High-strength low-expansion invar wire rod and method for producing the same
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHENGDU ADVANCED METAL MATERIALS IND TECH RES INST CO LTD
- Filing Date
- 2026-05-07
- Publication Date
- 2026-06-05
AI Technical Summary
Existing Invar alloys have low tensile strength, high coefficient of thermal expansion, and insufficient elongation under high load conditions. They cannot simultaneously meet the requirements of high strength, low expansion, and controllable elongation for large-capacity transmission lines, leading to increased wire sag and safety hazards, and higher infrastructure costs.
A high-strength, low-expansion coefficient Invar alloy wire preparation method based on core-shell structured nano-carbide is adopted. By precisely designing the alloy composition and optimizing the preparation process, a nanoscale composite precipitate phase is formed, including an NbC core and a Mo-V shell. Combined with three-stage deformation and asynchronous aging treatment, the high strength and low expansion coefficient of the alloy are achieved.
The alloy achieved a tensile strength exceeding 1500MPa, an elongation exceeding 1%, and a coefficient of thermal expansion of ≤2.55×10-6/℃ at 20-230℃ and ≤8.12×10-6/℃ at 230-290℃, meeting the high-end requirements of large-capacity transmission lines and improving the dimensional stability and safety of the wires.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of alloy preparation, specifically relating to a high-strength, low-expansion coefficient Invar alloy wire and its preparation method. Background Technology
[0002] Invar alloys possess an extremely low coefficient of thermal expansion (typically ≤1.5×10⁻⁶) within a temperature range of 20-200℃. -6 With an dimensional stability that is not affected by temperature changes, it is widely used as a core reinforcing material for high-capacity power transmission lines. It can effectively alleviate the thermal expansion and contraction deformation of the wires caused by temperature fluctuations and ensure the geometric stability of the power transmission lines.
[0003] As global power grids rapidly upgrade towards high-capacity, long-distance power transmission, the current-carrying capacity of transmission lines continues to rise, significantly increasing the weight of the lines and their thermal load during operation. However, traditional Invar alloys have significant performance limitations; their tensile strength is generally below 1300 MPa, making them prone to plastic deformation under high load conditions, leading to wire sag. This problem not only reduces safe spacing between lines, increasing the risk of phase-to-phase short circuits and ground discharges, but can also cause line breakage accidents due to excessive sag. Furthermore, sag severely restricts the span design of transmission lines, requiring additional steel towers, increased tower height, or the addition of intermediate support structures to meet safety requirements. This leads to a substantial increase in power infrastructure construction costs, land acquisition costs, and subsequent maintenance costs, significantly increasing the overall operating expenditure of the power system.
[0004] Currently, power grid upgrades impose three stringent requirements on reinforcing materials for transmission lines: high strength, low expansion, and controllable elongation. Tensile strength must be >1300MPa to suppress wire sag and reduce infrastructure investment; the coefficient of thermal expansion must be α (20~230℃) ≤3.7×10⁻⁶. -6 / ℃,α(230~290℃)≤10×10 -6 / ℃, to ensure dimensional stability; elongation must be >1% to meet the requirements of processing and forming and service safety under dynamic loads.
[0005] To improve the strength of Invar alloys, the industry has tried two main technical approaches, but both have significant drawbacks: Path 1: Adding conventional strengthening elements such as Mo, V, Ti, and Nb alone. While this method can increase the strength to 1100-1200 MPa, it will disrupt the Invar effect of the Fe-36Ni alloy, leading to a significant increase in the coefficient of thermal expansion. This results in increased deformation of the wire when the temperature changes, negating the core advantage of the Invar alloy as a reinforcing material and failing to meet dimensional stability requirements.
[0006] Pathway 2: Employing cold working strengthening technology. While this process can increase the strength to around 1300MPa without significantly affecting the coefficient of thermal expansion, it results in the alloy elongation dropping below 1%, leading to extremely poor plasticity. This makes the wires prone to brittle fracture during installation, transportation, and when subjected to dynamic stresses such as wind and snow loads, seriously threatening the operational safety of the lines.
[0007] Currently, existing technologies cannot achieve the synergistic effect of "high strength, low expansion coefficient, and controllable elongation," which has become a key technological bottleneck restricting the low-cost and high-safety operation of large-capacity transmission lines. Summary of the Invention
[0008] To address the technical shortcomings of existing Invar alloys in that they cannot simultaneously achieve the desired balance of strength, coefficient of thermal expansion, and elongation, this invention provides a high-strength, low-expansion-coefficient Invar alloy based on core-shell structured nanocarbide and its preparation method.
[0009] To achieve the above objectives, the present invention adopts the following technical solution: According to a first aspect of the present invention, a method for preparing a high-strength, low-expansion coefficient Invar alloy wire is provided, comprising the following steps: Raw materials meeting purity requirements are selected and formulated according to the following alloy composition ratio: by content percentage, C: 0.25%-0.32%, Mo: 1.8%-3.0%, V: 0.40%-0.70%, Nb: 0.08%-0.15%, B: 0.002%-0.005%, Si≤0.30%, Mn≤0.30%, S≤0.005%, P≤0.005%, O≤0.008%, N≤0.008%, Ni: 36.0%-37.0%, with the balance being Fe; The raw materials are smelted by vacuum induction melting and cast into alloy ingots under a protective atmosphere. The melting temperature is 1550-1600℃ and the refining time is 30-40 min. The alloy ingot is subjected to hot deformation treatment, primary cold deformation treatment, aging treatment, and secondary cold deformation treatment in sequence to obtain the Invar alloy wire. The temperature of the hot deformation treatment is 1180-1220℃, the cumulative deformation amount of the hot deformation treatment is 70-80%, the deformation amount of the primary cold deformation treatment is 55-75%, the aging treatment process is to hold at 600-640℃ for 6-10 hours, and the deformation amount of the secondary cold deformation treatment is 75-90%.
[0010] As a further embodiment, the contents of C, Mo, V, and Nb in the alloy composition satisfy the following formula: 0.87≤K= ≤1.12, Where K is the carbide equivalent balance factor, and [C], [Mo], [V], and [Nb] are the contents of C, Mo, V, and Nb, respectively.
[0011] As a further embodiment, the preparation method further includes: after the secondary cold deformation treatment, the Invar alloy wire is subjected to a stabilization treatment, wherein the stabilization treatment process involves holding the wire at a temperature of 250~280℃ for 1~2 hours, and then air cooling to room temperature.
[0012] As a further implementation, the aging process is followed by water cooling to room temperature after the heat preservation is completed.
[0013] As a further implementation method, the raw materials selected with the required purity include: Fe with a purity ≥ 99.95 wt%, Ni with a purity ≥ 99.98 wt%, Nb with a purity ≥ 99.95%, Mo with a purity ≥ 99.9 wt%, V with a purity ≥ 99.9 wt%, C with a purity ≥ 99.9%, Si with a purity ≥ 99.9%, Mn with a purity ≥ 99.9%, and B with a purity ≥ 99.9%.
[0014] According to a second aspect of the present invention, a high-strength, low-expansion coefficient Invar alloy wire is provided, which is prepared by the above-described preparation method.
[0015] As a further embodiment, the matrix of the Invar alloy wire is diffusely distributed with nano-precipitates containing Nb, Mo, V and C elements, and the average size of the nano-precipitates is 2~10 nm.
[0016] As a further embodiment, the Invar alloy wire has a tensile strength > 1500 MPa and an elongation > 1%.
[0017] As a further embodiment, the grain size of the Invar alloy wire is <3µm.
[0018] As a further embodiment, the coefficient of thermal expansion of the Invar alloy wire at 20-230℃ is ≤2.55×10⁻⁶. -6 / ℃, the coefficient of thermal expansion at 230-290℃ is ≤8.12×10 -6 / ℃.
[0019] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: This invention achieves an alloy with tensile strength >1500MPa, elongation >1%, and a low coefficient of thermal expansion α (20~230℃) ≤2.55×10⁻⁶ by precisely designing the alloy composition and proportions and optimizing the preparation process parameters. -6 / ℃ and α (230~290℃) ≤ 8.12×10 -6The performance index of / ℃ is maintained, while ensuring that the alloy has excellent processability and service stability, meeting the application requirements of high-end scenarios such as large-capacity power transmission lines. Attached Figure Description
[0020] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.
[0021] Figure 1 A flowchart illustrating the preparation method of the high-strength, low-expansion coefficient Invar alloy wire provided by this invention; Figure 2 Metallographic microstructure of a high-strength, low-expansion coefficient Invar alloy wire prepared according to an embodiment of the present invention; Figure 3 This is a high-magnification scanning microstructure of a high-strength, low-expansion coefficient Invar alloy wire prepared according to an embodiment of the present invention. Detailed Implementation
[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0023] Specific embodiments of the invention are disclosed herein as needed; however, it should be understood that the embodiments disclosed herein are merely examples of the invention that may be implemented in various alternative forms. In the following description, various operating parameters and components are described in several contemplated embodiments. These specific parameters and components are provided as examples only and are not intended to be limiting.
[0024] The endpoints and any values of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.
[0025] To achieve the aforementioned objectives, the first aspect of this invention provides a method for preparing high-strength, low-expansion coefficient Invar alloy wire, such as... Figure 1 As shown, the preparation method includes the following steps: S1: Select raw materials with the required purity and mix them according to the alloy composition ratio; S2: The raw materials are smelted by vacuum induction melting and cast into alloy ingots under a protective atmosphere. S3: The alloy ingot is subjected to hot deformation treatment, primary cold deformation treatment, aging treatment, and secondary cold deformation treatment in sequence to obtain Invar alloy wire.
[0026] In step S1, the alloy composition is as follows: by content percentage, C: 0.25%-0.32%, Mo: 1.8%-3.0%, V: 0.40%-0.70%, Nb: 0.08%-0.15%, B: 0.002%-0.005%, Si≤0.30%, Mn≤0.30%, S≤0.005%, P≤0.005%, O≤0.008%, N≤0.008%, Ni: 36.0%-37.0%, with the balance being Fe.
[0027] The alloy composition design of this invention is based on the Fe-Ni core system. By precisely controlling the ratio of each element and strictly controlling the impurity content, synergistic performance optimization is achieved. The specific design scheme is as follows: (1) Basic composition system: Fe-Ni is the core base, and the Ni content is precisely controlled at 36.0-37.0 wt%. By narrowing the Ni content range, the influence of multiple element additions on magnetic anisotropy is offset, ensuring the stability of the matrix Invar effect.
[0028] (2) Quaternary composite carbide forming elements: C: 0.25%-0.32%, precisely control the carbon content to ensure the volume fraction of the precipitated phase and avoid increasing the expansion coefficient of the solid solution carbon; Mo: 1.8%-3.0%, V: 0.40%-0.70%, to construct the outer shell layer of the composite carbide; Nb: 0.08%-0.15%, to utilize its high precipitation temperature to form a nanoscale "core" and induce the nucleation of the composite carbide.
[0029] (3) Grain boundary and interfacial active elements: B: 0.002%-0.005%, which reduces the interfacial energy of carbide / matrix through segregation, thereby achieving extremely fine dispersion of precipitated phase.
[0030] (4) Auxiliary performance adjustment elements: Si≤0.30%, Mn≤0.30%, mainly play the role of deoxidation and auxiliary improvement of Invar alloy strength, but the upper limit must be strictly controlled to prevent the excessive amount of elements from reducing the thermal expansion performance and elongation of the alloy.
[0031] (5) Impurity element control: S≤0.005%, P≤0.005%, strictly limit the content of the two types of elements to avoid them from forming brittle sulfides / phosphides with Mo and V, and ensure that the alloy elongation is >1%.
[0032] (6) Gas element control: O≤0.008%, N≤0.008%, strictly control the content of gas elements to avoid the formation of oxide inclusions, reduce the elongation of the alloy and increase the coefficient of thermal expansion.
[0033] In some embodiments, the contents of C, Mo, V, and Nb in the alloy composition satisfy the following formula: 0.87≤K= ≤1.12, Where K is the carbide equivalent balance factor, and [C], [Mo], [V], and [Nb] are the contents of C, Mo, V, and Nb, respectively.
[0034] By controlling the carbide equivalent balance factor within a specific range, it is ensured that the C element can completely fix Nb, V, and Mo into carbides, maximizing the volume fraction of the strengthening phase. Simultaneously, it avoids a significant decrease in the Curie temperature (Tc) caused by the substantial dissolution of residual metal elements in the matrix, thus keeping the coefficient of thermal expansion at an extremely low level. Ultimately, this achieves an excellent performance balance of "tensile strength > 1500 MPa - low coefficient of thermal expansion - elongation > 1%". The tensile strength of Invar alloy wire increases with increasing K value.
[0035] In some embodiments, in step S1, the raw materials selected with the required purity include: Fe with a purity ≥ 99.95 wt%, Ni with a purity ≥ 99.98 wt%, Nb with a purity ≥ 99.95%, Mo with a purity ≥ 99.9 wt%, V with a purity ≥ 99.9 wt%, C with a purity ≥ 99.9%, Si with a purity ≥ 99.9%, Mn with a purity ≥ 99.9%, and B with a purity ≥ 99.9%.
[0036] In step S2, during the vacuum induction melting process, the melting temperature is 1550-1600℃, and the refining time is 30-40 min. The melting temperature can typically, but not limited to, be set to 1550℃, 1560℃, 1570℃, 1580℃, 1590℃, or 1600℃; the refining time can typically, but not limited to, be set to 30 min, 32 min, 34 min, 36 min, 38 min, or 40 min.
[0037] In step S2, casting under a protective atmosphere aims to reduce carbon loss and compositional segregation. For example, in some embodiments, casting is performed under argon protection.
[0038] In step S3, the hot deformation treatment aims to utilize Nb to increase the recrystallization temperature and suppress recrystallization growth, thereby ensuring a fine recrystallized structure. The hot deformation treatment can be performed through hot rolling, hot forging, hot drawing / hot stretching, hot stamping, etc. The temperature of the hot deformation treatment is 1180-1220℃, and the cumulative deformation is 70-80%. The temperature of the hot deformation treatment can typically, but not limited to, be set to 1180℃, 1190℃, 1200℃, 1210℃, or 1220℃; the cumulative deformation can typically, but not limited to, be set to 70%, 72%, 74%, 76%, 78%, or 80%.
[0039] In step S3, the main purpose of the primary cold deformation treatment is to introduce high-density dislocation lines and dislocation cell structures into the austenitic matrix. These defects not only provide a large number of nucleation sites, but more importantly, through the dislocation segregation effect, they induce strong carbide-forming elements such as Nb, Mo, and V to form atomic clusters on the dislocation lines. The primary cold deformation treatment can be carried out by cold rolling, cold forging, cold drawing / cold stretching, cold stamping, etc. The deformation amount of the primary cold deformation treatment is 55%~75%. Experiments have shown that when the deformation amount is <50%, the uniformity of the precipitate distribution decreases significantly; while the deformation amount >75% will lead to excessive brittleness of the wire before aging and excessive growth of the precipitates during aging. The deformation amount of the primary cold deformation treatment can typically, but not limitedly, be set to 55%, 60%, 65%, 70%, and 75%.
[0040] In step S3, the aging treatment process involves holding at 600-640℃ for 6-10 hours. During the aging treatment, in the first step (nucleation stage): due to the extremely high chemical driving force of NbC, Nb atoms first nucleate at dislocation crossing points; in the second step (growth / shell stage): subsequently, Mo and V atoms migrate to the NbC core, coating its surface to form a composite carbide shell. Because of the order of nucleation of the precipitated phases, the NbC core forms first, followed by the formation of the Mo,V composite carbide shell around it; therefore, in this application, "aging treatment" is also referred to as "asynchronous aging treatment." The aging treatment temperature can typically, but not limited to, be set to 600℃, 610℃, 620℃, 630℃, or 640℃; the holding time can typically, but not limited to, be set to 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. In some embodiments, after the holding period during the aging treatment, the temperature is water-cooled to room temperature. Water cooling, rather than furnace cooling, is used to quickly lock in the matrix structure and prevent the carbide shell from coarsening during slow cooling, thereby maintaining low expansion characteristics.
[0041] In step S3, the purpose of the secondary cold deformation treatment is to generate strong dislocation entanglements around the already formed nano-precipitates, forming a stable dislocation cell structure and achieving the final leap in strength. Simultaneously, the large deformation causes the grains to become highly fibrous along the drawing direction, further improving the alloy's axial tensile modulus in the cable's service direction and reducing the coefficient of thermal expansion. The secondary cold deformation treatment can be performed through cold rolling, cold forging, cold drawing / cold stretching, cold stamping, etc. The deformation amount in the secondary cold deformation treatment is 75-90%. Typically, but not limited to, the deformation amount in the secondary cold deformation treatment can be set to 75%, 80%, 85%, or 90%.
[0042] In some embodiments, the preparation method further includes the following step: after the secondary cold deformation treatment, the Invar alloy wire is subjected to a stabilization treatment. The stabilization treatment process involves holding the wire at 250-280°C for 1-2 hours, followed by air cooling to room temperature. The purpose of the stabilization treatment is to eliminate the lattice distortion stress caused by the deformation during the secondary cold deformation treatment, release the suppressed magnetostrictive potential, and ensure that the coefficient of thermal expansion at 20-200°C is lower than the design limit. The stabilization treatment temperature can typically, but is not limited to, be set to 250°C, 260°C, 270°C, or 280°C; the holding time can typically, but is not limited to, be set to 1 hour, 1.5 hours, or 2 hours.
[0043] The preparation method of this invention adopts the core route of "three-stage deformation (hot deformation, primary cold deformation, secondary cold deformation) + asynchronous aging". By precisely controlling the contribution ratio of cold work hardening and precipitation strengthening, a deep synergy between mechanical and physical properties is achieved.
[0044] A second aspect of the present invention provides a high-strength, low-expansion coefficient Invar alloy wire prepared by the above-described preparation method.
[0045] Invar alloy wire contains nanoscale composite precipitates with a microscopic core-shell structure. The formation process is as follows: during asynchronous aging, NbC, due to its higher precipitation driving force, first nucleates and forms the core, followed by V and Mo elements segregating and growing towards the core to form the shell. This "inner Nb, outer Mo-V" composite structure exhibits higher thermal stability and stronger dislocation hindering ability compared to single carbides.
[0046] The alloy performance indicators of Invar alloy wire are as follows: (1) Mechanical properties: tensile strength > 1500MPa (target value 1550-1600MPa), elongation > 1% (at room temperature, GB / T228.1-2010 standard). (2) Thermal expansion properties: α (20~230℃) ≤ 2.55×10 -6 / ℃, α (230~290℃) ≤ 8.12×10 -6 / ℃ (GB / T4339-2008 standard); (3) Characteristics of precipitated phases: The nano-precipitated phases are Mo2C and (Mo,V,Nb)C, which are uniformly distributed in the matrix; (4) Grain size: <3um.
[0047] Invar alloy wire can effectively meet the stringent requirements of aerospace, precision instruments, electronic packaging and other scenarios with strict requirements for mechanical properties and dimensional stability. It is especially suitable as a core reinforcement material in high-capacity, long-distance power transmission lines, and can solve the problems of dimensional stability and safe operation under high load conditions faced by current power transmission lines.
[0048] The solution of this invention achieves the following effective results: Strength breakthrough: The tensile strength is increased from the conventional 1300MPa level to the 1500MPa level, effectively solving the problem of high-load sag in power transmission cables. Thermal stability: Thanks to the pinning effect of the Nb core, the coefficient of thermal expansion α of the alloy in the high-temperature range of 230-290℃ is less than 8.12×10⁻⁶. -6 / ℃, superior to existing patents. Synergistic effect of ductility and toughness: By purifying grain boundaries with trace amounts of boron and refining grains with nb, elongation >1% is maintained even under ultra-high strength, ensuring service safety under complex conditions. This invention achieves a perfect balance between "maximizing the volume fraction of precipitated phases" and "matrix magnetic purity" through a carbide equivalent balance factor. In particular, the introduction of Nb-B atom pairs successfully suppresses abnormal coarsening of carbides at extremely high dislocation densities. By constructing a nanoscale core-shell structure, it solves the industry problem of dimensional instability in traditional high-strength Invar alloys near the Curie point (230℃).
[0049] The present invention will be further explained in conjunction with specific embodiments below. Technical details not specified in the embodiments shall be performed in accordance with conventional technical operations.
[0050] 6.1 Implementation Example Design Examples 1-5 are set up with the core variables being the precise ratio of C, Nb, Mo, V, and B, with Fe as the balance. The auxiliary performance adjustment elements, impurity elements, and gaseous elements all meet the above composition design requirements. The specific ratios are shown in Table 1 below: Table 1 Alloy composition ratios (wt%) for Examples 1-5
[0051] 6.2 Preparation process parameters Examples 1-5 were prepared using the above method, and the specific process parameters are shown in Table 2 below: Table 2 Preparation process parameters of Examples 1-5
[0052] In Example 5, the finished wire after secondary cold drawing deformation underwent stabilization treatment, namely, it was kept at 270°C for 2 hours and then air-cooled.
[0053] 6.3 Performance Test Results The alloy samples from Examples 1-5 were tested for performance according to GB standards, and the test results are shown in Table 3 below: Table 3. Alloy property test results of Examples 1-5
[0054] As can be seen from the test results above (Tables 1 to 3), the Nb-Mo-VC quaternary synergistic regulation system constructed by introducing trace amounts of Nb and B elements in this invention exhibits significant regularity and advancement in performance improvement: 1. Evolution of Composition Ratio and Properties: As the contents of C, Mo, V, and Nb are strictly increased according to the formula: K = C / (0.0625Mo + 0.235V + 0.129Nb) = 0.87~1.12 (Examples 1→5), the tensile strength of the alloy steadily increases from 1477 MPa to 1624 MPa. Simultaneously, the coefficient of thermal expansion remains stable at α (20~230℃) ≤ 2.55 × 10⁻⁶. -6 / ℃, α (230~290℃)≤8.12×10 -6 The extremely low temperature of / ℃ demonstrates that precisely locking the solid solution elements using this equivalent formula can maximize the volume fraction of the strengthening phase and effectively eliminate the negative interference of multi-element additions on the Invar effect. The Invar alloy wire of this invention achieves an excellent synergy between ultra-high strength and low expansion coefficient. Based on precipitation kinetics and thermodynamic analysis, the underlying microstructure evolution mechanism is inferred as follows: During asynchronous aging, because the precipitation temperature and chemical driving force of NbC are significantly higher than those of VC and Mo2C, Nb atoms preferentially nucleate at high-energy interfaces such as dislocation crossover points, forming extremely fine nano-cores. With the extension of the holding time, V and Mo elements undergo epitaxial growth with this NbC core. This asynchronous nucleation and growth mechanism promotes the formation of a microscopic 'core-shell structure' or nanoscale composite precipitate phase (Nb-rich core, Mo and V-rich outer layer) inside the alloy. Compared with single carbides, this special composite structure has significantly higher thermal stability and stronger dislocation pinning ability, thus achieving a fundamental leap in alloy strength without destroying the Invar effect of the matrix.
[0055] 2. Synergistic enhancement mechanism of Nb and B: The NbC cores that precipitate first induce the dispersion growth of subsequent Mo-V carbides. In addition, the introduction of trace amounts of B forms "Nb-B atom pairs", which effectively reduces the interfacial energy between the precipitated phase and the matrix, and significantly alleviates the problem of drastic decrease in elongation under ultra-high strength (the elongation of Examples 1-5 all remained above 1.05%).
[0056] 3. Analysis of the Optimal Embodiment: Among them, Embodiment 3 (Ni=36.5wt%, C=0.30wt%, Mo=2.60wt%, V=0.55wt%, Nb=0.12wt%, B=0.0035wt%) exhibits the best overall performance matching: synergistic strength and plasticity: tensile strength reaches 1553MPa, which is in the ideal middle of the design range, and maintains a good elongation of 1.32%; excellent dimensional stability: the coefficient of thermal expansion at 20~230℃ is only 2.15×10⁻⁶. -6 / ℃, far below the industry standard (3.7×10 -6 The coefficient of thermal expansion at 230~290℃ is only 6.85×10⁻⁶℃. -6 / ℃, far below the industry standard (10×10). -6 / ℃); significant tissue refinement: Figure 2 and Figure 3 The metallographic microstructure and high-magnification scanning microstructure of the high-strength, low-expansion coefficient Invar alloy wire prepared in Example 3 show that the matrix grain size is only 2.1 μm and the nanophase distribution is extremely uniform.
[0057] This invention demonstrates that the core-shell nanophase structure constructed through an "aging precipitation" process, combined with precise compositional balance design, fully meets the composite requirements of "high strength, extremely low expansion, and excellent toughness" for high-capacity power transmission cables. Compared to the traditional C-Mo-V system, this invention achieves a fundamental leap in strength without sacrificing low expansion characteristics, exhibiting extremely high practical application value and technological leadership.
[0058] Finally, it should be noted that the embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
Claims
1. A method for preparing a high-strength, low-expansion coefficient Invar alloy wire, characterized in that, Includes the following steps: Raw materials meeting purity requirements are selected and formulated according to the following alloy composition ratio: by content percentage, C: 0.25%-0.32%, Mo: 1.8%-3.0%, V: 0.40%-0.70%, Nb: 0.08%-0.15%, B: 0.002%-0.005%, Si≤0.30%, Mn≤0.30%, S≤0.005%, P≤0.005%, O≤0.008%, N≤0.008%, Ni: 36.0%-37.0%, with the balance being Fe; The raw materials are smelted by vacuum induction melting and cast into alloy ingots under a protective atmosphere. The melting temperature is 1550-1600℃ and the refining time is 30-40 min. The alloy ingot is subjected to hot deformation treatment, primary cold deformation treatment, aging treatment, and secondary cold deformation treatment in sequence to obtain the Invar alloy wire. The temperature of the hot deformation treatment is 1180-1220℃, the cumulative deformation amount of the hot deformation treatment is 70-80%, the deformation amount of the primary cold deformation treatment is 55-75%, the aging treatment process is to hold at 600-640℃ for 6-10 hours, and the deformation amount of the secondary cold deformation treatment is 75-90%.
2. The method for preparing high-strength, low-expansion coefficient Invar alloy wire according to claim 1, characterized in that, The contents of C, Mo, V, and Nb in the alloy composition satisfy the following formula: 0.87≤K= ≤1.12， Where K is the carbide equivalent balance factor, and [C], [Mo], [V], and [Nb] are the contents of C, Mo, V, and Nb, respectively.
3. The method for preparing high-strength, low-expansion coefficient Invar alloy wire according to claim 1, characterized in that, Also includes: After the secondary cold deformation treatment, the Invar alloy wire is subjected to a stabilization treatment. The stabilization treatment process involves holding the wire at 250~280℃ for 1~2 hours, followed by air cooling to room temperature.
4. The method for preparing high-strength, low-expansion coefficient Invar alloy wire according to claim 1, characterized in that, After the heat preservation process is completed, the temperature is cooled to room temperature by water.
5. The method for preparing high-strength, low-expansion coefficient Invar alloy wire according to claim 1, characterized in that, The raw materials selected that meet the purity requirements include: Fe with a purity ≥ 99.95 wt%, Ni with a purity ≥ 99.98 wt%, Nb with a purity ≥ 99.95%, Mo with a purity ≥ 99.9 wt%, V with a purity ≥ 99.9 wt%, C with a purity ≥ 99.9%, Si with a purity ≥ 99.9%, Mn with a purity ≥ 99.9%, and B with a purity ≥ 99.9%.
6. A high-strength, low-expansion coefficient Invar alloy wire, characterized in that, It is prepared by any one of the preparation methods described in claims 1-5.
7. The high-strength, low-expansion coefficient Invar alloy wire according to claim 6, characterized in that, The matrix of the Invar alloy wire contains dispersed nano-precipitates containing Nb, Mo, V and C elements, and the average size of the nano-precipitates is 2~10 nm.
8. The high-strength, low-expansion coefficient Invar alloy wire according to claim 6, characterized in that, The Invar alloy wire has a tensile strength >1500MPa and an elongation >1%.
9. The high-strength, low-expansion coefficient Invar alloy wire according to claim 6, characterized in that, The grain size of the Invar alloy wire is <3µm.
10. The high-strength, low-expansion coefficient Invar alloy wire according to claim 6, characterized in that, The coefficient of thermal expansion of the Invar alloy wire is ≤2.55×10⁻⁶ at 20-230℃. -6 / ℃, the coefficient of thermal expansion at 230-290℃ is ≤8.12×10 -6 / ℃.