A casting process for large high carbon steel ingots

Abstract

The present invention relates to the technical field of steel ingot casting, and particularly to a casting process for large high-carbon steel ingots. The casting process comprises the following steps: first, adding carbon powder and lime to the bottom of the furnace, heating after power is applied, and adding alloy materials and auxiliary materials according to the material requirements; controlling the temperature of the molten steel in the molten pool to 1560°C and the slag content to ≤3%; then, performing oxygen blowing and fluxing, and transferring the molten steel to a ladle, adjusting the molten steel composition to obtain primary molten steel; transferring the ladle to an LF furnace for refining, adjusting the Ar gas pressure, applying power to uniformly slag, and adding SiC for deoxidation; after the slag color turns white, sampling and analysis are performed, and the chemical composition is adjusted to meet the process requirements before the ladle is hung; the ladle enters a VD furnace for vacuum refining, and after the composition test is qualified, the molten steel is transferred to the ladle; casting is performed, and after the casting is completed, casting is performed from the riser of the ingot mold to feed shrinkage; and after the casting is completed, annealing is performed. The casting process solves the technical problem of porosity and shrinkage cavities easily generated in large high-carbon steel ingots during casting.

Description

Technical Field

[0001] The invention relates to the technical field of steel ingot casting, in particular to a casting process for large high-carbon steel ingots. Background Art

[0002] High-carbon steel refers to steel with a carbon content ranging from 0.60% to 1.70%. It exhibits high strength and hardness and is specifically designed for toolmaking. The volumetric shrinkage of steel as it cools from liquid to room temperature consists of three components: liquidus shrinkage, solidification shrinkage, and solidus shrinkage. Liquidus shrinkage refers to the volumetric shrinkage that occurs when the pouring temperature drops to the liquidus temperature. This shrinkage is primarily dependent on the steel type, pouring temperature, and the liquidus temperature difference. Solidification shrinkage refers to the volumetric shrinkage during the liquid-solid transition from the beginning of solidification to complete solidification. Solidification shrinkage is related to the composition of the molten steel and the liquidus-solidus temperature difference. Generally speaking, steel with a carbon content of 0.6% to 1.0% experiences greater solidification shrinkage because the smaller (denser) gamma phase solidifies first, rather than the larger δ phase, in this carbon content range. Furthermore, the solidus-liquidus temperature difference is larger. Solidification shrinkage is directly related to the low-magnification structure of the ingot, making high-carbon steel prone to shrinkage cavities and porosity. Solidus shrinkage refers to the volumetric shrinkage that occurs when the solid state cools to room temperature after solidification. It is not only related to the chemical composition of the steel, but also to phase changes. For example, when δ → γ, the volume will shrink, and when γ → α, it will expand. In the absence of phase change, a decrease in temperature will cause shrinkage.

[0003] Phase transformation and solid-state shrinkage will generate structural stress and thermal stress, which will cause ingot cracks if not properly controlled. Due to the shrinkage characteristics of high-carbon steel, porosity is easily generated below the riser during bottom casting, affecting the quality of the ingot. The existing casting process is to use one ladle of molten steel to cast two trays of ingots, one tray of 40 tons and one tray of 20 tons. The casting method is to first heat the molten steel to 1495℃, and then cast a large 40-ton ingot and then a small 20-ton ingot by bottom casting. This casting method results in a high molten steel temperature when the large ingot is cast first, and a low molten steel temperature when the small ingot is cast later. Large high-carbon steel ingots are prone to defects such as porosity and shrinkage cavities during casting; high-carbon steel furnace matching also has the problem of poor casting.

[0004] Due to the wide solidification range of high-carbon steel, segregation is prone to occur during ingot solidification. Excessively high casting temperatures can easily produce columnar or transgranular structures, leading to central porosity, shrinkage cavities, and increased segregation. Corrosion of the refractory can easily cause loss of control or steel leakage in the casting control system, increasing the presence of non-metallic inclusions in the steel. Excessively low casting temperatures can easily cause the tundish nozzle to freeze, forcing casting to be interrupted and potentially deteriorating the surface quality of the ingot. Summary of the Invention

[0005] Aiming at the technical problem in the prior art that large high-carbon steel ingots are prone to porosity and shrinkage during casting, the present invention provides a casting process for large high-carbon steel ingots.

[0006] The technical solutions of the present invention are as follows:

[0007] A casting process for a large high-carbon steel ingot comprises the following steps:

[0008] (1) Electric furnace smelting: 500~1000kg of carbon powder and 900~1500kg of lime are added to the bottom of the furnace in advance, and then the furnace is heated after power is turned on. The alloy materials and auxiliary materials required for smelting are added multiple times according to the material requirements; the temperature of the molten steel in the molten pool is controlled to 1560℃, and the slag volume is controlled to be ≤3%; then oxygen blowing is carried out to assist fluxing. After the oxygen blowing is completed, the molten steel is transferred to the ladle, and the composition of the molten steel is adjusted in the ladle to obtain the primary molten steel. The primary molten steel is sampled for the first time during the off-furnace refining, and the C content in the molten steel is ≥0.45%;

[0009] (2) Refining outside the furnace: The ladle of primary molten steel is transferred to the LF furnace for refining. The Ar gas pressure is adjusted to ensure that the molten steel is slightly exposed to the slag surface. After the power is turned on, the slag is evenly slaged and 1~3kg / t of SiC powder is added for deoxidation. After the slag color turns white, the reduction time is ≥18min, and then sampling and analysis are performed at a temperature ≥1590℃. The chemical composition is adjusted to the process requirements based on the sampling analysis. After the slag is adjusted, the ladle is hung;

[0010] (3) Vacuum refining: Check the VD furnace equipment, adjust the steam pressure, and blow Ar gas; after the vacuum refining is completed, take samples for analysis, and adjust the composition of the molten steel according to the analysis results. After the composition test is qualified, the molten steel is transferred to the hanging bag;

[0011] (4) Casting: Control the temperature of the molten steel in the ladle to 1498~1500℃, and use the bottom casting method to cast under the protection of Ar gas. After the casting is completed, cast from the riser of the ingot mold to feed the shrinkage. The casting amount at the riser is 300~500kg;

[0012] (5) Annealing: The annealing process of the steel ingot after demolding is divided into hot ingot annealing and cold ingot annealing.

[0013] Furthermore, after the oxygen blowing and fluxing in step (1) is completed, the endpoint [C] target value is controlled to be ≥0.04%, the [P] target value is ≤0.006%, and the tapping temperature of the molten steel transferred to the ladle is ≥1650°C; during the composition adjustment process in the ladle, a recarburizer, a deoxidizer, molten steel, and slag are added to the ladle in sequence to obtain a primary molten steel; the composition of the primary molten steel is C: 0.50%~0.60%, Si: 0.35%~0.47%, Mn: 0.35%~0.47%, P≤0.013%, Cr: 2.75%~2.90%, Mo: 0.20%~0.27%, and the remainder is Fe and other inevitable impurities; when adding the molten steel, it is strictly forbidden for the upper floating slag to flow out.

[0014] Furthermore, the deoxidizer is Al, and the addition amount is 1 kg / t; the slag material is lime, and the addition amount is 15 kg / t.

[0015] Furthermore, the refining process outside the furnace includes the following steps:

[0016] A1: Adjust the slag condition. When the slag color turns white, the white slag reduction time is ≥18 min, and the temperature is ≥1590°C, take samples for analysis, and adjust the composition based on the results of the sampling and analysis.

[0017] A2 white slag is kept for ≥25min, deoxidizer SiC powder is added, white slag is kept in the furnace and the temperature is adjusted to 1620~1630℃;

[0018] A3 adjusts the chemical composition to the process requirements: add recarburizer or ferroalloy, and take a second sample analysis after the addition time is ≥8 minutes. Adjust the slag basicity to 2.5~3.0 5 minutes before the ladle is released. After the chemical composition of the molten steel meets the specified process requirements, start hanging the ladle; before the ladle is placed into the VD furnace, add Al wire at a rate of 3m / t; add Ca-Si wire at a rate of 2m / t.

[0019] Furthermore, the vacuum refining process comprises the following steps:

[0020] B1 Adjust the steam pressure of the VD furnace equipment to make the vacuum degree 66.7Pa, the time for the ladle to enter the VD furnace from the LF furnace ≤ 8min, the vacuum refining time ≥ 18min, and the Ar gas pressure 0.2~0.5Mpa;

[0021] After B2 vacuum refining is completed, samples are taken for analysis. Based on the analysis results, Al wire is added to the molten steel until the Al content reaches 0.025%. The H content and O content are controlled according to the requirements of the steel grade or ingot shape.

[0022] After the B3 content is tested to be qualified, the molten steel is transferred to the ladle and Ar gas is blown statically for 10 to 15 minutes. The Ar gas pressure is adjusted so that the molten steel does not overflow the slag surface.

[0023] Furthermore, the casting comprises the following steps:

[0024] C1 controls the temperature of the molten steel in the ladle. Under Ar gas protection, the bottom casting method is used to cast the small-sized ingot mold I. Increasing the pouring temperature to 1498~1500℃ can extend the solidification time and reduce the shrinkage of the ingot.

[0025] After the C2 ingot mold I is cast, the large-sized ingot mold II is cast using the bottom casting method;

[0026] After the casting of C3 ingot mold II is completed, casting is carried out from the riser of ingot mold I to feed the shrinkage. The casting amount is 300~500kg.

[0027] Furthermore, the riser of the ingot mold is in the shape of an inverted truncated cone, and the height of the riser is increased from 800mm to 1600mm, thereby increasing the pressure of the molten steel when being poured from the riser; the taper of the ingot mold is 3%.

[0028] Furthermore, hot ingot annealing: the hot ingot is demoulded and loaded into the furnace. When the temperature of the steel ingot drops to 600~700℃, heating is started, and the heating rate is ≤100℃ / h. When the temperature reaches 820±10℃, insulation is started. After the insulation time is up, the temperature is lowered with the furnace, and the cooling rate is ≤40℃ / h. When the temperature of the steel ingot is lower than 500℃, it is taken out of the furnace and air-cooled.

[0029] Furthermore, cold ingot annealing: the cold ingot is loaded into the furnace and started to be heated at a heating rate of ≤100℃ / h. After the temperature reaches 600±10℃, it is started to be kept warm. After keeping warm for 3 hours, it is heated again at a heating rate of ≤100℃ / h. After the temperature reaches 820±10℃, it is started to be kept warm. After the keeping warm time is up, the temperature is lowered with the furnace at a cooling rate of ≤40℃ / h. When the temperature of the steel ingot is lower than 500℃, it is taken out of the furnace and air-cooled. Q is the weight of the steel ingot in tons.

[0030] Furthermore, the holding time at 820±10°C = 7+Q / 4; the holding time is in h, and Q is the weight of the steel ingot in tons.

[0031] The beneficial effects of the present invention are:

[0032] (1) The present invention solves the problem of too low casting temperature when casting small steel ingots by increasing the casting temperature by 3-5°C and adjusting the casting sequence; casting the small steel ingots first can effectively reduce the casting time and reduce the degree of temperature drop of the molten steel in the ladle compared to casting the large steel ingots first.

[0033] (2) In the present invention, after the large ingot is cast, molten steel is added to the riser of the small ingot. On the one hand, this can keep the small ingot warm; the temperature of the added molten steel is 300-500°C higher than the temperature of the upper part of the small ingot, which can effectively slow down the cooling rate at the riser of the small ingot; on the other hand, due to the shrinkage characteristics of high carbon steel, the added molten steel can make up for the volume left after the high carbon steel shrinks.

[0034] (3) The present invention has modified the riser and ingot taper of the large steel ingot. Without reducing the riser, the riser is made into an inverted truncated cone shape and the riser height is increased. This method can increase the pressure at the riser during casting and effectively reduce the problem of looseness of the large steel ingot. At the same time, the taper of the ingot mold is appropriately increased, which is more conducive to concentrating the shrinkage and looseness defects of the steel ingot at the riser. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0036] Figure 1 It is a cross-sectional schematic diagram of the improved ingot mold and riser.

[0037] Figure 2 It is a cross-sectional schematic diagram of the original ingot mold and riser.

[0038] In the figure, 1-ingot mold body, 2-riser. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0040] Example 1

[0041] A casting process for a large high-carbon steel ingot comprises the following steps:

[0042] (1) Electric furnace smelting: 600 kg of carbon powder and 900 kg of lime were added to the bottom of the furnace in advance. After the furnace was powered on and heated, the alloy materials and auxiliary materials required for smelting were added several times according to the material requirements. The molten pool temperature was controlled at 1560 ° C and the slag volume was 3%. Oxygen blowing was then performed to assist fluxing. After the oxygen blowing was completed, the end point [C] target value was controlled to be 0.05%, and the [P] target value was controlled to be 0.003%. The temperature when the steel was transferred to the ladle was 1680 ° C. Recarburizer, deoxidizer, molten steel, and slag were added to the ladle in sequence to obtain primary molten steel. The deoxidizer was Al, and the addition amount was 1 kg / t. The slag was lime, and the addition amount was 15 kg / t. The final primary molten steel composition was C 0.52%, Si 0.35%, Mn 0.35%, P 0.010%, Cr 2.75%, Mo 0.20%, and the balance was Fe and other unavoidable impurities.

[0043] (2) The ladle containing the primary molten steel melted in the electric furnace is transferred to the LF furnace for refining. The refining process outside the furnace includes the following steps:

[0044] A1 adjusts the slag condition, turns the slag color to white, and reduces the white slag to 25 minutes. Initial sampling and analysis are performed at a temperature of 1590°C. Subsequent composition adjustments are made based on the sampling and analysis results.

[0045] A2 white slag is kept for 25 minutes, and the Ar gas pressure is adjusted to ensure that the molten steel is slightly exposed on the slag surface. After power is turned on, the slag is evenly dissolved and 1kg / t of SiC powder is added. The reducing atmosphere in the furnace is maintained and the temperature is adjusted to 1630℃.

[0046] A3 adds recarburizer and ferroalloy, and takes a second sample analysis 10 minutes after addition. Based on the analysis results, adjust the chemical composition to the process requirements; adjust the slag basicity to 2.5 5 minutes before unloading, and then start hanging the bag; before the bag is hoisted into the VD furnace, add Al wire at a rate of 3m / t; add Ca-Si wire at a rate of 2m / t;

[0047] (3) The vacuum refining process includes the following steps:

[0048] B1 Check the VD furnace equipment and adjust the steam pressure; make the vacuum degree 66.7Pa, the time for the ladle to enter the VD furnace from the LF furnace is 8min, the vacuum refining time is 18min, and the Ar gas pressure is 0.2Mpa;

[0049] After B2 vacuum refining is completed, samples are taken for analysis. Based on the analysis results, Al wire is added to the molten steel until the Al content reaches 0.025%. The H content and O content are controlled according to the requirements of the steel grade or ingot shape.

[0050] After the B3 content is tested and found to be qualified, the molten steel is transferred to a hanging ladle and Ar gas is blown statically for 10 minutes. The Ar gas pressure is adjusted so that the molten steel does not overflow from the slag surface.

[0051] (4) Casting includes the following steps:

[0052] C1 controls the temperature of the molten steel in the ladle to 1498℃, and uses the bottom casting method to cast the 20t scale steel ingot mold I under the protection of Ar gas;

[0053] After the C2 ingot mold I is cast, the 40t scale ingot mold II is cast using the bottom casting method;

[0054] After the casting of C3 ingot mold II is completed, casting and feeding are carried out from the riser of ingot mold I; the casting amount at the riser is 300kg; the size of the riser of ingot mold I is φ350 / φ200×1600mm; the size of the riser of ingot mold II is φ1100 / φ800×1600mm, and the taper of the ingot mold is 3%; the structural cross-section of the ingot mold is shown in Figure 1 ;

[0055] (5) Annealing is carried out using the hot ingot annealing process; the annealing steps are as follows: the hot ingot is demoulded and loaded into the furnace. When the temperature of the ingot drops to 700°C, heating is started at a heating rate of 90°C / h. When the temperature reaches 820°C, insulation is started for a time of 7h+Q / 4h. After the insulation time is up, the temperature is lowered with the furnace at a cooling rate of 40°C / h. When the temperature of the ingot is lower than 500°C, it is taken out of the furnace and air-cooled. The insulation time of a 20t ingot is 12h; the insulation time of a 40t ingot is 17h.

[0056] Example 2

[0057] A casting process for a large high-carbon steel ingot comprises the following steps:

[0058] (1) Electric furnace smelting: 1000 kg of carbon powder and 1500 kg of lime are added to the bottom of the furnace in advance, and then the furnace is powered on for heating. The alloy materials and auxiliary materials required for smelting are added multiple times according to the material requirements; the molten pool temperature is controlled at 1560 ° C and the slag volume is 3%; oxygen blowing is then performed to assist fluxing. After the oxygen blowing is completed, the end point [C] target value and [P] target value are controlled at 0.08% and 0.004%, respectively. The temperature when the steel is transferred to the ladle is 1700 ° C; recarburizer, deoxidizer, molten steel and slag are added to the ladle in sequence to obtain primary molten steel; the deoxidizer is Al, and the addition amount is 1 kg / t; the slag is lime, and the addition amount is 15 kg / t; the final primary molten steel composition is C 0.55%, Si 0.37%, Mn 0.47%, P 0.007%, Cr 2.90%, Mo 0.27%, and the balance is Fe and other unavoidable impurities;

[0059] (2) The ladle containing the primary molten steel melted in the electric furnace is transferred to the LF furnace for refining. The refining process outside the furnace includes the following steps:

[0060] A1 adjusts the slag condition, turns the slag color to white, and reduces the white slag to 25 minutes. Initial sampling and analysis are performed at a temperature of 1600°C. Subsequent composition adjustments are made based on the sampling and analysis results.

[0061] A2 white slag is kept for 30 minutes, and the Ar gas pressure is adjusted to ensure that the molten steel is slightly exposed on the slag surface. After power is turned on, the slag is evenly dissolved and 3kg / t of SiC powder is added. The reducing atmosphere in the furnace is maintained and the temperature is adjusted to 1620℃.

[0062] A3 adds recarburizer and ferroalloy, and takes a second sample analysis 10 minutes after addition. Based on the analysis results, adjust the chemical composition to the process requirements; adjust the slag basicity to 2.5 5 minutes before unloading, and then start hanging the bag; before the bag is hoisted into the VD furnace, add Al wire at a rate of 3m / t; add Ca-Si wire at a rate of 2m / t;

[0063] (3) The vacuum refining process includes the following steps:

[0064] B1 Check the VD furnace equipment and adjust the steam pressure; make the vacuum degree 66.7Pa, the time for the ladle to enter the VD furnace from the LF furnace is 5min, the vacuum refining time is 25min, and the Ar gas pressure is 0.5Mpa;

[0065] After B2 vacuum refining is completed, samples are taken for analysis. Based on the analysis results, Al wire is added to the molten steel until the Al content reaches 0.025%. The H content and O content are controlled according to the requirements of the steel grade or ingot shape.

[0066] After the B3 content is tested and found to be qualified, the molten steel is transferred to the hanging ladle and Ar gas is blown statically for 15 minutes. The Ar gas pressure is adjusted so that the molten steel does not turn over the slag surface.

[0067] (4) Casting includes the following steps:

[0068] C1 controls the temperature of the molten steel in the ladle to 1500℃ and uses the bottom casting method to cast the 20t scale steel ingot mold I under the protection of Ar gas;

[0069] After the C2 ingot mold I is cast, the 40t scale ingot mold II is cast using the bottom casting method;

[0070] After the casting of C3 ingot mold II is completed, casting and feeding are carried out from the riser of ingot mold I; the casting amount at the riser is 500kg; the size of the riser of ingot mold I is φ350 / φ200×1600mm; the size of the riser of ingot mold II is φ1100 / φ800×1600mm; the taper of the ingot mold is 3%; the structural cross-section of the ingot mold is shown in Figure 1 ;

[0071] (5) The cold ingot annealing process is used for annealing. The cold ingot annealing steps are as follows: the cold ingot is loaded into the furnace and heated at a heating rate of 100℃ / h. The temperature is raised to 600℃ and then kept warm. After keeping warm for 3 hours, the ingot is heated again at a heating rate of 100℃ / h. The temperature is raised to 830℃ and then kept warm. The holding time = 7h+Q / 4h. After the holding time is up, the ingot is cooled with the furnace at a cooling rate of 30℃ / h. When the ingot temperature is lower than 500℃, it is taken out of the furnace and air-cooled. The holding time of 20t ingot is 12h, and the holding time of 40t ingot is 17h.

[0072] Comparative Example 1

[0073] The same casting method as in Example 1 was used, except that the ingot mold before the improvement was used during the casting process. The size of the riser of the ingot mold was φ150 / φ150×800mm, and the taper of the ingot mold was 3%; see Figure 2 ; The mechanical properties of the steel ingots obtained in Example 1 and Comparative Example 1 were tested, and it was found that the compressive strength of the steel ingot of Comparative Example 1 was lower than the strength of the steel ingot of Example 1, and the internal structure of the steel ingot of Comparative Example 1 was looser than the internal structure of the steel ingot of Example 1.

[0074] Although the present invention has been described in detail with reference to the accompanying drawings and in conjunction with preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, persons of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be easily conceived by persons skilled in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention.

Claims

1. A casting process for large high carbon steel ingots, characterized in that: The following steps are involved: (1) Electric furnace smelting: 500~1000kg of carbon powder and 900~1500kg of lime are added to the bottom of the furnace in advance, and then the furnace is heated after power is turned on. The alloy materials and auxiliary materials required for smelting are added according to the material requirements; the temperature of the molten steel in the molten pool is controlled to 1560℃, and the slag volume is ≤3%; then oxygen blowing is carried out to assist fluxing. After the oxygen blowing is completed, the molten steel is transferred to the ladle, and the composition of the molten steel is adjusted in the ladle to obtain the primary molten steel. The primary molten steel is sampled for the first time during the off-furnace refining, and the C content in the molten steel is ≥0.45%; (2) Refining outside the furnace: The ladle of primary molten steel is transferred to the LF furnace for refining. The Ar gas pressure is adjusted to ensure that the molten steel is slightly exposed to the slag surface. After the power is turned on, the slag is evenly slaged and 1~3kg / t of SiC powder is added for deoxidation. After the slag color turns white, the reduction time is ≥18min, and then sampling and analysis are performed at a temperature ≥1590℃. The chemical composition is adjusted to the process requirements based on the sampling analysis. After the slag is adjusted, the ladle is hung; (3) Vacuum refining: Check the VD furnace equipment, adjust the steam pressure, and blow Ar gas; after the vacuum refining is completed, take samples for analysis, and adjust the composition of the molten steel according to the analysis results. After the composition test is qualified, start hanging the ladle; (4) Casting: Control the temperature of the molten steel in the ladle to 1498~1500℃, and use the bottom casting method to cast under the protection of Ar gas. After the casting is completed, cast from the riser of the ingot mold to feed the shrinkage. The casting amount at the riser is 300~500kg; (5) Annealing: After demoulding, the annealing process of the steel ingot is hot ingot annealing or cold ingot annealing; Casting includes the following steps: C1 uses the bottom casting method to cast the small-sized steel ingot mold I; After the C2 ingot mold I is cast, the large-sized ingot mold II is cast using the bottom casting method. The weight of the ingot mold II is greater than that of the ingot mold I. After the casting of C3 steel ingot mold II is completed, casting and feeding are carried out from the riser of steel ingot mold I; The riser of the ingot mold is an inverted cone type, and the taper of the ingot mold is 3%.

2. A casting process for a large high carbon steel ingot according to claim 1, characterized in that: After the oxygen blowing and fluxing in step (1) is completed, the endpoint [C] target value is controlled to be ≥0.04%, the [P] target value is ≤0.006%, and the tapping temperature of the molten steel transferred to the ladle is ≥1650°C; during the composition adjustment process in the ladle, a recarburizer, a deoxidizer, molten steel, and slag are added to the ladle in order to obtain primary molten steel; The chemical composition of the primary steel liquid is C: 0.50%~0.60%, Si: 0.35%~0.47%, Mn: 0.35%~0.47%, P≤0.013%, Cr: 2.75%~2.90%, Mo: 0.20%~0.27%, and the balance is Fe and other inevitable impurities.

3. A casting process for a large high carbon steel ingot as claimed in claim 2, characterized in that: The deoxidizer is Al, and the addition amount is 1kg / t; the slag is lime, and the addition amount is 15kg / t.

4. The casting process of a large high carbon steel ingot according to claim 1, characterized in that: The refining process outside the furnace includes the following steps: A1: Adjust the slag condition. When the slag color turns white, the white slag reduction time is ≥18 min, and the temperature is ≥1590°C, take samples for analysis, and adjust the composition based on the results of the sampling and analysis. A2 white slag is kept for ≥25min, deoxidizer SiC powder is added, white slag is kept in the furnace and the temperature is adjusted to 1620~1630℃; A3 adds recarburizer or ferroalloy, and takes a second sampling analysis after the addition time is ≥8 minutes, and adjusts the chemical composition to the process requirements; adjusts the slag basicity to 2.5~3.0 5 minutes before the ladle is taken out, and starts hanging the ladle after the chemical composition of the molten steel meets the specified process requirements; before the ladle is hoisted into the VD furnace, add Al wire at a rate of 3m / t; add Ca-Si wire at a rate of 2m / t.

5. The casting process of a large high carbon steel ingot according to claim 1, characterized in that: The vacuum refining process includes the following steps: B1 Adjust the steam pressure of the VD furnace equipment to make the vacuum degree 66.7Pa, the time for the ladle to enter the VD furnace from the LF furnace ≤ 8min, the vacuum refining time ≥ 18min, and the Ar gas pressure 0.2~0.5Mpa; After B2 vacuum refining is completed, samples are taken for analysis. Based on the analysis results, Al wire is added to the molten steel until the Al content reaches 0.025%. The H content and O content are controlled according to the requirements of the steel grade or ingot shape. After the B3 content is tested to be qualified, the molten steel is transferred to the ladle and Ar gas is blown statically for 10 to 15 minutes. The Ar gas pressure is adjusted so that the molten steel does not overflow the slag surface.

6. The casting process of a large high carbon steel ingot according to claim 1, characterized in that: The hot ingot annealing step in step (5) is as follows: after the hot ingot is demoulded, it is loaded into the furnace. When the temperature of the steel ingot drops to 600-700°C, heating is started at a heating rate of ≤100°C / h. When the temperature reaches 820±10°C, insulation is started. After the insulation time is up, the temperature is lowered with the furnace at a cooling rate of ≤40°C / h. When the temperature of the steel ingot is lower than 500°C, it is taken out of the furnace and air-cooled.

7. The casting process of a large high carbon steel ingot according to claim 1, characterized in that: Annealing of cold ingot in step (5): the cold ingot is loaded into the furnace and heated at a heating rate of ≤100℃ / h. After the temperature reaches 600±10℃, it is kept warm. After keeping warm for 3 hours, it is heated again at a heating rate of ≤100℃ / h. After the temperature reaches 820±10℃, it is kept warm. After the holding time is up, the temperature is lowered with the furnace at a cooling rate of ≤40℃ / h. When the temperature of the ingot is lower than 500℃, it is taken out of the furnace and air-cooled.

8. A casting process for a large high carbon steel ingot according to claim 6 or 7, characterized in that: Holding time at 820±10℃ = 7+Q / 4; the holding time is in h, and Q is the weight of the steel ingot in tons.

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