); 钢液 is the mass of molten steel, unit: t; β co is the CO gas content obtained by online gas analyzer, unit: %; M co is the molar volume of CO gas, take 22.4L / mol; [%C] 初始 is the initial carbon content of the molten steel; [%C] 当前 It is the current real-time carbon content of molten steel.

4. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar according to claim 1, characterized in that: The smelting process is as follows: Weigh the raw material composition ratio of molten steel; In the early melting stage, the furnace gas composition and concentration are measured by the smelting system, and the data information is uploaded to the control system. Iron, ferromolybdenum, ferronickel and 35wt% carbon powder are added to the furnace in sequence, and the intermediate frequency furnace smelting system is controlled to control the bottom blowing Ar flow rate based on the steel liquid composition, and the temperature is raised to 1600℃ until the steel liquid composition is completely melted; In the mid-term mixed bottom blowing stirring stage, the carbon content [%C] in the molten steel is measured by the smelting system to adjust the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 12-15NL / (min·t), and the CO2 gas accounts for 60-80% of the bottom blowing mixed gas. In the mid-term feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.3, ferrochrome, ferromanganese, ferrosilicon, ferrovanadium and 40wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 15-18NL / (min·t), and the CO2 gas accounts for 40-80% of the bottom blowing mixed gas; In the later feeding and bottom blowing stage, when the carbon content [%C] in the molten steel measured by the smelting system is less than 0.5, trace alloy elements and 25wt% carbon powder are added in sequence, and the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and the blowing flow rate in real time. The bottom blowing CO2-Ar mixed gas flow rate is 18-20NL / (min·t), and the CO2 gas accounts for 50-80% or 0 in the bottom blowing mixed gas; When the target carbon content [%C] is 0.48-0.55, the smelting system is controlled to measure the content of each element in the molten steel to reach the expected target value, completing the smelting of ultra-clean Cr-Ni-Mo-V molten steel.

5. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar according to claim 4, characterized in that: In the early melting stage, the bottom blowing flow rate of Ar is 3 to 5 NL / (min·t).

6. The method for smelting ultra-clean Cr-Ni-Mo-V molten steel using CO2-Ar according to claim 4, characterized in that: In the mid-term mixing and bottom blowing stirring stage, the carbon content [%C] in the molten steel measured by the smelting system is used to control the bottom blowing gas mixing ratio and injection flow rate in real time. The specific steps are as follows: When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12-15NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas; When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 12~15NL / (min·t), and the CO2 gas accounts for 70% of the bottom-blown mixed gas; When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 12~15NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas.

7. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar according to claim 4, characterized in that: In the mid-term feeding and bottom blowing stage, the carbon content [%C] in the molten steel measured by the monitoring system is used to control the bottom blowing gas mixing ratio and injection flow rate in real time. The specific steps are as follows: When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15-18NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas; When 0.6≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 15~18NL / (min·t), and the CO2 gas accounts for 60% of the bottom-blown mixed gas; When [%C]<0.6, the flow rate of the bottom-blown CO2-Ar mixed gas is 15~18NL / (min·t), and the CO2 gas accounts for 40% of the bottom-blown mixed gas.

8. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar according to claim 4, characterized in that: In the later stage of feeding and bottom blowing, the carbon content [%C] in the molten steel measured by the monitoring system is used to control the bottom blowing gas mixing ratio and injection flow rate in real time; the specific steps are as follows: When [%C]≥1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18-20NL / (min·t), and CO2 gas accounts for 80% of the bottom-blown mixed gas; When 0.55≤[%C]<1.0, the flow rate of the bottom-blown CO2-Ar mixed gas is 18~20NL / (min·t), and the CO2 gas accounts for 50% of the bottom-blown mixed gas; When [%C]<0.55, the bottom blowing gas flow rate is 18~20NL / (min·t), and the bottom blowing gas is pure Ar blowing.

9. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar according to claim 1, characterized in that: During the smelting process, the medium frequency furnace smelting system used includes a computer and control system (1), an online gas analyzer (2), a smoke filter (3), a medium frequency furnace (4), a flow controller (5), a CO2 gas cylinder (6) and an Ar gas cylinder (7); a bottom blowing nozzle is provided at the bottom of the medium frequency furnace (4), and the bottom blowing nozzle is connected to the flow controller (5) through a gas transmission pipeline, and the CO2 gas cylinder (6) and the Ar gas cylinder (7) are respectively connected to the flow controller (5) through an air intake pipeline, and the flow controller (5) is connected to the computer and control system (1); a gas flow pipe is provided at the upper end of the medium frequency furnace (4), and the gas flow pipe is connected to the smoke filter (3), and the smoke filter (3) is connected to the online gas analyzer (2), and the online gas analyzer (2) is connected to the computer and control system (1).

10. The method for smelting ultra-clean Cr-Ni-Mo-V steel liquid by using CO2-Ar according to claim 9, characterized in that: During the smelting process, the online gas analyzer (2) is used to analyze the composition and concentration of furnace gas in real time, and transmit the data to the computer and control system (1). The computer and control system (1) are used to predict the change of carbon content in molten steel based on the gas composition and concentration and bottom blowing gas flow rate in the medium frequency furnace (4), and control the gas mixing ratio and blowing flow rate of the flow controller (5) according to the change of carbon content in the molten steel; the medium frequency furnace (4) is used to smelt alloys.

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