Direct-current electric arc furnace smelting method capable of effectively controlling nitrogen

Abstract

The invention discloses a direct-current electric arc furnace smelting method capable of effectively controlling nitrogen. According to the direct-current electric arc furnace, a side argon blowing device is arranged on the furnace wall of a molten pool; the smelting comprises the processes of steel scrap burdening, blanking and power transmission, slagging and dephosphorizing, and oxygen blowing and carbon catching; and after oxygen blowing and carbon catching operation, low-power power transmission is carried out, a side argon blowing device is started to carry out argon blowing stirring for 1-2 minutes, and tapping is carried out after the tapping temperature requirement is met. According to the method, the nitrogen content of the molten steel is reduced by 5-15 ppm when the electric arc furnace is used for tapping compared with the technology without side argon blowing, and the initial cleanliness of the molten steel is obviously improved; and the nitrogen content is reduced to 65-75 ppm from 80-90 ppm under the original process condition, and the FeO% content of the final slag is further inhibited. According to the method, the side argon blowing device is additionally arranged for side blowing, and the stirring effect of the bottom electrode anode is combined, so that the stirring dead zone area of a molten pool is improved, the oxidability of end slag is reduced, and the original nitrogen content before tapping of molten steel is improved.

Description

Technical Field

[0001] This invention relates to the field of electric arc furnace steelmaking technology, and in particular to a DC electric arc furnace smelting method for steel grades that require effective control of the nitrogen content at the end of the electric arc furnace process. Background Technology

[0002] Domestic top-and-bottom blowing converter steelmaking possesses a complete bottom-blowing argon process. When producing ultra-low carbon automotive steel sheets requiring nitrogen control, argon is blown throughout the blowing process, or nitrogen-argon switching is adjusted using proportional valves as needed, resulting in very low final nitrogen levels, reaching less than 30 ppm. Both AC and DC electric arc furnaces, besides the inherent process factors (scrap steel, electric arc) causing high nitrogen levels in the molten steel, also have inferior nitrogen control capabilities compared to converter smelting processes. Currently, domestic three-phase AC electric arc furnaces already possess bottom-blowing technology, allowing for nitrogen-argon switching operations similar to converters to optimize economic and technical indicators. However, single-phase electrode DC electric arc furnaces, due to the use of bottom electrode anodes, do not have bottom-blowing systems installed because of safety risks associated with their installation. Instead, it utilizes the electromagnetic effect generated by the current between the bottom anode and the electrode of the electric arc furnace to achieve a uniform molten pool. Compared with converter steelmaking, this operating mode has obvious shortcomings in controlling the nitrogen content at the end of the molten steel. Because the stirring radius of the bottom anode current magnetic field is small and the stirring direction of the molten steel does not change, there is a "dead zone" in the molten pool area outside the stirring radius of the bottom anode current magnetic field.

[0003] For example, the June 2000 issue of *Special Steel*, titled "Electric Arc Furnace Bottom-Blowing Argon Stirring Process," developed an industrial trial using a bottom-blowing argon stirring process on an 80-ton furnace. The bottom-blowing system consisted of permeable bricks, a gas source, and flow and pressure regulators. Three permeable bricks were installed in the cold spot area between the three-phase electrodes at the bottom of the electric furnace, indicating the trial was conducted under three-phase electrode conditions. The 2011 issue of *Industrial Heating*, titled "Production Process and Metallurgical Effects of Electric Furnace Bottom-Blowing System," developed a bottom-blowing nitrogen-argon switching process and studied its coordination with the furnace wall lance, reducing dead zones and optimizing the technical and economic indicators of the electric arc furnace. This process is suitable for AC electric arc furnaces used for molten iron mixing. Patent application CN202410668444.6, "A Method for Producing Ultra-Low Carbon Steel via Electric Furnace Process," while emphasizing the synergistic reduction of oxygen and nitrogen content in the electric furnace system, more importantly emphasizes the deep denitrification effect after reaching the RH station, making it particularly suitable for the production of ultra-low carbon steel. Patent application CN202410780242.0 describes a method for producing nitrogen-containing low-carbon aluminum-killed molten steel, which focuses on converter systems and includes a bottom-blowing system for argon blowing control.

[0004] Therefore, there are few means to control nitrogen content in DC electric arc furnaces. Generally, it is achieved by creating foamed slag to submerge the arc and controlling the raw material structure. The increase in nitrogen content in molten steel is mainly controlled by refining and denitrification after the steel is tapped from the electric arc furnace and by protective technology measures in each stage. Further research is needed on how to reduce the initial nitrogen content at the end of the electric arc furnace. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an effective method for controlling nitrogen in the final nitrogen smelting process using a DC electric arc furnace.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: the DC electric arc furnace is equipped with a side-blowing argon device on the furnace wall of the molten pool; the smelting includes scrap steel batching, feeding and power supply, slag formation and dephosphorization, and oxygen blowing and carbon removal processes; after the oxygen blowing and carbon removal operation, low-power power supply is supplied, and the side-blowing argon device is turned on for argon blowing and stirring, and steel is tapped after the tapping temperature requirements are met.

[0007] Furthermore, the side-blowing argon device performs argon blowing and stirring for 1 to 2 minutes.

[0008] Furthermore, the low-power power supply has a voltage of 500–600V and a current of 85–95kA.

[0009] Furthermore, the side-blowing argon device is provided with two units, each with an argon blowing and stirring flow rate of 20–30 Nm³. 3 / h.

[0010] Furthermore, in the scrap steel batching process, the proportions are as follows: 15-20% high-quality pig iron, 10-15% self-produced crushed material, 15-20% small scrap steel, 25-35% medium scrap steel, and 10-20% high-quality heavy scrap.

[0011] Furthermore, the feeding and power supply process involves two loading stages. The scrap steel in the first stage is preheated to a surface temperature of 600–800°C, and the loading amount is 55–60% of the total loading amount. After the first stage is energized and melted, the second stage is fed in, and the scrap steel in the second stage is preheated to a surface temperature of 500–600°C.

[0012] Furthermore, in the material feeding and power supply process: after feeding, the power supply voltage is 900-1000V and the current is 85-95KA; after reaching the flat molten pool state, the power supply voltage is 600-700V and the current is 85-95KA.

[0013] Furthermore, the slag-making and dephosphorization process involves controlling the molten pool temperature to <1530℃, adding 15-20 kg / t of lime and 5-10 kg / t of lightly calcined dolomite, and performing foam-making slag dephosphorization and slag flow operations.

[0014] Furthermore, in the oxygen blowing and carbon extraction process: the carbon powder injection rate is 10-20 kg / t, and deoxidation and carbon extraction operations are performed simultaneously, with an oxygen blowing rate of 30-40 Nm³. 3 / h.

[0015] The beneficial effects of adopting the above technical solution are as follows: This invention utilizes the existing furnace wall-mounted oxygen lance jet and the existing needle-type bottom anode electromagnetic stirring area of ​​the DC electric arc furnace for numerical modeling research, and adds two side-blowing argon devices to the furnace wall of the molten pool; at the end of the slag formation, dephosphorization, and oxygen blowing carbon removal operations, the argon blowing cycle is increased by 1-2 minutes, utilizing the argon blowing operation combined with the electromagnetic stirring function of the current of the furnace bottom anode, that is, the operation of the DC electric arc furnace smelting endpoint nitrogen control mode is achieved through side-blowing argon + rotating magnetic field current stirring. This invention reduces the nitrogen content of molten steel by 5-15 ppm at the time of tapping from the electric arc furnace compared to the process without side-blowing argon technology, and significantly improves the initial cleanliness of the molten steel; the nitrogen content decreases from 80-90 ppm under the original process conditions to 65-75 ppm, and the FeO% content of the endpoint slag is further suppressed.

[0016] This invention, under the condition that the bottom anode structure of the furnace bottom cannot be changed to add a bottom blowing stirring system, innovatively proposes to use the existing side blowing system to add a side blowing argon device and combine it with the stirring effect of the bottom electrode anode to improve the area of ​​the dead zone of the molten pool, reduce the oxidizing properties of the final slag, and improve the original nitrogen content of the molten steel before tapping. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments.

[0018] The DC electric arc furnace uses bottom-electrode electromagnetic stirring, but there is a stirring dead zone in the molten pool outside the bottom-electrode electromagnetic stirring radius area where stirring cannot be completed. This DC electric arc furnace smelting method with effective nitrogen control adds a side-blowing argon device to the original oxygen lance on the furnace wall of the DC electric arc furnace. The argon lance of the side-blowing argon device can blow argon gas laterally into the stirring dead zone of the molten pool, which, together with the bottom-electrode electromagnetic stirring, reduces the area of ​​the stirring dead zone in the molten pool. It is best to add two side-blowing argon devices, located in the furnace door area and the eccentric furnace bottom area respectively. The blowing angle of the two side-blowing argon devices is maintained at an angle of 40° to 50°, preferably 45°, with the angle between the blowing angle of the two side-blowing argon devices and the plane of the molten steel in the molten pool. The blowing stirring direction of the side-blowing argon device is consistent with the stirring direction of the bottom anode electromagnetic stirring.

[0019] This effective nitrogen-controlled DC electric arc furnace smelting method can be implemented using either all scrap steel or scrap steel + hot-mixed molten iron. It is best to use all scrap steel, including scrap steel batching, feeding and power supply, slag formation and dephosphorization, oxygen blowing and carbon removal, and side-blowing stirring processes. The process is described below: (1) Scrap steel batching: The weight composition of scrap steel batching is as follows: 15-20% high-quality pig iron, 10-15% self-produced crushed scrap, 15-20% small scrap steel, 25-35% medium scrap steel, and 10-20% high-quality heavy scrap. Among them, the high-quality pig iron conforms to YB / T5296-2011 pig iron for steelmaking, the small scrap steel conforms to GB4223 scrap steel, small scrap steel Class 1 203A, the medium scrap steel conforms to GB4223 scrap steel, medium scrap steel 202A, and the high-quality heavy scrap steel conforms to GB4223 scrap steel, heavy scrap steel A1 grade. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding; 10% of the total amount of small scrap steel is used for bottom lining; the remaining materials are evenly distributed around the perimeter of the basket.

[0020] (2) Material feeding and power supply: Two-stage loading is adopted. The amount of material loaded in the first stage is 55-60% of the total loading. It is first preheated in the finger system to ensure that the flue gas preheating time is >30 minutes and the surface temperature is 600-800℃ before being loaded into the furnace. After the first stage of material is loaded, power supply is started. High voltage and high current are used for arc initiation, "well penetration" and waste melting operations. The voltage is 900-1000V and the current is 85-95KA. The combustion gun and oxygen gun are turned on to assist in cutting. At the same time, 10-15kg / t of lime is added. The power supply cycle is 6-10 minutes to melt the first stage of material.

[0021] The secondary material loading amount is 40-45% of the remaining total loading amount; during the power supply of the primary material, the secondary material basket is first preheated with scrap steel at the vertical shaft position, preheated to a surface temperature of 500-600℃; after the primary material is energized and melted, the secondary material is put into the furnace.

[0022] After the material is fed, high voltage and high current are still used in the early stage, with voltage of 900-1000V and current of 85-95KA; after reaching the flat molten pool stage, in order to control the arc length, medium voltage and high current are used for the molten waste operation, with voltage of 600-700V and current of 85-95KA, and a cycle of 10-20 minutes.

[0023] (3) Slag-making and dephosphorization process: shut off the combustion gun, control the temperature of the molten pool to <1530℃ during dephosphorization, add lime 15-20kg / t and lightly calcined dolomite 5-10kg / t in batches at the same time, preferably in 2-3 batches, and start the foam slag dephosphorization and slag flow operation gradually.

[0024] (4) Oxygen blowing and carbon extraction process: The carbon powder injection rate is controlled at 10-20 kg / t throughout the process, while deoxidation and carbon extraction are carried out simultaneously, with an oxygen blowing rate of 30-40 Nm. 3 / h, continue to supply power to raise the temperature until it reaches above 1580℃, then take the final sample for testing.

[0025] (5) Side-blowing stirring process: After taking the endpoint sample, power is supplied at low power for 1-2 minutes, with a voltage of 500-600V and a current of 85-95KA. At the same time, the side-blowing argon device is adjusted to perform side-blowing argon stirring for 1-2 minutes, with a side-blowing argon flow rate of 20-30Nm. 3 The steel is tapped at a rate of 1595–1635°C per hour.

[0026] (6) This method is applicable to steel grades with nitrogen control requirements, especially to the smelting of bearing steel, such as GCr15 steel. After adopting the above method, the nitrogen content in the molten steel can be controlled at 65-75 ppm, and the FeO content in the final slag can be controlled at 20-30%.

[0027] Example 1: Taking the smelting of GCr15 steel in a 130-ton nominal capacity electric arc furnace (furnace body holding capacity of 170 tons) as an example, the specific method of effective nitrogen control DC electric arc furnace smelting is as follows: (1) Scrap steel batching: 16% high-quality pig iron, 14% self-produced crushed scrap, 20% small scrap steel, 30% medium scrap steel, and 20% high-quality heavy scrap. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding. 10% of the total amount of small scrap steel is used for bottom lining. The remaining materials are evenly distributed around the perimeter of the basket.

[0028] (2) Charging and Power Supply: After closing the furnace door system, and starting the first charging of this batch after the second charging of the previous batch, preheating is carried out in the finger system for 42 minutes. The preheating surface temperature of the scrap steel is 670℃. The finger system is then opened to complete the first charging, which accounts for 56% of the total charging volume. After the secondary scrap steel basket reaches the vertical shaft position, scrap steel preheating is carried out. During this period, high voltage and high current are used for arc initiation, "shaft penetration", and scrap melting operations. The voltage fluctuation range is 900-1000V and the current fluctuation is 85-95KA. The combustion and oxygen lances are turned on to assist in cutting. A small amount of lime (10kg / t) is added, and the scrap is basically melted in 7 minutes.

[0029] After the primary material is melted and cleared, a finger-opening command is issued to load secondary material, accounting for 45% of the total loading. The surface temperature of the preheated scrap steel is 505℃. During this period, high voltage and high current are still used initially, with voltage fluctuation ranges of 900-1000V and current fluctuation ranges of 85-95KA. After reaching the flat molten pool stage, in order to control the arc length, a medium voltage of 600-700V and a high current of 85-95KA are used to continue the scrap melting operation, with a power supply cycle of 15 minutes.

[0030] (3) Slag formation and dephosphorization: At this time, the ignition gun is turned off, the temperature of the molten pool is controlled, and lime of 19 kg / t and lightly calcined dolomite of 5.7 kg / t are added in batches. The foam slag dephosphorization and slag flow operation is gradually started.

[0031] (4) Oxygen blowing and carbon removal: Gradually increase the carbon powder injection rate by 11 kg / t, while simultaneously performing deoxidation and carbon removal operations, with an oxygen blowing rate of 31.9 Nm. 3 / h, until 1580℃, take a sample of the melt for analysis.

[0032] (5) Side-blowing stirring: After sampling, power is supplied at low power for 1 minute, with a voltage of 500-600V and a current of 85-95KA. Two of the furnace wall guns are then turned on for argon blowing for 1.5 minutes at a flow rate of 25Nm³. 3 / h, take an endpoint sample to analyze C, P, S, determine oxygen, take a gas sample, measure the temperature at 1634℃ and tap the steel.

[0033] Example 2: Taking the smelting of GCr15 steel in a 130-ton nominal capacity electric arc furnace (furnace body holding capacity of 170 tons) as an example, the specific method of this effective nitrogen-controlled DC electric arc furnace smelting is as follows: (1) Scrap steel batching: 20% high-quality pig iron, 10% self-produced crushed scrap, 20% small scrap steel, 30% medium scrap steel, and 20% high-quality heavy scrap. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding. 10% of the total amount of small scrap steel is used for bottom lining. The remaining materials are evenly distributed around the perimeter of the basket.

[0034] (2) Charging and Power Supply: After closing the furnace door system, and starting the first charging of this batch after the second charging of the previous batch, preheating is carried out in the finger system for 42.5 minutes. The preheated surface temperature of the scrap steel is 674℃. The finger system is then opened to complete the first charging, which accounts for 56% of the total charging volume. After the secondary scrap steel basket reaches the vertical shaft position, scrap steel preheating is carried out. During this period, high voltage and high current are used for arc initiation, "shaft penetration", and scrap melting operations. The voltage fluctuation range is 900-1000V and the current fluctuation is 85-95KA. The combustion and oxygen lances are turned on to assist in cutting. 15kg / t of lime is added, and the scrap is basically melted in 7.5 minutes.

[0035] After the primary material is melted and cleared, a finger-opening command is issued to load secondary material, accounting for 44% of the total loading. The surface temperature of the preheated scrap steel is 542℃. During this period, high voltage and high current are still used initially, with voltage fluctuation ranges of 900-1000V and current fluctuation ranges of 85-95KA. After reaching the flat molten pool stage, in order to control the arc length, a medium voltage of 600-700V and a high current of 85-95KA are used to continue the scrap melting operation, with a power supply cycle of 14 minutes.

[0036] (3) Slag formation and dephosphorization: Turn off the ignition gun, control the temperature of the molten pool, add 20 kg / t of lime and 6.5 kg / t of lightly calcined dolomite in batches, and start the foam slag dephosphorization and slag flow operation gradually.

[0037] (4) Oxygen blowing and carbon removal: Gradually increase the carbon powder injection rate by 18 kg / t, while simultaneously performing deoxidation and carbon removal operations, with an oxygen blowing rate of 34.5 Nm³. 3 / h, until 1587℃ is reached, then a sample of the melt is taken for analysis.

[0038] (5) Side-blowing stirring: After sampling, power is supplied at low power for 2 minutes, with a power supply voltage of 500-600V and a current of 85-95KA. Two of the furnace wall guns are turned on to blow argon for 2 minutes at a flow rate of 25Nm. 3 / h, take an endpoint sample to analyze C, P, S, determine oxygen, take a gas sample, measure the temperature at 1627℃ and tap the steel.

[0039] Example 3: Taking the smelting of H13 steel in a 130-ton nominal capacity electric arc furnace (furnace body holding capacity of 170 tons) as an example, the specific method for effective nitrogen control in a DC electric arc furnace smelting is as follows: (1) Scrap steel batching: 15% high-quality pig iron, 12% self-produced crushed scrap, 24% small scrap steel, 35% medium scrap steel, and 14% high-quality heavy scrap. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding. 10% of the total amount of small scrap steel is used for bottom lining. The remaining materials are evenly distributed around the perimeter of the basket.

[0040] (2) Charging and Power Supply: After the furnace door system is closed, the first charge of this charge begins after the second charge of the previous charge is completed. Preheating is performed in the finger system for 32 minutes, with the preheated surface temperature of the scrap steel reaching 550°C. The finger system is then opened to complete the first charge, which accounts for 58% of the total charge. After the secondary scrap steel basket reaches the shaft position, the scrap steel is preheated. During this period, high voltage and high current are used for arc initiation, "shaft penetration," and scrap melting operations. The voltage fluctuation range is 900-1000V, and the current fluctuation is 85-95KA. The combustion and oxygen lances are turned on for auxiliary cutting, and 16kg / t of lime is added. The scrap is basically melted in 7.5 minutes.

[0041] After the primary material is melted and cleared, a finger-opening command is issued to load secondary material, accounting for 42% of the total loading. The surface temperature of the preheated scrap steel is 513℃. During this period, high voltage and high current are still used initially, with voltage fluctuation ranges of 900-1000V and current fluctuation ranges of 85-95KA. After reaching the flat molten pool stage, in order to control the arc length, a medium voltage of 600-700V and a high current of 85-95KA are used to continue the scrap melting operation, with a power supply cycle of 10 minutes.

[0042] (3) Slag formation and dephosphorization: shut off the ignition gun, control the temperature of the molten pool, add lime 16kg / t and lightly calcined dolomite 9kg / t in batches, and start the foam slag dephosphorization and slag flow operation gradually.

[0043] (4) Oxygen blowing and carbon removal: Gradually increase the carbon powder injection rate by 15 kg / t, while simultaneously performing deoxidation and carbon removal operations, with an oxygen blowing rate of 40.5 Nm.3 / h, until 1579℃, take a sample of the melt for analysis.

[0044] (5) Side-blowing stirring: After sampling, power is supplied at low power for 2.0 minutes, with a power supply voltage of 500-600V and a current of 85-95KA. Two of the furnace wall guns are turned on for argon blowing for 1.8 minutes at a flow rate of 20Nm³. 3 / h, take an endpoint sample to analyze C, P, S, determine oxygen, take a gas sample, measure the temperature at 1611℃ and tap the steel.

[0045] Example 4: Taking the smelting of GCr15 steel in a nominal capacity electric arc furnace of 130 tons (furnace body holding capacity of 170 tons) as an example, the specific method of effective nitrogen control DC electric arc furnace smelting is as follows: (1) Scrap steel batching: 18% high-quality pig iron, 12% self-produced crushed scrap, 23% small scrap steel, 34% medium scrap steel, and 13% high-quality heavy scrap. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding. 10% of the total amount of small scrap steel is used for bottom lining. The remaining materials are evenly distributed around the perimeter of the basket.

[0046] (2) Charging and Power Supply: After the furnace door system is closed, the first charge of this charge begins after the second charge of the previous charge is completed. Preheating is performed in the finger system for 36 minutes, with the preheated surface temperature of the scrap steel reaching 590°C. The finger system is then opened to complete the first charge, which accounts for 58% of the total charge. After the secondary scrap steel basket reaches the shaft position, the scrap steel is preheated. During this period, high voltage and high current are used for arc initiation, "shaft penetration," and scrap melting operations. The voltage fluctuation range is 900-1000V, and the current fluctuation range is 85-95KA. The combustion and oxygen lances are turned on for auxiliary cutting, and 15kg / t of lime is added. The scrap is basically melted in 7.5 minutes.

[0047] After the primary material is melted and cleared, a finger-opening command is issued to load secondary material, accounting for 42% of the total loading. The surface temperature of the preheated scrap steel is 548℃. During this period, high voltage and high current are still used initially, with voltage fluctuation ranges of 900-1000V and current fluctuation ranges of 85-95KA. After reaching the flat molten pool stage, in order to control the arc length, a medium voltage of 600-700V and a high current of 85-95KA are used to continue the scrap melting operation, with a power supply cycle of 11 minutes.

[0048] (3) Slag formation and dephosphorization: shut off the ignition gun, control the temperature of the molten pool, add 15 kg / t of lime and 9 kg / t of lightly calcined dolomite in batches, and start the foam slag dephosphorization and slag flow operation gradually.

[0049] (4) Oxygen blowing and carbon removal: Gradually increase the carbon powder injection rate by 15 kg / t, while simultaneously performing deoxidation and carbon removal operations, with an oxygen blowing rate of 39.5 Nm. 3 / h, until 1569℃ is reached, then a sample of the melt is taken for analysis.

[0050] (5) Side-blowing stirring: After sampling, power is supplied at low power for 1.5 minutes, with a voltage of 500-600V and a current of 85-95KA. Two of the furnace wall guns are turned on to blow argon for 1.5 minutes at a flow rate of 20Nm³. 3 / h, take an endpoint sample to analyze C, P, S, determine oxygen, take a gas sample, measure the temperature at 1619℃ and tap the steel.

[0051] Example 5: Taking the smelting of 20CrMnTi steel in a nominal capacity electric arc furnace (furnace body holding capacity of 170 tons) as an example, the specific method of this effective nitrogen-controlled DC electric arc furnace smelting is as follows: (1) Scrap steel batching: 17% high-quality pig iron, 15% self-produced crushed scrap, 23% small scrap steel, 33% medium scrap steel, and 12% high-quality heavy scrap. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding. 10% of the total amount of small scrap steel is used for bottom lining. The remaining materials are evenly distributed around the perimeter of the basket.

[0052] (2) Charging and Power Supply: After closing the furnace door system, and starting the first charging of this batch after the second charging of the previous batch, preheating is carried out in the finger system for 40 minutes. The preheating surface temperature of the scrap steel is 620℃. The finger system is then opened to complete the first charging, which accounts for 60% of the total charging volume. After the secondary scrap steel basket reaches the vertical shaft position, scrap steel preheating is carried out. During this period, high voltage and high current are used for arc initiation, "shaft penetration", and scrap melting operations. The voltage fluctuation range is 900-1000V and the current fluctuation is 85-95KA. The combustion and oxygen lances are turned on to assist in cutting. 20kg / t of lime is added, and the scrap is basically melted in 10 minutes.

[0053] After the primary material is melted and cleared, a finger-opening command is issued to load secondary material, accounting for 40% of the total loading. The surface temperature of the scrap steel is preheated to 500℃. During this period, high voltage and high current are still used initially, with voltage fluctuation ranges of 900-1000V and current fluctuation ranges of 85-95KA. After reaching the flat molten pool stage, in order to control the arc length, a medium voltage of 600-700V and a high current of 85-95KA are used to continue the scrap melting operation, with a power supply cycle of 9 minutes.

[0054] (3) Slag formation and dephosphorization: Turn off the ignition gun, control the temperature of the molten pool, add 20 kg / t of lime and 10 kg / t of lightly calcined dolomite in batches, and start the foam slag dephosphorization and slag flow operation gradually.

[0055] (4) Oxygen blowing and carbon removal: Gradually increase the carbon powder injection rate by 20 kg / t, and simultaneously carry out deoxidation and carbon removal operations, with an oxygen blowing rate of 41.6 Nm. 3 / h, until 1585℃ is reached, then a sample of the melt is taken for analysis.

[0056] (5) Side-blowing stirring: After sampling, power is supplied at low power for 2 minutes, with a voltage of 500-600V and a current of 85-95KA. Two of the furnace wall guns are then turned on for argon blowing for 1.5 minutes at a flow rate of 20Nm³. 3 / h, take an endpoint sample to analyze C, P, S, determine oxygen, take a gas sample, measure the temperature at 1640℃ and tap the steel.

[0057] Example 6: Taking the smelting of GCr15 steel in a nominal capacity electric arc furnace of 130 tons (furnace body holding capacity of 170 tons) as an example, the specific method of effective nitrogen control DC electric arc furnace smelting is as follows: (1) Scrap steel batching: 20% high-quality pig iron, 15% self-produced crushed scrap, 20% small scrap steel, 25% medium scrap steel, and 20% high-quality heavy scrap. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding. 10% of the total amount of small scrap steel is used for bottom lining. The remaining materials are evenly distributed around the perimeter of the basket.

[0058] (2) Charging and Power Supply: After closing the furnace door system, after the second charging of the previous heat is completed, the first charging of this heat begins. Preheating is carried out in the finger system for 43 minutes, and the surface temperature of the scrap steel is 610℃. The finger system is then opened to complete the first charging, which accounts for 56% of the total charging volume. After the secondary scrap steel basket reaches the vertical shaft position, scrap steel preheating is carried out. During this period, high voltage and high current are used for arc initiation, "shaft penetration", and scrap melting operations. The voltage fluctuation range is 900-1000V and the current fluctuation is 85-95KA. The combustion and oxygen guns are turned on to assist in cutting, and 17kg / t of lime is added. The scrap is basically melted in 9 minutes.

[0059] After the primary material is melted and cleared, a finger-opening command is issued to load secondary material, accounting for 44% of the total loading. The surface temperature of the scrap steel is preheated to 500℃. During this period, high voltage and high current are still used initially, with voltage fluctuation ranges of 900-1000V and current fluctuation ranges of 85-95KA. After reaching the flat molten pool stage, in order to control the arc length, a medium voltage of 600-700V and a high current of 85-95KA are used to continue the scrap melting operation, with a power supply cycle of 10 minutes.

[0060] (3) Slag formation and dephosphorization: shut off the ignition gun, control the temperature of the molten pool, add lime 16kg / t and lightly calcined dolomite 8kg / t in batches, and start the foam slag dephosphorization and slag flow operation gradually.

[0061] (4) Oxygen blowing and carbon removal: Gradually increase the carbon powder injection rate to 18 kg / t, while simultaneously performing deoxidation and carbon removal operations, with an oxygen blowing rate of 36.5 Nm³. 3 / h, until 1576℃, take a sample of the melt for analysis.

[0062] (5) Side-blowing stirring: After sampling, power is supplied at low power for 2 minutes, with a voltage of 500-600V and a current of 85-95KA. Two of the furnace wall guns are then turned on for argon blowing for 1.5 minutes at a flow rate of 20Nm³. 3 / h, take an endpoint sample to analyze C, P, S, determine oxygen, take a gas sample, measure the temperature at 1629℃ and tap the steel.

[0063] Example 7: Taking the smelting of GCr15 steel in a 130-ton nominal capacity electric arc furnace (furnace body holding capacity of 170 tons) as an example, the specific method of this effective nitrogen-controlled DC electric arc furnace smelting is as follows: (1) Scrap steel batching: 15% high-quality pig iron, 15% self-produced crushed scrap, 25% small scrap steel, 35% medium scrap steel, and 10% high-quality heavy scrap. The self-produced crushed scrap is evenly distributed in the center of the basket to prevent the electrodes from breaking during feeding. 10% of the total amount of small scrap steel is used for bottom lining. The remaining materials are evenly distributed around the perimeter of the basket.

[0064] (2) Charging and Power Supply: After closing the furnace door system, and starting the first charging of this batch after the second charging of the previous batch, preheating is carried out in the finger system for 43 minutes. The preheating surface temperature of the scrap steel is 630℃. The finger system is then opened to complete the first charging, which accounts for 60% of the total charging volume. After the secondary scrap steel basket reaches the vertical shaft position, scrap steel preheating is carried out. During this period, high voltage and high current are used for arc initiation, "shaft penetration", and scrap melting operations. The voltage fluctuation range is 900-1000V and the current fluctuation is 85-95KA. The combustion and oxygen lances are turned on to assist in cutting. 20kg / t of lime is added, and the scrap is basically melted in 10 minutes.

[0065] After the primary material is melted and cleared, a finger-opening command is issued to load secondary material, accounting for 40% of the total loading. The surface temperature of the scrap steel is preheated to 430℃. During this period, high voltage and high current are still used initially, with voltage fluctuation ranges of 900-1000V and current fluctuation ranges of 85-95KA. After reaching the flat molten pool stage, in order to control the arc length, a medium voltage of 600-700V and a high current of 85-95KA are used to continue the scrap melting operation, with a power supply cycle of 9 minutes.

[0066] (3) Slag formation and dephosphorization: shut off the ignition gun, control the temperature of the molten pool, add lime (19 kg / t) and lightly calcined dolomite (10 kg / t) in batches, and start the frothy slag dephosphorization and slag flow operation.

[0067] (4) Oxygen blowing and carbon removal: Gradually increase the carbon powder injection rate by 20 kg / t, while simultaneously performing deoxidation and carbon removal operations, with an oxygen blowing rate of 38.6 Nm³. 3 / h, until 1575℃ is reached, then a sample of the melt is taken for analysis.

[0068] (5) Side-blowing stirring: After sampling, power is supplied at low power for 2 minutes, with a voltage of 500-600V and a current of 85-95KA. Two of the furnace wall guns are then turned on for argon blowing for 1.5 minutes at a flow rate of 20Nm³. 3 / h, take an endpoint sample to analyze C, P, S, determine oxygen, take a gas sample, measure the temperature at 1631℃ and tap the steel.

[0069] The final steelmaking composition and tapping temperature of each embodiment are shown in Table 1, and the FeO content and gaseous N content in the final slag are shown in Table 2. Table 1: Steel composition and tapping temperature at the final tapping point

[0070] Table 2: FeO content and N content in the final residue

[0071] In Tables 1 and 2, the comparative examples were smelted using conventional methods, and the steel grade was GCr15 with nitrogen control requirements.

[0072] As shown in Tables 1 and 2, for steel grades such as GCr15, H13, and 20CrMnTi that require nitrogen content control, the C and P contents of the tapped steel can be controlled after using the side-blown argon + bottom anode stirring method described in this paper, the (FeO)% content of the slag is relatively low, and the nitrogen content has a good control level for the nitrogen content at the end of the electric arc furnace.

Claims

1. A method for effectively controlling nitrogen in a DC electric arc furnace smelting process, characterized in that: The DC electric arc furnace is equipped with a side-blowing argon device on the furnace wall of the molten pool; the smelting includes scrap steel batching, feeding and power supply, slag formation and dephosphorization, and oxygen blowing and carbon removal processes; after the oxygen blowing and carbon removal operation, low-power power supply is supplied, and the side-blowing argon device is turned on for argon blowing and stirring, and the steel is tapped after the tapping temperature requirements are met.

2. The DC electric arc furnace smelting method for effective nitrogen control according to claim 1, characterized in that: The side-blowing argon device is used to blow argon and stir for 1 to 2 minutes.

3. The DC electric arc furnace smelting method for effective nitrogen control according to claim 1, characterized in that: The low-power power supply has a voltage of 500-600V and a current of 85-95KA.

4. The DC electric arc furnace smelting method for effective nitrogen control according to claim 1, characterized in that: The side-blowing argon device is equipped with two units, each with a argon blowing and stirring flow rate of 20–30 Nm³. 3 / h.

5. The DC electric arc furnace smelting method for effective nitrogen control according to claim 1, characterized in that, The scrap steel batching process uses the following proportions: 15-20% high-quality pig iron, 10-15% self-produced crushed scrap, 15-20% small scrap steel, 25-35% medium scrap steel, and 10-20% high-quality heavy scrap.

6. The DC electric arc furnace smelting method for effective nitrogen control according to claim 1, characterized in that, The feeding and power supply process involves two loading stages. The scrap steel in the first stage is preheated to a surface temperature of 600-800°C, and the loading amount is 55-60% of the total loading amount. After the first stage is energized and melted, the second stage is fed in, and the scrap steel in the second stage is preheated to a surface temperature of 500-600°C.

7. The DC electric arc furnace smelting method for effective nitrogen control according to claim 1, characterized in that, The material feeding and power supply process is as follows: after the material feeding is completed, the power supply voltage is 900-1000V and the current is 85-95KA; after reaching the flat molten pool state, the power supply voltage is 600-700V and the current is 85-95KA.

8. The DC electric arc furnace smelting method for effective nitrogen control according to claim 1, characterized in that, The slag-making and dephosphorization process involves controlling the molten pool temperature to be <1530℃, adding 15-20 kg / t of lime and 5-10 kg / t of lightly calcined dolomite, and performing foam-making, dephosphorization, and slag-flowing operations.

9. A method for effective nitrogen control in a DC electric arc furnace smelting according to any one of claims 1-8, characterized in that, The oxygen blowing and carbon extraction process involves a carbon powder injection rate of 10–20 kg / t, simultaneously performing deoxidation and carbon extraction operations, with an oxygen blowing rate of 30–40 Nm³. 3 / h.

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