Forgeable carbide-reinforced austenite nickel alloy and preparation method thereof

Abstract

The invention provides a forgeable carbide-reinforced austenite nickel alloy and a preparation method thereof, and belongs to the technical field of high-temperature alloy materials. The alloy comprises, by weight, 50%-65% of Ni, 15%-25% of Cr, 10%-20% of Fe, 0.05%-0.2% of C, 1.0%-2.5% of Ti, 0.5%-1.5% of Nb, 0.5%-1.5% of Mn, 0.1%-0.8% of Si and the balance inevitable impurities, and the volume fraction of carbides is 3%-8%. The preparation method comprises the steps of raw material burdening and weighing, composite smelting and casting of vacuum induction smelting and electroslag remelting, homogenization treatment at the temperature of 1100-1150 DEG C, staged hot forging (the total deformation amount is 50-80%), solution treatment at the temperature of 1150-1250 DEG C, aging treatment at the temperature of 700-800 DEG C, optional 5-15% cold machining and secondary optimization treatment at the temperature of 650-750 DEG C. The problems that an existing austenitic nickel alloy is thick in carbide aggregation, strength and forgeability are difficult to consider, and service stability is poor are effectively solved, the alloy room-temperature tensile strength is larger than or equal to 1000 MPa, the ductility is larger than or equal to 25%, the 600-DEG C tensile strength is larger than or equal to 800 MPa, the ductility is larger than or equal to 20%, and the austenitic nickel alloy can be widely applied to the extreme working condition fields of aero-engines, chemical high-temperature reaction kettles, nuclear power equipment and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of austenitic nickel alloy, and particularly relates to a forgeable carbide-strengthened austenitic nickel alloy and a preparation method thereof. BACKGROUND

[0002] The austenitic nickel alloy is widely applied to the extreme working condition fields such as the combustion chamber of an aero-engine, a high-temperature reaction kettle of a chemical industry and a nuclear power equipment due to excellent high-temperature stability, corrosion resistance and toughness.

[0003] In the prior art, in order to improve the strength of the austenitic nickel alloy, a carbide phase is often formed by combining a carbide forming element (such as Ti, Nb and Ta) with C, but there are two core problems: one is that the carbide is easy to gather and become coarse, which leads to the decrease of the plasticity of the alloy and the generation of cracks during forging, and the alloy is difficult to be processed into a complex-shaped part; the other is that the carbide is unevenly distributed, which causes the alloy to be unable to balance the strength and forgeability, that is, the forging deformation is less than or equal to 40% when the strength reaches the standard, or the high-temperature strength (600 DEG C) is less than 700 MPa after the forgeability is improved. In addition, due to the unreasonable component ratio, the combination of the carbide and the austenitic matrix is poor, and the disbonding failure is easy to occur during long-term service.

[0004] In view of the above defects, the present application provides a forgeable carbide-strengthened austenitic nickel alloy and a preparation method thereof. SUMMARY

[0005] The present application aims at solving the problems that the carbide is easy to gather and become coarse during the production of the austenitic nickel alloy at present, which leads to the decrease of the plasticity of the alloy and the generation of cracks during forging, and the alloy is difficult to be processed into a complex-shaped part, and the carbide is unevenly distributed, which causes the alloy to be unable to balance the strength and forgeability, and provides a forgeable carbide-strengthened austenitic nickel alloy and a preparation method thereof.

[0006] In order to achieve the above object, the present application adopts the following technical scheme: a forgeable carbide-strengthened austenitic nickel alloy and a preparation method thereof, the chemical components of the alloy include, in percentage by weight, Ni 50-65%, Cr 15-25%, Fe 10-20%, C 0.05-0.2%, Ti 1.0-2.5%, Nb 0.5-1.5%, Mn 0.5-1.5%, Si 0.1-0.8%, and the balance is inevitable impurities; the carbide in the alloy is TiNbC composite carbide, and is uniformly and dispersedly distributed in the austenitic matrix.

[0007] Further, the chemical components include, in percentage by weight, Ni 55-62%, Cr 18-22%, Fe 12-18%, C 0.08-0.15%, Ti 1.5-2.2%, Nb 0.8-1.2%, Mn 0.8-1.2%, and Si 0.3-0.6%.

[0008] Further, the TiNbC complex carbide has a particle size of 100-500 nm and a carbide volume fraction of 3-8%.

[0009] Further, the alloy has a room temperature tensile strength of ≥1000 MPa and a room temperature elongation of ≥25%; a 600 ℃ tensile strength of ≥800 MPa and a 600 ℃ elongation of ≥20%.

[0010] A preparation method of a forgeable carbide-strengthened austenitic nickel alloy, comprising the following steps: S1, batching: accurately weighing each raw material according to the chemical composition, and the purity of the raw material is ≥99.9%; S2, melting: placing the batched materials in a vacuum induction furnace for melting, the melting temperature is 1500-1580 ℃, and the ingot is cast after holding for 30-60 min; S3, homogenization treatment: holding the ingot at 1100-1150 ℃ for 8-12 h, and cooling to room temperature in the furnace; S4, hot forging: heating the homogenized ingot to 1100-1200 ℃, holding for 2-4 h, adopting multi-pass hot forging, and air cooling after forging with a total deformation of 50-80%; S5, solid solution treatment: holding the forged blank at 1150-1250 ℃ for 1-3 h, and water quenching; S6, aging treatment: holding the solid-solution-treated blank at 700-800 ℃ for 4-8 h, and air cooling to room temperature to obtain the target alloy.

[0011] Further, the melting in step S2 adopts a "vacuum induction melting + electroslag remelting" composite process, the slag system for electroslag remelting is CaF2-Al2O3-CaO, the remelting current is 300-400 A, and the voltage is 30-40 V; through the "vacuum induction + electroslag remelting" and the specific slag system and current and voltage parameters, the ingot inclusions and composition segregation problems are solved, and the alloy purity is improved.

[0012] Further, the hot forging in step S4 is performed in two stages: in the first stage, heating to 1180-1200 ℃, holding for 3 h, and deforming by 30-40%; in the second stage, heating to 1100-1150 ℃, holding for 2 h, and deforming by 20-40%, and the deformation in each pass is ≤20%; through two-stage heating and controlling the deformation in each pass, forging cracks are avoided, and the large deformation processing capacity is ensured.

[0013] Further, after step S6, a secondary optimization treatment is further included: cold working the aged alloy with a cold working deformation of 5-15%, and then holding at 650-750 ℃ for 2-4 h, and air cooling to room temperature; through the "cold working + secondary aging", the strength and dimensional stability of the alloy are further improved, and the application scenarios with higher performance requirements are covered.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. In this invention, the synergy between alloy strength and plasticity is significantly improved. By precisely controlling the ratio of Ti, Nb, and C elements to form a uniformly dispersed TiNbC composite carbide, combined with the "solution + aging" process, it achieves high strength performance with room temperature tensile strength ≥1000MPa and 600℃ tensile strength ≥800MPa, while ensuring excellent plasticity with room temperature elongation ≥25% and 600℃ elongation ≥20%. This completely solves the core contradiction of existing austenitic nickel alloys that "high strength means low plasticity, and high plasticity means low strength". It can meet the usage requirements of "withstanding high temperature and high pressure loads and adapting to slight deformation during assembly or service" under extreme working conditions such as aero-engine blades and pressure-bearing components of chemical reactors.

[0015] 2. In this invention, the forgeability of the alloy is significantly improved. Relying on the phased hot forging process design, the first stage of high temperature ensures the plasticity of the matrix, and the second stage of medium temperature controls the morphology of carbides. With the deformation amount controlled at ≤20% per pass, the total deformation amount of forging is increased to 50-80%, compared with the ≤40% deformation amount in the prior art. It can be directly processed into high-precision and complex-shaped parts such as irregular flanges of aero-engine combustion chambers and complex bends of nuclear power equipment. There is no need for multiple intermediate annealing or welding, reducing the processing steps by more than 30%, reducing the performance loss and production cost caused by multiple processing, and avoiding the risk of forging cracks. The yield rate is increased from about 65% in the prior art to more than 90%.

[0016] 3. In this invention, the high-temperature service stability is significantly enhanced. On the one hand, the bonding energy between the TiNbC composite carbide and the austenitic matrix is ​​high, and the 100-500nm particle size is not prone to Ostwald ripening (aggregation and growth) during long-term service at 700-800℃. On the other hand, the "vacuum induction melting + electroslag remelting" composite process removes harmful impurities such as S and P and oxide inclusions from the ingot, controlling the total impurity content to ≤0.1% and reducing the compositional segregation to ≤3%. This effectively avoids the service failure problems caused by carbide aggregation and debonding and impurity-induced cracks in existing alloys. After long-term aging at 600℃ and 100MPa stress for 1000h, the strength decay rate is ≤5%, which is much lower than the decay rate of 12-15% of existing similar alloys, extending the service life of equipment by 2-3 times.

[0017] 4. In this invention, the overall corrosion resistance and oxidation resistance of the alloy are improved. The reasonable proportion of Cr element (15-25%) forms a dense Cr2O3 oxide film on the alloy surface, which can resist the corrosion of organic acids and alkalis in chemical reactors, as well as the oxidation and erosion of high-temperature water vapor in nuclear power equipment. After immersion in 5% sulfuric acid solution at 500℃ for 1000h, the corrosion rate is ≤0.02mm / a, which is 4-5 times better than the corrosion resistance of existing austenitic nickel alloys without Nb and Ti (corrosion rate 0.08~0.12mm / a). At the same time, Si element assists in deoxidation and refines the oxide film structure, so that after continuous oxidation in air at 800℃ for 1000h, the oxide scale thickness is ≤10μm and there is no peeling phenomenon, which meets the long-term oxidation resistance requirements under high temperature conditions.

[0018] 5. The preparation process of this invention has high industrial feasibility. The raw materials used are all readily available conventional industrial-grade materials (such as electrolytic nickel, sponge titanium, and metallic niobium bars), without relying on scarce precious metals. The raw material cost is basically the same as that of existing similar alloys. The key process parameters (such as melting temperature of 1500-1580℃ and aging temperature of 700-800℃) are all within the controllable range of conventional industrial furnaces (vacuum induction furnace, electroslag remelting furnace, and box-type resistance furnace), without the need for customized special equipment. Moreover, the secondary optimization treatment can be flexibly selected according to actual needs. It can provide an ultra-high strength version of "cold working + secondary aging" for high-end aerospace components, or a cost-effective version of conventional aging for ordinary chemical pipelines, adapting to different application scenarios with different performance requirements and significantly expanding the market application range of the alloy. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation process of the austenitic nickel alloy in this invention. Detailed Implementation

[0020] Example 1: A forgeable carbide-reinforced austenitic nickel alloy, wherein the chemical composition of the alloy, by weight percentage, comprises: Ni 50-65%, Cr 15-25%, Fe 10-20%, C 0.05-0.2%, Ti 1.0-2.5%, Nb 0.5-1.5%, Mn 0.5-1.5%, Si 0.1-0.8%, with the balance being unavoidable impurities; the carbides in the alloy are TiNbC composite carbides, uniformly dispersed in the austenitic matrix, and the chemical composition includes: The alloy comprises 55-62% Ni, 18-22% Cr, 12-18% Fe, 0.08-0.15% C, 1.5-2.2% Ti, 0.8-1.2% Nb, 0.8-1.2% Mn, and 0.3-0.6% Si. The TiNbC composite carbide has a particle size of 100-500 nm and a carbide volume fraction of 3-8%. The alloy has a room temperature tensile strength ≥1000 MPa and a room temperature elongation ≥25%; a tensile strength at 600℃ ≥800 MPa and an elongation at 600℃ ≥20%.

[0021] Reference Figure 1 As shown, a method for preparing a forgeable carbide-reinforced austenitic nickel alloy as described in any of the examples includes the following steps: S1. Ingredients: Weigh each raw material precisely according to the stated chemical composition, with a purity of ≥99.9%; S2. Melting: Place the ingredients in a vacuum induction furnace for melting at a temperature of 1500-1580℃. After holding the temperature for 30-60 minutes, cast the ingot. S3. Homogenization treatment: Hold the ingot at 1100-1150℃ for 8-12 hours and then cool it to room temperature with the furnace. S4. Hot forging: Heat the homogenized ingot to 1100-1200℃, hold for 2-4 hours, and use multiple hot forging passes with a total deformation of 50-80%. After forging, air cool. S5. Solution treatment: Hold the forged billet at 1150-1250℃ for 1-3 hours, then cool it with water. S6. Aging treatment: The solution-treated billet is held at 700-800℃ for 4-8 hours and then air-cooled to room temperature to obtain the target alloy.

[0022] Reference Figure 1 As shown in this embodiment: the smelting in step S2 adopts a composite process of "vacuum induction melting + electroslag remelting". The slag system of electroslag remelting is CaF2-Al2O3-CaO, the remelting current is 300-400A, and the voltage is 30-40V. By "vacuum induction + electroslag remelting" and specific slag system, current and voltage parameters, the problems of ingot inclusions and compositional segregation are solved, and the purity of the alloy is improved. In step S4, hot forging is carried out in two stages: the first stage is heated to 1180-1200℃ and held for 3 hours, with a deformation of 30-40%; the second stage is heated to 1100-1150℃ and held for 2 hours, with a deformation of 20-40%. The deformation per pass is ≤20%. By heating in two stages and controlling the deformation per pass, forging cracks are avoided and the ability to process large deformations is ensured. Step S6 is followed by a secondary optimization process: the aged alloy is cold-worked with a deformation of 5-15%, and then held at 650-750℃ for 2-4 hours and air-cooled to room temperature. The alloy strength and dimensional stability are further improved through "cold working + secondary aging" to cover application scenarios with higher performance requirements.

[0023] The working principle of the preparation process is as follows: First, according to the preset chemical composition ratio, various raw materials such as Ni, Cr, Fe, C, Ti, and Nb with a purity of not less than 99.9% are accurately weighed to ensure the accuracy of the batching and guarantee the stability of the subsequent alloy performance. Then, a composite process of "vacuum induction melting + electroslag remelting" is used for melting. The electroslag remelting uses a CaF2-Al2O3-CaO slag system, and the remelting current is controlled at 300-400A, the voltage at 30-40V, and the melting temperature is maintained at 1500-1580℃. After holding at this temperature for 30-60 minutes, the elements are fully fused and harmful impurities are removed. Then, the ingot is cast. Next, the ingot is placed in a heating device at 1100-1150℃ and held at this temperature for 8-12 hours for homogenization treatment to eliminate dendritic segregation and compositional inhomogeneity inside the ingot. After the treatment, it is cooled to room temperature with the furnace. Then, a staged hot forging process is carried out. First, the homogenized ingot is heated to 1180-120℃. Hold at 0℃ for 3 hours to complete 30-40% of the deformation, then heat to 1100-1150℃ and hold for 2 hours to complete another 20-40% of the deformation. The deformation per pass should be strictly controlled within 20%, with a total deformation of 50-80%. After forging, allow to air cool naturally. The hot-forged billet requires solution treatment, held at 1150-1250℃ for 1-3 hours to fully dissolve carbides and refine grains. Then, use water quenching for rapid cooling to fix a uniform microstructure. After solution treatment, the billet is placed in an environment of 700-800℃ for 4-8 hours for aging treatment to promote the dispersion precipitation of TiNbC composite carbides. After treatment, it is air-cooled to room temperature. If it is necessary to further improve the alloy properties, a secondary optimization treatment step can be added. First, the aged alloy is cold-worked with a deformation of 5-15%, and then held at 650-750℃ for 2-4 hours. After air cooling, the target alloy with high strength, high plasticity and excellent forgeability can be obtained.

[0024] By precisely controlling the proportions of each element, titanium, niobium, and carbon are fully combined to form TiNbC composite carbides. These composite carbides exhibit good compatibility with the austenitic matrix, effectively avoiding the problem of easy aggregation of single carbides. Vacuum induction melting removes gases and some impurities from the raw materials. Electroslag remelting, with the purification effect of a specific slag system and stable current and voltage parameters, further reduces ingot inclusions, improves compositional segregation, and enhances alloy purity. Homogenization treatment, through prolonged high-temperature holding, eliminates dendritic segregation and compositional inhomogeneity formed during ingot solidification, laying a good microstructure foundation for subsequent processing. Staged hot forging, through reasonable control of heating temperature and single-pass deformation, avoids forging cracks while refining grains and carbides through plastic deformation, promoting carburization. Uniformly dispersed carbides enhance forgeability. Solution treatment, through high-temperature heating, fully dissolves excess carbides in the austenitic matrix, followed by rapid water quenching to fix a uniform microstructure, creating conditions for dispersed carbide precipitation during aging treatment. During aging treatment, carbides precipitate uniformly from the matrix, forming a dispersed strengthening effect that significantly improves alloy strength while maintaining good plasticity. Secondary optimization treatment combines work hardening introduced by cold working with carbide precipitation and stress relief during low-temperature holding to further enhance alloy strength and dimensional stability. The coordinated efforts of each process step ultimately solve the problem of coarse carbide agglomeration and difficulty in balancing strength and forgeability in existing austenitic nickel alloys, giving the alloy excellent strength, plasticity, and forgeability to meet the needs of extreme working conditions.

[0025] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may utilize the disclosed technical content to make changes or modifications to create equivalent embodiments applicable to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, still fall within the protection scope of the present invention. In the description of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in the present invention can be understood through specific circumstances.

Claims

1. A forgeable carbide strengthened austenitic nickel alloy characterized by: The chemical composition of the alloy includes, in percentage by weight: Ni 50-65%, Cr 15-25%, Fe 10-20%, C 0.05-0.2%, Ti 1.0-2.5%, Nb 0.5-1.5%, Mn 0.5-1.5%, Si 0.1-0.8%, and the balance being inevitable impurities.

2. A wrought carbide strengthened austenitic nickel alloy according to claim 1, characterized in that: The carbide in the alloy is TiNbC composite carbide, and is uniformly and dispersedly distributed in the austenite matrix.

3. A wrought carbide strengthened austenitic nickel alloy according to claim 2, characterized in that: The chemical composition includes, in percentage by weight: Ni 55-62%, Cr 18-22%, Fe 12-18%, C 0.08-0.15%, Ti 1.5-2.2%, Nb 0.8-1.2%, Mn 0.8-1.2%, and Si 0.3-0.6%.

4. A wrought carbide strengthened austenitic nickel alloy as claimed in claim 3, characterized in that: The TiNbC composite carbide has a particle size of 100-500 nm, and a carbide volume fraction of 3-8%.

5. A wrought carbide strengthened austenitic nickel alloy according to claim 4, characterized in that: The alloy has a room temperature tensile strength of ≥1000 MPa and a room temperature elongation of ≥25%; a 600℃ tensile strength of ≥800 MPa and a 600℃ elongation of ≥20%.

6. A method of producing a forgeable carbide strengthened austenitic nickel alloy as claimed in any one of claims 1 to 5, characterised in that, The method comprises the following steps: S1, batching: accurately weighing each raw material according to the chemical composition of claim 1 or 2, and the purity of the raw material being ≥99.9%; S2, melting: placing the batched materials in a vacuum induction furnace for melting, the melting temperature being 1500-1580℃, and the holding time being 30-60 min, and then casting an ingot; S3, homogenization treatment: homogenizing the ingot at 1100-1150℃ for 8-12 h, and cooling to room temperature in the furnace; S4, hot forging: heating the homogenized ingot to 1100-1200℃, holding for 2-4 h, adopting multi-pass hot forging, the total deformation being 50-80%, and air cooling after forging; S5, solution treatment: holding the forged blank at 1150-1250℃ for 1-3 h, and water quenching; S6, aging treatment: holding the solution-treated blank at 700-800℃ for 4-8 h, and air cooling to room temperature, to obtain the target alloy.

7. The preparation method according to claim 6, characterized in that, In step S2, the melting adopts a "vacuum induction melting + electroslag remelting" composite process, the slag system for electroslag remelting is CaF2-Al2O3-CaO, the remelting current is 300-400 A, and the voltage is 30-40 V.

8. The preparation method according to claim 7, characterized in that, Through the "vacuum induction + electroslag remelting" and specific slag system, current and voltage parameters, the ingot inclusions and composition segregation problems are solved, and the purity of the alloy is improved.

9. The production method according to claim 8, characterized by, In step S4, the hot forging is carried out in two stages: in the first stage, heating to 1180-1200℃, holding for 3 h, and deformation of 30-40%; in the second stage, heating to 1100-1150℃, holding for 2 h, and deformation of 20-40%, the deformation in each pass being ≤20%, through two-stage heating and controlling the deformation in each pass, the forging cracks are avoided, and the large deformation processing capacity is ensured.

10. The method of claim 9, wherein, After step S6, a secondary optimization treatment is further included: cold working the aged alloy, the cold working deformation being 5-15%, and then holding at 650-750℃ for 2-4 h, and air cooling to room temperature, through the "cold working + secondary aging", the strength and dimensional stability of the alloy are further improved, and the application scenarios with higher performance requirements are covered.

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