Preparation method of electroslag remelting high-purity strong deoxidizer calcium carbide and smelting method

Abstract

The application provides a preparation method and a smelting method of electroslag remelting high-purity strong deoxidizer calcium carbide, and belongs to the field of metallurgy. The method comprises the following steps: mixing graphite and lime to obtain a mixture; vacuum smelting the mixture to make the graphite and the lime undergo a carbothermic reduction reaction to obtain blocky calcium carbide; and cooling, crushing and screening the blocky calcium carbide to obtain calcium carbide powder. Through the whole-process control of high-purity raw materials, accurate proportioning, vacuum high-temperature smelting and inert gas protection processing, the calcium carbide deoxidizer with strong deoxidizing capacity and high chemical purity is prepared, which can realize deep deoxidation of molten steel when applied to electroslag remelting, and can simultaneously remove harmful elements such as sulfur, phosphorus and lead, thereby significantly improving the purity of the steel ingot.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and in particular to a method for preparing and smelting high-purity, strong deoxidizing agent calcium carbide by electroslag remelting. Background Technology

[0002] Electroslag remelting (ESR) is an important special metallurgical technology. By melting, refining, and resolidifying consumable electrodes in conductive slag, it effectively improves the crystal structure of ingots, reduces segregation, and increases metal purity. It is a key method for producing high-end bearing steel, die steel, and high-temperature alloys. During ESR, the molten steel or alloy comes into contact with atmospheric oxygen and unstable oxides in the slag, leading to oxygenation. Excessive oxygen content severely affects key mechanical properties such as fatigue performance and impact toughness, and may form harmful non-metallic inclusions. Therefore, deoxidation is one of the core process steps to ensure the quality of ESR products. Efficient and low-pollution deoxidation technology is an important research direction for further improving the quality of ESR products and meeting the extreme performance requirements of materials in aerospace, nuclear power, and other fields.

[0003] Currently, the most common deoxidation method in electroslag remelting is to directly add aluminum powder to the slag or molten steel in the crystallizer. However, aluminum powder itself contains impurities such as phosphorus and sulfur, which contaminate the molten steel during addition. Furthermore, its deoxidation product, Al2O3 inclusions, have high melting points, are small in size, and do not easily float, tending to remain in the steel and form brittle inclusions. Additionally, aluminum powder has limited deoxidation efficiency and lacks the ability to desulfurize, dephosphorize, or remove low-melting-point harmful elements such as phosphorus. The industry also uses silicon-calcium alloy powder added to the slag surface for deoxidation. Deoxidation and partial desulfurization can be achieved by utilizing the dual reducing properties of calcium and silicon. However, the preparation of silicon-calcium alloys also easily introduces phosphorus, sulfur, and trace amounts of harmful elements. Furthermore, calcium has a low boiling point and is easily volatilized at high temperatures, resulting in unstable deoxidation efficiency, low utilization rate, and inability to deeply dephosphorize. In addition, although ordinary industrial-grade calcium carbide (calcium carbide) has basic deoxidation capabilities, it contains impurities such as CaS, Ca3P2, and trace amounts of Pb, which will introduce harmful elements into the molten steel during use, resulting in poor control of S, P, and Pb. Therefore, existing electroslag remelting deoxidation technologies cannot achieve deep deoxidation of molten steel and simultaneous removal of sulfur, phosphorus, and low-melting-point harmful elements without introducing harmful impurities. Summary of the Invention

[0004] This application provides a method for preparing and smelting calcium carbide, a high-purity strong deoxidizer for electroslag remelting, to provide a new method for preparing calcium carbide, a high-purity strong deoxidizer for electroslag remelting, to achieve deep deoxidation of molten steel during electroslag remelting, and to simultaneously remove sulfur, phosphorus and low-melting-point harmful elements from the steel.

[0005] In a first aspect, embodiments of this application provide a method for preparing high-purity, strong deoxidizing agent calcium carbide by electroslag remelting, the method comprising: Graphite and lime with a set purity and a set particle size are mixed to obtain a mixture; Under a set vacuum degree, the mixture is vacuum melted to cause the graphite and lime to undergo a carbothermic reduction reaction to obtain blocky calcium carbide; The blocky calcium carbide is cooled, crushed, and sieved to obtain calcium carbide powder; Wherein, the molar ratio of CaO in the lime to C in the graphite is 1:(3.0~3.5); The vacuum melting process includes the following parameters: heating rate of 10℃ / min to 15℃ / min, temperature of 1650℃ to 1750℃, and holding time of 2h to 4h.

[0006] Optionally, the fixed carbon content of the graphite is >99.99%; The lime has a CaO content > 99.99%.

[0007] Optionally, the graphite has a particle size of 80 mesh to 200 mesh; The lime has a particle size of 80 mesh to 200 mesh.

[0008] Optionally, the set vacuum level is less than 0.1 Pa.

[0009] Optionally, the vacuum melting uses a vacuum melting furnace, which is a medium-frequency induction vacuum furnace or a resistance heating vacuum furnace equipped with a graphite heater. The vacuum melting furnace is equipped with a graphite crucible, and the mixture is loaded into the graphite crucible.

[0010] Secondly, embodiments of this application provide a method for smelting high-purity, strong deoxidizing agent calcium carbide by electroslag remelting, the method comprising: After a stable molten pool is established in the electroslag remelting furnace, deoxidizer particles are added to the surface of the molten pool or to the slag through a feeding system for electroslag remelting; the deoxidizer particles include calcium carbide powder prepared by any one of the methods in the first aspect.

[0011] Optionally, the feeding system includes a storage tank, a pneumatic conveying pipeline, and a feeder; The feeder is located above the molten pool of the electroslag remelting furnace and is used to continuously transport the calcium carbide powder to the surface of the molten pool or into the molten slag through the pneumatic conveying pipe. The feeder is a star feeder, a screw feeder, or a loss-in-weight feeder; The carrier gas used in the pneumatic conveying is argon.

[0012] Optionally, the deoxidizer particles further include calcium oxide powder, wherein the mass of the calcium oxide powder is 3% to 5% of the total mass of the deoxidizer particles.

[0013] Optionally, the parameters of the electroslag remelting include: slag system of 70% CaF2-30% Al2O3, smelting voltage of 46V, arc ignition current of 1500A, smelting current of 2950A-3500A, smelting time of 50min, and deoxidizer particle addition of 2kg / ton of steel.

[0014] Optionally, after electroslag remelting, the oxygen content of the steel ingot is ≤10ppm, the sulfur content is ≤0.0035%, the phosphorus content is ≤0.003%, and the lead content is <1ppm.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a novel method for preparing high-purity, strong deoxidizing agent calcium carbide through electroslag remelting. By controlling the entire process of high-purity raw materials, precise proportioning, vacuum high-temperature melting, and inert gas protection processing, a calcium carbide deoxidizer with both strong deoxidizing ability and high chemical purity is prepared, thereby fundamentally solving the problems of deep deoxidation and simultaneous impurity removal in the electroslag remelting process.

[0016] First, this application controls the purity of raw materials from the source by using high-purity graphite with a fixed carbon content of >99.99% and high-purity lime with a CaO content of >99.99%. This avoids the risk of harmful impurities such as phosphorus, sulfur, and lead carried by traditional deoxidizers (such as industrial aluminum powder, silicon calcium powder, or ordinary calcium carbide) entering the molten steel, thus laying a material foundation for achieving the goal of low sulfur, low phosphorus, and low lead in molten steel.

[0017] Secondly, this application ensures the full progress of the carbothermic reduction reaction and the efficient synthesis of high-purity calcium carbide through precise stoichiometric proportions and a vacuum high-temperature melting process. Specifically, the molar ratio of CaO to C is controlled at 1:3.0–3.5, which not only meets the theoretical reaction requirements but also compensates for carbon loss under high-temperature vacuum with an appropriate amount of excess carbon, ensuring the complete reaction of calcium oxide. Under a vacuum of less than 0.1 Pa, coupled with a heating rate of 10℃ / min–15℃ / min, a melting temperature of 1650℃–1750℃, and a holding time of 2h–4h, air in the reaction system is effectively eliminated, preventing the oxidation of raw materials. At the same time, the CO gas generated in the reaction is continuously extracted, pushing the chemical equilibrium towards the formation of calcium carbide, thereby obtaining a high-purity, highly active blocky calcium carbide product.

[0018] Based on this, this application completes the product post-processing through cooling, crushing, and sieving under inert gas protection to finally obtain a uniform (200 mesh) and pure calcium carbide powder. When this deoxidizer is applied to electroslag remelting, calcium carbide decomposes at high temperature to produce active calcium atoms and carbon. The two components work synergistically to achieve dual deoxidation: active calcium atoms directly combine with dissolved oxygen in the molten steel to form CaO, and carbon reacts with oxygen to generate CO bubbles. While achieving deep deoxidation (oxygen content ≤10ppm), the CO bubbles stir the molten pool, promoting the aggregation and flotation removal of non-metallic inclusions. More importantly, active calcium atoms simultaneously combine with harmful elements such as sulfur, phosphorus, and lead in the molten steel to form stable calcium compounds that float into the slag phase, thus simultaneously achieving integrated treatment of desulfurization, dephosphorization, and removal of low-melting-point harmful elements. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart illustrating a method for preparing high-purity, strong deoxidizing agent calcium carbide by electroslag remelting, as provided in an embodiment of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0024] To overcome the shortcomings of traditional electroslag remelting methods using Al powder and calcium silicate powder for deoxidation, such as the contamination of molten steel by deoxidizers carrying phosphorus / sulfur and other impurities, inconsistent deoxidation efficiency, inability to simultaneously remove harmful elements such as S / P / Pb / As / Sb, and the formation of stubborn inclusions by deoxidation products, this application provides a new vacuum-prepared high-purity calcium carbide deoxidizer production process and a new precise feeding process for electroslag remelting. This process can eliminate the introduction of harmful impurities by deoxidation auxiliaries from the source, achieving integrated deep deoxidation, desulfurization, dephosphorization, and removal of fusible harmful elements. It reduces the total oxygen, S, and P content in steel, decreases non-metallic inclusions, and improves the purity and hot-working yield of special steel alloy ingots. The specific technical solution of this application is as follows: Figure 1 This is a schematic flowchart illustrating a method for preparing high-purity, strong deoxidizing agent calcium carbide by electroslag remelting, as provided in an embodiment of this application.

[0025] like Figure 1 As shown in the embodiment of this application, a method for preparing high-purity, strong deoxidizing agent calcium carbide by electroslag remelting is provided. The method includes: S1. Mix graphite and lime with a set purity and a set particle size to obtain a mixture; S2. Under a set vacuum degree, the mixture is vacuum melted to allow graphite and lime to undergo a carbothermic reduction reaction to obtain blocky calcium carbide. S3. Cool, crush and sieve the blocky calcium carbide to obtain calcium carbide powder.

[0026] It should be noted that the S1 mixing step is a prerequisite for achieving homogenization of the carbothermic reduction reaction. By mechanically mixing the two solid raw materials, graphite and lime, the carbonaceous reducing agent (graphite) and the calcium source (lime) are brought into full contact at the microscale, creating favorable kinetic conditions for the subsequent solid-solid reaction under vacuum and high temperature.

[0027] The S2 vacuum melting step is the core process of the entire preparation method. Under the dual conditions of high temperature and vacuum, carbon in graphite undergoes a carbothermic reduction reaction with calcium oxide in lime: CaO + 3C → CaC2 + CO, converting solid calcium oxide into calcium carbide. The key role of the vacuum environment in this process is to remove air (especially oxygen and nitrogen) from the reaction system, preventing the raw materials from being oxidized at high temperatures, and simultaneously extracting the carbon monoxide gas generated in the reaction zone in a timely manner, promoting a continuous shift in chemical equilibrium towards the formation of calcium carbide, thereby improving the reaction conversion rate and product purity. The final obtained blocky calcium carbide is the effective component of the target deoxidizer.

[0028] The S3 cooling, crushing, and screening steps process large-sized lumps of calcium carbide obtained from vacuum melting into powdered deoxidizer suitable for electroslag remelting. After cooling the product to a safe processing temperature, the lumps are mechanically crushed to reduce the particle size to a suitable size, and then screened to obtain a powdered product with uniform particle size.

[0029] In some embodiments, the molar ratio of CaO in lime to C in graphite is 1:(3.0 to 3.5).

[0030] The molar ratio of CaO in lime to C in graphite is limited to 1:(3.0–3.5), providing a reasonable material ratio basis for the carbothermic reduction reaction. Excess carbon allows the reducing atmosphere required for the reaction to be maintained even when carbon undergoes volatilization and burn-off under high-temperature vacuum conditions. Simultaneously, excess carbon can act as an auxiliary deoxidizing element in the subsequent electroslag remelting stage without introducing harmful impurities, ensuring complete calcium oxide reaction and preventing unreacted residual CaO from affecting the purity of the deoxidizer. For example, the molar ratio of CaO to C can be 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, etc.

[0031] In some embodiments, vacuum melting includes the following parameters: heating rate of 10℃ / min to 15℃ / min, temperature of 1650℃ to 1750℃, and holding time of 2h to 4h.

[0032] The heating rate is limited to 10℃ / min to 15℃ / min to ensure good synchronization between the furnace temperature and the internal temperature of the material, guaranteeing uniform heat transfer throughout the reaction system and preventing uneven reactions caused by excessive temperature differences between the inside and outside of the material due to rapid heating, while also considering production efficiency. The temperature is limited to 1650℃ to 1750℃, covering the activation energy threshold required for the carbothermic reduction reaction, ensuring that the reactants have sufficiently high chemical activity and diffusion rate to allow the reaction to proceed fully, while also allowing reasonable operating margins for temperature control accuracy and loading variations in industrial equipment. The holding time is limited to 2h to 4h to provide sufficient kinetic time for the solid-solid reaction, ensuring that the reaction achieves a high conversion rate at the target temperature. For example, the heating rate can be 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, etc. The melting temperature can be 1650℃, 1660℃, 1670℃, 1680℃, 1700℃, 1710℃, 1720℃, 1730℃, etc. The holding time can be 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0033] In some embodiments, the fixed carbon content of graphite is >99.99%; The CaO content of lime is >99.99%.

[0034] By limiting the fixed carbon content to >99.99% and the CaO content of the lime to >99.99%, the purity of the deoxidizer product is controlled from the source. The high-purity raw materials contain extremely low levels of harmful impurities such as phosphorus, sulfur, and lead, avoiding contamination of the molten steel by impurities carried by the deoxidizer itself during deoxidation preparation and subsequent electroslag remelting deoxidation, thus ensuring that the final deoxidizer product has extremely high chemical purity.

[0035] In some embodiments, the graphite particle size is 80 mesh to 200 mesh; The particle size of lime is 80 mesh to 200 mesh.

[0036] By limiting the particle size of both graphite and lime to 80-200 mesh, the two powders achieve similar particle size distribution and flow characteristics during mixing, which facilitates uniform mixing. Simultaneously, increasing the specific surface area of ​​the raw material particles allows for a more thorough solid-solid reaction interface, shortens the average diffusion path of reactants, and helps reduce the reaction time. For example, the particle size of graphite can be 80 mesh, 95 mesh, 110 mesh, 125 mesh, 140 mesh, 155 mesh, 170 mesh, 185 mesh, etc., and the particle size of lime can be 80 mesh, 95 mesh, 110 mesh, 125 mesh, 140 mesh, 155 mesh, 170 mesh, 185 mesh, etc.

[0037] In some implementations, the vacuum level is set to be less than 0.1 Pa.

[0038] Setting the vacuum level to less than 0.1 Pa creates the low-pressure atmosphere required for the reaction. At this vacuum level, the residual oxygen and water vapor content in the system is extremely low, effectively preventing the oxidation of carbon and calcium at high temperatures. Simultaneously, the reaction byproduct CO gas is continuously and rapidly expelled from the reaction zone, shifting the chemical equilibrium towards the formation of calcium carbide, thereby improving the reaction conversion rate and product purity. For example, the vacuum level can be set to 0.01 Pa, 0.02 Pa, 0.03 Pa, 0.04 Pa, 0.05 Pa, 0.06 Pa, 0.07 Pa, 0.08 Pa, etc.

[0039] In some embodiments, vacuum melting uses a vacuum melting furnace, which is a medium-frequency induction vacuum furnace or a resistance heating vacuum furnace equipped with a graphite heater. The vacuum melting furnace is equipped with a graphite crucible, and the mixture is loaded into the graphite crucible.

[0040] Medium-frequency induction vacuum furnaces or resistance heating vacuum furnaces can meet the process requirements of high temperature (1650℃~1750℃) and vacuum degree (less than 0.1Pa), providing a stable thermal field and vacuum environment for carbothermic reduction reactions. Both the graphite heater and the graphite crucible are made of high-purity graphite, which does not chemically react with the reactants at high temperatures, thus avoiding the introduction of impurities into the product due to corrosion of the heating element or crucible material.

[0041] In some embodiments, graphite and lime are dried at 120°C for more than 4 hours before mixing to remove moisture.

[0042] In some embodiments, the calcium carbide preparation process mainly includes a raw material pretreatment unit, a vacuum melting furnace unit, and a product processing unit. The raw material pretreatment unit is used to crush and dry high-purity graphite and high-purity lime; the vacuum melting furnace unit includes a furnace body, a graphite heater, a temperature measuring device, a vacuum system, and a water cooling system, with a graphite crucible installed inside the furnace; the product processing unit includes a crusher and a screening machine under inert gas protection. The graphite heater is made of high-purity isostatic graphite; the graphite crucible is also made of high-purity graphite; the temperature measuring device uses an infrared thermometer or a W-Re thermocouple; the feeder uses a star feeder or a screw feeder to achieve quantitative and continuous addition of the powdered deoxidizer.

[0043] Based on a general inventive concept, embodiments of this application provide a method for smelting high-purity, strong deoxidizing agent calcium carbide by electroslag remelting, the method comprising: After a stable molten pool is established in the electroslag remelting furnace, deoxidizer particles are added to the surface of the molten pool or into the slag through a feeding system for electroslag remelting; the deoxidizer particles include calcium carbide powder prepared by any of the above methods.

[0044] In the electroslag remelting process, after the consumable electrode melts to form a molten pool, the prepared high-purity calcium carbide powder is continuously and uniformly added to the surface of the molten pool or into the slag through a feeding system. Calcium carbide decomposes at high temperatures to produce active calcium atoms (Ca) and carbon. The calcium atoms combine with oxygen in the molten steel to form calcium oxide (CaO), while the carbon reacts with oxygen in the molten steel to produce CO, which escapes as a gas and simultaneously acts as a gas stirrer. Due to the extremely strong affinity of calcium and carbon for oxygen, efficient deoxidation is achieved. The generated CaO enters the slag phase and is removed along with the slag; simultaneously, the active calcium can combine with S, P, Pb, As, and Sb in the molten steel to form stable calcium compounds that float into the slag, achieving simultaneous removal of multiple elemental impurities.

[0045] In some implementations, the feeding system includes a storage tank, a pneumatic conveying pipeline, and a feeder; The feeder is located above the molten pool in the electroslag remelting furnace and is used to continuously transport calcium carbide powder to the surface of the molten pool or into the molten slag through a pneumatic conveying pipeline. The feeder can be a star feeder, a screw feeder, or a loss-in-weight feeder; Argon is used as the carrier gas in pneumatic conveying.

[0046] The feeding system enables quantitative, continuous, and closed-loop conveying of deoxidizer during electroslag remelting. Star feeders, screw feeders, or loss-in-weight feeders precisely control the powder feed flow rate, ensuring the feed rate matches the smelting conditions. The deoxidizer is directly blown onto the surface of the molten pool via pneumatic conveying pipelines, ensuring uniform dispersion and full contact with the slag. The fully closed conveying process prevents the high-purity calcium carbide powder from contacting air and oxidizing during transport, while also eliminating dust leakage and environmental pollution, ensuring the stability of the composition and operational safety during the feeding process.

[0047] In some embodiments, the deoxidizer particles also include calcium oxide powder, the mass of which is 3% to 5% of the total mass of the deoxidizer particles.

[0048] Calcium oxide, acting as a fluxing agent, is combined with calcium carbide to lower the overall melting point of the composite deoxidizer particles, accelerating the dissolution rate of calcium carbide in slag and molten steel. This allows calcium carbide to disperse rapidly after addition, releasing active calcium atoms to participate in the deoxidation reaction. Simultaneously, the calcium oxide component, once incorporated into the slag system, helps adjust the composition of inclusions, making it easier for deoxidation-generated inclusions to aggregate, grow, and float for removal, thus achieving optimized control of inclusion morphology.

[0049] In some implementations, the parameters for electroslag remelting include: a slag system of 70% CaF2-30% Al2O3, a smelting voltage of 46V, an arc ignition current of 1500A, a smelting current of 2950A-3500A, a smelting time of 50min, and an addition amount of 2kg / ton of deoxidizer particles.

[0050] In some embodiments, after electroslag remelting, the oxygen content of the steel ingot is ≤10ppm, the sulfur content is ≤0.0035%, the phosphorus content is ≤0.003%, and the lead content is <1ppm.

[0051] The oxygen content was controlled at 10 ppm or below, indicating that calcium carbide deoxidizer can achieve deep deoxidation and significantly reduce the number of oxide inclusions in the steel. The sulfur and phosphorus contents were reduced to below 0.0035% and 0.003% respectively, proving that the active calcium atoms produced by the decomposition of calcium carbide combine with the sulfur and phosphorus in the molten steel to form stable calcium compounds that float into the slag, thus achieving simultaneous deep desulfurization and dephosphorization. The lead content was below 1 ppm, indicating that active calcium also has a significant removal effect on low-melting-point harmful elements.

[0052] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0053] Special steel consumable electrodes were selected, and the electroslag remelting slag system consisted of 70% CaF2 and 30% Al2O3. The smelting process parameters were: voltage 46V, arc ignition current 1500A, smelting current 2950A–3500A, and smelting time 50 minutes. The deoxidizer was added at a rate of 2 kg / ton of steel, in multiple additions during the mid-stage of electroslag remelting. The example and comparative examples differed only in the type of deoxidizer; all other process parameters were identical. After smelting, samples were taken to test the mass percentages of total oxygen (O), sulfur (S), phosphorus (P), and lead (Pb) in the steel ingots.

[0054] Example 1 The deoxidizer is a high-purity CaC2 powder prepared under vacuum. The preparation method is as follows: High-purity graphite (fixed carbon content 99.992%) and high-purity lime (CaO content 99.993%, P and S content extremely low) are separately crushed to 200 mesh and dried at 120℃ for 4 hours to remove moisture. They are then mixed evenly in a mixer at a molar ratio of CaO:C = 1:3.2. The mixture is then placed in a high-purity graphite crucible and compacted. It is placed in the homogenization zone of a vacuum melting furnace, and the vacuum is evacuated to <0.1 Pa. The temperature is increased to 1700℃ at a rate of 10℃ / min and held for 2 hours to carry out a carbothermic reduction reaction to synthesize high-purity calcium carbide. After the reaction, heating is stopped, and high-purity argon gas is introduced into the furnace to atmospheric pressure to accelerate cooling. When the temperature drops below 200℃, the mixture is removed from the furnace. The reaction product is taken out in an argon-filled glove box or sealed equipment, initially crushed with a jaw crusher, then finely crushed with a double roll crusher, and finally sieved to obtain 200-mesh high-purity calcium carbide powder. It is then immediately sealed and stored in a dry inert gas protected container to obtain 200-mesh high-purity calcium carbide powder.

[0055] During the electroslag remelting process, the amount of deoxidizer added is 2 kg / ton of steel. In the middle stage of smelting, it is added in multiple times by argon pneumatic conveying and evenly spread on the liquid surface in the crystallizer to complete the deoxidation.

[0056] Example 2 The deoxidizer is a composite granule of high-purity CaC2 powder and 4% calcium oxide, prepared under vacuum. The preparation method is as follows: High-purity graphite with a fixed carbon content of 99.994% and high-purity lime with a CaO content of 99.992% are mixed at a molar ratio of CaO:C = 1:3.3. After uniform mixing, the mixture is placed in a high-purity graphite crucible and placed in a vacuum melting furnace. The furnace is evacuated to <0.1 Pa and heated to 1700℃ at a rate of 15℃ / min, and held at this temperature for 2 hours to carry out a carbothermic reduction reaction to synthesize high-purity calcium carbide. After the reaction, the mixture is cooled, crushed, and sieved under argon protection to obtain 200-mesh high-purity calcium carbide powder. Then, the high-purity calcium carbide powder and 4% calcium oxide powder are uniformly mixed using a ball mill to prepare composite deoxidizer granules.

[0057] During the electroslag remelting process, the amount of deoxidizer added is 2 kg / ton of steel. In the middle stage of smelting, it is added in multiple times by argon pneumatic conveying and evenly spread on the liquid surface in the crystallizer to complete the deoxidation.

[0058] Comparative Example 1 The deoxidizer is industrial-grade calcium carbide (industrial calcium carbide) with a particle size of 100 mesh. During electroslag remelting, the deoxidizer is added at a rate of 2 kg / ton of steel, applied all at once during the mid-stage of smelting. All other process parameters remain consistent with the example.

[0059] Comparative Example 2 The deoxidizer is industrial aluminum powder with a particle size of 100 mesh. During the electroslag remelting process, the deoxidizer is added at a rate of 2 kg / ton of steel, and is added all at once during the middle stage of smelting. The aluminum powder reacts with dissolved oxygen in the steel to generate Al2O3, thus achieving deoxidation. The remaining process parameters are consistent with those in the example.

[0060] Comparative Example 3 The deoxidizer is industrial calcium silicate powder with a particle size of 100 mesh. During electroslag remelting, the deoxidizer is added at a rate of 2 kg / ton of steel, following conventional processes. All other process parameters remain consistent with the example.

[0061] After the electroslag remelting of Examples 1-2 and Comparative Examples 1-3, the surface quality and main elemental composition of the steel ingots were tested, as shown in Table 1.

[0062] Table 1. Impurity content and quality of steel ingots after electroslag remelting.

[0063] It can be seen that the oxygen content of the steel ingot in Example 1 is 10 ppm, the sulfur mass fraction is 0.0030%, the phosphorus mass fraction is 0.0025%, and the lead content is 0.2 ppm; the steel ingot has excellent appearance quality, a smooth surface, and no large-sized inclusions.

[0064] It can be seen that the oxygen content of the steel ingot in Example 2 is 8 ppm, the sulfur mass fraction is 0.0020%, the phosphorus mass fraction is 0.0018%, and the lead content is 0.1 ppm; the surface of the steel ingot is smooth and there are no large-sized inclusions, and the level of impurity control is better than that in Example 1.

[0065] It can be seen that the oxygen content of the steel ingot in Comparative Example 1 is 20 ppm, the sulfur mass fraction is 0.0185%, the phosphorus mass fraction is 0.025%, and the lead content is 10 ppm; the steel ingot has a slight slag adhesion problem and also shows point-like inclusion defects.

[0066] It can be seen that the oxygen content of the steel ingot in Comparative Example 2 is 25 ppm, the sulfur mass fraction is 0.0192%, the phosphorus mass fraction is 0.030%, and the lead content is 5 ppm; the slag skin of the steel ingot is relatively thick, and there are a large number of alumina inclusions inside the steel ingot.

[0067] It can be seen that the oxygen content of the steel ingot of Comparative Example 3 is 35 ppm, the sulfur mass fraction is 0.0151%, the phosphorus mass fraction is 0.020%, and the lead content is 5 ppm; a small number of pores are visible on the surface of the steel ingot, and there are large inclusions with a size >3 μm inside the steel matrix.

[0068] Compared with Comparative Examples 1-3, Examples 1-2 have lower oxygen control levels (≤10ppm), lower sulfur control levels (≤0.0030), lower phosphorus control levels (≤0.0025), and lower Pb control levels (≤0.2ppm). The steel ingot surface is smoother and free of large-sized inclusions.

[0069] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: (1) Significantly improved deoxidation efficiency: High-purity calcium carbide is used as the deoxidizer in electroslag remelting. The active calcium atoms produced by its decomposition at high temperature have a strong affinity for oxygen and can react quickly and deeply with dissolved oxygen in the molten steel, thus stabilizing the oxygen content of the molten steel at 10 ppm or below. In contrast, the Al2O3 inclusions produced by traditional aluminum powder deoxidation have high melting points, small sizes, and are not easy to aggregate and float, easily remaining in the steel to form brittle inclusions. The deoxidation efficiency is limited and it is impossible to reduce the oxygen content to a low level. The calcium in silicon calcium powder has a low boiling point and is easy to volatilize at high temperatures, resulting in unstable deoxidation efficiency, low utilization rate, and the presence of pores and large inclusions on the surface of the steel ingot. Ordinary industrial calcium carbide only has basic deoxidation capabilities, and the oxygen content control level is far lower than that of this application. This application significantly reduces oxide inclusions and effectively improves the impact toughness and fatigue life of steel.

[0070] (2) Preventing secondary pollution of molten steel from the source: This application uses high-purity graphite with a fixed carbon content >99.99% and high-purity lime with a CaO content >99.99% as raw materials to prepare deoxidizers in a vacuum environment, ensuring that the content of harmful impurities such as phosphorus, sulfur, and lead in the final product, high-purity calcium carbide, is extremely low, thus eliminating the problem of steel contamination caused by impurities carried by the deoxidizer itself from the source. Traditional aluminum powder and calcium silicate powder are prone to introducing phosphorus, sulfur, and trace harmful elements during the preparation process, which will contaminate the molten steel during the addition process; ordinary industrial calcium carbide itself contains CaS, Ca3P2, and trace Pb impurities, and harmful elements enter the molten steel during use, resulting in poor control of S, P, and Pb. The finished product of this application can reduce S to below 0.0035%, P to within 0.003%, and Pb to less than 1 ppm.

[0071] (3) Simultaneous deep removal of multiple elements: In the electroslag remelting process, the active calcium atoms of the high-purity calcium carbide in this application not only combine with oxygen in the molten steel to form CaO for deoxidation, but also combine with harmful elements such as S, P, Pb, As, and Sb in the molten steel to form stable calcium compounds that float into the slag, achieving integrated and synergistic treatment of deoxidation, desulfurization, dephosphorization, and removal of low-melting-point harmful elements. Traditional aluminum powder lacks dephosphorization and deep desulfurization capabilities and cannot remove Pb; silicon-calcium powder cannot perform deep dephosphorization; and ordinary industrial calcium carbide has poor control over harmful elements. This application effectively solves the problem of hot rolling cracking in special steel and significantly improves the rolling yield.

[0072] (4) Optimizing the electroslag system and promoting inclusion removal: After the CaO generated by the calcium carbide deoxidation reaction enters the slag phase, it can improve the physical properties of the electroslag system, reduce the viscosity of the molten slag, make the slag surface smooth and less prone to sticking to steel, and reduce the power consumption of smelting; at the same time, the CO gas generated by the reaction has a stirring effect on the molten pool, promoting the full aggregation, growth and flotation removal of various non-metallic inclusions. Compared with the problem of Al2O3 hard inclusions remaining in the steel and thick slag skin generated by aluminum powder deoxidation, this application effectively reduces the number of brittle inclusions in the steel and improves the surface quality of the steel ingot.

[0073] (5) The composite formulation further enhances the purity: In the preferred embodiment of this application, high-purity calcium carbide powder is compounded with CaO additive to prepare composite deoxidizer particles. Calcium oxide, as a co-solvent, can reduce the overall melting point of the composite particles, accelerate the dissolution rate of calcium carbide in slag and steel, further reduce the content of O, S, P and Pb in steel, and modify the morphology of inclusions to meet the smelting requirements of ultra-high purity special alloys in high-end fields such as aviation and nuclear power.

[0074] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing high-purity, strong deoxidizing agent calcium carbide by electroslag remelting, characterized in that, The method includes: Graphite and lime with a set purity and a set particle size are mixed to obtain a mixture; Under a set vacuum degree, the mixture is vacuum melted to cause the graphite and lime to undergo a carbothermic reduction reaction to obtain blocky calcium carbide; The blocky calcium carbide is cooled, crushed, and sieved to obtain calcium carbide powder; Wherein, the molar ratio of CaO in the lime to C in the graphite is 1:(3.0~3.5); The vacuum melting process includes the following parameters: heating rate of 10℃ / min to 15℃ / min, temperature of 1650℃ to 1750℃, and holding time of 2h to 4h.

2. The method according to claim 1, characterized in that, The graphite has a fixed carbon content >99.99%; The lime has a CaO content > 99.99%.

3. The method according to claim 1, characterized in that, The graphite has a particle size of 80 mesh to 200 mesh; The lime has a particle size of 80 mesh to 200 mesh.

4. The method according to claim 1, characterized in that, The set vacuum level is less than 0.1 Pa.

5. The method according to claim 1, characterized in that, The vacuum melting uses a vacuum melting furnace, which is a medium-frequency induction vacuum furnace or a resistance heating vacuum furnace equipped with a graphite heater. The vacuum melting furnace is equipped with a graphite crucible, and the mixture is loaded into the graphite crucible.

6. A method for smelting high-purity, strong deoxidizing agent calcium carbide by electroslag remelting, characterized in that, The method includes: After a stable molten pool is established in the electroslag remelting furnace, deoxidizer particles are added to the surface of the molten pool or into the slag through a feeding system for electroslag remelting; the deoxidizer particles include calcium carbide powder prepared by any one of claims 1 to 5.

7. The method according to claim 6, characterized in that, The feeding system includes a storage tank, a pneumatic conveying pipeline, and a feeder; The feeder is located above the molten pool of the electroslag remelting furnace and is used to continuously transport the calcium carbide powder to the surface of the molten pool or into the molten slag through the pneumatic conveying pipe. The feeder is a star feeder, a screw feeder, or a loss-in-weight feeder; The carrier gas used in the pneumatic conveying is argon.

8. The method according to claim 6, characterized in that, The deoxidizer particles also include calcium oxide powder, the mass of which is 3% to 5% of the total mass of the deoxidizer particles.

9. The method according to claim 6, characterized in that, The parameters for electroslag remelting include: slag system of 70% CaF2-30% Al2O3, smelting voltage of 46V, arc ignition current of 1500A, smelting current of 2950A-3500A, smelting time of 50min, and deoxidizer particle addition of 2kg / ton of steel.

10. The method according to claim 6, characterized in that, After electroslag remelting, the oxygen content of the steel ingot is ≤10ppm, the sulfur content is ≤0.0035%, the phosphorus content is ≤0.003%, and the lead content is <1ppm.

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