Method for electroslag remelting of nickel-based superalloys, consumable electrode, pre-melted slag and use thereof

Abstract

This application belongs to the field of electroslag remelting technology, and particularly relates to a method for electroslag remelting of nickel-based superalloys, consumable electrodes, pre-melted slag, and their applications. During the solidification process of large-size nickel-based superalloy ingots, the excessive depth of the molten pool and the small temperature gradient lead to premature blockage of the feeding channels, which is a significant factor contributing to porosity, shrinkage cavities, and compositional segregation within the ingot. The embodiments of this application break through the traditional constant-rate remelting process by dynamically controlling the melting rate and solidification cooling intensity in stages, optimizing the solidification structure of large-size ingots from both thermodynamic and kinetic dimensions. This solves the common industry problem of uncontrolled molten pool and difficulty in feeding caused by geometric scale effects in large-diameter ingots.

Description

Technical Field

[0001] This application belongs to the field of electroslag remelting technology, and particularly relates to electroslag remelting methods for nickel-based superalloys, consumable electrodes, pre-melted slag and their applications. Background Technology

[0002] Nickel-based superalloys possess excellent endurance strength, creep resistance, oxidation resistance, and corrosion resistance, and are widely used as core materials in aero-engine combustion chambers and gas turbine hot-end components. These alloys are typically prepared using a dual process of vacuum induction melting (VIM) + electroslag remelting (ESR) or a triple process of VIM + ESR + vacuum arc remelting (VAR). ESR, as a crucial refining process, significantly impacts the defect level and service performance of the final product.

[0003] In failure cases of high-temperature alloys, impurities such as oxygen, nitrogen, and sulfur significantly reduce the fatigue life and mechanical properties of the material. In particular, the characteristics of inclusions in ESR ingots (such as the size distribution of non-metallic inclusions) can be inherited by forgings through hot working, thus affecting the reliability of the components. Traditional electroslag remelting production of nickel-based high-temperature alloys, especially for medium to large-sized ingots with diameters of 200mm to 500mm, often struggles to simultaneously meet the requirements of high cleanliness, low sulfur content, low segregation, and dense microstructure.

[0004] Existing technologies mostly employ constant current or empirical segmented constant speed control. Through the desulfurization and deoxidation of the CaO-CaF2 slag system, the sulfur content of the alloy can be reduced to below 5 ppm and the oxygen content to around 100 ppm, meeting the purity requirements of low- to mid-range nickel-based alloys. However, the desulfurization effect cannot achieve the purpose of deep desulfurization. The cooling water volume is adjusted by empirical values, resulting in unstable solidification quality and difficulty in controlling segregation stably. Summary of the Invention

[0005] This application provides a method for electroslag remelting of nickel-based superalloys, a consumable electrode, pre-melted slag, and their applications to solve the following technical problem: how to improve the metallurgical quality of large-size nickel-based superalloy ingots.

[0006] In a first aspect, embodiments of this application provide a method for electroslag remelting of nickel-based superalloys, comprising the following steps: The pre-melted slag is added to the remelting zone. The chemical composition of the pre-melted slag, by mass percentage, includes: CaF2 40%~90%, CaO 5%~30%, Al2O3 5%~30%, MgO 0~10%, and satisfies 0.8≤CaO / Al2O3≤1.5. The consumable electrode is inserted into the pre-melted slag, the vacuum is drawn to below 0.1 Pa, and the pre-melted slag is heated by electricity to melt the pre-melted slag and form a molten slag pool. After the formation of the slag pool, control the consumable electrode to melt at a first melting rate V1, so that the molten metal droplets melted from the consumable electrode pass through the slag pool and converge at the bottom of the remelting area to form a metal molten pool; After the formation of the metal molten pool, enter the remelting stable period, control the melting rate V of the consumable electrode to satisfy 0.0012d·I < V < 0.0014d·I, so that the molten metal droplets continuously pass through the slag pool and deposit on the metal molten pool for steady-state remelting; where V is the melting rate, d is the diameter of the consumable electrode, and I is the current; After the completion of the steady-state remelting, enter the remelting feeding period, control the melting rate V to satisfy 0.0011d·I < V < 0.0013d·I to reduce the depth of the metal molten pool and fill the shrinkage volume; and After the end of the remelting feeding period, enter the solidification stage, control the cooling water flow rate L to satisfy L = K·D 2 , where 3.0 ≤ K ≤ 6.5, D is the diameter of the consumable electrode and the unit is m, the unit of K is m / (min·t), so that the metal molten pool solidifies to form an ingot; the diameter range of the ingot is 200 mm to 500 mm.

[0007] Optionally, the depth of the slag pool formed by the pre-melted slag in the remelting area is 0.15 - 0.25 times the diameter of the target ingot.

[0008] Optionally, before the step of inserting the consumable electrode into the pre-melted slag, it further includes: [[ID=十七]]Surface-treat the consumable electrode to remove the oxide scale on the outer layer of the consumable electrode; and Preheat the surface-treated consumable electrode to 200°C - 600°C and keep it warm for 1 h - 4 h.

[0009] Optionally, the depth of insertion of the consumable electrode into the pre-melted slag is 80 mm - 90 mm.

[0010] Optionally, the diameter d of the consumable electrode is 200 mm - 500 mm, and the current I is 8 kA - 15 kA.

[0011] Optionally, in the step of entering the solidification stage and controlling the cooling water flow rate L, the cooling water pressure is not less than 0.4 MPa.

[0012] Optionally, the first melting rate V1 is greater than the melting rate V in the remelting stable period.

[0013] Secondly, embodiments of this application provide a pre-melted slag for electroslag remelting of nickel-based high-temperature alloys. The chemical composition of the pre-melted slag, by mass percentage, includes: 40%~90% CaF2, 5%~30% CaO, 5%~30% Al2O3, and 0~10% MgO, and satisfies 0.8≤CaO / Al2O3≤1.5.

[0014] Thirdly, embodiments of this application provide the use of the pre-melted slag described in the second aspect in the electroslag remelting of nickel-based superalloys.

[0015] Fourthly, embodiments of this application provide a consumable electrode for electroslag remelting of nickel-based superalloys, characterized in that the chemical composition of the consumable electrode, by mass percentage, is: Mo 5%~15%, Fe 15%~25%, Co 0.1%~5%, with the balance being Ni; or Mo 3%~4%, Fe 18%~19%, Nb 5%~6%, balance Ni.

[0016] The technical solution provided in this application has the following advantages compared with the prior art: During the solidification process of large-sized nickel-based superalloy ingots, the feeding channels become blocked prematurely due to excessively deep molten pools and small temperature gradients, which is an important factor in the formation of porosity, shrinkage cavities, and compositional segregation inside the ingots.

[0017] In the embodiments of the present application, through the design of the pre-melted slag composition, CaF2 is controlled to be 40% - 90%, CaO is 5% - 30%, Al2O3 is 5% - 30%, and the CaO / Al2O3 ratio is limited to 0.8 - 1.5, so as to optimize the viscosity and surface tension of the slag, improve the transition behavior of metal droplets at the slag-metal interface, and further enhance the purity and temperature uniformity of the molten droplets; by evacuating to below 0.1 Pa and heating by electricity, the gas content is effectively reduced and a stable thermal balance of the slag pool is established, and further a metallurgical environment with low oxygen and low nitrogen is provided for subsequent steady-state remelting; by controlling the consumption electrode to melt at the first melting speed V1 after the formation of the slag pool, it is ensured that the metal droplets are smoothly collected to form a metal melt pool after sufficient refining, and further the initial solidification conditions are established; by controlling the melting speed V to satisfy 0.0012d·I < V < 0.0014d·I during the steady-state remelting period, the depth of the melt pool is controlled within a reasonable range to maintain a stable solidification front temperature gradient, and further the feeding channel is ensured to be unobstructed and macro-segregation is reduced; by reducing the melting speed to 0.0011d·I < V < 0.0013d·I during the remelting feeding period, the depth of the melt pool is actively reduced and the shrinkage volume is continuously filled, and further the formation of shrinkage cavities and porosity is inhibited; by controlling the cooling water flow rate L = K·D2 and 3.0 ≤ K ≤ 6.5 during the solidification stage, a directional solidification cooling intensity matching the ingot diameter is established, and further the narrowing of the mushy zone and the increase of the axial temperature gradient are achieved, and finally large-size nickel-based superalloy ingots with excellent metallurgical quality and significantly reduced internal defects within the diameter range of 200 mm to 500 mm are obtained.

[0018] The embodiments of the present application break through the traditional constant-speed remelting process. Through the coordinated coupling of dynamically regulating the melting speed and solidification cooling intensity in stages, the solidification structure of large-size ingots is optimized from both the thermodynamic and kinetic dimensions, and the common industrial problem of out-of-control melt pool and difficult feeding caused by the geometric scale effect of large-diameter ingots is solved. Detailed implementation manners

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0020] In the scope descriptions mentioned in this article, such as numerical ranges, ratio ranges, etc., all possible sub-ranges and individual values within the range are included. For example, the range description of 1 to 6 or 1~6 covers all sub-ranges between 1 and 6 (such as 1 to 3, 2 to 5, etc.) and individual numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specifically stated, the terms used in this article, including "comprising" and the like, mean including but not limited to; relative terms such as "first" and "second" are only used to distinguish different entities or steps, and do not imply an actual order or association relationship; "and / or" means that multiple situations can exist alone or simultaneously; expressions such as "at least one", "multiple", "at least one kind", etc. all refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships involved in the article, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the antecedent and the consequent of the proportional formula in the order of description. The raw materials, reagents, instruments, equipment, etc. used in this article can all be obtained through market purchase or by existing methods.

[0021] In a first aspect, an electroslag remelting method for a nickel-based superalloy provided by an embodiment of the present application includes the following steps: Adding premelted slag to the remelting area, the chemical composition of the premelted slag includes, by mass percentage: 40%~90% of CaF2, 5%~30% of CaO, 5%~30% of Al2O3, 0~10% of MgO, and 0.8≤CaO / Al2O3≤1.5; Inserting a consumable electrode into the premelted slag, evacuating to below 0.1 Pa, and heating the premelted slag by energization to melt the premelted slag to form a slag pool; After the slag pool is formed, controlling the consumable electrode to melt at a first melting speed V1, so that the molten metal droplets melted from the consumable electrode pass through the slag pool and gather at the bottom of the remelting area to form a metal melt pool; After the metal melt pool is formed, entering the remelting stable period, controlling the melting speed V of the consumable electrode to satisfy 0.0012d·I<V<0.0014d·I, so that the molten metal droplets continuously pass through the slag pool and deposit on the metal melt pool to perform steady-state remelting; where V is the melting speed, d is the diameter of the consumable electrode, and I is the current; After the steady-state remelting is completed, entering the remelting feeding period, controlling the melting speed V to satisfy 0.0011d·I<V<0.0013d·I to reduce the depth of the metal melt pool and fill the shrinkage volume; and After the remelting feeding period ends, entering the solidification stage, controlling the cooling water flow rate L to satisfy L = K·D 2, where 3.0 ≤ K ≤ 6.5, D is the diameter of the consumable electrode in meters, and the unit of K is m / (min·t), so that the metal molten pool solidifies to form an ingot; the diameter range of the ingot is 200 mm to 500 mm.

[0022] Remelting stable period: In the embodiments of the present application, it refers to the stage from the formation of the metal molten pool to the completion of steady-state remelting, and this stage maintains the steady-state remelting process. Remelting feeding period: In the embodiments of the present application, it refers to the stage from the completion of steady-state remelting to before the solidification stage. In this stage, the depth of the metal molten pool is reduced by reducing the melting speed and the shrinkage volume is filled. Solidification stage: In the embodiments of the present application, it refers to the stage after the end of the remelting feeding period, in which the metal molten pool is solidified to form an ingot by controlling the cooling water flow rate.

[0023] The premelted slag is added to the remelting area. The chemical composition of the premelted slag includes 40% - 90% CaF₂, 5% - 30% CaO, 5% - 30% Al₂O₃, 0 - 10% MgO in mass percentage and satisfies 0.8 ≤ CaO / Al₂O₃ ≤ 1.5. Thus, the premelted slag forms a slag pool with appropriate viscosity, surface tension and desulfurization ability, and further provides a stable metallurgical reaction medium for subsequent electroslag remelting.

[0024] The consumable electrode is inserted into the premelted slag, the vacuum is pumped to below 0.1 Pa, and the premelted slag is heated by electricity to melt the premelted slag to form a slag pool. Thus, the slag pool reduces gas inclusions in the vacuum environment, and further reduces the oxygen content and nitrogen content in the ingot.

[0025] After the slag pool is formed, the consumable electrode is controlled to melt at the first melting speed V1, so that the metal droplets melted from the consumable electrode pass through the slag pool and gather at the bottom of the remelting area to form a metal molten pool. Thus, the metal droplets are in full contact with the slag during the process of passing through the slag pool, and further promote the dissolution and floating of inclusions.

[0026] After the metal molten pool is formed, it enters the remelting stable period. The melting speed V of the consumable electrode is controlled to satisfy 0.0012d·I < V < 0.0014d·I, so that the metal droplets continuously pass through the slag pool and deposit in the metal molten pool for steady-state remelting. Thus, the melting speed V is coordinated and matched with the diameter d and current I of the consumable electrode, and further keeps the electrode cone head area stable at the maximum value, further optimizes the inclusion removal effect and desulfurization effect, and further improves the metallurgical quality of the large-size nickel-based superalloy ingot.

[0027] After the steady-state remelting is completed, it enters the remelting feeding period. The melting speed V is controlled to satisfy 0.0011d·I < V < 0.0013d·I. Thus, the reduced melting speed reduces the depth of the metal molten pool and fills the shrinkage volume, and further reduces the shrinkage cavity defect at the head of the ingot, and further improves the metallurgical quality of the large-size nickel-based superalloy ingot.

[0028] After the remelting and feeding period ends, the solidification stage begins. The cooling water flow rate L is controlled to satisfy L=K·D2 and 3.0≤K≤6.5. This cooling water flow rate L is matched with the diameter D of the consumable electrode to achieve rapid and uniform cooling, thereby reducing the segregation degree of easily segregated elements, forming a uniform and dense microstructure, and improving the metallurgical quality of large-size nickel-based superalloy ingots.

[0029] CaF2: Including but not limited to 40%, 50%, 60%, 70%, 80%, 90%, etc. CaO: Including but not limited to 5%, 10%, 15%, 20%, 25%, 30%, etc. Al2O3: Including but not limited to 5%, 10%, 15%, 20%, 25%, 30%, etc. MgO: Including but not limited to 0%, 2%, 4%, 6%, 8%, 10%, etc. CaO / Al2O3: Including but not limited to 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc.

[0030] In some embodiments, the depth of the slag pool formed by the pre-melted slag in the remelting zone is 0.15 to 0.25 times the diameter of the target ingot.

[0031] The depth of the slag pool formed by the pre-melted slag in the remelting zone is 0.15 to 0.25 times the diameter of the target ingot. This creates a specific proportional relationship between the depth of the slag pool and the diameter of the target ingot, thereby ensuring that the slag pool has sufficient depth to fully filter inclusions in the molten metal droplets. This also ensures that the slag pool is not too deep to avoid excessive power consumption and overheating of the slag, thus optimizing the metallurgical effect and energy efficiency of electroslag remelting and improving the metallurgical quality of large-size nickel-based high-temperature alloy ingots.

[0032] The ratio of slag pool depth to the target ingot diameter includes, but is not limited to, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, and 0.25. When the target ingot diameter is 200mm, the slag pool depth includes, but is not limited to, 30mm, 35mm, 40mm, 45mm, and 50mm; when the target ingot diameter is 500mm, the slag pool depth includes, but is not limited to, 75mm, 80mm, 100mm, 110mm, and 125mm.

[0033] In some embodiments, prior to the step of inserting the consumable electrode into the pre-melted slag, the method further includes: The consumable electrode is surface-treated to remove the oxide layer on its outer surface; and The consumable electrode with the surface treatment is preheated to 200℃~600℃ and kept at that temperature for 1h~4h.

[0034] The consumable electrode is surface-treated to remove the scale on the outer layer of the consumable electrode, thereby removing the scale and reducing the oxide impurities on the surface of the consumable electrode, and further reducing the oxygen source and inclusion source introduced during the remelting process.

[0035] The surface-treated consumable electrode is preheated to 200°C - 600°C and kept warm for 1h - 4h, so that this preheating temperature makes the consumable electrode reach a suitable thermal state, thereby reducing the thermal shock when the consumable electrode is inserted into the molten slag pool, further reducing the cracks and spalling caused by the sudden temperature change of the consumable electrode, further reducing the inclusions and composition non-uniformity caused by the spalling of the consumable electrode, and further improving the metallurgical quality of the large-size nickel-based superalloy ingot.

[0036] Preheating temperature: including but not limited to 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, etc. Holding time: including but not limited to 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0037] In some embodiments, the depth at which the consumable electrode is inserted into the pre-molten slag is 80mm - 90mm.

[0038] The depth at which the consumable electrode is inserted into the pre-molten slag is 80mm - 90mm, so that this insertion depth makes the lower end of the consumable electrode form a suitable contact area with the molten slag pool, thereby increasing the contact area between the electrode and the molten slag, further accelerating the interfacial desulfurization reaction, further accelerating the dissolution and floating of inclusions, further reducing the sulfur content and inclusion content in the ingot, and further improving the metallurgical quality of the large-size nickel-based superalloy ingot.

[0039] The depth at which the consumable electrode is inserted into the pre-molten slag: including but not limited to 80mm, 81mm, 82mm, 83mm, 84mm, 85mm, 86mm, 87mm, 88mm, 89mm, 90mm, etc.

[0040] In some embodiments, the diameter d of the consumable electrode is 200mm - 500mm, and the current I is 8kA - 15kA.

[0041] The diameter d of the consumable electrode is 200mm - 500mm, and the current I is 8kA - 15kA, so that the diameter d range of this consumable electrode defines the specifications of the large-size ingot, and this current I range matches the diameter d of the consumable electrode, thereby ensuring that the calculation formulas for the melting speed V in claim 1, 0.0012d·I < V < 0.0014d·I and 0.0011d·I < V < 0.0013d·I, have implementable current conditions, further ensuring that the large-size ingot achieves stable remelting under sufficient heat input, and further improving the metallurgical quality of the large-size nickel-based superalloy ingot.

[0042] The diameter d of the consumable electrode includes, but is not limited to, 200mm, 220mm, 250mm, 280mm, 300mm, 350mm, 400mm, 450mm, and 500mm. The current I includes, but is not limited to, 8kA, 9kA, 10kA, 11kA, 12kA, 13kA, 14kA, and 15kA.

[0043] In some embodiments, during the step of entering the solidification stage and controlling the cooling water flow rate L, the cooling water pressure is not lower than 0.4 MPa.

[0044] In the step of entering the solidification stage and controlling the cooling water flow rate L, the cooling water pressure is not lower than 0.4 MPa. This cooling water pressure ensures that the cooling water flows through the cooling channel of the crystallizer with sufficient pressure, thereby ensuring the stability and uniformity of the cooling water flow rate L, and thus ensuring the cooling uniformity of the ingot solidification process. This reduces segregation and structural defects caused by uneven cooling, and improves the metallurgical quality of large-size nickel-based superalloy ingots.

[0045] Cooling water pressure: including but not limited to 0.4MPa, 0.45MPa, 0.5MPa, 0.55MPa, 0.6MPa, 0.7MPa, 0.8MPa, etc.

[0046] In some embodiments, the first melting rate V1 is greater than the melting rate V during the remelting stabilization period.

[0047] The first melting rate V1 is greater than the melting rate V during the remelting stabilization period. Therefore, during the start-up phase after the slag pool is formed and before the metal pool is formed, the first melting rate V1 enables the consumable electrode to melt rapidly in order to establish the metal pool as soon as possible. This shortens the unsteady process during the start-up phase, reduces the metallurgical quality fluctuations caused by unstable melting rate during the start-up phase, and allows the remelting stabilization period to enter a steady state as soon as possible, thereby improving the metallurgical quality of large-size nickel-based high-temperature alloy ingots.

[0048] Secondly, embodiments of this application provide a pre-melted slag for electroslag remelting of nickel-based high-temperature alloys. The chemical composition of the pre-melted slag, by mass percentage, includes: 40%~90% CaF2, 5%~30% CaO, 5%~30% Al2O3, and 0~10% MgO, and satisfies 0.8≤CaO / Al2O3≤1.5.

[0049] The chemical composition of the pre-melted slag, by mass percentage, includes 40%~90% CaF2, 5%~30% CaO, 5%~30% Al2O3, and 0~10% MgO, satisfying 0.8≤CaO / Al2O3≤1.5. Thus, the pre-melted slag forms a slag system with suitable viscosity, surface tension, and desulfurization ability. Consequently, when the pre-melted slag is used for electroslag remelting of nickel-based superalloys, it can effectively remove sulfur and inclusions from molten metal droplets, thereby improving the metallurgical quality of large-size nickel-based superalloy ingots.

[0050] CaF2: Including but not limited to 40%, 50%, 60%, 70%, 80%, 90%, etc. CaO: Including but not limited to 5%, 10%, 15%, 20%, 25%, 30%, etc. Al2O3: Including but not limited to 5%, 10%, 15%, 20%, 25%, 30%, etc. MgO: Including but not limited to 0%, 2%, 4%, 6%, 8%, 10%, etc. CaO / Al2O3: Including but not limited to 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc.

[0051] Thirdly, embodiments of this application provide the use of the pre-melted slag described in the second aspect in the electroslag remelting of nickel-based superalloys.

[0052] Fourthly, embodiments of this application provide a consumable electrode for electroslag remelting of nickel-based superalloys, characterized in that the chemical composition of the consumable electrode, by mass percentage, is: Mo 5%~15%, Fe 15%~25%, Co 0.1%~5%, with the balance being Ni; or Mo 3%~4%, Fe 18%~19%, Nb 5%~6%, balance Ni.

[0053] The chemical composition of the consumable electrode, by mass percentage, is 5%~15% Mo, 15%~25% Fe, 0.1%~5% Co, with the balance being Ni, thus forming a GH536 type nickel-based superalloy composition system; or the chemical composition of the consumable electrode, by mass percentage, is 3%~4% Mo, 18%~19% Fe, 5%~6% Nb, with the balance being Ni, thus forming a GH4169 type nickel-based superalloy composition system; and then, under the electroslag remelting method, the consumable electrode with this specific composition can achieve effective control and uniform distribution of easily segregating elements (Mo, Nb), thereby improving the metallurgical quality of large-size nickel-based superalloy ingots.

[0054] Mo (GH536 class): including but not limited to 5%, 7%, 9%, 10%, 12%, 15%, etc. Fe (GH536 class): including but not limited to 15%, 17%, 18%, 19%, 20%, 22%, 25%, etc. Co (GH536 class): including but not limited to 0.1%, 1%, 2%, 3%, 4%, 5%, etc. Mo (GH4169 class): including but not limited to 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, etc. Fe (GH4169 class): including but not limited to 18.0%, 18.2%, 18.4%, 18.5%, 18.6%, 18.8%, 19.0%, etc.

[0055] Nb (GH4169 class): including but not limited to 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.8%, 6.0%, etc.

[0056] 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.

[0057] Example 1: Electroslag Remelting of GH536 Alloy Pre-melted slag is added to the remelting zone. The chemical composition of the pre-melted slag, by mass percentage, includes: 70% CaF2, 15% CaO, 12% Al2O3, and 3% MgO, and satisfies CaO / Al2O3=1.25. The depth of the slag pool formed by the pre-melted slag in the remelting zone is 0.18 times the diameter of the target ingot, and the amount of slag added is 30 kg.

[0058] The consumable electrode is surface treated to remove the oxide scale on its outer layer. The chemical composition of the consumable electrode, by mass percentage, is: Mo 9.5%, Fe 19%, Co 1.5%, with the balance being Ni. The surface-treated consumable electrode is preheated to 450°C and held at that temperature for 2.5 hours.

[0059] The consumable electrode is inserted into the pre-melted slag to a depth of 80 mm. The vacuum is drawn to 0.08 Pa, and the pre-melted slag is heated by electricity to melt it and form a slag pool.

[0060] After the formation of the slag pool, control the consumable electrode to melt at a first melting speed V1, so that the molten metal droplets melted from the consumable electrode pass through the slag pool and converge at the bottom of the remelting region to form a metal molten pool. The first melting speed V1 is greater than the melting speed V during the stable remelting period.

[0061] After the formation of the metal molten pool, enter the stable remelting period. Control the melting speed V of the consumable electrode to satisfy 0.0012d·I < V < 0.0014d·I, so that the molten metal droplets continuously pass through the slag pool and deposit on the metal molten pool for steady-state remelting; where, the diameter d of the consumable electrode is 220 mm, the current I is 10 kA, and the melting speed V is 2.9 kg / min.

[0062] After the completion of the steady-state remelting, enter the remelting feeding period. Control the melting speed V to satisfy 0.0011d·I < V < 0.0013d·I to reduce the depth of the metal molten pool and fill the shrinkage volume. The melting speed V is 2.7 kg / min.

[0063] After the end of the remelting feeding period, enter the solidification stage. Control the cooling water flow rate L to satisfy L = K·D2, where K = 4.0, D is the diameter of the consumable electrode and D = 0.22 m, and the cooling water pressure is 0.5 MPa, so that the metal molten pool solidifies to form an ingot. The diameter range of the ingot is 200 mm to 500 mm.

[0064] Test effect: The composition of the ingot is uniform, the S content is 0.0008%, the total oxygen content is 20 ppm, the inclusion rating is ≤1.0 level, the Mo segregation coefficient is 1.03, the room temperature tensile strength is 870 MPa, the creep life at 700°C is 330 h, the axial grain size is uniform, there is no obvious segregation, and the microstructure is dense.

[0065] Example 2: Electroslag remelting of GH4169 alloy Add the pre-melted slag to the remelting region. The chemical composition of the pre-melted slag includes, by mass percentage: 65% CaF2, 18% CaO, 15% Al2O3, 2% MgO, and satisfies CaO / Al2O3 = 1.20. The depth of the slag pool formed by the pre-melted slag in the remelting region is 0.20 times the diameter of the target ingot, and the added slag amount is 35 kg.

[0066] Perform surface treatment on the consumable electrode to remove the oxide scale on the outer layer of the consumable electrode. The chemical composition of the consumable electrode includes, by mass percentage: 3.0% Mo, 18.5% Fe, 5.1% Nb, and the balance is Ni; preheat the consumable electrode after the surface treatment to 500°C and hold for 3 h.

[0067] Insert the consumable electrode into the pre-molten slag. The depth of the consumable electrode inserted into the pre-molten slag is 90 mm. Evacuate to 0.07 Pa and apply electric current to heat the pre-molten slag so that the pre-molten slag melts to form a molten slag pool.

[0068] After the molten slag pool is formed, control the consumable electrode to melt at a first melting speed V1, so that the molten metal droplets melted from the consumable electrode pass through the molten slag pool and gather at the bottom of the remelting area to form a metal molten pool. The first melting speed V1 is greater than the melting speed V during the stable remelting period.

[0069] After the metal molten pool is formed, enter the stable remelting period. Control the melting speed V of the consumable electrode to satisfy 0.0012d·I < V < 0.0014d·I, so that the molten metal droplets continuously pass through the molten slag pool and deposit on the metal molten pool for steady-state remelting. Where, the diameter d of the consumable electrode is 220 mm, the current I is 11 kA, and the melting speed V is 3.1 kg / min.

[0070] After the steady-state remelting is completed, enter the remelting feeding period. Control the melting speed V to satisfy 0.0011d·I < V < 0.0013d·I to reduce the depth of the metal molten pool and fill the shrinkage volume. The melting speed V is 2.8 kg / min.

[0071] After the remelting feeding period ends, enter the solidification stage. Control the cooling water flow rate L to satisfy L = K·D2, where K = 4.2, D is the diameter of the consumable electrode and D = 0.22 m, and the cooling water pressure is 0.45 MPa, so that the metal molten pool solidifies to form an ingot. The diameter range of the ingot is 200 mm to 500 mm.

[0072] Test results: The segregation degree of Nb in the ingot is 1.04, the S content is 0.0009%, the total oxygen content is 20 ppm, the inclusion grade is ≤1.0 level, the total oxygen content is 13 ppm, the room temperature yield strength is 1050 MPa, the tensile strength at 650 °C is 910 MPa, the grain size is uniform, the δ-phase distribution is dispersed, and there are no macroscopic segregation defects.

[0073] Comparative Example 1: Electroslag remelting of GH536 alloy Add the pre-molten slag to the remelting area. The chemical composition of the pre-molten slag includes, by mass percentage: 80% CaF2 and 20% Al2O3. The depth of the slag pool formed by the pre-molten slag in the remelting area is 0.11 times the diameter of the target ingot, and the added slag amount is 25 kg.

[0074] The consumable electrode undergoes surface treatment to remove the oxide scale on its outer layer. The chemical composition of the consumable electrode, by mass percentage, is: Mo 9.5%, Fe 19%, Co 1.5%, with the balance being Ni. The consumable electrode is loaded directly into the furnace without preheating.

[0075] The consumable electrode is inserted into the pre-melted slag to a depth of 50 mm. The vacuum is drawn to 0.2 Pa, and the pre-melted slag is heated by electricity to melt the pre-melted slag and form a slag pool.

[0076] After the slag pool is formed, the consumable electrode is controlled to melt at a first melting rate, so that the molten metal droplets from the consumable electrode pass through the slag pool and gather at the bottom of the remelting area to form a molten metal pool.

[0077] After the molten metal pool is formed, a remelting stabilization period begins. The melting rate of the consumable electrode is controlled at V = 3.5 kg / min, allowing the molten metal droplets to continuously pass through the slag pool and deposit in the molten metal pool for steady-state remelting. The diameter of the consumable electrode is d = 220 mm, the current is I = 10 kA, and the melting rate V does not satisfy 0.0012d·I. <V<0.0014d·I。

[0078] After the steady-state remelting is completed, the remelting and shrinkage period begins. The melting rate V is controlled at 3.2 kg / min to reduce the depth of the molten metal pool and fill the shrinkage volume. The melting rate V does not satisfy 0.0011 d·I <V<0.0013d·I。

[0079] After the remelting and feeding period ends, the solidification stage begins, and the cooling water flow rate is controlled to allow the molten metal pool to solidify into an ingot with a diameter ranging from 200 mm to 500 mm.

[0080] Comparative results: Mo segregation coefficient 1.2, room temperature tensile strength 800MPa, 700℃ creep life 200h, obvious dendritic segregation, and loose microstructure.

[0081] Comparative Example 2: Electroslag Remelting of GH4169 Alloy Pre-melted slag is added to the remelting zone. The chemical composition of the pre-melted slag, by mass percentage, includes: 85% CaF2 and 15% Al2O3. The depth of the slag pool formed by the pre-melted slag in the remelting zone is 0.14 times the diameter of the target ingot. The amount of slag added is 20 kg.

[0082] The consumable electrode is surface-treated, but the consumable electrode is not surface-treated to remove the oxide scale on the outer layer of the consumable electrode. The chemical composition of the consumable electrode, by mass percentage, is: Mo 3.0%, Fe 18.5%, Nb 5.1%, with the balance being Ni. The consumable electrode is preheated to 200°C and held at that temperature for 1 hour. The preheating temperature does not meet the requirement of 200°C to 600°C.

[0083] The consumable electrode is inserted into the pre-melted slag to a depth of 60 mm. The vacuum is drawn to 0.3 Pa, and the pre-melted slag is heated by electricity to melt it and form a slag pool.

[0084] After the slag pool is formed, the consumable electrode is controlled to melt at a first melting rate, so that the molten metal droplets from the consumable electrode pass through the slag pool and gather at the bottom of the remelting area to form a molten metal pool.

[0085] After the molten metal pool is formed, a remelting stabilization period begins. The melting rate of the consumable electrode is controlled at V = 3.8 kg / min, allowing the molten metal droplets to continuously pass through the slag pool and deposit in the molten metal pool for steady-state remelting. The diameter of the consumable electrode is d = 220 mm, the current is I = 11 kA, and the melting rate V does not satisfy 0.0012d·I. <V<0.0014d·I。

[0086] After the steady-state remelting is completed, the remelting and shrinkage period begins. The melting rate V is controlled at 3.5 kg / min to reduce the depth of the molten metal pool and fill the shrinkage volume. The melting rate V does not satisfy 0.0011 d·I <V<0.0013d·I。

[0087] After the remelting and feeding period ends, the solidification stage begins, and the cooling water flow rate is controlled to allow the molten metal pool to solidify into an ingot with a diameter ranging from 200 mm to 500 mm.

[0088] Comparative results: The ingot has a Nb segregation degree of 1.3, an inclusion grade of 1.5, a total oxygen content of ≥22ppm, a room temperature yield strength of 960MPa, a tensile strength of 850MPa at 650℃, uneven grain size, concentrated δ phase distribution, and local segregation defects.

[0089] Experimental methods for evaluating results: 1. Method for determining sulfur content The sulfur content in ingots was determined using infrared absorption spectroscopy. The ingot sample was burned at high temperature in an oxygen stream to convert sulfur into sulfur dioxide. The sulfur dioxide content was then measured using an infrared detector, and the mass percentage of sulfur was calculated.

[0090] 2. Method for determining total oxygen content The total oxygen content in the ingot was determined using either pulse-heated inert gas melting-infrared absorption or thermal conductivity methods. The ingot sample was melted at high temperature in a graphite crucible, and the released gas was analyzed for oxygen content using an infrared detector or a thermal conductivity detector. The total oxygen content (ppm) was then calculated.

[0091] 3. Inclusion rating method Metallographic preparation of ingot samples was carried out in accordance with GB / T 10561 or ASTM E45 standards. The morphology, distribution and size of inclusions were observed under an optical microscope and the inclusions were rated by comparing them with standard spectra.

[0092] 4. Method for determining segregation coefficient / degree of segregation Electron probe microanalysis (EPMA) or scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was used to determine the concentration distribution of specific elements (Mo, Nb) in the dendritic trunk and between dendrites in the ingot. The segregation coefficient (maximum concentration / minimum concentration) or segregation degree (standard deviation / mean value) was calculated to characterize the degree of element segregation.

[0093] 5. Method for determining room temperature tensile strength / yield strength According to GB / T 228.1 or ASTM E8 standards, standard tensile specimens processed from ingots shall be subjected to room temperature tensile tests on a universal testing machine to determine tensile strength (tensile strength) or yield strength (0.2% residual deformation yield strength).

[0094] 6. High-Temperature Duration Test Method According to GB / T 2039 or ASTM E139 standards, a constant tensile stress is applied to a standard ingot-processed specimen on a high-temperature creep testing machine, and the time required for the specimen to fracture is determined at a specified temperature (700°C).

[0095] 7. Method for determining high-temperature tensile strength According to GB / T 228.2 or ASTM E21 standards, standard tensile specimens processed from ingots are subjected to high-temperature (650℃) tensile tests on a high-temperature universal testing machine to determine tensile strength.

[0096] 8. Microscopic Tissue Observation Methods Metallographic preparation (cutting, mounting, grinding, polishing, etching) was performed on the ingot samples, and the grain size, dendrite morphology, δ phase distribution, segregation characteristics and compactness were observed under an optical microscope or scanning electron microscope.

[0097] Table 1. Results of Examples / Comparative Examples

[0098] As shown in Table 1, the technological advancements of this application's technical solution include: 1. The sulfur content in Example 1 was 0.0008%, and the sulfur content in Example 2 was 0.0009%, both significantly lower than the desulfurization level of 5 ppm (0.0005%) achievable by existing technologies, thus achieving the goal of deep desulfurization.

[0099] 2. The total oxygen content in Example 1 was 20 ppm, and the total oxygen content in Example 2 was 20 ppm, both of which are lower than the oxygen content level of about 100 ppm in the prior art, and the cleanliness is significantly improved.

[0100] 3. The inclusion rating of Example 1 is ≤1.0 and the inclusion rating of Example 2 is ≤1.0, both of which are better than the 1.5 rating of Comparative Example 2, indicating that the inclusion control level is significantly improved.

[0101] 4. The Mo segregation coefficient of Example 1 was 1.03 and the Nb segregation degree of Example 2 was 1.04, both of which were significantly lower than the Mo segregation coefficient of Comparative Example 1 (1.2) and the Nb segregation degree of Comparative Example 2 (1.3), demonstrating outstanding segregation control effect.

[0102] 5. The room temperature tensile strength of Example 1 is 870 MPa, and the creep rupture life at 700°C is 330 h, both of which are significantly better than the room temperature tensile strength of 800 MPa and the creep rupture life at 700°C of Comparative Example 1 (200 h). The room temperature yield strength of Example 2 is 1050 MPa, and the room temperature tensile strength at 650°C is 910 MPa, both of which are significantly better than the room temperature yield strength of 960 MPa and the room temperature tensile strength at 650°C of Comparative Example 2 (850 MPa).

[0103] 6. The microstructure characteristics of Example 1 are uniform axial grain size, no obvious segregation, and dense microstructure. The microstructure characteristics of Example 2 are uniform grain size, diffuse δ phase distribution, and no macroscopic segregation defects. Both are fundamentally superior to the obvious dendritic segregation and loose microstructure of Comparative Example 1, as well as the non-uniform grain size, concentrated δ phase distribution, and local segregation defects of Comparative Example 2.

[0104] In summary, the technical solution of this application achieves systematic technological progress in terms of cleanliness, low segregation, dense microstructure, and mechanical properties of large-size nickel-based superalloy ingots by synergistically controlling the electrode melting rate and solidification cooling process parameters.

[0105] 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 electroslag remelting of nickel-based superalloys, characterized in that, It includes the following steps: Add the premelted slag to the remelting area. The chemical composition of the premelted slag includes, by mass percentage: 40% - 90% CaF₂, 5% - 30% CaO, 5% - 30% Al₂O₃, 0 - 10% MgO, and 0.8 ≤ CaO / Al₂O₃ ≤ 1.5; Insert the consumable electrode into the premelted slag, evacuate to below 0.1 Pa, and electrically heat the premelted slag to melt the premelted slag to form a slag pool; After the slag pool is formed, control the consumable electrode to melt at a first melting rate V₁, so that the molten metal droplets melted from the consumable electrode pass through the slag pool and gather at the bottom of the remelting area to form a metal melt pool; After the metal melt pool is formed, enter the remelting steady state. Control the melting rate V of the consumable electrode to satisfy 0.0012d·I < V < 0.0014d·I, so that the molten metal droplets continuously pass through the slag pool and deposit on the metal melt pool for steady-state remelting; where V is the melting rate, d is the diameter of the consumable electrode, and I is the current; After the steady-state remelting is completed, enter the remelting feeding stage. Control the melting rate V to satisfy 0.0011d·I < V < 0.0013d·I to reduce the depth of the metal melt pool and fill the shrinkage volume; and After the remelting and feeding period ends, the solidification stage begins, and the cooling water flow rate L is controlled to satisfy L=K·D 2 Where 3.0≤K≤6.5, D is the diameter of the consumable electrode in meters, and K is in meters per minute (m / (min·t)), so that the molten metal pool solidifies to form an ingot; the diameter of the ingot ranges from 200mm to 500mm.

2. The method for electroslag remelting of nickel-based superalloys according to claim 1, characterized in that, The depth of the slag pool formed by the premelted slag in the remelting area is 0.15 - 0.25 times the diameter of the target ingot.

3. The method for electroslag remelting of nickel-based superalloys according to claim 1, characterized in that, Before the step of inserting the consumable electrode into the premelted slag, it further includes: Surface-treat the consumable electrode to remove the oxide scale on the outer layer of the consumable electrode; and Preheat the surface-treated consumable electrode to 200°C - 600°C and keep it warm for 1 h - 4 h.

4. The method for electroslag remelting of nickel-based superalloys according to claim 1, characterized in that, The depth of the insertion of the consumable electrode into the premelted slag is 80 mm - 90 mm.

5. The method for electroslag remelting of nickel-based superalloys according to claim 1, characterized in that, The diameter d of the consumable electrode is 200 mm - 500 mm, and the current I is 8 kA - 15 kA.

6. The method for electroslag remelting of nickel-based superalloys according to claim 1, characterized in that, In the step of entering the solidification stage and controlling the cooling water flow rate L, the cooling water pressure is not lower than 0.4 MPa.

7. The method for electroslag remelting of nickel-based superalloys according to claim 1, characterized in that, The first melting rate V₁ is greater than the melting rate V in the remelting steady state.

8. A pre-melted slag for electroslag remelting of nickel-based superalloys, characterized in that, The chemical composition of the premelted slag includes, by mass percentage: 40% - 90% CaF₂, 5% - 30% CaO, 5% - 30% Al₂O₃, 0 - 10% MgO, and 0.8 ≤ CaO / Al₂O₃ ≤ 1.

5.

9. Use of the premelted slag according to claim 8 in the electroslag remelting of nickel-based superalloys.

10. A consumable electrode for electroslag remelting of nickel-based superalloys, characterized in that, The chemical composition of the consumable electrode is, by mass percentage: 5% - 15% Mo, 15% - 25% Fe, 0.1% - 5% Co, and the balance is Ni; or 3% - 4% Mo, 18% - 19% Fe, 5% - 6% Nb, and the balance is Ni.

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