A method for purifying and remelting a k447 nickel-based superalloy return material

Abstract

This application belongs to the field of high-temperature alloy technology, and particularly relates to a purification and remelting method for K447 nickel-based high-temperature alloy recycled material. No existing technology has been found that combines stepwise Al addition with a three-layer gradient slag system for K447 recycled material. This purification and remelting method involves adding the first portion of Al to the initial alloy melt during the Al-Ti deep deoxidation refining stage for deep deoxidation, and reserving the second portion of Al in a consumable electrode rod to reduce MgO in the slag system during slag remelting. Combined with the adsorption and removal of inclusions by the three-layer gradient slag system containing rare earth oxides in the middle layer, this method achieves purification and remelting of the K447 recycled material, effectively removing inclusions, reducing oxygen, nitrogen, and sulfur content, and inhibiting Al burn-off, with an Al recovery rate ≥95%.

Description

Technical Field

[0001] This application belongs to the field of high-temperature alloy technology, and in particular relates to a purification and remelting method for recycled K447 nickel-based high-temperature alloy. Background Technology

[0002] K447 nickel-based superalloys contain a large amount of precious metal elements, generating a significant amount of recycled materials during alloy production and subsequent processing, including ingot risers, large scraps, head and tail cut-offs, edge scraps, and machining chips. Effective recycling and reuse of these recycled materials can significantly reduce raw material costs and achieve efficient recycling of precious metal resources. However, the direct reuse of these recycled materials faces severe technical challenges.

[0003] The O, N, and S contents in the recycled material are significantly higher than in the virgin material. The recycled material contains a large number and size of inclusions, and both the number and size of inclusions increase significantly with the increase in the proportion of recycled material. K447 alloy is a high-Al nickel-based superalloy, and the amount of Al2O3 inclusions in its recycled material is much higher than in the virgin material, causing loss of alloying elements, compositional deviations, and microstructural deterioration. During the remelting process of K447 alloy recycled material, some alloying elements suffer severe oxidation loss, increasing the difficulty of deoxidation and further increasing the number of inclusions. The purity requirements for alloys in key components of gas turbines are extremely stringent. The trace inclusions and gases remaining in the recycled material can become crack initiation sources during service, directly threatening the operational safety of the gas turbine.

[0004] Currently, the purification treatment of high-temperature alloy return materials mainly adopts technical routes such as a dual process of carbon deoxidation refining and electroslag remelting, electron beam melting, and composite salt purification treatment. When using the dual process of carbon deoxidation refining and electroslag remelting, a large amount of Al2O3 inclusions in the return material are difficult to completely remove during the carbon deoxidation refining stage, and remain significantly after electroslag remelting, failing to meet the ultra-high purity requirements of K447 alloy for gas turbines. Electron beam melting equipment involves large investments, high costs, and low production efficiency. Composite salt purification treatment is effective in removing surface contaminants, but its ability to remove internal inclusions is limited. The above-mentioned existing technologies do not address the unique characteristics of K447 alloy's high Al content and the easy oxidation of alloying elements during return material remelting, failing to control the oxidation loss of alloying elements while removing a large amount of Al2O3 inclusions in the return material, thus failing to meet the purity requirements of K447 alloy for gas turbines. Summary of the Invention

[0005] This application provides a purification and remelting method for recycled K447 nickel-based superalloy material to solve the following technical problem: how to purify and remelt recycled K447 nickel-based superalloy material to remove inclusions, reduce oxygen, nitrogen and sulfur content and inhibit Al burn-off.

[0006] This application provides a purification and remelting method for recycled K447 nickel-based superalloy material, comprising the following steps: The K447 recycled material was mixed with some new material and melted to obtain the initial alloy melt; The initial alloy melt was subjected to carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining in sequence to obtain a refined alloy melt. The refined alloy melt is cast into a consumable electrode rod; The consumable electrode rod was electroslag remelted in a three-layer gradient slag system to obtain K447 electroslag ingot. The addition of Al is carried out in a stepwise manner: the first part of Al is added to the initial alloy melt during the deep deoxidation and refining stage of Al and Ti, and works with Ti to remove dissolved oxygen in the melt and suppress the formation of primary coarse Al2O3 inclusions; the second part of Al is added before the refining alloy melt is cast and reserved in the consumable electrode rod, so that it can enter the slag-gold interface with the melting of the consumable electrode rod during the electroslag remelting process, reduce MgO in the slag system to generate new Al2O3 inclusions; The three-layer gradient slag system includes a bottom slag, an intermediate slag, and a top slag. The intermediate slag contains rare earth oxides, which are used to adsorb and remove the newly formed Al2O3 inclusions. The K447 return material accounts for no more than 60% of the total furnace charge by mass.

[0007] Optionally, before mixing and melting the K447 recycled material with a portion of the virgin material, the method further includes a recycled material pretreatment step; the recycled material pretreatment step includes: The K447 return material is classified according to its source and form to obtain ingot riser and large scrap, head and tail cut-off material and edge scrap, and machining chips; The ingot riser and large pieces of residual material are cleaned and crushed. The cut-off material and scrap material are subjected to acid washing, water washing and drying treatment; The machining chips are subjected to degreasing, crushing, magnetic separation, alkaline washing, and water washing and drying in sequence. The ingot risers and large scraps after surface cleaning and crushing, the head and tail cut-offs and edge scraps after pickling, washing and drying, and the machining chips after degreasing, crushing, magnetic separation, alkaline washing and washing and drying are stored separately.

[0008] Optionally, the carbon deoxidation refining temperature is 1550℃~1580℃, the refining time is 45min~90min, and the vacuum degree is ≤5Pa; The carbon deoxidation refining process includes bottom-blown argon stirring, with a flow rate of 0.3 L / min to 0.6 L / min.

[0009] Optionally, the mass of the first portion of Al is 0.05% to 0.15% of the mass of the initial alloy melt, and the mass of the second portion of Al is 0.2% to 0.5% of the mass of the refined alloy melt.

[0010] Optionally, the composite purifying agent comprises 40% to 60% by mass of CaO, 20% to 40% by mass of Al2O3, and 5% to 15% by mass of MgO, wherein the mass of the composite purifying agent is 0.5% to 1.0% of the mass of the initial alloy melt.

[0011] Optionally, bottom-blown argon stirring is performed in the carbon deoxidation refining and the Al and Ti deep deoxidation refining; After the adsorption and refining of the composite purifier is completed, the bottom blowing argon stirring is stopped, and the refined alloy melt is cooled to 1420℃~1450℃. Argon gas is introduced into the surface of the refined alloy melt to 0.04MPa~0.06MPa. After a film is formed on the surface of the refined alloy melt, it is cast into the consumable electrode rod.

[0012] Optionally, the bottom slag comprises 40%–50% CaF2, 20%–30% Al2O3, 15%–25% CaO, and 5%–10% MgO, and the thickness of the bottom slag accounts for 25%–30% of the total thickness of the three-layer gradient slag system; The intermediate slag layer comprises CaF250%–60% by mass, Al2O315%–25% by mass, CaO10%–20% by mass, MgO33%–8% by mass, and rare earth oxides1%–3% by mass. The thickness of the intermediate slag layer accounts for 40%–50% of the total thickness of the three-layer gradient slag system. The top slag comprises 60%–70% CaF2, 10%–20% Al2O3, and 5%–15% CaO. The thickness of the top slag accounts for 20%–35% of the total thickness of the three-layer gradient slag system.

[0013] Optionally, the rare earth oxide includes Ce2O3 and / or La2O3.

[0014] Optionally, the electroslag remelting is protected by argon gas, the flow rate of the argon gas is 5L / min to 15L / min, and the melting rate of the electroslag remelting is 4kg / min to 8kg / min.

[0015] Optionally, the method further includes purity detection and circulation control steps: The K447 electroslag ingot was subjected to O content testing, N content testing, S content testing, and inclusion rating. The K447 electroslag ingots with O content ≤5ppm, N content ≤3ppm, S content ≤3ppm, D-class inclusions ≤0.5 grade, and maximum inclusion size ≤3μm are deemed qualified and used for the remelting production of K447 alloy. K447 electroslag ingots with O content > 5 ppm, or N content > 3 ppm, or S content > 3 ppm, or D-class inclusions > 0.5 grade, or inclusions with maximum size > 3 μm are crushed and returned to the step of mixing K447 return material with some new material and melting it for reprocessing. The K447 recycled material from the same batch shall not be recycled more than 3 times. After more than 3 times, the K447 recycled material shall be mixed with the new material at a mass ratio of not less than 50%.

[0016] The technical solution provided in this application has the following advantages compared with the prior art: This purification and remelting method involves mixing K447 recycled material with a portion of virgin material and melting them to obtain an initial alloy melt. This initial alloy melt is then subjected to sequential carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining to obtain a refined alloy melt. This refined alloy melt is then cast into a consumable electrode rod, which is then electroslag remelted under a three-layer gradient slag system to obtain a K447 electroslag ingot. The addition of Al is done in stages: the first portion of Al is added to the initial alloy melt during the Al and Ti deep deoxidation refining stage, working synergistically with Ti to remove dissolved oxygen from the melt and inhibit the formation of primary coarse Al2O3 inclusions; the second portion of Al is added before casting and pre-retained in the consumable electrode rod, where it is then used in electroslag remelting. During slag remelting, the consumable electrode rod melts and enters the slag-gold interface, reducing MgO in the slag system to generate small, diffusely distributed new Al2O3 inclusions. These new Al2O3 inclusions are then adsorbed, degraded, and removed by the intermediate slag layer containing rare earth oxides. Thus, on the one hand, the deoxidation of Al and the reduction of MgO are separated in time, avoiding the large primary inclusions and severe Al burn-off caused by a one-time addition of aluminum. On the other hand, the MgO reduction reaction continuously consumes the oxygen potential in the slag at the slag-gold interface and simultaneously achieves in-situ capture of inclusions. This removes inclusions, reduces the content of O, N, and S, and inhibits Al burn-off, achieving purified remelting of K447 nickel-based superalloy return material.

[0017] Existing technologies do not offer a technical solution combining stepwise Al addition with a three-layer gradient slag system for K447 recycled material. This purification remelting method adds the first portion of Al to the initial alloy melt during the Al-Ti deep deoxidation refining stage for deep deoxidation. The second portion of Al is reserved in the consumable electrode rod to reduce MgO in the slag system during remelting. Combined with the adsorption and removal of inclusions by the three-layer gradient slag system containing rare earth oxides in the middle layer, this method achieves purified remelting of K447 recycled material, effectively removing inclusions, reducing oxygen, nitrogen, and sulfur content, and inhibiting Al burn-off, with an Al yield ≥95%. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within the range. For example, a range description of 1 to 3 or 1~3 covers all sub-ranges (such as 1 to 2, 2 to 3, etc.) and single numbers (such as 1.5, 2, 2.7) between 1 and 3. Unless otherwise specified, the terms used herein include terms such as "include" to indicate, but are not limited to; relational terms such as "first" and "second" are used only to distinguish different entities or steps and do not imply an actual order or relationship; and / or indicate that multiple situations may exist alone or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. Proportional relationships mentioned herein, such as mass ratio and molar ratio, should be understood as the correspondence between the antecedent and consequent of a proportional expression, according to the order of description. Unless otherwise specified, all terms such as content, amount added, and dosage mentioned herein are based on mass; for example, an addition / addition amount of 1% means that the additive / addition accounts for 1% of the total mass of the system; a content of 10% means that the component has a mass fraction of 10% in the composition. All raw materials, reagents, instruments, and equipment used in this document can be obtained commercially or prepared using existing methods.

[0020] This application provides a purification and remelting method for recycled K447 nickel-based superalloy material, comprising the following steps: S1. Mix the K447 recycled material with some new material and melt it to obtain the initial alloy melt; S2. The initial alloy melt is subjected to carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining in sequence to obtain a refined alloy melt. S3. The refined alloy melt is cast into a consumable electrode rod; S4. The consumable electrode rod is electroslag remelted in a three-layer gradient slag system to obtain K447 electroslag ingot. The addition of Al is carried out in a stepwise manner: the first part of Al is added to the initial alloy melt during the deep deoxidation and refining stage of Al and Ti, and works with Ti to remove dissolved oxygen in the melt and suppress the formation of primary coarse Al2O3 inclusions; the second part of Al is added before the refining alloy melt is cast and reserved in the consumable electrode rod, so that it can enter the slag-gold interface with the melting of the consumable electrode rod during the electroslag remelting process, and reduce MgO in the slag system to generate new Al2O3 inclusions. The three-layer gradient slag system includes a bottom slag, an intermediate slag, and a top slag, wherein the intermediate slag contains rare earth oxides. The K447 return material accounts for no more than 60% of the total furnace charge by mass.

[0021] K447 nickel-based superalloy: refers to a nickel-based cast superalloy with nickel as the matrix and containing elements such as Cr, Co, W, Mo, Ta, and Hf. The Al content of the K447 nickel-based superalloy is 5.30%–5.70%. This K447 nickel-based superalloy is used in the production of key components for gas turbines. K447 nickel-based superalloy return material: refers to recyclable alloy waste generated during the production and subsequent processing of K447 nickel-based superalloy, including ingot risers, large scraps, head and tail cut-offs, edge scraps, and machining chips. Initial alloy melt: refers to the liquid alloy obtained by mixing and melting K447 return material with some virgin material. Carbon deoxidation refining: refers to the refining process that uses the reaction of carbon and oxygen to generate carbon monoxide gas under vacuum conditions to remove dissolved oxygen from the initial alloy melt. Al and Ti deep deoxidation refining: refers to the refining process that adds Al and Ti to the initial alloy melt to further reduce the oxygen content. Composite purifier adsorption refining: refers to the refining process of adding a composite purifier to the initial alloy melt to adsorb suspended inclusions. Refined alloy melt: refers to the liquid alloy obtained after carbon deoxidation refining, deep Al and Ti deoxidation refining, and composite purifier adsorption refining. Consumable electrode rod: refers to an electrode rod cast from the refined alloy melt for electroslag remelting. Three-layer gradient slag system: refers to a slag system structure with different compositions and functions, consisting of a bottom layer slag, an intermediate layer slag, and a top layer slag, during electroslag remelting. Stepwise method: refers to a method of adding Al in two separate stages: a first part Al and a second part Al.

[0022] Parameter Influence Analysis: Percentage of K447 recycled material in total furnace charge: If the percentage of K447 recycled material in total furnace charge exceeds 60%, the amount of inclusions and gas content brought in by the K447 recycled material will exceed the removal capacity of the purification remelting method, resulting in the purity of K447 electroslag ingots not meeting the standards; if the percentage of K447 recycled material in total furnace charge is too low, the recycling rate of K447 recycled material will be insufficient and the effect of reducing raw material costs will not be significant.

[0023] In some embodiments, before mixing and melting the K447 recycled material with a portion of the virgin material, the method further includes a recycled material pretreatment step; the recycled material pretreatment step includes: The K447 return material is classified according to its source and form to obtain ingot riser and large scrap, head and tail cut-off material and edge scrap, and machining chips; The ingot riser and large pieces of residual material are cleaned and crushed. The cut-off material and scrap material are subjected to acid washing, water washing and drying treatment; The machining chips are subjected to degreasing, crushing, magnetic separation, alkaline washing, and water washing and drying in sequence. The ingot risers and large scraps after surface cleaning and crushing, the head and tail cut-offs and edge scraps after pickling, washing and drying, and the machining chips after degreasing, crushing, magnetic separation, alkaline washing and washing and drying are stored separately.

[0024] This purification and remelting method includes a pretreatment step for the recycled K447 material before mixing and melting it with some new material. This pretreatment step classifies the recycled K447 material according to its source and form, resulting in ingot risers and large scraps, head and tail cut-offs and edge scraps, and machining chips. The ingot risers and large scraps undergo surface cleaning and crushing. The head and tail cut-offs and edge scraps undergo acid pickling, water washing, and drying. The machining chips undergo degreasing, crushing, magnetic separation, alkaline washing, and water washing. The washing and drying process involves storing the ingot riser and large scraps after surface cleaning and crushing, the head and tail cut-off materials and edge scraps after pickling and water washing and drying, and the machining chips after degreasing, crushing, magnetic separation, alkaline washing and water washing and drying. This process removes surface contaminants from the K447 return material and reduces inclusions and gases introduced by the K447 return material. In this way, the K447 nickel-based superalloy return material is purified and remelted to remove inclusions and control gas content.

[0025] In some embodiments, the carbon deoxidation refining temperature is 1550℃~1580℃, the refining time is 45min~90min, and the vacuum degree is ≤5Pa; The carbon deoxidation refining process includes bottom-blown argon stirring, with a flow rate of 0.3 L / min to 0.6 L / min.

[0026] This purification and remelting method controls the carbon deoxidation refining temperature to 1550℃~1580℃, the refining time to 45min~90min, and the vacuum degree to ≤5Pa. The carbon deoxidation refining includes bottom blowing argon stirring, and the flow rate of the bottom blowing argon stirring is controlled to 0.3L / min~0.6L / min. This promotes the reaction of carbon and oxygen in the initial alloy melt to generate carbon monoxide and accelerates the rise and escape of carbon monoxide bubbles. In this way, the K447 nickel-based superalloy return material is purified and remelted to remove inclusions and control the gas content.

[0027] The temperature for carbon deoxidation refining is 1550℃~1580℃, including but not limited to: 1550℃, 1560℃, 1570℃, 1580℃, etc.; the refining time is 45min~90min, including but not limited to: 45min, 60min, 75min, 90min, etc.; the vacuum degree is ≤5Pa, including but not limited to: 1Pa, 2Pa, 3Pa, 4Pa, 5Pa, etc.; the flow rate of bottom-blown argon stirring is 0.3L / min~0.6L / min, including but not limited to: 0.3L / min, 0.4L / min, 0.5L / min, 0.6L / min, etc.

[0028] This purification remelting method controls the addition of Al in the first part to 0.05% to 0.15% of the initial alloy melt mass, and the addition of Al in the second part to 0.2% to 0.5% of the refined alloy melt mass. This allows for the synergistic completion of deep deoxidation with less Al and Ti during the deep deoxidation refining stage, avoiding the formation of a large amount of primary coarse Al2O3 inclusions inside the melt due to the addition of a large amount of Al at once. The remaining Al is reserved in the consumable electrode rod for the reduction reaction of MgO contained in the slag system and for Al composition compensation during electroslag remelting. This achieves purification remelting of K447 nickel-based superalloy return material to remove inclusions, control gas content, and suppress Al burn-off.

[0029] The first portion of Al comprises 0.05% to 0.15% of the initial alloy melt mass, including but not limited to: 0.05%, 0.08%, 0.10%, 0.12%, 0.15%, etc.; the second portion of Al comprises 0.2% to 0.5% of the refined alloy melt mass, including but not limited to: 0.2%, 0.3%, 0.35%, 0.4%, 0.5%, etc. In some embodiments, the composite purifying agent comprises 40% to 60% of CaO, 20% to 40% of Al₂O₃, and 5% to 15% of MgO, wherein the mass of the composite purifying agent is 0.5% to 1.0% of the initial alloy melt mass.

[0030] This purification and remelting method controls the composition of the composite purifying agent to be 40%–60% by mass of CaO, 20%–40% by mass of Al2O3, and 5%–15% by mass of MgO. The mass of the composite purifying agent is controlled to be 0.5%–1.0% of the mass of the initial alloy melt. The composite purifying agent is used to adsorb Al2O3 inclusions in the initial alloy melt, thereby achieving purification and remelting of K447 nickel-based superalloy return material to remove inclusions and control gas content.

[0031] The composite purifying agent includes CaO 40%–60% by mass, including but not limited to: 40%, 45%, 50%, 55%, 60% by mass, etc.; Al2O3 20%–40% by mass, including but not limited to: 20%, 25%, 30%, 35%, 40% by mass, etc.; MgO 5%–15% by mass, including but not limited to: 5%, 8%, 10%, 12%, 15% by mass, etc.; the mass of the composite purifying agent is 0.5%–1.0% of the initial alloy melt mass, including but not limited to: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0032] In some embodiments, bottom-blown argon agitation is performed in the carbon deoxidation refining and the Al and Ti deep deoxidation refining; After the adsorption and refining of the composite purifier is completed, the bottom blowing argon stirring is stopped, and the refined alloy melt is cooled to 1420℃~1450℃. Argon gas is introduced into the surface of the refined alloy melt to 0.04MPa~0.06MPa. After a film is formed on the surface of the refined alloy melt, it is cast into the consumable electrode rod.

[0033] The purification and remelting method involves bottom-blowing argon stirring during carbon deoxidation refining and Al and Ti deep deoxidation refining. After the composite purifying agent adsorption refining is completed, the bottom-blowing argon stirring is stopped, and the refined alloy melt is cooled to 1420℃~1450℃. Argon gas is then introduced onto the surface of the refined alloy melt to a pressure of 0.04MPa~0.06MPa. After a film forms on the surface of the refined alloy melt, the refined alloy melt is cast into a consumable electrode rod. This avoids the adverse disturbance of the formed film caused by bottom-blowing argon stirring after the composite purifying agent adsorption refining is completed, and reduces secondary oxidation and gas absorption of the refined alloy melt. This process achieves purification and remelting of K447 nickel-based high-temperature alloy return material to remove inclusions and control gas content.

[0034] The refined alloy melt is cooled to 1420℃~1450℃, including but not limited to: 1420℃, 1430℃, 1440℃, 1450℃, etc.; argon gas is introduced into the surface of the refined alloy melt to 0.04MPa~0.06MPa, including but not limited to: 0.04MPa, 0.05MPa, 0.06MPa, etc.

[0035] In some embodiments, the bottom slag comprises 40%–50% by mass of CaF2, 20%–30% by mass of Al2O3, 15%–25% by mass of CaO, and 5%–10% by mass of MgO, and the thickness of the bottom slag accounts for 25%–30% of the total thickness of the three-layer gradient slag system; The intermediate slag layer comprises CaF250%–60% by mass, Al2O315%–25% by mass, CaO10%–20% by mass, MgO33%–8% by mass, and rare earth oxides1%–3% by mass. The thickness of the intermediate slag layer accounts for 40%–50% of the total thickness of the three-layer gradient slag system. The top slag comprises 60%–70% CaF2, 10%–20% Al2O3, and 5%–15% CaO. The thickness of the top slag accounts for 20%–35% of the total thickness of the three-layer gradient slag system.

[0036] This purification and remelting method controls the composition of the bottom slag to be CaF2 40%–50% by mass, Al2O3 20%–30% by mass, CaO 15%–25% by mass, and MgO 5%–10% by mass, with the thickness of the bottom slag controlled to be 25%–30% of the total thickness of the three-layer gradient slag system. The composition of the middle layer slag is controlled to be CaF2 50%–60% by mass, Al2O3 15%–25% by mass, CaO 10%–20% by mass, MgO 3%–8% by mass, and rare earth oxides 1%–3% by mass, with the thickness of the middle layer slag controlled to be 40%–50% of the total thickness of the three-layer gradient slag system. The composition of the top layer slag is controlled to be CaF2 60%–70% by mass, Al2O3 10%–20% by mass, and CaO 10%–20% by mass. The thickness of the top slag is controlled at 5% to 15% by mass and is 20% to 35% of the total thickness of the three-layer gradient slag system. This allows the bottom slag to adsorb Al2O3 inclusions, the middle slag to remove residual inclusions, and the top slag to ensure the conductivity and fluidity of the slag system. This enables the purification and remelting of K447 nickel-based superalloy return material to remove inclusions and control gas content.

[0037] The bottom slag includes CaF2 40%–50% by mass, including but not limited to: 40%, 45%, 50% by mass, etc.; Al2O3 20%–30% by mass, including but not limited to: 20%, 25%, 30% by mass, etc.; CaO 15%–25% by mass, including but not limited to: 15%, 20%, 25% by mass, etc.; MgO 5%–10% by mass, including but not limited to: 5%, 7%, 10% by mass, etc.; the thickness of the bottom slag accounts for 25%–30% of the total thickness of the three-layer gradient slag system, including but not limited to: 25%, 27%, 30%, etc.

[0038] The intermediate slag layer comprises CaF2 50%–60% by mass, including but not limited to 50%, 55%, and 60% by mass; Al2O3 15%–25% by mass, including but not limited to 15%, 20%, and 25% by mass; CaO 10%–20% by mass, including but not limited to 10%, 15%, and 20% by mass; MgO 3%–8% by mass, including but not limited to 3%, 5%, and 8% by mass; and rare earth oxides 1%–3% by mass, including but not limited to 1%, 2%, and 3% by mass. The thickness of the intermediate slag layer accounts for 40%–50% of the total thickness of the three-layer gradient slag system, including but not limited to 40%, 45%, and 50%.

[0039] The top slag comprises CaF2 at 60%–70% by mass, including but not limited to 60%, 65%, and 70% by mass; Al2O3 at 10%–20% by mass, including but not limited to 10%, 15%, and 20% by mass; and CaO at 5%–15% by mass, including but not limited to 5%, 10%, and 15% by mass. The thickness of the top slag accounts for 20%–35% of the total thickness of the three-layer gradient slag system, including but not limited to 20%, 25%, 30%, and 35%.

[0040] In some embodiments, the rare earth oxides include Ce2O3 and / or La2O3.

[0041] This purification and remelting method limits rare earth oxides to Ce2O3 and / or La2O3, thereby transforming residual Al2O3 into fine spherical rare earth oxide sulfides and changing the precipitation path of inclusions through Ce2O3 and / or La2O3, thus achieving purification and remelting of K447 nickel-based superalloy return material to remove inclusions and control gas content.

[0042] In some embodiments, the electroslag remelting is protected by argon gas, the flow rate of which is 5 L / min to 15 L / min, and the melting rate of the electroslag remelting is 4 kg / min to 8 kg / min.

[0043] This purification remelting method employs argon protection during electroslag remelting, with the flow rate of the argon protection controlled at 5L / min to 15L / min and the melting rate of the electroslag remelting controlled at 4kg / min to 8kg / min. This avoids secondary oxidation of K447 electroslag ingots during the electroslag remelting process and controls the depth of the molten pool and solidification conditions, thereby achieving purification remelting of K447 nickel-based superalloy return material to remove inclusions and control gas content.

[0044] The flow rate for argon protection is 5L / min to 15L / min, including but not limited to: 5L / min, 8L / min, 10L / min, 12L / min, 15L / min, etc.; the melting rate for electroslag remelting is 4kg / min to 8kg / min, including but not limited to: 4kg / min, 5kg / min, 6kg / min, 7kg / min, 8kg / min, etc.

[0045] In some embodiments, the method further includes purity detection and circulation control steps: The K447 electroslag ingot was subjected to O content testing, N content testing, S content testing, and inclusion rating. The K447 electroslag ingots with O content ≤5ppm, N content ≤3ppm, S content ≤3ppm, D-class inclusions ≤0.5 grade, and maximum inclusion size ≤3μm are deemed qualified and used for the remelting production of K447 alloy. K447 electroslag ingots with O content > 5 ppm, or N content > 3 ppm, or S content > 3 ppm, or D-class inclusions > 0.5 grade, or inclusions with maximum size > 3 μm are crushed and returned to the step of mixing K447 return material with some new material and melting it for reprocessing. The K447 recycled material from the same batch shall not be recycled more than 3 times. After more than 3 times, the K447 recycled material shall be mixed with the new material at a mass ratio of not less than 50%.

[0046] This purification and remelting method involves testing the O, N, and S content of K447 electroslag ingots and rating the inclusions. K447 electroslag ingots with O content ≤ 5 ppm, N content ≤ 3 ppm, S content ≤ 3 ppm, Class D inclusions ≤ 0.5, and maximum inclusion size ≤ 3 μm are deemed qualified and used for the remelting of K447 alloy. Ingots with O content > 5 ppm, N content > 3 ppm, S content > 3 ppm, Class D inclusions > 0.5, or inclusions > 0.5 are deemed unqualified and used for the remelting of K447 alloy. K447 electroslag ingots with a maximum size > 3μm are returned to the carbon deoxidation refining step for reprocessing. The number of times the same batch of K447 recycled material is recycled is controlled to no more than 3 times. K447 recycled material that has been recycled more than 3 times is mixed with new material at a mass ratio of no less than 50%. This establishes the purity standard and number of times the K447 recycled material is recycled and prevents the continuous accumulation of inclusions. In this way, the K447 nickel-based superalloy recycled material is purified and remelted to remove inclusions and control the gas content.

[0047] In some embodiments, the K447 recycled high-temperature alloy is used in the production of key components for gas turbines.

[0048] K447 is a high-Al nickel-based casting superalloy. Its recycled material, after purification and remelting, is mainly used to manufacture key hot-end components such as gas turbine blades and guide vanes. These components have the most stringent requirements for O, N, and S content and inclusion size.

[0049] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0050] Example 1 A purification and remelting method for recycled K447 nickel-based superalloy material, the purification and remelting method comprising the following steps: The purification and remelting method involves mixing and melting K447 recycled material with some new material to obtain an initial alloy melt; wherein, the K447 recycled material consists of ingot risers and large scrap pieces, and the K447 recycled material accounts for 60% of the total furnace charge by mass.

[0051] The purification and remelting method involves sequentially subjecting the initial alloy melt to carbon deoxidation refining, deep deoxidation refining of Al and Ti, and adsorption refining with a composite purifying agent to obtain a refined alloy melt. The carbon deoxidation refining temperature is 1560℃, the refining time is 60 min, and the vacuum degree is 5 Pa. The carbon deoxidation refining includes bottom-blown argon stirring at a flow rate of 0.4 L / min. The addition of Al is done in steps, including: the purification and remelting method adding the first portion of Al... The first portion of Al is added to the initial alloy melt during the deep deoxidation and refining of Al and Ti. The mass of the first portion of Al is 0.10% of the mass of the initial alloy melt, and it works with Ti to remove dissolved oxygen from the melt. In the purification remelting method, a second portion of Al is added before casting the refined alloy melt and is reserved in the consumable electrode rod. The mass of the second portion of Al is 0.35% of the mass of the refined alloy melt. The second portion of Al is used for the reduction reaction of MgO contained in the slag system during the electroslag remelting. The composite purifying agent includes 50% by mass of CaO, 30% by mass of Al2O3, and 10% by mass of MgO. The mass of the composite purifying agent is 0.8% of the mass of the initial alloy melt.

[0052] The purification and remelting method involves casting the refined alloy melt into a consumable electrode rod. The purification and remelting method includes bottom-blowing argon stirring during the carbon deoxidation refining and the deep deoxidation refining of Al and Ti. After the composite purifying agent adsorption refining is completed, the purification and remelting method stops the bottom-blowing argon stirring and cools the refined alloy melt to 1440°C. Argon gas is then introduced onto the surface of the refined alloy melt at 0.05 MPa. After a film forms on the surface of the refined alloy melt, the purification and remelting method casts the refined alloy melt into the consumable electrode rod.

[0053] The purification and remelting method involves electroslag remelting the consumable electrode rod under a three-layer gradient slag system to obtain a K447 electroslag ingot. The three-layer gradient slag system comprises a bottom layer slag, an intermediate layer slag, and a top layer slag. The intermediate layer slag contains rare earth oxides. The bottom layer slag comprises 45% by mass of CaF2, 25% by mass of Al2O3, 20% by mass of CaO, and 10% by mass of MgO, with a thickness accounting for 28% of the total thickness of the three-layer gradient slag system. The intermediate layer slag comprises 55% by mass of CaF2, 20% by mass of Al2O3, 18% by mass of CaO, 5% by mass of MgO, and 2% by mass of the rare earth oxides, with a thickness accounting for 45% of the total thickness of the three-layer gradient slag system. The top layer slag comprises 65% by mass of CaF2, 2% by mass of Al2O3, and 2% by mass of the rare earth oxides. The top slag layer comprises 20% by mass and 15% by mass of CaO, and its thickness accounts for 27% of the total thickness of the three-layer gradient slag system; the rare earth oxide is Ce2O3; the electroslag remelting is protected by argon gas with a flow rate of 10 L / min and a melting rate of 6 kg / min.

[0054] The purification and remelting method is used to detect the O content, N content, S content, and inclusion rating of the K447 electroslag ingot. The K447 electroslag ingot has an O content of 5 ppm, an N content of 3 ppm, an S content of 2.8 ppm, an Al content of 5.56%, an Al yield of 96%, a D-class inclusion level of 0.5, and a maximum inclusion size of 2.2 μm.

[0055] Example 2 A purification and remelting method for recycled K447 nickel-based superalloy material, the purification and remelting method comprising the following steps: The purification and remelting method involves mixing and melting K447 recycled material with a portion of new material to obtain an initial alloy melt; wherein the K447 recycled material is machining chips, and the K447 recycled material accounts for 50% of the total furnace charge by mass.

[0056] Before the purification and remelting method mixes and melts the K447 recycled material with some new material, the purification and remelting method further includes a recycled material pretreatment step. The recycled material pretreatment step includes: classifying the K447 recycled material according to its source and form to obtain ingot risers and large scraps, head and tail cut-off materials and edge scraps, and machining chips; subjecting the machining chips to degreasing, crushing, magnetic separation, alkaline washing, and water washing and drying treatments in sequence; and storing the machining chips after the degreasing, crushing, magnetic separation, alkaline washing, and water washing and drying treatments.

[0057] The purification and remelting method involves sequentially subjecting the initial alloy melt to carbon deoxidation refining, deep deoxidation refining of Al and Ti, and adsorption refining with a composite purifying agent to obtain a refined alloy melt. The carbon deoxidation refining temperature is 1560℃, the refining time is 75 min, and the vacuum degree is 5 Pa. The carbon deoxidation refining includes bottom-blowing argon stirring at a flow rate of 0.4 L / min. The Al is added in a stepwise manner, which includes: the Al is added in a stepwise manner, and the stepwise method... The formula includes: the purification remelting method adding a first portion of Al to the initial alloy melt during the deep deoxidation and refining of Al and Ti, wherein the mass of the first portion of Al is 0.10% of the mass of the initial alloy melt; the purification remelting method adding a second portion of Al before casting the refined alloy melt and reserving it in the consumable electrode rod, wherein the mass of the second portion of Al is 0.35% of the mass of the refined alloy melt, and the second portion of Al is used for the reduction reaction of MgO contained in the slag system during the electroslag remelting; the composite purifying agent includes 50% by mass of CaO, 30% by mass of Al2O3, and 10% by mass of MgO, wherein the mass of the composite purifying agent is 0.8% of the mass of the initial alloy melt.

[0058] The purification and remelting method involves casting the refined alloy melt into a consumable electrode rod. The purification and remelting method includes bottom-blowing argon stirring during the carbon deoxidation refining and the deep deoxidation refining of Al and Ti. After the composite purifying agent adsorption refining is completed, the purification and remelting method stops the bottom-blowing argon stirring and cools the refined alloy melt to 1440°C. Argon gas is then introduced onto the surface of the refined alloy melt at 0.05 MPa. After a film forms on the surface of the refined alloy melt, the purification and remelting method casts the refined alloy melt into the consumable electrode rod.

[0059] The purification and remelting method involves electroslag remelting the consumable electrode rod under a three-layer gradient slag system to obtain a K447 electroslag ingot. The three-layer gradient slag system comprises a bottom layer slag, an intermediate layer slag, and a top layer slag. The intermediate layer slag contains rare earth oxides. The bottom layer slag comprises 45% by mass of CaF2, 25% by mass of Al2O3, 20% by mass of CaO, and 10% by mass of MgO, with a thickness accounting for 28% of the total thickness of the three-layer gradient slag system. The intermediate layer slag comprises 55% by mass of CaF2, 20% by mass of Al2O3, 18% by mass of CaO, 5% by mass of MgO, and 3% by mass of the rare earth oxides, with a thickness accounting for 45% of the total thickness of the three-layer gradient slag system. The top layer slag comprises 65% by mass of CaF2, 20% by mass of Al2O3, and 6% by mass of CaO. The top slag layer accounts for 27% of the total thickness of the three-layer gradient slag system, with 15% by mass. The rare earth oxide is La2O3. The electroslag remelting is protected by argon gas with a flow rate of 10 L / min and a melting rate of 6 kg / min.

[0060] The purification and remelting method involves detecting the O, N, and S content of the K447 electroslag ingot and rating the inclusions. The K447 electroslag ingot has an O content of 4 ppm, an N content of 3 ppm, an S content of 2.7 ppm, an Al content of 5.32%, an Al yield of 95%, a D-class inclusion level of 0.5, and a maximum inclusion size of 2.0 μm.

[0061] Example 3 A purification and remelting method for recycled K447 nickel-based superalloy material, the purification and remelting method comprising the following steps: The purification and remelting method involves mixing and melting K447 recycled material with some new material to obtain an initial alloy melt; wherein, the K447 recycled material consists of head and tail cut-off material and edge scrap, and the K447 recycled material accounts for 40% of the total furnace charge by mass.

[0062] Before the purification and remelting method mixes and melts the K447 recycled material with some new material, the purification and remelting method further includes a recycled material pretreatment step. The recycled material pretreatment step includes: classifying the K447 recycled material according to its source and form to obtain ingot risers and large scraps, head and tail cut-off materials and edge scraps, and machining chips; performing acid pickling and water washing and drying treatments on the head and tail cut-off materials and edge scraps; and storing the head and tail cut-off materials and edge scraps after the acid pickling and water washing and drying treatments.

[0063] The purification and remelting method involves sequentially subjecting the initial alloy melt to carbon deoxidation refining, deep deoxidation refining of Al and Ti, and adsorption refining with a composite purifying agent to obtain a refined alloy melt. The carbon deoxidation refining temperature is 1550℃, the refining time is 45 min, and the vacuum degree is 3 Pa. The carbon deoxidation refining includes bottom-blowing argon stirring at a flow rate of 0.3 L / min. The addition of Al is done in steps, specifically by adding Al in stages... Step method: The purification remelting method adds a first portion of Al to the initial alloy melt during the deep deoxidation and refining of Al and Ti, the mass of the first portion of Al being 0.05% of the mass of the initial alloy melt; the purification remelting method adds a second portion of Al before casting and reserves it in the consumable electrode rod, the mass of the second portion of Al being 0.20% of the mass of the refined alloy melt, the second portion of Al being used for the reduction reaction of MgO contained in the slag system in the electroslag remelting; the composite purifying agent includes 40% by mass of CaO, 40% by mass of Al2O3, and 15% by mass of MgO, the mass of the composite purifying agent being 1.0% of the mass of the initial alloy melt.

[0064] The purification and remelting method involves casting the refined alloy melt into a consumable electrode rod. The purification and remelting method includes bottom-blowing argon stirring during the carbon deoxidation refining and the deep deoxidation refining of Al and Ti. After the composite purifying agent adsorption refining is completed, the purification and remelting method stops the bottom-blowing argon stirring and cools the refined alloy melt to 1420°C. Argon gas is then introduced onto the surface of the refined alloy melt at 0.04 MPa. After a film forms on the surface of the refined alloy melt, the purification and remelting method casts the refined alloy melt into the consumable electrode rod.

[0065] The purification and remelting method involves electroslag remelting the consumable electrode rod under a three-layer gradient slag system to obtain a K447 electroslag ingot. The three-layer gradient slag system comprises a bottom layer slag, an intermediate layer slag, and a top layer slag. The intermediate layer slag contains rare earth oxides. The bottom layer slag comprises 40% by mass of CaF2, 30% by mass of Al2O3, 25% by mass of CaO, and 5% by mass of MgO, with a thickness accounting for 25% of the total thickness of the three-layer gradient slag system. The intermediate layer slag comprises 50% by mass of CaF2, 23% by mass of Al2O3, 18% by mass of CaO, 8% by mass of MgO, and 1% by mass of the rare earth oxides, with a thickness accounting for 50% of the total thickness of the three-layer gradient slag system. The top layer slag comprises 60% by mass of CaF2, 20% by mass of Al2O3, and 1% by mass of CaO. 20% by mass, the thickness of the top slag accounts for 25% of the total thickness of the three-layer gradient slag system; the rare earth oxide is La2O3; the electroslag remelting is protected by argon gas, the flow rate of the argon gas protection is 5L / min, and the melting rate of the electroslag remelting is 4kg / min.

[0066] The purification and remelting method involves detecting the O content, N content, S content, and inclusion rating of the K447 electroslag ingot. The K447 electroslag ingot has an O content of 4 ppm, an N content of 2 ppm, an S content of 2.0 ppm, an Al content of 5.71%, an Al yield of 97%, a D-class inclusion rating of 0, and a maximum inclusion size of 1.2 μm.

[0067] Example 4 A purification and remelting method for recycled K447 nickel-based superalloy material, the purification and remelting method comprising the following steps: The purification and remelting method involves mixing and melting K447 recycled material with a portion of new material to obtain an initial alloy melt; wherein the K447 recycled material is machining chips, and the K447 recycled material accounts for 40% of the total furnace charge by mass.

[0068] Before the purification and remelting method mixes and melts the K447 recycled material with some new material, the purification and remelting method further includes a recycled material pretreatment step. The recycled material pretreatment step includes: classifying the K447 recycled material according to its source and form to obtain ingot risers and large scraps, head and tail cut-off materials and edge scraps, and machining chips; subjecting the machining chips to degreasing, crushing, magnetic separation, alkaline washing, and water washing and drying treatments in sequence; and storing the machining chips after the degreasing, crushing, magnetic separation, alkaline washing, and water washing and drying treatments.

[0069] The purification remelting method involves sequentially subjecting the initial alloy melt to carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining to obtain a refined alloy melt. The carbon deoxidation refining temperature is 1580℃, the refining time is 90 min, and the vacuum degree is 1 Pa. The carbon deoxidation refining includes bottom-blown argon stirring at a flow rate of 0.6 L / min. The Al addition is done in steps: a first portion of Al is added to the initial alloy melt during the Al and Ti deep deoxidation refining, with a mass of 0.15% of the initial alloy melt mass; a second portion of Al is added before casting and reserved in the consumable electrode rod, with a mass of 0.50% of the refined alloy melt mass. This second portion of Al is used for the reduction reaction of MgO in the slag system during electroslag remelting. The composite purifying agent includes CaO. The composite purifying agent comprises 60% by mass, 20% by mass of Al2O3, and 5% by mass of MgO, with the mass of the composite purifying agent being 0.5% of the mass of the initial alloy melt.

[0070] The purification and remelting method involves casting the refined alloy melt into a consumable electrode rod. The purification and remelting method includes bottom-blowing argon stirring during the carbon deoxidation refining and the deep deoxidation refining of Al and Ti. After the composite purifying agent adsorption refining is completed, the purification and remelting method stops the bottom-blowing argon stirring and cools the refined alloy melt to 1450°C. Argon gas is then introduced onto the surface of the refined alloy melt at 0.06 MPa. After a film forms on the surface of the refined alloy melt, the purification and remelting method casts the refined alloy melt into the consumable electrode rod.

[0071] The purification and remelting method involves electroslag remelting the consumable electrode rod under a three-layer gradient slag system to obtain a K447 electroslag ingot. The three-layer gradient slag system comprises a bottom layer slag, an intermediate layer slag, and a top layer slag. The intermediate layer slag contains rare earth oxides. The bottom layer slag comprises 50% by mass of CaF2, 20% by mass of Al2O3, 20% by mass of CaO, and 10% by mass of MgO, with a thickness accounting for 30% of the total thickness of the three-layer gradient slag system. The intermediate layer slag comprises 60% by mass of CaF2, 18% by mass of Al2O3, 12% by mass of CaO, 7% by mass of MgO, and 3% by mass of the rare earth oxides, with a thickness accounting for 40% of the total thickness of the three-layer gradient slag system. The top layer slag comprises 70% by mass of CaF2, 15% by mass of Al2O3, and 1% by mass of CaO. The thickness of the top slag is 15% by mass, accounting for 30% of the total thickness of the three-layer gradient slag system; the rare earth oxide is Ce2O3; the electroslag remelting is protected by argon gas, the flow rate of the argon gas protection is 15 L / min, and the melting rate of the electroslag remelting is 8 kg / min.

[0072] The purification and remelting method involves detecting the O content, N content, S content, and inclusion rating of the K447 electroslag ingot. The K447 electroslag ingot has an O content of 4 ppm, an N content of 3 ppm, an S content of 1.7 ppm, an Al content of 5.55%, an Al yield of 96%, a D-class inclusion rating of 0, and a maximum inclusion size of 1.8 μm.

[0073] Example 5 A purification and remelting method for recycled K447 nickel-based superalloy material, the purification and remelting method comprising the following steps: The purification and remelting method involves mixing and melting K447 recycled material with some new material to obtain an initial alloy melt; wherein, the K447 recycled material includes ingot risers and large scraps, head and tail cut-offs and edge scraps, and the K447 recycled material accounts for 55% of the total furnace charge by mass.

[0074] Before the purification and remelting method mixes and melts the K447 recycled material with some new material, the purification and remelting method further includes a recycled material pretreatment step. The recycled material pretreatment step includes: classifying the K447 recycled material according to its source and form to obtain ingot risers and large scraps, head and tail cut-off materials and edge scraps, and machining chips; cleaning and crushing the ingot risers and large scraps; pickling and washing and drying the head and tail cut-off materials and edge scraps; and storing the ingot risers and large scraps after surface cleaning and crushing, and the head and tail cut-off materials and edge scraps after pickling and washing and drying.

[0075] The purification remelting method involves sequentially subjecting the initial alloy melt to carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining to obtain a refined alloy melt. The carbon deoxidation refining temperature is 1570℃, the refining time is 75 min, and the vacuum degree is 2 Pa. The carbon deoxidation refining includes bottom-blown argon stirring at a flow rate of 0.5 L / min. The Al is added in steps: a first portion of Al is added to the initial alloy melt during the Al and Ti deep deoxidation refining, with a mass of 0.12% of the initial alloy melt mass; a second portion of Al is added before casting and reserved in the consumable electrode rod, with a mass of 0.40% of the refined alloy melt mass. This second portion of Al is used for the reduction reaction of MgO in the slag system during electroslag remelting. The composite purifying agent comprises CaO 55% by mass, Al₂O₃ 25% by mass, and MgO. 12% by mass, the mass of the composite purifying agent is 0.6% of the mass of the initial alloy melt.

[0076] The purification and remelting method involves casting the refined alloy melt into a consumable electrode rod. The purification and remelting method includes bottom-blowing argon stirring during the carbon deoxidation refining and the deep deoxidation refining of Al and Ti. After the composite purifying agent adsorption refining is completed, the purification and remelting method stops the bottom-blowing argon stirring and cools the refined alloy melt to 1430°C. Argon gas is then introduced onto the surface of the refined alloy melt at 0.05 MPa. After a film forms on the surface of the refined alloy melt, the purification and remelting method casts the refined alloy melt into the consumable electrode rod.

[0077] The purification and remelting method involves electroslag remelting the consumable electrode rod under a three-layer gradient slag system to obtain a K447 electroslag ingot. The three-layer gradient slag system comprises a bottom layer slag, an intermediate layer slag, and a top layer slag. The intermediate layer slag contains rare earth oxides. The bottom layer slag comprises 48% by mass of CaF2, 22% by mass of Al2O3, 3% by mass of CaO, and 7% by mass of MgO, with a thickness accounting for 26% of the total thickness of the three-layer gradient slag system. The intermediate layer slag comprises 58% by mass of CaF2, 18% by mass of Al2O3, 16% by mass of CaO, 6% by mass of MgO, and 2% by mass of the rare earth oxides, with a thickness accounting for 48% of the total thickness of the three-layer gradient slag system. The top layer slag comprises 68% by mass of CaF2, 16% by mass of Al2O3, and 1% by mass of CaO. The thickness of the top slag is 16% by mass, accounting for 26% of the total thickness of the three-layer gradient slag system; the rare earth oxide is La2O3; the electroslag remelting is protected by argon gas, the flow rate of the argon gas protection is 12L / min, and the melting rate of the electroslag remelting is 7kg / min.

[0078] The purification and remelting method involves detecting the O, N, and S content of the K447 electroslag ingot and rating its inclusions. The K447 electroslag ingot has an O content of 5 ppm, an N content of 3 ppm, an S content of 2.5 ppm, an Al content of 5.68%, an Al yield of 96%, a D-class inclusion level of 0.5, and a maximum inclusion size of 2.4 μm.

[0079] Comparative Example 1 (using aluminum replenishment from the slag pool instead of pre-placed Al in the consumable electrode) A method for remelting recycled K447 nickel-based superalloy material includes the following steps: The K447 recycled material is mixed with some new material and melted to obtain an initial alloy melt; wherein the K447 recycled material is the ingot riser and large scrap, accounting for 50% of the total furnace charge by mass.

[0080] The initial alloy melt was subjected to carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining in sequence to obtain a refined alloy melt. The carbon deoxidation refining temperature was 1560℃, the time was 60 min, the vacuum degree was 5 Pa, and the bottom-blown argon stirring flow rate was 0.4 L / min. A first portion of Al was added during the Al and Ti deep deoxidation refining, with a mass of 0.10% of the initial alloy melt mass. No second portion of Al was added before casting, i.e., no second portion of Al was reserved in the consumable electrode rod. The composite purifying agent comprised 50% CaO, 30% Al₂O₃, and 10% MgO, with a mass of 0.8% of the initial alloy melt mass.

[0081] The refined alloy melt is cooled to 1440°C, and argon gas is introduced to 0.05 MPa. After a film forms on the surface, it is cast into a consumable electrode rod.

[0082] The consumable electrode rod was electroslag remelted in a three-layer gradient slag system, and aluminum powder was added directly to the slag pool in batches during the electroslag remelting process. The amount of aluminum powder added was 0.35% of the mass of the refined alloy melt, resulting in K447 electroslag ingots. The composition, thickness ratio and rare earth oxide types of the three-layer gradient slag system were the same as in Example 1. The argon protection flow rate was 10 L / min and the melting rate was 6 kg / min.

[0083] Test results: O content was 12 ppm, N content was 5 ppm, S content was 3.5 ppm, Al content was 5.31%, Al yield was 86%, D-class inclusions were grade 1.5, and the maximum size of the inclusions was 5.3 μm.

[0084] Analysis: When aluminum powder is directly added to the slag pool, it mainly reacts with the top slag and oxygen in the atmosphere at the top of the slag pool and is largely burned off. It is difficult to stably reach the slag-gold interface to participate in the directional reduction of MgO. Moreover, the sudden addition of aluminum powder causes violent local reactions in the slag pool and intensifies slag entrapment. The generated Al2O3 inclusions are large in size and are mechanically entrained into the molten metal pool. As a result, the O, N, and S contents and the level of inclusions are significantly deteriorated, and the Al recovery rate is only 86%.

[0085] Comparative Example 2 (using a single-layer slag system instead of a three-layer gradient slag system) A method for remelting recycled K447 nickel-based superalloy material includes the following steps: The K447 recycled material is mixed with some new material and melted to obtain an initial alloy melt; wherein the K447 recycled material is the ingot riser and large scrap, accounting for 50% of the total furnace charge by mass.

[0086] The initial alloy melt was subjected to carbon deoxidation refining, deep deoxidation refining of Al and Ti, and adsorption refining with a composite purifying agent in sequence to obtain a refined alloy melt. The carbon deoxidation refining temperature was 1560℃, the time was 60 min, the vacuum degree was 5 Pa, and the bottom-blown argon stirring flow rate was 0.4 L / min. Al was added in steps: the first part of Al was added during the deep deoxidation refining of Al and Ti, and its mass was 0.10% of the initial alloy melt mass; the second part of Al was added before casting and reserved in the consumable electrode rod, and its mass was 0.35% of the refined alloy melt mass, used for the reduction reaction of MgO contained in the slag system during electroslag remelting. The composite purifying agent consisted of 50% CaO, 30% Al₂O₃, and 10% MgO, and its mass was 0.8% of the initial alloy melt mass.

[0087] The refined alloy melt is cooled to 1440°C, and argon gas is introduced to 0.05 MPa. After a film forms on the surface, it is cast into a consumable electrode rod.

[0088] The consumable electrode rod was electroslag remelted in a single-layer slag system to obtain K447 electroslag ingot; the composition of the single-layer slag system was CaF2 55% by mass, Al2O3 20% by mass, CaO 20% by mass, MgO 5% by mass, and it did not contain rare earth oxides, and there was no gradient structure of bottom slag, middle slag and top slag; the argon gas protection flow rate was 10L / min, and the melting rate was 6kg / min.

[0089] Test results: O content was 8 ppm, N content was 5 ppm, S content was 2.8 ppm, Al content was 5.53%, Al recovery rate was 95%, Class D inclusions were grade 1.0, and the maximum size of inclusions was 3.6 μm.

[0090] Analysis: Since a second part of Al is reserved in the electrode, the burning loss of Al is still suppressed (Al recovery rate is 95%). However, the single-layer slag system lacks the ability of the intermediate rare earth oxide to modify and adsorb the newly formed Al2O3 inclusions. It also lacks the directional collection of inclusions by the bottom slag and the oxygen isolation and flow regulation effect of the top slag. As a result, the O and N contents are too high and the inclusions are not up to standard in terms of grade and size.

[0091] Comparative Example 3 (without stepwise Al control, all Al is added at once during the vacuum induction stage) A method for remelting recycled K447 nickel-based superalloy material includes the following steps: The K447 recycled material is mixed with some new material and melted to obtain an initial alloy melt; wherein the K447 recycled material is the ingot riser and large scrap, accounting for 50% of the total furnace charge by mass.

[0092] The initial alloy melt was sequentially subjected to carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining to obtain a refined alloy melt. The carbon deoxidation refining temperature was 1560℃, the time was 60 min, the vacuum degree was 5 Pa, and the bottom-blown argon stirring flow rate was 0.4 L / min. Al was not added in stages, but rather all Al was added at once during the Al and Ti deep deoxidation refining, at a rate of 0.45% of the initial alloy melt mass. No further Al was added before casting, and the Al content in the consumable electrode rod was the nominal composition of K447, with no additional Al reserved. The composite purifying agent comprised 50% CaO, 30% Al₂O₃, and 10% MgO, with a mass of 0.8% of the initial alloy melt mass.

[0093] The refined alloy melt is cooled to 1440°C, and argon gas is introduced to 0.05 MPa. After a film forms on the surface, it is cast into a consumable electrode rod.

[0094] The consumable electrode rod was electroslag remelted in a three-layer gradient slag system to obtain K447 electroslag ingot; the composition, thickness ratio and rare earth oxide types of the three-layer gradient slag system were the same as in Example 1; the argon protection flow rate was 10 L / min and the melting rate was 6 kg / min.

[0095] Test results: O content was 11.0 ppm, N content was 5 ppm, S content was 2.6 ppm, Al content was 5.43%, Al recovery rate was 90%, Class D inclusions were grade 1.5, and the maximum size of inclusions was 4.8 μm.

[0096] Analysis: When all Al is added to the vacuum induction melt at once, a large number of primary Al2O3 inclusions are generated in a short time and collide and grow together. The composite purifying agent adsorption and refining is not enough to completely remove them. The remaining coarse inclusions enter the electroslag remelting with the electrode. At the same time, there is no Al reserved in the electrode, and the slag-gold interface lacks a reducing agent during the electroslag remelting stage. The oxygen potential in the slag is too high, which causes further Al loss. The Al recovery rate is only 90%, and the purity index is inferior to that of the other examples.

[0097] Table 1. Effect data of each embodiment and comparative example.

[0098] As shown in Table 1, Examples 1-5 all met the requirements of O content ≤ 5 ppm, N content ≤ 3 ppm, S content ≤ 3 ppm, D-class inclusions ≤ 0.5 grade, maximum inclusion size ≤ 3 μm, and Al recovery ≥ 95%. Comparative Example 1 used a slag pool for aluminum replenishment, Comparative Example 2 used a single-layer slag system, and Comparative Example 3 eliminated stepwise Al control; their purity indicators or Al recovery rates were significantly deteriorated. It can be seen that only by combining the first part of Al (0.05% to 0.15% of the initial alloy melt mass) for deep deoxidation in the vacuum induction stage with the second part of Al (0.2% to 0.5% of the refined alloy melt mass) pre-placed in the consumable electrode rod, and the three-layer gradient slag system of MgO in the reducing slag and rare earth oxides in the middle layer, can the deep removal of inclusions, effective control of gas content, and significant suppression of Al burn-off be achieved simultaneously.

[0099] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for purifying and remelting recycled K447 nickel-based superalloy material, characterized in that, Includes the following steps: The K447 recycled material was mixed with some new material and melted to obtain the initial alloy melt; The initial alloy melt was subjected to carbon deoxidation refining, Al and Ti deep deoxidation refining, and composite purifying agent adsorption refining in sequence to obtain a refined alloy melt. The refined alloy melt is cast into a consumable electrode rod; The consumable electrode rod was electroslag remelted in a three-layer gradient slag system to obtain K447 electroslag ingot. The addition of Al is carried out in a stepwise manner: the first part of Al is added to the initial alloy melt during the deep deoxidation and refining stage of Al and Ti, and works with Ti to remove dissolved oxygen in the melt and suppress the formation of primary coarse Al2O3 inclusions; the second part of Al is added before the refining alloy melt is cast and reserved in the consumable electrode rod, so that it can enter the slag-gold interface with the melting of the consumable electrode rod during the electroslag remelting process, reduce MgO in the slag system to generate new Al2O3 inclusions; The three-layer gradient slag system includes a bottom slag, an intermediate slag, and a top slag. The intermediate slag contains rare earth oxides, which are used to adsorb and remove the newly formed Al2O3 inclusions. The K447 return material accounts for no more than 60% of the total furnace charge by mass.

2. The purification and remelting method according to claim 1, characterized in that, Before mixing and melting the K447 recycled material with a portion of the new material, the method further includes a recycled material pretreatment step; The return material pretreatment steps include: The K447 return material is classified according to its source and form to obtain ingot riser and large scrap, head and tail cut-off material and edge scrap, and machining chips; The ingot riser and large pieces of residual material are cleaned and crushed. The cut-off material and scrap material are subjected to acid washing, water washing and drying treatment; The machining chips are subjected to degreasing, crushing, magnetic separation, alkaline washing, and water washing and drying in sequence. The ingot risers and large scraps after surface cleaning and crushing, the head and tail cut-offs and edge scraps after pickling, washing and drying, and the machining chips after degreasing, crushing, magnetic separation, alkaline washing and washing and drying are stored separately.

3. The purification and remelting method according to claim 1, characterized in that, The carbon deoxidation refining temperature is 1550℃~1580℃, the refining time is 45min~90min, and the vacuum degree is ≤5Pa; The carbon deoxidation refining process includes bottom-blown argon stirring, with a flow rate of 0.3 L / min to 0.6 L / min.

4. The purification and remelting method according to claim 1, characterized in that, The mass of the first portion of Al is 0.05% to 0.15% of the mass of the initial alloy melt; the mass of the second portion of Al is 0.2% to 0.5% of the mass of the refined alloy melt.

5. The purification and remelting method according to claim 1, characterized in that, The composite purifying agent comprises 40% to 60% by mass of CaO, 20% to 40% by mass of Al2O3, and 5% to 15% by mass of MgO. The mass of the composite purifying agent is 0.5% to 1.0% of the mass of the initial alloy melt.

6. The purification and remelting method according to claim 1, characterized in that, Bottom-blown argon gas stirring is performed in the carbon deoxidation refining and the Al and Ti deep deoxidation refining; After the adsorption and refining of the composite purifier is completed, the bottom blowing argon stirring is stopped, and the refined alloy melt is cooled to 1420℃~1450℃. Argon gas is introduced into the surface of the refined alloy melt to 0.04MPa~0.06MPa. After a film is formed on the surface of the refined alloy melt, it is cast into the consumable electrode rod.

7. The purification and remelting method according to claim 1, characterized in that, The bottom slag comprises 40%–50% CaF2, 20%–30% Al2O3, 15%–25% CaO, and 5%–10% MgO. The thickness of the bottom slag accounts for 25%–30% of the total thickness of the three-layer gradient slag system. The intermediate slag layer comprises CaF250%–60% by mass, Al2O315%–25% by mass, CaO10%–20% by mass, MgO33%–8% by mass, and rare earth oxides1%–3% by mass. The thickness of the intermediate slag layer accounts for 40%–50% of the total thickness of the three-layer gradient slag system. The top slag comprises 60%–70% CaF2, 10%–20% Al2O3, and 5%–15% CaO. The thickness of the top slag accounts for 20%–35% of the total thickness of the three-layer gradient slag system.

8. The purification and remelting method according to claim 1, characterized in that, The rare earth oxides include Ce2O3 and / or La2O3.

9. The purification and remelting method according to claim 1, characterized in that, The electroslag remelting is protected by argon gas, the flow rate of which is 5L / min to 15L / min, and the melting rate of the electroslag remelting is 4kg / min to 8kg / min.

10. The purification and remelting method according to claim 1, characterized in that, The method also includes purity detection and circulation control steps: The K447 electroslag ingot was subjected to O content testing, N content testing, S content testing, and inclusion rating. The K447 electroslag ingots with O content ≤5ppm, N content ≤3ppm, S content ≤3ppm, D-class inclusions ≤0.5 grade, and maximum inclusion size ≤3μm are deemed qualified and used for the remelting production of K447 alloy. K447 electroslag ingots with O content > 5 ppm, or N content > 3 ppm, or S content > 3 ppm, or D-class inclusions > 0.5 grade, or inclusions with maximum size > 3 μm are crushed and returned to the step of mixing K447 return material with some new material and melting it for reprocessing. The K447 recycled material from the same batch shall not be recycled more than 3 times. After more than 3 times, the K447 recycled material shall be mixed with the new material at a mass ratio of not less than 50%.

Images