Preparation method of rare earth functional 4J36H low-expansion corrosion-resistant high-strength nickel-based alloy material

Abstract

The invention relates to the technical field of alloy materials, in particular to a preparation method of a rare earth functional 4J36H low-expansion corrosion-resistant high-strength nickel-based alloy material. The invention discloses a preparation method of a rare earth functional 4J36H low-expansion corrosion-resistant high-strength nickel-based alloy material, which comprises the following steps of: adopting a gradient oxygen control-pulse rare earth cloud-coherent precipitation-low-temperature back infiltration four-step closed-loop process, firstly, locking oxygen into a nanocluster pre-planted electrode through vacuum melting, atomization and mechanical alloying; and then in the electroslag remelting stage, a saturated rare earth cloud is formed through current synchronous pulse wire feeding, then through solid solution and air cooling aging, nanoclusters become coherent precipitation substrates, oxide-metal double-scale strengthening is achieved, and finally solid-state rare earth back infiltration self-healing is conducted on a surface depletion zone. The obtained alloy has ultralow expansion, high strength and long-acting corrosion resistance at the same time, and the bottleneck that stability must be sacrificed for traditional high strength and a coating must be added for corrosion resistance is broken through.

Description

[0001] This invention relates to the field of alloy materials technology, specifically to a method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material. Background Technology

[0002] 4J36 alloy (Invar Fe-36Ni) is renowned for its extremely low coefficient of linear expansion within the temperature range of -60℃ to 250℃, making it a commonly used material in precision instruments, aerospace equipment, and other fields requiring high dimensional stability. However, traditional 4J36 alloy also has significant drawbacks: relatively low strength, moderate oxidation and corrosion resistance, and unsuitability for long-term use at temperatures above 400℃. In applications requiring a balance between strength and stability, modified alloys with added elements such as cobalt are typically used to improve mechanical properties. However, the addition of alloying elements often disrupts the Invar alloy's lattice and magnetostrictive mechanism, leading to a deterioration in thermal expansion properties.

[0003] Recently, some studies have drawn on the concept of oxide dispersion strengthened alloys, attempting to introduce nano-oxide phases into Invar alloys to improve strength. For example, CN111235467A discloses an oxide-based iron-based composite master alloy, its preparation method, and its application. This method involves adding a small amount of oxides to conventional steel smelting and hot / cold working processes to improve steel performance. CN111254343A discloses a method for preparing oxide dispersion strengthened steel and its application. This method involves preparing oxides into a mixed powder, mixing it with base powder, sintering the mixed powder in a smelting furnace, adding raw materials of other elements, smelting, and then casting. After solidification, the ingot yields oxide dispersion strengthened steel. This preparation method not only does not change the original hot / cold working process of the steel but also further improves its processing performance. However, due to the tendency of iron-nickel composition segregation, traditional vacuum casting of large-size ingots often results in uneven composition and microstructure, leading to differences in expansion properties in different parts, which exceeds the requirements of large tooling applications.

[0004] In summary, how to innovate a preparation method that introduces a small amount of oxygen to form a nano-reinforcing phase without sacrificing expansion performance, so as to ensure ultra-low expansion of the Invar matrix while significantly improving the strength and corrosion resistance of the alloy and realizing the efficient utilization of rare earth elements, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing rare earth functional 4J36H low-expansion corrosion-resistant high-strength nickel-based alloy material, so as to solve the technical problems such as expansion-strength inversion and poor corrosion resistance consistency in the prior art.

[0006] The specific technical solution is as follows: A method for preparing a rare earth functional 4J36H low-expansion corrosion-resistant high-strength nickel-based alloy material, the method comprising: firstly, using gradient oxygen control to lock oxygen into nanoclusters and introduce them into the electrode; then, using pulsed rare earth clouds to saturate and homogenize them during the remelting stage; subsequently, using solid solution aging to induce coherent precipitation of strengthening phases in the clusters; and finally, using low-temperature re-diffusion to replenish the surface rare earth, thereby connecting the four links of oxygen-rare earth-precipitation-corrosion resistance into a continuous closed loop.

[0007] Furthermore, the gradient oxygen control involves controlling the target oxygen content at 30~120ppm. Under these conditions, the Fe-Ni-Cr-Mo based alloy melt is vacuum melted, atomized, and powdered. It is then mixed with rare earth aluminate (REAlO3) nanocluster pre-powder and mechanically alloyed. Finally, it is cold isostatically pressed into a consumable electrode, thereby realizing the transformation of oxygen from an impurity to a reinforcing phase.

[0008] Furthermore, the pulsed rare earth cloud is formed by feeding a La-Nd-Y (lanthanum-neodymium-yttrium) intermediate alloy into the molten pool in a current pulse synchronous wire feeding method within a calcium fluoride-alumina-magnesium oxide-cerium oxide (CaF2-Al2O3-MgO-CeO2) slag system, thereby creating a locally saturated rare earth cloud, suppressing macroscopic segregation, and improving the rare earth yield.

[0009] Furthermore, the strengthening phase precipitation is achieved through solid solution and aging treatment, which allows the pre-solidified nano-oxide γ″-Ni3(Nb,Mo) (γ phase) to coherently precipitate and nucleate on the substrate, forming an oxide-intermetallic compound composite reinforcement that balances high strength and low expansion.

[0010] Furthermore, the low-temperature re-infiltration involves solid-state diffusion at 480℃ for 12 hours, which increases the rare earth concentration in the surface 50μm layer, eliminates the rare earth depletion zone under chloride ion environment, and significantly improves pitting corrosion resistance, thereby constructing an integrated closed loop of oxygen-rare earth-precipitation-corrosion resistance.

[0011] A method for preparing a rare-earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material includes the following steps: S1: Industrial pure iron and electrolytic nickel are added to a vacuum induction melting furnace. A vacuum is drawn and the furnace is powered on to raise the temperature, holding for 30 minutes to remove gas. The power is then increased, and after the material surface collapses, the temperature is maintained. Cr and Mo are added sequentially, and the mixture is electromagnetically stirred for 5 minutes. The power is then reduced, graphite particles are added, and the reaction is allowed to proceed for 5 minutes until the oxygen activity drops to 80 ppm. Nb-Fe and Ta-Ce master alloys are then added, and the temperature is raised and held for 4 minutes. The power is then cut off to break the vacuum, and the molten steel is injected into an atomizing ladle through a tundish. The temperature is controlled at 1550±5℃, and the atomization process takes ≤8 minutes from start to finish. After atomization, d is obtained. 50=95μm powder. The powder and nano REALO3 pre-made powder were loaded into an alloying vessel, evacuated and then purged with argon to 0.1MPa. Planetary ball milling was then started for a total time of 8 hours. After the reaction was completed, the powder was sieved to 100 mesh.

[0012] S2: The sieved powder is placed into a rubber sleeve for vibration shaping at a frequency of 50 Hz for 3 minutes. After sealing, it is placed in a cold isostatic press at a pressurization rate of 5 MPa / min and held for 10 minutes to obtain an electrode blank. The blank is then kept in a 120℃ oven for 4 hours to remove adsorbed water. Pure nickel arc-starting plates are then welded to the upper and lower parts to obtain a consumable electrode.

[0013] S3: The consumable electrode is moved into the electroslag furnace, and the slag system is prepared by taking CaF2, Al2O3, MgO and CeO2. The melting depth is 80mm. The steady-state current is set to 2600A, and the La-Nd-Y wire is synchronously pulsed every 30 seconds. The waveform is coupled, and the eight-zone water cooling maintains a gradient of 200℃ / m and sequentially switches 10~20Hz / 0.12T electromagnetic stirring. The melting rate is 1.8kg / min, and a crack-free ingot is obtained.

[0014] S4: Samples from crack-free ingots were solution-quenched at 1150℃ for 1 hour to obtain a supersaturated matrix. This matrix was then air-cooled and aged to allow pre-solidified nano-REAlO3 clusters to become coherent nucleation sites for γ″-Ni3(Nb,Mo), resulting in dual-scale precipitation between the oxide and metal. The finalized sample was placed in a high-temperature diffusion furnace for solid rare earth re-infiltration. After re-infiltration, the sample underwent furnace cooling, polishing, final processing, cleaning, and performance testing to obtain a low-expansion, corrosion-resistant, and high-strength nickel-based alloy material.

[0015] Furthermore, the nano-REALO3 pre-formed powder described in S1, its d 50 The size is 15~60nm; the oxygen content of the 95μm powder is locked at 80~120ppm; the total time for planetary ball milling is 6~10 hours.

[0016] Furthermore, the pressure boosting rate of 5 MPa / min mentioned in S2 needs to be increased to 150~250 MPa.

[0017] Furthermore, the steady-state current set in S3 has a current density of 20~30 A / cm². 2 The synchronous pulse delivery of La-Nd-Y filaments every 30 seconds involves delivering 0.08 to 0.12 pulses of La-Nd-Y filaments each time.

[0018] Furthermore, the air-cooled aging described in S4 is carried out at 700~800℃ for 6~10 hours; the solid rare earth re-infiltration is carried out at 450~500℃ for 10~14 hours.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) Significantly improve alloy strength and maintain ultra-low expansion coefficient: This invention improves strength and dimensional stability in a wide temperature range and eliminates chloride ion depletion zone by coherent strengthening of nanoclusters and self-healing of surface rare earth elements; at the same time, the electrode powder cold isostatic pressing and pulse electroslag remelting process significantly reduce the machining allowance and achieve near-net-shape forming of complex components.

[0020] (2) Improve the utilization rate and purity of rare earth materials, and ensure stable and consistent performance: Through the pulse wire feeding of rare earth iron / nickel master alloy, rare earth fully exerts its deoxidation, desulfurization and modification inclusion effects during the smelting stage, thereby improving the ductility and fatigue performance of the material from the source.

[0021] (3) Imparting self-healing corrosion resistance to materials and significantly improving chloride corrosion resistance: Through a unique rare earth infiltration process, this invention constructs a stable film layer rich in rare earth oxides on the surface of the material. Rare earth oxides have excellent corrosion resistance and self-passivation properties. This infiltration layer can inhibit the formation and expansion of pitting corrosion in chlorine-containing media, and significantly improve pitting potential and salt spray resistance life.

[0022] (4) The process route has good compatibility and can be used for the preparation of large components: The gradient oxygen control powder metallurgy, electroslag remelting refining, conventional heat treatment and solid diffusion process adopted in this invention are all mature or feasible methods in industry, and have scalability and stability. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material according to the present invention.

[0024] Figure 2 This is a TEM image of the nano-REAlO3 clusters and the γ″-Ni3(Nb,Mo) coherent precipitate phase in Example 1 of the present invention.

[0025] Figure 3 This is a graph showing the relationship between current density and pitting potential in Experiment Example 1 of this invention.

[0026] Figure 4 This is a comparison chart of the experimental results for thermal expansion coefficient, pitting potential, room temperature tensile strength, oxygen content, and rare earth yield in Experiment Example 1 of this invention. Detailed Implementation

[0027] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0028] The technical solution designed by this invention to solve the existing problems includes the following key points: 1. Gradient oxygen control Traditional methods consistently treat oxygen as an impurity that must be removed, leading to repeated deoxidation processes in vacuum melting, ladle refining, and electroslag remelting. This results in prolonged melting time, significant loss of rare earth elements, and a final reduction in oxygen content, which easily triggers secondary oxidation inclusions later on. In contrast, this invention, after vacuum induction melting, does not aim for ultra-low oxygen levels as in traditional methods, but intentionally retains a suitable amount of oxygen. The melt is then broken into fine droplets by high-pressure argon atomization. These droplets rapidly absorb oxygen and solidify during flight, forming oxygen-rich supersaturated powder. This powder, along with pre-prepared nano-scale rare earth aluminate (REAlO3) clusters, is fed into a planetary ball mill jar. Under high-energy impact and shearing, the nano-clusters are firmly embedded within the powder particles, becoming composite powder with self-reinforcing nuclei. Cold isostatic pressing ensures dense bonding of the composite powder, with the clusters uniformly locked within the electrode framework. During subsequent remelting, these nanonuclei enter the molten pool with the melt, providing ideal nucleation sites for subsequent precipitation and laying a high-density nucleation substrate for subsequent two-scale precipitation. Therefore, gradient oxygen control is manifested in actively locking the total oxygen at 30~120ppm throughout the entire process, with a distribution that is high at the beginning and low at the end. The oxygen content in the powder is approximately 100ppm due to atomization oxygen absorption and mechanical alloying in the first stage, and only slightly reduced to 80~120ppm in the second stage of electroslag remelting, without the need for extreme deoxidation. The oxygen content decreases in a gradient from powder to electrode to remelted ingot, but is never lower than 30ppm, ensuring that the nano-REAlO3 clusters survive throughout the process and continue to play a nucleation role.

[0029] 2. Pulse wire feeding In the electroslag remelting stage, existing technologies generally use one-time block feeding or constant low-speed wire feeding to replenish rare earth elements. The residence time in the molten pool is short and the local concentration fluctuates greatly. This invention changes the one-time block feeding or constant low-speed wire feeding method to pulse wire feeding synchronized with the current waveform: whenever the current in the molten pool rises to the peak value, a quantitative amount of lanthanum-neodymium-yttrium wire (La-Nd-Y wire) is injected instantaneously, and a supersaturated rare earth cloud is formed in the local area of ​​the molten pool. During the pulse interval, the convection in the molten pool weakens, giving rare earth atoms sufficient time to diffuse to the solid-liquid interface and be captured, rather than being lost with the slag. At the same time, the quaternary slag system of calcium fluoride-alumina-magnesium oxide-cerium oxide (CaF2-Al2O3-MgO-CeO2) forms a low-viscosity, high-flow protective film on the surface of the molten pool, which not only stabilizes the arc and promotes the floating of inclusions, but also continuously replenishes Ce (cerium) to the molten pool through CeO2, inhibiting rare earth burn-off. Combined with the alternating action of stepped cooling and electromagnetic stirring, dendrites are broken up and macroscopic element segregation is suppressed, resulting in a highly uniform distribution of rare earth in the ingot, laying the compositional basis for subsequent dual-scale precipitation.

[0030] 3. Coherent precipitation Conventional methods to improve strength include cold work hardening or single γ-phase precipitation. However, cold work leads to easily recoverable dislocation pile-up, and excessive γ-phase precipitation disrupts the low expansion characteristics of the Invar alloy matrix, resulting in increased strength but also increased expansion performance. In this invention, when the ingot is heated to the solution temperature, the pre-implanted nano-oxides, due to their lattice constant being close to that of the matrix and their low surface energy, become the substrate for preferential nucleation of the γ-phase. During subsequent aging, Ni, Nb, and Mo atoms aggregate towards these substrates, forming dense γ″-Ni3(Nb,Mo) precipitates that remain coherent with the matrix. The oxide nuclei provide pinning points, and the γ-precipitated phase provides resistance; together, they suppress dislocation slip, allowing the material to withstand higher stresses without compromising its low expansion characteristics due to excessive precipitation, thus achieving a simultaneous improvement in strength and dimensional stability. Figure 2 As shown in the TEM image, the nanolayered precipitates are coherent with the matrix, and together they form an oxide-γ dual-scale reinforced framework, providing a structural basis for high strength and low expansion performance.

[0031] 4. Low-temperature re-osmosis Traditional methods for improving surface corrosion resistance rely on additional coatings, laser cladding, or shot peening, which are complex processes with drawbacks such as weak interfacial bonding, stress concentration, and high maintenance costs. This invention, however, places the workpiece in a sealed furnace filled with lanthanum fluoride (LaF3) powder after finishing, where solid-state diffusion occurs at temperatures only slightly higher than the operating temperature. La and Ce atoms migrate along grain boundaries and vacancy channels to the surface, forming a new rare-earth enrichment layer within 50 μm of depth within 12 hours, filling the rare-earth gaps caused by previous processing or oxidation. This layer preferentially forms a dense rare-earth oxide film in subsequent salt spray or chloride-containing environments, preventing pitting corrosion and eliminating the rare-earth depletion zones common in traditional Invar alloys, achieving a closed-loop process from internal strengthening to surface protection.

[0032] Example 1

[0033] A method for preparing a rare-earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material includes the following steps: S1: Add 52.85 parts of industrial pure iron and 35.75 parts of electrolytic nickel to a vacuum induction melting furnace, evacuate to ≤5Pa, and heat to 400℃ for 30 minutes to remove gas. Then increase the power to 250kW, maintain the temperature at 1600±10℃ after the material surface collapses, add Cr and Mo sequentially, stir electromagnetically for 5 minutes, then reduce the power to 150kW, add 0.02 parts of graphite particles, react for 5 minutes until the oxygen activity drops to 80ppm. Add Nb-Fe and Ta-Ce master alloys, heat to 1650℃, hold for 4 minutes, then turn off the power to break the vacuum, and inject the molten steel into an atomizing ladle through the tundish. Control the temperature at 1550±5℃, the ladle nozzle diameter is 3mm, the argon pressure is 4.5MPa, and the flow rate is 800Nm. 3 / h, atomization from start to finish ≤8 minutes. After atomization, the powder falls into a water-cooled powder collection tank with an oxygen content ≤100ppm, yielding d 50 =95μm powder, 84.6 parts. Mix 84.6 parts of powder with 0.30 parts of d 50 =30nm REALO3 pre-formed powder was loaded into an alloying vessel, evacuated, and then purged with argon to 0.1MPa. Planetary ball milling was then started at 300rpm with a rotation-to-revolution ratio of 1:2. The rotation was switched every 30 minutes, with a total time of 8 hours. The cooling water temperature of the vessel wall was ≤25℃. After the reaction was completed, the powder was sieved to 100 mesh, with a powder yield of ≥98% and an oxygen content gradient of 100~110ppm.

[0034] S2: The sieved powder is placed into a 120mm diameter rubber sleeve and vibrated to shape it. The vibration table frequency is 50Hz, the time is 3 minutes, and the loose density of the powder is 4.2g / cm³. 3After sealing, the electrode blank is placed in a cold isostatic press at a pressurization rate of 5 MPa / min until it reaches 200 MPa. The pressure is maintained for 10 minutes to obtain an electrode blank with dimensions of 118 × 900 mm and a relative density of ≥82%. The blank is then kept in a 120℃ oven for 4 hours to remove adsorbed water. Pure nickel arc-starting plates are then welded onto the upper and lower parts to obtain a consumable electrode.

[0035] S3: Transfer the consumable electrode into the electroslag furnace, prepare the slag system with 27 parts CaF2, 12.3 parts Al2O3, 7.4 parts MgO, and 2.5 parts CeO2, and melt to a depth of 80 mm. Set the steady-state current to 2600 A and the current density to 25 A / cm³. 2 Simultaneously, 0.1 parts of La-Nd-Y wire are pulsed every 30 seconds, with waveform coupling. Eight-zone water cooling maintains a gradient of 200℃ / m and sequentially switches between 10~20Hz / 0.12T electromagnetic stirring. The melting rate is 1.8kg / min, resulting in a crack-free ingot.

[0036] S4: A sample was cut from a crack-free ingot and subjected to solution rinsing at 1150℃ for 1 hour to obtain a supersaturated matrix. This matrix was then aged by air cooling at 750℃ for 8 hours. The pre-solidified nano-REAlO3 clusters became coherent nucleation sites for γ″-Ni3(Nb,Mo), resulting in dual-scale precipitation between the oxide and metal. TEM samples were prepared by mechanically grinding a 3mm diameter disc to 50μm, followed by ion thinning at 3.5kV, and then photographed at 200kV. The density of the nanolayered precipitation was statistically analyzed using the continuity of the lattice fringes. The results are as follows: Figure 2 The 100μm low-magnification overview and 100nm high-magnification coherent image are shown. The finely packaged sample was placed in a high-temperature diffusion furnace and subjected to solid rare earth re-diffusion at 480℃ for 12 hours. After rare earth re-diffusion, it must be furnace cooled, polished, finished, cleaned, and its performance tested to obtain a low-expansion, corrosion-resistant, and high-strength nickel-based alloy material.

[0037] Example 2 The preparation method is the same as in Example 1, except that: S1:d 50 =30nm nano-REALO3 pre-formed powder replaced with d 50 =15nm nano REALO3 pre-formed powder; total time of 8 hours was replaced with total time of 6 hours; oxygen content gradient of 100~110ppm was replaced with oxygen content gradient of 80~85ppm; S2: The pressure increase to 200MPa is replaced with an increase to 150MPa; S3: Current density 25A / cm² 2 Replace with a current density of 20 A / cm 2 The 0.1 part La-Nd-Y wire delivered every 30 seconds pulse is replaced with 0.08 parts La-Nd-Y wire delivered every 30 seconds pulse. S4: 750℃×8h air-cooled aging is replaced with 700℃×6h air-cooled aging; 480℃×12h solid rare earth re-infiltration is replaced with 450℃×10h solid rare earth re-infiltration. All other steps are the same.

[0038] Example 3

[0039] The preparation method is the same as in Example 1, except that: S1:d 50 =30nm nano-REALO3 pre-formed powder replaced with d 50 =60nm nano REALO3 pre-formed powder; total time of 8 hours is replaced with total time of 10 hours; oxygen content gradient of 100~110ppm is replaced with oxygen content gradient of 115~120ppm; S2: Increase to 200MPa is replaced with increase to 250MPa; S3: Current density 25A / cm² 2 Replace with a current density of 30A / cm 2 The 0.1 part La-Nd-Y wire delivered every 30 seconds pulse is replaced with 0.12 parts La-Nd-Y wire delivered every 30 seconds pulse. S4: 750℃×8h air-cooled aging is replaced with 800℃×10h air-cooled aging; 480℃×12h solid rare earth re-infiltration is replaced with 500℃×14h solid rare earth re-infiltration. All other steps are the same.

[0040] Comparative Example 1 The gradient oxygen control step is omitted, and the traditional ultra-low oxygen route is followed. In this method, the vacuum melting stage is vacuumed to ≤5Pa, and carbon / aluminum particles are added in batches at 1600℃ for deep deoxidation and heat preservation for floating, reducing the oxygen activity to ≈30ppm. The electroslag remelting uses low-oxygen CaF2-Al2O3 slag and continuously feeds aluminum particles. The shallow molten pool solidifies quickly to reduce secondary oxygen absorption, and no oxygen-containing minerals are added throughout the process.

[0041] Comparative Example 2 The preparation method is the same as in Example 1, except that: S4: The pulse wire feeding step is omitted and replaced with a one-time feeding of the same amount of rare earth blocks, without pulse current; All other steps are the same.

[0042] Comparative Example 3 The preparation method is the same as in Example 1, except that: S4: The solution treatment and aging steps are omitted. After the ingot is taken out of the furnace, it is only air-cooled to room temperature, and the 1150℃×1h solution treatment and 750℃×8h aging are no longer performed. All other steps are the same.

[0043] Comparative Example 4 The preparation method is the same as in Example 1, except that: S4: The step of rare earth re-infiltration at 480℃ is omitted; All other steps are the same.

[0044] Experimental Example 1 The low-expansion, corrosion-resistant, and high-strength nickel-based alloy materials prepared in Examples 1-3 and Comparative Examples 1-4 were tested: (1) Coefficient of thermal expansion: Referring to GB / T 4339-2021 "Corrosion of metals and alloys - Guidelines for the importance assessment of stress corrosion cracks detected in service", a round bar with a diameter of 6 mm and a length of L0 was cut from the finished product, and the two ends were ground parallel. The test was performed using a pusher-type thermomechanical analyzer. The temperature was increased by 5℃ / min, and the data at 20℃, 300℃ and 20℃ were recorded. The test was repeated twice, and the length change ΔL at four points of 20℃, 100℃, 200℃ and 300℃ was collected. The coefficient of thermal expansion was calculated using the formula: coefficient of thermal expansion = (ΔL / L0) / ΔT. The average coefficient of thermal expansion from 20℃ to 200℃ was given. Three tests were conducted on the finished product, and the average value of the results was taken.

[0045] (2) Pitting potential: Refer to GB / T 17899-1999 "Method for measuring pitting potential of stainless steel", take a 10mm×10mm working surface from the finished product, and seal the rest with epoxy resin or silicone rubber, leaving an area of ​​1cm². 2 Grind with 2000-grit sandpaper, remove oil with alcohol, and dry for later use. Prepare a 3.5% sodium chloride solution using analytical grade reagents and deionized water. Under experimental conditions of 25±1℃, completely immerse the sample in the sodium chloride solution. Use an electrochemical comprehensive tester to scan the potentiodynamic properties in the sodium chloride solution; the current jump is 0.9 mA / cm. 2 The corresponding breakdown potential is the pitting potential. Three samples were tested, and the results were averaged, expressed as mV vs. SCE. Figure 3 As shown in the figure, the current density is 0~1 mA·cm. -2 Within the range, Example 1 is at 0.9 mA·cm -2 The breakdown potential at point 1 is 625mV, while that in Comparative Example 4 is 540mV, and the seven lines are clearly separated; 0.9mA·cm -2 The vertical line indicates the breakdown potential (Epit), which is consistent with the average value in Table 1.

[0046] (3) Room temperature tensile strength: Referring to GB / T 228.1-2021 "Metallic materials—Tensive testing—Part 1: Room temperature test method", a round bar with a diameter of 5 mm and a gauge length of 50 mm was cut from the finished product, and the two ends were ground parallel. The bar was stretched to the point of fracture using a universal tensile testing machine at a speed of 1~10 mm / min in an environment of 23±5℃. The room temperature tensile strength was obtained by dividing the maximum force by the original cross-sectional area. Three samples were tested, and the average value of the results was taken.

[0047] (4) Oxygen content: Referring to EJ / T 20171-2018 "Determination of oxygen content in metallic uranium and uranium alloys - pulse heating inert gas melting-infrared absorption method", the sample was melted at high temperature in a helium atmosphere, and the released CO2 was quantified by an infrared detector, and the oxygen mass fraction could be read directly. Three samples were taken for the experiment, and the average value of the results was taken.

[0048] (5) Rare earth recovery rate: Referring to GB / T 223.79-2007 "Iron and Steel - Determination of Multi-element Content - Inductively Coupled Plasma Atomic Emission Spectrometry", the total mass of the added La-Nd-Y wire was weighed, i.e. the mass of rare earth added. After remelting, the total mass of the steel ingot was weighed. 1g samples were drilled from the ingot head and 1g from the ingot tail, and the amount of rare earth was determined by inductively coupled plasma mass spectrometry. The average value was taken to calculate the mass of rare earth in the ingot. The rare earth recovery rate was calculated using the formula: Rare earth recovery rate = (mass of rare earth in the ingot / mass of rare earth added) × 100%. Three samples were weighed and calculated, and the average value of the results was taken.

[0049] Table 1. Comparison of experimental results between Examples 1-3 and Comparative Examples 1-4

[0050] The experimental results of Examples 1-3 and Comparative Examples 1-4 are shown in Table 1. Figure 4 As shown, the low-expansion, corrosion-resistant, and high-strength nickel-based alloy material obtained by this invention has a stable coefficient of thermal expansion of 1.55~1.60×10⁻⁶ at 20~200℃. -6 K -1 With a pitting potential of 625mV and a room temperature tensile strength of 1070MPa, and controllable oxygen content and rare earth recovery, it is significantly superior to the traditional route, achieving a triple improvement in high strength, ultra-low expansion and long-term corrosion resistance, and is therefore identified as the best implementation point.

[0051] Example 2 has lower coefficients of thermal expansion, pitting potential, and room temperature tensile strength than Example 1. This is mainly because 15nm clusters are prone to agglomeration and insufficient ball milling leads to a decrease in the nucleation base. The 150MPa static pressure also increases electrode porosity, resulting in a 200A / cm² resistance. 2The current and aging time of 700℃×6h were below the optimal window, resulting in reduced γ-phase precipitation. Re-infiltration at 450℃×10h resulted in insufficient rare earth element increment in the surface layer, limiting corrosion resistance improvement. Overall performance was weaker than Example 1. Example 3 also exhibited lower thermal expansion coefficient, pitting potential, and room temperature tensile strength than Example 1. The main reason for this was the remelting and floating of 60nm clusters and oxygen locking to the upper limit of 120ppm, leading to increased inclusions. (30A / cm) 2 High overheating and increased rare earth burn-off; aging at 800℃ for 10 hours coarsens the γ phase; re-infiltration at 500℃ for 14 hours leads to an increase in the brittle phase on the surface, and the overall performance fails to surpass that of Example 1.

[0052] Due to the lack of key technologies, Comparative Examples 1-4 showed varying degrees of reduction in overall performance compared to the Examples. Comparative Example 1 lacked the key technology of gradient oxygen control, and its data were inferior to Example 1. It failed to introduce nanoclusters and reduce oxygen to an extremely low level, resulting in a lack of a coherent nucleation matrix in the melt, preventing the high-density precipitation of the γ phase and insufficient matrix strengthening. Simultaneously, the low-oxygen environment caused significant rare earth element loss during the smelting stage, resulting in a yield of only 45%. Overall strength and corrosion resistance were lower than Example 1, demonstrating that gradient oxygen control and nanoclusters are crucial prerequisites for achieving low expansion and high strength. Comparative Example 2 lacked the pulsed wire feeding stage, instead using a one-time lumpy addition of rare earth elements. The rare earth concentration in the molten pool was momentarily too high and then rapidly lost, leading to uneven composition and increased macroscopic segregation. The lack of synchronous current pulse stirring and saturation cloud effect resulted in a rare earth yield of only 38%, sparse precipitate distribution, insufficient matrix strengthening, increased thermal expansion coefficient, and significantly lower tensile strength and pitting potential compared to the overall Examples. This demonstrates the importance of pulsed wire feeding and saturation rare earth cloud mechanisms for compositional uniformity and performance. The decisive role of solid solution and aging; Comparative Example 3 omitted solid solution and aging, the nanoclusters still existed but there was no subsequent coherent precipitation of the γ phase, the matrix lacked dislocation pinning, and the strength decreased significantly; without high-temperature activation of rare earth diffusion, the surface protective film was incomplete, and the pitting potential decreased; although gradient oxygen and pulsed rare earth were retained, due to the lack of precipitation strengthening, the coefficient of thermal expansion and corrosion resistance both fell below the range of the examples, and the overall performance was lower than all examples, verifying that solid solution and aging dual-scale precipitation are necessary steps to simultaneously improve strength and dimensional stability; comparison In Example 4, due to the omission of the 480℃ low-temperature rare earth re-infiltration, the surface rare earth concentration decreased by approximately 0.03% compared to Example 1, and the pitting potential decreased from 625mV to 540mV, which is lower than the range of all examples. Although gradient oxygen, pulsed rare earth addition, and coherent precipitation were retained, the surface depletion zone was not filled, the passivation film ruptured prematurely under chloride ion environment, and the corrosion resistance significantly decreased to below the lowest level of the examples. This confirms that low-temperature rare earth re-infiltration is an indispensable link in achieving long-term corrosion resistance and completing the oxygen-rare earth-precipitation-corrosion resistance closed loop.

[0053] In summary, this invention achieves efficient and uniform distribution of rare earth elements through a four-step closed-loop process: gradient oxygen control, pulsed rare earth cloud formation, coherent precipitation, and low-temperature re-mothering. It converts impurity oxygen into nano-reinforcing cores, uses pulsed current to synchronously feed the wire, and balances high strength with low expansion through dual-scale coherent precipitation. Furthermore, it achieves self-healing surface depletion zones through solid-state re-mothering, thus surpassing traditional processes in three aspects: low expansion, corrosion resistance, and high strength.

Claims

1. A method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material, comprising preparing a consumable electrode using pure iron and electrolytic nickel as the matrix, then subjecting the consumable electrode to electroslag remelting, subjecting the material obtained from electroslag remelting to solution-aging treatment, and finally performing post-treatment to complete the preparation, characterized in that... The preparation of the consumable electrode involves the formation of a pre-embedded nano-oxide by combining the oxygen-rich supersaturated powder formed on the substrate with nano-rare earth particles. Oxygen is actively introduced, but its content is controlled to decrease gradually during the composite process, thus converting impurity oxygen into substrate oxygen. The electroslag remelting employs a pulsed wire feeding process synchronized with the remelting current waveform, instantly forming a locally supersaturated rare earth cloud within the remelting space. This, combined with the slag system, suppresses rare earth burn-off. The solution-aging treatment involves the coherent precipitation of the pre-embedded nano-oxide and metal elements at two scales, synergistically suppressing dislocation slip. The post-treatment includes a solid rare earth re-infiltration process to form an anti-corrosion protective layer.

2. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 1, characterized in that, Includes the following steps: S1: Industrial pure iron and electrolytic nickel are put into a reaction vessel, vacuumed, heated and kept warm to remove gas, then the power is increased and chromium and molybdenum are added in sequence, and the mixture is stirred evenly with electromagnetic stirring. Then the power is reduced and graphite particles and intermediate alloy are added. After the power is turned off and the vacuum is broken, the mixture is atomized to make powder. The resulting oxygen-enriched supersaturated powder and nano-rare earth particles are loaded into a ball mill jar, vacuumed and filled with argon, and ball-milled in a planetary manner until the reaction is complete, and then sieved. S2: The pre-embedded nano-oxides after sieving are loaded into a mold and vibrated to shape them; after sealing, they are placed in a reaction machine, pressurized and then held to obtain an electrode blank. The blank is kept warm in an oven to remove adsorbed water, and pure nickel arc-starting plates are welded on the top and bottom to obtain a consumable electrode. S3: Move the consumable electrode into the reaction vessel, prepare the slag system, set the steady-state current, synchronously pulse rare earth wire every 30 seconds, couple it with the peak waveform of the sinusoidal current, maintain the 200℃ / m gradient in the eight-zone water cooling and sequentially switch the working parameters of the electromagnetic stirring to obtain a crack-free ingot. S4: The sample is cut from the crack-free ingot, subjected to solid solution rinsing and then air cooling aging, and pre-embedded nano-oxides become coherent nucleation sites, forming a dual-scale precipitation between oxide and metal. The sample is then packaged for solid rare earth re-infiltration. After rare earth re-infiltration, it must be furnace cooled, polished, finished, cleaned and tested for performance to finally obtain a low-expansion, corrosion-resistant and high-strength nickel-based alloy material.

3. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, The rare earth nanoparticles mentioned in S1 are rare earth aluminate oxide clusters with a median volume diameter of 15~60nm; the oxygen content of the powder obtained by atomization is locked at 80~120ppm; the total time for planetary ball milling is 6~10 hours.

4. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, The intermediate alloy mentioned in S1 is a niobium-iron binary alloy block and a tantalum-cerium binary alloy block.

5. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, The pressurization described in S2 has a pressurization rate of 5 MPa / min and a target pressure value of 150~250 MPa.

6. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, S3 describes setting a steady-state current with a current density of 20~30 A / cm². 2 The synchronous pulse feeding of rare earth wire every 30 seconds, the rare earth wire is nickel-niobium-molybdenum wire, and the amount of wire fed in a single feeding accounts for 0.08%~0.12% of the total mass of the electrode.

7. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, The slag system described in S3 is a quaternary slag consisting of calcium fluoride, alumina, magnesium oxide, and cerium oxide, accounting for 54.3%, 24.7%, 14.9%, and 5.0% respectively. Among them, calcium fluoride provides low melting point and high fluidity, alumina adjusts viscosity and resistance, magnesium oxide enhances desulfurization and stabilizes the electric arc, and cerium oxide serves as a rare earth reservoir, continuously replenishing the molten pool with cerium during the remelting process.

8. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, The solid solution water quenching described in S4 is characterized by heating the crack-free ingot to 1150°C at a rate of ≤10°C / min and holding it at that temperature for 1 hour, followed by immediate immersion in flowing water at ≤25°C for rapid cooling, so that the alloying elements are completely dissolved in the matrix and precipitation is suppressed.

9. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, The air-cooling aging described in S4 is carried out at 700~800℃ for 6~10 hours; the solid rare earth re-infiltration is carried out by burying the finely packaged sample in calcium fluoride powder and holding it at 450~500℃ with argon gas for 10~14 hours, during which rare earth atoms diffuse along the grain boundaries to the surface to form the corrosion-resistant protective layer.

10. The method for preparing a rare earth functional 4J36H low-expansion, corrosion-resistant, high-strength nickel-based alloy material as described in claim 2, characterized in that, The low-expansion, corrosion-resistant, and high-strength nickel-based alloy material described in S4 has a thermal expansion coefficient of ≤1.61×10⁻⁶ at 20~200℃. -6 K -1 Tensile strength at room temperature ≥1000MPa, pitting potential ≥610mV.

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