Wire rod, steel wire, and methods for manufacturing same

Abstract

The present invention relates to a high-manganese wire rod, a steel wire, and methods for manufacturing same and, more specifically, to a steel wire and a high-manganese wire rod for armor ensuring excellent non-magnetic properties due to having reduced surface quality deterioration and any increase in permeability being effectively suppressed, and methods for manufacturing same.

Description

Wire rod, steel wire and method of manufacturing the same

[0001] The present disclosure relates to high-manganese wire rods, steel wires, and methods for manufacturing the same, and more specifically, to high-manganese wire rods, steel wires, and methods for manufacturing the same that have excellent non-magnetic properties and are to be applied as steel wires for armor, such as submarine cables or pipes.

[0002] Submarine cables and pipelines are installed in the ocean to transmit intercontinental communications, transport electricity, and transport energy resources such as oil.

[0003] Since such submarine cables and pipelines are highly susceptible to physical damage from strong ocean currents or tides, high water pressure, complex seabed topography, and ship anchors, they are essentially equipped with armor on their outer casings to protect them from the external environment.

[0004] While various materials can be used for this armor, steel wire with strong corrosion resistance and durability is primarily used to maximize physical protection.

[0005] Conventionally, non-magnetic austenitic stainless steel was used as the steel wire for the armor of submarine cables to prevent magnetization caused by AC transmission, thereby reducing heat generation and transmission losses. However, in the case of such austenitic stainless steel, martensitic transformation occurs during processing, forming an excessive amount of ferromagnetic α'-martensite, and consequently, there is a disadvantage in that non-magnetism is significantly reduced.

[0006] To overcome these disadvantages, there have been attempts to suppress α'-martensite transformation by increasing the content of manganese (Mn), which stabilizes austenite; however, in this case, high-temperature ductility is low and impurities such as P (phosphorus) accumulate, increasing the crack sensitivity of the steel. In addition, problems may arise such as increased manufacturing costs and reduced price competitiveness due to the inclusion of more than 10 weight percent of expensive alloying elements such as Ni and Cr in the alloy composition.

[0007] As such, when the crack sensitivity of wire rods and steel wires increases, not only is the surface quality of the wire rod degraded during casting and hot rolling, but the surface quality of the steel wire is also significantly degraded during the drawing process of the wire rod, leading to an increase in permeability. Furthermore, due to deformations such as bending and warping of the cable that inevitably occur during the manufacturing, installation, and maintenance of submarine cables, the permeability increases further, which ultimately leads to a problem where the non-magnetic properties of the steel wire deteriorate.

[0008] Therefore, there is a need to develop stainless steel with excellent non-magnetic properties and surface quality.

[0009] One aspect of the present disclosure is to provide a high-manganese austenitic wire rod applicable as a steel wire for armor, a high-manganese wire rod and steel wire that maintain excellent non-magnetic properties by minimizing the deterioration of the surface quality of the steel wire and effectively suppressing the increase in permeability, and a method for manufacturing the same.

[0010] Another aspect of the present disclosure is to provide a high-manganese wire rod, a steel wire, and a method for manufacturing the same, which can effectively reduce the manufacturing costs of wire rods and steel wires by minimizing the content of expensive alloying elements such as Ni and Cr and increasing the content of relatively inexpensive alloying elements such as Mn and C.

[0011] The technical problems intended to be solved in this document are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this invention belongs from the description below.

[0012] A high-manganese wire according to one embodiment of the present disclosure comprises, in weight%, C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities, satisfies the following formula (1), comprises 95.0% or more of austenite in the microstructure, and may have a cross-sectional diameter of 5 mm to 8 mm.

[0013] Equation (1): [Mn]+33.514×[C]≥29 (where [Mn] is the weight% of Mn and [C] is the weight% of C)

[0014] In addition, a high-manganese wire according to one embodiment of the present disclosure may contain 0.50% or less of Cu and 0.50% or less of N in weight%.

[0015] In addition, a high-manganese wire according to one embodiment of the present disclosure has a relative permeability (μ r ) may be greater than 1.00 and less than 1.02.

[0016] In addition, a high-manganese wire according to one embodiment of the present disclosure may contain one or more of ε-martensite, α'-martensite, carbides, and inclusions in a microstructure of less than 5.0 area%.

[0017] In addition, a high-manganese steel wire according to one embodiment of the present disclosure may contain, in weight percent, C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities, satisfy the following formula (1), and may contain 95.0% or more of austenite in the microstructure, and may have a tensile strength of 600 MPa to 900 MPa.

[0018] Equation (1): [Mn]+33.514×[C]≥29 (where [Mn] is the weight% of Mn and [C] is the weight% of C)

[0019] In addition, the high-manganese steel wire according to one embodiment of the present disclosure may have an austenite average grain size of 10 μm to 30 μm.

[0020] In addition, the high-manganese steel wire according to one embodiment of the present disclosure may have a reduction in area (RA) of 40% or more.

[0021] In addition, a high-manganese steel wire according to one embodiment of the present disclosure has a relative permeability (μ r ) may be greater than 1.00 and less than 1.02.

[0022] In addition, a high-manganese steel wire according to one embodiment of the present disclosure may contain one or more of ε-martensite, α'-martensite, carbides, and inclusions in a microstructure of less than 5.0 area%.

[0023] In addition, a high-manganese steel wire according to one embodiment of the present disclosure may include a zinc plating layer.

[0024] In addition, a high-manganese steel wire according to one embodiment of the present disclosure may contain 0.50% or less of Cu and 0.50% or less of N in weight%.

[0025] In addition, a method for manufacturing a high-manganese wire rod according to one embodiment of the present disclosure may include: preparing a billet satisfying the following formula (1) and containing C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, and the remainder being Fe and unavoidable impurities; maintaining the billet at 1000°C to 1150°C for 120 minutes to 180 minutes; rolling the billet into a wire rod to form a cross-sectional diameter of 5mm to 8mm; coiling the wire rod at 750°C to 980°C after the wire rod rolling; and cooling the wire rod to 400°C or less at a cooling rate satisfying the following formula (2) after the coiling.

[0026] Equation (1): [Mn]+33.514×[C]≥29

[0027] Equation (2): Cooling rate after winding ≥ 15 × [C] + [Cr]

[0028] (Here, [Mn] represents the weight percentage of Mn, [C] represents the weight percentage of C, and [Cr] represents the weight percentage of Cr)

[0029] In addition, a method for manufacturing a high-manganese steel wire according to one embodiment of the present disclosure comprises the steps of: preparing a billet satisfying the following formula (1) and containing C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, and the remainder being Fe and unavoidable impurities; maintaining the billet at 1000°C to 1150°C for 120 minutes to 180 minutes; rolling the billet into a wire rod to form a cross-sectional diameter of 5 mm to 8 mm; and coiling the wire rod at 750°C to 980°C after the wire rod rolling. The method may include a step of manufacturing a high-manganese wire rod by cooling to 400°C or lower at a cooling rate satisfying the following equation (2) after the above-mentioned winding, and then manufacturing a steel wire by drawing the wire rod within 20% of the total drawing amount.

[0030] Equation (1): [Mn]+33.514×[C]≥29

[0031] Equation (2): Cooling rate after winding ≥ 15 × [C] + [Cr]

[0032] (Here, [Mn] represents the weight percentage of Mn, [C] represents the weight percentage of C, and [Cr] represents the weight percentage of Cr)

[0033] In addition, a method for manufacturing a high-manganese steel wire according to one embodiment of the present disclosure may include a heat treatment step of maintaining the wire at 800°C to 1000°C for a time satisfying the following equation (3) after the step of drawing the wire.

[0034] Equation (3): 170 - 0.15 × T ≤ heat treatment holding time ≤ 190 - 0.15 × T (where T is the heat treatment temperature (°C) and the unit of heat treatment holding time is minutes (min))

[0035] In addition, a method for manufacturing a high-manganese steel wire according to one embodiment of the present disclosure may include a quenching step after the heat treatment step.

[0036] In addition, a method for manufacturing a high-manganese steel wire according to one embodiment of the present disclosure may include a step of performing a plating treatment on the steel wire after the step of drawing the wire rod or the step of quenching.

[0037] In addition, in the method for manufacturing a high-manganese steel wire according to one embodiment of the present disclosure, the plating treatment may be performed in one or more of Zn and Zn-Al.

[0038] According to the present disclosure, by including manganese and carbon in an appropriate amount satisfying Equation (1) in the alloy composition of the wire rod and steel wire, the martensite transformation is minimized to effectively suppress the deterioration of the surface quality of the wire rod and steel wire, while maintaining a relative permeability of a preset appropriate range, thereby providing a wire rod and steel wire having excellent non-magnetism.

[0039] In addition, during the manufacturing process of wire rods and steel wires, the content of expensive alloying elements such as Ni and Cr is minimized, and the content of low-cost alloying elements such as C and Mn is increased, thereby effectively reducing total manufacturing costs and improving the price competitiveness of the product.

[0040] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below.

[0041] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0042] The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof.

[0043] Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense. For instance, singular expressions in this specification include plural expressions unless the context clearly indicates an exception.

[0044] Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0045] The present invention will be described in more detail below through examples. These examples are intended solely to explain the invention more specifically, and it will be obvious to those skilled in the art that the scope of the invention is not limited by these examples according to the gist of the invention.

[0046] Unless otherwise specifically stated in this specification, the % indicating the content of each element is based on weight.

[0047] Seonjae

[0048] First, a high-manganese wire according to the present disclosure will be described.

[0049] A wire rod according to one embodiment of the present disclosure comprises, in weight percent, C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities, and comprises 95.0% or more of austenite in the microstructure, and may have a cross-sectional diameter of 5 mm to 8 mm.

[0050] Hereinafter, the reason for the numerical limitation of the alloy component content in the embodiments of the present invention will be explained.

[0051] C (Carbon): 0.10 wt% or more, 0.40 wt% or less

[0052] Carbon (C) is an element that can most effectively increase strength while simultaneously enhancing the stability of austenite; a 0.1% increase in C results in a strength increase of 100 MPa. Furthermore, increasing the carbon content can reduce the Ms and Md temperatures at which austenite transforms into ε-martensite or α'-martensite during cooling. If the carbon content is less than 0.10 wt%, the austenite becomes unstable, which may lead to the formation of ε-martensite or α'-martensite during cooling or drawing, which affects the steel's relative permeability (μ). r The non-magnetic properties may be reduced by increasing the carbon content. In addition, if the carbon content exceeds 0.40 wt%, the strength of the steel increases excessively, and carbides are formed, which can drastically reduce the workability of the steel. Therefore, it is desirable to control the carbon content to 0.10 wt% or more and 0.40 wt% or less. More preferably, it may be 0.15 wt% or more and 0.35 wt% or less, and even more preferably, it may be 0.20 wt% or more and 0.30 wt% or less.

[0053] Si (Silicon): 0.20% or more, 1.00% or less

[0054] Silicon (Si) is a solid solution strengthening element that typically increases tensile strength to 14 MPa to 16 MPa when added at 0.1%, and it is an element that effectively suppresses internal oxidation of steel at high temperatures. If the Si content is less than 0.20 wt%, internal oxidation occurs due to heat during the steel manufacturing process, making it prone to cracking on the surface and potentially causing wire breakage during wire drawing. Furthermore, if the Si content exceeds 1.00 wt%, not only is the workability of the steel reduced due to excessive solid solution, but the surface quality may also deteriorate as oxides are formed along grain boundaries during the steel manufacturing process, potentially causing cracks on the surface. For the reasons mentioned above, the silicon (Si) content is preferably 0.20% or more and 1.00% or less, more preferably 0.40% or more and 0.80% or less, and even more preferably 0.50% to 0.70%.

[0055] Mn (Manganese): 18.00% or more, 26.00% or less

[0056] Manganese (Mn) is an effective element for stabilizing austenite, and if the Mn content is less than 18 wt%, ε-martensite is likely to form in steel with low carbon content. Since ε-martensite itself has non-magnetic properties similar to austenite, it does not significantly affect the relative permeability of the steel; however, because ε-martensite is a relatively metastable phase, it can easily transform into α'-martensite through plastic deformation such as drawing at room temperature, which can lead to reduced workability and a decrease in non-magnetic properties. Furthermore, if the Mn content exceeds 26 wt%, there is a problem of reduced productivity as manufacturing costs increase excessively compared to the degree of improvement in the material properties of the steel. In the present invention, it is preferable to control the Mn content to 18.00% or more and 26.00% or less, more preferably 20.00% or more and 24.00% or less, and even more preferably 21.00% or more and 23.00% or less.

[0057] Meanwhile, the manganese content can satisfy the following formula (1).

[0058] Equation (1): [Mn]+33.514×[C]≥29

[0059] In the above formula (1), [Mn] represents the weight percentage of Mn and [C] represents the weight percentage of C. When the relationship between the Mn content and the C content in formula (1) is less than 29, for the high-manganese wire rod and steel wire according to one embodiment of the present disclosure, a phase transformation may occur depending on the heat treatment conditions and the amount of drawing, which may increase the relative permeability of the steel and reduce non-magnetism.

[0060] Chrome (Cr): 1.00% or more, 5.00% or less

[0061] When an appropriate amount of chromium (Cr) is added, it contributes to austenite stabilization, thereby improving the impact toughness of the steel. It also dissolves into the austenite to exhibit solid solution strengthening effects, thereby improving the tensile strength of the steel while simultaneously improving the corrosion resistance of the steel. To achieve the target strength of the present invention, it is preferable that the Cr content be 1.00% or more and 5.00% or less. If the Cr content is less than 1.00 wt%, it is difficult to expect improvements in impact toughness, tensile strength, and corrosion resistance. If the Cr content exceeds 5.00 wt%, in the case of steel with a high carbon content, Cr-based carbides are formed at the austenite grain boundaries, increasing the risk of cracking. Therefore, it is preferable to limit the Cr content to 1.00% or more and 5.00% or less, more preferably 2.00% or more and 4.00% or less, and even more preferably 2.50% or more and 3.50% or less.

[0062] At this time, the high-manganese wire according to the present invention may optionally include the following elements in the alloy composition described above.

[0063] Cu (Copper): 0 or more, 0.50 wt% or less

[0064] Copper (Cu) increases stacking fault energy, facilitating slip and improving processability. Meanwhile, in the case of steel with a high carbon content, it suppresses carbon diffusion and effectively delays the growth of carbides, thereby increasing the dissolved carbon content and increasing tensile strength. When the Cu content exceeds 0.50 wt%, it suppresses the formation of carbides, which can result in increased tensile strength. In the present disclosure, the desired properties can be easily obtained even with a composition without adding Cu, but optionally, copper may be included in an amount of 0.50 wt% or less to improve formability without increasing tensile strength.

[0065] N (Nitrogen): 0 or more, 0.50 wt% or less

[0066] Nitrogen (N), like carbon, is an austenite-stabilizing element that improves the toughness of steel and effectively increases stacking fault energy to promote slip, thereby improving the formability of steel. In the present disclosure, the desired properties can be easily obtained even with a composition without adding N, but optionally, nitrogen may be included to enhance the austenite-stabilizing effect. In this case, if N is added excessively, nitrides may be formed, which can degrade the surface quality and formability of the steel, so the N content may be limited to 0.50% or less.

[0067] The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be incorporated during the conventional steel manufacturing process, they cannot be excluded. As these impurities are known to any skilled person in the conventional steel manufacturing process, all details thereof are not specifically mentioned in this specification.

[0068] Meanwhile, the microstructure of the above wire rod may contain 95.0% or more austenite in area percent. It is preferable that the microstructure of the above wire rod consists of a single austenite phase, and it is most preferable to have a microstructure consisting of 100% austenite phase in area fraction.

[0069] In addition, the microstructure of the above wire may contain one or more of ε-martensite (epsilon martensite), α'-martensite (alpha martensite), carbides, and inclusions in an area of ​​less than 5.0%.

[0070] At this time, ε-martensite (epsilon martensite) is a martensite structure having a hexagonal close-packed (HCP) crystal structure. As previously explained, it is a metastable phase, and when observed through EBSD analysis, it appears as a thin, plate-like form and tends to be aligned in a specific direction. This ε-martensite can easily transform into α'-martensite through plastic deformation, such as drawing, at room temperature.

[0071] The above α'-martensite (alpha martensite) has a crystal structure of body-centered tetragonal (BCT) or body-centered cubic (BCC) lattice and appears relatively block-like when observed through EBSD analysis. If the above α'-martensite is present in the microstructure, the workability of the wire may be reduced, and at the same time, the non-magnetic properties may also be reduced.

[0072] The above carbide is formed by the combination or precipitation of a metal element and carbon, and may include one or more of chromium carbides (Cr3C2, Cr7C3) and tungsten carbides (WC).

[0073] The above inclusions are impurity particles formed by the reaction of sulfur (S), oxygen (O2), nitrogen (N2), etc., with elements in the molten steel, and the above inclusions may include one or more of oxides, sulfides, nitrides, and composite inclusions combined therefrom.

[0074] That is, the high-manganese wire according to one embodiment of the present invention can effectively suppress the deterioration of processability and non-magnetic properties by suppressing martensite transformation through an alloy composition satisfying the above formula (1) and containing ε-martensite, α'-martensite, carbides, and inclusions in the microstructure at less than 5.0 area%.

[0075] In addition, the above wire has a relative permeability (μ r ) may be greater than 1.00 and less than 1.02.

[0076] At this time, the above permeability (μ) r ) is a physical property indicating how easily a magnetic field can pass through a material or how much a medium is magnetized with respect to a given magnetic field, and can be measured using Brockhaus’s Single Sheet Test, and the relative permeability (μ) r ) is the degree to which a magnetic field passes relative to a vacuum, and this relative permeability (μ r ) can be expressed as μ / μ0 (where μ is the permeability of the medium and μ0 is the permeability of vacuum). Generally, when this relative permeability is high, the magnetism of the material increases and non-magnetism tends to decrease.

[0077] In addition, the cross-sectional diameter of the above wire is preferably 5 mm to 8 mm, but is not limited thereto and can be appropriately set according to the application environment.

[0078] steel wire

[0079] Furthermore, a high-manganese steel wire according to one embodiment of the present disclosure may comprise, in weight percent, C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities.

[0080] At this time, similar to the wire material described above, in the alloy composition described above, the content of manganese and carbon can satisfy the following equation (1).

[0081] Equation (1): [Mn]+33.514×[C]≥29

[0082] In the above formula (1), [Mn] represents the weight percentage of Mn and [C] represents the weight percentage of C. As explained above, if the relationship between the Mn content and the C content in formula (1) is less than 29, then for the high-manganese steel wire according to one embodiment of the present disclosure, a phase transformation may occur depending on the heat treatment conditions and the amount of drawing, thereby increasing the relative permeability of the steel wire and decreasing non-magnetism.

[0083] In addition, the alloy composition described above may optionally include one or more of copper (Cu) and nitrogen (N) in an amount of 0 to 0.50 weight% each.

[0084] The microstructure of the above steel wire may contain 95.0% or more austenite in area %.

[0085] In addition, the microstructure of the above steel wire may contain one or more of ε-martensite, α'-martensite, carbides, and inclusions in an area of ​​less than 5.0%.

[0086] At this time, the area fraction of the metal structure and the average grain size of the high-manganese wire or steel wire can be measured by the following method. First, a specimen of length 10 mm is cut at a designated location on the wire or steel wire and embedded in resin. Then, the specimen is etched with Nital solution after alumina polishing, with the cut surface perpendicular to the longitudinal direction of the wire or steel wire. Subsequently, EBSD phase analysis is performed on a 4000 µm x 4000 µm area using a scanning electron microscope (SEM) to calculate the area fraction of the austenite structure and the average grain size.

[0087] The above steel wire preferably has an austenite average grain size (AGS) of 10㎛ or more and 30㎛ or less, and more preferably 15㎛ or more and 25㎛ or less.

[0088] In addition, the tensile strength of the steel wire measured at room temperature using a ZWICK Z250 tensile testing machine from Zwick / Roell may be 600 MPa or more and 900 MPa or less, preferably 630 MPa or more and 870 MPa or less, and more preferably 650 MPa or more and 850 MPa or less.

[0089] The above steel wire may have a reduction of area (RA, Reduction of Area) of 40% or more.

[0090] The cross-sectional reduction rate of the above steel wire is calculated based on the measured value obtained by performing a tensile test in the thickness direction (Z direction) of a JIS 13B size specimen at room temperature using a ZWICK Z250 tensile testing machine from Zwick / Roell. When the cross-sectional area of ​​the material before tensile (drawing) is A0 (mm²) and the cross-sectional area of ​​the material after final tensile (drawing) is A1 (mm²), the cross-sectional reduction rate RA (%) can be expressed as (A0-A1) / A0×100.

[0091] If the above cross-sectional reduction rate is less than 40%, the amount of deformation introduced into the steel is insufficient, making it difficult to refine the grain size; consequently, wire breakage may occur during the manufacture, installation, or operation of a cable using the above steel wire. If the cross-sectional reduction rate is 40% or more, sufficient deformation can be introduced through hot working to refine the grain size, and the above steel wire is desirable as the value of the wire breakage reduction rate increases.

[0092] In addition, the above steel wire has a relative permeability (μ r ) may be greater than 1.00 and less than 1.02.

[0093] As explained above, the relative permeability (μr ) can be derived from the permeability value measured using Brockhaus’s Single Sheet Test, which represents the degree of magnetic field passage relative to a vacuum. The above relative permeability (μ r As ) increases, the magnetism of the steel wire becomes stronger, while the non-magnetic properties weaken.

[0094] In addition, the steel wire may include a zinc plating layer on its surface. If the steel wire includes a zinc plating layer, its corrosion resistance to seawater is enhanced, so improved durability can be expected when applied as armor for submarine cables and / or pipes.

[0095] As such, the high-manganese steel wire according to the present disclosure, compared to conventional austenitic stainless steel wire for armor, exhibits excellent surface quality and excellent non-magnetism by satisfying a preset range of relative permeability through an alloy composition satisfying Equation (1), and also effectively reduces total manufacturing costs by minimizing expensive alloying elements during the manufacturing process compared to conventional high-manganese steel wire, and accordingly, can have excellent price competitiveness.

[0096] A method for manufacturing high-manganese wire rod and steel wire according to the present disclosure is as follows.

[0097] Method for manufacturing wire rods and steel wires

[0098] Hereinafter, an example of a method for manufacturing wire rods and steel wires according to the present invention will be described. However, the method for manufacturing wire rods and steel wires according to the present invention is not necessarily limited thereto.

[0099] A method for manufacturing a wire rod according to one embodiment of the present invention comprises, in weight%, a step of preparing a billet satisfying the following formula (1) and containing C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities, and maintaining the billet at 1000℃ to 1150℃ for 120 minutes to 180 minutes; a step of rolling the billet into a wire rod to form a cross-sectional diameter of 5mm to 8mm; a step of coiling at 750℃ to 980℃ after rolling the wire rod; and a step of cooling to 330℃ to 470℃ at a cooling rate satisfying the following formula (2) after coiling.

[0100] Equation (1): [Mn]+33.514×[C]≥29

[0101] Equation (2): Cooling rate after winding ≥ 15 × [C] + [Cr]

[0102] (Here, [Mn] represents the weight percentage of Mn, [C] represents the weight percentage of C, and [Cr] represents the weight percentage of Cr)

[0103] That is, the high-manganese wire rod according to the present invention can be manufactured by preparing a billet with an alloy composition satisfying the above-described formula (1), and then passing it through the processes of heating and holding, wire rod rolling, coiling, and cooling.

[0104] To examine this in detail, first, billet heating is a process of heating and maintaining the billet at a constant temperature by loading it into a furnace for producing wire rods, and it is preferable to maintain it at 1000℃ to 1150℃ for 120 minutes to 180 minutes.

[0105] The above temperature range is an austenite single-phase region. If it exceeds 1150°C, there is a risk that the austenite grains will be formed coarsely, and if it is less than 1000°C, there is a problem of reduced productivity due to the heating and holding process taking too long. Therefore, 1000°C to 1150°C is preferred, more preferably 1070°C to 1130°C, and even more preferably 1090°C to 1110°C.

[0106] In addition, if the time maintained in the above-described temperature range is less than 120 minutes, residual carbons, etc. in the billet may not be sufficiently dissolved, and if the above-described temperature range is maintained for a long time, productivity may be significantly reduced, so it is desirable to limit the upper limit of the heating and holding time to 180 minutes, and more preferably, it may be 130 minutes to 170 minutes.

[0107] At this time, the alloy composition of the billet may optionally include one or more of copper (Cu) and nitrogen (N) in an amount of 0 to 0.50% or less.

[0108] It is preferable to manufacture a wire rod having a cross-sectional diameter of 5 mm to 8 mm by rolling a billet heated and maintained under the conditions described above. At this time, the cross-sectional diameter of the wire rod is more preferably 5.3 mm to 7.8 mm, and even more preferably 5.5 mm to 7.5 mm.

[0109] The above wire rod rolling process can be carried out according to a conventional hot rolling process, and preferably, it is carried out at 950°C to 1100°C.

[0110] It is preferable to wind the wire produced according to the above-described process at 750°C to 980°C, and more preferably at 760°C to 970°C.

[0111] At this time, if the winding temperature is less than 750℃, the winding shape of the wire coil becomes poor during winding, which may have an adverse effect on workability, and if the winding temperature exceeds 980℃, the high-temperature exposure time is prolonged, leading to the formation of deteriorated structures such as decarburization on the surface, which may cause problems such as a decrease in physical properties.

[0112] After the above-described winding step, the high-manganese wire of the present invention can be manufactured by cooling to 330°C to 470°C in a Stelmor cooling zone, wherein the cooling rate of the wire after winding can satisfy the following equation (2).

[0113] Equation (2): Cooling rate after winding ≥ 15 × [C] + [Cr]

[0114] (Here, [Mn] represents the weight percentage of Mn, [C] represents the weight percentage of C, and [Cr] represents the weight percentage of Cr)

[0115] The cooling rate after winding of the wire satisfying the above equation (2) is controlled according to the carbon and chromium content of the high-manganese wire, which is independent of phase change, and if the cooling rate is excessively slow, chromium carbide (Cr) formed by the combination of carbon (C) and chromium (Cr) 23 This is to prevent the corrosion resistance of the wire rod from being reduced due to the precipitation of C6, etc.

[0116] The present invention can manufacture a high-manganese steel wire having target properties using a high-manganese wire produced by the manufacturing method described above.

[0117] In the method for manufacturing a high-manganese steel wire according to the present invention, it is preferable to draw the high-manganese wire rod, and after the step of drawing, one or more processes among heat treatment, quenching, or plating may be performed optionally.

[0118] To examine this in more detail, in the step of drawing the high-manganese wire rod produced by the above manufacturing method, it is desirable to process the wire rod such that the total amount of wire drawn is within 20%. More preferably, the total amount of wire drawn may be 10% to 20%, and even more preferably 13% to 17%.

[0119] If the total amount of wire drawing exceeds 20%, work hardening occurs rapidly due to twin deformation during wire drawing, so it is desirable that the upper limit of the total amount of wire drawing is 20%, and to achieve this, it is desirable that the wire drawing reduction rate per pass of the wire be limited to within 10%.

[0120] At this time, before drawing the wire, the wire can be prepared by pickling.

[0121] In addition, the above-mentioned wire has a scale layer on its surface, and in the method for manufacturing a steel wire according to the present invention, it is obvious that a process of removing the scale from the surface of the wire through a descaler that peels off the scale may be additionally performed before the wire passes through a wire drawing die for wire drawing.

[0122] Meanwhile, as previously described, after the above-described fresh processing, one or more processes among heat treatment, quenching, or plating may be performed optionally.

[0123] The above heat treatment is maintained at 800°C to 1000°C after drawing the wire rod, and the heat treatment holding time may satisfy the following equation (3).

[0124] Equation (3): 170 - 0.15 × T ≤ heat treatment holding time ≤ 190 - 0.15 × T

[0125] Here, T is the heat treatment temperature (°C), and the unit of the heat treatment holding time derived through the above equation (3) can be set to minutes (min).

[0126] At this time, if the heat treatment temperature is substituted into the above equation (3), the heat treatment holding time may be 20 to 70 minutes, and preferably 30 to 60 minutes.

[0127] The above heat treatment is a process for growing austenite grains to lower the tensile strength of the steel wire. If the heat treatment temperature is below 800°C or the time is less than 170-0.15×T, additional time is required to grow the grains, which increases manufacturing costs. If the heat treatment temperature exceeds 1000°C or the time exceeds 190-0.15×T, the tensile strength of the steel wire may be lowered and workability improved, but the grains become excessively coarse, the austenite phase becomes unstable, and ε-martensite transformation occurs over a wide area, which may increase relative permeability and decrease non-magnetism. Therefore, it is desirable to control the time to be below that level.

[0128] The above quenching is intended to rapidly cool the steel wire that has undergone the heat treatment to impart hardness, and water or oil, etc., may be used as a cooling medium.

[0129] The above plating treatment is intended to impart corrosion resistance to seawater for application as armor for submarine cables and / or pipes, and after the above drawing process, the steel wire may be plated with zinc (Zn) or zinc-aluminum (Zn-Al), etc. As the plating method, electrolytic plating, hot-dip plating, or thermal spray coating may be utilized, but is not limited thereto and may be plated in various ways.

[0130] In addition, the plating treatment of the above steel wire can be performed even after the heat treatment and quenching.

[0131] The high-manganese steel wire according to the present invention, manufactured by the method described above, has a microstructure containing an austenite phase of 95% or more in area fraction, a tensile strength of 600 MPa to 900 MPa, and satisfies a relative permeability greater than 1 and less than 1.02, thereby maintaining excellent surface quality and non-magnetic properties.

[0132] The present invention is to be explained in more detail through the following examples. However, the following examples are intended only to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention.

[0133] Examples

[0134] Steel having the alloy composition of Table 1 below was steeled in a converter, then cast into a bloom and rolled into a billet, or directly cast into a continuous casting billet to produce a billet with a cross-sectional area of ​​160x160 mm². Subsequently, it was maintained at a temperature of approximately 1050°C for 150 minutes in a wire rod heating furnace and rolled to a wire diameter of 6.0 mm through wire rod rolling under normal conditions. The coiling temperature was varied from 780 to 880°C, and then cooled to approximately 400°C by adjusting the airflow rate during Stelmor cooling so that the average cooling rate was 15×[C%]+[Cr%] or higher depending on the content of C and Cr.

[0135] As a result of measuring the microstructure of the wire rod manufactured as described above using an Electron Backscatter Diffraction Pattern Analyzer (EBSD) with the model name JSM 7200F, it was confirmed that the austenite was 95% or more and composed of some ε-martensite based on the area ratio of the C cross-section. In addition, the occurrence of cracks was indicated by checking whether cracks occurred on the surface when the cast billet was manufactured together with the value of Equation (1) ([Mn%]+33.514×[C%] value).

[0136] In addition, the relative permeability, which is the ratio of permeability in vacuum and atmosphere, was measured using the Ferromaster instrument from Stefan Mayer Instruments.

[0137] Classification Alloy Composition (Weight%) Wire Phase Fraction (%) Formula (1) Value (≥29) Crack Occurrence Relative Permeability C Si M N Cr Cu N Austenite Phase ε-Martensite Other Invention Example 1 0.1 20.9 2 5.5 1.5 200.00 4 99.8 0.2 0 29.5 No occurrence 1.00 1 Invention Example 2 0.2 10.6 8 23.4 2.5 800.00 5 99.9 0.1 0 30.4 No occurrence 1.00 2 Invention Example 3 0.3 30.4 2 20.1 2.7 100.00 4 10000 31.2 No occurrence 1.00 1 Invention Example 4 0.3 90.2 11 8. 43.9800.0051000031.5None 1.001Invention Example 50.370.4420.53.620.420.0061000032.9None 1.002Invention Example 60.290.6522.34.820.340.0071000032.0None 1.001Invention Example 70.130.5125.74.970.160.24999.90.1030.1None 1.002Invention Example 80.180.5324.61. 600.250.461000030.6None1.002ComparisonExample10.130.3822.10.6800.00594.15.9026.5None1.023ComparisonExample20.210.3219.90.7500.00594.25.8026.9None1.023ComparisonExample30.170.2918.20.8800.00690.79.3023.9None1.035ComparisonExample40.110.4524.40.780 0.45 10000 28.1 Occurrence 1.015 Comparative Example 50.1 10.3 225.1 0.5 200.5 4 10000 28.8 Occurrence 1.016 Comparative Example 60.2 11.1 325.3 6.1 100.00 6 10000 32.3 Occurrence 1.00 4 Comparative Example 70.3 30.1 326.1 6.2 10.6 30.00 4 10000 37.2 Occurrence 1.00 2 Comparative Example 80.2 30.4 723.1 6.2 100.00 5 10000 30.8 Occurrence 1.00 5

[0138] Table 1 shows the alloy composition and microstructure of Invention Examples 1 to 8 and Comparative Examples 1 to 8, the value of Equation (1) according to the alloy composition, whether surface cracks occur, and the relative permeability.

[0139] Looking at Table 1 above, it can be seen that Invention Examples 1 to 8 satisfy the alloy composition according to the present invention, but in the case of Comparative Examples, except for Comparative Examples 2 to 4, they have a composition different from the elemental content set in the present invention.

[0140] Based on this, when examining the microstructure of the wire, that is, the phase fraction, Inventive Examples 1 to 8 show an area fraction of the austenite phase of 99% or more and a fraction of the martensite and other phases of less than 5%, whereas Comparative Examples 1 to 3 show an austenite phase of less than 95% and a martensite of more than 5%, indicating that they have a relatively unstable austenite phase compared to the Inventive Examples.

[0141] In addition, the value of Equation (1) in Invention Examples 1 to 8 is 29 or higher, whereas the value of Comparative Examples 1 to 5 does not reach 29, and it can be seen that the alloy composition of the Comparative Examples does not satisfy Equation (1).

[0142] Accordingly, in the cracking status item of Table 1 above, unlike the inventive example in which no surface cracks occurred, Comparative Examples 4 to 8 all showed cracks, indicating poor surface quality. In addition, although Comparative Examples 1 to 4 did not show surface cracks, their relative permeability exceeded 1.02, so it can be predicted that they would exhibit relatively inferior non-magnetism when compared to the inventive example, which showed a relative permeability value of 1.001 to 1.002.

[0143] Next, Table 2 shows the changes in the average austenite grain size, tensile strength, and microstructure according to the heat treatment temperature and holding time for Invention Example 5 of Table 1 above.

[0144] Classification (Invention Example 5) Freshness Reduction Rate (%) Heat Treatment Conditions Cooling Method Austenite Average Grain Size (㎛) Tensile Strength (MPa) ε-Martensite Phase Fraction (%) Temperature (°C) Holding Time (min) Determination of Heat Treatment Conditions Pre-heat Treatment Post-heat Treatment Pre-heat Treatment Post-heat Treatment Pre-heat Treatment Post-heat Treatment Invention Example 5-a 16.5 800 30 hours Water Cooling 14.3 12.8 10 80 86 00 6.5 Invention Example 5-b 800 60 Satisfied 17.8 79 70.7 Invention Example 5-c 900 20 hours 14.9 820 5.8 Invention Example 5-d 900 40 Satisfied 21.4 77 81.2 Invention Example 5-e 1000 40 Satisfied 28.3 71 20.2 Invention Example 5-f 1000 60 hours Exceeded 36.7 68 37.1

[0145] As shown in Table 2, after 16.5% fresh processing of Invention Example 5, the tensile strength is 1080 MPa, the austenite grain size is 14.3 μm, and the ε-martensite phase fraction is measured to be 0%.

[0146] At this time, when examining the heat treatment temperature and holding time of each of the invention examples 5-a to 5-f, it is confirmed that while there is no problem with the heat treatment temperature, in the case of invention examples 5-a, 5-c, and 5-f, Equation (3) is not satisfied regarding the heat treatment holding time. Accordingly, in the case of 5-a, it can be seen that the austenite grain size after heat treatment is smaller than before heat treatment, and recrystallization and grain growth are not sufficiently achieved, and in the case of 5-f, it can be seen that the austenite grain size after heat treatment reaches 36.7 μm and the grains grow very coarsely.

[0147] In addition, in the case of Invention Examples 5-a, 5-c, and 5-f, it was found that the fraction of the ε-martensite phase after heat treatment exceeded 5%, so it can be easily predicted that it can be easily transformed into α'-martensite by plastic deformation such as drawing at room temperature, and accordingly, workability will be reduced and non-magnetic properties will also be reduced.

[0148] Through such a composition, the high-manganese wire and steel wire according to the present invention can effectively suppress the deterioration of the surface quality of the wire and steel wire by minimizing martensitic transformation through an alloy composition satisfying Equation (1) and containing appropriate amounts of manganese and carbon, while maintaining a preset appropriate range of relative permeability, thereby providing wire and steel wire with excellent surface quality and non-magnetism.

[0149] In addition, the method for manufacturing high-manganese wire rods and steel wires according to the present invention can improve the price competitiveness of products by effectively reducing total manufacturing costs through minimizing the content of expensive alloying elements such as Ni and Cr and increasing the content of low-cost alloying elements such as C and Mn.

[0150] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and concept of the claims set forth below.

Claims

1. In weight%, C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities, and Satisfying the following equation (1), The microstructure contains 95.0 area% or more of austenite, and Wire with a cross-sectional diameter of 5 mm to 8 mm. Equation (1): [Mn]+33.514×[C]≥29 (Here, [Mn] represents the weight percentage of Mn, and [C] represents the weight percentage of C) 2. In Claim 1, The above wire is, Cu 0.50 wt% or less, Wire rod containing 0.50 weight% or less of N.

3. In Claim 1, The above wire is, Relative Permeability (μ) r Wire that is greater than 1.00 and less than 1.

02.

4. In Claim 1, The above wire is, A wire rod containing one or more of ε-martensite, α'-martensite, carbides, and inclusions in a microstructure of less than 5.0 area%.

5. In wt%, C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities, and Satisfying the following equation (1), The microstructure contains 95.0 area% or more of austenite, and Steel wire having a tensile strength of 600 MPa to 900 MPa. Equation (1): [Mn]+33.514×[C]≥29 (Here, [Mn] represents the weight percentage of Mn, and [C] represents the weight percentage of C) 6. In Claim 5, The above steel wire is, Steel wire having an austenite average grain size of 10㎛ to 30㎛.

7. In Claim 5, The above steel wire is, Steel wire with a reduction in area (RA) of 40% or more.

8. In Claim 5, The above steel wire is, Relative Permeability (μ) r Steel wire, where ) is greater than 1.00 and less than 1.

02.

9. In Claim 5, The above steel wire is, Steel wire containing one or more of ε-martensite, α'-martensite, carbides, and inclusions in a microstructure of less than 5.0 area%.

10. In Claim 5, The above steel wire is, Cu 0.50 wt% or less, Steel wire containing 0.50 weight% or less of N.

11. In Claim 5, The above steel wire is, Steel wire containing a zinc plating layer.

12. In wt%, containing C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, and the remainder being Fe and unavoidable impurities, After preparing a billet that satisfies the following equation (1), A step of maintaining at 1000℃ to 1150℃ for 120 minutes to 180 minutes; A step of forming the above billet into a cross-sectional diameter of 5 mm to 8 mm by wire rolling; A step of coiling at 750°C to 980°C after the above wire rod rolling; and A method for manufacturing a wire rod, comprising the step of cooling to 400°C or lower at a cooling rate satisfying the following equation (2) after the above winding. Equation (1): [Mn]+33.514×[C]≥29 Equation (2): Cooling rate after winding ≥ 15 × [C] + [Cr] (Here, [Mn] represents the weight percentage of Mn, [C] represents the weight percentage of C, and [Cr] represents the weight percentage of Cr) 13. In wt%, C: 0.10% or more and 0.40% or less, Si: 0.20% or more and 1.00% or less, Mn: 18.00% or more and 26.00% or less, Cr: 1.00% or more and 5.00% or less, the remainder being Fe and unavoidable impurities, and After preparing a billet that satisfies the following equation (1), A step of maintaining at 1000℃ to 1150℃ for 120 minutes to 180 minutes; A step of forming the above billet into a cross-sectional diameter of 5 mm to 8 mm by wire rolling; A step of coiling at 750°C to 980°C after the above wire rolling; and After the step of manufacturing a high-manganese wire rod, the step of cooling to 400°C or lower at a cooling rate satisfying the following equation (2) after the above-mentioned winding; A step of manufacturing steel wire by drawing the above wire rod to a total drawing amount of within 20%; A method for manufacturing steel wire comprising Equation (1): [Mn]+33.514×[C]≥29 Equation (2): Cooling rate after winding ≥ 15 × [C] + [Cr] (Here, [Mn] represents the weight percentage of Mn, [C] represents the weight percentage of C, and [Cr] represents the weight percentage of Cr) 14. In Claim 13, After the step of drawing the above wire, A method for manufacturing a steel wire, comprising: a heat treatment step of maintaining the temperature at 800°C to 1000°C for a time satisfying the following equation (3). Equation (3): 170 - 0.15 × T ≤ heat treatment holding time ≤ 190 - 0.15 × T (where T is the heat treatment temperature (°C) and the unit of heat treatment holding time is minutes (min)) 15. In Claim 14, After the above heat treatment step, A method for manufacturing steel wire comprising a quenching step.

16. In claim 13 or claim 15, After the step of drawing the above wire or the step of quenching the above wire, A method for manufacturing a steel wire, comprising the step of performing a plating treatment.

17. In Claim 16, The above plating treatment is, A method for manufacturing steel wire, performed using one or more of Zn or Zn-Al.