High-strength wire rod having non-magnetic properties and method for manufacturing same

Abstract

The present disclosure relates to a wire rod used as a material for a core wire for a power line, and more particularly, to a wire rod having both high strength and non-magnetic properties, and a method for manufacturing the same.

Description

[0001] This application is a divisional application of the Chinese patent application with the application date of October 6, 2020, the application number of “202080070032.2”, and the invention name of “High-strength wire rod having non-magnetic characteristics and manufacturing method thereof”, and the original application is the Chinese national stage application of international application PCT / KR2020 / 013577. TECHNICAL FIELD

[0002] The present disclosure relates to a wire rod used as a material for a core wire for a power line, and more particularly, to a wire rod having high strength and non-magnetic characteristics and a manufacturing method thereof. BACKGROUND

[0003] A domestic or foreign power line is formed of a double structure in which, on the outside of the power line, an aluminum (Al) or aluminum alloy wire is used for power transmission, and, at the center of the power line, a steel wire, an invar wire, or a composite material wire is used to maintain rigidity.

[0004] Power transmission is performed by suspending a power line between a power pole and a steel tower, and during power transmission, the temperature of the transmission line increases due to resistance and electromagnetic induction (induction from the core wire side), thereby causing the power line to sag. This phenomenon is called “sag”.

[0005] In addition, since heat generation in the transmission line eventually causes power loss, the global trend focuses on the development of rigidity to exhibit low sag characteristics and non-magnetic properties.

[0006] The core wire for power transmission currently used is manufactured by adopting a high-strength carbon steel wire, an invar / invar alloy wire, or a composite material wire, and in the application of these materials, there are advantages and disadvantages as follows:

[0007] (1) The high-strength carbon steel wire is the most widely used material due to its high strength and low price, but due to the magnetic properties of carbon steel, temperature increase and power loss caused by electromagnetic induction are generated thereby. In addition, its thermal expansion coefficient is at the level of 11 × 10 -6 / ℃ to 14 × 10 -6 / ℃, thereby causing serious sag.

[0008] (2) In order to compensate for the disadvantages of the carbon steel wire as described above, invar (36% Ni) and invar alloy have been developed and partially applied, and in particular, the low thermal expansion coefficient (0.2 × 10 -6 / ℃ to 5 × 10 -6However, the invar steel and invar steel alloy exhibit ferromagnetic properties at or below the Curie temperature (about 230°C), so that electromagnetic induction phenomena are very common compared to the case of using a carbon steel wire. Therefore, power loss is high compared to the case of using a power line using a carbon steel wire, and in addition, a large amount of expensive nickel (Ni) is added, thereby causing an economic disadvantage.

[0009] (3) As a composite wire developed by using only the advantages of high-strength carbon steel wire and invar steel and invar steel alloy, a wire rod is manufactured using carbon fiber, ceramic, plastic, etc., and then applied. The thermal expansion coefficient of the composite wire is lower than or equal to the thermal expansion coefficient of the invar steel wire. In addition, electromagnetic induction phenomena do not occur due to the non-magnetic properties, so that power loss is at a very low level, and thus, the composite wire can be a core wire having the best properties. However, the cost is very high, so that there is a limitation in applying the wire.

[0010] Therefore, there is a need to develop a material exhibiting non-magnetic properties suitable as a material for a core wire for a power line, showing low sagging properties and a low thermal expansion coefficient, and being economically advantageous.

[0011] (Patent Document 1): Korean Patent Registration No. 10-0361969

[0012] (Patent Document 2): Korean Patent Registration No. 10-0507904 SUMMARY

[0013] TECHNICAL PROBLEM

[0014] An aspect of the present disclosure is to provide a wire rod suitable as a material for a core wire for a power line and having high strength, non-magnetic properties, and a low thermal expansion coefficient, and a manufacturing method thereof.

[0015] The object of the present disclosure is not limited to the above description. The object of the present disclosure will be understood from the entire content of the present specification, and those skilled in the art to which the present disclosure pertains will have no difficulty understanding additional objects of the present disclosure.

[0016] TECHNICAL SOLUTION

[0017] According to an aspect of the present disclosure, a non-magnetic wire rod contains, by weight: 27% to 42% of manganese (Mn), 0.35% or less (excluding 0%) of carbon (C), 0.5% or less of silicon (Si), 0.03% or less of phosphorus (P), and 0.03% or less of sulfur (S), and Fe and other inevitable impurities in the balance, wherein the Néel temperature of the wire rod is higher than 150°C.

[0018] According to another aspect of the present disclosure, a method for manufacturing a non-magnetic wire includes: preparing a steel piece or ingot including, by weight, 27% to 42% of manganese (Mn), 0.35% or less (excluding 0%) of carbon (C), 0.5% or less of silicon (Si), 0.03% or less of phosphorus (P), and 0.03% or less of sulfur (S), and a balance of Fe and other unavoidable impurities; heat-treating the steel piece or ingot at a temperature range of 1000°C to 1250°C to manufacture a billet; and subjecting the billet to wire rolling at a temperature range of 800°C to 1250°C to manufacture a wire, wherein a Neel temperature of the wire is higher than 150°C.

[0019] Advantageous Effects

[0020] As described above, according to one exemplary embodiment in the present disclosure, a wire having high strength and non-magnetic properties without using expensive elements or materials and showing low sagging properties is provided, which is economically advantageous. In addition, the wire of the present disclosure can be appropriately used as a material for a core wire of a power line. DETAILED DESCRIPTION

[0021] The present inventors identified limitations of existing materials used as a core wire of a power line and conducted intensive research to develop a material showing high strength, non-magnetic properties, and low sagging properties at a low cost.

[0022] Accordingly, manganese (Mn) was identified for providing a wire as a target material, thereby greatly reducing manufacturing costs and providing a high-strength wire. In particular, it was identified that due to excellent non-magnetic properties, the present disclosure can have an effect of greatly reducing power loss when used in a practical environment, and a wire showing low sagging properties due to a low coefficient of thermal expansion was provided, thereby completing the present disclosure.

[0023] Hereinafter, the present disclosure will be described in detail.

[0024] The non-magnetic wire according to one exemplary embodiment in the present disclosure can include, by weight, 27% to 42% of manganese (Mn), 0.35% or less (excluding 0%) of carbon (C), 0.5% or less of silicon (Si), 0.03% or less of phosphorus (P), and 0.03% or less of sulfur (S).

[0025] Hereinafter, reasons for limiting the alloy composition of the wire provided in the present disclosure as described above will be described in detail.

[0026] Meanwhile, unless otherwise specifically stated in the present disclosure, the content of each element is by weight, and the ratio of the structure is by area.

[0027] Manganese (Mn): 27% to 42%

[0028] Since manganese (Mn) shows a stable austenite structure at a higher content, it promotes wire drawing of the wire. When Mn is added in an amount of 25% or more, this effect can be obtained, but in this case, the Neel temperature of the wire decreases to less than 150°C and does not reach 150°C, which is a continuous use temperature of a power line (for example, a heat-resistant aluminum power line), making it difficult to apply the wire to actual use.

[0029] That is, a material having a Mn content level of 25% shows a low Neel temperature and tends to expand with a coefficient of thermal expansion of more than 20 x 10 -6 / °C due to a paramagnetic effect at or above the Neel temperature, and thus, it is difficult to manufacture a wire suitable for a core wire for a power line from the alloy system.

[0030] In consideration of the fact, Mn can be included in 27% or more in the present disclosure. However, when the content is greater than 42%, the Neel temperature is rather decreased, and the Mn content is increased, and thus, the manufacturing cost is increased.

[0031] Therefore, Mn can be included in 27% to 42% in the present disclosure.

[0032] Carbon (C): 0.35% or less (excluding 0%)

[0033] Carbon (C) is an element that is advantageous to improve austenite stabilization, and improves wire drawing properties of the wire. In addition, since carbon (C) has an excellent strength improvement effect, it can be added in order to secure the strength of steel including a certain amount or more of Mn.

[0034] However, when C is excessively added, the coefficient of thermal expansion of the wire tends to rapidly increase, and thus, in consideration of the fact, the content can be limited to 0.35% or less and excluding 0%.

[0035] Silicon (Si): 0.5% or less

[0036] Silicon (Si) is an element that is inevitably added in the process of deoxidation and dephosphorization of steel. When added, Si does not have a special influence on the physical properties of the wire, but it is advantageous to reduce the content if possible. Specifically, since Si can be included up to 0.5% in processes such as deoxidation and dephosphorization, the content thereof can be limited to 0.5% or less.

[0037] Phosphorus (P): 0.03% or less and sulfur (S): 0.03% or less

[0038] Phosphorus (P) and sulfur (S) are impurities that are inevitably introduced during the manufacturing process of steel, and when their contents are greater than 0.03%, respectively, cracks occur during continuous casting and ingot casting. Therefore, it is necessary to control the contents of P and S to 0.03% or less.

[0039] As described above, the wire of the present disclosure can be manufactured by only containing a certain amount of Mn and C and controlling the contents of impurity elements. However, for the purpose of further improving the physical properties of the wire, niobium (Nb) can also be contained.

[0040] Niobium (Nb): 3.5% or less

[0041] When added in a certain amount, niobium (Nb) is effective in reducing the thermal expansion coefficient of the wire, and can have a strength improvement effect by forming Nb carbide.

[0042] However, when the content of Nb is greater than 3.5%, the wire tends to be brittle due to improved strength, and thus the content can be limited to 3.5% or less.

[0043] The remaining component of the present disclosure is iron (Fe). However, since in the common manufacturing process, unintended impurities can be inevitably introduced from raw materials or the surrounding environment, it can not be possible to exclude the component. Since these impurities are known to any person skilled in the common manufacturing process, the entire content thereof is not particularly mentioned in the present specification.

[0044] The non-magnetic wire of the present disclosure having the above-described alloy composition can contain an austenite single-phase structure as a microstructure, and by having such an austenite single-phase structure, it can maintain non-magnetic even when receiving external energy.

[0045] In particular, due to the optimization of the alloy composition, the non-magnetic wire of the present disclosure has an austenite phase with high stability, and thus the wire of the present disclosure can have the characteristics of a relative magnetic permeability of 1.05 μ or less and a thermal expansion coefficient at room temperature of 10 x 10 -6 / ℃ or less.

[0046] The energy loss of materials exposed to electromagnetic fields induced by eddy currents is closely related to the material's magnetism. Eddy current generation increases with increasing magnetism, leading to increased energy loss. Generally, magnetism is proportional to permeability (μ). That is, magnetism increases with increasing permeability. Permeability is defined as the ratio of the induced magnetic field (B) to the magnetic field (H), defined by the equation μ = B / H. In other words, as permeability decreases, the material's magnetism decreases, and therefore, when the material is exposed to an electric field, energy loss due to eddy currents on the surface is prevented to increase energy efficiency. Therefore, it is advantageous to use non-magnetic wires with low coefficients of thermal expansion as the core material for electric power lines to prevent energy loss and ensure low sag characteristics.

[0047] Furthermore, since the non-magnetic wires disclosed herein have a Nel temperature higher than 150°C, they can be appropriately used as core wires for power lines.

[0048] Here, the Nell temperature refers to the temperature at which a paramagnetic material becomes an antiferromagnetic material, and it means that the higher the temperature, the wider the temperature range at which magnetostriction occurs.

[0049] In the following, a method for manufacturing non-magnetic wire according to another exemplary embodiment of the present disclosure will be described in detail.

[0050] First, a billet can be manufactured by preparing a steel part or ingot that meets the above alloy composition and then heat-treating the steel part or ingot at a temperature range of 1000°C to 1250°C.

[0051] When the temperature is below 1000℃ during heat treatment, the resistance to thermal deformation increases, which reduces productivity. However, when the temperature is above 1250℃, the grains may become coarser, which reduces toughness.

[0052] Heat-treated billets can be rolled into wire rods to obtain wire.

[0053] Here, wire rod rolling is performed as hot rolling, and can be carried out in a temperature range of 800°C to 1250°C. When the temperature is below 800°C in hot rolling, the load increases during rolling and the resistance to deformation may increase, but when the temperature is above 1250°C, the grains may become excessively coarsened, thereby reducing toughness.

[0054] After hot rolling as described above, it is cooled to room temperature to obtain wire with the desired microstructure and mechanical properties.

[0055] Here, since cooling can depend on the conditions applied in the manufacturing process of common wires, there are no particular limitations on cooling in this disclosure, and any person skilled in the art can easily perform cooling. However, by way of example, cooling can be performed as water cooling at a cooling rate of 5°C / second or greater.

[0056] The final wire manufactured using the alloy composition and manufacturing conditions proposed in this disclosure has a highly stable austenitic phase as its microstructure, thereby ensuring excellent non-magnetic properties and having a low coefficient of thermal expansion and high strength.

[0057] The present disclosure will be specifically described below through the following embodiments. However, it should be noted that the following embodiments are only used to illustrate the present disclosure in detail by way of example and are not intended to limit the scope of the claims. This is because the scope of the claims is determined by the matters described in the claims and the matters reasonably inferred from them.

[0058] (Example)

[0059] Prepare an ingot with the alloy composition shown in Table 1 below, and then heat it at 1200°C to produce a billet. Immediately after heating, hot roll the billet to a diameter of 8 mm at 800°C to 1200°C, and then water cool it at a cooling rate of 5°C / second or greater to produce a wire with a diameter of 8 mm.

[0060] Subsequently, the mechanical properties of each wire (Nell temperature, coefficient of thermal expansion, and relative permeability) were measured.

[0061] The Nell temperature of each wire was derived using the Thermo-Calc program, and the coefficient of thermal expansion was measured using dilatometry. Furthermore, the relative permeability, as the ratio of permeability in vacuum to that in air, was measured using a Ferromaster instrument purchased from Stefan Mayer Instruments. The values ​​of each physical property are shown in Table 2 below.

[0062] Meanwhile, carbon steel wire (KS D 3559 HSWR 67A) and Invar alloy (36% Ni), which have been used as materials for power lines, were prepared for comparison, and their mechanical properties were measured in the same manner. The results are shown.

[0063] [Table 1]

[0064]

[0065] [Table 2]

[0066]

[0067] It was found that carbon steel wire (Conventional Example 1), used as a material for power lines, has a high relative permeability, resulting in low non-magnetic properties, and that the coefficient of thermal expansion is relatively high.

[0068] Invar alloy wire with 36% nickel (Conventional Example 2) has the lowest coefficient of thermal expansion but very high relative permeability and exhibits a Curie temperature of 230°C.

[0069] As mentioned above, carbon steel wire generates a lot of heat during use due to the high coefficient of thermal expansion and high magnetic permeability of carbon, causing sag and resulting in high power loss. Meanwhile, Invar alloys are advantageous in terms of sag due to their excellent coefficient of thermal expansion, but their magnetic permeability is 8 to 9 times that of carbon steel, and they also exhibit a large amount of heat generation, resulting in high power loss.

[0070] Comparative Examples 1 and 2, containing 25% manganese (Mn), have Nell temperatures below 150°C, limiting their practical applications. It was determined that although the coefficient of thermal expansion is relatively high, the microstructure, formed by austenite with a large amount of manganese, significantly improves the magnetic permeability.

[0071] Meanwhile, it was found that the Invention Examples 1 to 12, which contain 27% or more manganese (Mn), have a Nel temperature of 150°C or higher, a much lower coefficient of thermal expansion compared to conventional carbon steel wire, and an excellent relative permeability of 1.05 or less, thus exhibiting excellent nonmagnetic properties.

[0072] Considering the results, as the Mn content in the wire increases, the Nell temperature rises, and at this temperature (Nell temperature) or lower, volume changes due to electromagnetic properties occur, which offset thermal expansion and thus reduce the coefficient of thermal expansion.

[0073] In particular, when Mn is contained in steel at 27% or more, the coefficient of thermal expansion at room temperature decreases to 10 × 10⁻⁶. -6 / ℃ or lower. In addition, Invar and Invar alloys exhibit ferromagnetic properties at Curie temperature or lower, but unlike Invar and Invar alloys, the wires of this disclosure exhibit antiferromagnetic properties at Nell temperature or lower to obtain nonmagnetic properties.

[0074] Furthermore, the wire disclosed herein allows for the manufacture of high-strength steel wire through the austenitic work hardening effect during wire drawing.

[0075] As an example, the tensile strength of a wire with a diameter of 8 mm (Example 1 of the invention) is about 600 MPa, but when it is drawn to a diameter of 6 mm, the tensile strength increases to 1300 MPa. Furthermore, when it is drawn to a diameter of 4 mm, the tensile strength increases to 1700 MPa, and when it is drawn to a diameter of 3 mm, the tensile strength increases to 2100 MPa.

[0076] Therefore, the wire of this disclosure can have significantly improved tensile strength by increasing the amount of processing, but shows a trend toward reduced toughness and higher strength, and thus the target stiffness can be matched by heat treatment between manufacturing processes.

[0077] Currently, since materials with tensile strengths of 1300 MPa or greater are used as materials for power lines, and even tensile strengths as high as 2100 MPa are applied, the wires of this disclosure can be subjected to wire drawing by adjusting the amount of processing and the number of heat treatments so that the physical properties of the wires are matched with those required for actual use, and then applied.

[0078] This application also includes the following aspects:

[0079] 1. A non-magnetic high-strength wire, comprising, by weight: 27% to 42% manganese (Mn), 0.35% or less and excluding 0% carbon (C), 0.5% or less silicon (Si), 0.03% or less phosphorus (P), and 0.03% or less sulfur (S), with the balance being Fe and other unavoidable impurities.

[0080] The Nel temperature of the wire is above 150°C.

[0081] 2. The non-magnetic high-strength wire according to aspect 1 further comprises: 3.5% or less niobium (Nb).

[0082] 3. The non-magnetic high-strength wire according to aspect 1, wherein the wire comprises an austenitic single-phase structure as its microstructure.

[0083] 4. The non-magnetic high-strength wire according to aspect 1, wherein the coefficient of thermal expansion of the wire at room temperature is 10 × 10⁻⁶. -6 / ℃ or less.

[0084] 5. The non-magnetic high-strength wire according to aspect 1, wherein the relative permeability of the wire is 1.05 μ or less.

[0085] 6. A method for manufacturing non-magnetic high-strength wire, the method comprising:

[0086] Prepare steel parts or ingots containing, by weight: 27% to 42% manganese (Mn), 0.35% or less and excluding 0% carbon (C), 0.5% or less silicon (Si), 0.03% or less phosphorus (P), and 0.03% or less sulfur (S), with the balance being Fe and other unavoidable impurities.

[0087] The steel part or the steel ingot is heat-treated in a temperature range of 1000°C to 1250°C to produce a billet, and

[0088] The billet is subjected to wire rolling in a temperature range of 800°C to 1250°C to produce wire.

[0089] The Nel temperature of the wire is above 150°C.

[0090] 7. The method for manufacturing non-magnetic high-strength wire according to aspect 6, wherein the steel component or the steel ingot further contains 3.5% or less niobium (Nb).

Claims

1. A non-magnetic high-strength wire, comprising, by weight: 27% to 42% manganese (Mn), 0.35% or less and excluding 0% carbon (C), 0.5% or less silicon (Si), 0.03% or less phosphorus (P), and 0.03% or less sulfur (S), with the balance being Fe and other unavoidable impurities. The Nel temperature of the wire is above 150°C, and The wire described therein has a diameter.

2. The non-magnetic high-strength wire according to claim 1 further comprises: 3.5% or less niobium (Nb).

3. The non-magnetic high-strength wire according to claim 1, wherein the wire comprises an austenitic single-phase microstructure.

4. The non-magnetic high-strength wire according to claim 1, wherein the coefficient of thermal expansion of the wire at room temperature is 9.8 × 10⁻⁶. -6 / ℃ or less.

5. The non-magnetic high-strength wire according to claim 1, wherein the relative permeability of the wire is 1.05 μ or less.

6. A method for manufacturing non-magnetic high-strength wire, the method comprising: Prepare steel parts or ingots containing, by weight: 27% to 42% manganese (Mn), 0.35% or less and excluding 0% carbon (C), 0.5% or less silicon (Si), 0.03% or less phosphorus (P), and 0.03% or less sulfur (S), with the balance being Fe and other unavoidable impurities. The steel part or the steel ingot is heat-treated in a temperature range of 1000°C to 1250°C to produce a billet, and The billet is subjected to wire rolling in a temperature range of 800°C to 1250°C to produce wire. The Nel temperature of the wire is above 150°C.

7. The method for manufacturing non-magnetic high-strength wire according to claim 6, wherein the steel part or the steel ingot further contains 3.5% or less niobium (Nb).

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