Preparation method of large-size nickel ingot for AEM electrolytic bath

Abstract

The invention relates to the technical field of metallurgical industry, in particular to a preparation method of a large-size nickel ingot for an AEM electrolytic bath, which comprises the following steps: in a vacuum or argon-filled state, electrolytic nickel and carbon are jointly subjected to vacuum induction melting, carbon is used for degassing and impurity removal, then Ti, Mn and Si are supplemented, and an induction ingot is cast; and the induction ingot is subjected to electroslag remelting and scalping, and the large-specification nickel ingot for the AEM electrolytic cell is obtained. According to the method, N9996 electrolytic nickel is used as a raw material, a duplex impurity removal process and alloying are carried out through vacuum induction melting and electroslag remelting, a deoxidizing agent is supplemented in the vacuum induction melting process, impurity elements in the N9996 electrolytic nickel are deeply removed and alloyed, the content of the impurity elements in the N9996 electrolytic nickel is reduced, grain refinement is achieved, and the N9996 electrolytic nickel is obtained. And the standard of high-quality nickel ingots is achieved, the performance of a follow-up rolled tape is improved, and surface defects are greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical industry technology, specifically relating to a method for preparing large-size nickel ingots for AEM electrolytic cells, providing high-quality ingots for subsequent rolling into nickel coils. Background Technology

[0002] Anion exchange membrane electrolyzers (AEMs), as a new type of electrolyzer for hydrogen production from water electrolysis, have advantages such as being free of iridium precious metals, high safety, adaptability to the volatility of renewable energy, and relatively low energy consumption. In anion exchange membrane electrolyzers, pure nickel plates have good ductility but low hardness, and are prone to deformation during assembly due to excessive sealing pressure, leading to electrolyte leakage. Existing technologies use a method of tying electrodes + primary consumable melting (var) + secondary consumable melting (var) to obtain nickel ingots, and then roll the nickel ingots to obtain nickel strips. Because the nickel strips often suffer from perforation and peeling during the rolling process, the performance and yield of the nickel strips are seriously affected. Therefore, the quality of the nickel ingot billet directly affects its subsequent rolling, heat treatment, slitting and other production processes. Summary of the Invention

[0003] To address the shortcomings of the existing technology, the present invention aims to provide a method for preparing large-size nickel ingots for AEM electrolytic cells. This invention utilizes a combination of adding trace alloying elements and advanced smelting technology to improve the quality of large-size nickel ingots for AEM electrolytic cells, thereby ensuring the performance and overall quality of subsequently rolled nickel strips and plates. It solves the following problems: 1. Improves tensile strength, enhancing the strength of nickel strips and plates in high-temperature environments, enabling their application in high-temperature environments; 2. Resolves the problems of perforation and peeling in nickel strips and plates during rolling caused by smelting issues.

[0004] To achieve the above-mentioned technical objectives, the present invention proposes the following technical solution: This invention protects a method for preparing large-size nickel ingots for AEM electrolytic cells, comprising the following steps: Ni9996 electrolytic nickel and carbon are mixed and then melted using a vacuum induction arc melting process until the Ni9996 electrolytic nickel is smelted into a liquid metal, thus achieving the mixing of Ni9996 electrolytic nickel and carbon. The electrolytic nickel is selected from Ni9996 electrolytic nickel to ensure the purity of the raw material and reduce the influence of impurity elements.

[0005] In the Ni9996 electrolytic nickel and carbon mixture, the mass percentage of carbon is 0.006wt%±0.0005wt%.

[0006] Without turning on the vacuum pump, the molten metal was electromagnetically stirred, and the composition of the molten metal was tested.

[0007] Turn on the vacuum pump, continue electromagnetic stirring, and carry out refining. During the refining and vacuum induction arc melting process, carbon is used to react with O, H and N in the molten metal to remove impurities from Ni9996 electrolytic nickel.

[0008] After refining, the temperature is lowered to the melting temperature. Ti is added to the molten metal first, then the temperature is raised to the refining temperature, and Mn and Si are added. After mixing evenly, samples are taken to test the composition, so that the mass percentages of each component are as follows: Ni ≥ 99.5%, C < 0.005%, Si 0.02%~0.04%, Mn 0.02%~0.04%, Ti 0.08%~0.12%, S ≤ 0.001%, P ≤ 0.002%, Fe 0.01%~0.1%. The deoxidizer consists of titanium, manganese, and silicon. Titanium, manganese, and silicon are used to achieve grain refinement strengthening. The principle of grain refinement strengthening is: 1. Grain refinement strengthening is a strengthening mechanism that improves the mechanical properties of metal materials by reducing the grain size. It is listed as one of the four major metal strengthening methods. According to the Hall-Page relation (σ_y = σ_0 + k·d) -1 / 2 1) The smaller the average grain diameter, the higher the yield strength of the material. 2. Modification treatment: Adding refractory solid particles to molten metal increases the number of crystal nuclei and prevents grain growth; 1) Titanium: Trace amounts of titanium (0.12%) can refine the casting structure of nickel, eliminate intergranular cracks, and improve the strength and thermoplasticity of nickel; titanium can significantly improve the thermal strength, resistivity, thermoelectric potential and recrystallization temperature of nickel; titanium is a strong deoxidizer and can reduce the gas content in nickel. 2) Manganese: Adding a small amount of manganese to pure nickel can increase the tensile strength by 10%~15%, while the elongation decreases by less than 5%; the addition of manganese can also reduce the surface tension and viscosity of molten nickel, making it more fluid during casting and reducing casting defects; manganese can act as a heterogeneous nucleation core during solidification, inhibiting the coarse growth of nickel grains, making the microstructure more uniform and fine, thereby improving the comprehensive performance of the material; manganese has the function of deoxidation and desulfurization. 3) Silicon: Adding silicon to pure nickel increases tensile strength by 20%~30%, but decreases elongation by 10%~15%. Silicon also has deoxidizing and desulfurizing effects. Based on these reasons, this invention uses titanium, manganese, and silicon as deoxidizers to achieve grain refinement and improved mechanical properties.

[0009] Argon gas was introduced and the induction ingot was poured. After pouring, it was cooled. The cooling conditions were: first, it was cooled in an argon atmosphere for 180 minutes, and then it was cooled in open air for 60 minutes to obtain the induction ingot.

[0010] The induction ingot is subjected to electroslag remelting. Electroslag remelting (ESR) is a special metallurgical technology that uses electric current to heat slag and then melts the metal. Its core advantages are metal purification, uniform composition, and improved ingot quality. It is widely used in the production of key metal materials in the field of high-end equipment manufacturing. In this invention, the main purpose is to achieve deep purification. Then, the ingot is cooled, the surface oxide scale is removed, and slag is added for cleaning to obtain a large-size nickel ingot for AEM electrolytic cell. The cooling conditions are: cooling in an argon atmosphere for 180 minutes.

[0011] Preferably, the vacuum induction arc melting is carried out in a vacuum induction arc melting furnace with a melting capacity of 12 tons, so as to realize the preparation of large-sized nickel ingots.

[0012] Preferably, during the vacuum induction arc melting process, Ni9996 electrolytic nickel is added to the vacuum induction arc melting furnace in batches to improve the effect of vacuum induction arc melting.

[0013] Preferably, the conditions for vacuum induction arc melting are: melting for 8 to 9 hours at ≤0.5 Pa, 1500 W ± 50 W, and 1530 °C ± 5 °C.

[0014] The preferred refining conditions are: refining for 1 hour at <5 Pa, 1500 W ± 50 W, and 1550 °C ± 5 °C.

[0015] Preferably, the amount of Ti added is 0.12wt%±0.008wt%, the amount of Mn added is 0.03wt%±0.008wt%, and the amount of Si added is 0.03wt%±0.008wt%.

[0016] Preferably, the casting is carried out under an argon pressure of 30±1bpa, and the casting is non-electric casting. The casting process is slow at first and then fast. The casting temperature is 1550℃~1560℃, and the entire casting process is controlled within 20 minutes.

[0017] Preferably, during the casting process, after the shrinkage cavity contour shrinks, nickel molten metal is replenished sequentially until the shrinkage cavity is completely filled. The shrinkage time is not less than 10 minutes. The induction ingot stays in the vacuum induction arc melting furnace for 180±10 minutes before being opened and lifted out.

[0018] Preferably, the conditions for electroslag remelting are: argon purging after vacuuming, so that the top pressure reaches 1.5 × 10⁻⁶. 3 Pa; the gas flow rate before melting is 30L / min±3L / min, the slag amount is 400kg, and the power is 400KW~1500KW. The set value is not allowed to be changed. If fluctuation occurs, the allowable fluctuation range is the set value±200KW. Melt for 7h~8h first, and then use AC arc stabilizing current to compensate for shrinkage. The compensation time is ≥3h.

[0019] Preferably, Ni9996 electrolytic nickel is shot peened before smelting.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention utilizes a combination of adding trace alloying elements and advanced smelting technology to achieve uniform microstructure, enhanced strength, and fine-grained reinforcement. Regarding the advanced smelting technology, this invention employs a combination of vacuum induction arc melting and electroslag melting. The electromagnetic stirring in vacuum induction arc melting ensures component uniformity, while the slag cleaning in electroslag melting achieves deep purification. The advantages of electroslag melting are: firstly, significant purification effect, effectively removing harmful elements and inclusions from the ingot, meeting the "cleanliness requirements" of high-end materials; secondly, ensuring the quality stability of the ingot, with directional solidification reducing internal defects, resulting in a 10%~20% increase in the yield of subsequent processing. Based on the combination of vacuum induction arc melting and electroslag melting, the quality of large-size nickel ingots for AEM electrolytic cells is effectively improved, ensuring the performance and overall quality of subsequently rolled nickel plates and strips. Adding trace alloying elements solves the following problems: 1. Improving tensile strength (based on step S5 of this invention). The principle of improving tensile strength is modification treatment: adding refractory solid particles to the molten metal increases the number of crystal nuclei, prevents grain growth, and enhances the strength of nickel strip in high-temperature environments, enabling its application in high-temperature environments; 2. Due to smelting problems, perforation and peeling of nickel strip occur during rolling. This invention solves the perforation and peeling problems using steps S3, S4, S5, and S8. The "deformation compatibility difference" between inclusions (oxides, sulfides, nitrides) and the base metal is the most common cause of perforation and peeling. If gases such as H, O, and N dissolved in the molten metal do not escape in time during ingot solidification, they will form subcutaneous bubbles or internal looseness. These bubbles will rupture during subsequent perforation processing. This invention achieves excellent smelting quality (inclusions <1μm, gas content <10×10⁻). 6 Even with slight deviations in processing parameters, the risk of peeling will be significantly reduced.

[0021] This invention takes into account the numerous impurity elements in pure nickel. Through comprehensive comparison and verification using mathematical statistics, the elements responsible for strengthening were identified. Therefore, a deoxidizer was added to the molten metal after refining. The advantages of using a deoxidizer are: 1) It preferentially reacts chemically with oxygen in the melt to generate stable oxide inclusions (such as SiO2), preventing nickel from being oxidized and reducing nickel burn-off; 2) It reduces the oxygen content in pure nickel, decreasing internal defects such as porosity and inclusions in the ingot, thus improving material purity; 3) It improves the mechanical properties of pure nickel, including increasing strength, toughness, and corrosion resistance; 4) It optimizes the processing performance of pure nickel, making subsequent casting, forging, and welding processes smoother and reducing the risk of cracking. In summary, by focusing on degassing, desulfurization, removal of non-metallic inclusions, and grain refinement, the metallurgical quality and economic benefits are improved.

[0022] 2. This invention uses Ni9996 electrolytic nickel as raw material. After pretreatment of the raw material, it undergoes a two-stage impurity removal process of vacuum induction arc melting and electroslag remelting, followed by alloying (step S5). The entire production process is carried out under vacuum or argon-filled conditions to ensure the removal of harmful elements (O, N, H) in the melting environment during the melting process. This process deeply removes and alloys impurities in Ni9996 electrolytic nickel, reducing the content of impurities and refining the grains to achieve high-quality nickel ingot standards. Furthermore, using Ni9996 electrolytic nickel as raw material improves production efficiency and nickel ingot quality, with an ingot qualification rate of over 98%. This results in improved performance of subsequent rolled strip and a significant reduction in surface defects (by over 90%).

[0023] 3. This invention uses N9996 electrolytic nickel as raw material, and performs a two-stage impurity removal process and alloying through vacuum induction melting and electroslag remelting. During the vacuum induction melting process, a deoxidizer is added to deeply remove and alloy impurity elements in the N9996 electrolytic nickel, thereby reducing the impurity element content and refining the grains to meet the standards of high-quality nickel ingots. In addition, using N9996 electrolytic nickel as raw material improves production efficiency and the quality of large-size nickel ingots for AEM electrolytic cells, with an ingot qualification rate of over 98%, improving the performance of subsequent rolled strip and significantly reducing surface defects. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of large-sized nickel ingots for the AEM electrolytic cell of this invention.

[0025] Figure 2 This is a physical image of the induction ingot from Example 1.

[0026] Figure 3 This is a physical image of the electroslag smelting ingot from Example 1.

[0027] Figure 4 This is a photograph of the finished nickel ingot from Example 1. Detailed Implementation

[0028] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content.

[0029] This invention provides a novel method for preparing large-size nickel ingots for AEM electrolytic cells. Existing methods for preparing nickel ingots for AEM electrolytic cells involve: electrode binding + primary consumable melting (var) + secondary consumable melting (var). Compared to existing methods, this invention achieves element addition, impurity removal, and uniform microstructure. Specifically, by improving the melting equipment and changing the traditional melting process, trace elements are first added through a vacuum induction arc melting stage, followed by electroslag remelting to remove impurities from the nickel ingot (S3, S4, S5, and S8 of this invention). This results in a uniform microstructure, enhanced strength, and finer grain reinforcement. This solves the problems of low hardness (approximately 70 HV), bridging, and electrolyte leakage caused by deformation due to excessive sealing pressure during assembly in existing pure nickel plates and strips for AEM electrolytic cells. It also solves the perforation and peeling phenomena that occur during the rolling process.

[0030] The technical solution of the present invention will be studied below using examples and comparative examples. The specific research methods and results are shown below: Example 1 A method for preparing large-sized nickel ingots for AEM electrolytic cells, such as... Figure 1 As shown, it includes the following steps: S1. Cut N9996 electrolytic nickel into several 150mm×150mm sizes, and then perform shot peening on the surface to remove the surface oxide layer, thus obtaining treated electrolytic nickel.

[0031] S2. Add raw materials to a 12t vacuum induction melting furnace, first adding carbon and 5 tons of processed electrolytic nickel. Seal the furnace chamber, evacuate to below 0.5MPa, start the vacuum induction melting furnace, gradually increase the power to full power 1500W in stages, and gradually raise the temperature to 1530±5℃ for melting. Fill the furnace in three batches: 2 tons of processed electrolytic nickel, 2 tons of processed electrolytic nickel, and 1 ton of processed electrolytic nickel. The mass percentage of carbon in the total amount of carbon and processed electrolytic nickel is 0.006wt%. Melt until it becomes a liquid metal. Melt for a total of 8 hours, ensuring that the final melt weight and liquid level are normal.

[0032] S3. Stir the molten metal electromagnetically at 1530±5℃ and test the composition of the molten metal. Stir for 40 minutes without turning on the vacuum pump.

[0033] S4. Continue to electromagnetically stir the molten metal, turn on the vacuum pump, and raise the temperature to 1550±5℃ to maximize the liquid level. Refine for 1 hour to ensure that all components are fully mixed and homogeneous.

[0034] S5. Lower the temperature inside the vacuum induction melting furnace to 1530±5℃, add 0.12% titanium, raise the temperature to 1550±5℃, and continue to add 0.03% manganese and 0.03% silicon. Stir thoroughly, take a sample to test the composition, which is Ni≥99.5%, C<0.005%, Si 0.02%~0.04%, Mn 0.02%~0.04%, Ti 0.08%~0.12%, S≤0.001%, P≤0.002%, Fe0.01%~0.1%, which meets the composition requirements.

[0035] S6. Argon gas is introduced into the vacuum induction melting furnace at a pressure of 30 bpa, and the casting is carried out at a temperature of 1560±5℃.

[0036] S7. After casting, the induction ingot is first cooled with argon gas for 180 minutes, and then cooled with air for 60 minutes to obtain the induction ingot, which is then taken out of the furnace.

[0037] S8. The induction ingot is then subjected to electroslag melting, specifically: after vacuuming, argon is purged to achieve a top pressure of 1.5 × 10⁻⁶. 3 Pa; the gas flow rate before melting is 30L / min, the slag amount is 400kg, the power is 1000KW, and the set value is not allowed to be changed. If fluctuation occurs, the allowable fluctuation range is the set value ±200KW. Melt for 8 hours first, then use AC arc stabilizing current to compensate for shrinkage. The compensation time is ≥3 hours. After the electroslag melting is completed, cool with argon for 180 minutes to obtain the electroslag melted ingot.

[0038] S9. After unloading from the furnace and machining the surface oxide scale, the tail end is cleaned with slag to obtain the finished nickel ingot.

[0039] Repeat the operation of Example 1 and make two parallel samples of Example 1 to obtain large-size nickel ingots for AEM electrolytic cells in Examples 2 and 3.

[0040] Example 4 A method for preparing large-sized nickel ingots for AEM electrolytic cells, such as... Figure 1 As shown, it includes the following steps: S1. Cut N9996 electrolytic nickel into several 150mm×150mm sizes, and then perform shot peening on the surface to remove the surface oxide layer, thus obtaining treated electrolytic nickel.

[0041] S2. Add raw materials to a 12t vacuum induction melting furnace, first adding carbon and 5 tons of processed electrolytic nickel. Seal the furnace chamber, evacuate to below 0.5MPa, start the vacuum induction melting furnace, gradually increase the power to full power 1450W in stages, and gradually raise the temperature to 1530±5℃ for melting. Fill the furnace in three batches: 2 tons of processed electrolytic nickel, 2 tons of processed electrolytic nickel, and 1 ton of processed electrolytic nickel. The mass percentage of carbon in the total amount of carbon and processed electrolytic nickel is 0.0055wt%. Melt until it becomes liquid metal. Melt for a total of 8.5 hours, ensuring that the final melt weight and liquid level are normal.

[0042] S3. Stir the molten metal electromagnetically at 1530±5℃ and test the composition of the molten metal. Stir for 50 minutes without turning on the vacuum pump.

[0043] S4. Continue to electromagnetically stir the molten metal, turn on the vacuum pump, and refine it for 1 hour at <5Pa and 1550±5℃ to maximize the liquid level and ensure that all components are fully mixed and homogeneous.

[0044] S5. Lower the temperature inside the vacuum induction melting furnace to 1530±5℃, add 0.12% titanium, raise the temperature to 1550±5℃, and continue to add 0.03% manganese and 0.03% silicon. Stir thoroughly, take a sample to test the composition, which is Ni≥99.5%, C<0.005%, Si 0.02%~0.04%, Mn 0.02%~0.04%, Ti 0.08%~0.12%, S≤0.001%, P≤0.002%, Fe0.01%~0.1%, which meets the composition requirements.

[0045] S6. Argon gas is introduced into the vacuum induction melting furnace at a pressure of 30 bpa, and the casting is carried out at a temperature of 1560±5℃.

[0046] S7. After casting, the induction ingot is first cooled with argon gas for 180 minutes, and then cooled with air for 60 minutes to obtain the induction ingot, which is then taken out of the furnace.

[0047] S8. The induction ingot is then subjected to electroslag melting, specifically: after vacuuming, argon is purged to achieve a top pressure of 1.5 × 10⁻⁶. 3 Pa; the gas flow rate before melting is 33L / min, the slag amount is 400kg, the power is 1500KW, and the set value is not allowed to be changed. If fluctuation occurs, the allowable fluctuation range is the set value ±200KW. Melt for 7 hours first, then use AC arc stabilizing current to compensate for shrinkage. The compensation time is ≥3 hours. After the electroslag melting is completed, cool with argon for 180 minutes to obtain the electroslag melted ingot.

[0048] S9. After unloading from the furnace and machining the surface oxide scale, the tail end is cleaned with slag to obtain the finished nickel ingot.

[0049] Repeat the operation of Example 1 and make two parallel samples of Example 1 to obtain large-size nickel ingots for AEM electrolytic cells in Examples 2 and 3.

[0050] Example 5 A method for preparing large-sized nickel ingots for AEM electrolytic cells, such as... Figure 1 As shown, it includes the following steps: S1. Cut N9996 electrolytic nickel into several 150mm×150mm sizes, and then perform shot peening on the surface to remove the surface oxide layer, thus obtaining treated electrolytic nickel.

[0051] S2. Add raw materials to a 12t vacuum induction melting furnace, first adding carbon and 5 tons of processed electrolytic nickel. Seal the furnace chamber, evacuate to below 0.5MPa, start the vacuum induction melting furnace, gradually increase the power to full power 1550W in stages, and gradually raise the temperature to 1530±5℃ for melting. Fill the furnace in three batches: 2 tons of processed electrolytic nickel, 2 tons of processed electrolytic nickel, and 1 ton of processed electrolytic nickel. The mass percentage of carbon in the total amount of carbon and processed electrolytic nickel is 0.0065wt%. Melt until it becomes a liquid metal. Melt for a total of 9 hours, ensuring that the final melt weight and liquid level are normal.

[0052] S3. Stir the molten metal electromagnetically at 1530±5℃ and test the composition of the molten metal. Stir for 60 minutes without turning on the vacuum pump.

[0053] S4. Continue to electromagnetically stir the molten metal, turn on the vacuum pump, and refine it for 1 hour at <5Pa and 1550±5℃ to maximize the liquid level and ensure that all components are fully mixed and homogeneous.

[0054] S5. Lower the temperature inside the vacuum induction melting furnace to 1530±5℃, add 0.12% titanium, raise the temperature to 1550±5℃, and continue to add 0.03% manganese and 0.03% silicon. Stir thoroughly, take a sample to test the composition, which is Ni≥99.5%, C<0.005%, Si 0.02%~0.04%, Mn 0.02%~0.04%, Ti 0.08%~0.12%, S≤0.001%, P≤0.002%, Fe0.01%~0.1%, which meets the composition requirements.

[0055] S6. Argon gas is introduced into the vacuum induction melting furnace at a pressure of 30 bpa, and the casting is carried out at a temperature of 1560±5℃.

[0056] S7. After casting, the induction ingot is first cooled with argon gas for 180 minutes, and then cooled with air for 60 minutes to obtain the induction ingot, which is then taken out of the furnace.

[0057] S8. The induction ingot is then subjected to electroslag melting, specifically: after vacuuming, argon is purged to achieve a top pressure of 1.5 × 10⁻⁶. 3 Pa; the gas flow rate before melting is 27L / min, the slag amount is 400kg, and the power is 400KW. The set values ​​are not allowed to be changed. If fluctuations occur, the allowable fluctuation range is the set value ±200KW. Melt for 7.5h first, then use AC arc stabilizing current to compensate for shrinkage. The compensation time is ≥3h. After the electroslag melting is completed, cool with argon for 180min to obtain the electroslag melted ingot.

[0058] S9. After unloading from the furnace and machining the surface oxide scale, the tail end is cleaned with slag to obtain the finished nickel ingot.

[0059] Repeat the operation of Example 1 and make two parallel samples of Example 1 to obtain large-size nickel ingots for AEM electrolytic cells in Examples 2 and 3.

[0060] Comparative Example 1 A method for preparing large-sized nickel ingots for AEM electrolytic cells is the same as the preparation steps in Example 1, except that no deoxidizer is added, and includes the following steps: S1. Cut N9996 electrolytic nickel into several 150mm×150mm sizes, and then perform shot peening on the surface to remove the surface oxide layer, thus obtaining treated electrolytic nickel.

[0061] S2. Add raw materials to a 12t vacuum induction melting furnace, first adding carbon and 5 tons of processed electrolytic nickel. Seal the furnace chamber, evacuate to below 0.5MPa, start the vacuum induction melting furnace, gradually increase the power to full power 1500W in stages, and gradually raise the temperature to 1530±5℃ for melting. Fill the furnace in three batches: 2 tons of processed electrolytic nickel, 2 tons of processed electrolytic nickel, and 1 ton of processed electrolytic nickel. The mass percentage of carbon in the total amount of carbon and processed electrolytic nickel is 0.006wt%. Melt until it becomes a liquid metal. Melt for a total of 8 hours, ensuring that the final melt weight and liquid level are normal.

[0062] S3. Stir the molten metal electromagnetically at 1530±5℃ and test the composition of the molten metal. Stir for 40 minutes without turning on the vacuum pump.

[0063] S4. Continue to electromagnetically stir the molten metal, turn on the vacuum pump, and raise the temperature to 1550±5℃ to maximize the liquid level. Refine for 1 hour to ensure that all components are fully mixed and homogeneous.

[0064] S5. Reduce the temperature inside the vacuum induction melting furnace to 1530±5℃, take samples for composition testing, and the composition is Ni≥99.5%, C<0.005%, Si<0.01%, Mn<0.01%, Ti<0.01%, S≤0.001%, P≤0.002%, Fe<0.01%, which meets the composition requirements.

[0065] S6. Argon gas is introduced into the vacuum induction melting furnace at a pressure of 30 bpa, and the molten metal is poured at a pouring temperature of 1560±5℃.

[0066] S7. After casting, the induction ingot is first cooled with argon gas for 180 minutes, and then cooled with air for 60 minutes to obtain the induction ingot, which is then taken out of the furnace.

[0067] S8. The induction ingot is then subjected to electroslag melting, specifically: after vacuuming, argon is purged to achieve a top pressure of 1.5 × 10⁻⁶. 3 Pa; the gas flow rate before melting is 30L / min, the slag amount is 400kg, the power is 1000KW, and the set value is not allowed to be changed. If fluctuation occurs, the allowable fluctuation range is the set value ±200KW; AC arc current compensation is used, and the compensation time is ≥3h. After the electroslag melting is completed, argon gas is used for cooling for 180min to obtain the electroslag melted ingot.

[0068] S9. After unloading from the furnace and machining the surface oxide scale, the tail end is cleaned with slag to obtain the finished nickel ingot.

[0069] Repeat the operation of Comparative Example 1 and make a parallel sample of Comparative Example 1 to obtain the large-size nickel ingot for AEM electrolytic cell of Comparative Example 2.

[0070] In Examples 1-3 and Comparative Examples 1-2, the physical images of the induction ingot, electroslag smelting ingot, and finished nickel ingot of Example 1 are shown below. Figures 2-4 As shown in Table 1, the chemical composition of large-sized nickel ingots used in AEM electrolytic cells is as follows: Table 1. Optimal Chemical Composition of Ni9996 Electrolytic Nickel Since the chemical composition of the parallel samples is slightly different, the performance of Examples 1-3 and Comparative Examples 1-2 is different. The performance was measured by forging, hot rolling, pickling, rolling and annealing the AEM electrolytic cells of Examples 1-3 and Comparative Examples 1-2 with large nickel ingots to obtain nickel plates and strips with a thickness of 1.0 mm. The performance of the nickel plates and strips was measured and the results are shown in Table 2.

[0071] Table 2. Transverse mechanical properties, hardness, and grain size of nickel plates. As shown in Table 2, the nickel plates and strips of Examples 1 to 3 differ in chemical composition from those of Comparative Examples 1 to 2, but their mechanical properties, hardness, and grain size are significantly improved.

[0072] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing large-size nickel ingots for AEM electrolytic cells, characterized in that, Includes the following steps: Ni9996 electrolytic nickel and carbon are mixed and then subjected to vacuum induction arc melting until Ni9996 electrolytic nickel is melted into liquid metal. In the Ni9996 electrolytic nickel and carbon mixture, the mass percentage of carbon is 0.006wt%±0.0005wt%. Without turning on the vacuum pump, the molten metal was electromagnetically stirred and the composition of the molten metal was tested. Turn on the vacuum pump, continue electromagnetic stirring, and proceed with refining; After refining, the temperature is lowered to the melting temperature. Ti is first added to the molten metal, then the temperature is raised to the refining temperature, and Mn and Si are added. After mixing evenly, samples are taken to test the composition, so that the mass percentage of each component reaches the following: Ni ≥ 99.5%, C < 0.005%, Si 0.02%~0.04%, Mn 0.02%~0.04%, Ti 0.08%~0.12%, S ≤ 0.001%, P ≤ 0.002%, Fe 0.01%~0.1%. Argon gas is introduced and the induction ingot is poured in. After pouring, it is cooled to obtain an induction ingot. The induction ingot is electroslag smelted, and then cooled, the surface oxide scale is removed by turning, and slag is added for cleaning to obtain a large-size nickel ingot for AEM electrolytic cell.

2. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 1, characterized in that, Vacuum induction arc melting is carried out in a vacuum induction arc melting furnace with a melting capacity of 12 tons.

3. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 2, characterized in that, During the vacuum induction arc melting process, Ni9996 electrolytic nickel is added to the vacuum induction arc melting furnace in batches.

4. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 1, characterized in that, The conditions for vacuum induction arc melting are: melting for 8 to 9 hours at ≤0.5 Pa, 1500 W ± 50 W, and 1530 °C ± 5 °C.

5. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 1, characterized in that, The refining conditions are: refining for 1 hour at <5 Pa, 1500 W ± 50 W, and 1550 °C ± 5 °C.

6. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 1, characterized in that, The amount of Ti added is 0.12wt%±0.008wt%, the amount of Mn added is 0.03wt%±0.008wt%, and the amount of Si added is 0.03wt%±0.008wt%.

7. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 1, characterized in that, The casting was carried out under an argon pressure of 30±1bpa. The casting was done without electricity, and the casting process was slow at first and then fast. The casting temperature was 1550±5℃.

8. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 1, characterized in that, The conditions for electroslag remelting are: after vacuuming, argon is purged to achieve a top pressure of 1.5 × 10⁻⁶. 3 Pa; the gas flow rate before melting is 30L / min±3L / min, the slag amount is 400kg, and the power is 400KW~1500KW. The set value is not allowed to be changed. If fluctuation occurs, the allowable fluctuation range is the set value±200KW. Melt for 7h~8h first, and then use AC arc stabilizing current to compensate for shrinkage. The compensation time is ≥3h.

9. The method for preparing large-size nickel ingots for AEM electrolytic cells according to claim 1, characterized in that, Ni9996 electrolytic nickel underwent shot peening before smelting.

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