RH smelting system and method for ultra-low carbon steel

Abstract

The ultra-low carbon steel RH smelting system comprises a ladle furnace and a vacuum tank which are sequentially communicated, the vacuum tank is connected with a vacuum pipeline, the outlet end of the vacuum pipeline is connected with a pretreatment device, waste gas treated by the pretreatment device is discharged, the vacuum tank is located above the ladle furnace, and the vacuum tank is located above the ladle furnace. The vacuum tank is provided with an ascending pipe and a descending pipe, one end of the ascending pipe and one end of the descending pipe respectively extend into the ladle furnace, the other ends of the ascending pipe and the descending pipe are respectively communicated with a vacuum cavity of the vacuum tank, the position of the ascending pipe is fixedly connected with a three-way circulating pipe, and the position of the descending pipe is provided with a vacuum sealing cavity; the vacuum sealing cavity is arranged on the periphery of the descending pipe, the ascending pipe and the descending pipe are arranged in an asymmetric structure, and the length of the ascending pipe is larger than that of the descending pipe. The method is suitable for a pure steel production process for controlling gas inclusion ([N] and [O]) in steel and preventing recarburization and nitrogen absorption.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel metallurgy, and particularly relates to an RH smelting system and method for ultra-low carbon steel. BACKGROUND

[0002] RH method is an important secondary refining method, which has a series of advantages such as short processing cycle, large production capacity, good refining effect and easy operation, and has been widely used in steelmaking production. So far, RH has been transformed from the original single degassing equipment to a multifunctional secondary refining equipment including vacuum decarburization, oxygen blowing decarburization, powder injection desulfurization, temperature compensation, uniform temperature and composition. Moreover, with the progress of technology and the expansion of refining function, it has shown remarkable superiority in the production of ultra-low carbon steel, and is an indispensable secondary treatment device in modern steel plants. To ensure the equipment utilization rate of RH, improve the processing capacity and processing ratio of RH, it is an urgent problem to be solved. The existing technology still has the following technical bottlenecks in the RH refining of ultra-low carbon steel: insufficient decarburization precision, traditional natural decarburization is difficult to stably reduce the carbon content to below 200ppm, forced oxygen blowing is easy to cause C-O reaction overreaction, leading to steel liquid spatter, vacuum tank refractory melting loss, composition control conflict: improper timing of deoxidizing alloying easily causes secondary oxidation or carbon increase (such as the addition of coolant in the later stage leading to the rise of carbon content), uncontrollable element burning loss, lack of quantitative compensation model for manganese and silicon element burning loss during the process of top gun oxygen blowing, and low composition hit rate.

[0003] In the prior art, the coordinated control of top gun oxygen blowing parameters (flow rate, timing) and circulation gas and vacuum degree lacks systematic procedures, resulting in poor stability of ultra-low carbon steel production and less than 80% of qualified rate.

[0004] In view of the above factors, an RH smelting system and method for ultra-low carbon steel are provided, which are suitable for the pure steel production process for controlling gas inclusions ([N], [O]) in steel and preventing carbon increase and nitrogen absorption. SUMMARY

[0005] The purpose of the present application is to provide an RH smelting system and method for ultra-low carbon steel to solve the problems raised in the background art.

[0006] The purpose of the present application is achieved by the following technical scheme: an RH smelting system for ultra-low carbon steel, comprising a ladle furnace and a vacuum tank connected in sequence, the vacuum tank being connected with a vacuum pipeline, the outlet end of the vacuum pipeline being connected with a pretreatment device, and the exhaust gas treated by the pretreatment device being discharged;

[0007] The vacuum tank is located above the ladle furnace, the vacuum tank is located above the ladle furnace, the vacuum tank is provided with an ascending pipe and a descending pipe, one end of the ascending pipe and one end of the descending pipe respectively extend into the ladle furnace, and the other ends respectively communicate with the vacuum cavity of the vacuum tank.

[0008] The three-way circulation pipe is fixedly connected at the position of the ascending pipe, and the vacuum sealing cavity is arranged at the position of the descending pipe.

[0009] Further, the ascending pipe and the descending pipe are arranged in an asymmetric structure, wherein the length of the ascending pipe is greater than the length of the descending pipe.

[0010] Further, the vacuum sealing cavity is integrally formed with the descending pipe, and a vacuum channel is formed between the vacuum sealing cavity and the descending pipe.

[0011] A spaced support block is arranged between the vacuum sealing cavity and the descending pipe, and the support block is located above the molten steel.

[0012] Further, the vacuum sealing cavity and the descending pipe adopt unfired magnesia-spinel bricks, and the support block adopts unfired magnesia-spinel bricks and is arranged along the circumference of the descending pipe.

[0013] Further, a top lance is arranged at the top of the vacuum tank, and the top lance adopts an MFB top lance.

[0014] Further, the flow rate of the MFB top lance is ≤1800 Nm 3 / h, and the vacuum degree is <0.27 kPa.

[0015] An application method of an RH refining system for ultra-low carbon steel, comprising the following steps:

[0016] Pre-inspection of equipment: confirm the accuracy of temperature measurement and oxygen determination equipment, the starting time of 1B pump ≤4 minutes, the maximum vacuum degree ≤0.10 kPa, and the immersion tube aperture = 600 mm; wash tank operation: use 2 batches of low-carbon aluminum killed steel to clean the vacuum tank before smelting to remove the cold steel of hot elbow pipe; ladle management: the first 2 batches are cast with low-carbon aluminum killed steel to ensure that there is no residual steel or slag at the ladle opening and bottom.

[0017] Accurate control of alloying: early decarburization: add low-carbon ferromanganese (control \[Mn\] ≤0.20%) and phosphorus-sulfur adjusting agent; deoxidation constraint: strictly prohibit the addition of aluminum during decarburization; after adding aluminum for deoxidation at the end of decarburization, circulate for 2 minutes, and then add other alloys or ≤800 kg of cooling agent; aluminum compensation calculation: the aluminum content in FeTi needs to be considered when adding aluminum;

[0018] The application method of the RH refining system comprises: smelting of ultra-low carbon aluminum killed steel ([C] target ≤150 ppm)

[0019] Step 1: Pretreatment

[0020] The tank was cleaned with two furnaces of SPHC steel (low carbon aluminum killed) to remove the cold steel from the vacuum tank. The start-up time of pump 1B was confirmed to be 3.8 minutes, the diameter of the impregnation tube was 602 mm, and the temperature measuring gun error was ±2℃.

[0021] Step 2: Top Gun Decision

[0022] Open the MFB top gun gas valve (gas flow rate 30-50 m³ / h), ignite the gas, and gradually adjust the gas opening to a gas flow rate of 100-200 m³ / h. Adjust the oxygen flow rate to 100-150 m³ / h. Place the gun below the indoor baking position below the waiting point for blowing.

[0023] The initial state is: [O] = 380ppm, [C] = 350ppm, T = 1585℃ (target T~R~ = 1600℃). [O] low, [C] high, T low → execute top gun decarburization + heating.

[0024] Step 3: Forced decarbonization

[0025] A three-way circulation pipe is fixedly connected to the riser pipe, allowing 1500 NL / min of circulation gas to be introduced, and 1750 Nm of oxygen is blown in by the MFB top lance. 3 / h, decarburization complete: [C] = 120ppm, vacuum degree 18kPa;

[0026] Step 4: Deoxidation and alloying

[0027] In step 3 above, after a 2-minute delay, aluminum is added for deoxidation. The aluminum replenishment is calculated according to the formula G = 1.0 × Q (Q = 15 Nm). 3 →Add 15kg of aluminum), continuously circulate for 2 minutes, then add electrolytic manganese to compensate for manganese loss (oxygen blowing rate 200Nm). 3 →Manganese loss 0.016% →Replenish manganese 120kg);

[0028] Step 5: Chemical heating

[0029] Heating trigger conditions: ① Deoxidized steel: Start when the difference between the target temperature T~R~ and the actual temperature T~front~ is >10℃; ② Undeoxidized steel: Add Al / Si deoxidation first before heating.

[0030] ΔT ~ net ~ = 1605 - 1585 = 20℃ → Oxygen blowing rate Q = 20 × 10 = 200 Nm 3 The circulating gas flow rate was 1200 NL / min, the vacuum degree was 4.5 kPa, and the final temperature of the molten steel was 1608℃.

[0031] Step 6: Pure degassing*

[0032] Circulation gas 2000 NL / min, vacuum 0.08 kPa, for 8 min, end composition: [C]=135 ppm, [O]=12 ppm, [Mn]=0.35%, hit target.

[0033] A method for applying an RH refining system for ultra-low carbon steel, comprising the following steps:

[0034] Pre-inspection of equipment: confirm the accuracy of temperature measurement and oxygen determination equipment, 1B pump start-up time ≤4 minutes, maximum vacuum ≤0.10 kPa, immersion tube aperture = 600 mm; washing tank operation, use 2 heats of low-carbon aluminum killed steel to clean the vacuum tank before smelting, and remove hot elbow pipe cold steel; ladle management, cast low-carbon aluminum killed steel in the first 2 ladles, and ensure that there is no residual steel or slag at the ladle opening / ladle bottom;

[0035] Accurate control of alloying: early decarburization: add low-carbon ferromanganese (control [Mn] ≤0.20%) and phosphorus-sulfur adjusting agent; deoxidation constraint: strictly prohibit the addition of aluminum during decarburization; after adding aluminum for deoxidation at the end of decarburization, circulate for 2 minutes, and then add other alloys or ≤800 kg of coolant; aluminum compensation calculation: the aluminum content in FeTi needs to be taken into account when adding aluminum;

[0036] The method for applying the RH refining system further comprises: ultra-low carbon aluminum-silicon killed steel ([C] target ≤180 ppm);

[0037] Step 1: top lance decision

[0038] Open the MFB top lance gas valve (gas flow 30-50 m / h), after igniting the gas, gradually adjust the gas opening degree to a gas flow of 100-200 m, adjust the oxygen flow to 100-150 m, and lower the lance to the indoor roasting position below the blowing point for roasting;

[0039] Wherein, the initial state: [O]=550 ppm, [C]=280 ppm, T=1590℃ (target T~R~ =1605℃), check the decision table: [O] high, [C] low, T low → perform natural decarburization + top lance heating;

[0040] Step 2: natural decarburization

[0041] Three-way circulation pipe circulation gas 2000 NL / min, vacuum 0.25 kPa, decarburization for 15 min → [C]=170 ppm;

[0042] Step 3: deoxidation before heating

[0043] Add Fe-Si pre-deoxidation to prevent over-oxidation, ΔT~net~=1610-1590=20℃ → oxygen blowing amount Q=200 Nm 3, according to G=0.75*Q, the aluminum-silicon is compensated (150 kg of Al-Si alloy is added), and the silicon is compensated according to the burning loss table: [Si]=0.18%→burning loss rate 0.015%→30 kg of silicon is compensated, the end point [C]=175ppm, T=1607℃, and [Si]=0.22% meets the standard.

[0044] The application method of the RH smelting system of the ultra-low carbon steel has the following advantages: the carbon content control precision is ± 15ppm (originally ± 50ppm), the manganese loss in the heating process is reduced by 35%, the [N] in the steel is less than or equal to 25ppm, and the [O] is less than or equal to 15ppm.

[0045] The application method of the RH smelting system of the ultra-low carbon steel is suitable for the pure steel production process for smelting control of the ultra-low carbon steel ([C]<200ppm), control of the gas inclusions ([N], [O]) in the steel and prevention of carbon increase and nitrogen absorption.

[0046] Compared with the prior art, the application has the following advantages:

[0047] The application is suitable for the pure steel production process for control of the gas inclusions ([N], [O]) in the steel and prevention of carbon increase and nitrogen absorption.

[0048] In the early decarburization stage, low-carbon manganese iron (controlling [Mn]≤0.20%) and phosphorus sulfur adjusting agents are added, deoxidation is constrained, and aluminum is strictly prohibited during the decarburization process; after aluminum deoxidation at the end of decarburization, circulation is performed for 2 minutes, other alloys or ≤800 kg of cooling agents are added, aluminum compensation calculation is performed, and the aluminum content in FeTi needs to be taken into account when aluminum is added.

[0049] Through the device and the method, the carbon content control precision is ± 15ppm (originally ± 50ppm), the manganese loss in the heating process is reduced by 35%, the [N] in the steel is less than or equal to 25ppm, and the [O] is less than or equal to 15ppm.

[0050] 50ppm), the manganese loss in the heating process is reduced by 35%, the [N] in the steel is less than or equal to 25ppm, and the [O] is less than or equal to 15ppm, and the service life of the vacuum tank refractory is prolonged by 30%. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a schematic diagram of the overall connection of the application;

[0052] Figure 2 is a schematic diagram of the series connection of the condensers of the application;

[0053] Figure 3 is a schematic diagram of the cross section of the condenser of the application. DETAILED DESCRIPTION

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0055] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0056] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0057] like Figures 1-3 As shown, an RH smelting system for ultra-low carbon steel includes a ladle furnace 1 and a vacuum tank 2 connected in sequence. The vacuum tank 2 is connected to a vacuum pipe 3, and the outlet end of the vacuum pipe 3 is connected to a pretreatment device 4. The waste gas treated by the pretreatment device 4 is discharged externally.

[0058] The vacuum tank 2 is located above the ladle furnace 1. The vacuum tank 2 is equipped with an ascending pipe 5 and a descending pipe 6. One end of the ascending pipe 5 and one end of the descending pipe 5 extend into the ladle furnace 1, and the other end is connected to the vacuum chamber of the vacuum tank 2.

[0059] A three-way circulation pipe 7 is fixedly connected to the position of the riser pipe 5, and a vacuum sealing cavity 8 is provided at the position of the downcomer pipe 6, with the vacuum sealing cavity 8 located on the periphery of the downcomer pipe 6.

[0060] To facilitate the adsorption of slag at the bottom during use, the riser pipe 5 and the downcomer pipe 6 are arranged in an asymmetrical structure, wherein the length of the riser pipe 5 is greater than the length of the downcomer pipe 6.

[0061] In order to facilitate the isolation of air flow by setting up a vacuum sealing cavity 8 during use, the vacuum sealing cavity 8 and the downcomer 5 are integrally formed to form a vacuum channel between the vacuum sealing cavity 8 and the downcomer 5;

[0062] A spaced support block is provided between the vacuum sealing cavity and the downcomer 5, and the support block is located above the molten steel.

[0063] To enhance durability during use, the riser 5, vacuum sealing cavity, and downcomer 6 are constructed of non-fired magnesia spinel bricks, and the support blocks, also made of non-fired magnesia spinel bricks, are evenly distributed around the circumference of the downcomer 6. The riser 5 and downcomer 6 have different inner diameters, with the inner diameter of the downcomer 6 being larger than that of the riser 5.

[0064] In order to facilitate the cooling of exhaust gas during use and to adsorb the trace dust contained in the exhaust gas by water, the pretreatment device 4 includes a gas cooler 9 and a condenser 10 connected in series, and three condensers 10 are provided.

[0065] Gas cooler 9 is a prior art disclosure. The gas cooler is a ventilation tank with an outer wall composed of cooling water pipes. When the exhaust gas passes through the tank, the flow rate drops sharply. Dust is deposited in the ash discharge pipe at the bottom of the tank under the action of gravity, while the cleaner gas exchanges heat with the water-cooled pipe wall, thereby cooling the exhaust gas.

[0066] At least two stages of steam jet pumps are connected in series with the steam jet pump installed on the adjacent condenser 10 at the connection position between the vacuum pipe 3 and the gas cooler 9.

[0067] A steam jet pump is installed on the adjacent condenser 10. Exhaust gas and steam enter from the bottom of the tank and then exit from the top. During the rising process, the gas comes into full contact with the water curtain sprayed from the water spray nozzle, which cools the exhaust gas. The trace dust contained in the exhaust gas is adsorbed by the water, while the steam is cooled and turned into water before being discharged.

[0068] The condenser 10 consists of a ventilated tank and a spray layer distributed in the upper and middle parts of the tank. The spray layer includes several spray pipes arranged at intervals, and nozzles are provided on the spray pipes. The spray layer is connected to an external pipeline and sprays spray liquid by pumping.

[0069] The top of the vacuum tank 2 is provided with a top gun 11, which is an MFB top gun;

[0070] The MFB top gun flow rate is ≤1800 Nm. 3 / h, vacuum degree <0.27kPa.

[0071] An application method for an RH smelting system for ultra-low carbon steel includes the following steps:

[0072] Equipment pre-inspection: Confirm the accuracy of the temperature and oxygen determination equipment, the start-up time of pump 1B ≤ 4 minutes, the maximum vacuum degree ≤ 0.10 kPa, and the immersion tube orifice diameter = 600 mm; Cleaning operation: Before smelting, clean the vacuum tank with two heats of low-carbon aluminum killed steel to remove cold steel from the hot bending tube; Ladle management: Cast low-carbon aluminum killed steel in the first two ladles to ensure that there is no residual steel residue at the ladle mouth / bottom;

[0073] Precise control of alloying: Early stage of decarburization: add low-carbon ferromanganese (control [Mn] ≤ 0.20%) and phosphorus-sulfur adjuster; Deoxidation constraint: aluminum is strictly prohibited during decarburization; after decarburization, add aluminum and circulate for 2 minutes before adding other alloys or ≤ 800 kg of coolant; Aluminum compensation calculation: the aluminum content in FeTi must be taken into account when adding aluminum;

[0074] The application methods of the RH smelting system include: smelting of ultra-low carbon aluminum-killed steel ([C] target ≤150ppm)

[0075] Step 1: Preprocessing

[0076] The tank was cleaned with two furnaces of SPHC steel (low carbon aluminum killed) to remove the cold steel from the vacuum tank. The start-up time of pump 1B was confirmed to be 3.8 minutes, the diameter of the impregnation tube was 602 mm, and the temperature measuring gun error was ±2℃.

[0077] Step 2: Top Gun Decision

[0078] Open the MFB top gun gas valve (gas flow rate 30-50 m³ / h), ignite the gas, and gradually adjust the gas opening to a gas flow rate of 100-200 m³ / h. Adjust the oxygen flow rate to 100-150 m³ / h. Place the gun below the indoor baking position below the waiting point for blowing.

[0079] The initial state is: [O] = 380ppm, [C] = 350ppm, T = 1585℃ (target T~R~ = 1600℃). [O] low, [C] high, T low → execute top gun decarburization + heating.

[0080] Step 3: Forced decarbonization

[0081] A three-way circulation pipe is fixedly connected to the riser pipe, allowing 1500 NL / min of circulation gas to be introduced, and 1750 Nm of oxygen is blown in by the MFB top lance. 3 / h, decarburization complete: [C] = 120ppm, vacuum degree 18kPa;

[0082] Step 4: Deoxidation and alloying

[0083] In step 3 above, after a 2-minute delay, aluminum is added for deoxidation. The aluminum replenishment is calculated according to the formula G = 1.0 × Q (Q = 15 Nm). 3→Add 15kg of aluminum), continuously circulate for 2 minutes, then add electrolytic manganese to compensate for manganese loss (oxygen blowing rate 200Nm). 3 →Manganese loss 0.016% →Replenish manganese 120kg);

[0084] Step 5: Chemical heating

[0085] Heating trigger conditions: ① Deoxidized steel: Start when the difference between the target temperature T~R~ and the actual temperature T~front~ is >10℃; ② Undeoxidized steel: Add Al / Si deoxidation first before heating.

[0086] ΔT ~ net ~ = 1605 - 1585 = 20℃ → Oxygen blowing rate Q = 20 × 10 = 200 Nm 3 The circulating gas flow rate was 1200 NL / min, the vacuum degree was 4.5 kPa, and the final temperature of the molten steel was 1608℃.

[0087] Step 6: Pure degassing

[0088] The circulating gas flow rate was 2000 NL / min, the vacuum was 0.08 kPa, and the duration was 8 min. The final composition was: [C] = 135 ppm, [O] = 12 ppm, [Mn] = 0.35%, and the target was hit.

[0089] Element burn-off compensation table

[0090]

[0091] Full-process timing control (RH-E mode)

[0092]

[0093]

[0094] Aluminum consumption calculation model:

[0095] Steel grade Aluminium consumption formula Low carbon aluminium killed steel G = 1.0 x Q Medium-low carbon aluminium-silicon killed steel G = (0.7-0.8) x Q High carbon aluminium-silicon killed steel G = 0.6 x Q

[0096] An application method for an RH smelting system for ultra-low carbon steel includes the following steps:

[0097] Equipment pre-inspection: Confirm the accuracy of the temperature and oxygen determination equipment, the start-up time of pump 1B ≤ 4 minutes, the maximum vacuum degree ≤ 0.10 kPa, and the immersion tube orifice diameter = 600 mm; Cleaning operation: Before smelting, clean the vacuum tank with two heats of low-carbon aluminum killed steel to remove cold steel from the hot bending tube; Ladle management: Cast low-carbon aluminum killed steel in the first two ladles to ensure that there is no residual steel residue at the ladle mouth / bottom;

[0098] Precise control of alloying: Early stage of decarburization: add low-carbon ferromanganese (control [Mn] ≤ 0.20%) and phosphorus-sulfur adjuster; Deoxidation constraint: aluminum is strictly prohibited during decarburization; after decarburization, add aluminum and circulate for 2 minutes before adding other alloys or ≤ 800 kg of coolant; Aluminum compensation calculation: the aluminum content in FeTi must be taken into account when adding aluminum;

[0099] The application methods of RH smelting systems also include: ultra-low carbon aluminum-silicon killed steel ([C] target ≤180ppm);

[0100] Step 1: Decision-making with the gun on the ground

[0101] Open the MFB top gun gas valve (gas flow rate 30-50 m³ / h), ignite the gas, and gradually adjust the gas opening to a gas flow rate of 100-200 m³ / h. Adjust the oxygen flow rate to 100-150 m³ / h. Place the gun below the indoor baking position below the waiting point for blowing.

[0102] The initial state is: [O] = 550ppm, [C] = 280ppm, T = 1590℃ (target T~R~ = 1605℃). According to the decision table: [O] high, [C] low, T low → execute natural decarbonization + top gun heating.

[0103] Step 2: Natural decarbonization

[0104] Three-way circulation pipe, circulating gas 2000NL / min, vacuum degree 0.25kPa, decarburization 15min → [C]=170ppm;

[0105] Step 3: Deoxygenate first, then raise the temperature

[0106] Fe-Si pre-deoxidation is added to prevent peroxidation; ΔT ~ net ~ = 1610 - 1590 = 20℃ → oxygen blowing rate Q = 200 Nm 3 Add aluminum and silicon according to G = 0.75 × Q (add 150 kg of Al-Si alloy), and add silicon according to the burn-off table: [Si] = 0.18% → burn-off rate 0.015% → add 30 kg of silicon, the endpoint [C] = 175 ppm, T = 1607℃, [Si] = 0.22% meets the standard.

[0107] Element burn-off compensation table

[0108]

[0109] Full-process timing control (RH-E mode)

[0110]

[0111]

[0112] Aluminum consumption calculation model:

[0113] Steel grade Aluminium consumption formula Low carbon aluminium killed steel G = 1.0 x Q Medium-low carbon aluminium-silicon killed steel G = (0.7-0.8) x Q High carbon aluminium-silicon killed steel G = 0.6 x Q

[0114] An application method for an RH smelting system for ultra-low carbon steel, with carbon content control accuracy of ±15ppm (original ±50ppm), manganese loss during heating process reduced by 35%, and [N] ≤25ppm and [O] ≤15ppm in steel.

[0115] The application method of an RH smelting system for ultra-low carbon steel is applicable to the production process of pure steel that controls gas inclusions ([N], [O]) in ultra-low carbon steel ([C] < 200ppm) and prevents carbon increase and nitrogen absorption.

[0116] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0117] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An RH smelting system for ultra-low carbon steel, characterized in that: It includes a ladle furnace (1) and a vacuum tank (2) connected in sequence. The vacuum tank (2) is connected to a vacuum pipe (3). The outlet end of the vacuum pipe (3) is connected to a pretreatment device (4). The waste gas treated by the pretreatment device (4) is discharged outside. The vacuum tank (2) is located above the ladle furnace (1). The vacuum tank (2) is equipped with an ascending pipe (5) and a descending pipe (6). One end of the ascending pipe (5) and one end of the descending pipe (5) extend into the ladle furnace (1), and the other end is connected to the vacuum chamber of the vacuum tank (2). A three-way circulation pipe (7) is fixedly connected to the position of the riser pipe (5), and a vacuum sealing cavity (8) is provided at the position of the downcomer pipe (6). The vacuum sealing cavity (8) is located on the periphery of the downcomer pipe (6).

2. The RH smelting system for ultra-low carbon steel according to claim 1, characterized in that: The riser (5) and the faller (6) are arranged in an asymmetrical structure, wherein the length of the riser (5) is greater than the length of the faller (6).

3. The RH smelting system for ultra-low carbon steel according to claim 2, characterized in that: The vacuum sealing cavity (8) and the downcomer (5) are integrally formed to form a vacuum channel between the vacuum sealing cavity (8) and the downcomer (5); A spaced support block is provided between the vacuum sealing cavity and the downcomer (5), and the support block is located above the molten steel.

4. The RH smelting system for ultra-low carbon steel according to claim 2, characterized in that: The riser (5), vacuum sealing cavity and the fallr (6) are made of non-fired magnesia spinel bricks, and the support blocks are made of non-fired magnesia spinel bricks and are evenly distributed around the circumference of the fallr (6).

5. The RH smelting system for ultra-low carbon steel according to claim 4, characterized in that: The pretreatment device (4) includes a gas cooler (9) and a condenser (10) connected in series, and three condensers (10) are provided; The condenser (10) consists of a ventilated tank and a spray layer distributed in the upper and middle parts of the tank. The spray layer includes several spray pipes arranged at intervals, and nozzles are provided on the spray pipes. The spray layer is connected to an external pipeline and sprays spray liquid by pumping.

6. The RH smelting system for ultra-low carbon steel according to claim 3, characterized in that: The top of the vacuum tank (2) is provided with a top gun (11), and the top gun (11) is an MFB top gun; The MFB top gun flow rate is ≤1800 Nm. 3 / h, vacuum degree <0.27kPa.

7. An application method of the RH smelting system for ultra-low carbon steel according to claim 6, characterized in that: Includes the following steps: Equipment pre-inspection: Confirm the accuracy of the temperature and oxygen determination equipment, the start-up time of pump 1B ≤ 4 minutes, the maximum vacuum degree ≤ 0.10 kPa, and the immersion tube orifice diameter = 600 mm; Cleaning operation: Before smelting, clean the vacuum tank with two heats of low-carbon aluminum killed steel to remove cold steel from the hot bending tube; Ladle management: Cast low-carbon aluminum killed steel in the first two ladles to ensure that there is no residual steel residue at the ladle mouth / bottom; Precise control of alloying: Early stage of decarburization: add low-carbon ferromanganese (control [Mn] ≤ 0.20%) and phosphorus-sulfur adjuster; Deoxidation constraint: aluminum is strictly prohibited during decarburization; after decarburization, add aluminum and circulate for 2 minutes before adding other alloys or ≤ 800 kg of coolant; Aluminum compensation calculation: the aluminum content in FeTi must be taken into account when adding aluminum; The application methods of the RH smelting system include: smelting of ultra-low carbon aluminum-killed steel ([C] target ≤150ppm) Step 1: Preprocessing The tank was cleaned with two furnaces of SPHC steel (low carbon aluminum killed) to remove the cold steel from the vacuum tank. The start-up time of pump 1B was confirmed to be 3.8 minutes, the diameter of the impregnation tube was 602 mm, and the temperature measuring gun error was ±2℃. Step 2: Top Gun Decision Open the MFB top gun gas valve (gas flow rate 30-50 m³ / h), ignite the gas, and gradually adjust the gas opening to a gas flow rate of 100-200 m³ / h. Adjust the oxygen flow rate to 100-150 m³ / h. Place the gun below the indoor baking position below the waiting point for blowing. Initial state: [O] = 380ppm, [C] = 350ppm, T = 1585℃ (target T~R~ = 1600℃) [O] low, [C] high, T low → execute top gun decarburization + heating; Step 3: Forced decarbonization A three-way circulation pipe is fixedly connected to the riser pipe, allowing 1500 NL / min of circulation gas to be introduced, and 1750 Nm of oxygen is blown in by the MFB top lance. 3 / h, decarburization complete: [C] = 120ppm, vacuum degree 18kPa; Step 4: Deoxidation and alloying In step 3 above, after a 2-minute delay, aluminum is added for deoxidation. The aluminum replenishment is calculated according to the formula G = 1.0 × Q (Q = 15 Nm). 3 →Add 15kg of aluminum), continuously circulate for 2 minutes, then add electrolytic manganese to compensate for manganese loss (oxygen blowing rate 200Nm). 3 →Manganese loss 0.016% →Replenish manganese 120kg); Step 5: Chemical heating Heating trigger conditions: ① Deoxidized steel: Start when the difference between the target temperature T~R~ and the actual temperature T~front~ is >10℃; ② Undeoxidized steel: Add Al / Si deoxidation first before heating. ΔT ~ net ~ = 1605 - 1585 = 20℃ → Oxygen blowing rate Q = 20 × 10 = 200 Nm 3 The circulating gas flow rate was 1200 NL / min, the vacuum degree was 4.5 kPa, and the final temperature of the molten steel was 1608℃. Step 6: Pure degassing* The circulating gas flow rate was 2000 NL / min, the vacuum was 0.08 kPa, and the duration was 8 min. The final composition was: [C] = 135 ppm, [O] = 12 ppm, [Mn] = 0.35%, and the target was hit.

8. An application method of the RH smelting system for ultra-low carbon steel according to claim 6, characterized in that: Includes the following steps: Equipment pre-inspection: Confirm the accuracy of the temperature and oxygen determination equipment, the start-up time of pump 1B ≤ 4 minutes, the maximum vacuum degree ≤ 0.10 kPa, and the immersion tube orifice diameter = 600 mm; Cleaning operation: Before smelting, clean the vacuum tank with two heats of low-carbon aluminum killed steel to remove cold steel from the hot bending tube; Ladle management: Cast low-carbon aluminum killed steel in the first two ladles to ensure that there is no residual steel residue at the ladle mouth / bottom; Precise control of alloying: Early stage of decarburization: add low-carbon ferromanganese (control [Mn] ≤ 0.20%) and phosphorus-sulfur adjuster; Deoxidation constraint: aluminum is strictly prohibited during decarburization; after decarburization, add aluminum and circulate for 2 minutes before adding other alloys or ≤ 800 kg of coolant; Aluminum compensation calculation: the aluminum content in FeTi must be taken into account when adding aluminum; The application methods of RH smelting systems also include: ultra-low carbon aluminum-silicon killed steel ([C] target ≤180ppm); Step 1: Decision-making with the gun on the ground Open the MFB top gun gas valve (gas flow rate 30-50 m³ / h), ignite the gas, and gradually adjust the gas opening to a gas flow rate of 100-200 m³ / h. Adjust the oxygen flow rate to 100-150 m³ / h. Place the gun below the indoor baking position below the waiting point for blowing. The initial state is: [O] = 550ppm, [C] = 280ppm, T = 1590℃ (target T~R~ = 1605℃). According to the decision table: [O] high, [C] low, T low → execute natural decarbonization + top gun heating. Step 2: Natural decarbonization Three-way circulation pipe, circulating gas 2000NL / min, vacuum degree 0.25kPa, decarburization 15min → [C]=170ppm; Step 3: Deoxygenate first, then raise the temperature Fe-Si pre-deoxidation is added to prevent peroxidation; ΔT ~ net ~ = 1610 - 1590 = 20℃ → oxygen blowing rate Q = 200 Nm 3 Add aluminum and silicon according to G = 0.75 × Q (add 150 kg of Al-Si alloy), and add silicon according to the burn-off table: [Si] = 0.18% → burn-off rate 0.015% → add 30 kg of silicon, the endpoint [C] = 175 ppm, T = 1607℃, [Si] = 0.22% meets the standard.

9. An application method of the RH smelting system for ultra-low carbon steel according to claim 8, characterized in that: Carbon content control accuracy: ±15ppm (original ±50ppm), manganese loss during heating process is reduced by 35%, [N] in steel ≤25ppm, [O] ≤15ppm.

10. An application method of the RH smelting system for ultra-low carbon steel according to claim 8 is applicable to the production process of pure steel by controlling gas inclusions ([N], [O]) in ultra-low carbon steel ([C] < 200ppm) and preventing carbon increase and nitrogen absorption.

Images