A method for preparing a high-toughness, high-grain-coarsening-resistant carburizing gear steel

Abstract

This invention relates to a method for preparing high-toughness, high-resistance-to-grain-coarsening carburized gear steel. The process route is as follows: electric furnace smelting, ladle refining, vacuum refining, inert gas protected electrode billet casting, constant melting rate electroslag remelting in a protective atmosphere, high-temperature homogenization treatment, multi-directional forging, post-forging pretreatment, post-forging machining, and post-forging pretreatment. The product, in its quenched and tempered state, exhibits fine grain size, high impact toughness, and a fine, uniform grain distribution. After quenching and tempering, Nb(CN), AlN, and V(CN) precipitates fully pin the grain boundaries, refining the austenite grains and inhibiting abnormal austenite grain growth during carburizing. This method can be used in the manufacture of heavy-duty and high-strain gear parts such as wind turbine gearbox gears, large-module gears, and heavy-duty gears.

Description

[0001] This application is a divisional application for a high-toughness, high-resistance-to-grain-coarsening carburized gear steel and a method for preparing the same.

[0002] The original application was filed on March 12, 2024.

[0003] The original application number was 2024102770052;

[0004] The original invention application was titled: A high-toughness, high-resistance-to-grain-coarsening carburized gear steel and its preparation method. Technical Field

[0005] This invention relates to the field of mold steel preparation technology, and in particular to a high-toughness, high-resistance-to-grain-coarsening carburized gear steel and its preparation method. Background Technology

[0006] Gears are fundamental components of the equipment manufacturing industry, embodying core manufacturing technologies and widely applied across various sectors of the national economy. Gear transmission devices are essential products supporting national economic development, experiencing among the fastest growth rates globally in industries such as engineering machinery manufacturing, shipbuilding, automobiles, and wind power generation. This has driven rapid growth in gear products such as engineering machinery transmission devices, marine gearboxes, automotive transmissions, and wind turbine gearboxes. Gear steel is one of the most critical materials among special alloy steels used in automobiles, railways, ships, and engineering machinery, and is a key material for manufacturing core components that ensure safety. Gear steel is developing towards higher performance, longer lifespan, smoother gear operation, lower noise, enhanced safety, lower cost, easier processing, and greater variety.

[0007] As gear diameters continue to increase, the requirements for gear tooth toughness become increasingly stringent, while controlling deformation in different areas of the gear during carburizing and quenching becomes increasingly difficult. Simply increasing machining allowances to address deformation will result in uneven carburized layer thickness and inconsistent mechanical properties in different areas. This can easily lead to gear failure during actual service due to performance inconsistencies, causing significant economic losses. Therefore, in actual production, customers have placed higher demands on the performance and uniformity of the gear blank before carburizing and quenching, while simultaneously reducing the pre-carburizing and quenching temperature heating rate (1-4℃ / min) and increasing the carburizing holding time (≥40h).

[0008] To meet the needs of customers and the market, we have developed a high-toughness, high-resistance-to-grain-coarsening carburized gear steel by strictly controlling the production process. This steel meets the market's demand for large-size gears in high-end manufacturing and can be widely used in the manufacture of heavy-duty and high-strain gear parts such as wind power gearbox gears, large-module gears, and heavy-duty gears. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing carburized gear steel with high toughness and high resistance to grain coarsening. The product has a uniform microstructure and fine and uniform grain distribution in the quenched and tempered state, and a uniform microstructure after quenching and tempering. After quenching and tempering, the Nb (CN), AlN, and V (CN) precipitates fully pin the grain boundaries and refine the austenite grains. At the same time, it can inhibit the abnormal growth of austenite grains during carburizing, so that the material has high toughness and high resistance to grain coarsening.

[0010] To achieve the above-mentioned objectives, a method for preparing a carburized gear steel with high toughness and high resistance to grain coarsening is provided, comprising the following main steps:

[0011] S1, Electric furnace smelting:

[0012] Based on the chemical composition content of the steel to be smelted, scrap steel and alloy materials of ferrochrome, ferrovanadium, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, and ferroniobium are prepared in advance. In the electric furnace, scrap steel is smelted in batches according to the smelting weight. The molten steel temperature is ≥1650℃ and the slag is removed by oxidation. After slag removal, ferrochrome, ferrovanadium, ferrosilicon alloy, lime and fluorite are added to adjust the chemical composition and dephosphorize. The tapping temperature is ≥1620℃. Aluminum wire is added during the tapping process for deoxidation.

[0013] The chemical composition by mass percentage is as follows: C 0.16%~0.20%, Mn 0.50%~0.90%, Si 0.18%~0.35%, S≤0.002%, P≤0.010%, Cr 1.50%~1.80%, Mo 0.25%~0.35%, V 0.07%~0.12%, Ni 1.40%-1.70%, Al 0.02%~0.04%, Nb 0.02%~0.035%, N 75~150ppm, Cu≤0.10%, with the remainder being Fe. The residual gas content is as follows: H≤1.5ppm, O≤13ppm.

[0014] While ensuring hardenability, Al, Nb, V, and N composite microalloying can suppress the total amount of liquid carbide formation (Nb and V easily precipitate at high temperatures to form liquid carbides, and excessive Al content will reduce the impact toughness of the material). Combined with high-temperature homogenization, this significantly reduces overall segregation in the forging. Furthermore, forging, post-forging heat treatment, and tempering before furnace exit ensure the refinement of the overall grain size. Ultimately, this achieves the suppression of austenite grain growth by fine nitride particles during carburizing, mitigating abnormal austenite grain growth during the carburizing process.

[0015] S2, Ladle refining furnace refining:

[0016] After smelting in the electric furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and refining pre-melted slag is added, wherein CaO:Al2O3:MgO=45:45:6. Alloy materials are added according to the actual composition to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation is completed, the white slag is removed, and then the furnace is reheated and new slag is added to create white slag for the second time.

[0017] S3, Vacuum refining furnace refining:

[0018] The vacuum refining furnace is pumped in stages until the final vacuum degree is ≥67Pa. The vacuum time is maintained for more than 15 minutes, and the target value of residual hydrogen is ≤1.5ppm. After degassing, samples are taken for analysis. After the composition is qualified, argon gas is softly blown into the hoisting bag.

[0019] S4. Casting electrode blank:

[0020] Preheat the ingot mold to 40~70℃, then fill the ingot mold with argon gas for 3~6 minutes for each ingot mold, then remove the argon gas pipe, cover the ingot mold with a lid and then cast;

[0021] S5. Electrode blank annealing:

[0022] The electrode blank after demolding in step S4 is annealed, and the riser and ingot tail are sawn off after annealing.

[0023] S6, Electroslag Remelting:

[0024] The electrode blank obtained in step S5 is first subjected to surface machining on a lathe to remove the surface iron oxide scale; then, dummy electrode welding is performed.

[0025] The smelting process employs a ternary slag system of calcium fluoride, alumina, and calcium oxide. The pre-melted slag system is purified through a secondary refining process, resulting in silica ≤0.6% and ferrous oxide ≤0.15%.

[0026] S7, Forging:

[0027] The electroslag ingot obtained in step S6 is heated and subjected to diffusion homogenization treatment at a temperature of 1260-1300℃ for 25-40 hours. Then, it is upsetting and drawing in three directions (X, Y, and Z) to form an intermediate billet. The billet is then reheated to 1150-1200℃ and held for 2-4 hours. Finally, it is drawn straight and rounded to form the finished product, with a main deformation rate of ≥40% per pass.

[0028] S8. Post-forging heat treatment:

[0029] The forging billet obtained in step S7 is subjected to the following treatments after forging: alternating water and air cooling until the core temperature of the billet is ≤450℃; air cooling for 15~20 minutes, so that the highest surface temperature of the workpiece is 200-250℃, then placed in a heat treatment furnace, heated to 920~940℃, held for 15~20 hours, furnace cooled to 900℃, and then air cooled to 550~650℃. It is then reheated to 650~700℃ and held for 25~40 hours for normal tempering.

[0030] S9, post-forging machining

[0031] After the forging billet obtained in step S8 is inspected and flattened, rough machining is used to remove the surface iron oxide scale.

[0032] S10, Conditioning and tempering:

[0033] The workpiece obtained in step S9 is placed in a heating furnace and heated to 890~910℃, held for 20~30 hours. After holding, water is used for extreme cooling control, and the core temperature is ≤350℃ after cooling. After cooling, the workpiece is placed in an annealing furnace, heated to 630~650℃, held for 25~40 hours, and furnace cooled to ≤350℃ before being removed from the furnace. Rapid cooling after forging suppresses the precipitation of Al / (Nb+V+N) and network carbides. This is because premature precipitation of Al / (Nb+V+N) and network carbides inhibits recrystallization during normalizing, weakening the austenite grain refinement effect of normalizing.

[0034] Specifically, in step S1, during the tapping process, aluminum wire is added at a rate of 1 kg / t for deoxidation.

[0035] Specifically, in step S2, after the secondary white slag formation, 2-3 kg / ton of firebricks are added to adjust the slag fluidity, and AL wire is fed to control the aluminum content according to the target.

[0036] Specifically, in step S3, the time for soft blowing of nitrogen is 15~39 min, the temperature of the hoisting bag is 1560~1580℃, and the nitrogen increase operation is completed, with a target range of [N] of 75~150 ppm.

[0037] Preferably, in step S4, the casting process is protected by argon gas with asbestos cloth attached. The argon gas flow rate is 15~30 m3 / h, the casting time is 4~10 min, the electrode blank diameter is 400~908 mm, and the casting is demolded after 3~6 h.

[0038] Specifically, in step S5, the annealing temperature is 860℃, the holding time is 1~1.5min / mm, and the furnace is cooled to 300~400℃ before being removed from the furnace.

[0039] Preferably, in step S6, the dummy electrode welding adopts inverted electrode blank welding to ensure the verticality of the welding electrode blank and the quality of the weld. At the same time, according to the segregation mechanism of molten steel melting and solidification, the degree of component segregation of electroslag ingot is greatly reduced by inverted electrode blank welding.

[0040] Furthermore, in step S6, the starting melting rate of the steady-state stage of electroslag smelting is 13 kg / min, and the ending melting rate is 11 kg / min, resulting in an electroslag ingot. After cooling in the electric furnace for 90-120 minutes, it is sent to the forging process.

[0041] The present invention provides a method for preparing high-toughness, high-resistance-to-grain-coarsening carburized gear steel, which has the following advantages compared with the prior art:

[0042] (1) The high-toughness, high-resistance-to-grain-coarsening carburized gear steel prepared by the present invention has a uniform microstructure and fine and uniform grain distribution in the quenched and tempered state, and a uniform microstructure after quenching and tempering. After quenching and tempering, the Nb(CN), AlN, and V(CN) precipitates fully pin the grain boundaries and refine the austenite grains, while inhibiting the abnormal growth of austenite grains during carburizing. This gives the material high toughness and high resistance to grain coarsening. It can be widely used in the manufacture of heavy-duty and high-strain gear parts such as wind turbine gearbox gears, large module gears, and heavy-duty gears.

[0043] (2) By improving the preparation process and changing the component content, the purity of the steel is improved. Among them, P≤0.010%, S≤0.002%, gas content N 75~150ppm, H≤1.5ppm, O≤13ppm. At the same time, by carefully selecting smelting raw materials, optimizing steelmaking process, and controlling key control points of casting process, such as casting temperature and casting speed, the precise control of component segregation and inclusion content of electrode billet is achieved.

[0044] (3) By using protective atmosphere smelting, appropriate constant melting rate control, reasonable selection of pre-melted slag, and electrode billet smelting sequence, the purity of electroslag ingots is guaranteed, which further improves the crystal structure, component segregation, especially the control of liquid carbides and density.

[0045] (4) Through high-temperature diffusion over a long period of time at ultra-high temperature, carbides are effectively dissolved and diffused, which greatly improves the segregation of components in electroslag ingots;

[0046] (5) Through multi-directional deformation, full crushing and compaction of the as-cast structure, combined with high-temperature diffusion, the banding and anisotropy are more effectively improved;

[0047] (6) After forging, the billet is directly cooled by water. The corresponding cooling process is formulated for billets of different specifications and sizes by using the thermal simulation software Deform-HT to ensure that the core temperature of the billet is ≤500℃, which fully inhibits the precipitation of network carbides and the growth of austenite grains.

[0048] (6) After solution treatment, the billet is directly cooled in water. The corresponding cooling process is formulated for billets of different specifications and sizes using the thermal simulation software Deform-HT to ensure that the core temperature of the billet is ≤350℃. Attached Figure Description

[0049] Figure 1 Photograph of the austenite grain size of the gear steel obtained in Example 1 after carburizing;

[0050] Figure 2 This is a normal distribution diagram of the grain size of the gear steel after carburizing obtained in Example 1;

[0051] Figure 3 Photograph of the austenite grain size of the gear steel after carburizing, obtained in Example 2;

[0052] Figure 4 This is a normal distribution diagram of the grain size of the gear steel after carburizing obtained in Example 2;

[0053] Figure 5 Photograph of the austenite grain size of the gear steel after carburizing, obtained in Example 3;

[0054] Figure 6 This is a normal distribution diagram of the grain size of the gear steel after carburizing obtained in Example 3;

[0055] Figure 7 Photograph of the austenite grain size of the gear steel after carburizing, obtained in Example 4;

[0056] Figure 8 This is a normal distribution diagram of the grain size of the gear steel after carburizing obtained in Example 4;

[0057] Figure 9 Photograph of the austenite grain size of the gear steel after carburizing, obtained in Example 5;

[0058] Figure 10 This is a normal distribution diagram of the grain size of the gear steel obtained in Example 5 after carburizing. Detailed Implementation

[0059] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0060] Example 1

[0061] A type of hot-work gear steel, by mass fraction, is basically composed of the elements shown in Table 1:

[0062] Table 1

[0063]

[0064] A method for preparing high-toughness carburized gear steel, the method is as follows:

[0065] S1, Electric furnace smelting:

[0066] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1650℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag with a basicity range of 2.1. The molten steel in the electric furnace undergoes dephosphorization and desulfurization treatment. When the steel temperature reaches 1630℃, aluminum wire is added for deoxidation, and then the steel is tapped. Aluminum wire is added at a rate of 1 kg / t for deoxidation. The alloy materials are ferrochrome alloy, ferrovanadium alloy, ferrosilicon alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy, and ferromanganese alloy. After the scrap steel is added to the electric furnace and heated to complete melting, ferrosilicon alloy and ferromanganese alloy are added first.

[0067] S2, Ladle refining furnace refining:

[0068] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and pre-melted refining slag is added. The slag composition is CaO:Al₂O₃:MgO = 45:45:6. This process creates primary white slag. Based on the deviation between the actual and target compositions of the molten steel in the refining furnace base, appropriate alloy materials (ferrochrome, ferrovanadium, ferromolybdenum, ferronickel, ferroniobium alloys) are added to complete composition fine-tuning, desulfurization, and deoxidation. After this process, the white slag is removed, and the steel is reheated to a temperature of 1649°C. Pre-melted refining slag and red bricks are then added for secondary white slag production. In the primary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg. In the secondary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg, along with 2.0 kg of red bricks. Al wire is fed to control the aluminum content according to the target.

[0069] S3, Vacuum refining furnace refining:

[0070] The vacuum refining furnace is pumped in stages to achieve a final vacuum of 67 Pa. The vacuum is maintained twice for 20 minutes each time, with a target nitrogen value of 75-150 ppm. After degassing, samples are taken for analysis. Once the composition is deemed acceptable, argon gas is blown into the ladle. The argon blowing time is 15 minutes, and the ladle temperature is 1575℃. This completes the nitrogen enhancement operation, with a target [N] range of 75-150 ppm.

[0071] S4. Casting electrode blank:

[0072] The ingot mold was preheated to 50℃, then argon gas was introduced into the mold for 5 minutes per mold. The argon gas pipe was then removed, the mold was covered, and casting was performed, followed by demolding. Throughout the casting process, the casting was protected with argon gas using an asbestos-lined cloth, with an argon gas flow rate of 20 m³ / h. 3 / h, casting time is 7min, electrode blank diameter is 730mm, demolding is performed after 5h;

[0073] S5. Electrode blank annealing:

[0074] The electrode blank after demolding in step S4 is annealed at 860℃ for 18 hours, then furnace cooled to 350℃ and removed from the furnace. After annealing, the riser and ingot tail are sawn off.

[0075] S6, Electroslag Remelting:

[0076] The electrode blank obtained in step S5 is surface-cleaned using a shot blasting machine to remove surface iron oxide scale, revealing a metallic luster; a dummy electrode is welded to the tail of the electrode blank, and then it is placed in an electroslag furnace, wherein the dummy electrode is welded by welding an inverted electrode blank.

[0077] A ternary slag was prepared using CaF2, Al2O3, and CaO. The ternary slag was then pre-melted and subjected to secondary refining and purification to achieve a SiO2 content of 0.55% and an FeO content of 0.14%. The slag was then cooled to room temperature under a protective atmosphere.

[0078] The ternary slag is preheated to 800℃, and then added to an electroslag furnace for electroslag remelting to obtain electroslag ingots. The specific steps of electroslag remelting are as follows: the starting melting rate of the steady-state stage of electroslag smelting is 13 kg / min, the ending melting rate is 11 kg / min, and the electroslag ingots are obtained. Then the electric furnace is stopped and cooled for 100 minutes before being sent to the forging process.

[0079] S7, Forging:

[0080] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1280℃ and held for 35 hours to perform high-temperature diffusion homogenization. Then, it is upset, drawn, and forged into a billet. It is then upset and drawn in multiple directions (X, Y, and Z) to the finished size. Finally, it is heated to 1200℃ and held for 3 hours to directly draw and round the billet into a material.

[0081] S8. Post-forging heat treatment:

[0082] The forged billet obtained in step S7 is subjected to the following treatments: alternating water and air cooling until the core temperature reaches 430°C; air cooling for 20 minutes until the surface temperature reaches a maximum of 220°C; then it is placed in a heat treatment furnace, heated to 930°C, held for 18 hours, furnace cooled to 900°C, and then air cooled to 600°C. Finally, it is reheated to 660°C and held for 35 hours for normal tempering.

[0083] S9, post-forging machining

[0084] After the forging billet obtained in step S8 is inspected and flattened, rough machining is used to remove the surface iron oxide scale.

[0085] S10, Conditioning and tempering:

[0086] The workpiece obtained in step S9 is placed in a heating furnace and heated to 900°C, and held at that temperature for 25 hours. After holding, water is used for extreme cooling control, and the core temperature is 300°C after cooling. After cooling, the workpiece is placed in an annealing furnace, heated to 640°C, held at that temperature for 35 hours, and then removed from the furnace when the temperature drops to 300°C.

[0087] Example 2

[0088] A type of hot-work gear steel, by mass fraction, is basically composed of the elements shown in Table 2:

[0089] Table 2

[0090]

[0091] S1, Electric furnace smelting:

[0092] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1650℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag with a basicity range of 2.1. The molten steel in the electric furnace undergoes dephosphorization and desulfurization treatment. When the steel temperature reaches 1630℃, aluminum wire is added for deoxidation, and then the steel is tapped. Aluminum wire is added at a rate of 1 kg / t for deoxidation. The alloy materials are ferrochrome alloy, ferrovanadium alloy, ferrosilicon alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy, and ferromanganese alloy. After the scrap steel is added to the electric furnace and heated to complete melting, ferrosilicon alloy and ferromanganese alloy are added first.

[0093] S2, Ladle refining furnace refining:

[0094] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and pre-melted refining slag is added to reduce and create primary white slag, with CaO:Al2O3:MgO = 45:45:6. Based on the deviation between the actual and target compositions of the molten steel in the refining furnace base, appropriate alloy materials (ferrochrome alloy, ferrovanadium alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy) are added to complete composition fine-tuning, desulfurization, and deoxidation. After the operation, the white slag is removed, and the steel is reheated to a temperature of 1650℃. Pre-melted refining slag and red bricks are added for secondary white slag production. In the primary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg; in the secondary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg, and 2.0 kg of red bricks are added.

[0095] S3, Vacuum refining furnace refining:

[0096] The vacuum refining furnace is pumped in stages to achieve a final vacuum of 67 Pa. The vacuum is maintained for 20 minutes twice, with a nitrogen target value of 75-150 ppm. After degassing, samples are taken for analysis. Once the composition is qualified, argon gas is blown into the ladle. The argon blowing time is 15 minutes, and the ladle temperature is 1580℃.

[0097] S4. Casting electrode blank:

[0098] The ingot mold was preheated to 50℃, then argon gas was introduced into the mold for 5 minutes per mold. The argon gas pipe was then removed, the mold was covered, and casting was performed, followed by demolding. Throughout the casting process, the casting was protected with argon gas using an asbestos-lined cloth, with an argon gas flow rate of 20 m³ / h. 3 / h, casting time is 7min, electrode blank diameter is 730mm, demolding is performed after 5h;

[0099] S5. Electrode blank annealing:

[0100] The electrode blank after demolding in step S4 is annealed at 860℃ for 18 hours, then furnace cooled to 350℃ and removed from the furnace. After annealing, the riser and ingot tail are sawn off.

[0101] S6, Electroslag Remelting:

[0102] The electrode blank obtained in step S5 is surface-cleaned using a shot blasting machine to remove surface iron oxide scale, revealing a metallic luster; a dummy electrode is welded to the tail of the electrode blank, and then it is placed in an electroslag furnace; wherein, the dummy electrode is welded by welding an inverted electrode blank.

[0103] A ternary slag was prepared using CaF2, Al2O3, and CaO. The ternary slag was then pre-melted and subjected to secondary refining and purification to achieve a SiO2 content of 0.55% and an FeO content of 0.14%. The slag was then cooled to room temperature under a protective atmosphere.

[0104] The ternary slag is preheated to 800℃, and then added to an electroslag furnace for electroslag remelting to obtain electroslag ingots. The specific steps of electroslag remelting are as follows: the starting melting rate of the steady-state stage of electroslag smelting is 13 kg / min, the ending melting rate is 11 kg / min, and the electroslag ingots are obtained. Then the electric furnace is stopped and cooled for 100 minutes before being sent to the forging process.

[0105] S7, Forging:

[0106] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1280℃ and held for 35 hours to perform high-temperature diffusion homogenization. Then, it is upset, drawn, and forged into a billet. It is then upset and drawn in multiple directions (X, Y, and Z) to the finished size. Finally, it is heated to 1200℃ and held for 3 hours to directly draw and round the billet into a material.

[0107] S8. Post-forging heat treatment:

[0108] The forged billet obtained in step S7 is subjected to the following treatments after forging: alternating water and air cooling until the core temperature of the billet reaches 420°C; air cooling for 20 minutes until the highest surface temperature reaches 230°C; then it is placed in a heat treatment furnace, heated to 930°C, held for 18 hours, furnace cooled to 900°C, and then air cooled to 600°C. Finally, it is reheated to 660°C and held for 35 hours for normal tempering.

[0109] S9, post-forging machining

[0110] After the forging billet obtained in step S8 is inspected and flattened, rough machining is used to remove the surface iron oxide scale.

[0111] S10, Conditioning and tempering:

[0112] The workpiece obtained in step S9 is placed in a heating furnace and heated to 900°C, and held at that temperature for 25 hours. After holding, water is used for extreme cooling control, and the core temperature is 340°C after cooling. After cooling, the workpiece is placed in an annealing furnace, heated to 640°C, held at that temperature for 35 hours, and then removed from the furnace when the temperature drops to 300°C.

[0113] Example 3

[0114] A type of hot-work gear steel, by mass fraction, is basically composed of the elements shown in Table 3:

[0115] Table 3

[0116]

[0117] S1, Electric furnace smelting:

[0118] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1650℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag with a basicity range of 2.1. The molten steel in the electric furnace undergoes dephosphorization and desulfurization treatment. When the steel temperature reaches 1630℃, aluminum wire is added for deoxidation, and then the steel is tapped. Aluminum wire is added at a rate of 1 kg / t for deoxidation. The alloy materials are ferrochrome alloy, ferrovanadium alloy, ferrosilicon alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy, and ferromanganese alloy. After the scrap steel is added to the electric furnace and heated to complete melting, ferrosilicon alloy and ferromanganese alloy are added first.

[0119] S2, Ladle refining furnace refining:

[0120] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and pre-melted refining slag is added for reduction to create primary white slag, wherein CaO:Al2O3:MgO = 45:45:6. Based on the deviation between the actual and target compositions of the molten steel in the refining furnace base, appropriate alloy materials (ferrochrome alloy, ferrovanadium alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy) are added to complete composition fine-tuning, desulfurization, and deoxidation. After the operation, the white slag is removed, and the steel is reheated to a temperature of 1649℃. Pre-melted refining slag and red bricks are added for secondary white slag production. In the primary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg; in the secondary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg, and 2.0 kg of red bricks are added.

[0121] S3, Vacuum refining furnace refining:

[0122] The vacuum refining furnace is pumped in stages to achieve a final vacuum of 67 Pa. The vacuum is maintained for 20 minutes twice, with a nitrogen target value of 75-150 ppm. After degassing, samples are taken for analysis. Once the composition is qualified, argon gas is blown into the ladle. The argon blowing time is 25 minutes, and the ladle temperature is 1570℃.

[0123] S4. Casting electrode blank:

[0124] The ingot mold was preheated to 50℃, then argon gas was introduced into the mold for 5 minutes per mold. The argon gas pipe was then removed, the mold was covered, and casting was performed, followed by demolding. Throughout the casting process, the casting was protected with argon gas using an asbestos-lined cloth, with an argon gas flow rate of 20 m³ / h. 3 / h, casting time is 7min, electrode blank diameter is 730mm, demolding is performed after 5h;

[0125] S5. Electrode blank annealing:

[0126] The electrode blank after demolding in step S4 is annealed at 860℃ for 18 hours, then furnace cooled to 350℃ and removed from the furnace. After annealing, the riser and ingot tail are sawn off.

[0127] S6, Electroslag Remelting:

[0128] The electrode blank obtained in step S5 is surface-cleaned using a shot blasting machine to remove surface iron oxide scale, revealing a metallic luster; a dummy electrode is welded to the tail end of the electrode blank, and then it is placed in an electroslag furnace; wherein, the dummy electrode is welded using an inverted electrode blank.

[0129] A ternary slag was prepared using CaF2, Al2O3, and CaO. The ternary slag was then pre-melted and subjected to secondary refining and purification to achieve a SiO2 content of 0.55% and an FeO content of 0.14%. The slag was then cooled to room temperature under a protective atmosphere.

[0130] The ternary slag is preheated to 800℃, and then added to an electroslag furnace for electroslag remelting to obtain electroslag ingots. The specific steps of electroslag remelting are as follows: the starting melting rate of the steady-state stage of electroslag smelting is 13 kg / min, the ending melting rate is 11 kg / min, and the electroslag ingots are obtained. Then the electric furnace is stopped and cooled for 100 minutes before being sent to the forging process.

[0131] S7, Forging:

[0132] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1280℃ and held for 35 hours to perform high-temperature diffusion homogenization. Then, it is upset, drawn, and forged into a billet. It is then upset and drawn in multiple directions (X, Y, and Z) to the finished size. Finally, it is heated to 1200℃ and held for 3 hours to directly draw and round the billet into a material.

[0133] S8. Post-forging heat treatment:

[0134] The forged billet obtained in step S7 is subjected to the following treatments after forging: alternating water and air cooling until the core temperature of the billet reaches 440°C; air cooling for 20 minutes until the highest surface temperature reaches 220°C; then it is placed in a heat treatment furnace, heated to 930°C, held for 18 hours, furnace cooled to 900°C, and then air cooled to 600°C. Finally, it is reheated to 660°C and held for 35 hours for normal tempering.

[0135] S9, post-forging machining

[0136] After the forging billet obtained in step S8 is inspected and flattened, rough machining is used to remove the surface iron oxide scale.

[0137] S10, Conditioning and tempering:

[0138] The workpiece obtained in step S9 is placed in a heating furnace and heated to 900°C, and held at that temperature for 25 hours. After holding, water is used for extreme cooling control, and the core temperature is 315°C after cooling. After cooling, the workpiece is placed in an annealing furnace, heated to 640°C, held at that temperature for 35 hours, and then removed from the furnace when cooled to 300°C.

[0139] Example 4

[0140] A type of hot-work gear steel, by mass fraction, is basically composed of the elements shown in Table 4:

[0141] Table 4

[0142]

[0143] S1, Electric furnace smelting:

[0144] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1650℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag with a basicity range of 2.1. The molten steel in the electric furnace undergoes dephosphorization and desulfurization treatment. When the steel temperature reaches 1630℃, aluminum wire is added for deoxidation, and then the steel is tapped. Aluminum wire is added at a rate of 1 kg / t for deoxidation. The alloy materials are ferrochrome alloy, ferrovanadium alloy, ferrosilicon alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy, and ferromanganese alloy. After the scrap steel is added to the electric furnace and heated to complete melting, ferrosilicon alloy and ferromanganese alloy are added first.

[0145] S2, Ladle refining furnace refining:

[0146] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and pre-melted refining slag is added for reduction to create primary white slag, wherein CaO:Al2O3:MgO = 45:45:6. Based on the deviation between the actual and target compositions of the molten steel in the refining furnace base, appropriate alloy materials (ferrochrome alloy, ferrovanadium alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy) are added to complete composition fine-tuning, desulfurization, and deoxidation. After the operation, the white slag is removed, and the steel is reheated to a temperature of 1649℃. Pre-melted refining slag and red bricks are added for secondary white slag production. In the primary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg; in the secondary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg, and 2.0 kg of red bricks are added.

[0147] S3, Vacuum refining furnace refining:

[0148] The vacuum refining furnace is pumped in stages to achieve a final vacuum of 67 Pa. The vacuum is maintained twice for 20 minutes each time, with a nitrogen target value of 75-150 ppm. After degassing, samples are taken for analysis. Once the composition is deemed acceptable, argon gas is blown into the ladle. The argon blowing time is 30 minutes, and the ladle temperature is 1575℃.

[0149] S4. Casting electrode blank:

[0150] The ingot mold was preheated to 50℃, then argon gas was introduced into the mold for 5 minutes per mold. The argon gas pipe was then removed, the mold was covered, and casting was performed, followed by demolding. Throughout the casting process, the casting was protected with argon gas using an asbestos-lined cloth, with an argon gas flow rate of 20 m³ / h. 3 / h, casting time is 7min, electrode blank diameter is 730mm, demolding is performed after 5h;

[0151] S5. Electrode blank annealing:

[0152] The electrode blank after demolding in step S4 is annealed at 860℃ for 18 hours, then furnace cooled to 350℃ and removed from the furnace. After annealing, the riser and ingot tail are sawn off.

[0153] S6, Electroslag Remelting:

[0154] The electrode blank obtained in step S5 is surface-cleaned using a shot blasting machine to remove surface iron oxide scale, revealing a metallic luster; a dummy electrode is welded to the tail of the electrode blank, and then it is placed in an electroslag furnace; wherein, the dummy electrode is welded by welding an inverted electrode blank.

[0155] A ternary slag was prepared using CaF2, Al2O3, and CaO. The ternary slag was then pre-melted and subjected to secondary refining and purification to achieve a SiO2 content of 0.55% and an FeO content of 0.14%. The slag was then cooled to room temperature under a protective atmosphere.

[0156] The ternary slag is preheated to 800℃, and then added to an electroslag furnace for electroslag remelting to obtain electroslag ingots. The specific steps of electroslag remelting are as follows: the starting melting rate of the steady-state stage of electroslag smelting is 13 kg / min, the ending melting rate is 11 kg / min, and the electroslag ingots are obtained. Then the electric furnace is stopped and cooled for 100 minutes before being sent to the forging process.

[0157] S7, Forging:

[0158] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1280℃ and held for 35 hours to perform high-temperature diffusion homogenization. Then, it is upset, drawn, and forged into a billet. It is then upset and drawn in multiple directions (X, Y, and Z) to the finished size. Finally, it is heated to 1200℃ and held for 3 hours to directly draw and round the billet into a material.

[0159] S8. Post-forging heat treatment:

[0160] The forged billet obtained in step S7 is subjected to the following treatments after forging: alternating water and air cooling until the core temperature of the billet reaches 435°C; air cooling for 20 minutes until the highest surface temperature reaches 240°C; then it is placed in a heat treatment furnace, heated to 930°C, held for 18 hours, furnace cooled to 900°C, and then air cooled to 600°C. Finally, it is reheated to 660°C and held for 35 hours for normal tempering.

[0161] S9, post-forging machining

[0162] After the forging billet obtained in step S8 is inspected and flattened, rough machining is used to remove the surface iron oxide scale.

[0163] S10, Conditioning and tempering:

[0164] The workpiece obtained in step S9 is placed in a heating furnace and heated to 900°C, and held at that temperature for 25 hours. After holding, water is used for extreme cooling control, and the core temperature is 340°C after cooling. After cooling, the workpiece is placed in an annealing furnace, heated to 640°C, held at that temperature for 35 hours, and then removed from the furnace when the temperature drops to 300°C.

[0165] Example 5

[0166] A type of hot-work gear steel, by mass fraction, is basically composed of the elements shown in Table 5:

[0167] Table 5

[0168]

[0169] S1, Electric furnace smelting:

[0170] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1650℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag with a basicity range of 2.1. The molten steel in the electric furnace undergoes dephosphorization and desulfurization treatment. When the steel temperature reaches 1630℃, aluminum wire is added for deoxidation, and then the steel is tapped. Aluminum wire is added at a rate of 1 kg / t for deoxidation. The alloy materials are ferrochrome alloy, ferrovanadium alloy, ferrosilicon alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy, and ferromanganese alloy. After the scrap steel is added to the electric furnace and heated to complete melting, ferrosilicon alloy and ferromanganese alloy are added first.

[0171] S2, Ladle refining furnace refining:

[0172] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and pre-melted refining slag is added for reduction to create primary white slag, wherein CaO:Al2O3:MgO = 45:45:6. Based on the deviation between the actual and target compositions of the molten steel in the refining furnace base, appropriate alloy materials (ferrochrome alloy, ferrovanadium alloy, ferromolybdenum alloy, ferronickel alloy, ferroniobium alloy) are added to complete composition fine-tuning, desulfurization, and deoxidation. After the operation, the white slag is removed, and the steel is reheated to a temperature of 1649℃. Pre-melted refining slag and red bricks are added for secondary white slag production. In the primary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg; in the secondary white slag production, the amount of pre-melted refining slag added per ton of steel is 45 kg, and 2.5 kg of red bricks are added.

[0173] S3, Vacuum refining furnace refining:

[0174] The vacuum refining furnace is pumped in stages to achieve a final vacuum of 67 Pa. The vacuum is maintained for 20 minutes twice, and the target nitrogen value is 75~150 ppm. After degassing, the components are sampled and analyzed. After the components are qualified, argon gas is blown into the ladle. The argon blowing time is 39 minutes, and the ladle temperature is 1580℃.

[0175] S4. Casting electrode blank:

[0176] The ingot mold was preheated to 50℃, then argon gas was introduced into the mold for 5 minutes per mold. The argon gas pipe was then removed, the mold was covered, and casting was performed, followed by demolding. Throughout the casting process, the casting was protected with argon gas using an asbestos-lined cloth, with an argon gas flow rate of 20 m³ / h. 3 / h, casting time is 7min, electrode blank diameter is 730mm, demolding is performed after 5h;

[0177] S5. Electrode blank annealing:

[0178] The electrode blank after demolding in step S4 is annealed at 860℃ for 18 hours, then furnace cooled to 350℃ and removed from the furnace. After annealing, the riser and ingot tail are sawn off.

[0179] S6, Electroslag Remelting:

[0180] The electrode blank obtained in step S5 is surface-cleaned using a shot blasting machine to remove surface iron oxide scale, revealing a metallic luster; a dummy electrode is welded to the tail of the electrode blank, and then it is placed in an electroslag furnace; wherein, the dummy electrode is welded by welding an inverted electrode blank.

[0181] A ternary slag was prepared using CaF2, Al2O3, and CaO. The ternary slag was then pre-melted and subjected to secondary refining and purification to achieve a SiO2 content of 0.55% and an FeO content of 0.14%. The slag was then cooled to room temperature under a protective atmosphere.

[0182] The ternary slag is preheated to 800℃, and then added to an electroslag furnace for electroslag remelting to obtain electroslag ingots. The specific steps of electroslag remelting are as follows: the starting melting rate of the steady-state stage of electroslag smelting is 13 kg / min, the ending melting rate is 11 kg / min, and the electroslag ingots are obtained. Then the electric furnace is stopped and cooled for 100 minutes before being sent to the forging process.

[0183] S7, Forging:

[0184] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1280℃ and held for 35 hours to perform high-temperature diffusion homogenization. Then, it is upset, drawn, and forged into a billet. It is then upset and drawn in multiple directions (X, Y, and Z) to the finished size. Finally, it is heated to 1200℃ and held for 3 hours to directly draw and round the billet into a material.

[0185] S8. Post-forging heat treatment:

[0186] The forged billet obtained in step S7 is subjected to the following treatments: alternating water and air cooling until the core temperature reaches 440°C; air cooling for 20 minutes until the surface temperature reaches a maximum of 245°C; then it is placed in a heat treatment furnace, heated to 930°C, held for 18 hours, furnace cooled to 900°C, and then air cooled to 600°C. Finally, it is reheated to 660°C and held for 35 hours for normal tempering.

[0187] S9, post-forging machining

[0188] After the forging billet obtained in step S8 is inspected and flattened, rough machining is used to remove the surface iron oxide scale.

[0189] S10, Conditioning and tempering:

[0190] The workpiece obtained in step S9 is placed in a heating furnace and heated to 900°C, and held at that temperature for 25 hours. After holding, water is used for extreme cooling control, and the core temperature is 340°C after cooling. After cooling, the workpiece is placed in an annealing furnace, heated to 640°C, held at that temperature for 35 hours, and then removed from the furnace when the temperature drops to 300°C.

[0191] To verify the mechanical properties of the hot-work gear steel provided by the preparation method of this invention, the inventors took five samples of each of the gear steels obtained in Examples 1 to 5 for impact toughness testing. Simultaneously, samples were taken for a carburizing process (heating rate 1℃ / min before carburizing, carburizing temperature 930℃, holding time 30h) to test the grain size. The test data are shown in Table 6.

[0192] Table 6

[0193]

[0194] From Table 6 and Figures 1-5 visible:

[0195] 1. According to GB / T34474.1 (Series B), the banded microstructure is rated as Grade 1. The gear material exhibits uniform chemical composition, minimal microsegregation, and indistinct carbon-rich / depleted zones. This facilitates the complete dissolution of carbides during austenitization, reducing the quantity and size of undissolved carbides; further, the carbides are dispersed and precipitated during tempering, thereby improving transverse impact toughness.

[0196] 2. During the quenching process, most alloying elements of this gear material dissolve into the matrix and precipitate out from the matrix during tempering. These are mainly carbides (nitrides) of Al, Mo, Cr, V, and Nb. These fine precipitates play a dispersive strengthening role during use, improving the material's performance. The Charpy V-notch impact resistance of this gear material in the tooth region is ≥40J, and the average Charpy V-notch impact resistance is ≥45J.

[0197] 3. During the carburizing process, most alloying elements in this gear material dissolve into the matrix. However, the undissolved fine precipitates of Al, V, and Nb carbides (nitrides) act as uniform pinning agents to the austenite grain boundaries, effectively inhibiting abnormal austenite grain growth. The average grain size is ≥9, with no coarse grains below grade 5. This ensures good toughness in the gear teeth after carburizing.

[0198] Therefore, it can be seen that the gear steel prepared by this method has high toughness and high resistance to grain coarsening, which well meets the needs of large-size, heavy-duty gear production.

Claims

1. A method for preparing a carburized gear steel with high toughness and high resistance to grain coarsening, characterized in that, The main steps are as follows: S1, Electric furnace smelting: Based on the chemical composition content of the steel to be smelted, scrap steel and alloy materials of ferrochrome, ferrovanadium, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, and ferroniobium are prepared in advance. In the electric furnace, scrap steel is smelted in batches according to the smelting weight. The molten steel temperature is ≥1650℃ and the slag is removed by oxidation. After slag removal, ferrochrome, ferrovanadium, ferrosilicon alloy, lime and fluorite are added to adjust the chemical composition and dephosphorize. The tapping temperature is ≥1620℃. Aluminum wire is added during the tapping process for deoxidation. The chemical composition by mass percentage is as follows: C 0.16%~0.20%, Mn 0.50%~0.90%, Si 0.18%~0.35%, S≤0.002%, P≤0.010%, Cr 1.50%~1.80%, Mo 0.25%~0.35%, V 0.07%~0.12%, Ni 1.40%-1.70%, Al 0.02%~0.04%, Nb 0.02%~0.035%, N 75~150ppm, Cu≤0.10%, with the remainder being Fe. The residual gas content is as follows: H≤1.5ppm, O≤13ppm. S2, Ladle refining furnace refining: After smelting in the electric furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and refining pre-melted slag is added, wherein CaO:Al2O3:MgO=45:45:

6. Alloy materials are added according to the actual composition to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation is completed, the white slag is removed, and then the furnace is reheated and new slag is added to create white slag for the second time. S3, Vacuum refining furnace refining: The vacuum refining furnace is pumped in stages until the final vacuum degree is ≥67Pa. The vacuum time is maintained for more than 15 minutes, and the target value of residual hydrogen is ≤1.5ppm. After degassing, samples are taken for analysis. After the composition is qualified, argon gas is softly blown into the hoisting bag. S4. Casting electrode blank: Preheat the ingot mold to 40~70℃, then fill the ingot mold with argon gas for 3~6 minutes for each ingot mold, then remove the argon gas pipe, cover the ingot mold with a lid and then cast; S5. Electrode blank annealing: The electrode blank after demolding in step S4 is annealed, and the riser and ingot tail are sawn off after annealing. S6, Electroslag Remelting: The electrode blank obtained in step S5 is first subjected to surface machining on a lathe to remove the surface iron oxide scale; then, dummy electrode welding is performed. The smelting process employs a ternary slag system of calcium fluoride, alumina, and calcium oxide. The pre-melted slag system is purified through a secondary refining process, resulting in silica ≤0.6% and ferrous oxide ≤0.15%. S7, Forging: The electroslag ingot obtained in step S6 is heated and subjected to diffusion homogenization treatment at a temperature of 1260-1300℃ for 25-40 hours. Then, it is upsetting and drawing in three directions (X, Y, and Z) to form an intermediate billet. The billet is then reheated to 1150-1200℃ and held for 2-4 hours. Finally, it is drawn and rounded to the finished product, with a main deformation rate of ≥40% per pass. S8. Post-forging heat treatment: The forging billet obtained in step S7 is subjected to post-forging heat treatment: water-air alternating cooling until the core temperature of the billet is ≤450℃; air cooling for 15~20min, so that the highest surface temperature of the workpiece is 200-250℃, then it is placed in a heat treatment furnace, heated to 920~940℃, held for 15~20h, furnace cooled to 900℃, then removed from the furnace and air cooled to 550~650℃; reheated to 650~700℃, held for 25~40h for normal tempering treatment; S9. Post-forging machining: After the forging billet obtained in step S8 is inspected and flattened, rough machining is used to remove the surface iron oxide scale. S10, Conditioning and tempering: The workpiece obtained in step S9 is placed in a heating furnace and heated to 890~910℃, and held for 20~30h. After holding, water is used for extreme cooling control, and the core temperature is ≤350℃ after cooling. After cooling, the workpiece is placed in an annealing furnace, heated to 630~650℃, held for 25~40h, and removed from the furnace when the temperature is ≤350℃.

2. The method for preparing a high-toughness, high-resistance-to-grain-coarsening carburized gear steel according to claim 1, characterized in that, In step S1, during the tapping process, aluminum wire is added at a rate of 1 kg / t for deoxidation.

3. The method for preparing a high-toughness, high-resistance-to-grain-coarsening carburized gear steel according to claim 1 or 2, characterized in that, In step S2, 2-3 kg / ton of firebricks are added to the secondary white slag to adjust the slag fluidity, and AL wire is fed to control the aluminum content according to the target.

4. The method for preparing a high-toughness, high-resistance-to-grain-coarsening carburized gear steel according to claim 1 or 2, characterized in that, In step S3, the time for soft blowing of nitrogen is 15~39 min, the temperature of the hoisting bag is 1560~1580℃, and the nitrogen increase operation is completed, with a target range of [N] of 75~150 ppm.

5. The method for preparing a high-toughness, high-resistance-to-grain-coarsening carburized gear steel according to claim 1 or 2, characterized in that, In step S4, the casting process is protected by argon gas with asbestos cloth attached. The argon gas flow rate is 15~30 m3 / h, the casting time is 4~10 min, the electrode blank diameter is 400~908 mm, and the casting is demolded after 3~6 h.

6. The method for preparing a high-toughness, high-resistance-to-grain-coarsening carburized gear steel according to claim 1 or 2, characterized in that, In step S5, the annealing temperature is 860℃, the holding time is 1~1.5min / mm, and the furnace is cooled to 300~400℃ before being removed from the furnace.

7. The method for preparing a high-toughness, high-resistance-to-grain-coarsening carburized gear steel according to claim 1, characterized in that, In step S6, the dummy electrode welding is performed using inverted electrode blank welding.

8. The method for preparing a high-toughness, high-resistance-to-grain-coarsening carburized gear steel according to claim 7, characterized in that, In step S6, the starting melting rate of the steady-state stage of electroslag smelting is 13 kg / min, and the ending melting rate is 11 kg / min, resulting in an electroslag ingot. After cooling in the electric furnace for 90-120 minutes, it is sent to the forging process.

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