High-quality clean electroslag ingot oxygen-free low-vacuum smelting method

Abstract

This invention discloses a method for high-quality, clean electroslag ingot smelting in an oxygen-free, low-vacuum environment. It employs a multi-functional protective atmosphere vacuum pressurized electroslag furnace with upper and lower furnace chambers and a dedicated meshing device for sealing. This furnace offers excellent sealing and rapid evacuation, allowing the entire crystallizer to be placed in the lower chamber. The low vacuum prevents slag from being sucked up, ensuring a smooth electroslag remelting process, minimizing slag boiling, stabilizing the molten steel, and resulting in high-quality electroslag ingots. An oxygen detector is used to monitor the oxygen content within the furnace. Vacuuming is initiated when the oxygen content reaches 0 ppm to ensure an oxygen-free environment. Smelting at a vacuum level of 3000–5000 Pa ensures that the molten slag does not detach from the molten steel surface due to evacuation force, while also guaranteeing electroslag remelting under low vacuum conditions. Using refined slag as the furnace slag significantly reduces the formation of inclusions in the electroslag ingots and allows for the smelting of various high-quality, clean, special electroslag steels. Hydrogen diffusion annealing is used to remove hydrogen, ensuring that the hydrogen content in the electroslag ingot is ≤1.0 ppm.

Description

Technical Field

[0001] This invention belongs to the field of electroslag remelting technology, specifically relating to a method for oxygen-free, low-vacuum smelting of high-quality clean electroslag ingots. Background Technology

[0002] With the development of the steel industry, the electroslag remelting (ESR) steel market is highly competitive, and users have increasingly higher requirements for the quality and cleanliness of ESR steel products. Currently, for certain special-purpose ESR ingots used in China, the requirements for non-metallic inclusions are as follows: coarse series A and B are grade 0, C is grade 0, and D is grade 0; fine series A, B, and C are grade 0, and D ≤ 0.5; DS inclusions ≤ 1, making production quite difficult. Furthermore, the P content of the ESR steel must be controlled within the range of ≤ 0.010%, the S content within the range of ≤ 0.005%, H ≤ 1 ppm, O ≤ 20 ppm, N ≤ 20 ppm, and the upper and lower deviations of the high-alloy (total content above 5%) composition must be controlled within 5%, with no obvious surface defects, making production extremely difficult. In particular, some high-temperature alloys, stainless steels, and mold steels contain easily oxidizable elements such as Al, Ti, and Si, and the requirements for high-quality clean ESR ingots cannot be met using atmospheric pressure ESR furnaces or inert gas protected ESR furnaces.

[0003] Vacuum electroslag remelting (VER) is a new generation of electroslag smelting technology that has emerged in recent years. VER combines the characteristics of both vacuum smelting and electroslag smelting. Atmospheric pressure electroslag smelting suffers from drawbacks such as high burn-off of reactive elements, increased content of harmful gases, and difficulty in controlling the composition at the ingot's beginning and end. VER features faster solidification speed and precise control over the entire melting and solidification process; fewer columnar crystals in the ingot's transition region; no increase or decrease in [O], [H], and [N]; and lower banded segregation. Simultaneously, VER reduces the burn-off of elements such as Ti, Al, and Si. However, in VER, the vacuum level below 600 Pa makes arc initiation and slag formation difficult. High vacuum requires high suction force, which can easily cause slag boiling, leading to instability in the molten steel and poor surface quality of the electroslag ingot. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention aims to produce electroslag ingots using a multifunctional protective atmosphere vacuum pressurized electroslag furnace. This furnace has good sealing performance, fast vacuuming speed, and large furnace space, which can ensure a smooth electroslag remelting process and prevent slag from boiling. At the same time, it ensures an oxygen-free environment inside the furnace and controls the vacuum degree to 3000-5000 Pa for smelting. This ensures that the slag does not detach from the steel surface due to the suction force, and that electroslag remelting can be carried out under relatively low vacuum conditions, thus ensuring smelting quality and obtaining high-quality clean electroslag ingots.

[0005] To achieve the above-mentioned objectives, this invention provides a method for high-quality, clean electroslag ingot oxygen-free, low-vacuum smelting, the method comprising the following technical solutions:

[0006] ① It is produced using a multi-functional protective atmosphere vacuum pressure electroslag furnace, and the consumable electrode (bulk) and slag are pretreated.

[0007] ② The basic electrical system for electroslag remelting is a voltage of 20-50V and a current of 700-4500A; it uses conductive slag containing TiO2 or an electroslag ingot of the same steel grade with a diameter of 13mm and a height of 25mm to initiate the arc; the ingot initiation plate is made of the same steel grade as the electroslag ingot and is rusted by shot blasting or laser rust removal machine.

[0008] ③ When the electroslag remelting smelting begins, high-purity argon gas is first introduced, and the oxygen detection equipment is turned on to reduce the oxygen in the furnace to 0 ppm; after the oxygen in the furnace is reduced to 0 ppm, the arc ignition and slag formation are started, and the voltage is controlled at 20-46V and the current is controlled at 700-2900A.

[0009] After the furnace lid is sealed, high-purity argon gas is directly injected into the furnace. An oxygen detector is used to detect the oxygen content in the furnace. When the oxygen content reaches 0 ppm, a vacuum is drawn to ensure an oxygen-free environment inside the furnace. The operation is simple and the oxygen content is controllable.

[0010] ④ After slag formation is completed, the oxygen level in the furnace is reduced to 0 ppm again (during slag formation, decomposition oxygen will be generated in the slag and billet). Then, the rotary vane vacuum pump is turned on to reduce the vacuum level in the furnace from atmospheric pressure to 3000-5000 Pa. The evacuation time is controlled within 2-3 minutes.

[0011] Using a vacuum of 3000-5000 Pa for smelting ensures that the slag does not detach from the steel surface due to the suction force, preventing the slag from boiling and stabilizing the steel. It also ensures electroslag remelting under lower vacuum conditions, guaranteeing the quality of electroslag ingot smelting.

[0012] ⑤ During the electroslag refining period, the vacuum degree inside the furnace is maintained at 3000-5000Pa, with a deviation of no more than ±200Pa. The voltage is controlled at 30-32V and the current at 2400-2750A. During the feeding period, the time is controlled within 5 minutes, the voltage remains unchanged, and the current decreases by 500-700A per minute.

[0013] ⑥ Power off and cool in mold for 40-60 minutes; after exiting the furnace, easily crackable steel or steel with an alloy content of more than 15% should be cooled in an electroslag ingot for 24-36 hours, while other steel grades should be air-cooled.

[0014] ⑦ After slow cooling, perform hydrogen diffusion annealing. (See attached diagram) Figure 1The annealing curve shown is as follows: In specific operation, the electroslag ingot is loaded into a resistance furnace (maximum temperature above 1000℃) and the furnace door is closed; the temperature is initially raised from room temperature to 200℃, with no requirement for the heating rate; the temperature is then raised from 200℃ to 850-870℃, with the heating rate controlled within 40℃ / h, and held at 850-870℃ for 10-12 hours; the temperature is then lowered to 680±10℃, with the cooling rate controlled within 20℃ / h, and held at 680±10℃ for 30-35 hours; the temperature is then lowered again to 100℃, with the cooling rate controlled within 25℃ / h; and then the ingot is removed from the furnace.

[0015] Hydrogen diffusion annealing is a heat treatment process for metallic materials. By heating an electroslag ingot to a specific temperature two or more times and holding it at that temperature for a certain time, hydrogen atoms diffuse out from the grains or intergranular spaces within the steel, reducing the hydrogen content and promoting the healing of microcracks, thereby improving the material's properties and ductility. This treatment is commonly used in the manufacture of high-strength steel, titanium alloys, and some precision components, particularly in the nuclear industry and aerospace, where it is widely applied to high-quality, clean, and specialized steels. This hydrogen diffusion annealing method can further remove the hydrogen content from the electroslag ingot, achieving a hydrogen content of ≤1.0 ppm.

[0016] In the above technical solution, further, the multifunctional protective atmosphere vacuum pressurized electroslag furnace described in step ① has upper and lower furnace chambers and a meshing device; it can place the crystallizer into the lower furnace chamber and is equipped with an oxygen detection instrument. Using the multifunctional protective atmosphere vacuum pressurized electroslag furnace, with its upper and lower furnace chambers and a dedicated meshing device for sealing, results in excellent airtightness and a fast vacuuming speed (approximately 2-3 minutes to evacuate the furnace from atmospheric pressure to 5000 Pa). Furthermore, the large furnace chamber space allows the entire crystallizer to be placed in the lower furnace chamber. Under low vacuum, the slag is less likely to be sucked up, preventing it from separating from the molten steel. This ensures a smooth electroslag remelting process, reduces the risk of slag boiling, ensures the stability of the molten steel, and ultimately results in electroslag ingots with good surface quality.

[0017] Furthermore, the consumable electrode (bulk) mentioned in step ① must be a vacuum induction ingot produced by a vacuum induction furnace, with a specification of ∮100mm and an electroslag ingot with a production ingot shape of ∮150mm.

[0018] Furthermore, the FeO on the surface of the consumable electrode described in step ① must first be peeled off by turning or shot blasted to remove rust.

[0019] Furthermore, the slag mentioned in step ① is a refined slag, whose main components by mass content are: CaF2: 45-50%, Al2O3: 20-25%, CaO: 15-20%, MgO: 5-10%, SiO2≤0.15%, H2O≤0.5%, FeO≤0.03%, and C≤0.06%. The SiO2 and TiO2 content can be appropriately increased, while the CaF2 and Al2O3 content can be decreased, depending on the specific steel grade; the slag quantity is 3-4 kg / furnace. This slag system not only significantly reduces the generation of inclusions in electroslag ingots but also adapts to the smelting of various high-quality, clean, special electroslag steels.

[0020] Furthermore, the slag mentioned in step ① is dried by baking until it is red-hot, at a baking temperature of 600-950℃, and for a baking time of more than 6 hours.

[0021] Furthermore, in step ④, the output power of the rotary vane vacuum pump is controlled at 20-40% of the total power to ensure stable vacuum control with a vacuum fluctuation range of ±200Pa.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] ① The multi-functional protective atmosphere vacuum pressurized electroslag furnace is used. It has upper and lower furnace chambers, which are sealed with a special meshing device, ensuring good airtightness and fast evacuation speed. The furnace chamber has a large space, which can put the entire crystallizer into the lower furnace chamber. Under low vacuum, it is not easy to suck up the slag, so that the slag does not separate from the molten steel. This ensures that the electroslag remelting process is smooth, does not easily cause the slag liquid to boil, ensures the stability of the molten steel, and produces electroslag ingots with good surface quality.

[0024] ② This invention uses a sealed furnace lid to directly inject high-purity argon gas into the furnace. An oxygen detector is used to detect the oxygen content inside the furnace. When the oxygen content reaches 0 ppm, a vacuum is drawn to ensure an oxygen-free environment inside the furnace. The operation is simple and the oxygen content is controllable.

[0025] ③ This invention employs a vacuum of 3000–5000 Pa for smelting, ensuring that the slag does not detach from the molten steel surface due to suction force, while also guaranteeing electroslag remelting under relatively low vacuum conditions, thus ensuring the quality of the electroslag ingot. Hydrogen diffusion annealing is used to further remove the hydrogen content from the electroslag ingot, resulting in hydrogen content ≤ 1.0 ppm.

[0026] ④ The mold steel produced using the technical solution of this invention has significantly improved toughness, strength, wear resistance, resistance to thermal fatigue cracking, resistance to metal adhesion, resistance to erosion, and resistance to oxidation. Its service life is longer than that of ordinary electroslag remelted mold steel. When producing high-temperature alloys, the loss of active elements during the electroslag remelting process is greatly reduced, and the composition can be precisely controlled and the gas content can be stably controlled. The Ti-containing stainless steel produced has controlled levels of easily oxidized Ti, resulting in stable quality. Attached Figure Description

[0027] Figure 1 This is an annealing curve diagram of hydrogen diffusion annealing in the technical solution of the present invention;

[0028] Figure 2 This is an annealing curve diagram of hydrogen diffusion annealing in Example 1;

[0029] Figure 3 This is an annealing curve diagram of hydrogen diffusion annealing in Example 2;

[0030] Figure 4 This is an annealing curve diagram of hydrogen diffusion annealing in Example 3. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

[0032] Example 1

[0033] The high-temperature alloy GH4169 is produced using the technical solution of this invention. The main components of the GH4169 vacuum induction ingot are shown in Table 1. In addition, its O content is 10 ppm, H content is 4 ppm and N content is 10 ppm.

[0034] Table 1. Composition and content of GH4169 vacuum induction ingot

[0035] C％ Si% Mn% P％ S％ Al％ Cr％ Co% Ni% Ti% Mo% Fe% 0.04 0.32 0.18 0.009 0.002 0.68 17.74 0.06 50.8 0.85 2.96 27.9

[0036] The specific process flow for the oxygen-free, low-vacuum smelting method of high-quality clean electroslag ingots is as follows:

[0037] ① Production is carried out using a 50kg multi-functional protective atmosphere vacuum pressure electroslag furnace. The billet (consumable electrode) and slag are pretreated. The 50kg multi-functional protective atmosphere vacuum pressure electroslag furnace has upper and lower furnace chambers, a meshing device for good sealing, the ability to place the crystallizer into the lower furnace chamber, and an oxygen detection instrument. The FeO on the surface of the consumable electrode is first removed by machining to remove the scale and rust. The billet specification is ∮100mm, and the produced ingot shape is ∮150mm. Refined slag is used as the slag, and its main composition by mass content is CaF2: 50%, Al2O3: 25%, CaO: 17.5%, MgO: 5%, TiO2: 2.5%, SiO2≤0.05%, H2O≤0.05%, FeO≤0.03%, C≤0.06%, and the slag quantity is 3.5kg / furnace. The slag is heated to red-hot and dried at a temperature of 600℃ for 6 hours.

[0038] ② The basic electrical system for electroslag is a voltage of 30-50V and a current of 700-4500A; conductive slag containing TiO2 is used as the arc igniter; the ignition plate is made of the same steel as the electroslag ingot and is rusted by a laser rust removal machine.

[0039] ③ When the electroslag remelting smelting begins, high-purity argon gas is first introduced, and the oxygen detection equipment is turned on to reduce the oxygen in the furnace to 0 ppm. After the oxygen in the furnace is reduced to 0 ppm, the arc ignition and slag formation are started, with the voltage controlled at 31-46V and the current controlled at 700-2500A.

[0040] ④ After slag formation is complete, once the oxygen level in the furnace drops to 0 ppm again (during slag formation, the slag billet will produce decomposition oxygen), turn on the rotary vane vacuum pump to reduce the vacuum level in the furnace from atmospheric pressure to 5000 Pa. Adjust the output power of the rotary vane vacuum pump appropriately to ensure stable vacuum control, with a fluctuation range of ±100 Pa.

[0041] ⑤ During the electroslag refining period, the vacuum degree inside the furnace is maintained at 5000Pa, with a deviation of no more than ±200Pa; the voltage is controlled at 30~31V and the current is controlled at 2700~2750A; during the feeding period, the time is controlled within 5 minutes, the voltage remains unchanged, and the current decreases by 700A per minute until the current is 0A.

[0042] ⑥ Power off and cool the mold for 40 minutes; after exiting the furnace, cool the electroslag ingot bucket for 24 hours.

[0043] ⑦ After slow cooling, perform hydrogen diffusion annealing. The annealing curve is shown below. Figure 2 As shown, in specific operation, the electroslag ingot is loaded into the resistance furnace (maximum temperature above 1000℃), and the furnace door is closed; the temperature is initially raised from room temperature to 200℃, with no requirement for the heating rate; the temperature is then raised from 200℃ to 850℃, with the heating rate controlled within 40℃ / h, and held at 850℃ for 12 hours; then the temperature is lowered to 680℃, with the cooling rate controlled within 20℃ / h, and held at 680℃ for 35 hours; the temperature is then lowered again to 100℃, with the cooling rate controlled within 25℃ / h; and then the ingot is removed from the furnace.

[0044] The GH4169 electroslag ingot produced using the technical solution of Example 1 above has good surface quality, no arcing, waistline, or slag inclusion defects, and good feeding effect; the specific component mass content is shown in Table 2.

[0045] Table 2. Composition of GH4169 electroslag ingots produced in Example 1

[0046] Location C％ Si% Mn% P％ S％ Al％ Cr％ Co% Ni% Ti% Mo% Fe% upper part 0.043 0.32 0.18 0.009 0.002 0.67 17.74 0.06 50.8 0.85 2.96 27.9 lower part 0.043 0.32 0.18 0.009 0.002 0.69 17.74 0.07 50.8 0.80 2.96 27.9

[0047] Furthermore, the GH4169 electroslag ingot has an O content of 10 ppm, an H content of 1 ppm, and an N content of 9 ppm. Its inclusion content is shown in Table 3.

[0048] Table 3. Inclusion content of GH4169 electroslag ingots produced in Example 1.

[0049]

[0050] Example 2

[0051] The stainless steel 1Cr17Ni9Ti is produced using the technical solution of this invention. The main components of the 1Cr17Ni9Ti vacuum induction ingot are shown in Table 4. In addition, its O content is 17ppm, H content is 4ppm and N content is 15ppm.

[0052] Table 4. Composition content (%) of 1Cr17Ni9Ti vacuum induction ingot

[0053] C Si Mn P S Cr Ni Ti 0.056 0.56 1.36 0.007 0.002 17.07 9.03 0.22

[0054] The specific process flow for the oxygen-free, low-vacuum smelting method of high-quality clean electroslag ingots is as follows:

[0055] ① Production is carried out using a 50kg multi-functional protective atmosphere vacuum pressure electroslag furnace. The billet (consumable electrode) and slag are pretreated. The 50kg multi-functional protective atmosphere vacuum pressure electroslag furnace has upper and lower chambers, sealed by a meshing device, with good airtightness, allowing the crystallizer to be placed in the lower chamber. It is equipped with oxygen detection instruments. The FeO on the surface of the consumable electrode is first removed by machining to remove the scale and rust. The billet specification used is ∮100mm, and the produced ingot shape is ∮150mm. Refined slag is used as the slag, and its main composition by mass content is CaF2: 50%, Al2O3: 25%, CaO: 19.5%, MgO: 5%, TiO2: 0.5%, SiO2≤0.15%, H2O≤0.5%, FeO≤0.03%, C≤0.06%, and the slag quantity is 4.0kg / furnace. The slag is heated to red-hot and dried at a temperature of 650℃ for 6 hours.

[0056] ② The basic electrical system for electroslag is a voltage of 30-50V and a current of 700-4500A; an arc-starting column of the same steel grade as the electroslag ingot with a diameter of 13mm and a height of 25mm is used as the arc-starting agent; the ingot-starting plate is made of the same steel grade as the 1Cr17Ni9Ti electroslag ingot and is rust-removed by shot blasting.

[0057] ③ When the electroslag remelting smelting begins, high-purity argon gas is first introduced, and the oxygen detection equipment is turned on to reduce the oxygen in the furnace to 0 ppm; after the oxygen in the furnace is reduced to 0 ppm, the arc ignition and slag formation are started, and the voltage is controlled at 30-46V and the current is controlled at 700-2700A.

[0058] ④ After slag formation is complete, once the oxygen level in the furnace drops to 0 ppm again (during slag formation, the slag billet will produce decomposition oxygen), turn on the rotary vane vacuum pump to reduce the vacuum level in the furnace from atmospheric pressure to 3000 Pa. Adjust the output power of the rotary vane vacuum pump appropriately to ensure stable vacuum control, with a fluctuation range of ±200 Pa.

[0059] ⑤ During the electroslag refining period, the vacuum degree inside the furnace is maintained at 3000Pa, with a deviation of no more than ±200Pa. The voltage is controlled at 30~32V and the current is controlled at 2700~2750A. During the feeding period, the time is controlled within 5 minutes, the voltage remains unchanged, and the current decreases by 700A per minute.

[0060] ⑥ Power off and cool the mold for 60 minutes; after exiting the furnace, cool the electroslag ingot bucket for 36 hours.

[0061] ⑦ After slow cooling, perform hydrogen diffusion annealing. The annealing curve is shown below. Figure 3 As shown, in specific operation, the electroslag ingot is loaded into the resistance furnace (maximum temperature above 1000℃), and the furnace door is closed; the temperature is initially raised from room temperature to 200℃, with no requirement for the heating rate; the temperature is then raised from 200℃ to 870℃, with the heating rate controlled within 40℃ / h, and held at 870℃ for 12 hours; then the temperature is lowered to 680℃, with the cooling rate controlled within 20℃ / h, and held at 680℃ for 35 hours; the temperature is then lowered again to 100℃, with the cooling rate controlled within 25℃ / h; and then the ingot is removed from the furnace.

[0062] The 1Cr17Ni9Ti electroslag ingot produced using the technical solution of Example 2 above has good surface quality, is free from arcing, waist-like defects, and slag inclusions, and exhibits good feeding effect. The specific upper and lower components of the 1Cr17Ni9Ti electroslag ingot produced in Example 2 are shown in Table 5.

[0063] Table 5. Composition of 1Cr17Ni9Ti electroslag ingots produced in Example 2 (wt%)

[0064] Location C Si Mn P S Cr Ni Ti upper part 0.056 0.56 1.36 0.007 0.002 17.07 9.03 0.22 lower part 0.057 0.59 1.35 0.008 0.003 17.09 9.05 0.21

[0065] Furthermore, the 1Cr17Ni9Ti electroslag ingot has an O content of 15 ppm, a H content of 0.3 ppm, and a N content of 13 ppm. Its inclusion content is shown in Table 6.

[0066] Table 6. Inclusion content of 1Cr17Ni9Ti electroslag ingots produced in Example 2.

[0067]

[0068] Example 3

[0069] The technical solution of this invention is used to produce mold steel H13. The main components of H13 vacuum induction ingot are shown in Table 7. In addition, the O content in H13 steel is 20ppm, the H content is 7ppm and the N content is 16ppm.

[0070] Table 7 H13 Vacuum Induction Spindle Composition Content (wt%)

[0071] C Si Mn P S Cr Mo V 0.425 0.913 0.366 0.009 0.005 4.98 1.134 0.832

[0072] The specific process flow for the oxygen-free, low-vacuum smelting method of high-quality clean electroslag ingots is as follows:

[0073] ① Production is carried out using a 50kg multi-functional protective atmosphere vacuum pressure electroslag furnace. The consumable electrodes and slag undergo pretreatment. The 50kg multi-functional protective atmosphere vacuum pressure electroslag furnace has upper and lower chambers, a meshing device for good sealing, allows the crystallizer to be placed in the lower chamber, and is equipped with an oxygen detection instrument. The FeO on the surface of the consumable electrodes is first removed by machining to remove scale and rust. The billet used is ∮100mm, producing electroslag ingots with a diameter of ∮150mm. Refined slag is used as the slag, with the main components being CaF2: 50%, Al2O3: 25%, CaO: 18%, MgO: 5%, SiO2: 2%, H2O≤0.05%, FeO≤0.03%, C≤0.06%, and a slag quantity of 3.6kg / furnace. The slag is then heated to red-hot temperature and dried at 750℃ for 7 hours.

[0074] ② The basic electrical system for electroslag remelting is a voltage of 30-49V and a current of 700-4400A; H13 steel with a diameter of 13mm and a height of 25mm is used as the arc igniter; the ingot plate is made of H13 steel and is derusted by shot blasting.

[0075] ③ When the electroslag remelting smelting begins, high-purity argon gas is first introduced, and the oxygen detection equipment is turned on to reduce the oxygen in the furnace to 0 ppm; after the oxygen in the furnace is reduced to 0 ppm, the arc ignition and slag formation are started, and the voltage is controlled at 30-45V and the current is controlled at 750-2700A.

[0076] ④ After slag formation is complete, once the oxygen level in the furnace drops to 0 ppm again (during slag formation, the slag billet will produce decomposition oxygen), turn on the rotary vane vacuum pump to reduce the vacuum level in the furnace from atmospheric pressure to 4500 Pa. Adjust the output power of the rotary vane vacuum pump appropriately to ensure stable vacuum control, with a fluctuation range of ±150 Pa.

[0077] ⑤ During the electroslag refining period, the vacuum degree inside the furnace is maintained at 4500Pa, with a deviation of no more than ±200Pa. The voltage is controlled at 30~31V and the current is controlled at 2700~2720A. During the feeding period, the time is controlled within 5 minutes, the voltage remains unchanged, and the current decreases by 600A per minute until the current is 0A.

[0078] ⑥ Power off and cool the mold for 50 minutes; after removing it from the oven, air cool to room temperature.

[0079] ⑦ After slow cooling, perform hydrogen diffusion annealing. The annealing curve is shown below. Figure 4 As shown, in specific operation, the electroslag ingot is loaded into the resistance furnace (maximum temperature above 1000℃), and the furnace door is closed; the temperature is initially raised from room temperature to 200℃, with no requirement for the heating rate; the temperature is then raised from 200℃ to 855℃, with the heating rate controlled within 40℃ / h, and held at 855℃ for 11 hours; the temperature is then lowered to 685℃, with the cooling rate controlled within 20℃ / h, and held at 685℃ for 33 hours; the temperature is then lowered again to 100℃, with the cooling rate controlled within 25℃ / h; and then the ingot is removed from the furnace.

[0080] The H13 electroslag ingot produced using the technical solution of Example 3 above has good surface quality, no arcing, waistband, or slag inclusion defects, and good feeding effect; the specific composition is shown in Table 8.

[0081] Table 8. Composition of H13 electroslag ingots produced in Example 3 (wt%)

[0082] Location C Si Mn P S Cr Mo V upper part 0.425 0.913 0.366 0.009 0.002 4.99 1.135 0.832 lower part 0.420 0.90 0.37 0.010 0.003 4.98 1.130 0.835

[0083] Furthermore, the H13 electroslag ingot contains 18 ppm of O, 0.5 ppm of H, and 17 ppm of N. Its inclusion content is shown in Table 9.

[0084] Table 9. Inclusion content of H13 electroslag ingots produced in Example 3

[0085]

[0086] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for oxygen-free, low-vacuum smelting of high-quality clean electroslag ingots, characterized in that, The method includes the following technical solutions: ① The process is carried out using a multi-functional protective atmosphere vacuum pressure electroslag furnace, and the consumable electrodes and slag are pretreated. ② The basic electrical system for electroslag is a voltage of 20-50V and a current of 700-4500A; it uses conductive slag containing TiO2 or an electroslag ingot of the same steel grade with a diameter of 13mm and a height of 25mm to initiate the arc; the ingot ingot plate is made of the same steel grade as the electroslag ingot and is rusted by shot blasting or laser rust removal machine. ③ When the electroslag remelting smelting begins, high-purity argon gas is first introduced, and the oxygen detection equipment is turned on to reduce the oxygen in the furnace to 0 ppm; after the oxygen in the furnace is reduced to 0 ppm, the arc ignition and slag formation are started, and the voltage is controlled at 20-46V and the current is controlled at 700-2900A. ④ After slag formation is completed and the oxygen level in the furnace reaches 0 ppm again, turn on the rotary vane vacuum pump to reduce the vacuum level in the furnace from atmospheric pressure to 3000-5000 Pa. ⑤ During the electroslag refining period, the vacuum degree inside the furnace is maintained at 3000-5000Pa, with a deviation of no more than ±200Pa. The voltage is controlled at 30-32V and the current at 2400-2750A. During the feeding period, the time is controlled within 5 minutes, the voltage remains unchanged, and the current decreases by 500-700A per minute. ⑥ Power off and cool in mold for 40-60 minutes; after exiting the furnace, easily crackable steel or steel with an alloy content of more than 15% should be cooled in an electroslag ingot bucket for 24-36 hours, while other steel grades should be air-cooled. ⑦ After slow cooling, perform hydrogen diffusion annealing.

2. The method according to claim 1, characterized in that, The multifunctional protective atmosphere vacuum pressurized electroslag furnace described in step ① has upper and lower furnace chambers, a meshing device that allows the crystallizer to be placed into the lower furnace chamber, and is equipped with an oxygen detection instrument.

3. The method according to claim 1, characterized in that, The consumable electrode mentioned in step ① is a vacuum induction ingot produced by a vacuum induction furnace, with a specification of ∮100mm and an electroslag ingot with a production ingot shape of ∮150mm.

4. The method according to claim 1, characterized in that, In step ①, the FeO on the surface of the consumable electrode is first peeled off by turning or shot blasting to remove rust.

5. The method according to claim 1, characterized in that, The slag mentioned in step ① is refined slag, whose main components by mass content are CaF2: 45-50%, Al2O3: 20-25%, CaO: 15-20%, MgO: 5-10%, SiO2≤0.15%, H2O≤0.5%, FeO≤0.03%, C≤0.06%; the slag amount is 3-4 kg / furnace.

6. The method according to claim 1, characterized in that, The slag described in step ① is dried by baking until it turns red-hot, at a baking temperature of 600-950℃, for a baking time of more than 6 hours.

7. The method according to claim 1, characterized in that, The output power of the rotary vane vacuum pump in step ④ is controlled at 20-40% of the total power, and the vacuum fluctuation range is controlled at ±200Pa.

8. The method according to claim 1, characterized in that, During the hydrogen expansion annealing operation described in step ⑦, the electroslag ingot is loaded into the resistance furnace and the furnace door is closed. The temperature is initially raised from room temperature to 200°C, with no specific heating rate requirement. The temperature is then raised from 200°C to 850–870°C, with the heating rate controlled within 40°C / h, and held at 850–870°C for 10–12 hours. The temperature is then lowered to 680±10°C, with the cooling rate controlled within 20°C / h, and held at 680±10°C for 30–35 hours. The temperature is then lowered again to 100°C, with the cooling rate controlled within 25°C / h. The ingot is then removed from the furnace.

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