Low-expansion high-torsion invar wire and method of making same

Abstract

The application discloses a low-expansion high-torsion invar alloy wire and a manufacturing method thereof, and relates to the technical field of low-expansion precision alloy materials. The low-expansion high-torsion invar alloy wire is composed of the following components: C: 0.15-0.30%; Mn: 0.20-0.50%; Si: 0.10-0.30%; Ni: 35.0-38.0%; Mo: 2.0-3.0%; V: 0.4-0.8%; Cr: 0.01-0.05%; Nb: 0.01-0.05%; W: 0.1-0.3%; S: <=0.02%; P: <=0.02%; and the balance of Fe and inevitable impurities. According to the scheme, chromium, niobium and tungsten are compounded and matched with molybdenum and vanadium, so that dispersed carbides are generated in the invar alloy wire to realize precipitation strengthening, and niobium refines grains and improves plasticity and toughness; and the elements are matched to stabilize austenite structure, and the strength and torsion bearing capacity of the alloy are synergistically improved.

Description

Technical Field

[0001] This application relates to the field of low-expansion precision alloy materials technology, and in particular to a low-expansion, high-torsion Invar alloy wire and its manufacturing method. Background Technology

[0002] Invar alloys are classic low-expansion precision alloys. They achieve stable low-expansion characteristics in the room-to-medium temperature range thanks to their nickel-iron matrix, and are widely used in precision cables, instrument components, and other fields. These applications place several performance requirements on Invar alloy wires, demanding not only a low coefficient of thermal expansion but also good strength and torsional properties.

[0003] Existing methods for strengthening Invar alloy wires are relatively limited, mostly relying on the addition of a single carbide-forming element or increasing the carbon content to improve material strength. Such strengthening methods tend to reduce the alloy's ductility and toughness, making it difficult to balance expansion properties and mechanical properties. Some alloy systems have simple element combinations that cannot simultaneously meet the stringent requirements for torsional performance in precision applications, leading to torsional failure in the finished materials and making it difficult to achieve a harmonious balance between low expansion characteristics and torsional mechanical properties. Summary of the Invention

[0004] The purpose of this application is to provide a low-expansion, high-torsion Invar alloy wire and its manufacturing method, aiming to solve the technical problem that existing Invar alloy wires are difficult to simultaneously achieve low expansion characteristics and high torsional performance.

[0005] To achieve the above objectives, this application provides a low-expansion, high-torsion Invar alloy wire, with the following chemical composition by mass percentage: C: 0.15–0.30%; Mn: 0.20–0.50%; Si: 0.10–0.30%; Ni: 35.0–38.0%; Mo: 2.0–3.0%; V: 0.4–0.8%; Cr: 0.01–0.05%; Nb: 0.01–0.05%; W: 0.1–0.3%; S: ≤0.02%; P: ≤0.02%; the balance being Fe and unavoidable impurities.

[0006] In some optional embodiments, the chemical composition, by mass percentage, further includes: Co: ≤0.2%; Cu: ≤0.1%.

[0007] In some alternative embodiments, the total mass percentage of the unavoidable impurities does not exceed 0.05%.

[0008] In some alternative embodiments, the matrix of the low-expansion, high-torsion Invar alloy wire contains dispersed carbide particles formed by Cr, Nb, W, and carbon.

[0009] In some alternative embodiments, the low-expansion, high-torsion Invar alloy wire has a matrix grain formed by Nb element refinement.

[0010] This application provides a method for preparing low-expansion, high-torsion Invar alloy wire, the method comprising: Complete the batching and smelting, ingot shaping and forging flaw detection to obtain qualified billets; The qualified billet is subjected to hot rolling, solution treatment, one-time cold drawing surface treatment and aging tempering to obtain a preformed billet. The obtained preformed billet is subjected to billet finishing and peeling and large deformation drawing to obtain low expansion and high torsion Invar alloy wire finished product.

[0011] In some optional embodiments, the process of batching and smelting, ingot shaping, and forging flaw detection is completed to obtain qualified billets, including: The low-expansion, high-torsion Invar alloy wire is prepared according to the chemical composition ratio, and alloy ingots are obtained by vacuum melting and casting. Argon gas is introduced in the later stage of vacuum melting to implement atmosphere protection. The alloy ingots are peeled, sawn, and forged into billets of predetermined specifications in sequence; The forged billets are subjected to flaw detection, and the billets with detected defects are repaired to obtain qualified billets.

[0012] In some optional embodiments, the obtained qualified billet is subjected to hot rolling, solution treatment, one-time cold drawing surface treatment, and aging and tempering treatment to obtain a preformed billet, including: The qualified billet is hot rolled, with the initial rolling temperature controlled at 1020-1070℃ and the final rolling temperature at 800-870℃, to obtain a coiled material with a diameter of 12-15 mm. The coiled material is kept at 950-1100℃ for 0.5 hours and then quenched. The oxide scale on the surface of the quenched material is removed and it is cold-drawn to a diameter of 9-10 mm. The cold-drawn billet is aged at 300-600℃ for 2 hours and then air-cooled to room temperature to obtain a preformed billet.

[0013] In some optional embodiments, the obtained preformed billet is subjected to billet finishing peeling and large deformation drawing to obtain a low-expansion, high-torsion Invar alloy wire product, including: The preformed blank is peeled to remove the surface oxide scale and surface defects. The stripped billet is cold-drawn, and the cold-drawing deformation is controlled to be greater than 70%. The billet is processed to a diameter of 3.0 to 5.5 mm to obtain a low-expansion, high-torsion Invar alloy wire product.

[0014] The above-mentioned technical solution of this application has at least the following beneficial technical effects: The technical solution of this application, by compounding trace amounts of chromium, niobium, and tungsten into nickel-iron Invar alloy, and with the synergistic effect of molybdenum and vanadium, can form dispersed carbides in the Invar alloy matrix, which is conducive to precipitation strengthening to improve the strength of Invar alloy wire. Niobium can refine the grain of Invar alloy matrix, which is beneficial to improving the plasticity and toughness of Invar alloy wire. The proportions of each component are well matched, which can stabilize the austenitic matrix structure of the alloy and help maintain the low expansion characteristics of Invar alloy wire. The precise matching of each element synergistically regulates the matrix structure and precipitated phases, so that the Invar alloy wire can significantly improve the matrix strength and torsional bearing capacity while maintaining excellent low expansion performance. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of an embodiment of the method for preparing low-expansion, high-torsion Invar alloy wire provided in this application. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of this application. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0017] The embodiments described in this application are only some, not all, of the embodiments described herein. All other embodiments obtained by those skilled in the art based on the embodiments described herein without inventive effort are within the scope of protection of this application.

[0018] Invar alloys are classic low-expansion precision alloys. They achieve stable low-expansion characteristics in the room-to-medium temperature range thanks to their nickel-iron matrix, and are widely used in precision cables, instrument components, and other fields. These applications place several performance requirements on Invar alloy wires, demanding not only a low coefficient of thermal expansion but also good strength and torsional properties.

[0019] Existing methods for strengthening Invar alloy wires are relatively limited, mostly relying on the addition of a single carbide-forming element or increasing the carbon content to improve material strength. Such strengthening methods tend to reduce the alloy's ductility and toughness, making it difficult to balance expansion properties and mechanical properties. Some alloy systems have simple element combinations that cannot simultaneously meet the stringent requirements for torsional performance in precision applications, leading to torsional failure in the finished materials and making it difficult to achieve a harmonious balance between low expansion characteristics and torsional mechanical properties.

[0020] To address the aforementioned technical problems, this application provides a low-expansion, high-torsion Invar alloy wire.

[0021] The technical solution of this application, by compounding trace amounts of chromium, niobium, and tungsten into nickel-iron Invar alloy, and with the synergistic effect of molybdenum and vanadium, can form dispersed carbides in the Invar alloy matrix, which is conducive to precipitation strengthening to improve the strength of Invar alloy wire. Niobium can refine the grain of Invar alloy matrix, which is beneficial to improving the plasticity and toughness of Invar alloy wire. The proportions of each component are well matched, which can stabilize the austenitic matrix structure of the alloy and help maintain the low expansion characteristics of Invar alloy wire. The precise matching of each element synergistically regulates the matrix structure and precipitated phases, so that the Invar alloy wire can significantly improve the matrix strength and torsional bearing capacity while maintaining excellent low expansion performance.

[0022] In some alternative embodiments, the chemical composition of the Invar alloy wire, by mass percentage, is as follows: C: 0.15–0.30%; Mn: 0.20–0.50%; Si: 0.10–0.30%; Ni: 35.0–38.0%; Mo: 2.0–3.0%; V: 0.4–0.8%; Cr: 0.01–0.05%; Nb: 0.01–0.05%; W: 0.1–0.3%; S: ≤0.02%; P: ≤0.02%; the balance being Fe and unavoidable impurities.

[0023] In this embodiment, molybdenum and vanadium are strong carbide-forming elements, preferentially combining with carbon to precipitate carbides in the Invar alloy wire, playing a preliminary precipitation strengthening role. Chromium, niobium, and tungsten can form more stable dispersed carbides with carbon. Niobium has a significant grain-refining effect, inhibiting the high-temperature growth of austenite grains; chromium and tungsten can dissolve into the matrix and carbides, improving the stability of the precipitated phase.

[0024] By controlling Cr to 0.01–0.05%, a small amount of chromium dissolves in the austenitic matrix and participates in the construction of composite carbides, improving the interfacial bonding strength between carbides and the matrix and inhibiting carbide coarsening. By controlling Nb to 0.01–0.05%, niobium preferentially forms nanoscale niobium carbides, which pin grain boundaries during hot working and continuously hinder austenitic grain growth. By controlling W to 0.1–0.3%, tungsten strengthens the matrix and improves the thermal stability of carbides, weakening the tendency of precipitate aggregation and growth during the aging stage. By controlling Mo to 2.0–3.0%, molybdenum strengthens austenite and forms molybdenum carbides with carbon, supplementing the precipitation strengthening effect. By controlling V to 0.4–0.8%, vanadium easily forms fine vanadium carbides, which precipitate uniformly within the grains, filling the strengthening gaps between Cr and Nb precipitates. The above content ranges work together to promote the multi-scale dispersion of various carbides, simultaneously achieving grain boundary strengthening and intragranular precipitation strengthening.

[0025] If Cr and Nb are below 0.01% and W is below 0.1%, it is difficult to form sufficient dispersed carbides, resulting in insufficient grain refinement. If Cr and Nb are above 0.05% and W is above 0.3%, coarse carbides are easily formed, inducing stress concentration and impairing the alloy's torsional properties. Mo values ​​are 2.0–3.0% and V values ​​are 0.4–0.8%. If the content is too low, the strengthening effect is insufficient; if the content is too high, continuous carbides are easily formed, disrupting the continuity of the matrix and increasing the alloy's coefficient of thermal expansion.

[0026] The five elements are matched in proportion, the carbides are dispersed and the grain size is controllable, and the austenitic matrix is ​​stabilized. While ensuring the low expansion characteristics of the alloy, the strength and torsional load-bearing capacity are improved.

[0027] Optionally, C can be 0.15%, 0.19%, 0.22%, 0.26%, 0.30%, etc., or any value between the above values.

[0028] Optionally, Mn can be 0.20%, 0.28%, 0.35%, 0.42%, 0.50%, etc., or any value between the above values.

[0029] Optionally, Si can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, etc., or any value between the above values.

[0030] Optionally, Ni can be 35.0%, 35.8%, 36.5%, 37.2%, 38.0%, etc., or any value between the above values.

[0031] Optionally, Mo can be 2.0%, 2.25%, 2.5%, 2.75%, 3.0%, etc., or any value between the above values.

[0032] Optionally, V can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., or any value between the above values.

[0033] Optionally, Cr can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, or any value between the above values.

[0034] Optionally, Nb can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc., or any value between the above values.

[0035] Optionally, W can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc., or any value between the above values.

[0036] Optionally, S can be 0.005%, 0.010%, 0.013%, 0.016%, 0.020%, etc., or any value between the above values.

[0037] Optionally, P can be 0.004%, 0.009%, 0.012%, 0.017%, 0.020%, etc., or any value between the above values.

[0038] In some optional embodiments, the chemical composition, by mass percentage, further includes: Co: ≤0.2%; Cu: ≤0.1%.

[0039] Optionally, Co can be 0%, 0.05%, 0.10%, 0.15%, 0.20%, etc., or any value between the above values.

[0040] Optionally, Cu can be 0%, 0.025%, 0.050%, 0.075%, 0.10%, etc., or any value between the above values.

[0041] In some alternative embodiments, the total mass percentage of unavoidable impurities does not exceed 0.05%.

[0042] Optionally, the total unavoidable impurity content can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc., or any value between the above values.

[0043] In some optional embodiments, the matrix of the Invar alloy wire contains dispersed carbide particles formed by Cr, Nb, W and carbon, which helps to create multiple obstacles to dislocation movement and enhance the matrix's ability to resist plastic deformation.

[0044] In some alternative embodiments, the Invar alloy wire has matrix grains refined by Nb elements, which can suppress austenite grain growth, reduce grain size, shorten crack propagation paths, and improve the alloy's ability to withstand alternating torsional deformation.

[0045] This application provides a method for preparing low-expansion, high-torsion Invar alloy wire. This method is used to prepare the low-expansion, high-torsion Invar alloy wire described above, and includes the following steps: Step S1: Complete the batching and smelting, ingot shaping and forging flaw detection to obtain qualified billets; In some optional embodiments, step S1 further includes the following specific steps: Step S11: Prepare the alloy ingots according to the chemical composition ratio of low expansion and high torsion Invar alloy wire, melt and cast them using a vacuum melting process, and introduce argon gas for atmosphere protection in the later stage of vacuum melting. Step S12: The alloy ingot is peeled, sawn, and forged into a billet of a preset size in sequence; Step S13: Perform flaw detection on the forged billet, and repair the billet with detected defects to obtain a qualified billet.

[0046] Step S2: The obtained qualified billet is subjected to hot rolling, solution treatment, one-time cold drawing surface treatment and aging tempering to obtain a preformed billet; In some optional embodiments, step S2 further includes the following specific steps: Step S21: Hot rolling is performed on qualified billets, with the initial rolling temperature controlled at 1020-1070℃ and the final rolling temperature at 800-870℃, to obtain coiled material with a diameter of 12-15 mm. Optionally, the initial rolling temperature can be 1020℃, 1032℃, 1045℃, 1058℃, 1070℃, etc., or any value between the above values.

[0047] Optionally, the final rolling temperature can be 800℃, 818℃, 835℃, 852℃, 870℃, or any value between the above values.

[0048] Optionally, the diameter of the coiled material can be 12 mm, 12.8 mm, 13.5 mm, 14.2 mm, 15 mm, or any value between the above.

[0049] Step S22: Place the coiled material in an environment of 950-1100℃ for 0.5h and then quench it. Remove the oxide scale from the surface of the quenched blank and cold draw it to a diameter of 9-10 mm. Optionally, the solution treatment temperature can be 950℃, 988℃, 1025℃, 1062℃, 1100℃, or any value between the above values.

[0050] Optionally, the diameter of the cold-drawn billet can be 9 mm, 9.25 mm, 9.5 mm, 9.75 mm, 10 mm, or any value between the above.

[0051] Step S23: The cold-drawn billet is kept at 300-600℃ for 2 hours for aging treatment, and then air-cooled to room temperature to obtain a preformed billet.

[0052] Optionally, the aging temperature can be 300℃, 375℃, 450℃, 525℃, 600℃, or any value between the above values.

[0053] Step S3: Perform finishing and peeling of the obtained preformed billet and large deformation drawing process to obtain low expansion and high torsion Invar alloy wire finished product.

[0054] In some optional embodiments, step S3 includes the following specific steps: Step S31: Peel the preformed blank to remove surface oxide scale and surface defects; Step S32: Perform cold drawing on the stripped billet, controlling the cold drawing deformation to be greater than 70%, and process the billet to a diameter of 3.0 to 5.5 mm to obtain a low-expansion, high-torsion Invar alloy wire finished product.

[0055] Optionally, the cold drawing deformation amount can be 72%, 76%, 80%, 84%, 88%, etc., or any value between the above values.

[0056] Optionally, the diameter of the finished billet can be 3.0 mm, 3.6 mm, 4.2 mm, 4.8 mm, 5.5 mm, or any value between the above.

[0057] Example 1 A low-expansion, high-torsion Invar alloy wire, with the following chemical composition by mass percentage: C: 0.223%; Mn: 0.27%; Si: 0.20%; Ni: 36.68%; Mo: 2.50%; V: 0.60%; Co: 0.12%; Cu: 0.055%; Cr: 0.03%; Nb: 0.03%; W: 0.20%; S: 0.012%; P: 0.010%; the balance being Fe and unavoidable impurities, with the total mass percentage of impurities ≤ 0.05%.

[0058] The preparation method of the above-mentioned low-expansion, high-torsion Invar alloy wire includes the following steps: 1) Batching and smelting: Batchute according to the above chemical composition ratio, and smelt in a vacuum furnace. The vacuum degree is controlled at 2.5 Pa. Argon gas is introduced for protection in the later stage of smelting. After the alloy ingot is demolded, the billet is peeled and sawn to remove the surface oxide scale and defects. 2) Forging inspection: The billet processed in step 1) is forged into a diameter of 65 mm. After forging, the billet is inspected for defects. The billet with defects is sawed and ground to obtain qualified billet. 3) Hot rolling and solution treatment: The billet obtained in step 2) is hot rolled into a 14 mm diameter coil. The initial rolling temperature is 1040℃, and the final rolling temperature is 835℃. After hot rolling, the coil is placed in a heat treatment furnace and held at 1025℃ for 0.5 h before water quenching. 4) Cold drawing and surface treatment: The blank obtained in step 3) is surface treated by peeling process, and then cold drawn to a diameter of 9.5 mm; 5) Aging treatment: Place the billet with a diameter of 9.5 mm in an aging furnace and hold it at 450℃ for 2 hours for aging treatment. After aging, air cool to room temperature. 6) Finished product drawing: The aged billet is surface treated again by peeling process, and then cold drawn to a diameter of 4.2 mm with a cold drawing deformation of 78%, to obtain low expansion and high torsion Invar alloy wire finished product.

[0059] Example 2 A low-expansion, high-torsion Invar alloy wire, with the following chemical composition by mass percentage: C: 0.30%; Mn: 0.50%; Si: 0.30%; Ni: 38.0%; Mo: 3.0%; V: 0.80%; Co: 0.20%; Cu: 0.10%; Cr: 0.05%; Nb: 0.05%; W: 0.30%; S: 0.020%; P: 0.020%; the balance being Fe and unavoidable impurities, with the total mass percentage of impurities ≤ 0.05%.

[0060] The preparation method of the above-mentioned low-expansion, high-torsion Invar alloy wire includes the following steps: 1) Batching and smelting: Batchute according to the above chemical composition ratio, and smelt in a vacuum furnace. The vacuum degree is controlled at 2.5 Pa. Argon gas is introduced for protection in the later stage of smelting. After the alloy ingot is demolded, the billet is peeled and sawn to remove the surface oxide scale and defects. 2) Forging inspection: The billet processed in step 1) is forged into a diameter of 65 mm. After forging, the billet is inspected for defects. The billet with defects is sawed and ground to obtain qualified billet. 3) Hot rolling and solution treatment: The billet obtained in step 2) is hot rolled into a 15 mm diameter coil. The initial rolling temperature is 1070℃, and the final rolling temperature is 870℃. After hot rolling, the coil is placed in a heat treatment furnace and held at 1100℃ for 0.5 h before water quenching. 4) Cold drawing and surface treatment: The blank obtained in step 3) is surface treated by peeling process, and then cold drawn to a diameter of 10 mm; 5) Aging treatment: Place the billet with a diameter of 10 mm in an aging furnace and hold it at 600℃ for 2 hours for aging treatment. After aging, air cool to room temperature. 6) Finished product drawing: The aged billet is surface treated again by peeling process, and then cold drawn to a diameter of 5.5 mm with a cold drawing deformation of 88%, to obtain low expansion and high torsion Invar alloy wire finished product.

[0061] Example 3 A low-expansion, high-torsion Invar alloy wire, with the following chemical composition by mass percentage: C: 0.15%; Mn: 0.20%; Si: 0.10%; Ni: 35.0%; Mo: 2.0%; V: 0.40%; Co: 0%; Cu: 0%; Cr: 0.01%; Nb: 0.01%; W: 0.10%; S: 0.005%; P: 0.004%; the balance being Fe and unavoidable impurities, with the total mass percentage of impurities ≤ 0.05%.

[0062] The preparation method of the above-mentioned low-expansion, high-torsion Invar alloy wire includes the following steps: 1) Batching and smelting: Batchute according to the above chemical composition ratio, and smelt in a vacuum furnace. The vacuum degree is controlled at 2.5 Pa. Argon gas is introduced for protection in the later stage of smelting. After the alloy ingot is demolded, the billet is peeled and sawn to remove the surface oxide scale and defects. 2) Forging inspection: The billet processed in step 1) is forged into a diameter of 65 mm. After forging, the billet is inspected for defects. The billet with defects is sawed and ground to obtain qualified billet. 3) Hot rolling and solution treatment: The billet obtained in step 2) is hot rolled into a 12 mm diameter coil. The initial rolling temperature is 1020℃, and the final rolling temperature is 800℃. After hot rolling, the coil is placed in a heat treatment furnace and held at 950℃ for 0.5 h before water quenching. 4) Cold drawing and surface treatment: The blank obtained in step 3) is surface treated by peeling process, and then cold drawn to a diameter of 9 mm; 5) Aging treatment: Place the billet with a diameter of 9 mm in an aging furnace and hold it at 300℃ for 2 hours for aging treatment. After aging, air cool to room temperature. 6) Finished product drawing: The aged billet is surface treated by pickling, and then cold-drawn to a diameter of 3.0 mm with a cold drawing deformation of 60%, to obtain low expansion and high torsion Invar alloy wire finished product.

[0063] Comparative Example 1 A low-expansion, high-torsion Invar alloy wire has the following chemical composition by mass percentage: C: 0.29%; Mn: 0.50%; Si: 0.20%; Ni: 36.5%; Mo: 2.4%; V: 0.6%; Co: 0.18%; Cu: 0.08%, with the balance being Fe and unavoidable impurities. The composition system does not contain Cr, Nb, or W elements. The preparation process is consistent with that of Example 1.

[0064] Table 1: Summary of parameters for Examples 1-3 and Comparative Examples Note: In Table 1, "none" means that the corresponding element is not added to the alloy formula; "-" means that no quantitative constraint conditions are set for this component in the sample.

[0065] Table 2: Summary of test results for Examples 1-3 and the comparative examples As shown in Table 2, the low-expansion, high-torsion Invar alloy wire prepared in Example 1 has a tensile strength of 1148 MPa, a yield strength of 1098 MPa, an elongation of 9.0%, a conductivity of 2.26% IACS, a torsion cycle of 83 times, and a coefficient of thermal expansion of 15~230℃. The grain size is 11.5 grade. This embodiment uses intermediate components and suitable processes within the scope of this application. Cr, Nb, and W form dispersed carbides and refine the austenite grains. Combined with peeling process, 78% cold drawing deformation, and aging treatment at 450℃, the microstructure is uniform and stable, and all properties meet the preset indicators, achieving a synergistic match of high strength, good plasticity, low expansion and high torsional performance.

[0066] The low-expansion, high-torsion Invar alloy wire prepared in Example 2 has a tensile strength of 1091 MPa, a yield strength of 1051 MPa, an elongation of 14%, a conductivity of 2.31% IACS, a torsion resistance of 35 times, and a coefficient of thermal expansion of 15–230 °C. The grain size is grade 10.5. In this embodiment, the upper limit of the component selection range was selected, and the upper limit of the process temperature of 600°C was selected. The high aging temperature promotes the coarsening of precipitated particles and weakens the dispersion strengthening effect. Although the strength index barely meets the standard, the grain growth reduces the resistance to alternating deformation, and the torsion cycle is less than 60 times, which cannot meet the application requirements.

[0067] The low-expansion, high-torsion Invar alloy wire prepared in Example 3 has a tensile strength of 1105 MPa, a yield strength of 1076 MPa, an elongation of 7.2%, a conductivity of 2.33% IACS, a torsion cycle of 12 times, and a coefficient of thermal expansion of 15~230℃. The grain size is grade 11. In this embodiment, the composition was selected from the lower limit of the range. Acid pickling was used instead of peeling during the finished product drawing stage, and the cold drawing deformation was only 60%, failing to meet the requirement of greater than 70%. Microscopic defects remain on the surface of the wire, and the work hardening caused by cold deformation is insufficient. Stress concentration easily occurs under load, significantly deteriorating torsional performance and failing to meet the usage standards.

[0068] The low-expansion, high-torsion Invar alloy wire prepared in Comparative Example 1 has a tensile strength of 1015 MPa, a yield strength of 965 MPa, an elongation of 10.5%, a conductivity of 2.33% IACS, a torsion cycle of 5 times, and a coefficient of thermal expansion of 15–230 °C. The grain size ranges from 8.0 to 11.0. This alloy does not contain Cr, Nb, or W, and lacks grain refinement and dispersion strengthening mechanisms. The matrix strength cannot meet the lower limit requirement, the stability of the austenitic structure decreases, the coefficient of thermal expansion exceeds the limit, the microstructure uniformity is poor, and the torsional performance is severely inadequate.

[0069] The test results above show that by adding Cr, Nb, and W elements in a reasonable ratio, combined with appropriate aging temperature, peeling surface treatment, and a cold drawing deformation of more than 70% of the finished product, this application can control the grain size and precipitate distribution inside the alloy, and achieve a synergistic balance of low expansion, high strength and high torsional performance. The lack of any key technical feature will cause some key performance indicators to fail to meet the application requirements.

[0070] This application aims to protect a low-expansion, high-torsion Invar alloy wire and its manufacturing method. By compounding trace amounts of chromium, niobium, and tungsten into nickel-iron Invar alloy wire, and with the synergistic effect of molybdenum and vanadium, dispersed carbides can be formed in the Invar alloy matrix, which is beneficial for precipitation strengthening to improve the strength of the Invar alloy wire. Niobium can refine the grains of the Invar alloy matrix, which is beneficial for improving the plasticity and toughness of the Invar alloy wire. The proportions of each component are well matched, which can stabilize the austenitic matrix structure of the alloy and help maintain the low expansion characteristics of the Invar alloy wire. The precise matching of each element synergistically regulates the matrix structure and precipitated phases, so that the Invar alloy wire can significantly improve the matrix strength and torsional load-bearing capacity while maintaining excellent low expansion performance.

[0071] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of this application and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of this application should be included within the protection scope of this application. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A low-expansion, high-torsion Invar alloy wire, characterized in that, The chemical composition, by mass percentage, is as follows: C: 0.15–0.30%; Mn: 0.20–0.50%; Si: 0.10–0.30%; Ni: 35.0–38.0%; Mo: 2.0–3.0%; V: 0.4–0.8%; Cr: 0.01–0.05%. Nb ：0.01～0.05%； W：0.1～0.3%； S: ≤0.02%; P: ≤0.02%; balance is Fe and unavoidable impurities.

2. The low-expansion, high-torsion Invar alloy wire according to claim 1, characterized in that, The chemical composition, by mass percentage, also includes: Co: ≤0.2%; Cu: ≤0.1%.

3. The low-expansion, high-torsion Invar alloy wire according to claim 1, characterized in that, The total mass percentage of the unavoidable impurities shall not exceed 0.05%.

4. The low-expansion, high-torsion Invar alloy wire according to claim 1, characterized in that, The matrix of the low-expansion, high-torsion Invar alloy wire contains dispersed carbide particles formed by Cr, Nb, W, and carbon.

5. The low-expansion, high-torsion Invar alloy wire according to claim 1, characterized in that, The low-expansion, high-torsion Invar alloy wire has a matrix grain formed by Nb element refinement.

6. A method for preparing low-expansion, high-torsion Invar alloy wire, wherein the method is used to prepare low-expansion, high-torsion Invar alloy wire as described in any one of claims 1 to 5, characterized in that, The method for preparing the low-expansion, high-torsion Invar alloy wire includes: Complete the batching and smelting, ingot shaping and forging flaw detection to obtain qualified billets; The qualified billet is subjected to hot rolling, solution treatment, one-time cold drawing surface treatment and aging tempering to obtain a preformed billet. The obtained preformed billet is subjected to billet finishing and peeling and large deformation drawing to obtain low expansion and high torsion Invar alloy wire finished product.

7. The method for preparing low-expansion, high-torsion Invar alloy wire according to claim 6, characterized in that, The process of batching and smelting, ingot shaping, and forging flaw detection is completed to obtain qualified billets, including: The low-expansion, high-torsion Invar alloy wire is prepared according to the chemical composition ratio, and alloy ingots are obtained by vacuum melting and casting. Argon gas is introduced in the later stage of vacuum melting to implement atmosphere protection. The alloy ingots are peeled, sawn, and forged into billets of predetermined specifications in sequence; The forged billets are subjected to flaw detection, and the billets with detected defects are repaired to obtain qualified billets.

8. The method for preparing low-expansion, high-torsion Invar alloy wire according to claim 7, characterized in that, The obtained qualified billets are subjected to hot rolling, solution treatment, one-time cold drawing surface treatment, and aging and tempering treatment to obtain pre-formed billets, including: The qualified billet is hot rolled, with the initial rolling temperature controlled at 1020-1070℃ and the final rolling temperature at 800-870℃, to obtain a coiled material with a diameter of 12-15 mm. The coiled material is kept at 950-1100℃ for 0.5 hours and then quenched. The oxide scale on the surface of the quenched material is removed and it is cold-drawn to a diameter of 9-10 mm. The cold-drawn billet is aged at 300-600℃ for 2 hours and then air-cooled to room temperature to obtain a preformed billet.

9. The method for preparing low-expansion, high-torsion Invar alloy wire according to claim 8, characterized in that, The obtained preformed billet is subjected to billet finishing, peeling, and large deformation drawing processes to produce low-expansion, high-torsion Invar alloy wire products, including: The preformed blank is peeled to remove the surface oxide scale and surface defects. The stripped blank is cold-drawn, and the cold-drawing deformation is controlled to be greater than 70%. The blank is processed to a diameter of 3.0 to 5.5 mm to obtain a low-expansion, high-torsion Invar alloy wire product.

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