Method and apparatus for producing high purity nickel-magnesium alloy using a vacuum induction furnace crucible in the final stage

Abstract

This invention discloses a method and equipment for producing high-purity nickel-magnesium alloys using a late-stage crucible in a vacuum induction furnace, belonging to the field of alloy smelting technology. The method includes: selecting a vacuum induction furnace with a late-stage crucible; adding a nickel source to the late-stage crucible and melting it at atmospheric pressure to 1480℃~1500℃; adding industrial covering salt to form a liquid molten salt covering layer; adding a magnesium source in batches for alloying under the condition of flue gas capture by a mobile dust collector hood; and obtaining a high-purity nickel-magnesium alloy through homogenization and casting. The late-stage crucible refers to a crucible whose inner lining has reached the end of its service life. This invention pioneers the concept of reusing late-stage crucibles, using crucibles that would otherwise be dismantled and scrapped for nickel-magnesium alloy production. Single-batch output can reach 4 to 10 tons, with a carbon content ≤0.010% and an oxygen content ≤5ppm. The atmospheric pressure operation process is simple and safe, and combined with mobile dust collection, it achieves clean production, realizing the industrial-scale mass production of nickel-magnesium alloys, with significant economic benefits and environmental value.

Description

Technical Field

[0001] This invention relates to the field of alloy smelting technology, specifically to a method and equipment for producing high-purity nickel-magnesium alloys using a crucible at the end of a vacuum induction furnace. Background Technology

[0002] Nickel-magnesium alloys, as highly efficient additives, play an irreplaceable role in the smelting of high-temperature alloys, stainless steel, and special steels. Magnesium can deeply deoxidize, purify grain boundaries, refine grains, and modify inclusions, significantly improving the mechanical and processing properties of materials. However, due to magnesium's low melting point (650℃), low boiling point (1107℃), and high vapor pressure, it cannot be directly added to molten steel and must be pre-formed into a nickel-magnesium master alloy.

[0003] Currently, there are several main technical routes for the preparation of nickel-magnesium alloys, but all of them have inherent defects, especially in that they cannot be mass-produced industrially: Graphite crucible induction furnace melting method: This method uses high-purity graphite crucibles in a small-scale induction furnace for melting. This method has the following problems: ① Extremely low output: Limited by the size and strength of the graphite crucible, the single-batch output is only 25-100 kg, which cannot meet the ton-level demand for nickel-magnesium alloys in modern special metallurgical industries; ② High cost and resource waste: After the alloy solidifies, the crucible must be broken to remove it, resulting in "one furnace, one crucible," leading to serious resource waste; ③ High carbon content in the product: The graphite crucible carburizes the alloy at high temperatures, resulting in a carbon content typically exceeding 0.1%, requiring users to grind the surface carbon layer before use; ④ Poor environmental performance: The lack of a dust removal system generates a large amount of "magnesium fumes" during magnesium addition, seriously endangering the health of operators.

[0004] New Crucible Vacuum Induction Furnace Melting Method: This method uses new crucibles made of magnesia or aluminum-magnesia spinel, and melts them in a vacuum induction furnace, supplemented by molten salt covering. This method solves the carbon increase problem to some extent, but still has the following shortcomings: ① High equipment cost: Using new crucibles or crucibles with normal furnace life for production results in high costs for crucible bridging and sintering; ② Complex vacuum condition control: It requires operation under specific vacuum levels and the introduction of argon gas, which requires high process control; ③ Limited output increase: Although the vacuum induction furnace itself has a large capacity, the actual scale used for nickel-magnesium alloy production is still small (about 1 ton) due to the depreciation cost of new crucibles and the complexity of the process, failing to fully utilize the capacity advantage of large equipment; ④ Failure to achieve maximum resource utilization.

[0005] In the field of special steel smelting, the crucible lining of vacuum induction furnaces (usually made of MgO or Al2O3) has a limited service life. With each smelting furnace cycle, the crucible lining is subjected to erosion and corrosion from the high-temperature molten steel, resulting in micro-cracks and localized thinning. When the crucible reaches the end of its service life, continuing to smelt high-purity, high-composition-controlled steel grades (such as high-temperature alloys, precision alloys, and stainless steel) poses a safety risk of contaminating the molten steel or even causing leakage. Therefore, the industry practice is to directly dismantle and break down the crucibles at the end of their service life and replace them with new ones. This results in a waste of expensive refractory materials and increases the time cost of shutting down for crucible replacement. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by proposing a method and equipment for producing high-purity nickel-magnesium alloys using crucibles at the end of a vacuum induction furnace. This method utilizes "scrap" crucibles that have reached the end of their service life and can no longer be used to smelt standard steel grades. Combined with atmospheric pressure molten salt covering protection, it enables large-scale production of nickel-magnesium master alloys in batches of 4 tons or more, allowing the crucibles to retain their value before being scrapped, achieving a dual breakthrough in both production scale and resource utilization.

[0007] A first aspect of the present invention provides a method for producing high-purity nickel-magnesium alloys using a crucible at the end of a vacuum induction furnace, comprising the following steps: Step 1, Equipment Selection: Select a vacuum induction furnace with a final-stage crucible; the final-stage crucible refers to a crucible whose inner lining has reached its service life limit. The service life limit means that the working layer of the inner lining of the crucible has micro-cracks and / or local erosion, but the overall structure of the crucible is intact, without penetrating cracks, and still has the ability to bear nickel-magnesium alloy melt. Step 2, Raw material preparation: Prepare nickel source, magnesium source and industrial covering salt. Prepare nickel and magnesium materials according to the theoretical value that the magnesium content in the high-purity nickel-magnesium alloy is 18%~22% by mass. The nickel mass fraction in the nickel source is ≥99.95% and the magnesium mass fraction in the magnesium source is ≥99.8%. Step 3, Base Nickel Melting: Add the nickel source into the final crucible, start the induction heating power supply under normal pressure to completely melt the nickel source and raise the temperature to 1480℃~1500℃; Step 4: Establishing a molten salt coating layer: After the nickel liquid temperature stabilizes, add industrial coating salt to the final crucible. The amount added is 3% to 5% of the weight of the nickel liquid. Use the sensible heat of the nickel liquid to melt the industrial coating salt and form a liquid molten salt coating layer. Step 5, Magnesium alloying and flue gas collection: Adjust the mobile dust hood above the opening of the final crucible and turn on the dust collector; under normal pressure and molten salt coverage, add the magnesium source to the final crucible in batches. The magnesium source passes through the liquid molten salt coverage layer and enters the nickel liquid to melt. The magnesium fumes generated are collected by the mobile dust hood. Step 6, Homogenization and Casting: After all the magnesium source is added, turn on the electromagnetic stirring, measure and adjust the temperature to 1350℃~1400℃, and then cast the nickel-magnesium alloy melt to obtain a high-purity nickel-magnesium alloy ingot.

[0008] Furthermore, in step 1, the material of the final crucible is fused magnesia or corundum.

[0009] Furthermore, in step 2, the nickel source is a nickel plate or nickel block, the magnesium source is a metallic magnesium block, and the industrial covering salt is industrial sodium chloride and / or industrial potassium chloride.

[0010] Furthermore, in step 4, the thickness of the liquid molten salt coating is controlled to be 30mm~50mm.

[0011] Further, in step 5, the movable dust hood is adjusted to a position 200mm~400mm above the opening of the final crucible.

[0012] Furthermore, in step 5, the magnesium source is added to the final crucible in batches, and the total magnesium addition time is controlled to be 20 to 30 minutes; wherein the magnesium source is a 20 mm to 80 mm metal magnesium block.

[0013] Furthermore, in step 5, the actual amount of magnesium source added is increased by 1% to 3% compared to the theoretical value as compensation for burn-off.

[0014] Furthermore, in the high-purity nickel-magnesium alloy ingot, the mass content of Mg is 18%~22%, the mass content of C is ≤0.010%, and the mass content of O is ≤5ppm.

[0015] Furthermore, the total amount of high-purity nickel-magnesium alloy produced in a single batch by the method is 4 to 10 tons.

[0016] A second aspect of the present invention provides an apparatus for producing high-purity nickel-magnesium alloys using a crucible at the end of a vacuum induction furnace, comprising: The melting chamber serves as the main chamber for melting. A side feeding chamber, connected to the side wall of the smelting chamber, is used to feed raw materials into the smelting chamber; An induction heating assembly includes an induction coil and a final crucible. The induction coil is arranged around the outer periphery of the final crucible, which is located inside a melting chamber and is used to hold and heat the raw materials to form a nickel-magnesium alloy melt with a liquid molten salt coating on its surface. A sluice assembly includes a sluice chamber and a sluice, the sluice chamber being connected to the side wall of the melting chamber, the sluice being disposed in the sluice chamber, and the inlet of the sluice being connected to the melting chamber for discharging the nickel-magnesium alloy melt; A casting assembly includes an ingot mold chamber, a rotating ingot tray, and an ingot mold. The ingot mold chamber is connected to the chute chamber. The rotating ingot tray is located at the bottom of the ingot mold chamber. The ingot mold is mounted on the rotating ingot tray. The outlet of the chute is aligned with the opening of the ingot mold. The flue gas purification assembly includes a mobile dust hood, a dust removal fan, and a dust collector. The mobile dust hood is adjusted above the opening of the final crucible. The dust removal fan is connected to the mobile dust hood and the dust collector via pipelines. The dust collector is used to receive and purify the flue gas delivered by the fan.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: This invention pioneers the concept of "reusing end-of-life crucibles," utilizing end-of-life crucibles that would otherwise be dismantled and scrapped for the production of high-purity nickel-magnesium alloys. Single-batch output can reach 4 to 10 tons, with a carbon content of ≤0.010% and an oxygen content of ≤5ppm. The atmospheric pressure operation process is simple and safe, and with the addition of mobile dust removal, clean production is achieved, enabling the industrial-scale mass production of nickel-magnesium alloys with significant economic benefits and environmental value. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0019] Figure 1 This is a schematic diagram of an apparatus for producing high-purity nickel-magnesium alloy using a final crucible in a vacuum induction furnace, as described in an embodiment of the present invention. The reference numerals are: 1. Melting chamber; 2. Induction coil; 3. Final crucible; 4. Side feeding chamber; 5. Raw material; 6. Nickel-magnesium alloy melt; 7. Liquid molten salt covering layer; 8. Sluice box; 9. Sluice box; 10. Ingot mold chamber; 11. Rotary ingot tray; 12. Ingot mold; 13. Mobile dust collector hood; 14. Dust collector fan; 15. Dust collector. Detailed Implementation

[0020] To better understand the above technical solutions, the technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0021] A first aspect of the present invention provides a method for producing high-purity nickel-magnesium alloys using a crucible at the end of a vacuum induction furnace, comprising the following steps: Step 1, Equipment Selection: Select a vacuum induction furnace with a final crucible; Understandably, a "final stage crucible" refers to a crucible whose inner lining has reached its service life limit and can no longer be used to smelt the appropriate steel grades. The service life limit means that the working layer of the crucible lining has developed a network of microcracks and / or localized erosion. Continuing to use it to smelt high-quality special steels would pose a risk of contaminating the molten steel or causing leakage. However, the crucible's overall structure remains intact, without penetrating cracks, and it still has the ability to support the molten nickel-magnesium alloy.

[0022] Step 2, Raw Material Preparation: Prepare nickel source, magnesium source, and industrial covering salt. Produce nickel and magnesium materials according to the theoretical value that the magnesium content in high-purity nickel-magnesium alloy is 18%~22% by mass. The mass fraction of nickel in the nickel source is ≥99.95%, and the mass fraction of magnesium in the magnesium source is ≥99.8%. Optionally, the nickel source is a nickel plate or nickel block with a purity ≥99.95%; the magnesium source is a metallic magnesium block with a purity ≥99.8%; and the industrial covering salt is selected from one or two of sodium chloride and potassium chloride. Preferably, the ingredients are prepared in a weight ratio of nickel to magnesium of 4:1.

[0023] Step 3, Base Nickel Melting: Add the nickel source to the final crucible, close the furnace lid and keep the vent valve open to maintain atmospheric pressure inside the furnace, start the induction heating power supply, completely melt the nickel source and raise the temperature to 1480℃~1500℃.

[0024] Step 4: Establishing a molten salt coating layer: After the nickel liquid temperature stabilizes, add industrial coating salt to the final crucible. The amount added is 3% to 5% of the weight of the nickel liquid. Use the sensible heat of the nickel liquid to melt the industrial coating salt and form a liquid molten salt coating layer.

[0025] Step 5, Magnesium Alloying and Fume Collection: Adjust the mobile dust hood to above the mouth of the final crucible and turn on the dust collector; under normal pressure and molten salt coverage, add the magnesium source to the final crucible in batches. The magnesium source passes through the liquid molten salt coverage layer and enters the nickel liquid to melt. The generated magnesium fumes are collected by the mobile dust hood.

[0026] Step 6, Homogenization and Casting: After all the magnesium source is added, turn on the electromagnetic stirring, measure and adjust the temperature to 1350℃~1400℃, and then cast the nickel-magnesium alloy melt to obtain a high-purity nickel-magnesium alloy ingot.

[0027] This invention discloses a method for producing high-purity nickel-magnesium alloys using a late-stage crucible in a vacuum induction furnace. This method utilizes "scrap" crucibles that have reached their service life limit and are no longer suitable for smelting standard steel grades. By combining this with atmospheric pressure molten salt covering protection technology, it enables large-scale production of nickel-magnesium master alloys. This allows the late-stage crucibles to fulfill their "final value" before being scrapped, achieving a breakthrough in both production scale and resource utilization. It solves the technical problems of low nickel-magnesium alloy production (below kilogram / ton level), serious waste of crucible resources, high production costs, high carbon content in the product, and poor environmental performance in existing technologies.

[0028] In some embodiments, in step 1, the final crucible is made of fused magnesia (MgO) or corundum (Al2O3).

[0029] Specifically, using MgO or Al2O3 crucibles completely eliminates the carbon source, resulting in high product purity and no risk of carbon enrichment. Combined with the adsorption effect of molten salt covering on inclusions, the carbon content of the resulting nickel-magnesium alloy can be controlled below 0.010%, and the oxygen content below 5 ppm, allowing for direct use without grinding.

[0030] In some embodiments, in step 2, the industrial covering salt is industrial sodium chloride and / or industrial potassium chloride.

[0031] In some embodiments, in step 4, the thickness of the liquid molten salt coating is controlled to be 30 mm to 50 mm.

[0032] Understandably, industrial covering salt needs to be dried before use, optionally at 140℃~160℃ for 1~3 hours. After the nickel melt temperature stabilizes, the pre-dried industrial covering salt is slowly added to the final crucible, where it is rapidly melted by the sensible heat of the nickel melt. Because the density of the molten salt is much lower than that of the nickel melt, it will automatically float to the surface and spread on the nickel melt, forming a continuous, dense liquid molten salt covering layer. Controlling the thickness of the liquid molten salt covering layer to 30mm~50mm can isolate oxygen, preventing a violent reaction between Mg and oxygen in the air after addition, which would lead to Mg oxidation, while also effectively suppressing magnesium volatilization and splashing.

[0033] In some embodiments, in step 5, the movable dust hood is adjusted to be 200mm to 400mm above the opening of the final crucible.

[0034] Specifically, adjusting the mobile dust collector hood to 200mm~400mm above the opening of the final crucible ensures good dust removal. Start the mobile dust collector hood and turn on the dust removal fan; while maintaining normal pressure and molten salt coverage, add the crushed magnesium blocks to the final crucible in batches and small quantities; the magnesium blocks penetrate the molten salt layer and enter the nickel melt for melting. The magnesium fumes generated during this process are captured by the mobile dust collector hood and sent to the dust removal system for purification.

[0035] In some embodiments, in step 5, the magnesium source is added to the final crucible in batches, and the total magnesium addition time is controlled to be 20 minutes to 30 minutes. The magnesium source is a 20mm to 80mm metal magnesium block.

[0036] Specifically, the total magnesium addition time should be controlled between 20 and 30 minutes to balance the reaction rate and operational safety. If the time is too short (e.g., added all at once), a large amount of solid magnesium will enter the molten nickel in a short period, and some of the magnesium may fail to melt in time and rise above the molten salt surface, exposing it to air and potentially burning. If the time is too long, it will reduce production efficiency and increase magnesium volatilization loss. A magnesium addition cycle of 20 to 30 minutes allows the magnesium to melt steadily in batches into the molten nickel, avoiding splashing caused by violent reactions and effectively inhibiting magnesium oxidation and volatilization. The magnesium blocks can be added in 6 to 8 batches to ensure that each addition is effectively coated by the liquid molten salt layer and melts rapidly.

[0037] The size of the magnesium blocks also has a significant impact on melting efficiency and safety. If the blocks are too small (such as powder or fine shavings), they are prone to flying when added and may cause localized splashing due to an overly vigorous reaction; if the blocks are too large, melting is slow, and they tend to accumulate on the surface of the molten salt, increasing the risk of combustion and volatilization. Therefore, breaking the magnesium blocks into sizes of 20mm to 80mm ensures rapid melting and facilitates batch feeding operations.

[0038] In some embodiments, the total amount of high-purity nickel-magnesium alloy produced in a single batch is 4 to 10 tons.

[0039] Specifically, the target nickel-magnesium alloy is formulated with a magnesium content of 18% to 22%, preferably at a nickel:magnesium weight ratio of 4:1. Considering the unavoidable loss of magnesium during burning, the actual amount of magnesium added is increased by 1% to 3% compared to the theoretical value as compensation for loss. The total batch size is designed to be at least 4 tons per batch to fully utilize the production capacity of the large vacuum induction furnace. Preferably, the total amount of high-purity nickel-magnesium alloy produced per batch is 4 to 10 tons.

[0040] In some embodiments, the qualified nickel-magnesium alloy melt is poured into a steel ingot mold preheated to 200°C~300°C. After the alloy ingot has completely solidified and cooled, it is demolded and sampled for chemical composition analysis. The resulting high-purity nickel-magnesium alloy ingot has a Mg content of 18%~22%, a C content ≤0.010%, and an O content ≤5ppm. It is understood that the liquid molten salt coating enters the steel ingot mold during casting, and the density difference causes it to remain on the upper surface of the alloy; it is then knocked off after cooling.

[0041] A second aspect of the present invention provides an apparatus for producing high-purity nickel-magnesium alloys using a crucible at the end of a vacuum induction furnace, comprising: Melting chamber 1 serves as the main chamber for melting; Side feeding chamber 4 is connected to the side wall of melting chamber 1 and is used to feed raw material 5 into melting chamber 1; The induction heating assembly includes an induction coil 2 and a final crucible 3. The induction coil 2 is arranged around the outer periphery of the final crucible 3. The final crucible 3 is located inside the melting chamber 1 and is used to hold and heat the raw material 5 to form a nickel-magnesium alloy melt 6 with a liquid molten salt coating layer 7 on its surface. The sluice assembly includes a sluice chamber 8 and a sluice 9. The sluice chamber 8 is connected to the side wall of the melting chamber 1. The sluice 9 is disposed in the sluice chamber 8. The inlet of the sluice 9 is connected to the melting chamber 1 and is used to discharge the nickel-magnesium alloy melt 6. The casting assembly includes an ingot mold chamber 10, a rotating ingot plate 11, and an ingot mold 12. The ingot mold chamber 10 is connected to the chute chamber 8. The rotating ingot plate 11 is located at the bottom of the ingot mold chamber 10, and the ingot mold 12 is installed on the rotating ingot plate 11. The outlet of the chute 9 is aligned with the opening of the ingot mold 12. The flue gas purification assembly includes a mobile dust collector 13, a dust collector fan 14, and a dust collector 15. The mobile dust collector 13 is adjusted to be above the opening of the final crucible 3. The dust collector fan 14 is connected to the mobile dust collector 13 and the dust collector 15 through pipelines. The dust collector 15 is used to receive and purify the flue gas delivered by the fan.

[0042] In summary, the embodiments of the present invention have the following beneficial effects compared with the prior art: (1) First-ever industrial-scale mass production of nickel-magnesium alloys: Compared with the small-scale production of kilograms or tons in existing technologies, the embodiments of this invention rely on the capacity advantage of large vacuum induction furnaces, and the output per batch can reach more than 4 tons. This leap in production scale enables nickel-magnesium alloys to truly move from "laboratory / small workshop production" to "industrial mass production", which can meet the growing ton-level demand for nickel-magnesium alloys in modern special metallurgical industries and has significant industrial upgrading significance.

[0043] (2) Pioneering the concept of "reusing end-of-life crucibles" to maximize resource utilization: Unlike existing technologies that use new crucibles or crucibles of normal furnace life, this invention proposes for the first time to utilize end-of-life crucibles that have reached the end of their service life and can no longer be used to smelt formal steel grades for nickel-magnesium alloy production. This reverse thinking of "turning waste into treasure" allows crucibles that should have been dismantled and scrapped to play their final role, significantly reducing the consumption of refractory materials and the time cost of stopping production to repair crucibles. This is a breakthrough against the existing prejudice of "crucible scrapping" technology.

[0044] (3) High product purity and no risk of carbon increase: Compared with the existing technology of nickel-magnesium alloys smelted using graphite crucibles, the present invention uses an MgO / Al2O3 crucible, which completely eliminates the carbon source. Combined with the adsorption effect of molten salt covering on inclusions, the carbon content of the obtained nickel-magnesium alloy can be controlled below 0.010%, and the oxygen content can be controlled below 5ppm. Users can use it directly without grinding.

[0045] (4) Simple, safe and easy to control process: Compared with the complex process in the prior art that requires precise control under a specific vacuum degree and argon protection, the present invention adopts atmospheric pressure operation, does not require a vacuum system and gas protection, has a wide process window, and is simple and safe to operate.

[0046] (5) Green and environmentally friendly, achieving clean production: The dual protection mechanism of "physical isolation by liquid molten salt covering layer" and "forced ventilation by mobile dust removal hood" is adopted to solve the problem of magnesium fume emission during smelting and protect the occupational health of operators.

[0047] Example 1: Mass production of 4.8-ton-class nickel-magnesium alloy (Ni-20Mg) This embodiment describes in detail the actual production process of 4.8 tons of nickel-magnesium alloy (Ni-20Mg) and verifies the feasibility of the present invention in mass production.

[0048] Step 1: Equipment Preparation A 6-ton vacuum induction furnace at a special steel plant, with crucibles made of fused magnesia (MgO), had been used 35 times, reaching the plant's maximum service life limit for magnesia crucibles (typically 32-35 times). Inspection revealed fine network cracks and localized corrosion on the inner wall of the crucible, rendering it unsuitable for smelting nickel-based superalloys requiring high purity. The original plan was to shut down the furnace, dismantle the furnace, and replace the crucible.

[0049] This final crucible is now being used to produce a 4.8-ton batch of nickel-magnesium alloy. The crucible is thoroughly cleaned of any remaining cold steel and slag, and the insulation resistance of the induction coil is checked to be greater than 0.5 MΩ. The movable dust collector hood is adjusted to the standby position, and the dust collection system uses a pulse-jet bag filter.

[0050] Step 2: Raw material preparation Pure nickel: #1 electrolytic nickel plate, purity ≥99.95%, C≤0.005%. Weigh 4000 kg.

[0051] Magnesium metal: Magnesium ingots are crushed into small pieces of 20mm~80mm with a purity of ≥99.9%. Considering the loss during burning, 1020kg of magnesium blocks were actually weighed (theoretical addition amount is 1000kg, with a 2% compensation for loss during burning).

[0052] Covering agent: Industrial anhydrous sodium chloride (NaCl), purity ≥95%, dried at 150℃ for 2 hours. Calculate 200kg based on 5% of the weight of the nickel liquid (4000kg nickel liquid × 5% = 200kg).

[0053] Step 3: Melting Nickel 4000 kg of nickel plates were loaded into the final crucible. The furnace lid was closed, and the vent valve was opened to maintain atmospheric pressure inside the furnace. Induction heating was started, and after about 1 hour and 40 minutes, the nickel plates were completely melted, and the temperature of the molten nickel reached 1480℃.

[0054] Step 4: Molten salt coating 200 kg of dry NaCl was slowly added into the crucible through the side feeding hopper. The NaCl rapidly absorbed heat and melted. After about 3 minutes, a clear layer of liquid salt evenly covered the surface of the nickel melt, forming a molten salt coating layer with an estimated thickness of about 40 mm.

[0055] Step 5: Mass magnesium alloying and flue gas capture Open the furnace lid, start the dust removal system, and move the mobile dust collector hood to approximately 300mm directly above the crucible. Turn on the blower. Begin the magnesium addition process: Place 1020kg of crushed magnesium blocks into the side feeding hopper, adding approximately 145kg (1 / 7 of the total magnesium) at 3-minute intervals. Repeat this process 7 times, taking approximately 21 minutes to add all 1020kg of magnesium blocks. Throughout the magnesium addition process, a large amount of white smoke was visible being drawn into the dust collector hood, with no smoke escaping.

[0056] Step 6: Homogenization and Casting After adding magnesium, the electromagnetic stirring was started for 2 minutes. At the end of stirring, the temperature was measured at 1380℃. 4.8 tons of nickel-magnesium alloy molten material were then poured into a steel ingot mold.

[0057] Step 7, Test Results Sampling and analysis were performed on the upper, middle, and lower parts of the alloy ingot. Mg content: 19.8%, 20.2%, 20.1%, the Mg content meets the requirements of Ni-20Mg alloy.

[0058] C content: 0.008%, 0.008%, 0.009%, C content ≤0.010%.

[0059] O content: 0.0003%, 0.0004%, 0.0003%, O content less than 5ppm.

[0060] Surface quality: Silvery-white metallic luster, free of oxide scale and slag, can be used directly in steelmaking without polishing.

[0061] Step 8: Crucible unloading After producing 4.8 tons of nickel-magnesium alloy in this furnace, the final crucible will be dismantled as planned and a new crucible will be made.

[0062] Example 2: Mass production of 8-ton nickel-magnesium alloy Step 1: Equipment Preparation The crucible for producing MgO from the end-stage of another 12-ton vacuum induction furnace at a special steel plant was found to have fine network cracks and localized corrosion on its inner wall. The original plan was to shut down the furnace, dismantle the furnace, and replace the crucible. However, this end-stage crucible is now being used to produce an 8-ton batch of nickel-magnesium alloy.

[0063] Step 2: Raw material preparation Pure nickel: #1 electrolytic nickel plate, purity ≥99.95%, C≤0.005%. Weigh 6660kg.

[0064] Magnesium metal: Magnesium ingots are crushed into small pieces of 20mm~80mm with a purity of ≥99.9%. Considering the loss due to burning, 1700kg of magnesium blocks were actually weighed (theoretical addition amount is 1665kg, with a burning loss compensation of 2.1%).

[0065] Covering agent: Industrial anhydrous sodium chloride (NaCl), purity ≥95%, dried at 150℃ for 2 hours. Calculate 333 kg based on 5% of the weight of the molten nickel.

[0066] Step 3: Melting Nickel Load 6660 kg of nickel plates into the final crucible. Close the furnace lid, open the vent valve, and maintain atmospheric pressure inside the furnace. Start the induction heating to melt all the nickel plates, reaching a nickel molten temperature of 1480℃.

[0067] Step 4: Molten salt coating 333 kg of dry NaCl was slowly added into the crucible through the side feeding hopper. The liquid salt layer evenly covered the surface of the nickel liquid, forming a molten salt coating layer with an estimated thickness of about 40 mm.

[0068] Step 5: Mass magnesium alloying and flue gas capture Open the furnace lid, start the dust removal system, and move the mobile dust collector hood to approximately 300mm directly above the crucible. Turn on the blower. Begin the magnesium addition process: Place 1700kg of crushed magnesium blocks into the side feeding hopper, adding approximately 240kg at 3-minute intervals, for a total of 7 additions. The process takes approximately 21 minutes to add all 1700kg of magnesium blocks. Throughout the magnesium addition process, a large amount of white smoke was visible being drawn into the dust collector hood, with no smoke escaping.

[0069] Step 6, Homogenization and Casting: After adding magnesium, the electromagnetic stirring was started for 2 minutes. At the end of stirring, the temperature was measured at 1380℃. Eight tons of molten nickel-magnesium alloy were then poured into a steel ingot mold.

[0070] Step 7, Test Results: Sampling and analysis were performed on the upper, middle, and lower parts of the alloy ingot. Mg content: 19.6%, 20.3%, 20.1%, the Mg content meets the requirements of Ni-20Mg alloy.

[0071] C content: 0.008%, 0.010%, 0.009%, C content ≤0.010%.

[0072] O content: 0.0003%, 0.0004%, 0.0004%, O content less than 5ppm.

[0073] Surface quality: Silvery-white metallic luster, free of oxide scale and slag, can be used directly in steelmaking without polishing.

[0074] Step 8: Crucible unloading After producing 8 tons of nickel-magnesium alloy in this furnace, the final crucible will be dismantled as planned and a new crucible will be made.

[0075] Comparative Example 1: Traditional Graphite Crucible Method Refer to Examples 1-8 in CN119710320A, where a non-vacuum induction furnace is used, equipped with a graphite crucible, and covered with a composite molten salt containing KCl, NaCl, KF, MgCl2, CeCl3 and / or LaCl3, to melt nickel-magnesium alloys under non-vacuum conditions.

[0076] The method has the following drawbacks: using a new graphite crucible poses a risk of carbon increase and requires destructive removal of the alloy; the molten salt contains rare earth chlorides, resulting in high costs; the yield per batch is small; and when Comparative Example 1 in CN119710320A uses molten salt with only two components, NaCl and KCl, its C content is 0.06%.

[0077] Comparative Example 2: New Crucible Vacuum Induction Furnace Method See Example 1 of CN100473734C: Ni-35%Mg alloy was smelted using a new 50 kg magnesia crucible vacuum induction furnace, with a single batch yield of 50 kg.

[0078] This method requires the use of new crucibles (which are costly to sinter), requires control of vacuum and introduction of argon gas (which is a complex process), and the output is still limited to less than ton (0.05 tons), which cannot achieve the industrial-scale production of more than 4 tons as proposed in this invention.

[0079] Comparative Example 3: New Crucible Vacuum Induction Furnace Method Referring to Example 1 of CN117051275A, Ni-20Mg alloy was smelted in a vacuum induction furnace using a newly sintered aluminum-magnesium spinel crucible, with a single batch yield of 0.97 tons.

[0080] This method requires the use of new crucibles (which are costly to sinter), requires control of vacuum and introduction of argon gas (which is a complex process), and the output is still limited to 0.97 tons, which cannot reach the industrial-scale production of more than 4 tons as proposed in this invention.

[0081] Table 1 Comparison of nickel-magnesium alloy production in the examples and comparative examples

[0082] Table 1 shows a comparison between the examples and comparative examples of nickel-magnesium alloy production. It can be seen that the embodiments of the present invention achieve a dual breakthrough in both production scale and resource utilization. (1) Leapfrog increase in production scale: In the existing technology, the production of nickel-magnesium alloys has long been limited to the kilogram level (Comparative Example 2) or less than the ton level (Comparative Example 3), which has become a bottleneck restricting its large-scale application in the field of special metallurgy. Examples 1 and 2, relying on the capacity advantage of large vacuum induction furnaces and combined with the reuse of crucibles at the end, have for the first time increased the single batch production of nickel-magnesium alloys to more than 4 tons, which is 4 to 160 times that of traditional methods. This leap from "laboratory / small workshop scale" to "industrial large-scale production" is not a simple scaling up of equipment, but requires overcoming a series of technical problems brought about by mass production, such as the uniformity of magnesium addition, temperature control, and flue gas capture. This invention has successfully achieved this scale leap by combining batch magnesium addition, molten salt covering, and mobile dust removal technologies.

[0083] (2) Pioneering the concept of "end-of-life crucible reuse": Although Comparative Examples 2 and 3 also used refractory crucibles and molten salt coverings, they all used new crucibles or crucibles with normal furnace life, and the output was limited. In the field of special steel smelting, when crucibles reach the end of their service life, the industry's technical bias and conventional practice is to directly dismantle and break them down, and then re-build new crucibles. The embodiments of this invention break this technical bias, creatively combining "end-of-life crucibles" with "mass nickel-magnesium alloy production", allowing crucibles that should have been scrapped to play their final role and realizing the ultimate utilization of resources.

[0084] (3) Synergistic effect of multiple technologies: This invention is not an improvement of a single technology, but an organic combination of multiple technologies such as "reuse of the end crucible", "atmospheric pressure molten salt covering", "mobile dust removal", and "large-scale batch addition of magnesium", which produce synergistic effects: the end crucible solves the cost problem, the atmospheric pressure molten salt covering solves the problem of magnesium volatilization and oxidation, the mobile dust removal solves the environmental protection problem, and the large-scale batch addition of magnesium solves the uniformity problem in large-scale production. The superposition of these technological effects makes this invention surpass the existing technology in all four dimensions of cost, scale, purity and environmental protection.

[0085] In summary, this invention breaks through the traditional understanding of crucible lifespan in existing technologies, solves the long-standing industry problem that nickel-magnesium alloys cannot be mass-produced industrially, and possesses outstanding inventiveness.

[0086] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for producing high-purity nickel-magnesium alloy using a crucible at the end of a vacuum induction furnace, characterized in that, Includes the following steps: Step 1, Equipment Selection: Select a vacuum induction furnace with a final-stage crucible; the final-stage crucible refers to a crucible whose inner lining has reached its service life limit. The service life limit means that the working layer of the inner lining of the crucible has micro-cracks and / or local erosion, but the overall structure of the crucible is intact, without penetrating cracks, and still has the ability to bear nickel-magnesium alloy melt. Step 2, Raw material preparation: Prepare nickel source, magnesium source and industrial covering salt. Prepare nickel and magnesium materials according to the theoretical value that the magnesium content in the high-purity nickel-magnesium alloy is 18%~22% by mass. The nickel mass fraction in the nickel source is ≥99.95% and the magnesium mass fraction in the magnesium source is ≥99.8%. Step 3, Base Nickel Melting: Add the nickel source into the final crucible, start the induction heating power supply under normal pressure to completely melt the nickel source and raise the temperature to 1480℃~1500℃; Step 4: Establishing a molten salt coating layer: After the nickel liquid temperature stabilizes, add industrial coating salt to the final crucible. The amount added is 3% to 5% of the weight of the nickel liquid. Use the sensible heat of the nickel liquid to melt the industrial coating salt and form a liquid molten salt coating layer. Step 5, Magnesium alloying and flue gas collection: Adjust the mobile dust hood above the opening of the final crucible and turn on the dust collector; under normal pressure and molten salt coverage, add the magnesium source to the final crucible in batches. The magnesium source passes through the liquid molten salt coverage layer and enters the nickel liquid to melt. The magnesium fumes generated are collected by the mobile dust hood. Step 6, Homogenization and Casting: After all the magnesium source is added, turn on the electromagnetic stirring, measure and adjust the temperature to 1350℃~1400℃, and then cast the nickel-magnesium alloy melt to obtain a high-purity nickel-magnesium alloy ingot.

2. The method according to claim 1, characterized in that, In step 1, the material of the final crucible is fused magnesia or corundum.

3. The method according to claim 1, characterized in that, In step 2, the nickel source is a nickel plate or nickel block, the magnesium source is a metallic magnesium block, and the industrial covering salt is industrial sodium chloride and / or industrial potassium chloride.

4. The method according to claim 1, characterized in that, In step 4, the thickness of the liquid molten salt coating is controlled to be 30mm~50mm.

5. The method according to claim 1, characterized in that, In step 5, the movable dust cover is adjusted to be 200mm~400mm above the opening of the final crucible.

6. The method according to claim 1, characterized in that, In step 5, the actual amount of magnesium source added is increased by 1% to 3% compared to the theoretical value as compensation for burn-off.

7. The method according to claim 1, characterized in that, In step 5, the magnesium source is added to the final crucible in batches, and the total magnesium addition time is controlled to be 20 to 30 minutes; wherein the magnesium source is a 20 mm to 80 mm metal magnesium block.

8. The method according to claim 1, characterized in that, In the high-purity nickel-magnesium alloy ingot, the mass content of Mg is 18%~22%, the mass content of C is ≤0.010%, and the mass content of O is ≤5ppm.

9. The method according to any one of claims 1 to 8, characterized in that, The method produces a total of 4 to 10 tons of high-purity nickel-magnesium alloy per batch.

10. An apparatus for producing high-purity nickel-magnesium alloys using a crucible at the end of a vacuum induction furnace, characterized in that, The apparatus for implementing the method according to any one of claims 1 to 9, the apparatus comprising: The melting chamber (1) serves as the main chamber for melting. Side feeding chamber (4), connected to the side wall of the melting chamber (1), is used to feed raw materials (5) into the melting chamber (1). The induction heating assembly includes an induction coil (2) and a final crucible (3). The induction coil (2) is arranged around the outer periphery of the final crucible (3). The final crucible (3) is located inside the melting chamber (1) and is used to hold and heat the raw material (5) to form a nickel-magnesium alloy melt (6) with a liquid molten salt coating layer (7) on its surface. The sluice assembly includes a sluice chamber (8) and a sluice (9). The sluice chamber (8) is connected to the side wall of the melting chamber (1). The sluice (9) is disposed in the sluice chamber (8). The inlet of the sluice (9) is connected to the melting chamber (1) for discharging the nickel-magnesium alloy melt (6). The casting assembly includes an ingot mold chamber (10), a rotating ingot disk (11), and an ingot mold (12). The ingot mold chamber (10) is connected to the chute chamber (8). The rotating ingot disk (11) is located at the bottom of the ingot mold chamber (10). The ingot mold (12) is mounted on the rotating ingot disk (11). The outlet of the chute (9) is aligned with the opening of the ingot mold (12). The flue gas purification assembly includes a mobile dust hood (13), a dust removal fan (14), and a dust collector (15). The mobile dust hood (13) is adjusted to be above the opening of the final crucible (3). The dust removal fan (14) is connected to the mobile dust hood (13) and the dust collector (15) respectively through pipelines. The dust collector (15) is used to receive and purify the flue gas delivered by the fan.

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