Refined cast steel and method of production

Abstract

The present application relates to the technical field of refined steel material, in particular to a refined cast steel and a preparation method, which comprises the following raw materials in mass ratio: 800 parts of scrap steel with C content of 0.1%, 200 parts of pig iron with C content of 3.5%, 18.5 parts of manganese iron, 24 parts of chromium iron, 5 parts of metallic nickel, 3 parts of molybdenum iron, 0.2 parts of vanadium iron, 0.02 parts of boron iron, and 11.5 parts of deoxidizer; wherein the deoxidizer comprises 10 parts of silicon iron for pre-deoxidization and 1.5 parts of aluminum for final deoxidization; the prepared refined cast steel contains 0.25% of C, 1.7% of Mn, 2.3% of Cr, 0.5% of Ni, 0.3% of Mo, 0.09% of V, and 0.0035% of B, and the rest is Fe; the refined cast steel is subjected to dephosphorization and desulfurization treatment by slagging and slag making, and meanwhile, the argon blowing step in the pouring process is adopted; the preliminary treatment is rapidly realized by using the reactivity of active gas, the side effects in the early stage are eliminated by using the inertness and stirring capacity of argon, deep refining is realized, and the P and S elements in the refined cast steel are effectively controlled.

Description

A Refined Cast Steel and its Preparation Method Technical Field

[0001] This invention relates to the field of refined steel materials technology, specifically to a refined cast steel and its preparation method. Background Technology

[0002] Refined cast steel refers to a class of engineering materials that have undergone specific refining processes to optimize cast steel (steel produced by casting) in order to improve its purity, compositional uniformity and mechanical properties.

[0003] Cast steel is an iron-based material with a carbon content typically between 0.1% and 0.6% (as opposed to cast iron). It is produced directly as part blanks through smelting and casting (such as sand casting and investment casting). Its advantage is that it can form complex structures, but its disadvantages include potential problems such as porosity, shrinkage cavities, and compositional segregation.

[0004] In the steelmaking or casting process, impurities (such as sulfur, phosphorus, gases [H / N / O], inclusions) in molten steel are removed by ladle refining techniques (such as LF furnace refining, VD vacuum degassing, VOD vacuum oxygen blowing decarburization, etc.) or post-casting heat treatment, the alloy composition is adjusted, the microstructure uniformity is improved, and thus the performance is enhanced.

[0005] However, current refined cast steel has problems with excessive S / P ratio or high P content. The main reason for this problem is that P and S elements are not fully oxidized during the refining process.

[0006] For example, the invention patent with patent application number 202411220974.0 specifically discloses a multi-functional refining device for cast steel. By setting up a dephosphorization device, the injection of oxygen increases the oxygen activity in the molten steel, which improves the oxidation rate of phosphorus in the molten steel and helps to more effectively separate phosphorus-containing slag from the molten steel.

[0007] Therefore, in the process of refining cast steel, it is necessary to effectively control the sufficiency of oxidation of P and S elements. Summary of the Invention

[0008] To address the above problems, this invention provides a refined cast steel and its preparation method. The refined cast steel undergoes dephosphorization and desulfurization treatment through slag removal and slag formation. Simultaneously, an argon blowing step is incorporated into the casting process. This argon blowing involves injecting nitrogen, carbon monoxide, water vapor, and air into the molten steel, followed by the introduction of argon. The reactivity of these active gases rapidly achieves preliminary treatment, while the inertness and stirring ability of argon eliminate early side effects, achieving deep refining and effective control of P and S elements within the refined cast steel.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A refined cast steel comprises the following raw materials in the following mass ratio:

[0011] 800 parts of scrap steel with a carbon content of 0.1%, 200 parts of pig iron with a carbon content of 3.5%, 18.5 parts of ferromanganese, 24 parts of ferrochrome, 5 parts of metallic nickel, 3 parts of ferromolybdenum, 0.2 parts of ferrovanadium, 0.02 parts of ferroboron, and 11.5 parts of deoxidizer.

[0012] The deoxidizer includes 10 parts of ferrosilicon for pre-deoxidation and 1.5 parts of aluminum for final deoxidation.

[0013] The refined cast steel produced contains 0.25% C, 1.7% Mn, 2.3% Cr, 0.5% Ni, 0.3% Mo, 0.09% V, 0.0035% B, and the remainder is Fe.

[0014] Furthermore, the present invention replaces the method for preparing the above-described refined cast steel, and includes the following steps:

[0015] Step a: Loading. Lay 10 parts of ferrosilicon and 5 parts of ferromanganese at the bottom of the electric arc furnace, and load 800 parts of scrap steel and 200 parts of pig iron on the top layer. Load 5 parts of alloy nickel plate along with the scrap steel.

[0016] Step b, slag removal and slag making: After melting and cleaning, remove the initial slag, add 50 parts of lime and 10 parts of fluorite as slag-making materials, raise the temperature to 1620℃, hold for 10 minutes, and dephosphorize and desulfurize to S≤0.02% and P≤0.025%.

[0017] Step c, alloying: At 1620℃, add 24 parts of ferrochrome and 3 parts of ferromolybdenum, stir and keep warm for 15 minutes to ensure complete dissolution. At 1600℃, add the remaining 13.5 parts of ferromanganese and stir for 5 minutes. 10 minutes before tapping, at 1580℃, first add 0.1 parts of ferrovanadium and stir for 3 minutes, then add 1.5 parts of aluminum ingot, 0.02 parts of ferroboron, and the remaining 0.09 parts of ferrovanadium. Stir rapidly for 2 minutes to avoid boron oxidation and burn-off. Then, power on for melting, gradually increasing the power to 400kW. During the melting period, the temperature is controlled at 1550-1600℃, and the melting time is 60-70 minutes.

[0018] Step d: Adjust the composition and perform spectral analysis. If C is insufficient, add ≤0.1% carbon powder; if S / P exceeds the standard, add lime and fluorite for slag treatment.

[0019] Step e: Casting. At 1520-1540℃, pour molten steel into the resin sand mold at a pouring speed of 5-15 kg / s, keeping the pouring cup fully filled. After pouring, allow the sand mold temperature to drop to ≤200℃ for 4-6 hours.

[0020] Step f: Heat treatment. Immediately after unpacking, the product is transferred to an annealing furnace for annealing, normalizing, and annealing treatment in sequence.

[0021] As an improvement, in step f, the initial annealing is heated to 500℃ at a rate of 50℃ / h, held for 2 hours, and then cooled to room temperature in the furnace to eliminate casting stress. The normalizing treatment is heated to 920±10℃, and the holding time is calculated based on the workpiece thickness of 1mm / min. The air speed is 5-10m / s, and the cooling is uniform. The tempering treatment is heated to 620±10℃, with a target hardness of HB220-250. The holding time is the same as that of normalizing. The furnace is heated, and after holding, the furnace is air-cooled to room temperature.

[0022] As an improvement, in step e, the resin sand mold is preheated to 150-200℃ during casting.

[0023] As an improvement, in step e, before casting, the ladle used to hold the molten steel is heated and baked by a ladle baking device.

[0024] As an improvement, the baking equipment includes a support frame, a rotating arm, a top cover plate, a rolling device, and a baking mechanism;

[0025] The bracket is fixedly installed, the rotating arm is rotatably mounted on the bracket, the upper cover is mounted on the rotatable end of the rotating arm, and the baking mechanism is mounted on the upper cover. The baking mechanism includes a combustion unit and an auxiliary combustion unit.

[0026] As an improvement, the combustion unit includes a gas pipe, a gas valve, a flame nozzle, and a metal hose;

[0027] The gas pipe is connected to an external gas supply device. A gas valve is installed on the gas pipe to control the opening and closing range of the gas pipe. The flame nozzle is installed at the center of the upper cover plate and is connected to the gas pipe through a metal flexible hose.

[0028] As an improvement, the flame nozzle is provided with a cone with adjustable height and a baffle rod arranged in a ring and staggered along the inner diameter of the flame nozzle.

[0029] As an improvement, the auxiliary combustion unit includes an auxiliary gas pipe, a butterfly valve, a fan, and a flexible connecting pipe;

[0030] The auxiliary air pipe is connected to an external air supply device. A butterfly valve is installed on the auxiliary air pipe to control the opening and closing amplitude of the auxiliary air pipe. The auxiliary air pipe is connected to the flame nozzle through a flexible hose, with the connection point located between the cone and the baffle rod.

[0031] As an improvement, an argon blowing mechanism is also installed on the upper cover plate, which includes an air inlet pipe, a telescopic pipe, and a telescopic rod;

[0032] The air intake pipe is connected to an external air supply device, and the other end of the air intake pipe is connected to the air distribution area set inside the upper cover plate. The telescopic pipe is set below the upper cover plate, and the telescopic pipe is connected to the air distribution area. The telescopic pipe is driven to extend and retract by the telescopic rod installed on the upper cover plate.

[0033] The beneficial effects of this invention are as follows:

[0034] This invention performs dephosphorization and desulfurization treatment on refined cast steel through slag removal and slag formation, while simultaneously incorporating an argon blowing step during the casting process. In this argon blowing process, nitrogen, carbon monoxide, water vapor, and air are injected into the molten steel, followed by the injection of argon. The reactivity of the active gases is used to quickly achieve preliminary treatment, while the inertness and stirring ability of argon are used to eliminate the side effects of the initial stage, thereby achieving deep refining and effective control of P and S elements inside the refined cast steel.

[0035] This invention reduces costs while ensuring treatment effectiveness by "reacting first and then purifying" (e.g., using inexpensive N2 for pretreatment and then refining with Ar). It is especially suitable for steel grades that have strict restrictions on gaseous impurities (N, O) but require efficient pre-treatment (e.g., stainless steel decarburization and low-nitrogen steel refining).

[0036] This invention incorporates an argon blowing mechanism into the ladle baking equipment. This mechanism further refines the molten steel in the ladle, resulting in a simpler structure. Simultaneously, the argon blowing mechanism functions as a moisture removal device during ladle baking, while the auxiliary gas pipe of the ladle baking equipment serves as a channel for removing gaseous impurities during the argon blowing process. These complementary and mutually reinforcing mechanisms work together to promote the overall improvement of the ladle.

[0037] In summary, this invention has the advantages of high-quality refined cast iron, fewer impurities, and fewer internal defects in cast steel. It is particularly suitable for the field of refined cast steel materials technology and has broad application prospects. Attached Figure Description

[0038] Figure 1 is a schematic flowchart of the method of Embodiment 1 of the present invention;

[0039] Figure 2 is a three-dimensional structural diagram of the device according to Embodiment 2 of the present invention;

[0040] Figure 3 is a schematic diagram of the three-dimensional structure of the steel ladle in Embodiment 2 of the present invention;

[0041] Figure 4 is a three-dimensional structural schematic diagram of the baking mechanism in Embodiment 2 of the present invention;

[0042] Figure 5 is a schematic diagram of the three-dimensional structure of the baking mechanism in Embodiment 2 of the present invention;

[0043] Figure 6 is a top view of the baking mechanism of Embodiment 2 of the present invention;

[0044] Figure 7 is a schematic cross-sectional view of the flame nozzle in Embodiment 2 of the present invention;

[0045] Figure 8 is a schematic diagram of the telescopic tube in the extended state of Embodiment 2 of the present invention;

[0046] Figure 9 is a schematic diagram of the retracted state of the telescopic tube in Embodiment 2 of the present invention;

[0047] Figure 10 is a three-dimensional structural diagram of the telescopic rod according to Embodiment 2 of the present invention.

[0048] The markings in the attached diagram are: bracket 1, rotating arm 2, upper cover plate 3, winch 4, baking mechanism 5, combustion unit 51, gas pipe 511, gas valve 512, flame nozzle 513, metal hose 514, cone 515, baffle bar 516, auxiliary combustion unit 52, auxiliary gas pipe 521, butterfly valve 522, fan 523, flexible connecting pipe 524, argon blowing mechanism 6, air inlet pipe 61, telescopic pipe 62, telescopic rod 63, ladle 8, turntable assembly 81, rotating table 811, swing arm 812, hydraulic actuator 813. Detailed Implementation

[0049] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0050] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims in the appendix.

[0051] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0052] When this specification uses the prefixes "known to those skilled in the art," "prior art," or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those conventionally used in the art at the time the invention was proposed, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0053] It should be noted that the two or more aspects (or embodiments) disclosed in the context of this specification can be arbitrarily combined with each other, and the resulting technical solutions (such as methods or systems) are part of the original disclosure of this specification and also fall within the protection scope of this invention.

[0054] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless being based on weight would not be in accordance with the common understanding of those skilled in the art.

[0055] Example 1:

[0056] As shown in Figure 1, a refined cast steel comprises the following raw materials in the following mass ratio:

[0057] 800 parts of scrap steel with a carbon content of 0.1%, 200 parts of pig iron with a carbon content of 3.5%, 18.5 parts of ferromanganese, 24 parts of ferrochrome, 5 parts of metallic nickel, 3 parts of ferromolybdenum, 0.2 parts of ferrovanadium, 0.02 parts of ferroboron, and 11.5 parts of deoxidizer.

[0058] The deoxidizer includes 10 parts of ferrosilicon for pre-deoxidation and 1.5 parts of aluminum for final deoxidation.

[0059] The refined cast steel produced contains 0.25% C, 1.7% Mn, 2.3% Cr, 0.5% Ni, 0.3% Mo, 0.09% V, 0.0035% B, and the remainder is Fe.

[0060] The method for preparing the above-mentioned refined cast steel according to this application includes the following steps:

[0061] Step a: Loading. Lay 10 parts of ferrosilicon and 5 parts of ferromanganese at the bottom of the electric arc furnace, and load 800 parts of scrap steel and 200 parts of pig iron on the top layer. Load 5 parts of alloy nickel plate along with the scrap steel.

[0062] Step b, slag removal and slag making: After melting and cleaning, remove the initial slag, add 50 parts of lime and 10 parts of fluorite as slag-making materials, raise the temperature to 1620℃, hold for 10 minutes, and dephosphorize and desulfurize to S≤0.02% and P≤0.025%.

[0063] Step c, alloying: At 1620℃, add 24 parts of ferrochrome and 3 parts of ferromolybdenum, stir and keep warm for 15 minutes to ensure complete dissolution. At 1600℃, add the remaining 13.5 parts of ferromanganese and stir for 5 minutes. 10 minutes before tapping, at 1580℃, first add 0.1 parts of ferrovanadium and stir for 3 minutes, then add 1.5 parts of aluminum ingot, 0.02 parts of ferroboron, and the remaining 0.09 parts of ferrovanadium. Stir rapidly for 2 minutes to avoid boron oxidation and burn-off. Then, power on for melting, gradually increasing the power to 400kW. During the melting period, the temperature is controlled at 1550-1600℃, and the melting time is 60-70 minutes.

[0064] Step d: Adjust the composition and perform spectral analysis. If C is insufficient, add ≤0.1% carbon powder; if S / P exceeds the standard, add lime and fluorite for slag treatment.

[0065] Step e: Casting. At 1520-1540℃, pour molten steel into the resin sand mold at a pouring speed of 5-15 kg / s, keeping the pouring cup fully filled. After pouring, allow the sand mold temperature to drop to ≤200℃ for 4-6 hours.

[0066] Step f: Heat treatment. Immediately after unpacking, the product is transferred to an annealing furnace for annealing, normalizing, and annealing treatment in sequence.

[0067] In step f, the initial annealing is performed by heating the furnace at 50℃ / h to 500℃, holding for 2 hours, and then cooling to room temperature to eliminate casting stress. The normalizing treatment is performed at a heating temperature of 920±10℃, with the holding time calculated based on the workpiece thickness of 1mm / min, and the air speed of 5-10m / s. The furnace is then cooled uniformly. The tempering treatment is performed at a heating temperature of 620±10℃, with a target hardness of HB220-250. The holding time is the same as that for normalizing. The furnace is then heated, held, and then air-cooled to room temperature.

[0068] Furthermore, in step e, during casting, the resin sand mold is preheated to 150-200℃.

[0069] Based on the target composition (C 0.25%, Mn 1.7%, Cr 2.3%, etc.), and combined with the burn-off rate of each element in smelting (e.g., Mn burn-off 8%, Cr burn-off 5%), this application reverse-calculates the amount of raw materials to be added. Scrap steel and pig iron are the main raw materials, supplemented with alloy ingots (Mn, Cr, Ni, Mo, etc.) and microalloying elements (V, B). This ensures that the content of each element in the initial batch is slightly higher than the target value, so that the burn-off is offset and the target is met.

[0070] The raw materials are rapidly melted at high temperature (1600℃) in an electric arc furnace to form a uniform molten steel. After melting and cleaning, the initial slag (containing silicon, aluminum oxides, and some sulfur and phosphorus impurities) is removed to reduce the burden on subsequent refining. The temperature is then raised to 1620℃ for slag formation, dephosphorization, and desulfurization: lime (CaO, strongly alkaline) and fluorite (CaF2, flux) are added to form a high-basicity slag (CaO / SiO≈3-4). The slag is maintained at 1620℃ for 10 minutes to allow phosphorus to be converted into Ca(PO4)2.

[0071] 2) Sulfur (forming CaS) fully enters the slag phase, with S≤0.02% and P≤0.025%, which is lower than the impurity standard of ordinary steel (usually S≤0.035% and P≤0.035%).

[0072] Furthermore, by laying 10 kg of ferrosilicon (Fe-Si) at the bottom of the furnace, Si reacts with [O] in the molten steel to generate SiO2 (which enters the slag), reducing the initial oxygen content of the molten steel ([O] ≤ 0.005%). Before tapping, 1.5 kg of aluminum ingot (Al) is added twice. Al reacts with [O] to generate high-melting-point AlO3 particles, which float to the slag layer. Finally, the [O] in the molten steel is ≤ 0.002%, avoiding the risk of cracks caused by oxide inclusions.

[0073] In addition, Ni (melting point 1455℃), Mn (1246℃), Cr (1857℃, requires high temperature to dissolve), and Mo (2623℃, added to the electric furnace in advance) are added in order of melting point from low to high to ensure that the alloy is fully dissolved and the burn-off is stable.

[0074] If C is insufficient (e.g., target 0.25%, actual measurement 0.23%), add carbon powder (particle size ≤1mm to avoid sulfur increase); if S / P exceeds the standard, add lime + fluorite for secondary removal to ensure composition fluctuation ≤±0.02% (key elements).

[0075] Furthermore, the temperature of the molten steel is controlled at 1580-1590℃ (approximately 50℃ above the liquidus) to avoid cold shut defects caused by low-temperature casting; the sand mold is preheated to 200℃ to reduce casting stress. After heating to the austenitic region, air cooling transforms coarse grains (such as as-cast dendrites) into fine lamellar pearlite + ferrite, achieving a grain size of 8-9 (ASTM standard), increasing strength by 15-20%. Normalizing stress is eliminated, resulting in a dispersed distribution of carbides, increasing impact toughness by 30%, and preventing brittle fracture.

[0076] In summary, compared to conventional steelmaking (which involves only one slag formation), this method, through a high-temperature, high-basicity slag system and two deoxidation processes, reduces the S / P content to the national standard premium level (GB / T 11352-2021 for high-quality cast steel: S / P ≤ 0.030%), significantly reducing the risks of hot brittleness (S) and cold brittleness (P) and improving the steel's hot and cold working properties. AlO3 inclusions are ≤ 5 μm in size and 60% less in quantity than with conventional deoxidation, avoiding defects exceeding the standard during flaw detection (such as ultrasonic testing).

[0077] By using preset burn-off rates (e.g., Mn 8%, Cr 5%) and real-time spectral detection, the composition fluctuation range is controlled within ±0.015% (C) and ±0.05% (Mn / Cr), which is far higher than the industry average (usually ±0.05% / ±0.1%), ensuring the stable performance of different batches of steel (tensile strength fluctuation ≤5MPa).

[0078] V (0.09%) and B (0.0035%) are added in the form of intermediate alloys (such as Fe-V, Fe-B) to avoid segregation caused by direct addition (B is easily oxidized and V is easily formed into carbides), ensuring that they are evenly distributed at the grain boundaries and exerting the best effect of refining grains (V) and improving hardenability (B).

[0079] The carbonitriding precipitation of V (forming V(C,N) particles with a size ≤10nm) inhibits austenite grain growth, and the grain size after normalizing is 2-3 grades finer than that of steel without V, while the strength (σb≥850MPa) and toughness (Akv≥40J) are improved simultaneously.

[0080] Example 2:

[0081] As shown in Figure 2-10, this embodiment provides a ladle baking device for heating and baking the ladle used to hold molten steel before casting, as described in Embodiment 1.

[0082] Specifically, the baking equipment includes a support frame 1, a rotating arm 2, an upper cover plate 3, a rolling device 4, and a baking mechanism 5;

[0083] The bracket 1 is fixedly installed, the rotating arm 2 is rotatably mounted on the bracket 1, the upper cover plate 3 is installed at the rotatable end of the rotating arm 2, the winch 4 drives the rotating arm 2 to rotate and swing, and the baking mechanism 5 is installed on the upper cover plate 3. The baking mechanism 5 includes a combustion unit 51 and an auxiliary combustion unit 52.

[0084] After the top cover plate 3 covers the opening at the top of the ladle, the combustion unit 51 and the auxiliary combustion unit 52 respectively discharge combustible gas and air or oxygen to heat the inside of the ladle, remove moisture from the inside of the ladle, and preheat the temperature of the ladle.

[0085] The combustion unit 51 includes a gas pipe 511, a gas valve 512, a flame nozzle 513, and a metal hose 514.

[0086] The gas pipe 511 is connected to an external gas supply device. A gas valve 512 is installed on the gas pipe 511 to control the opening and closing range of the gas pipe 511. A flame nozzle 513 is installed at the center of the upper cover plate 3. The flame nozzle 513 is connected to the gas pipe 511 through a metal hose 514.

[0087] Furthermore, the flame nozzle 513 is provided with a cone 515 that is adjustable in height and a baffle rod 516 arranged in a ring and staggered along the inner diameter of the flame nozzle 513.

[0088] Furthermore, the auxiliary combustion unit 52 includes an auxiliary gas pipe 521, a butterfly valve 522, a fan 523, and a flexible connecting pipe 524;

[0089] The auxiliary air pipe 521 is connected to an external air supply device. A butterfly valve 522 is installed on the auxiliary air pipe to control the opening and closing amplitude of the auxiliary air pipe 521. The auxiliary air pipe 521 is connected to the flame nozzle 513 through a hose 524. The connection point is located above the cone 515 and the baffle rod 516.

[0090] In addition, an argon blowing mechanism 6 is also installed on the upper cover plate 3. The argon blowing mechanism 6 includes an air inlet pipe 61, a telescopic pipe 62 and a telescopic rod 63.

[0091] The air intake pipe 61 is connected to an external air supply device, and the other end of the air intake pipe 61 is connected to the air distribution area 31 set inside the upper cover plate 3. The telescopic pipe 62 is set below the upper cover plate 3. The telescopic pipe 62 is connected to the air distribution area 31, and the telescopic pipe 62 is driven to extend and retract by the telescopic rod 63 installed on the upper cover plate 3.

[0092] It should be noted that during the ladle heating process, the gas pipe 511 supplies combustible gas, such as coal gas or natural gas, to the flame nozzle 513, while the auxiliary gas pipe 521 supplies air or oxygen and other combustion-supporting gases to the flame nozzle 513. The two gases converge at the flame nozzle 513, mix evenly, and are then injected into the ladle to heat the interior. At this time, the exhaust gases formed inside the ladle after combustion, such as water vapor and carbon dioxide, are discharged outward through the telescopic pipe 62 in the argon blowing mechanism 6. The telescopic pipe 62 is in a retracted state under the action of the telescopic rod 63 to prevent the flame from the flame nozzle 513 from damaging it.

[0093] After the ladle has undergone baking, the argon blowing mechanism 6 introduces gases into the ladle in the following order: nitrogen, carbon monoxide, water vapor, air, and argon. This process treats the molten steel inside the ladle. The first stage involves blowing in reactive gases (N2, CO, air, and water vapor) to quickly achieve preliminary treatment (such as decarburization, inclusion removal, and composition adjustment) or reduce costs (N2 is cheaper than Ar). For example, in decarburization, air / CO is first blown in to reduce the carbon content through oxidation, quickly achieving the target composition. For inclusion removal, O2 gas is blown in to promote the aggregation and growth of inclusions (such as AlO3), or N2 is blown in to form bubble nuclei, increasing the chance of inclusions colliding and rising. In the second stage, the process switches to argon gas. The inertness and stirring ability of argon eliminate the side effects of the previous stage, achieving deep refining. Degassing and purification: Argon bubbles adsorb residual H2, N2 and other gases (especially excess N2 introduced by reactive gases) as they rise, further reducing the gas content; Inclusion removal: Continuous stirring promotes the full floating of inclusions, while avoiding the introduction of new reactive gases (e.g., after stopping N2 blowing, to prevent excessive nitrogen addition to the molten steel); Uniform composition and temperature: Argon stirring makes the composition and temperature of the molten steel more uniform, creating conditions for subsequent casting.

[0094] During this process, the auxiliary gas pipe, in conjunction with the fan, discharges various impurity gases generated during the argon blowing process.

[0095] Furthermore, it should be noted that using the telescopic tube 62 as the exhaust pipe of the argon blowing mechanism requires it to penetrate deep into the molten steel. However, the top cover plate 3 needs to block the top opening of the ladle, which would cause the exhaust pipe of the fixed-length argon blowing mechanism to interfere with the opening of the ladle. Therefore, this application adopts a telescopic mechanism to avoid the interference problem and also avoid the problem of the telescopic tube 62 being dried by the flame for a long time.

[0096] As a preferred embodiment, the ladle 8 in this application adopts a rotating and switching double-headed ladle structure. While one set of ladles is being baked, the other set is being used for molten steel casting. The cyclical switching between the two sets of ladles greatly improves work efficiency. Specifically, the ladle 8 is equipped with two sets of ladles that are rotated and switched by a turntable assembly 81 located below. The turntable assembly 81 consists of a turntable 811, two sets of swing arms 812, and two sets of hydraulic actuators 813. The turntable 811 is driven to rotate by a motor in conjunction with an acceleration gear set, while the swing arms 812 are symmetrically mounted on the turntable 811. The ladle 8 is placed on the corresponding swing arm 812, and the hydraulic actuator 813 drives the corresponding swing arm 812 to swing, thereby causing the ladle 8 to tilt.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing refined cast steel, characterized in that: The refined cast steel comprises, by mass ratio, 800 parts scrap steel with a carbon content of 0.1%, 200 parts pig iron with a carbon content of 3.5%, 18.5 parts ferromanganese, 24 parts ferrochrome, 5 parts metallic nickel, 3 parts ferromolybdenum, 0.2 parts ferrovanadium, 0.02 parts ferroboron, and 11.5 parts deoxidizer; wherein the deoxidizer includes 10 parts ferrosilicon for pre-deoxidation and 1.5 parts aluminum for final deoxidation; the prepared refined cast steel contains 0.25% C, 1.7% Mn, 2.3% Cr, 0.5% Ni, 0.3% Mo, 0.09% V, 0.0035% B, and the remainder being Fe; The method for preparing refined cast steel includes the following steps: Step a, charging: 10 parts ferrosilicon and 5 parts ferromanganese are laid at the bottom of the electric arc furnace, and 800 parts scrap steel and 200 parts pig iron are loaded on the top layer. 5 parts alloy nickel plates are loaded with the scrap steel; Step b, slag removal and slag formation: After melting and clearing, the initial slag is removed, and 50 parts lime and 10 parts fluorite are added as slag-forming materials. The temperature is raised to 1620℃ and held for 10 minutes to dephosphorize and desulfurize to S≤0.02% and P≤0.025%; Step c, alloying: At 1620℃, 24 parts ferrochrome and 3 parts ferromolybdenum are added, stirred, and held for 15 minutes to ensure complete dissolution. The temperature is then raised to 1600℃. Add the remaining 13.5 parts of ferromanganese and stir for 5 minutes. 10 minutes before tapping, add 0.1 parts of ferrovanadium at 1580℃ and stir for 3 minutes. Add 1.5 parts of aluminum ingot, 0.02 parts of ferroboron, and the remaining 0.09 parts of ferrovanadium. Stir rapidly for 2 minutes to avoid boron oxidation and burn-off. Then, power on for melting, gradually increasing the power to 400kW. Control the temperature during melting at 1550-1600℃ and the melting time at 60-70 minutes. For step d, adjust the composition and take samples for spectral analysis. If C is insufficient, add ≤0.1% carbon powder. If S / P exceeds the standard, add lime and fluorite for slag treatment. Step e, Casting: Before casting, the ladle used to hold the molten steel is heated and baked using a ladle baking device. After the ladle has been baked, gases are introduced into the ladle in the following order: nitrogen, carbon monoxide, water vapor, air, and argon, to treat the molten steel inside. At 1520-1540℃, the molten steel is poured into the resin sand mold at a pouring speed of 5-15 kg / s, keeping the pouring cup full. 4-6 hours after pouring, the sand mold temperature drops to ≤200℃. Step f, Heat Treatment: Immediately after opening the mold, the ladle is transferred to an annealing furnace for annealing, normalizing, and tempering treatments in sequence.

2. The preparation method according to claim 1, characterized in that: In step f, the initial annealing temperature is increased to 500℃ at 50℃ / h, held for 2 hours, and then cooled to room temperature in the furnace to eliminate casting stress. The normalizing treatment is heated to 920±10℃, and the holding time is calculated based on the workpiece thickness of 1mm / min. The air speed is 5-10m / s, and the temperature is cooled uniformly. The tempering treatment is heated to 620±10℃, with a target hardness of HB220-250. The holding time is the same as that for normalizing. The temperature is increased in the furnace, held, and then air-cooled to room temperature.

3. The preparation method according to claim 1, characterized in that: In step e, during casting, the resin sand mold is preheated to 150-200℃.

4. The preparation method according to claim 1, characterized in that: The baking equipment includes a support frame, a rotating arm, a top cover plate, a winch, and a baking mechanism. The support frame is fixedly installed, the rotating arm is rotatably mounted on the support frame, the top cover plate is mounted on the rotatable end of the rotating arm, and the baking mechanism is mounted on the top cover plate. The baking mechanism includes a combustion unit and an auxiliary combustion unit.

5. The preparation method according to claim 4, characterized in that: The combustion unit includes a gas pipe, a gas valve, a flame nozzle, and a metal hose; the gas pipe is connected to an external gas supply device, the gas valve is installed on the gas pipe to control the opening and closing range of the gas pipe, and the flame nozzle is installed at the center of the upper cover plate, and the flame nozzle is connected to the gas pipe through a metal hose.

6. The preparation method according to claim 5, characterized in that: The flame nozzle is equipped with a cone with adjustable height and a baffle rod arranged in a ring and staggered along the inner diameter of the flame nozzle.

7. The preparation method according to claim 6, characterized in that: The auxiliary combustion unit includes an auxiliary gas pipe, a butterfly valve, a fan, and a flexible connecting pipe. The auxiliary gas pipe is connected to an external gas supply device. The butterfly valve is installed on the auxiliary gas pipe to control the opening and closing range of the auxiliary gas pipe. The auxiliary gas pipe is connected to the flame nozzle through a flexible hose, with the connection point located above the cone and the baffle rod.

8. The preparation method according to claim 7, characterized in that: The upper cover plate is also equipped with an argon blowing mechanism, which includes an air inlet pipe, a telescopic pipe and a telescopic rod. The air inlet pipe is connected to an external gas supply device, and the other end of the air inlet pipe is connected to a gas distribution area set inside the upper cover plate. The telescopic pipe is set below the upper cover plate and is connected to the gas distribution area. The telescopic pipe is driven to extend and retract by the telescopic rod installed on the upper cover plate.

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