High-purity molten iron smelting apparatus and method for hundred-ton-grade ductile iron cylinder

Abstract

The present invention relates to the technical field of smelting industry, and relates to a high-purity molten iron smelting apparatus and method for a hundred-ton-grade ductile iron cylinder, solving at least one of problems in the prior art that a single induction furnace smelting apparatus cannot simultaneously meet requirements of molten iron amount, chemical composition, process temperature, molten iron purity, homogenization, and precision, and has difficulty in control of graphite morphology in a finished metallographic structure. The apparatus comprises: an induction furnace, a first ladle refining furnace, a second ladle refining furnace, a distribution device, and a nodularization device. The present invention uses two ladle refining furnaces, and achieves precise control of key alloy components such as C, P, S in molten iron by means of primary rough refining in the induction furnace and secondary refining in the ladle refining furnace. The secondarily refined molten iron is distributed via the distribution device and then transferred to the nodularization treatment device for nodularization, thus ensuring uniformity and homogeneity of the overall composition of a hundred-ton-grade cylindrical casting.

Description

A 100-ton ductile iron cylinder high-purity casting molten iron smelting device and method Technical Field

[0001] The present invention relates to the technical field of smelting industry, and in particular to a smelting device and method for a 100-ton-class ductile iron cylinder with high-purity cast molten iron. Background Art

[0002] Spent fuel, also known as irradiated nuclear fuel, generally refers to nuclear fuel in a nuclear power plant's reactor that has been depleted of uranium to a certain level and can no longer sustain nuclear reactions. Spent fuel contains a large amount of radioactive elements, poses a significant environmental hazard, and has a long half-life, necessitating proper disposal. This disposal process includes storage, transportation, post-processing, and deep geological disposal. Spent fuel storage and transportation units (SFUs) serve as the storage and transportation vessels for this process. As of 2021, China has 22 nuclear power plants in operation or under construction, creating an increasingly urgent need for spent fuel disposal. Due to the unique nature of spent fuel, its storage and transportation equipment places extremely high technical demands, resulting in high technical complexity and high cost. Currently, this equipment is primarily imported, with no domestic alternatives available, making it a high-value-added, bottleneck-prone project.

[0003] In the existing technology, ductile iron castings are mainly produced by using cupolas or induction furnaces to produce raw iron. After spheroidizing and inoculating treatment, they are cast into shape and then undergo a series of processes such as boxing, cleaning, and heat treatment. The amount of molten iron that can be provided at a time is limited by the nominal capacity of the smelting furnace body, mostly ranging from several tons to dozens of tons. Its composition is limited by the raw materials and smelting process, and fluctuates greatly. The single induction heating method leads to poor process temperature controllability and a lack of inclusion removal process means, making it difficult to control the overall metallurgical quality of the raw iron.

[0004] However, the cylinder of the storage and transportation device weighs more than 100 tons, and the technical conditions are strict and the casting process is special. A single induction furnace smelting device cannot simultaneously meet the metallurgical quality requirements such as molten iron volume, chemical composition, process temperature, purity and uniformity.

[0005] Summary of the Invention

[0006] In view of the above analysis, the embodiments of the present invention aim to provide a high-purity cast molten iron smelting device and method for a hundred-ton ductile iron cylinder, so as to solve at least one of the problems in the prior art that a single induction furnace smelting device cannot simultaneously meet the requirements of molten iron quantity, chemical composition, process temperature, molten iron purity, homogenization, precision, and difficulty in controlling the graphite morphology of the metallographic structure of the finished product for the cylinder of a storage and transportation device weighing more than a hundred tons.

[0007] The purpose of the present invention is mainly achieved through the following technical solutions:

[0008] The present invention provides a 100-ton-class ductile iron cylinder high-purity cast iron smelting device, the device comprising:

[0009] Induction furnace: The induction furnace includes a first station and a second station, which are used for rough smelting of molten iron to obtain rough smelting molten iron in the first station and rough smelting molten iron in the second station;

[0010] First ladle refining furnace: the crude molten iron from the first station enters the first ladle refining furnace for primary refining to obtain primary refined molten iron;

[0011] Second ladle refining furnace: the primary refined molten iron and the second-station rough molten iron are sequentially fed into the second ladle refining furnace for secondary refining to obtain secondary refined molten iron;

[0012] Distribution equipment: The secondary refined molten iron is distributed and transferred in the distribution equipment;

[0013] Spheroidizing equipment: The molten iron that is divided and transferred is spheroidized in the spheroidizing equipment.

[0014] The present invention also provides a method for smelting molten iron using the device, the method comprising the following steps:

[0015] (1) Induction furnace rough refining: cold steel material, cast pig iron, alloy nickel plate and graphite carbon powder are added to the first station for rough refining to obtain the first station rough refining molten iron, and cast pig iron and graphite carbon powder are added to the second station for rough refining to obtain the second station rough refining molten iron;

[0016] (2) Secondary refining in a ladle refining furnace: adding the crude iron smelted in the first station to a first ladle refining furnace for primary refining to obtain primary refined iron smelting; adding the primary refined iron smelting and the crude iron smelting in the second station to a second ladle refining furnace for secondary refining to obtain secondary refined iron smelting;

[0017] (3) The secondary refined molten iron is transferred and distributed in the distribution equipment in turn, and then transferred to the spheroidizing treatment equipment for spheroidizing treatment.

[0018] Furthermore, the mass of cold steel materials in the raw materials for molten iron production is strictly limited to 15-20% of the total mass of cold steel materials, pig iron and alloy nickel plates.

[0019] Furthermore, the steel material is roughly smelted for dephosphorization and decarburization in an electric arc furnace, refined for carbon adjustment and desulfurization in a ladle furnace, and then cast into a billet in an atmospheric injection mold.

[0020] Furthermore, the cold steel material described in step (1) includes C0.25-0.45%, Si≤0.01%, Mn≤0.05%, P≤0.005%, S≤0.005%, Cr≤0.05%, Mo≤0.05%, and trace amounts of Sb, W, V, Pb, As, Sn, and Zr in terms of mass percentage.

[0021] Furthermore, in step (1), the cast pig iron includes, by mass percentage, C 4.50-4.70%, Si 0.40-0.60%, Mn≤0.100%, P≤0.030%, S≤0.025%, Cr≤0.010%, Ni≤0.10%, Mo≤0.010%, and Ti≤0.050%.

[0022] Furthermore, in step (1), the mass fraction of Ni in the alloy nickel plate is greater than 99.5%.

[0023] Furthermore, in step (1), the process temperature of the molten iron in the first and second rough refining stations is ≤1550°C, and the iron is tapped after the charge is completely melted and kept at 1500-1520°C for 5-20 minutes.

[0024] Furthermore, in step (2), the entire primary refining and secondary refining process adopts a ladle bottom blowing argon stirring method.

[0025] Furthermore, in step (2), slag making treatment is performed in both the primary refining and the secondary refining. The slag making materials in the primary refining are metallurgical lime and fluorite, and the mass ratio of metallurgical lime to fluorite is 4:1. The slag making material in the secondary refining is fluorite.

[0026] Furthermore, in step (2), the process temperature of the molten iron in the primary refining and the secondary refining is ≤1550°C.

[0027] Furthermore, in step (2), cold steel and cast pig iron are added during the primary refining process to adjust the quality and weight composition of the molten iron.

[0028] Furthermore, before the spheroidization treatment in step (3), argon is blown from the bottom of the ladle to uniformly adjust the temperature of the molten iron so that the spheroidization treatment temperature is 1350-1450°C.

[0029] Furthermore, step (3) also includes transporting the molten iron after the spheroidization treatment to the casting process for final inoculation, slag removal and pouring.

[0030] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0031] (1) Compared with the traditional ductile iron molten iron manufacturing device, the device of the present invention breaks through the problems of the existing traditional device and molten iron manufacturing process that only use induction furnace smelting to accurately control the composition and temperature of molten iron, and the homogenization and identity of the composition and temperature of the raw molten iron for spheroidization. The present invention adopts two ladle refining furnaces, and adopts induction furnace rough refining and ladle refining furnace secondary refining to achieve accurate control of key alloy components such as C, P, and S in the molten iron; the secondary refined molten iron is divided and mixed by the mixing equipment, and then transported to the spheroidization treatment equipment for spheroidization treatment to ensure the identity and homogenization degree of the overall composition of the cylinder casting; in the absence of large-scale professional equipment, the device of the present invention can use conventional smelting equipment, through process and technical route innovation, not only can it provide highly homogenized 100-ton-level raw molten iron for spheroidization at one time, but also the product quality meets the strict technical requirements, solving the problem of single-furnace smelting of ductile iron cylinder molten iron for 100-ton-level spent fuel storage and transportation equipment, and all technical indicators of the finished product physical and chemical testing are better than the product outline design requirements;

[0032] (2) In the present invention, except for cold steel, cast pig iron, and alloy nickel plate, no alloy is added to adjust the target composition of the molten iron in the process, so as to avoid the increase of residual elements caused by the addition of alloy, which affects the purity of the molten iron and reduces the final evaluation of the graphite morphology of the product metallographic structure. In particular, in the secondary refining process of molten iron production, the proprietary alloy design composition control process must be strictly implemented;

[0033] (3) The molten iron smelting method of the present invention controls the slag composition through a scientific slag-making process, thereby achieving purification of the molten iron while controlling sulfur, significantly reducing the content of endogenous and exogenous inclusions in the molten iron, and adopting a large-tonnage ladle refining furnace secondary refining process, so that the molten iron can simultaneously meet the special technical requirements of precise control of the designed composition, high purity and low inclusions, high uniformity of composition and temperature, and one-time smelting of 100-ton products in the same furnace. It is a new technical route and technical concept with obvious technical advancement, thereby obtaining ductile iron products with excellent performance indicators;

[0034] (4) Since molten iron with a high phosphorus content is prone to produce phosphorus eutectic phenomenon at the crystal interface, which leads to deterioration of the matrix structure and reduction of mechanical properties of the finished casting, it is required that the P content of the original molten iron at the spheroidization site is ≤ 0.020%. The traditional molten iron smelting route (induction furnace melting + off-furnace treatment) cannot meet this technical requirement. The main reason is that the phosphorus content of domestic casting pig iron is basically above 0.025%. It is impossible to control the P element within the target composition range by melting in an induction furnace alone. Therefore, the cold steel material used in the method of the present invention is subjected to a primary roughing in an electric arc furnace, a secondary refining in a ladle refining furnace, and finally is cast into a billet by atmospheric pouring. The P content of the cold steel material is controlled below 0.001% through a special process, thereby achieving a final spheroidization raw iron weight P ≤ 0.020%, thereby solving the process limitation that the induction furnace smelting molten iron cannot remove P;

[0035] (5) In the present invention, the C content in the raw iron water during the spheroidization treatment is within 3.50-4.00%. During the induction furnace smelting, tapping, pouring, mixing, ladle furnace tapping, separation, and spheroidization treatment processes, the high-temperature high-carbon iron water has a certain amount of carbon burnout or carbon loss. In order to ensure the product target C, it is necessary to perform carbon addition operation with graphite carbon powder during the induction furnace smelting process, and the C component value in the induction furnace tapping should meet the final carbon weight value of the refining process. The present invention controls the factors affecting carbon fluctuations within a minimum range through precise raw material detection, ingredient design, and process experience carbon loss, thereby achieving precise control of carbon in the smelting process;

[0036] (6) The present invention controls the temperature of the molten iron during the roughing and refining process. The process design has taken into account the need to compensate for the subsequent temperature drop of the molten iron during the transportation, distribution and waiting process by the temperature of the molten iron during the secondary refining process, thereby accurately achieving the optimal process temperature requirements for the spheroidization treatment of the molten iron;

[0037] (7) The method of the present invention uses argon blowing and stirring at the bottom of the ladle during refining to achieve high uniformity of molten iron temperature and composition, and uses slag making to promote the floating of endogenous and exogenous inclusions in the molten iron so that they are adsorbed and removed by metallurgical slag, thereby achieving high purity of molten iron, high uniformity of composition and temperature, and precise control of the optimal process temperature for spheroidization treatment that cannot be achieved by traditional molten iron manufacturing processes; since high-pressure argon has strong stirring kinetic energy, it strengthens the mass transfer process from the bottom to the surface of the molten iron, and the air-permeable bricks at the bottom of the ladle produce fine high-purity argon bubbles equivalent to countless micro vacuum chambers. During the process of argon bubbles floating up and increasing in volume as the static pressure of the molten iron decreases, hydrogen and nitrogen gases in the molten iron enter the argon bubbles, and various inclusions are also adsorbed to the iron-slag interface in the collision with the surface of the argon bubbles and adsorbed and removed by the alkaline slag; the method of the present invention controls the S content in the molten iron before spheroidization to 0.004-0.009%, which can significantly improve the spheroidization inoculation effect and improve the metallographic structure and graphite shape of the casting.

[0038] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0040] FIG1 is a schematic diagram of a 100-ton ductile iron cylinder high-purity cast iron smelting device and process route of the present invention;

[0041] FIG2 is a metallographic structure diagram (magnification 50 microns) of a spent fuel storage and transportation cylinder made of ductile iron prepared in Example 2 of the present invention after corrosion;

[0042] FIG3 is a metallographic structure diagram (magnification 200 microns) of a spent fuel storage and transportation cylinder made of ductile iron prepared in Example 2 of the present invention before corrosion;

[0043] FIG4 is a physical picture of the spent fuel storage and transportation cylinder made of ductile iron material after semi-finishing in Example 2 of the present invention. DETAILED DESCRIPTION

[0044] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0045] In a specific embodiment of the present invention, as shown in FIG1 , the present invention provides a 100-ton-class ductile iron cylindrical high-purity cast iron smelting device, the device comprising:

[0046] Induction furnace: The induction furnace includes a first station and a second station, which are used for rough smelting of molten iron to obtain rough smelting molten iron in the first station and rough smelting molten iron in the second station;

[0047] First ladle refining furnace: the crude molten iron from the first station enters the first ladle refining furnace for primary refining to obtain primary refined molten iron;

[0048] Second ladle refining furnace: the primary refined molten iron and the second-station rough molten iron are sequentially fed into the second ladle refining furnace for secondary refining to obtain secondary refined molten iron;

[0049] Distribution equipment: The secondary refined molten iron is distributed and transferred in the distribution equipment;

[0050] Spheroidizing equipment: The molten iron that is divided and transferred is spheroidized in the spheroidizing equipment.

[0051] During implementation, the working principle of the device is as follows: the raw materials are roughly refined in the first and second stations of the induction furnace respectively, the molten iron roughly refined in the first station enters the first ladle refining furnace for primary refining, and after the primary refining, the molten iron enters the second ladle refining furnace, and then the molten iron roughly refined in the second station is added to the second ladle refining furnace for secondary refining. After the secondary refined molten iron is separated by the separation equipment, it enters the spheroidization treatment equipment for spheroidization treatment.

[0052] Compared with the prior art, the device of this embodiment breaks through the traditional process of only using induction furnace smelting. The present invention adopts two ladle refining furnaces, and adopts induction furnace rough refining and ladle refining furnace secondary refining to achieve precise control of key alloy components such as C, P, and S in the molten iron; the secondary refined molten iron is distributed through the distribution equipment, and then transferred to the spheroidization treatment equipment for spheroidization treatment to ensure the identity and homogeneity of the overall composition of the cylinder casting; in the absence of large-scale professional equipment, the device of the present invention utilizes conventional smelting equipment and innovates the process and technical route. It can not only provide highly homogenized 100-ton-level spheroidization raw iron at one time, but also the product quality meets strict technical requirements, solving the problem of single-furnace smelting of ductile iron cylinder molten iron of 100-ton-level spent fuel storage and transportation device, and all technical indicators of the physical and chemical testing of the finished product are better than the product outline design requirements.

[0053] The present invention also provides a method for smelting molten iron using the device, the method comprising the following steps:

[0054] (1) Induction furnace rough refining: cold steel material, cast pig iron, alloy nickel plate and graphite carbon powder are added to the first station for rough refining to obtain the first station rough refining molten iron, and cast pig iron and graphite carbon powder are added to the second station for rough refining to obtain the second station rough refining molten iron;

[0055] (2) Secondary refining in a ladle refining furnace: adding the crude iron smelted in the first station to a first ladle refining furnace for primary refining to obtain primary refined iron smelting; adding the primary refined iron smelting and the crude iron smelting in the second station to a second ladle refining furnace for secondary refining to obtain secondary refined iron smelting;

[0056] (3) The secondary refined molten iron is transferred and distributed in the distribution equipment in turn, and then transferred to the spheroidizing treatment equipment for spheroidizing treatment.

[0057] The high-purity molten iron for the ductile iron cylinder in this embodiment can be used not only to prepare spent fuel storage cylinders, but also cylinders for other storage and transportation devices. Its technical route and process method are applicable to molten iron manufacturing processes with the same or similar quality, composition, and temperature requirements.

[0058] It should be noted that a certain amount of C element loss occurs in the molten iron during the rough smelting, tapping and iron addition processes. The process is corrected by empirical parameters, and the specific values ​​are related to the smelting time, molten iron composition, tapping method and tapping temperature.

[0059] In this embodiment, aside from cold steel, cast pig iron, and alloy nickel plates, no alloys are added to adjust the target molten iron composition. This prevents the addition of alloys from increasing residual elements, which could affect the purity of the molten iron and reduce the final evaluation of the product's metallographic structure and graphite morphology. In particular, during the secondary refining process of molten iron production, a proprietary alloy design and composition control process must be strictly implemented. The auxiliary materials are graphite powder, metallurgical lime, and fluorite. In the induction furnace rough refining process, graphite powder is permitted for carbon addition and nickel plates for nickel adjustment. In the refining process, cold steel and cast pig iron are used to adjust the molten iron volume and composition, supplemented by metallurgical lime and fluorite as necessary for slag formation. No other raw or auxiliary materials are used.

[0060] It should be noted that during the secondary refining process in the ladle furnace, in addition to cold steel materials and cast pig iron, the adjustment of the chemical composition C of the molten iron in this process shall not be made by adding elemental carbon such as graphite electrode powder, carbon powder, etc. to the molten iron. The purpose is to avoid the loss of control of the key component C of high-temperature molten iron due to the error of elemental carbon yield and detection and inspection instruments in the detection and judgment of the chemical composition of the final product.

[0061] Furthermore, using the example of a 160-ton ladle refining furnace, the 145 tons of molten iron from the 160-ton ladle furnace must be transferred to the distribution station for iron distribution and transfer. The distribution order is: 60-ton transfer ladles first, followed by 80-ton transfer ladles; the transfer order is: 60-ton transfer ladles first, followed by 80-ton transfer ladles. After distribution, the temperature of the molten iron in the transfer ladles is measured to be between 1440°C and 1460°C. To avoid excessive temperature drops and the need for reheating, the interval between transfer, distribution, and spheroidization after tapping is strictly controlled to 30-60 minutes. When the transfer ladles reach the spheroidization station, a disposable temperature probe is inserted at least 200mm below the molten iron surface. If the temperature is too low, the molten iron is returned to the refining station for heating. If the temperature is too high, the molten iron is cooled by bottom argon blowing.

[0062] Spheroidizing and inoculation pouring: In the casting process, 145 tons of molten iron is divided into 60 tons and 80 tons of molten iron. After spheroidizing, slag removal, and silicon flotation inoculation, the molten iron is poured into the casting cavity through dedicated pouring basins at different locations at regular intervals. To ensure the molten iron surface rises quickly, the two pourings should be completed simultaneously. The process spheroidizing temperature is 1350-1450°C, and the actual spheroidizing temperature is 1405°C. To meet the purity requirements of the molten iron in the cavity, the remaining molten iron in the refining ladle after the mixing should be no less than 3 tons, and the actual measured amount is 5 tons.

[0063] Specifically, the mass of cold steel material in the raw materials for molten iron production must account for 15-20% of the total mass of cold steel material, pig iron and alloy nickel plate. The cold steel material is roughly dephosphorized and decarburized in an electric arc furnace, refined in a ladle furnace for carbon adjustment and desulfurization, and then cast into billets in an atmospheric casting process.

[0064] In a specific embodiment, the cold steel material in step (1) comprises, by mass percentage, C 0.25-0.45%, Si≤0.01%, Mn≤0.05%, P≤0.005%, S≤0.005%, Cr≤0.05%, Mo≤0.05%, and trace amounts of Sb, W, V, Pb, As, Sn, and Zr.

[0065] It should be noted that in this embodiment, the cold steel material is prepared by the above method, with a block weight of 250-6000 kg. The component ratios in the steel material are controlled. Preferably, the main components tested are C 0.25%, Si ≤ 0.01%, P ≤ 0.001%, and S ≤ 0.002%. The purpose of this setting is to meet a series of technical condition restrictions such as the quality and weight composition of the subsequent molten iron smelting.

[0066] Specifically, in step (1), the cast pig iron includes C 4.50-4.70%, Si 0.40-0.60%, Mn≤0.100%, P≤0.030%, S≤0.025%, Cr≤0.010%, Ni≤0.10%, Mo≤0.010%, and Ti≤0.050% in percentage by mass, and the cast pig iron block weighs 5 kg.

[0067] Specifically, in step (1), the mass fraction of Ni in the alloy nickel plate is greater than 99.5%. In this embodiment, the alloy nickel plate is Ni9950.

[0068] It should be noted that the graphite carbon powder in this embodiment has a carbon content greater than 99% and a particle size less than 1 mm.

[0069] Specifically, in step (1), the temperatures of the first and second rough refining stations are both ≤1550°C, and the iron is tapped after the charge is completely cleared at 1500-1520°C for 5-20 minutes.

[0070] Specifically, in step (2), the primary refining and the secondary refining are all carried out by ladle bottom blowing argon stirring.

[0071] It should be noted that the temperature and composition of the molten iron are highly uniformed by blowing argon from the bottom of the ladle, and slag making is used to promote the floating of endogenous and exogenous inclusions in the molten iron so that they are adsorbed and removed by the metallurgical slag, thereby achieving high purity of the molten iron that cannot be achieved by traditional molten iron manufacturing processes, high uniformity of composition and temperature, and precise control of the optimal process temperature for spheroidization treatment.

[0072] Specifically, in step (2), slag treatment is performed in both the primary refining and the secondary refining. The slag-forming materials in the primary refining are metallurgical lime and fluorite, and the mass ratio of metallurgical lime to fluorite is 4:1. The slag-forming material in the secondary refining is fluorite.

[0073] It should be noted that in this embodiment, first-grade metallurgical lime is selected, and its main technical indicators, by mass percentage, are CaO ≥ 90%, MgO ≤ 5.0%, SiO2 ≤ 2.0%, S ≤ 0.03%, caustic soda ≤ 4%, activity ≥ 320 (activity 4 mol / L, 40°C ± 1°C 10 min), and lump size is 20-100 mm. Fluorite lump ore, brand FL-85, has main technical indicators of (CaF2) ≥ 85%, (SiO2) ≤ 14.3%, P ≤ 0.06%, S ≤ 0.10%, and lump size is 5-100 mm. All raw and auxiliary materials used are required to be clean, dry, and clearly labeled. Large pieces of metal cutting materials need to be marked with specific unit weights.

[0074] In this embodiment, the first ladle refining furnace and the second ladle refining furnace are both newly built barrel-shaped ladle furnaces, and the refractory bricks of the working layer are magnesia carbon, which are cold-mixed and pressed by sintered magnesia sand, flaky graphite, organic binder and antioxidant. The first use requires a special baking curve for 24 hours, and the energy medium is natural gas or industrial coal gas. After the fire is stopped, the infrared temperature at 1 / 2 of the inner wall is greater than 1000°C. 30 minutes after the fire is stopped, the bottom of the inner bag is visually red hot, the infrared temperature at 1 / 2 of the inner wall is not less than 750°C, and the infrared temperature at 1 / 2 of the outer wall is not less than 150°C, so as to ensure that the newly built ladle furnace is thoroughly baked and close to the thermal saturation state, and the refractory bricks have no residual moisture or crystallized water to ensure the safety of the smelting process, and at the same time ensure that the molten iron does not increase due to environmental factors during the smelting process [H].

[0075] It should be noted that in this embodiment, cold steel materials and cast pig iron are used to adjust the quality and weight composition of molten iron, and metallurgical lime and fluorite are used to form slag, and the slag ratio is CaO:CaF2=4:1. The graphite electrode is heated and desulfurized. After the crude molten iron in the second station is smelted, it is added to the second ladle refining furnace. After the mixing is completed, fluorite is added to the second ladle refining furnace to form slag and the arc is heated. Bottom blowing argon is used to stir the composition temperature uniformly. After sampling, the iron can be tapped when the composition temperature is appropriate, and then the subsequent iron-water mixing and spheroidization inoculation treatment are carried out.

[0076] Specifically, the temperature of the primary refining and the secondary refining in step (2) is ≤1550°C.

[0077] Specifically, in step (2), cold steel material and cast pig iron are added during the primary refining process to adjust the quality and weight composition of the molten iron.

[0078] It should be noted that in ladle furnace refining: (1) when cold steel and cast pig iron are added, slag-forming materials need to be added at the same time to allow the graphite electrode arc to heat up, the slag to desulfurize and remove various internal and external inclusions in the molten iron by adsorption. During the traditional molten iron induction furnace smelting process, the slag on the surface of the molten pool is mainly composed of acidic SiO2, which comes from the primary gangue in the raw material foundry pig iron in the molten iron. Compared with the alkaline slag mainly composed of CaO, the acidic slag cannot be desulfurized and has a weaker inclusion adsorption capacity; (2) Since the carbonization of high-carbon molten iron in the form of carbon powder is prone to cause undissolved graphite particles to enter the casting cavity, and the carbon powder recovery rate is greatly affected by various factors and fluctuates greatly, the C weight of the molten iron component is adjusted to the lower limit of the specification during the rough refining stage of the induction furnace, and the refining process only uses foundry pig iron and cold steel materials for carbon adjustment; (3) Stirring the molten iron by blowing argon from the bottom of the ladle can greatly shorten the process of molten iron uniformity and inclusion removal, improve the purity and uniformity of the molten iron, and have technical advantages that traditional processes cannot match. High-pressure argon gas has strong stirring kinetic energy, which enhances the mass transfer process of molten iron from the bottom to the surface. The air-permeable bricks at the bottom of the ladle produce fine high-purity argon bubbles, which are equivalent to countless miniature vacuum chambers. As the argon bubbles float up and their volume increases as the static pressure of the molten iron decreases, H and N gases in the molten iron enter the argon bubbles. Various inclusions are also adsorbed by the collision with the surface of the argon bubbles and brought to the iron-slag interface, where they are adsorbed and removed by the alkaline slag. The process parameters are: argon-blown square bricks at the bottom of the ladle, with two eyes for ventilation, a flow rate of 150NL / min-300NL / min at 1 / 2 radius, an argon purity greater than 99.99%, and in actual operation, the slag surface should not be raised more than 200mm×200mm. A complete temperature uniformity and homogenization cycle is between 10min-15min depending on the height of the molten iron in the ladle; (4) In the refining process, in addition to the composition meeting the design requirements, the temperature of the molten iron should also take into account the temperature drop compensation of the subsequent molten iron during the transfer, distribution, and waiting process, and on this basis, the optimal process temperature for the final molten iron spheroidization treatment is achieved. In actual operation, the empirical formula for the transfer temperature drop rate is: transfer time t = 20min-30min, temperature drop rate ΔT / t≈1.5℃ / min; transfer time t = 30min-45min, temperature drop rate ΔT / t≈1.0℃ / min. In the process design, the secondary refining tapping temperature T = 1480℃-1520℃.

[0079] Specifically, in step (3), according to mass percentage, the molten iron before spheroidization treatment comprises C 3.50-4.00%, Si 0.30-0.40%, P≤0.020%, S 0.004-0.009%, and Ni 0.55-0.65%.

[0080] Specifically, before the spheroidization treatment in step (3), argon is blown from the bottom of the ladle to even out the temperature of the molten iron, so that the spheroidization treatment temperature is 1350-1450°C.

[0081] It should be noted that the process spheroidization temperature is based on the tapping temperature of the second ladle refining furnace. The cooling rate of the molten iron transfer, distribution and waiting process is determined by an empirical formula, supplemented by the ladle bottom blowing argon operation to accurately control the optimal process temperature range of the spheroidization treatment.

[0082] Specifically, step (3) also includes transporting the molten iron after the spheroidization treatment to the casting process for final inoculation, slag removal and pouring.

[0083] Specifically, the steel ladles and iron ladles involved in the molten iron are baked using a special baking curve before use. The refractory materials in the molten iron holding and transportation device are nearly saturated with heat, and the temperature drop rate of the molten iron flow process tends to be stable, thereby achieving precise control of the molten iron spheroidization treatment temperature.

[0084] In the present invention, the C content of the molten iron before spheroidization treatment is 3.50-4.00%. During the induction furnace rough refining, iron tapping, ladle pouring, mixing, ladle furnace iron tapping, separation and spheroidization treatment processes, the high-temperature and high-carbon molten iron has a certain amount of carbon burnout or carbon loss. In order to ensure the product target C, it is necessary to carry out carbon addition operation with graphite carbon powder during the induction furnace smelting process, and the C component value in the iron tapped from the induction furnace should meet the final carbon weight value of the refining process.

[0085] It should be noted that precise control of the C element in the molten iron process is the most critical technical difficulty in the entire molten iron manufacturing process. As the most important element affecting the metallographic structure and mechanical properties of the finished tank body, the starting point of the process design of the vast majority of the technical routes used in the present invention is the precise control of the C element process. In the entire process of molten iron manufacturing, due to the many carbon loss links and large fluctuations, it is difficult to accurately control the C element in the final finished molten iron by carbonizing with graphite carbon powder. After many experiments, the inventors further optimized the process technology route, and through precise detection of raw materials, ingredient design, and process experience carbon loss, the factors affecting carbon fluctuations are controlled within a minimum range, thereby achieving precise control of the smelting process.

[0086] Secondly, inaccurate carbon yield during carbonization of graphite and carbon powder often leads to process defects such as graphite flotation and slag inclusion in the metallographic structure of the cylinder after spheroidization. Furthermore, carbon loss in high-carbon hot metal occurs throughout the entire manufacturing process. The specific carbon loss values ​​are: for a carbon mix of 2.50%-3.50%, a carbon loss of ΔC is 0.15%; for a carbon mix of 4.50%-5.50%, a carbon loss of ΔC is 0.20%.

[0087] Furthermore, to enhance the spheroidizing inoculation effect and improve the graphite properties of the casting metallurgical structure, the S content in the spheroidized base iron is controlled to 0.004-0.009%, with a target S content of 0.006%. This process value is derived from analysis of test data from multiple pilot tests and metallographic examination results, and is specifically related to the effectiveness of the spheroidizing inoculation process and the evaluation of the graphite properties of the casting metallurgical structure. The main difficulty in controlling this element in the ladle refining furnace is the uncontrollable amount of S removal as the smelting process progresses. Optimal S values ​​in the base iron are achieved through process path design, selection of different slag systems, and optimal refining time control.

[0088] Since molten iron with a high phosphorus content is prone to produce phosphorus eutectic phenomenon at the crystal interface, which leads to deterioration of the matrix structure and reduced mechanical properties of the finished casting, the P content of the original molten iron at the spheroidizing point is required to be ≤0.020%. The traditional molten iron smelting route (induction furnace melting + off-furnace treatment) cannot meet this technical requirement. The main reason is that the phosphorus content of domestic casting pig iron is basically above 0.025%. It is impossible to control the P element within the target composition range by induction furnace melting alone. Therefore, the cold steel material used in the method of the present invention is smelted in an electric arc furnace, refined in a ladle furnace, and finally cast into a billet by atmospheric pouring, so that the P content is controlled below 0.001%, thereby achieving a weighted P ≤ 0.020%, thereby solving the process limitation of induction furnace smelting molten iron that cannot remove P.

[0089] Example 1

[0090] As shown in FIG1 , this embodiment provides a 100-ton ductile iron cylindrical high-purity cast iron smelting device, which includes:

[0091] Induction furnace: The induction furnace includes a first station and a second station, which are used for rough smelting of molten iron to obtain rough smelting molten iron in the first station and rough smelting molten iron in the second station;

[0092] First ladle refining furnace: the crude molten iron from the first station enters the first ladle refining furnace for primary refining to obtain primary refined molten iron;

[0093] Second ladle refining furnace: the primary refined molten iron and the second-station rough molten iron are sequentially fed into the second ladle refining furnace for secondary refining to obtain secondary refined molten iron;

[0094] Distribution equipment: The secondary refined molten iron is distributed and transferred in the distribution equipment;

[0095] Spheroidizing equipment: The molten iron that is divided and transferred is spheroidized in the spheroidizing equipment.

[0096] Example 2

[0097] This embodiment is explained by taking ductile iron material QT400-18AL and a total amount of spheroidized iron liquid of 140 tons as an example.

[0098] 1. Technical requirements:

[0099] The technical requirements for the evaluation of the shell material (melting and finished products) (wt.%) are shown in Table 1;

[0100] The technical standards of special steel materials for ductile iron (wt.%) are shown in Table 2;

[0101] The technical standards (wt.%) of ultrapure pig iron for ductile iron are shown in Table 3.

[0102] Table 1 Technical requirements for shell material evaluation (melting and finished products) (wt.%)

[0103] Table 2 Technical standards for ductile iron special steel materials (wt.%)

[0104] Table 3 Technical standards for ultrapure pig iron for ductile iron (wt.%)

[0105] 2. Main equipment:

[0106] One nominal 40-ton EBT (eccentric bottom tapping method, which can effectively control the amount of slag discharged during tapping compared to the trough tapping method) electric arc furnace is used for the rough refining of cold steel materials in this embodiment; one nominal 60-ton double-station medium-frequency induction furnace is used for the preliminary smelting of molten iron; four magnesia-carbon brick barrel-type ladles, with nominal capacities of 160 tons, 130 tons, 90 tons, and 40 tons respectively, are used as metallurgical containers for molten iron refining and transfer; one refining station of 160 tons and one of 130 tons, which can realize metallurgical functions such as power supply and heating, argon blowing and stirring, slag making and desulfurization, and heat preservation and waiting; one barrel-type iron ladle of 80 tons and one of 60 tons are used as metallurgical containers for molten iron spheroidization treatment and pouring.

[0107] 3. Equipment inspection and status requirements:

[0108] (1) Before charging the arc furnace, check the basket to ensure that there is no scrap iron or steel left on the basket to prevent mixing.

[0109] (2) For the electric arc furnace, the slag in the front furnace must be cleaned out, and smelting is not allowed in the later stages of the furnace. The Mo content of the steel grade in the previous furnace should be less than 0.20%.

[0110] (3) The induction furnace body and the upper furnace slag are completely cleaned out, and there should be no visible pieces of sticky steel and slag on the steel trough, furnace wall and furnace bottom;

[0111] (4) Refining ladle, newly built ladle, after baking, the thermal state is good, try to pass argon to check the air permeability of the bottom air brick;

[0112] (5) Hot exchange ladle, the ladle is in good thermal condition after baking, there is no residual steel residue at the bottom and edge of the ladle, and the slag of the previous heat of smelting steel is a refined ladle with a powder slag system mainly composed of CaO and SiO2;

[0113] (6) For the transfer ladle and the new ladle, check the condition of the iron side of the ladle after the bricks are laid; implement the new ladle baking process, the baking time is greater than 24 hours, measure the temperature before adding iron, and require the middle part of the ladle wall lining to be greater than 750℃. After baking, remove the baked refractory material peeling in the ladle by suction;

[0114] (7) The baking temperature of the molten iron ladle is 500℃-800℃. The baking time of the new ladle is more than 24h, and the baking time of the old ladle is more than 12h. It can be extended appropriately in humid weather. The temperature of the molten iron ladle should be measured before spheroidizing treatment. The temperature of the middle part of the lining should be 150℃-300℃, and the temperature of the middle part of the ladle shell should be more than 100℃.

[0115] 4. Preparation of raw materials and auxiliary materials:

[0116] 32 tons of steel, 125 tons of foundry pig iron, 2000 kg of first-grade metallurgical lime, 1000 kg of fluorite, 1000 kg of nickel alloy plate, and 300 kg of graphite carbon powder. All of these raw materials must be accompanied by alloy composition test reports and must undergo on-site re-inspection and verification before use. They must be accurately weighed, clearly labeled, clean and dry, and free of contamination. Large pieces of steel must also be labeled with their specific mass.

[0117] The steel materials in this embodiment are all made in-house. Specifically, they are smelted in an electric arc furnace, refined in a ladle furnace, and finally cast into billets by atmospheric pouring. In terms of mass percentage, the steel materials include C 0.25%, Si≤0.01%, P≤0.001%, and S≤0.002%.

[0118] The cast pig iron comprises C 4.50%, Si 0.40%, Mn≤0.100%, P≤0.030%, S≤0.025%, Cr≤0.010%, Ni≤0.10%, Mo≤0.010%, and Ti≤0.050%;

[0119] The nickel alloy plate contains Ni>99.50%, with the grade Ni9950;

[0120] The carbon content of the graphite carbon powder is greater than 99%, and the particle size of the graphite carbon powder is less than 1 mm. The main technical indicators of the first-class metallurgical lime are CaO ≥ 90%, MgO ≤ 5.0%, SiO2 ≤ 2.0%, S ≤ 0.03%, ignition loss ≤ 4%, activity ≥ 320 (activity 4 mol / L, 40°C ± 1°C 10 min), and the lump size is 20 mm-100 mm.

[0121] Fluorite, brand FL-85, main technical indicators are CaF2≥85%, SiO2≤14.3%, P≤0.06%, S≤0.10%, block size 5mm-100mm.

[0122] The method for smelting molten iron using the device described in Example 1 in this embodiment includes the following steps:

[0123] (1) Rough refining in induction furnace: 25t of steel material, 35t of cast pig iron, 800kg of alloy nickel plate, 75kg of graphite carbon powder and 2.75% of carbon are roughly smelted in the first station of induction furnace. After melting, samples are taken for full analysis. The temperature of molten iron is not higher than 1550℃ during the whole smelting process. After all the materials are melted, the first heat preservation treatment is carried out at 1500-1520℃ for 5-20min. The iron can be tapped and the first station rough refining molten iron is obtained. If the amount of slag is abnormally large during the smelting process (more than 200kg by visual observation), the amount of slag under the ladle must be strictly controlled or the slag removal operation must be performed;

[0124] 61 tons of cast pig iron, 125 kg of graphite carbon powder and 4.85% of carbon are added to the second station of the induction furnace for rough refining. After smelting, samples are taken for full analysis. The temperature of the molten iron during the smelting process is not higher than 1550°C. After all the charge is smelted, the second holding treatment is carried out at 1500-1520°C for 5-20 minutes, and then the iron can be tapped to obtain the second station rough refining molten iron.

[0125] (2) The first ladle refining furnace adopts a capacity of 130 tons, and the key points of process control are: the diameter of the ladle nozzle is Φ100mm, the baking temperature is greater than 1000℃, the iron temperature is greater than 900℃, the thermal state is good, and the iron temperature drop is less than 50℃; after the crude molten iron of the first station is added to the first ladle refining furnace, sampling and slag making are carried out. The slag making materials are 1000kg of metallurgical lime and 250kg of fluorite. During the smelting process, an appropriate amount of fluorite is added according to the fluidity of the slag. The temperature of the molten iron is kept constant throughout the refining process. The temperature should not exceed 1550℃. The temperature should be raised uniformly with medium voltage. When the temperature reaches 1500-1520℃, a 5-20 minute holding operation should be performed. Argon should be blown from the bottom throughout the process. During the holding process, the argon flow rate should be adjusted so that the slag layer is not exposed on the molten iron surface. The argon flow rate can be appropriately increased when raising the temperature and adding cast iron and steel materials to enhance the mass and heat transfer process of the molten iron. The composition and amount of molten iron should be adjusted by adding steel materials and cast iron. The tapping temperature should be 1500-1520℃. The molten iron should contain 3.05-3.15% C, ≤0.40% Si, ≤0.020% P, ≤0.002% S, and 1.00-1.05% Ni. The molten iron volume should be controlled at 81-85t. Carbon powder is strictly prohibited to increase carbon, that is, to obtain a single refined molten iron.

[0126] The second ladle refining furnace is selected with a capacity of 160 tons. The key points of process control are: the diameter of the ladle nozzle is Φ100mm, the baking temperature is greater than 1000℃, the iron temperature is greater than 900℃, the thermal state is good, and the iron temperature drop is less than 50℃; the first refined molten iron is added to the second ladle refining furnace, and then the second station rough molten iron of the induction furnace is added; after the addition, sampling and slag making are carried out. The slag making material is 750kg of the first batch of fluorite. After the chemical composition results are reported, an appropriate amount of metallurgical lime is added according to the S content to continue desulfurization to meet the internal control specifications. Metallurgical lime is added to iron The water temperature is 1500-1520°C. During the refining process, the molten iron temperature must not exceed 1550°C. A medium voltage is applied to uniformly increase the temperature. When the temperature reaches 1500-1520°C, a holding operation is performed for 5-20 minutes. Argon is blown from the bottom throughout the process. During the holding process, the argon flow rate is adjusted so that the slag layer is not exposed on the molten iron surface. When the temperature is increased, the argon flow rate can be appropriately increased to enhance the mass and heat transfer process of the molten iron. The smelting time is 60-120 minutes, the tapping temperature T is 1480-1520°C, the optimal composition range of the molten iron is C 3.70-3.80%, Si 0.30-0.40%, P ≤ 0.020%, S 0.004-0.009%, and Ni 0.55-0.65%. The molten iron volume is controlled at 140-145 tons. Carbon powder is strictly prohibited to increase carbon. This is to obtain secondary refined molten iron.

[0127] (3) Key points for controlling the molten iron transfer and distribution process: Check the weighing equipment, overhead crane equipment, hydraulic system, motor system and other mechanical equipment in advance to ensure that they are in normal working condition; measure the temperature of the middle part of the lining of the transfer ladle 30 minutes before the secondary refined iron water is distributed, and it is required to be visually red hot. The temperature is greater than 900℃, which can be regarded as the transfer ladle is approximately in a hot saturated state. The empirical formula for the temperature drop of the molten iron during the transfer process is valid; the amount of molten iron distributed is 80t and 60t respectively. After distribution, the temperature of the molten iron in the transfer ladle is measured and samples are taken; the spheroidization temperature is 1395-1405℃, and the molten iron spheroidization temperature is accurately controlled by blowing argon from the bottom of the ladle. The single-eye argon flow rate is 30-50NL / min, and the molten iron temperature drop rate is 1.5-2.0℃ / min. It is strictly forbidden to use a large argon flow rate to cool the molten iron; from the completion of distribution to the start of spheroidization, the entire process time should be controlled within 30-45min. In this example, the 140 tons of molten iron for spheroidization requires secondary refining in a 160-ton ladle furnace. After adjusting the composition and temperature and homogenizing the molten iron, it is then distributed for spheroidization. Each on-site operation is supervised by a dedicated person, and on-site safety procedures are strictly followed, with safety precautions and emergency plans in place. After spheroidization is complete, the ladle is transported to the casting process for final inoculation, slag removal, and pouring.

[0128] (1) The main components of the molten iron smelted by the method of this embodiment after spheroidization inoculation are as follows:

[0129] C 3.77%, Si 1.53%, Mn 0.11%, P 0.015%, S 0.005%, Ni 0.61%, Cr 0.04%, Mo 0.03%, H 1.6ppm, O 10ppm, N 33ppm. It can be seen that the purity of the molten iron smelted by the method of the present invention is higher than that produced by the traditional technical route.

[0130] (II) The ductile iron QT400-18AL prepared in this example was fabricated into spent fuel storage and transportation cylinders. The metallographic structure (50 micrometer magnification) of a sampled cylinder after corrosion is shown in Figure 2. As shown in Figure 2, the graphite structure of the casting is approximately circular, with evenly distributed graphite precipitated along grain boundaries, ranging in size from 30 to 50 micrometers. Subsequent performance testing also demonstrated that the metallurgical quality of the casting exhibits a high degree of uniformity and purity not found in conventional castings. The metallographic structure of the cylinder before corrosion (200 micrometer magnification) is shown in Figure 3. As can be seen, the metallographic structure changes little before and after spent fuel corrosion.

[0131] (III) The actual workpiece on site after semi-finishing of the spent fuel storage and transportation cylinder made of ductile iron in this embodiment is shown in Figure 4. Subsequent non-destructive testing results show that the casting fully meets the technical requirements specified in the design outline.

[0132] Example 3

[0133] This embodiment adopts the same method as that of Example 2 to smelt molten iron, except that the mass of the steel material in the raw materials accounts for 15% of the total mass of the steel material, pig iron and alloy nickel plate, the carbon content in the steel material is 0.35%, the carbon content in the cast pig iron is 4.60%, and the silicon content is 0.50%.

[0134] Example 4

[0135] This embodiment adopts the same method as that of Example 2 to smelt molten iron, except that the mass of the steel material in the raw materials accounts for 17.5% of the total mass of the steel material, pig iron and alloy nickel plate, the carbon content in the steel material is 0.45%, the carbon content in the cast pig iron is 4.70%, and the silicon content is 0.60%.

[0136] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A 100-ton ductile iron cylinder high-purity cast iron smelting device, characterized in that: The device comprises: Induction furnace: The induction furnace includes a first station and a second station, which are used for rough molten iron, and obtains rough molten iron from the first station and the second station; First ladle refining furnace: the first station crude molten iron enters the first ladle refining furnace for primary refining to obtain primary refined molten iron; Second ladle refining furnace: the primary refined molten iron and the second-station rough molten iron are sequentially fed into the second ladle refining furnace for secondary refining to obtain secondary refined molten iron; Distribution equipment: the secondary refined molten iron is distributed and transported in the distribution equipment; Spheroidizing equipment: The divided and transferred molten iron is spheroidized in the spheroidizing equipment.

2. A method for smelting molten iron using the device according to claim 1, characterized in that: The method comprises the following steps: (1) Induction furnace rough refining: including adding cold steel material, cast iron, alloy nickel plate and graphite carbon powder to the first station for rough refining to obtain the first station rough refining molten iron, adding cast iron and graphite carbon powder to the second station for rough refining to obtain the second station rough refining molten iron; (2) Secondary refining in a ladle refining furnace: adding the crude molten iron from the first station into the first ladle refining furnace for primary refining to obtain primary refined molten iron, and adding the primary refined molten iron and the crude molten iron from the second station into the second ladle refining furnace in sequence for secondary refining to obtain secondary refined molten iron; (3) The secondary refined molten iron is transferred and distributed in the distribution equipment in turn, and then transferred to the spheroidizing treatment equipment for spheroidizing treatment.

3. The method for smelting molten iron according to claim 2, characterized in that: The mass of cold steel in the raw materials for molten iron production accounts for 15-20% of the total mass of cold steel, pig iron and alloy nickel plates.

4. The method for smelting molten iron according to claim 2, characterized in that: The cold steel material is roughly smelted to remove phosphorus and carbon in an electric arc furnace, refined in a ladle furnace to adjust carbon and desulfurize, and then cast into a billet in an atmospheric injection mold.

5. The method for smelting molten iron according to claim 2, characterized in that: The cold steel material in step (1) comprises, by mass percentage, C 0.25-0.45%, Si≤0.01%, Mn≤0.05%, P≤0.005%, S≤0.005%, Cr≤0.05%, and Mo≤0.05%.

6. The method for smelting molten iron according to claim 2, characterized in that: In step (1), the cast iron comprises, by mass percentage, C 4.50-4.70%, Si 0.40-0.60%, Mn≤0.100%, P≤0.030%, S≤0.025%, Cr≤0.010%, Ni≤0.10%, Mo≤0.010%, and Ti≤0.050%.

7. The method for smelting molten iron according to claim 2, characterized in that: In step (1), the mass fraction of Ni in the alloy nickel plate is greater than 99.5%.

8. The method for smelting molten iron according to claim 2, characterized in that: In step (1), the process temperature of the molten iron in the first and second stations is ≤1550°C, and the iron is tapped after the charge is completely melted and kept at 1500-1520°C for 5-20 minutes.

9. The method for smelting molten iron according to claim 2, characterized in that: In step (2), the entire process of primary refining and secondary refining adopts the ladle bottom blowing argon stirring method.

10. The method for smelting molten iron according to claim 2, characterized in that: In step (2), slag making treatment is performed in both the primary refining and the secondary refining. Specifically, the slag component requirements are as follows: the slag making materials in the primary refining are metallurgical lime and fluorite, and the mass ratio of metallurgical lime to fluorite is 4:

1. The slag making material in the secondary refining is fluorite.

11. The method for smelting molten iron according to claim 2, characterized in that: The process temperature of the molten iron in the primary refining and the secondary refining in step (2) is ≤1550°C.

12. The method for smelting molten iron according to claim 2, characterized in that: In step (2), cold steel and cast iron are added during the primary refining process to adjust the quality and weight composition of the molten iron.

13. The method for smelting molten iron according to any one of claims 2 to 12, characterized in that: Before the spheroidization treatment in step (3), argon is blown from the bottom of the ladle to even out the temperature of the molten iron so that the spheroidization treatment temperature is 1350-1450°C.

14. The method for smelting molten iron according to claim 2, characterized in that: Step (3) also includes transporting the molten iron after the spheroidization treatment to the casting process for final inoculation, slag removal and pouring.

Images