Rare earth elastic alloy strip for high-performance elastic element and preparation method of rare earth elastic alloy strip

Abstract

The invention discloses a rare earth modified cobalt-based elastic alloy strip for a high-performance elastic element and a preparation method of the rare earth modified cobalt-based elastic alloy strip. Co, Ni, Cr and Mo serve as matrix components of the alloy, and a proper amount of rare earth yttrium is introduced on the basis of the matrix components; the thin-gauge alloy strip is prepared through the process steps of vacuum smelting, electroslag remelting, homogenization treatment, forging, hot rolling, solution treatment, cold rolling, aging treatment and the like. The rare earth yttrium is added, so that MnS and silicate inclusions in the alloy can be modified and refined, grain refinement is promoted in the solidification and hot working process, the grain boundary stability is improved, stress concentration is effectively reduced, the strength and plasticity of the alloy are improved, and the fatigue life of the alloy is prolonged. Experimental results show that the alloy strip has excellent comprehensive mechanical properties and performance consistency while maintaining good processability, and is suitable for the fields of aero-engines and other high-reliability elastic elements.

Description

Technical Field

[0001] This invention relates to the field of high-performance metallic elastic materials, specifically a rare-earth elastic alloy strip for high-performance elastic elements and its preparation method. Background Technology

[0002] As aerospace, advanced power equipment, and high-end mechanical systems develop towards higher speeds, higher loads, and longer lifespans, key elastic components must withstand alternating loads, high stress amplitudes, and complex environmental conditions for extended periods during service. This places higher demands on the strength, elastic limit, fatigue life, and performance consistency of materials. Cobalt-based elastic alloys, due to their excellent strength, elastic properties, and fatigue resistance, are widely used in aero-engine diaphragms, elastic supports, and high-reliability elastic structures. Among these, traditional cobalt-based elastic alloy strips such as 3J21 are the most maturely applied.

[0003] However, in practical engineering applications, it has been found that existing cobalt-based elastic alloy strips still have limited room for improvement in fatigue life under long-term cyclic loading. The main reason is that the unavoidable non-metallic inclusions such as MnS and silicates in the alloy are easily elongated and distributed in a banded shape during hot working, becoming the main source of fatigue crack initiation. At the same time, the large grain size and insufficient grain boundary stability will also accelerate crack propagation under high stress conditions, affecting the reliability of the elastic element.

[0004] To address these issues, existing technologies typically improve purity and optimize smelting and heat treatment processes. However, relying solely on process control offers limited ability to regulate inclusion morphology and grain boundary structure, making it difficult to simultaneously achieve a synergistic improvement in high strength, high plasticity, and long fatigue life without significantly increasing costs. Particularly in the fabrication of thin-gauge strips, the deterioration of inclusion morphology and microstructural instability become more pronounced with increasing deformation, further hindering the application of elastic alloy strips in high-end fields.

[0005] Therefore, how to effectively modify inclusions, refine grains, and improve grain boundary stability through reasonable alloy design while maintaining the original composition system and mature preparation process of cobalt-based elastic alloys, thereby significantly improving the fatigue performance and performance consistency of the alloy, has become an urgent technical problem to be solved in this field. In view of this, a rare-earth modified cobalt-based elastic alloy strip for high-performance elastic elements and its preparation method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance rare-earth elastic alloy strip for elastic elements and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a rare earth elastic alloy strip for high-performance elastic elements, wherein the chemical composition of the alloy strip, by weight percentage (wt%), is: Co: 39.5-40.5%, Ni: 14.5-15.5%, Cr: 19.5-20.5%, Mo: 6.8-7.2%, Mn: 0.50-1.00%, Si: 0.10-0.30%, C: ≤0.05%, P: ≤0.015%, S: ≤0.010%, Y: 0.02-0.08%, with the balance being Fe and unavoidable impurity elements; The alloy strip is a cold-rolled strip with a thickness of 0.08 to 0.15 mm, used for elastic elements under high fatigue conditions.

[0008] A method for preparing a rare-earth elastic alloy strip for high-performance elastic elements, characterized by comprising the following steps: Step A: Vacuum Induction Melting (VIM) is carried out by preparing alloy raw materials according to the chemical composition ratio defined in claim 1, and melting the alloy raw materials by vacuum induction melting. After melting, yttrium metal is added to obtain an alloy melt and casting it to form a VIM electrode rod. Step B: Electroslag Remelting (ESR) The obtained VIM electrode rod is subjected to electroslag remelting (ESR) using high basicity pre-melted slag to further remove inclusions and gases, and obtain an ingot with uniform composition and dense structure. Step C: Homogenization treatment of electroslag ingots. The electroslag ingots are homogenized to eliminate component segregation and stabilize the microstructure. Step D: Forging, hot forging is performed on the electroslag ingot after homogenization treatment to obtain a forging billet with uniform structure; Step E: Hot-roll the forging billet to obtain hot-rolled strip; Step F: Hot rolling, solution treatment, the hot-rolled strip obtained in step E is subjected to solution treatment and quenching; Step G: Cold rolling, the solution-treated strip is subjected to multiple cold rolling passes to obtain cold-rolled strip of the target thickness; Step H: Heat treatment. The cold-rolled strip obtained in step G is subjected to aging heat treatment to obtain the finished product, a high-elasticity rare-earth modified cobalt-based elastic alloy strip.

[0009] Preferably, in step A, when the alloy raw material is melted using vacuum induction melting (VIM), the high-purity raw material is melted and refined under a high vacuum condition with a vacuum degree not exceeding 1 Pa. After refining, yttrium blocks preheated to 150-200°C are added to the molten pool through a feeding bin 1-2 minutes before tapping, and electromagnetic stirring is performed after feeding to ensure that the yttrium is evenly distributed in the alloy melt. Subsequently, it is cast to form a VIM electrode rod.

[0010] Preferably, in step B, the VIM electrode rod obtained in step A is subjected to electroslag remelting (ESR) treatment. The ESR uses high-basicity pre-melted slag as the ESR medium to remelt the VIM electrode rod to further remove non-metallic inclusions and gases in the alloy, so that the ESR ingot obtained after remelting has a uniform composition and dense structure.

[0011] Preferably, in step C, the electroslag ingot obtained in step B is homogenized at a temperature of 1180℃±10℃, and the homogenization holding time is not less than 20h, so as to eliminate alloy composition segregation and stabilize the as-cast structure.

[0012] Preferably, in step D, the electroslag ingot after homogenization in step C is subjected to hot forging, wherein the initial forging temperature is 1150°C and the final forging temperature is not lower than 900°C, in order to break up the as-cast structure and obtain a forged billet with a uniform structure.

[0013] Preferably, in step E, the forging billet obtained in step D is subjected to hot rolling treatment, wherein the initial rolling temperature is 1100℃ and the final rolling temperature is not lower than 900℃, so as to obtain a hot-rolled strip with a thickness of 5 to 10 mm.

[0014] Preferably, in step F, the hot-rolled strip obtained in step E is subjected to solution treatment at 1080℃±10℃, and then water quenched after the solution treatment is completed to obtain a uniform solution structure.

[0015] Preferably, in step G, the strip after solution treatment and water quenching in step F is subjected to multiple cold rolling processes, with the deformation amount controlled at 60% to 70% in each cold rolling process; during the cold rolling process, intermediate solution treatment is performed at 1080℃±10℃; and after the intermediate solution treatment, the strip is rolled to the target thickness of 0.10mm using a 20-roll precision rolling mill.

[0016] Preferably, in step H, the strip obtained in step G, cold-rolled to the final size, is subjected to aging treatment at 600℃±5℃ for 6 hours under a protective atmosphere, and then air-cooled to obtain the finished strip.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: By introducing an appropriate amount of rare earth yttrium into cobalt-based elastic alloy strips, and combining processes such as vacuum smelting, electroslag remelting, homogenization treatment, hot working, solution treatment, cold rolling, and aging treatment, the present invention achieves effective control over the microstructure and inclusion morphology of the alloy while maintaining the alloy matrix composition system and mature preparation route. The silicate inclusions are modified and refined, and grain refinement and grain boundary stability are promoted during solidification and subsequent hot working. This significantly improves the strength, plasticity and fatigue performance of the alloy under thin strip conditions. Experimental verification shows that, under the same thickness conditions, the tensile strength, specified non-proportional elongation strength and rotational bending fatigue life of the alloy strip of this invention are significantly improved compared with the alloy without rare earth addition. Moreover, the performance dispersion between different batches is significantly reduced, showing good performance consistency and stability. In practical applications such as elastic diaphragms for aero-engines, this invention effectively reduces the failure probability, meets the requirements of high reliability and long service life, and solves the problems of stress concentration, coarse grains and limited fatigue life improvement caused by inclusions in existing cobalt-based elastic alloy strips. Attached Figure Description

[0018] Figure 1 This is a flowchart of the preparation process of the present invention; Figure 2 This is a comparison chart of the tensile strength of different rare earth Y addition amounts in this invention; Figure 3 This is a comparison chart of yield strength for different amounts of rare earth Y added according to the present invention; Figure 4 This is a comparison chart of elongation rates with different amounts of rare earth Y added according to the present invention; Figure 5 This is a hardness comparison chart of different rare earth Y addition amounts in this invention; Figure 6 A comparison chart of fatigue life with different rare earth Y addition amounts in this invention; Figure 7 A typical metallographic photograph of the alloy strip of Embodiment 1 of the present invention; Figure 8 A typical metallographic photograph of the alloy strip of Embodiment 2 of the present invention; Figure 9 Here are typical metallographic images of the alloy strip from Embodiment 3 of the present invention; Figure 10 This is a typical metallographic photograph of the comparative alloy strip of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1-4 This invention provides a technical solution: a high-performance rare-earth elastic alloy strip for elastic elements and its preparation method, which are described in detail below. It should be understood that the following embodiments are only used to illustrate the technical solution of this invention and are not intended to limit the scope of protection of this invention.

[0021] The high-performance rare-earth elastic alloy strip for elastic elements described in this invention belongs to a typical cobalt-based elastic alloy system. While maintaining high strength and elastic modulus, it places higher demands on the material's fatigue life, microstructure stability, and dimensional consistency. Addressing the problems of inclusion-induced fatigue cracks, microstructure instability, and difficulty in controlling the thickness of finished strips under high fatigue conditions in existing cobalt-based elastic alloys, this invention introduces trace amounts of rare-earth yttrium into the alloy system and combines this with a preparation process that integrates vacuum smelting, electroslag remelting, homogenization treatment, precision hot working, and multi-stage heat treatment. This achieves effective purification and refinement of the alloy microstructure, thereby obtaining an alloy strip that possesses both high fatigue performance and stable service performance.

[0022] In the technical solution of the present invention, the preparation method is carried out in accordance with the technical route of "vacuum smelting - electroslag remelting - homogenization - hot working - precision rolling - heat treatment". The process steps are coordinated with each other in terms of temperature control, microstructure evolution and deformation degree to ensure that the final alloy strip meets the expected requirements in terms of compositional uniformity, microstructure stability and mechanical properties.

[0023] Specifically, a method for preparing a rare-earth elastic alloy strip for high-performance elastic elements is characterized by comprising the following steps: Step A: Vacuum Induction Melting (VIM) is performed by preparing alloy raw materials according to the chemical composition ratio defined in claim 1, and melting the alloy raw materials using a vacuum induction melting method. After melting, yttrium is added, wherein the amount of yttrium is preferably 0.035% to 0.055%, and the alloy melt is obtained and cast to form a VIM electrode rod.

[0024] Step B: Electroslag Remelting (ESR) The obtained VIM electrode rod is subjected to electroslag remelting (ESR) using high basicity pre-melted slag to further remove inclusions and gases, and obtain an ingot with uniform composition and dense structure. Step C: Homogenization treatment of electroslag ingots. The electroslag ingots are homogenized to eliminate component segregation and stabilize the microstructure. Step D: Forging, hot forging is performed on the electroslag ingot after homogenization treatment to obtain a forging billet with uniform structure; Step E: Hot-roll the forging billet to obtain hot-rolled strip; Step F: Hot rolling, solution treatment, the hot-rolled strip obtained in step E is subjected to solution treatment and quenching; Step G: Cold rolling, the solution-treated strip is subjected to multiple cold rolling passes to obtain cold-rolled strip of the target thickness; Step H: Heat treatment. The cold-rolled strip obtained in step G is subjected to aging heat treatment to obtain the finished product, a high-elasticity rare-earth modified cobalt-based elastic alloy strip.

[0025] Specifically, in step A, when the alloy raw material is melted using vacuum induction melting (VIM), the high-purity raw material is melted and refined under a high vacuum condition with a vacuum degree not exceeding 1 Pa. After refining, yttrium blocks preheated to 150-200°C are added to the molten pool through a feeding bin 1-2 minutes before tapping. After feeding, the yttrium is thoroughly electromagnetically stirred to ensure that the yttrium is evenly distributed in the alloy melt. Subsequently, it is cast to form a VIM electrode rod.

[0026] In this embodiment, step A employs vacuum induction melting (VIM) to smelt the alloy raw materials. Vacuum induction melting can effectively reduce the content of gases such as oxygen and nitrogen in the melt under a high vacuum environment, reducing the formation of gas inclusions and oxide inclusions from the source, laying the foundation for obtaining a high-purity alloy microstructure. Since the rare earth elastic alloy involved in this invention has high requirements for fatigue performance and elastic stability, if the inclusion content is high during the melting process, it is very likely to become the initiation source of fatigue cracks during subsequent use. Therefore, it is necessary to use high vacuum conditions to purify and control the melt in the early stage of smelting.

[0027] Specifically, the alloy raw materials are melted and refined under a vacuum degree not exceeding 1 Pa to ensure that the main alloying elements are fully melted and uniformly distributed. After refining, yttrium ingots preheated to 150–200°C are added to the molten pool 1–2 minutes before tapping. Preheating the yttrium reduces the temperature difference between it and the melt, minimizing splashing and burn-off during its addition, thus improving the effective utilization rate of yttrium in the alloy. Simultaneously, controlling the timing of yttrium addition shortly before tapping helps suppress excessive volatilization and oxidation of yttrium at high temperatures, ensuring its stable presence in the alloy.

[0028] After yttrium is added, electromagnetic stirring generated by an induction coil creates a stable convection state within the melt, promoting rapid diffusion and uniform distribution of yttrium and preventing localized enrichment or segregation. Following this process, the melt is cast into a VIM electrode rod for subsequent electroslag remelting, providing a homogeneous and highly pure initial electrode material for the next electroslag remelting process. Specifically, in step B, the VIM electrode rod obtained in step A is subjected to electroslag remelting (ESR) treatment. The ESR uses high-basicity pre-melted slag as the electroslag medium to remelt the VIM electrode rod, so as to further remove non-metallic inclusions and gases in the alloy, so that the electroslag ingot obtained after remelting has a uniform composition and dense structure.

[0029] In this embodiment, step B employs electroslag remelting (ESR) to remelt the VIM electrode rod obtained in step A. As a secondary refining process, ESR can further purify and regulate the microstructure of the alloy melt during melting and solidification, which is particularly crucial for cobalt-based alloys requiring high fatigue and high elasticity.

[0030] Specifically, the VIM electrode rod obtained in step A is used as a consumable electrode and remelted under the coverage and protection of a high-basicity pre-melted electroslag. During the remelting process, the high-basicity pre-melted slag effectively adsorbs and removes oxide inclusions, sulfide inclusions, and other non-metallic inclusions from the melt, while simultaneously reducing the gas content in the melt, thereby significantly improving the overall purity of the alloy. The isolation effect of the electroslag layer also prevents direct contact between the melt and the external environment, reducing the occurrence of secondary oxidation.

[0031] During electroslag remelting, the alloy melts and resolidifies gradually from bottom to top, resulting in a stable solidification interface that facilitates the formation of a dense and uniform as-cast microstructure. Especially for the trace rare-earth yttrium-modified cobalt-based elastic alloy involved in this invention, electroslag remelting effectively suppresses the segregation of rare-earth elements during solidification, allowing yttrium to be more uniformly distributed in the alloy matrix. This provides a stable and consistent initial microstructure for subsequent homogenization and hot working processes.

[0032] Through the above electroslag remelting steps, electroslag ingots with uniform composition, dense structure, and significantly reduced inclusion content are finally obtained, creating favorable conditions for subsequent homogenization and thermal processing.

[0033] Specifically, in step C, the electroslag ingot obtained in step B is homogenized at a temperature of 1180℃±10℃, and the homogenization holding time is not less than 20h, in order to eliminate alloy composition segregation and stabilize the as-cast structure.

[0034] In this embodiment, step C involves homogenizing the electroslag ingot obtained in step B. While the alloy ingot after electroslag remelting is relatively homogeneous in macroscopic composition, it may still exhibit some degree of elemental segregation and microstructural inhomogeneity at the microscopic level. If it directly enters the hot working process, it can easily induce localized stress concentration during subsequent deformation, thereby affecting the microstructural stability and fatigue performance of the finished strip. Therefore, this invention employs a dedicated homogenization step to further optimize the microstructure of the electroslag ingot.

[0035] Specifically, the electroslag ingot is heated to a temperature range of 1180℃±10℃ and held at this temperature for no less than 20 hours. This temperature range is close to the diffusion-active range of the main alloying elements in the alloy system, which can effectively promote the full diffusion of elements such as Co, Ni, Cr, Mo, and trace rare earth elements such as yttrium in the matrix, thereby eliminating residual dendritic segregation and micro-region compositional inhomogeneity in the as-cast microstructure. At the same time, the long holding time is beneficial to stabilizing the overall microstructure of the alloy, providing initial conditions with highly consistent composition and microstructure for subsequent hot forging and hot rolling processes.

[0036] The above homogenization treatment can make the internal structure of the electroslag ingot more uniform, significantly reduce the risk of hot working cracking caused by component segregation, and improve the plasticity and processing stability of the alloy in subsequent large deformation processing, laying the foundation for the preparation of high-quality, highly consistent elastic alloy strips.

[0037] Specifically, in step D, the electroslag ingot after homogenization in step C is subjected to hot forging. The initial forging temperature of the hot forging is 1150°C, and the final forging temperature is not lower than 900°C, in order to break up the as-cast structure and obtain a forging billet with a uniform structure.

[0038] In this embodiment, step D involves hot forging the electroslag ingot after the homogenization treatment in step C. The forging process further breaks down the as-cast structure under conditions of significant plastic deformation, eliminating any remaining coarse grains and promoting the homogenization and densification of the alloy's internal structure, thereby providing a fine-structured and stable forging blank for subsequent hot rolling.

[0039] Specifically, during the forging process, the electroslag ingot is heated to 1150℃ as the initial forging temperature. Under this temperature condition, the alloy exhibits good high-temperature plasticity, which is beneficial for achieving large deformation forging without cracking. As the forging process progresses, the final forging temperature is controlled to be no lower than 900℃ to avoid forging cracks or structural damage caused by a decrease in alloy plasticity at excessively low temperatures. By rationally controlling the forging temperature range, effective grain refinement of the alloy can be achieved while ensuring processing safety.

[0040] Through the above forging steps, the internal density and microstructure uniformity of the electroslag ingot can be significantly improved, transforming the original cast microstructure into a deformed microstructure suitable for subsequent rolling processing, thereby creating a good microstructure basis for obtaining stable and uniform hot-rolled strip in the subsequent hot rolling process.

[0041] Specifically, in step E, the forging billet obtained in step D is subjected to hot rolling. The initial rolling temperature is 1100℃ and the final rolling temperature is not lower than 900℃, so as to obtain a hot-rolled strip with a thickness of 5 to 10 mm.

[0042] In this embodiment, step E involves hot rolling the forged billet after step D. The hot rolling process in this invention is mainly used to further process the forged billet into a strip shape with a certain thickness range, while simultaneously refining the microstructure and improving grain orientation under large deformation conditions, creating suitable initial dimensions and microstructure conditions for subsequent precision cold rolling.

[0043] Specifically, during hot rolling, the forging billet is heated to 1100℃ as the initial rolling temperature, ensuring the alloy maintains good plastic deformation capacity at this temperature, facilitating a smooth transition to the rolling state. During rolling, the final rolling temperature is controlled to be no lower than 900℃ to avoid rolling cracks or surface defects caused by a decrease in material plasticity due to excessively low temperatures. By rationally controlling the hot rolling temperature range, the stability of the rolling process can be ensured while allowing the alloy to undergo sufficient dynamic recovery and recrystallization during hot deformation, which is beneficial for obtaining a uniform and fine microstructure.

[0044] After the above hot rolling process, a hot-rolled strip with a thickness of 5–10 mm is obtained. This thickness range can meet the requirements of subsequent solution treatment and multi-pass cold rolling for material size and microstructure, while avoiding adverse effects on the subsequent precision rolling process due to excessively large or small initial thickness, thus achieving a good balance between processing efficiency and finished product quality.

[0045] Specifically, in step F, the hot-rolled strip obtained in step E is subjected to solution treatment at 1080℃±10℃, and then water quenched after the solution treatment is completed to obtain a uniform solution structure.

[0046] In this embodiment, step F involves solution treatment of the strip obtained by hot rolling in step E. Solution treatment allows the precipitates formed during hot rolling to redissolve in the matrix, resulting in a uniformly distributed and stable solid solution structure, providing a good plastic basis for large deformation processing during subsequent cold rolling.

[0047] Specifically, the hot-rolled strip obtained in step E is heated to a temperature range of 1080℃±10℃ and held at this temperature for a sufficient time to allow the major alloying elements and trace amounts of rare earth yttrium to fully dissolve in the matrix. This solution treatment temperature ensures effective dissolution of precipitates while avoiding abnormal grain growth or microstructural instability caused by excessively high temperatures. After solution treatment, the strip is water-quenched to rapidly suppress the re-precipitation of high-temperature microstructures during cooling, thereby maintaining a uniform solution microstructure.

[0048] Specifically, in step G, the strip after solution treatment and water quenching in step F is subjected to multiple cold rolling processes, with the deformation amount controlled at 60% to 70% in each cold rolling process; during the cold rolling process, intermediate solution treatment is carried out at 1080℃±10℃; and after the intermediate solution treatment, the strip is rolled to the target thickness of 0.10mm by a 20-roll precision rolling mill.

[0049] In this embodiment, step G involves performing multiple cold rolling processes on the strip after solution treatment and water quenching in step F, combined with intermediate solution treatment, to gradually obtain the target thickness and stable microstructure. Since the rare earth modified cobalt-based elastic alloy strip prepared by this invention has high requirements for thickness accuracy and microstructure uniformity, relying solely on continuous cold rolling can easily cause severe work hardening, thereby affecting subsequent rolling stability and finished product performance. Therefore, it is necessary to rationally set intermediate solution treatment steps during the cold rolling process.

[0050] Specifically, the solution-treated strip undergoes multi-pass cold rolling, with the deformation per pass controlled at 60-70%. By controlling the deformation per pass, sufficient plastic deformation can be ensured while avoiding defects such as cracks, edge splits, or delamination caused by excessive instantaneous deformation. During multi-pass cold rolling, as the cumulative deformation increases, significant work hardening gradually occurs within the strip. Therefore, intermediate solution treatment is performed at appropriate rolling stages.

[0051] The intermediate solution treatment is carried out at 1080℃±10℃, which effectively releases the dislocations and strain energy formed during cold rolling and promotes the microstructure to return to a uniform solid solution state, thereby significantly improving the strip's ability to continue deforming. Through intermediate solution treatment, the problem of insufficient plasticity caused by work hardening accumulation during cold rolling can be avoided, ensuring the smooth progress of subsequent cold rolling processes.

[0052] After intermediate solution treatment, the strip is finally cold-rolled using a 20-roll precision rolling mill to achieve a target thickness of 0.10 mm. The 20-roll precision rolling mill features high rolling stiffness and high thickness control accuracy, enabling stable rolling of ultra-thin strips under large deformation conditions. This effectively ensures the consistency and surface quality of the finished strip in the thickness direction, thus meeting the dimensional accuracy and service stability requirements of high-performance elastic components.

[0053] Specifically, in step H, the strip obtained in step G, cold-rolled to the final size, is subjected to aging treatment at 600℃±5℃ for 6 hours under a protective atmosphere, and then air-cooled to obtain the finished strip.

[0054] In this embodiment, step H involves performing an aging heat treatment on the alloy strip that has been cold-rolled in step G and reached its final dimensions. This aging treatment allows for further control of the alloy's microstructure while maintaining the strip's dimensional stability, resulting in a comprehensive performance profile that combines high elasticity, high strength, and good fatigue resistance.

[0055] Specifically, the cold-rolled strip obtained in step G is placed in a protective atmosphere and aged at 600℃±5℃ for 6 hours. This aging temperature range promotes the formation of fine, dispersed strengthening phases in the alloy matrix while preventing excessive growth of precipitates that could adversely affect elastic properties. By rationally controlling the aging temperature and holding time, the alloy can be strengthened while maintaining its good elastic recovery ability and microstructure stability.

[0056] After aging, the strip is air-cooled. Air cooling avoids the introduction of additional thermal stress due to excessively rapid cooling, while ensuring that the microstructure formed during aging is stably preserved, thereby obtaining a high-performance elastic alloy strip with uniform properties and stable dimensions.

[0057] To facilitate comparative analysis of the changes in alloy properties under different yttrium addition levels, the following examples are provided.

[0058] Example 1: Adding 0.035 wt% yttrium In Example 1, 0.035 wt% yttrium (Y) was added to the matrix alloy as the rare earth modification level. This addition amount corresponds to the lower limit of the yttrium content range of the present invention and is used to verify the improvement effect on the alloy microstructure and mechanical properties under the condition of lower yttrium addition.

[0059] In the preparation process, the alloy raw materials are first prepared according to the following weight percentages: The composition is: Co 40.0%, Ni 15.0%, Cr 20.0%, Mo 7.0%, Mn 0.8%, Si 0.2%, C 0.03%, P 0.008%, S 0.005%, with the balance being Fe.

[0060] The above-mentioned alloy raw materials are smelted and refined using a vacuum induction melting (VIM) process under a vacuum degree not exceeding 1 Pa. One to two minutes before tapping, yttrium ingots preheated to 150–200°C are added to the molten pool, and after thorough electromagnetic stirring, are cast to form VIM electrode rods.

[0061] Subsequently, the VIM electrode rod is subjected to electroslag remelting (ESR). During the ESR process, a high-basicity pre-melted slag is used to further purify the melt, resulting in an ESR ingot with uniform composition and dense structure. After homogenization annealing at 1180℃±10℃ for no less than 20 hours, the ESR ingot is hot forged at an initial forging temperature of 1150℃ and a final forging temperature of no less than 900℃ to obtain a forging billet.

[0062] The forged billet is hot-rolled at an initial rolling temperature of 1100℃ and a final rolling temperature of not less than 900℃ to obtain a hot-rolled strip with a thickness of 5-10mm. The hot-rolled strip is then solution-treated at 1080℃±10℃ and water-quenched, followed by multi-pass cold rolling, with the deformation per pass controlled at 60-70%. During the cold rolling process, an intermediate solution treatment is performed at 1080℃±10℃, and finally the strip is rolled to the target thickness of 0.10mm using a 20-roll precision mill.

[0063] The obtained cold-rolled strip was aged at 600℃±5℃ for 6 hours under a protective atmosphere, followed by air cooling, to obtain the rare-earth modified cobalt-based elastic alloy strip of Example 1. Chemical composition analysis showed that the final measured yttrium content was 0.032 wt%.

[0064] Mechanical property tests were conducted on the alloy strip obtained in Example 1. The results showed that, with a strip thickness of 0.10 mm, its tensile strength (σb) was 1820 MPa, its specified non-proportional elongation strength (σ0.2) was 1610 MPa, its Vickers hardness (HV) was 540, and its elongation (δ) was 6.5%. A rotational bending fatigue test was conducted under a stress amplitude of 800 MPa, and the median fatigue life reached 2.1 × 10⁻⁶. 6 Second-rate.

[0065] [Example 2: Adding 0.045 wt% yttrium] In Example 2, 0.045 wt% yttrium (Y) was added to the matrix alloy as the rare earth modification level. This addition amount is in the middle range of the yttrium content range of the present invention, corresponding to the optimal performance point determined by the present invention, and is used to verify the improvement effect on the comprehensive mechanical properties and fatigue properties of the alloy under the condition of medium yttrium addition.

[0066] In the preparation process, the alloy raw materials are first prepared according to the following weight percentages: The composition is: Co 40.0%, Ni 15.0%, Cr 20.0%, Mo 7.0%, Mn 0.8%, Si 0.2%, C 0.03%, P 0.008%, S 0.005%, with the balance being Fe.

[0067] The above-mentioned alloy raw materials are smelted and refined using a vacuum induction melting (VIM) process under a vacuum degree not exceeding 1 Pa. One to two minutes before tapping, yttrium ingots preheated to 150–200°C are added to the molten pool, and after thorough electromagnetic stirring, are cast to form VIM electrode rods.

[0068] Subsequently, the VIM electrode rod is subjected to electroslag remelting (ESR). During the ESR process, a high-basicity pre-melted slag is used to further purify the melt to remove inclusions and gaseous impurities, resulting in an ESR ingot with uniform composition and dense structure. After homogenization annealing at 1180℃±10℃ for no less than 20 hours, the ESR ingot is hot forged at an initial forging temperature of 1150℃ and a final forging temperature of no less than 900℃ to obtain a forging billet.

[0069] The forged billet is hot-rolled at an initial rolling temperature of 1100℃ and a final rolling temperature of not less than 900℃ to obtain a hot-rolled strip with a thickness of 5-10mm. The hot-rolled strip is then solution-treated at 1080℃±10℃ and water-quenched, followed by multi-pass cold rolling, with the deformation per pass controlled at 60-70%. During the cold rolling process, an intermediate solution treatment is performed at 1080℃±10℃, and finally, the strip is stably rolled to the target thickness of 0.10mm using a 20-roll precision mill.

[0070] The obtained cold-rolled strip was aged at 600℃±5℃ for 6 hours under a protective atmosphere, followed by air cooling, to obtain the rare-earth modified cobalt-based elastic alloy strip of Example 2. Chemical composition analysis showed that the final measured yttrium content was 0.043 wt%.

[0071] Mechanical property tests were conducted on the alloy strip obtained in Example 2. The results showed that, with a strip thickness of 0.10 mm, its tensile strength (σb) was 1850 MPa, its specified non-proportional elongation strength (σ0.2) was 1650 MPa, its Vickers hardness (HV) was 560, and its elongation (δ) was 6.0%. A rotational bending fatigue test was conducted under a stress amplitude of 800 MPa, and the median fatigue life reached 2.5 × 10⁻⁶. 6 This value represents the highest among all embodiments. Metallographic observation of the alloy microstructure revealed that the alloy strip corresponding to this embodiment has the finest grain size, the smallest and most dispersed inclusion size, indicating that under this yttrium addition level, rare earth yttrium achieves the optimal overall effect on alloy microstructure purification and grain boundary stabilization.

[0072] Example 3: Adding 0.055 wt% yttrium In Example 3, 0.055 wt% yttrium (Y) was added to the matrix alloy as the rare earth modification level. This addition amount is close to the upper limit of the yttrium content range of the present invention. It was used to verify the changes in the mechanical properties and microstructure of the alloy under higher yttrium addition conditions, and to evaluate the trend of further increasing the yttrium content on the alloy properties.

[0073] In the preparation process, the alloy raw materials are first prepared according to the following weight percentages: The composition is: Co 40.0%, Ni 15.0%, Cr 20.0%, Mo 7.0%, Mn 0.8%, Si 0.2%, C 0.03%, P 0.008%, S 0.005%, with the balance being Fe.

[0074] The above-mentioned alloy raw materials are smelted and refined using a vacuum induction melting (VIM) process under a vacuum degree not exceeding 1 Pa. One to two minutes before tapping, yttrium ingots preheated to 150–200°C are added to the molten pool, and after thorough electromagnetic stirring, are cast to form VIM electrode rods.

[0075] Subsequently, the VIM electrode rod is subjected to electroslag remelting (ESR). During the ESR process, a high-basicity pre-melted slag is used to further purify the melt, resulting in an ESR ingot with uniform composition and dense structure. After homogenization annealing at 1180℃±10℃ for no less than 20 hours, the ESR ingot is hot forged at an initial forging temperature of 1150℃ and a final forging temperature of no less than 900℃ to obtain a forging billet.

[0076] The forged billet is hot-rolled at an initial rolling temperature of 1100℃ and a final rolling temperature of not less than 900℃ to obtain a hot-rolled strip with a thickness of 5-10mm. The hot-rolled strip is then solution-treated at 1080℃±10℃ and water-quenched, followed by multi-pass cold rolling, with the deformation per pass controlled at 60-70%. During the cold rolling process, an intermediate solution treatment is performed at 1080℃±10℃, and finally, the strip is stably rolled to the target thickness of 0.10mm using a 20-roll precision mill.

[0077] The obtained cold-rolled strip was aged at 600℃±5℃ for 6 hours under a protective atmosphere, followed by air cooling, to obtain the rare-earth modified cobalt-based elastic alloy strip of Example 3. Chemical composition analysis showed that the final measured yttrium content was 0.052 wt%.

[0078] Mechanical property tests were conducted on the alloy strip obtained in Example 3. The results showed that, with a strip thickness of 0.10 mm, its tensile strength (σb) was 1845 MPa, and its overall strength was basically equivalent to that of Example 2, but its elongation (δ) decreased to 5.5%. A rotational bending fatigue test was conducted under a stress amplitude of 800 MPa, and the median fatigue life was 2.3 × 10⁻⁶. 6 This is lower than that of Example 2.

[0079] Microscopic analysis of the alloy structure revealed that, under the yttrium addition conditions, a very small amount of Y–O–S composite inclusions appeared in the alloy, and the size of the inclusions was slightly larger than that in Example 2. This indicates that when the yttrium addition is close to the upper limit of the present invention, the beneficial effects of rare earth yttrium in purifying inclusions and stabilizing grain boundaries tend to be saturated, and new inclusion phases may be introduced, thereby having a certain adverse effect on the plasticity and fatigue properties of the alloy.

[0080] [Comparative Example: No Yttrium Added] The comparative example did not add any rare earth element yttrium (Y) to the matrix alloy composition, while the remaining alloy chemical composition and preparation process were exactly the same as those in the above examples, in order to compare and analyze the effects of rare earth yttrium on the alloy microstructure and properties.

[0081] In the preparation process, the alloy raw materials are first prepared according to the following weight percentages: The composition is: Co 40.0%, Ni 15.0%, Cr 20.0%, Mo 7.0%, Mn 0.8%, Si 0.2%, C 0.03%, P 0.008%, S 0.005%, with the balance being Fe.

[0082] The above-mentioned alloy raw materials were melted and refined using a vacuum induction melting (VIM) process under a vacuum degree not exceeding 1 Pa. After melting, no rare earth elements were added, and the VIM electrode rods were directly cast to form VIM electrode rods. Subsequently, the VIM electrode rods were subjected to electroslag remelting (ESR). During the ESR process, high-basicity pre-melted slag was used to purify the melt, resulting in ESR ingots.

[0083] After undergoing homogenization annealing at 1180℃±10℃ for no less than 20 hours, the electroslag ingot is hot-forged at an initial forging temperature of 1150℃ and a final forging temperature of no less than 900℃ to obtain a forging billet. Subsequently, it is hot-rolled at an initial rolling temperature of 1100℃ and a final rolling temperature of no less than 900℃ to obtain a hot-rolled strip with a thickness of 5-10mm.

[0084] Hot-rolled strip was solution-treated at 1080℃±10℃ and water-quenched, followed by multi-pass cold rolling. The deformation per pass was controlled at 60-70%. An intermediate solution treatment was performed at 1080℃±10℃ during the cold rolling process. Finally, the strip was rolled to the target thickness of 0.10mm using a 20-roll precision mill. The strip, cold-rolled to the target thickness, was then aged at 600℃±5℃ for 6 hours under a protective atmosphere, followed by air cooling to obtain the comparative alloy strip.

[0085] Mechanical property tests were conducted on the alloy strip obtained in the comparative example. The results showed that, with a strip thickness of 0.10 mm, its tensile strength (σb) was 1790 MPa, its specified non-proportional elongation strength (σ0.2) was 1550 MPa, its Vickers hardness (HV) was 520, and its elongation (δ) was 5.0%. However, under a stress amplitude of 800 MPa, the median fatigue life in a rotating bending fatigue test was only 1.6 × 10⁻⁶. 6 The number of times is the lowest in all embodiments.

[0086] Metallographic observation of the comparative alloy revealed that its grain size was significantly larger than that of the example group, and a large number of silicate and sulfide inclusions distributed in bands were observed in the matrix. This indicates that without the addition of rare earth yttrium, the alloy has a weak ability to control inclusions, and the uniformity and stability of the microstructure are relatively poor, which has an adverse effect on the strength, plasticity and fatigue properties of the alloy.

[0087] Systematic experiments and mechanistic analysis revealed that adding an appropriate amount of rare earth yttrium significantly improved the microstructure and overall properties of the alloy. Scanning electron microscopy and energy dispersive spectroscopy (EDS) analysis showed that the original MnS and silicate inclusions in Examples 1-3 were partially or completely modified into smaller, more rounded, and less thermoplastic yttrium oxides or yttrium oxysulfides, which are less prone to elongation during hot working, thus effectively reducing stress concentration. Grain size statistics showed that the average grain size in the comparative example was approximately 25 μm, while the average grain size in Example 2 was refined to approximately 15 μm. Grain refinement is the main reason for the increased strength and enhanced resistance to fatigue crack initiation. Fatigue fracture analysis further indicated that fatigue cracks in the comparative example mostly originated near the strip-shaped inclusions at grain boundaries, while cracks in Example 2 originated more dispersedly and mostly at fine secondary phases or inclusions, indicating that the stress concentration effect was significantly weakened. Comprehensive analysis suggests that yttrium synergistically enhances alloy performance primarily through three effects: purifying grain boundaries, modifying inclusions, and promoting grain refinement. Performance consistency statistics indicate that the alloy strip prepared by this invention exhibits good stability across different batches, with a standard deviation of less than 25 MPa for the specified non-proportional elongation strength and a fatigue life dispersion coefficient of less than 8%. In practical application verification, the alloy strip obtained in Example 2 was processed into a diaphragm for a certain type of aero-engine. Bench tests conducted by the user unit showed that its failure probability under design life conditions was reduced by approximately 70% compared to diaphragms made from traditional 3J21 strip, meeting the requirements for high reliability and long service life.

[0088] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A rare-earth elastic alloy strip for high-performance elastic elements, characterized in that, The chemical composition of the alloy strip, by weight percentage (wt%), is as follows: Co: 39.5-40.5%, Ni: 14.5-15.5%, Cr: 19.5-20.5%, Mo: 6.8-7.2%, Mn: 0.50-1.00%, Si: 0.10-0.30%, C: ≤0.05%, P: ≤0.015%, S: ≤0.010%, Y: 0.02-0.08%, with the balance being Fe and unavoidable impurity elements; The alloy strip is a cold-rolled strip with a thickness of 0.08 to 0.15 mm, used for elastic elements under high fatigue conditions.

2. The method for preparing a high-performance elastic element rare earth elastic alloy strip according to claim 1, characterized in that, Includes the following steps: Step A: Vacuum Induction Melting (VIM) is carried out by preparing alloy raw materials according to the chemical composition ratio defined in claim 1, and melting the alloy raw materials by vacuum induction melting. After melting, yttrium metal is added to obtain an alloy melt and casting it to form a VIM electrode rod. Step B: Electroslag Remelting (ESR) The obtained VIM electrode rod is subjected to electroslag remelting (ESR) using high basicity pre-melted slag to further remove inclusions and gases, and obtain an ingot with uniform composition and dense structure. Step C: Homogenization treatment of electroslag ingots. The electroslag ingots are homogenized to eliminate component segregation and stabilize the microstructure. Step D: Forging, hot forging is performed on the electroslag ingot after homogenization treatment to obtain a forging billet with uniform structure; Step E: Hot-roll the forging billet to obtain hot-rolled strip; Step F: Hot rolling, solution treatment, the hot-rolled strip obtained in step E is subjected to solution treatment and quenching; Step G: Cold rolling, the solution-treated strip is subjected to multiple cold rolling passes to obtain cold-rolled strip of the target thickness; Step H: Heat treatment. The cold-rolled strip obtained in step G is subjected to aging heat treatment to obtain the finished product, a high-elasticity rare-earth modified cobalt-based elastic alloy strip.

3. The method for preparing a high-performance elastic element rare earth elastic alloy strip according to claim 2, characterized in that: In step A, when the alloy raw materials are melted using vacuum induction melting (VIM), the high-purity raw materials are melted and refined under high vacuum conditions with a vacuum degree not exceeding 1 Pa. After refining, yttrium blocks preheated to 150-200°C are added to the molten pool through the feeding bin 1-2 minutes before tapping. After feeding, the yttrium is thoroughly electromagnetically stirred to ensure that the yttrium is evenly distributed in the alloy melt. Then, it is cast to form a VIM electrode rod.

4. The method for preparing a rare-earth elastic alloy strip for high-performance elastic elements according to claim 2, characterized in that: In step B, the VIM electrode rod obtained in step A is subjected to electroslag remelting (ESR). The ESR uses high-basicity pre-melted slag as the electroslag medium to remelt the VIM electrode rod, so as to further remove non-metallic inclusions and gases in the alloy, so that the electroslag ingot obtained after remelting has a uniform composition and dense structure.

5. The method for preparing a high-performance elastic element rare earth elastic alloy strip according to claim 2, characterized in that: In step C, the electroslag ingot obtained in step B is homogenized at a temperature of 1180℃±10℃ for a holding time of not less than 20h to eliminate alloy composition segregation and stabilize the as-cast structure.

6. The method for preparing a rare-earth elastic alloy strip for high-performance elastic elements according to claim 2, characterized in that: In step D, the electroslag ingot after homogenization in step C is subjected to hot forging. The initial forging temperature of the hot forging is 1150°C and the final forging temperature is not lower than 900°C, in order to break up the as-cast structure and obtain a forged billet with a uniform structure.

7. The high-performance rare-earth elastic alloy strip for elastic elements and its preparation method according to claim 2, characterized in that: In step E, the forging billet obtained in step D is subjected to hot rolling. The initial rolling temperature is 1100℃ and the final rolling temperature is not lower than 900℃, so as to obtain a hot-rolled strip with a thickness of 5 to 10 mm.

8. The method for preparing a rare-earth elastic alloy strip for high-performance elastic elements according to claim 2, characterized in that: In step F, the hot-rolled strip obtained in step E is subjected to solution treatment at 1080℃±10℃, and then water quenched after the solution treatment is completed to obtain a uniform solution structure.

9. The method for preparing a rare-earth elastic alloy strip for high-performance elastic elements according to claim 2, characterized in that: In step G, the strip after solution treatment and water quenching in step F is subjected to multiple cold rolling processes, with the deformation amount controlled at 60% to 70% in each cold rolling process; during the cold rolling process, intermediate solution treatment is carried out at 1080℃±10℃; and after the intermediate solution treatment, the strip is rolled to the target thickness of 0.10mm by a 20-roll precision rolling mill.

10. The method for preparing a rare-earth elastic alloy strip for high-performance elastic elements according to claim 2, characterized in that: In step H, the strip obtained in step G, cold-rolled to the final size, is subjected to aging treatment at 600℃±5℃ for 6 hours under a protective atmosphere, and then air-cooled to obtain the finished strip.

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