Method for preparing high-purity rare earth iron alloy through vacuum reduction smelting
Through vacuum reduction and smelting method, metal calcium and barium react with rare earth chloride under vacuum conditions, the existing rare earth ferroalloy has high oxygen content and poor cleanliness, and high-purity rare earth ferroalloys are prepared to meet the smelting needs of high-quality rare earth steel.
Patent Information
- Application Number
- CN202510390034.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-06-27
AI Technical Summary
The existing rare earth ferroalloy preparation methods cannot meet the needs of high-quality rare earth steel, and the product has high oxygen content and poor cleanliness.
The vacuum reduction and smelting method is used to prepare high-purity rare earth ferroalloys by reacting metal calcium and barium with rare earth chloride under vacuum conditions.
The preparation of high-purity rare earth ferroalloy is realized, the total impurity, oxygen content and sulfur content are reduced, and the smelting needs of high-quality rare earth steel are met.
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Figure CN120210451A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a method for preparing high-purity rare earth ferroalloy by vacuum reduction melting. Background Art
[0002] Rare earth elements have the functions of refining grains, improving properties, inhibiting harmful elements, deoxidizing and desulfurizing, and modifying in steel, which can improve various properties of steel. Due to the strong chemical activity of rare earth elements, most of them are added in the form of rare earth ferroalloy during smelting. Therefore, the quality of rare earth ferroalloy is particularly important for the smelting effect of rare earth steel.
[0003] At present, for rare earth ferroalloys such as rare earth ferrosilicon alloy, the main preparation methods include carbothermal method, silicothermal method and melting blending method. The carbothermal method has the characteristics of high rare earth recovery rate, short process and low production cost. The silicothermal method has the characteristics of flexibility and high efficiency. The melting blending method is used to produce specific rare earth ferrosilicon alloy with low silicon content. The common feature of these three methods is that the obtained rare earth ferroalloy products have a relatively high oxygen content and a large difference in cleanliness level, and currently cannot meet the requirements for producing high-quality rare earth steel. Summary of the Invention
[0004] In view of the above technical problems, the present invention provides a method for preparing high-purity rare earth ferroalloy by vacuum reduction melting, so as to solve the technical problem of how to prepare high-purity rare earth ferroalloy, especially the high-purity rare earth ferroalloy required for smelting high-quality rare earth steel.
[0005] The object of the present invention is mainly achieved through the following technical solutions:
[0006] The present invention provides a method for preparing high-purity rare earth ferroalloy by vacuum reduction melting, comprising the following steps:
[0007] Step S1: Add pure iron into the melting chamber of a vacuum melting furnace, add rare earth chloride and a reducing agent into the feeder of the vacuum melting furnace. After the vacuum degree in the vacuum melting furnace reaches 67 - 150 Pa and is maintained, start powering on to raise the temperature; the rare earth chloride is cerium chloride and / or lanthanum chloride; the reducing agent is calcium or barium;
[0008] Step S2: Raise the temperature of the molten iron to 1600 - 1650 °C and maintain it. Add the rare earth chloride and the reducing agent in the feeder into the molten iron, and process for 20 - 30 min. During the process, maintain the vacuum degree in the vacuum melting furnace at 67 - 150 Pa;
[0009] Step S3: After the treatment is completed, cast at 1600 - 1650 °C, and then keep warm for 5 - 15 min. During the process, maintain the vacuum degree in the vacuum melting furnace at 67 - 150 Pa;
[0010] Step S4: Cooling with the furnace to obtain a high-purity rare earth ferroalloy, while maintaining the vacuum degree in the vacuum melting furnace at 67 - 150 Pa during the process;
[0011] The high-purity rare earth ferroalloy is a ferroalloy containing rare earth cerium and / or lanthanum. By mass percentage, the iron content is 60 - 90%, the balance is cerium and / or lanthanum, the total impurity content is < 0.1%, the oxygen content is < 0.005%, and the sulfur content is < 0.002%.
[0012] Further, in step S1, by mass percentage, the iron content of pure iron is above 99.8%, the oxygen content is 0.02 - 0.04%, and the carbon content is 0.02 - 0.04%.
[0013] Further, in step S1, by mass percentage, the purity of calcium is above 99%, and the purity of barium is above 99%.
[0014] Further, in step S1, by mass percentage, the purity of rare earth chloride is above 99.5%.
[0015] Further, when preparing a high-purity rare earth ferroalloy containing rare earth cerium, the rare earth chloride in step S1 is cerium chloride; when preparing a high-purity rare earth ferroalloy containing rare earth lanthanum, the rare earth chloride in step S1 is lanthanum chloride; when preparing a high-purity rare earth ferroalloy containing rare earth cerium and lanthanum, the rare earth chloride in step S1 is cerium chloride and lanthanum chloride.
[0016] Further, the added mass of the rare earth chloride in step S1 is calculated based on the rare earth content in the rare earth chloride being 130 - 150% of the rare earth content in the high-purity rare earth ferroalloy to be prepared.
[0017] Further, the added mass of calcium in step S1 is calculated based on 2 - 3 times the mass required for complete reaction with the rare earth chloride.
[0018] Further, the added mass of barium in step S1 is calculated based on 1.5 - 2 times the mass required for complete reaction with the rare earth chloride.
[0019] Further, the particle size ranges of the rare earth chloride, calcium, and barium in step S1 are all 20 mm - 50 mm.
[0020] Further, the vacuum melting furnace in step S1 is a vacuum induction melting furnace or a vacuum arc melting furnace.
[0021] Compared with the prior art, the present invention can achieve at least one of the following technical effects:
[0022] (1) Under vacuum conditions, on the surface of molten iron at 1600 - 1650 °C, calcium and barium metals react with CeCl3 and LaCl3 in rare earth chlorides to obtain high-purity rare earth ferroalloy, reducing the cost of preparing rare earth master alloy using pure rare earth metals, and thus reducing the preparation cost of rare earth steel.
[0023] (2) Through the reasonable ratio of pure iron, rare earth chlorides and reducing agents, a high-purity rare earth ferroalloy with controllable composition is obtained, and the total impurity content, oxygen content and sulfur content are reduced to ideal levels.
[0024] (3) During the casting heat preservation and the high-temperature period of furnace cooling, relying on the density and volatility differences of various chlorides and metals, iron slag separation is achieved, thereby reducing the impurity content, oxygen content and sulfur content in the high-purity rare earth ferroalloy. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference numerals represent the same components.
[0026] Figure 1 It is a Gibbs free energy trend diagram of the reaction of Ca, Ba and CeCl3, LaCl3 at different temperatures. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0027] The following further describes in detail a method for preparing high-purity rare earth ferroalloy by vacuum reduction melting in combination with specific embodiments. These embodiments are only for the purpose of comparison and explanation, and the present invention is not limited to these embodiments.
[0028] The present invention provides a method for preparing high-purity rare earth ferroalloy by vacuum reduction melting, including the following steps:
[0029] Step S1: Add pure iron into the melting chamber of the vacuum melting furnace, add rare earth chlorides and reducing agents into the feeder of the vacuum melting furnace. Wait for the vacuum degree in the vacuum melting furnace to reach 67 - 150 Pa and maintain it, then start powering on to raise the temperature.
[0030] Step S2: Raise the temperature of the molten iron to 1600 - 1650 °C and maintain it. Add the rare earth chlorides and reducing agents in the feeder into the molten iron, and process for 20 - 30 min. During the process, maintain the vacuum degree in the vacuum melting furnace at 67 - 150 Pa.
[0031] Step S3: After the treatment is completed, cast at 1600 - 1650 °C, then keep it warm for 5 - 15 min. During the process, maintain the vacuum degree in the vacuum melting furnace at 67 - 150 Pa.
[0032] Step S4: Cooling with the furnace to obtain a high-purity rare earth ferroalloy, and maintaining the vacuum degree in the vacuum melting furnace at 67-150 Pa during the process.
[0033] It should be noted that the high-purity rare earth ferroalloy prepared by the present invention is a ferroalloy containing rare earth cerium and / or lanthanum. By mass percentage, the iron content is 60-90%, the balance is cerium and / or lanthanum, the total impurity content is <0.1%, the oxygen content is <0.005%, and the sulfur content is <0.002%.
[0034] Specifically, in step S1, the purity of iron is more than 99.8% by mass percentage, the oxygen content in iron is 0.02-0.04%, and the carbon content is 0.02-0.04%.
[0035] The rare earth chloride is cerium chloride and / or lanthanum chloride. Specifically, when preparing a high-purity rare earth ferroalloy containing rare earth cerium, the rare earth chloride is cerium chloride; when preparing a ferroalloy containing rare earth lanthanum, the rare earth chloride is lanthanum chloride; when preparing a high-purity rare earth ferroalloy containing rare earth cerium and lanthanum, the rare earth chloride is cerium chloride and lanthanum chloride. The purity of the rare earth chloride is more than 99.5% by mass percentage. According to the requirements of the composition of the high-purity rare earth ferroalloy to be prepared, the added mass of the rare earth chloride is calculated based on the fact that the rare earth content in the rare earth chloride is 130-150% of the rare earth content in the high-purity rare earth ferroalloy to be prepared.
[0036] The reducing agent is calcium or barium. The purities of calcium and barium are both more than 99% by mass percentage. The added mass of calcium is calculated as 2-3 times the mass required for complete reaction with the rare earth chloride, and the added mass of barium is calculated as 1.5-2 times the mass required for complete reaction with the rare earth chloride; the particle size ranges of the rare earth chloride, calcium, and barium are all 20 mm-50 mm. The vacuum melting furnace is an electric furnace, such as a vacuum induction melting furnace, a vacuum arc melting furnace, etc.
[0037] It should be noted that in step S2, the rare earth chloride will react with metallic calcium or barium. Specifically, for example:
[0038] 3Ca (l) +2CeCl 3(l) =3CaCl 2(l) +2Ce (l) ΔG 0 =-313245.14+5.60T (1)
[0039] 3Ca (l) +2LaCl 3(l) =3CaCl 2(l) +2La (l) ΔG 0 =-281921.54+24.75T (2)
[0040] 3Ba (l) +2CeCl 3(l) =3BaCl 2(l) +2Ce (l) ΔG 0 =-494239.58 + 29.43T (3)
[0041] 3Ba (l) +2LaCl 3(l) =3BaCl 2(l) +2La (l) ΔG 0 =-467673.74 + 51.23T (4)
[0042] Cerium chloride and / or lanthanum chloride react with metallic calcium or barium on the surface of molten iron at 1600 °C. The melting temperature of cerium chloride in reaction formulas (1), (2), (3), and (4) is 848 °C, the melting temperature of lanthanum chloride is 860 °C, the melting temperature of calcium chloride is 772 °C, the melting temperature of barium chloride is 960 °C, the melting temperature of metallic calcium is 839 °C, the melting temperature of metallic barium is 725 °C, the melting temperature of rare earth cerium is 798 °C, and the melting temperature of rare earth lanthanum is 921 °C. Therefore, they all exist in liquid form at the reaction temperature of 1600 °C.
[0043] According to reaction formulas (1), (2), (3), and (4), by setting the activity of pure metals and chlorides to 1, the Gibbs free energy trend diagrams of the reactions between Ca, Ba and CeCl3, LaCl3 at different temperatures as shown in Figure 1 can be obtained. As Figure 1 can be seen, between the thermodynamic temperatures of 1300 - 2000 K, that is, between 1027 - 1727 °C, metallic calcium and barium can react with rare earth chlorides CeCl3 and LaCl3 to form liquid rare earth cerium and lanthanum. Considering the melting point of ferroalloy and the kinetics of chemical reactions, the reaction temperature is limited to between 1600 - 1650 °C. At this temperature, the liquid rare earth cerium and lanthanum formed can be fully dissolved and dispersed in the molten iron to form rare earth ferroalloy; if the temperature is too high, exceeding 1650 °C, the superheat of the metal is too high, the physical and chemical activities are enhanced, and the burnout is serious, resulting in unnecessary energy and material losses.
[0044] It should be noted that during the post-casting heat preservation process in step S3 and the high-temperature period of furnace cooling in step S4, the reactants and products in step S2, such as cerium chloride, lanthanum chloride, calcium chloride, barium chloride, calcium, barium, cerium, and lanthanum, rely on the density and volatility differences to achieve the separation of iron slag. For example, under standard conditions, the densities of rare earth metals cerium and lanthanum are 6.70 g / cm 3 and 6.16 g / cm 3, relatively high; while the densities of cerium chloride, lanthanum chloride, calcium chloride, barium chloride, calcium, and barium under standard conditions are 3.97 g / cm 3 , 3.84 g / cm 3 , 2.15 g / cm 3 , 3.86 g / cm 3 , 1.55 g / cm 3 , 3.50 g / cm 3 , relatively low; in addition, the decomposition temperature of calcium chloride is about 1000 °C at most, the boiling point of barium chloride is 1560 °C, the volatilization temperature of calcium is 842 °C, and the volatilization temperature of barium is 1360 °C. Therefore, in the smelting temperature range of 1600 - 1650 °C in the present invention, the generated cerium and lanthanum exist in the molten iron, while cerium chloride, lanthanum chloride, calcium chloride, barium chloride, calcium, and barium float to the surface of the molten iron or escape, and are finally removed with the ingot head during casting.
[0045] In the ferroalloy containing rare earth cerium and / or lanthanum of the present invention, the content range of rare earth cerium and / or lanthanum in the ferroalloy is 10 - 40%. Moreover, as the contents of rare earth cerium and lanthanum increase, the melting point of the ferroalloy gradually decreases. For example, the melting point of the cerium ferroalloy containing 10% cerium is around 1500 °C, and the melting point of the cerium ferroalloy containing 40% cerium is around 1300 °C. Therefore, the holding time after casting in step S3 of the present invention shortens as the superheat of the rare earth ferroalloy increases. For example, the holding time after casting of the rare earth ferroalloy containing 10% rare earth is 5 min, and the holding time after casting of the rare earth ferroalloy containing 40% rare earth is 15 min.
[0046] It should be noted that the rare earth elements in the high-purity rare earth ferroalloy prepared by the present invention are obtained by the reaction of rare earth chlorides and metallic calcium or barium in the molten iron. The chemical reaction rate and equilibrium state in the molten iron are restricted by the activities of reactants Ca, CeCl3, LaCl3, and products Ce, La, CaCl2, BaCl2, etc. Since the reaction conditions for each furnace cannot be exactly the same, such as temperature fluctuations and differences in the distribution of substance concentrations, etc., there will be a fluctuation range of about 5% in the rare earth composition of the high-purity rare earth ferroalloy prepared by the present invention under the same batching conditions. However, since the high-purity rare earth ferroalloy of the present invention is an intermediate alloy added during the preparation of rare earth steel, the small fluctuation in the rare earth composition will not affect its use. Instead, the contents of non-metallic impurities such as O and S are the key elements affecting the quality of rare earth steel. Therefore, the key technical feature of the present invention is that the oxygen content in the high-purity rare earth ferroalloy is <0.005%, the sulfur content is <0.002%, and the total impurity content is <0.1%, rather than the precise control of the rare earth composition in the high-purity rare earth ferroalloy.
[0047] The purity of the high-purity rare earth ferroalloy prepared by the method of the present invention is above 99.9%. Compared with the prior art of first preparing pure rare earth metals and then preparing rare earth ferroalloys, it not only has lower requirements for raw materials, but also has a relatively simple preparation process, which can be completed in one step, and the purity of the final product is not lower than that of the same type of rare earth ferroalloys on the existing market.
[0048] Example 1
[0049] A method for vacuum reduction melting to prepare 200 kg of high-purity cerium ferroalloy with a cerium content of 40% includes the following steps:
[0050] Step S1: Add 120 kg of pure iron into the melting chamber of a vacuum induction melting furnace, add 242 kg of cerium chloride and 118.2 kg of calcium into the feeder of the vacuum induction melting furnace. Wait until the vacuum degree in the vacuum induction melting furnace reaches 67 Pa and remains stable, and then start powering on to raise the temperature.
[0051] The purity of iron is 99.8% by mass percentage, the oxygen content in iron is 0.02%, and the carbon content is 0.02%. The purity of cerium chloride is 99.5% by mass percentage, and the added mass of cerium chloride is calculated according to the rare earth content being 130% of the rare earth content in the high-purity rare earth ferroalloy to be prepared. The purity of calcium is 99% by mass percentage, and the added mass of calcium is calculated as twice the mass required for complete reaction with cerium chloride. The particle size ranges of both cerium chloride and calcium are 20 mm - 50 mm.
[0052] Step S2: Raise the temperature of the molten iron to 1600 °C and keep it. Add the rare earth chloride and calcium in the feeder into the molten iron, and process for 20 minutes. During the process, keep the vacuum degree in the vacuum induction melting furnace at 67 Pa.
[0053] Step S3: After the treatment is completed, cast at 1600 °C, and then keep warm for 5 minutes. During the process, keep the vacuum degree in the vacuum induction melting furnace at 67 Pa.
[0054] Step S4: Cool with the furnace to obtain the high-purity rare earth ferroalloy. During the process, keep the vacuum degree in the vacuum induction melting furnace at 67 Pa.
[0055] For the high-purity rare earth ferroalloy, by mass percentage, the iron content is 65%, the balance is cerium, the total impurity content is 0.099%, the oxygen content is 0.0049%, and the sulfur content is 0.0019%.
[0056] Example 2
[0057] A method for vacuum reduction melting to prepare 300 kg of high-purity rare earth ferroalloy with a lanthanum content of 10% includes the following steps:
[0058] Step S1: Add 270 kg of pure iron into the melting chamber of the vacuum arc melting furnace. Add 103.8 kg of lanthanum chloride and 76 kg of calcium into the feeder of the vacuum arc melting furnace. Wait until the vacuum degree in the vacuum arc melting furnace reaches 150 Pa and remains stable, then start powering on to increase the temperature.
[0059] The purity of iron is 99.9% by mass percentage, the oxygen content in iron is 0.04%, and the carbon content is 0.04%. The purity of lanthanum chloride is 99.9% by mass percentage. The added mass of lanthanum chloride is calculated based on the rare earth content being 150% of the rare earth content in the high-purity rare earth ferroalloy to be prepared. The purity of calcium is 99.9% by mass percentage. The added mass of calcium is calculated as 3 times the mass required for complete reaction with lanthanum chloride. The particle size ranges of both lanthanum chloride and calcium are 20 mm - 50 mm.
[0060] Step S2: Heat the molten iron to 1650 °C and keep it at this temperature. Add the lanthanum chloride and calcium in the feeder into the molten iron and process for 30 min. During the process, keep the vacuum degree in the vacuum arc melting furnace at 150 Pa.
[0061] Step S3: After the treatment is completed, cast at 1650 °C and then keep warm for 15 min. During the process, keep the vacuum degree in the vacuum arc melting furnace at 150 Pa.
[0062] Step S4: Cool with the furnace to obtain the high-purity rare earth ferroalloy. During the process, keep the vacuum degree in the vacuum arc melting furnace at 150 Pa.
[0063] For the high-purity rare earth ferroalloy, by mass percentage, the iron content is 85%, the balance is lanthanum, the total impurity content is 0.05%, the oxygen content is 0.002%, and the sulfur content is 0.001%.
[0064] Example 3
[0065] A method for preparing 200 kg of high-purity cerium ferroalloy with a cerium content of 40% by vacuum reduction melting, comprising the following steps:
[0066] Step S1: Add 120 kg of pure iron into the melting chamber of the vacuum induction melting furnace. Add 242 kg of cerium chloride and 304.3 kg of barium into the feeder of the vacuum induction melting furnace. Wait until the vacuum degree in the vacuum induction melting furnace reaches 67 Pa and remains stable, then start powering on to increase the temperature.
[0067] The purity of iron is 99.8% by mass, the oxygen content in iron is 0.02%, and the carbon content is 0.02%. The purity of cerium chloride is 99.5% by mass, and the added mass of cerium chloride is calculated based on the rare earth content being 130% of the rare earth content in the high-purity rare earth ferroalloy to be prepared. The purity of barium is 99% by mass, and the added mass of barium is calculated as 1.5 times the mass required for complete reaction with cerium chloride. The particle size ranges of both cerium chloride and barium are 20 mm - 50 mm.
[0068] Step S2: Heat the molten iron to 1600 °C and maintain it, add rare earth cerium chloride and barium in the feeder to the molten iron, and process for 20 min. During the process, maintain the vacuum degree in the vacuum induction melting furnace at 67 Pa.
[0069] Step S3: After the treatment is completed, cast at 1600 °C and then keep warm for 5 min. During the process, maintain the vacuum degree in the vacuum induction melting furnace at 67 Pa.
[0070] Step S4: Cool with the furnace to obtain a high-purity rare earth ferroalloy. During the process, maintain the vacuum degree in the vacuum induction melting furnace at 67 Pa.
[0071] For the high-purity rare earth ferroalloy, by mass percentage, the iron content is 63%, the balance is cerium, the total impurity content is 0.098%, the oxygen content is 0.0044%, and the sulfur content is 0.0016%.
[0072] Example 4
[0073] A method for preparing 300 kg of high-purity rare earth ferroalloy with 10% lanthanum content by vacuum reduction melting, comprising the following steps:
[0074] Step S1: Add 270 kg of pure iron into the melting chamber of the vacuum arc melting furnace, add 103.8 kg of lanthanum chloride and 173.8 kg of barium into the feeder of the vacuum arc melting furnace. Wait until the vacuum degree in the vacuum arc melting furnace reaches 150 Pa and is maintained, and then start powering on to heat up.
[0075] The purity of iron is 99.9% by mass, the oxygen content in iron is 0.04%, and the carbon content is 0.04%. The purity of lanthanum chloride is 99.9% by mass, and the added mass of lanthanum chloride is calculated based on the rare earth content being 150% of the rare earth content in the high-purity rare earth ferroalloy to be prepared. The purity of barium is 99.9% by mass, and the added mass of barium is calculated as 2 times the mass required for complete reaction with lanthanum chloride. The particle size ranges of both lanthanum chloride and barium are 20 mm - 50 mm.
[0076] Step S2: Heat the molten iron to 1650 °C and maintain it, add lanthanum chloride and barium in the feeder to the molten iron, and process for 30 min. During the process, maintain the vacuum degree in the vacuum arc melting furnace at 150 Pa.
[0077] Step S3: After the treatment, cast at 1650°C and then keep warm for 5 minutes, and maintain the vacuum degree in the vacuum arc melting furnace at 150 Pa during the process;
[0078] Step S4: Cool with the furnace to obtain a high-purity rare earth ferroalloy, and maintain the vacuum degree in the vacuum arc melting furnace at 150 Pa during the process.
[0079] For the high-purity rare earth ferroalloy, calculated by mass percentage, the iron content is 84%, the balance is lanthanum, the total impurity content is 0.06%, the oxygen content is 0.003%, and the sulfur content is 0.0013%.
[0080] Example 5
[0081] A method for preparing a 400-kg high-purity rare earth ferroalloy with 10% cerium content and 10% lanthanum content by vacuum reduction melting, comprising the following steps:
[0082] Step S1: Add 320 kg of pure iron into the melting chamber of a vacuum induction melting furnace, add 130 kg of cerium chloride, 129.4 kg of lanthanum chloride and 158.2 kg of calcium into the feeder of the vacuum induction melting furnace. Wait until the vacuum degree in the vacuum induction melting furnace reaches 100 Pa and is maintained, and then start power supply to increase the temperature;
[0083] The purity of iron is 99.85% by mass percentage, the oxygen content in iron is 0.03%, and the carbon content is 0.03%. The purities of cerium chloride and lanthanum chloride are 99.7% by mass percentage, and the added masses of cerium chloride and lanthanum chloride are calculated according to that the rare earth content therein is 140% of the rare earth content in the high-purity rare earth ferroalloy to be prepared. The purity of calcium is 99.5% by mass percentage, and the added mass of calcium is calculated according to 2.5 times the mass required for complete reaction with cerium chloride and lanthanum chloride. The particle size ranges of cerium chloride and calcium are both 20 mm - 50 mm.
[0084] Step S2: Heat the molten iron to 1625°C and keep it. Add the rare earth cerium chloride, lanthanum chloride and calcium in the feeder into the molten iron, and treat for 25 minutes, and maintain the vacuum degree in the vacuum induction melting furnace at 100 Pa during the process;
[0085] Step S3: After the treatment, cast at 1625°C and then keep warm for 10 minutes, and maintain the vacuum degree in the vacuum induction melting furnace at 100 Pa during the process;
[0086] Step S4: Cool with the furnace to obtain a high-purity rare earth ferroalloy, and maintain the vacuum degree in the vacuum induction melting furnace at 100 Pa during the process.
[0087] The high-purity rare earth ferroalloy, calculated by mass percentage, has an iron content of 80%, a cerium content of 10%, a lanthanum content of 10%, a total impurity content of 0.07%, an oxygen content of 0.0035%, and a sulfur content of 0.0025%.
[0088] As mentioned above, it is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.
Claims
1. A method for preparing high-purity rare earth iron alloy by vacuum reduction smelting, characterized in that: The method comprises the following steps: Step S1, adding pure iron into the smelting chamber of a vacuum smelting furnace, adding rare earth chloride and reducing agent into the feeder of the vacuum smelting furnace, and starting to supply power and heat up after the vacuum degree in the vacuum smelting furnace reaches 67-150 Pa and is maintained; the rare earth chloride is cerium chloride and / or lanthanum chloride; the reducing agent is calcium or barium; Step S2, the temperature of the molten iron is raised to 1600-1650°C and maintained, rare earth chloride and reducing agent in the feeder are added to the molten iron, and the treatment is carried out for 20-30 minutes, and the vacuum degree in the vacuum melting furnace is maintained at 67-150 Pa during the process; Step S3: After the treatment is completed, the casting is maintained at 1600-1650°C, and then the temperature is kept for 5-15 minutes. During the process, the vacuum degree in the vacuum melting furnace is maintained at 67-150 Pa; Step S4, cooling with the furnace to obtain a high-purity rare earth iron alloy, during which the vacuum degree in the vacuum melting furnace is maintained at 67-150 Pa; The high-purity rare earth iron alloy is an iron alloy containing rare earth cerium and / or lanthanum, and in terms of mass percentage, the iron content is 60-90%, the balance is cerium and / or lanthanum, the total amount of impurities is <0.1%, the oxygen content is <0.005%, and the sulfur content is <0.002%.
2. The method according to claim 1, characterized in that In the step S1, the pure iron has an iron content of more than 99.8%, an oxygen content of 0.02-0.04%, and a carbon content of 0.02-0.04% in terms of mass percentage.
3. The method according to claim 1, characterized in that In the step S1, the purity of the calcium is above 99%, and the purity of the barium is above 99% in terms of mass percentage.
4. The method according to claim 1, characterized in that In the step S1, the purity of the rare earth chloride is above 99.5% in terms of mass percentage.
5. The method according to claim 1, characterized in that: When preparing the high-purity rare earth iron alloy containing rare earth cerium, the rare earth chloride in step S1 is cerium chloride; when preparing the high-purity rare earth iron alloy containing rare earth lanthanum, the rare earth chloride in step S1 is lanthanum chloride; when preparing the high-purity rare earth iron alloy containing rare earth cerium and lanthanum, the rare earth chloride in step S1 is cerium chloride and lanthanum chloride.
6. The method according to claim 1, characterized in that The added mass of the rare earth chloride in the step S1 is calculated based on the rare earth content in the rare earth chloride being 130-150% of the rare earth content in the high-purity rare earth iron alloy to be prepared.
7. The method according to claim 1 or 6, characterized in that: The mass of the calcium added in step S1 is calculated as 2-3 times the mass required to completely react with the rare earth chloride.
8. The method according to claim 1 or 6, characterized in that: The mass of the barium added in step S1 is calculated as 1.5-2 times the mass required to completely react with the rare earth chloride.
9. The method according to claim 1, characterized in that: The particle sizes of the rare earth chloride, the calcium and the barium in step S1 are all in the range of 20 mm to 50 mm.
10. The method according to claim 1, characterized in that The vacuum melting furnace in step S1 is a vacuum induction melting furnace or a vacuum arc melting furnace.