Soft magnetic wire rod, steel wire, and method for manufacturing same

Abstract

The soft magnetic wire rod according to the present invention comprises, in wt%: 0.0001-0.0300% of C; 0.001-3.000% of Si; 0.001-0.500% of Mn; 0.001-0.100% of Al; 0.0001-0.0080% of P; 0.0001-0.0070% of S; 0.0001-0.0070% of N; and the balance of Fe and other inevitable impurities, satisfies formula (1) below, has a cross-sectional hardness of 201 HV or less as a Vickers hardness value, and has a hardness deviation between a center part and a surface layer part of 30 HV or less. Formula (1): 70 ≤ HVmax − (218[C] + 34[Si] + 25[Mn]) ≤ 155 (wherein HVmax is the maximum value among the cross-sectional hardness values, and [C], [Si], and [Mn] are the wt% of each element)

Description

Soft magnetic wire, steel wire and method of manufacturing the same

[0001] The present invention relates to a soft magnetic wire, a steel wire, and a method for manufacturing the same.

[0002] Recently, reducing the use of fossil fuels and efficiently utilizing generated electrical energy have become global issues in order to conserve energy and prevent global warming. Since most of the electrical energy currently produced is consumed by electric motors, increasing motor efficiency is essential for the efficient use of electricity.

[0003] Motors rotate an axis by utilizing the attractive and repulsive forces generated between the magnetic flux generated in the stator and the magnetic flux of the magnet attached to the rotor. Depending on the direction in which the magnetic flux is formed within, motors can be classified into radial flux motors and axial flux motors.

[0004] In a dual axial flux motor, the stator and rotor are arranged parallel to each other along the rotational axis, creating an air gap along the axial direction, which in turn forms the magnetic flux along the axial direction. Due to this structure, axial flux motors allow for a larger rotor diameter compared to radial motors, making them suitable for applications requiring high torque.

[0005] To use wire for the stator or rotor of an axial motor, hot-rolled wire is drawn to a predetermined diameter and then heat-treated to homogenize the microstructure and impart electromagnetic properties. Subsequently, the wire must be cut to a specific length; however, if the cut surface is not flat or burrs are generated after cutting, the electromagnetic properties obtained through heat treatment are degraded, leading to a significant decrease in performance. Burrs are thin, fin-shaped excess parts generated during the processing of metals, and if wire containing burrs is used in a motor, iron losses increase or magnetic flux density decreases. Therefore, if burrs are generated during cutting, separate operations such as grinding are required to remove them, which leads to increased manufacturing costs.

[0006] One aspect of the present invention for solving the aforementioned problem is to provide a soft magnetic wire, a steel wire, and a method for manufacturing the same, which are suitable for use as a stator or rotor of an axial motor by improving cutability.

[0007] The technical problems 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.

[0008] To achieve the above objective, a soft magnetic wire according to one embodiment of the present invention comprises, in weight%, C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, and the remainder being Fe and other unavoidable impurities. The wire satisfies the following formula (1), and the hardness of the cross section is 201 HV or less in Vickers hardness value, and the hardness difference between the center and the surface layer may be 30 HV or less.

[0009] Equation (1): 70 ≤ HVmax - (218[C] + 34[Si] + 25[Mn]) ≤ 155

[0010] (Here, HVmax is the maximum value among the cross-sectional hardness values, and [C], [Si], and [Mn] are the weight percent of each element)

[0011] The microstructure of the wire according to one embodiment of the present invention may include ferrite with an area fraction of 99% or more.

[0012] A soft magnetic steel wire according to one embodiment of the present invention comprises, in weight%, C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, the remainder being Fe and other unavoidable impurities, and the hardness of the cross-section is 220 HV or less in terms of Vickers hardness, and the hardness difference between the center and the surface layer may be 9 HV or less.

[0013] According to one embodiment of the present invention, the length of the plastically deformed portion of the steel wire when cut may be 25% or less of the diameter.

[0014] The steel wire according to one embodiment of the present invention may have a magnetic flux density of 1.76T or more.

[0015] According to one embodiment of the present invention, the steel wire may have a shear band number density of 1.0 band / mm² or less.

[0016] The microstructure of the steel wire according to one embodiment of the present invention may contain ferrite with an area fraction of 99% or more.

[0017] A method for manufacturing a soft magnetic steel wire according to one embodiment of the present invention comprises the steps of: preparing a wire rod satisfying the formula (1), comprising, in weight%, C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, and the remainder being Fe and other unavoidable impurities; and drawing the wire rod at room temperature with a reduction rate of 59~93% so that the number density of shear bands is 11.4 bands / mm² or more. and may include an annealing heat treatment step of heating the fresh wire at (A1-110)℃~(A1+200)℃ and maintaining it for at least 10 minutes.

[0018] According to one embodiment of the present invention, the wire may have a cross-sectional hardness of 201 HV or less as a Vickers hardness value, and a hardness difference between the center and the surface layer may be 30 HV or less.

[0019] The fresh wire according to one embodiment of the present invention may have a shear band count of 11.4 or more.

[0020] According to one embodiment of the present invention, the annealed heat-treated steel wire may have a cross-sectional hardness of 220 HV or less as a Vickers hardness value, and a hardness difference between the center and the surface layer may be 9 HV or less.

[0021] According to one embodiment of the present invention, the length of the plastically deformed portion of the steel wire when cut may be 25% or less of the diameter.

[0022] The annealed heat-treated steel wire according to one embodiment of the present invention may have a shear band number density of 1.0 bands / mm² or less.

[0023] The annealed heat-treated steel wire according to one embodiment of the present invention may have a magnetic flux density of 1.76T or higher.

[0024] According to the present invention, a soft magnetic wire, a steel wire, and a method for manufacturing the same can be provided, which are suitable for use as a stator or rotor of an axial motor by improving cutability.

[0025] The effects obtainable from the present invention 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 invention belongs from the description below.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The cutting performance of steel is closely related to mechanical properties, particularly strength and hardness. Since soft magnetic wire rods do not have as high a strength as general carbon steel, the detailed explanation of this invention will focus on hardness. Generally, as hardness increases, the occurrence of burrs decreases, thereby improving cutting performance; conversely, if hardness is low, ductility or malleability increases, making burr formation easier. Therefore, to obtain a soft magnetic wire rod with excellent cutting performance, the wire rod must possess a hardness of at least a certain level. Meanwhile, the hardness of the cross-section increases due to cutting deformation during cutting. At this time, the hardness of the surface layer increases more significantly than that of the center of the material, and this increase in hardness causes a reduction in the lifespan of the cutting tool.

[0031] In other words, to improve the cutability of soft magnetic wire, the hardness must be increased; however, since an excessive increase can actually reduce the lifespan of the cutting tool, an appropriate level of increase is required.

[0032] Accordingly, the present invention aims to provide a soft magnetic wire and steel wire with excellent cutability by controlling the alloy composition to adjust the hardness of the wire cross-section to an appropriate level while simultaneously reducing the hardness variation between the center and the surface layer.

[0033] A soft magnetic wire according to one embodiment of the present invention will be described in detail below.

[0034] A soft magnetic wire according to one embodiment of the present invention comprises, in weight%, C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, the remainder being Fe and other unavoidable impurities.

[0035] The reasons for limiting the compositional range of each alloying element are described below. Unless otherwise noted, units are weight percent.

[0036] The content of C can be 0.0001% to 0.0300%.

[0037] Carbon is the most important element determining strength and ductility in steel; as the carbon content increases, strength increases and ductility decreases. The lower limit of carbon for efficiently manufacturing steel may be 0.0001%, and if the carbon content is less than 0.0001%, manufacturing costs may increase significantly. The electromagnetic properties of steel improve as the ferrite fraction exhibiting ferromagnetism within the microstructure increases. If the carbon content exceeds 0.0300%, not only does the ferrite fraction decrease, but cementite, which hinders domain wall movement, precipitates, which can deteriorate electromagnetic properties. Therefore, it is desirable for the upper limit of carbon to be 0.0300%, and even more preferably 0.0280%.

[0038] The Si content can be 0.001% to 3.000%.

[0039] Si plays a role in increasing the resistivity of the material, thereby lowering iron loss and increasing strength. If the Si content is less than 0.001%, the effect of improving high-frequency iron loss and strength may be insufficient, and if it exceeds 3.000%, the hardness of the material increases, which may result in inferior productivity and cutting performance. Therefore, it is desirable that the Si content be between 0.001% and 3.000%, and more preferably between 0.001% and 2.700%.

[0040] The Mn content may be 0.001% to 0.500%.

[0041] Mn plays a role in improving iron loss by increasing the resistivity of the material and forming sulfides. If the Mn content is less than 0.001%, fine MnS may precipitate, which can lower magnetism, and if it exceeds 0.500%, it may promote the formation of a texture unfavorable to magnetism, which can reduce magnetic flux density. Therefore, it is preferable that the Mn content be 0.001% to 0.500%, and more preferably 0.001% to 0.400%.

[0042] The Al content may be 0.001% to 0.100%.

[0043] Al plays a role in increasing the resistivity of the material, thereby lowering iron loss and improving strength. If the Al content is less than 0.001%, it is insufficient for reducing high-frequency iron loss and improving strength, and fine nitrides may be formed, which can lower magnetism. On the other hand, if the Al content exceeds 0.100%, it can cause problems in all processes, such as steelmaking and continuous casting, and significantly reduce productivity. Therefore, it is desirable for the Al content to be between 0.001% and 0.100%, and more preferably between 0.001% and 0.050%.

[0044] The content of P can be 0.0001% to 0.0080%.

[0045] P is an impurity element that causes grain boundary segregation within steel, thereby degrading electromagnetic properties. Therefore, it is desirable for the P content to be 0.0080% or less, and more preferably 0.0060% or less. However, generally, it is contained at 0.0001% or more, and since additional processes requiring significant costs are required to reduce it to below that level, it is desirable for the lower limit of P to be 0.0001%.

[0046] The S content may be 0.0001% to 0.0070%.

[0047] Since S is not only an impurity element but also forms MnS which is harmful to electromagnetic properties, it is desirable that the S content be 0.0070% or less, and more preferably 0.0060% or less. However, generally, it is contained at 0.0001% or more, and since additional processes at considerable cost are required to reduce it to below that level, it is desirable that the lower limit of S be 0.0001%.

[0048] The content of N can be 0.0001% to 0.0070%.

[0049] N is a nitride-forming element, and when it combines with Al to form AlN, it acts as a pinning grain that inhibits grain growth during heat treatment after drawing, thereby increasing the number of grain boundaries that hinder domain wall movement and potentially deteriorating electromagnetic properties. Therefore, it is desirable for the N content to be 0.0070% or less, and more preferably 0.0065%. However, generally, it is contained at 0.0001% or more, and since additional processes requiring significant costs are required to reduce it to below that level, it is desirable for the lower limit of N to be 0.0001%.

[0050] 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 ordinary manufacturing process, they cannot be excluded. As these impurities are known to any person skilled in the ordinary manufacturing process, all details thereof are not specifically mentioned in this specification.

[0051] A soft magnetic wire according to one embodiment of the present invention can satisfy the following formula (1).

[0052] Equation (1): 70 ≤ HVmax - (218[C] + 34[Si] + 25[Mn]) ≤ 155

[0053] (Here, HVmax is the maximum value among the cross-sectional hardness values, and [C], [Si], and [Mn] are the weight percent of each element)

[0054] If the value of the above equation (1) is less than 70, the ductility of the steel may be excessively good, and the cut surface may not be smooth, and if it exceeds 155, the steel may become too hard and the cutting ability may be reduced.

[0055] A soft magnetic wire according to one embodiment of the present invention may have a cross-sectional hardness of 201 HV or less in Vickers hardness value, and a hardness difference between the center and the surface layer may be 30 HV or less.

[0056] The microstructure of the above soft magnetic wire may contain ferrite with an area fraction of 99% or more.

[0057] Hereinafter, a soft magnetic steel wire according to one embodiment of the present invention will be described.

[0058] A soft magnetic steel wire according to one embodiment of the present invention may comprise, in weight%, C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, the remainder being Fe and other unavoidable impurities.

[0059] The above soft magnetic steel wire may have a cross-sectional hardness of 220 HV or less in Vickers hardness value, and a hardness difference between the center and the surface layer may be 9 HV or less.

[0060] The above soft magnetic steel wire may have a plastic deformation portion length of 25% or less relative to its diameter when cut.

[0061] The above soft magnetic steel wire may have a magnetic flux density of 1.76T or more.

[0062] The above soft magnetic steel wire may have a shear band number density of 1.0 band / mm² or less.

[0063] The microstructure of the above soft magnetic steel wire may contain ferrite with an area fraction of 99% or more.

[0064] Hereinafter, a method for manufacturing a soft magnetic steel wire according to one embodiment of the present invention will be described.

[0065] A method for manufacturing a soft magnetic steel wire according to one embodiment of the present invention may include the steps of: preparing a wire material; drawing the wire material; and heating the drawn wire material and then performing annealing heat treatment.

[0066] The step of preparing a wire rod may include, in weight percent, a step of manufacturing a billet comprising C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, and the remainder being Fe and other unavoidable impurities; a step of heating the billet at 1000℃ to 1200℃; a step of rolling the heated billet; a step of finishing rolling at A1℃ to (A1+100)℃ after the rolling step; and a step of cooling after the finishing rolling step.

[0067] The reason for setting the composition and composition content of the above-mentioned wire material may be the same as that of the soft magnetic wire material according to one embodiment of the present invention described above.

[0068] When heating the billet at the above heating temperature, it is heated to an austenite (g) single-phase region, so that after hot rolling, the microstructure can consist only of ferrite (a).

[0069] When finish rolling is performed at the above finish rolling temperature, a phase transformation from austenite to ferrite begins, and the austenite can be completely eliminated. In addition, workability during drawing can be ensured.

[0070] The above wire may have a cross-sectional hardness of 201 HV or less in Vickers hardness values, and a hardness difference between the center and the surface layer may be 30 HV or less.

[0071] Higher hardness reduces burr formation and improves cutting performance; however, if it is too high, the lifespan of the cutting tool is reduced. Furthermore, the hardness of the cross-section naturally increases due to deformation during cutting. In this case, the hardness of the surface layer increases more significantly than that of the center of the material; if the hardness difference between the two parts exceeds a certain level, the likelihood of burr formation increases rapidly. Additionally, if the hardness is too low, increased ductility or malleability makes burr formation easier, which can lead to a deterioration of electromagnetic properties.

[0072] Accordingly, in the present invention, the wire has a cross-sectional hardness of 201 HV or less in Vickers hardness value, and the hardness difference between the center and the surface layer is controlled to 30 HV or less, thereby ensuring excellent electromagnetic properties along with improved cutability.

[0073] In addition, by controlling the hardness of the cross-section and the hardness difference between the center and the surface layer as described above, the length of the plastically deformed portion when cutting the steel wire using the above wire can be controlled to 25% or less of the diameter.

[0074] In addition, the above wire may contain ferrite in an area fraction of 99% or more as a microstructure. Since magnetic properties are important for soft magnetic wires, it is preferable that the microstructure of the above wire be a single-phase ferrite (a) structure. A single-phase ferrite structure means containing ferrite in an area fraction of 99% or more, or 100% of the area fraction.

[0075] The average grain size of the ferrite in the microstructure of the above wire rod may be 66 μm or larger. If the grain size of the wire rod is excessively small, the influence of grain boundaries hindering the movement of domain walls increases, which may lead to an increase in coercivity. Therefore, it is desirable to increase the grain size of the wire rod to reduce the density of grain boundaries. Accordingly, it is desirable that the average grain size of the ferrite microstructure of the above wire rod be 66 μm or larger.

[0076] The above-mentioned wire is subjected to a drawing step at room temperature with a reduction rate of 59 to 93% so that the number density of shear bands is 11.4 or more.

[0077] The aforementioned shear band refers to a narrow region where deformation is locally concentrated and can primarily occur due to material non-uniformity, strength reduction, plastic deformation, etc. During the drawing step, when the wire is drawn at room temperature, numerous shear bands are generated within the microstructure; since the phase transformation rate is rapid within the shear band, the grains formed there absorb surrounding grains and coarsen, making them prone to exhibiting abnormal grain growth behavior.

[0078] Meanwhile, reducing iron loss is important for use as a material for drive motor cores. Since iron loss decreases as the grain size of the steel increases while other variables remain constant, it is better to increase the grain size after drawing and annealing heat treatments. Therefore, it is preferable to have as many shear bands formed within the microstructure during drawing.

[0079] Accordingly, the above-mentioned freshening step can be performed such that the number density of shear bands is 11.4 bands / mm² or more, preferably 29.0 bands / mm² or more, and more preferably 35.0 bands / mm² or more.

[0080] In addition, if the reduction rate is too high, the shear bands generated during drawing may be destroyed by continued deformation, resulting in a segmented structure with a high dislocation density. This region has high stored energy and becomes a nucleation-promoting site during annealing, which ultimately leads to the refinement of the recrystallization structure. Therefore, annealing can be performed after drawing up to a reduction rate that maximizes the generation of shear bands. Considering this, it is desirable to perform the drawing step such that the reduction rate is 93% or less. If the reduction rate exceeds 93%, the generated shear bands may begin to break. On the other hand, if the reduction rate is too low, the generation of shear bands is insufficient, which may prevent proper abnormal grain growth; therefore, the reduction rate is performed at 59% or more, preferably 69% or more.

[0081] After the above drawing step, a step of heating and annealing heat treatment can be performed. Specifically, an annealing heat treatment is performed by heating the drawn wire at (A1-110)℃ to (A1+200)℃ and maintaining it for at least 10 minutes.

[0082] In the above annealing heat treatment step, the annealing heat treatment temperature is an important factor that can control the ratio of the length of the plastically deformed portion when the steel wire is cut. If the heat treatment temperature is too low, recrystallization does not proceed sufficiently, and deformation accumulated within the material due to the drawing process may remain; if it is too high, recrystallization proceeds rapidly and simultaneously within the material, which may result in the grain size becoming finer. Therefore, it is preferable to perform the annealing heat treatment at a temperature of (A1-110)℃ to (A1+200)℃.

[0083] In addition, in the above annealing heat treatment step, the annealing heat treatment temperature is a very important factor in determining the final microstructure. Since abnormal grain growth behavior does not appear if the heat treatment temperature is too low, the heat treatment can preferably be performed at (A1-110)°C or higher, more preferably at (A1-100)°C or higher, and most preferably at (Al-50)°C. Conversely, since a phase transformation to austenite may occur if the heat treatment temperature is too high, for stable operation, the heat treatment can preferably be performed at (A1+200)°C or lower, more preferably at (Al+100)°C, and most preferably at A1°C or lower. Since the holding time at the corresponding temperature also has the effect of determining the final microstructure, just like the temperature, it can be maintained for 10 minutes or more.

[0084] After the above annealing heat treatment step, the steel wire may have a cross-sectional hardness of 220 HV or less in Vickers hardness values, and a hardness difference between the center and the surface layer may be 9 HV or less. When the cross-sectional hardness and the hardness difference between the center and the surface layer of the steel wire are within the above ranges, excellent electromagnetic properties can be secured along with improved cutability of the steel wire.

[0085] After the above annealing heat treatment step, the length of the plastically deformed portion of the steel wire may be 25% or less of the diameter when cut. The plastically deformed portion is defined as the length of the part where the hardness of the surface layer exceeds 1.10 times the hardness value of the center due to the increase in hardness when cut; as the length of this plastically deformed portion increases, the resistance applied to the cutting tool during cutting increases, thereby reducing its lifespan. Accordingly, the present invention controls the length of the plastically deformed portion during cutting to 25% or less of the diameter, thereby ensuring excellent cutability of the steel wire.

[0086] After the above annealing heat treatment, the average grain size of the ferrite in the steel wire may be 260 μm or larger. If the grain size of the steel wire is excessively small, the influence of grain boundaries hindering the movement of domain walls increases, leading to an increase in coercivity. Therefore, it is desirable to increase the grain size to reduce the density of grain boundaries.

[0087] In addition, the above-mentioned annealed steel wire may have a shear band number density of 1.0 or less and a magnetic flux density of 1.76 T or more.

[0088] The present invention will be explained in more detail below through the following examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited thereto.

[0089] Example 1

[0090] A billet was manufactured as shown in Table 2 using steel having the alloy composition as shown in Table 1 below, the billet was heated to 1000~1200℃, hot-rolled under normal conditions, and cooled to manufacture a wire rod.

[0091] Classification Alloy Composition (Weight%) CSI Mn Al PSN Invention Steel 10.00 30.00 120.2 160.00 30.00 40.00 30.00 4 Invention Steel 20.00 42.3 370.2 510.00 80.00 30.00 30.00 4 Invention Steel 30.01 41.00 80.4 810.01 00.00 30.00 30.00 4 Invention Steel 40.00 20.9 860.1 580.00 20.00 30.00 30.00 3 Invention Steel 50.00 32.2 700 3740.00 10.00 30. 0020.003Comparison 10.0111.5510.1180.0100.0050.0040.007Comparison 20.0051.0040.3170.0050.0040.0030.004Comparison 30.0031.8720.4050.0040.0030.0040.005Comparison 40.0360.9440.2480.0030.0040.0030.004Comparison 50.0043.3170.2850.0040.0030.0040.005

[0092] The maximum cross-sectional hardness, center hardness, and surface hardness of the wire rod manufactured above were measured, and the results are shown in Table 2 below.

[0093] The cross-sectional hardness was measured at 22 points at 0.25 mm intervals from one side of the cross-section of the material using the Vickers measurement method, and the average and maximum values ​​of the measured values ​​were shown, with a load of 500 g applied.

[0094] The center hardness was expressed as the average value after measuring at 10 points at 1 mm intervals from the center of the material along the length direction.

[0095] Surface hardness was measured using a cross-sectional specimen of the material at 5 points at 1 mm intervals from a depth of 0.25 mm from the surface, and then at 5 points at 1 mm intervals from a depth of 0.50 mm from the surface, and the 10 values ​​were expressed as the average.

[0096] Maximum cross-sectional hardness (HV) Average cross-sectional hardness (HV) Center hardness (HV) Surface hardness (HV) of Equation (1) Value Example 1 Invention 18178757874.9 Example 2 Invention 218017216817493.4 Example 3 Invention 3201182186197150.4 Example 4 Invention 4185178161180147.1 Example 5 Invention 5198180194190110.8 Comparative Example 1 Comparative 1208193202202149.9 Comparative Example 2 Comparative 2192186154187148.8 Comparative Example 3 Comparative 324122719123566.6 Comparative Example 4 Comparative 4230209218226183.9 Comparative Example 5 Comparative 5326312283320205.2

[0097] Steel wire was manufactured by drawing the wire according to Tables 1 and 2 above at room temperature, then heating it to (A1-110)℃~(A1+200)℃ and maintaining it for at least 10 minutes for annealing heat treatment. At this time, the heat treatment temperatures of Examples 6 to 10 and Comparative Examples 6 to 12 are as shown in Table 3 below.

[0098] The cross-sectional hardness, center and surface hardness, and the length of the plastically deformed portion relative to the diameter of the steel wire manufactured above were measured, and the results are shown in Table 3 below.

[0099] The cross-sectional hardness, core hardness, and surface hardness were measured using the same method as for the wire rod.

[0100] The plastic deformation section length ratio was expressed as the ratio of the measured length to the wire diameter by measuring the length of the portion where the hardness of the surface layer at the time of cutting exceeds 1.10 times the hardness value of the center.

[0101] Classification Wire Heat Treatment Temperature (°C) Maximum Cross-sectional Hardness (HV) Average Cross-sectional Hardness (HV) Center Hardness (HV) Surface Hardness (HV) Length of Plasticly Deformed Part Ratio to Diameter (%) Example 6 Example 1 85 38 380 80 8225 Example 7 Example 2 9 18 17 8 17 11 72 17 520 Example 8 Example 3 9 18 20 41 85 19 520 118 Example 9 Example 4 9 58 17 8 170 16 41 73 13 Example 10 Example 5 9 58 220 20 120 821 516 Comparative Example 6 Example 1 79 69 99 59 19 628 Comparative Example 7 Example 283219318118319127 Comparative Example 8 Comparative Example 1102122320719821137 Comparative Example 9 Comparative Example 263119919316618227 Comparative Example 10 Comparative Example 398824824121923733 Comparative Example 11 Comparative Example 463125523822824130 Comparative Example 12 Comparative Example 5102135634230734643

[0102] As shown in Tables 2 and 3 above, in the case of the wire rods of Examples 1 to 5 satisfying the alloy composition according to the present invention and satisfying the value of Equation (1) being 70 or more and 155 or less, it was confirmed that the hardness of the cross-section was 201 HV or less and the hardness difference between the center and the surface layer was 30 HV or less. In addition, in the case of the steel wires of Examples 6 to 10 manufactured using the wire rods of Examples 1 to 5, it was confirmed that the hardness of the cross-section was 220 HV or less and the hardness difference between the center and the surface layer was 9 HV or less, and that the length of the plastically deformed portion relative to the diameter was 25% or less when the steel wire was cut.

[0103] On the other hand, Comparative Examples 6 and 7 used wire rods of Examples 1 and 2 that satisfied the alloy composition, cross-sectional hardness, and hardness difference between the center and the surface layer according to the present invention, but the cross-sectional hardness and hardness difference between the center and the surface layer of the steel wire were subjected to annealing heat treatment at the temperature shown in Table 3 above, and thus the results intended by the present invention were not satisfied. Accordingly, it was confirmed that the ratio of the length of the plastically deformed portion to the diameter at the time of cutting exceeded 25%. In addition, in the case of Comparative Examples 1 to 3, the hardness difference between the center and the surface layer of the wire rod exceeded 30 HV, and it was confirmed that the hardness of the steel wires of Comparative Examples 8 to 10 manufactured using them also exceeded 220 HV, the hardness difference between the center and the surface layer exceeded 9 HV, and the length of the plastically deformed portion to the diameter at the time of cutting also exceeded 25%.

[0104] Although the wire of Comparative Example 4 showed increased hardness due to exceeding the C content, the hardness of the surface layer of the material increased significantly. Consequently, it was confirmed that the steel wire of Comparative Example 11, manufactured using this material, exhibited a large hardness difference between the center and the surface layer, resulting in a plastic deformation length ratio of over 30% relative to the diameter. Additionally, although the wire of Comparative Example 5 showed high hardness due to exceeding the Si content, it was confirmed that the steel wire of Comparative Example 12, manufactured using this material, also exhibited a hardness difference between the center and the surface layer that was too large, resulting in a plastic deformation length ratio of over 40% relative to the diameter.

[0105] Example 2

[0106] A wire rod having the alloy composition shown in Table 4 below was manufactured, and a steel wire was manufactured using the wire rod.

[0107] Alloy Composition (Wt%) Al (°C) CsiMnAlPSN Example 1 10.00 50.06 80.26 40.00 50.00 80.00 40.00 48 44 Example 1 20.02 82.7 410.01 80.08 30.00 20.00 30.00 57 76 Example 1 30.00 11.56 40.14 20.09 20.00 30.00 30.00 610 39 Example 1 40.00 42.11 70.43 70.00 10.00 30.00 20 .003988 Comparative Example 1 30.035 0.074 0.238 0.005 0.005 0.004 0.005719 Comparative Example 1 40.0052.526 0.11 50.005 0.013 0.008 0.004766 Comparative Example 1 50.0031.028 0.217 0.023 0.005 0.012 0.005935 Comparative Example 1 60.016 0.5510.156 0.011 0.006 0.004 0.011735

[0108] The manufacturing conditions of the steel wire produced in Example 2 above, the number density of shear bands of the steel wire after drawing, the average grain size of ferrite of the steel wire after final annealing heat treatment, and the magnetic flux density after final annealing heat treatment were measured, and the results are shown in Table 5 below.

[0109] The shear band number density of the steel wire after drawing was expressed as the average value after measuring the number of shear bands by observing five central points of the longitudinal cross-section specimen with a scanning electron microscope (SEM) at 500 to 1000x magnification.

[0110] The average grain size of the ferrite was measured using the ASTM E112 method, and the average value was expressed after measuring at 5 random points at 1 / 4 of the diameter of the manufactured steel wire.

[0111] The magnetic flux density of the steel wire after the final annealing heat treatment was measured by cutting 100g of the wire, winding it into a circular ring shape, and then winding the copper wire 100 times. At this time, the inner diameter of the ring was 85mm and the outer diameter was 115mm.

[0112] Classification Alloy Steel Wire Manufacturing Conditions Number of Shear Bands Density (Pieces / mm²) Average Ferrite Grain Size (㎛) of Steel Wire After Final Annealing Heat Treatment Magnetic Flux Density B of Steel Wire After Final Annealing Heat Treatment 50 (T) Density of steel wire shear band number after final annealing heat treatment (pieces / mm²) Wire drawing reduction rate (%) Annealing heat treatment temperature (°C) Annealing heat treatment time (min) Number of repeated drawing and annealing heat treatment cycles (times) Comparative Example 13 Comparative Example 13 8 37 15 30 12.8 19 1.6 4 2.44 Comparative Example 14 Comparative Example 14 7 7 75 0 20 19.5 17 1.5 9 5.16 Comparative Example 15 Comparative Example 15 5 9 85 0 10 16.9 36 1.6 8 1.45 Comparative Example 16 Comparative Example 16 6 8 73 0 25 18.4 31.6 5 2.58 Comparative Example 17 Example 12 5 7 76 0 30 32.4 6 1.6 8 1.13 Comparative Example 1 8 Example 1 2776603039.71091.711.14 Example 11 Example 119383015111.42611.760.92 Example 12 Example 129376030229.15521.810.77 Example 13 Example 136894510249.110751.750.46 Example 14 Example 1492900202346.613131.990.25

[0113] As shown in Table 4 above, Comparative Examples 13 to 16 each had C, P, S, and N contents exceeding the range of the present invention as shown in Table 4, and thus showed low magnetic flux density after annealing heat treatment.

[0114] In the case of Comparative Example 17, the drawing reduction rate was found to be less than 59%, and therefore, the number density of shear bands after drawing, the average grain size of the steel wire after the final annealing heat treatment, and the magnetic flux density after the final annealing heat treatment were not satisfied. In addition, in the case of Comparative Example 18, the annealing heat treatment temperature was lower than (A1-110)℃, and thus the number density of shear bands after drawing, the average grain size of the steel wire after the final annealing heat treatment, and the magnetic flux density after the final annealing heat treatment were not satisfied.

[0115] On the other hand, in the case of Examples 11 to 14, in which the alloy composition and steel wire manufacturing conditions satisfied the scope of the present invention, the number density of shear bands after drawing, the average grain size of the steel wire after final annealing heat treatment, and the magnetic flux density after final annealing heat treatment were satisfied, and it was confirmed that the magnetic properties were superior compared to the comparative example.

[0116] Although embodiments of the invention disclosed above have been illustrated and described, the disclosed invention is not limited to the specific embodiments described above, and various modifications may be made by those skilled in the art to which the disclosed invention belongs without departing from the essence claimed in the claims.

Claims

1. In wt%, C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, the remainder being Fe and other unavoidable impurities, and The above wire satisfies the following formula (1), and is a soft magnetic wire that satisfies a hardness value of 201 HV or less in the cross section and a hardness difference between the center and the surface layer of 30 HV or less. Equation (1): 70 ≤ HVmax - (218[C] + 34[Si] + 25[Mn]) ≤ 155 (Here, HVmax is the maximum value among the cross-sectional hardness values, and [C], [Si], and [Mn] are the weight percent of each element) 2. In Paragraph 1, The microstructure of the above wire is a soft magnetic wire containing ferrite with an area fraction of 99% or more.

3. In wt%, it contains C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, and the remainder being Fe and other unavoidable impurities, A soft magnetic steel wire having a cross-sectional hardness of 220 HV or less in Vickers hardness and a hardness difference of 9 HV or less between the center and the surface layer.

4. In Paragraph 3, The above steel wire is a soft magnetic steel wire in which the length of the plastically deformed portion upon cutting is 25% or less of the diameter.

5. In Paragraph 3, The above steel wire is a soft magnetic steel wire with a magnetic flux density of 1.76T or higher.

6. In Paragraph 3, The above steel wire is a soft magnetic steel wire having a shear band number density of 1.0 band / mm² or less.

7. In Paragraph 3, The microstructure of the above steel wire is a soft magnetic steel wire containing ferrite with an area fraction of 99% or more.

8. A step of preparing a wire rod satisfying the following formula (1), comprising, in wt%, C: 0.0001~0.0300%, Si: 0.001~3.000%, Mn: 0.001~0.500%, Al: 0.001~0.100%, P: 0.0001~0.0080%, S: 0.0001~0.0070%, N: 0.0001~0.0070%, and the remainder being Fe and other unavoidable impurities; A step of drawing the above wire at room temperature with a reduction rate of 59–93% so that the number density of shear bands is 11.4 or more; and A method for manufacturing a soft magnetic steel wire comprising: an annealing heat treatment step of heating the above-mentioned fresh wire at (A1-110)~(A1+200)℃ and maintaining it for at least 10 minutes. Equation (1): 70 ≤ HVmax - (218[C] + 34[Si] + 25[Mn]) ≤ 155 (Here, HVmax is the maximum value among the cross-sectional hardness values, and [C], [Si], and [Mn] are the weight percent of each element) 9. In Paragraph 8, A method for manufacturing a soft magnetic steel wire in which the above-mentioned wire has a cross-sectional hardness of 201 HV or less as a Vickers hardness value and a hardness difference between the center and the surface layer of 30 HV or less.

10. In Paragraph 8, The above-mentioned drawn wire is a method for manufacturing a soft magnetic steel wire having a shear band count of 11.4 or more.

11. In Paragraph 8, A method for manufacturing a soft magnetic steel wire in which the above-mentioned annealed steel wire has a cross-sectional hardness of 220 HV or less and a hardness difference between the center and the surface layer of 9 HV or less.

12. In Paragraph 8, A method for manufacturing a soft magnetic steel wire in which the length of the plastically deformed portion is 25% or less of the diameter when the above-mentioned heat-treated steel wire is cut.

13. In Paragraph 8, The above-mentioned annealed steel wire is a method for manufacturing a soft magnetic steel wire having a shear band number density of 1.0 bands / mm² or less.

14. In Paragraph 8, The above-mentioned annealed steel wire is a method for manufacturing a soft magnetic steel wire having a magnetic flux density of 1.76T or higher.