Steel wire and twisted wire

Abstract

To provide a steel wire excellent in twist characteristics and fatigue characteristics, and a twisted wire using the same.SOLUTION: A steel wire including C:0.30-2.00%, Si: 0.01-2.00%, Mn: 0.01-1.00%, Al: 0.100% or less, P:0.050% or less, S:0.050% or less, N:0.015% or less, O:0.0100% or less and the remainder consisting of Fe and impurities has a metal structure consisting of a ferrite phase and a cementite phase, 100 MPa or less of the average residual stress in the axis direction on a surface layer and 2.0 or more of the integration degree of a ferrite {111} collective structure on the surface layer. A twisted wire includes the steel wire.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to steel wires and twisted wires.

Background Art

[0002] For example, in rubber products such as automobile tires, chemical fibers such as rayon, nylon, and polyester, or steel cords made of steel are used as reinforcing materials. These reinforcing materials play the role of the skeleton of automobile tires and have a great influence on the fuel efficiency, durability, and handling stability of vehicles equipped with these automobile tires. In recent years, from the viewpoint of improving these characteristics, the usage ratio of steel cords as reinforcing materials has been increasing.

[0003] As disclosed in Patent Documents 1 and 2, for example, steel cords having a stranded wire structure in which a plurality of steel element wires (filaments) are twisted together have been widely proposed. Such steel cords are manufactured through the following steps. First, dry wire drawing is performed on a wire rod having a wire diameter of 4 to 6 mm to obtain an intermediate steel wire having a wire diameter of about 1.0 to 3.0 mm. A heat treatment called patenting treatment is performed on this intermediate steel wire to soften the intermediate steel wire. Further, brass plating is formed on the surface of the softened intermediate steel wire, and further, wet wire drawing is performed on the intermediate steel wire to obtain a steel wire (filament) having a wire diameter of about 0.05 to 0.40 mm. Note that the brass plating is formed to enhance the adhesion between the rubber and the steel cord. Then, the steel wire thus obtained is subjected to a stranding process to manufacture a steel cord having a stranded wire structure.

[0004] As described above, for example, when manufacturing a steel cord, a stranding process is performed on filaments having a wire diameter of about 0.05 to 0.40 mm. Not only the filaments for steel cords but also the steel wires used for stranded wires are required to have good workability.

[0005] For example, in Patent Document 3, it has been proposed to improve the ductility by increasing the degree of aggregation of {111} planes parallel to the cross-section of steel wire through swaging. In Patent Document 4, it has been proposed to control the residual stress and improve the ductility by using a die with an elliptical cross-sectional shape of the hole, a die with a circular hole, and an elliptical die having a hole rotated 90 degrees with respect to the hole of the first die before the final stage of the final wire drawing process.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] On the other hand, in recent years, from the perspective of reducing environmental impact, the weight reduction of automotive tires and the improvement of tire life for promoting the fuel efficiency reduction of automobiles have been advanced. Along with this, high strength and high fatigue strength have been required for steel cords.

[0008] However, when the strength of the filament is improved to form a high-strength steel cord, the ductility of the filament is insufficient and the workability of the filament is reduced. For this reason, there is a problem that defects such as cracks occur in the high-strength filament during the stranding process. Also, when the strength of the filament is high, it may not be possible to perform the stranding process well, and there is a risk of stranding defects occurring.

[0009] Conventionally, it has been impossible to obtain a filament for steel cord that is excellent in both high strength and workability, and it has been impossible to stably manufacture a high-strength steel cord. Further, when the strength is increased, the fatigue strength may decrease, and the tire life has not been improved.

[0010] The present disclosure has been made in view of the above-described circumstances, and an object thereof is to provide a steel wire excellent in twisting characteristics and fatigue characteristics, and a twisted wire using the same.

Means for Solving the Problems

[0011] The means for solving the above problems include the following aspects. <1> The steel composition is, by mass%, C: 0.30 to 2.00%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, Al: 0.100% or less, P: 0.050% or less, S: 0.050% or less, N: 0.015% or less, and O: 0.0100% or less, including, with the balance being composed of Fe and impurities, the metal structure being composed of a ferrite phase and a cementite phase, the average residual stress in the axial direction on the surface layer being 100 MPa or less, and the aggregation degree of the ferrite {111} texture on the surface layer being 2.0 or more, a steel wire. <2> The steel composition is, by mass%, C: 0.30 to 2.00%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, Al: 0.100% or less, P: 0.050% or less, S: 0.050% or less, N: 0.015% or less, and O: 0.0100% or less, comprising, further containing one or more selected from the group consisting of the following Group A and Group B, the balance consisting of Fe and impurities, [Group A] Cr: 1.00% or less, Mo: 0.50% or less, Ti: 0.100% or less, Nb: 0.100% or less, V: 0.30% or less, B: 0.0100% or less, Cu: 0.50% or less, Ni: 0.50% or less, and Sn: one or more selected from the group consisting of 0.10% or less [Group B] Ca: 0.0050% or less, Mg: 0.0050% or less, Sb: 0.050% or less, and As: one or more selected from the group consisting of 0.050% or less The metallographic structure consists of a ferrite phase and a cementite phase, The average residual stress in the axial direction on the surface layer is 100 MPa or less, A steel wire having an aggregation degree of the ferrite {111} texture on the surface layer of 2.0 or more. <3> By mass, the steel wire according to <2>, having a steel composition containing the Group A. <4> By mass, the steel wire according to <2> or <3>, having a steel composition containing the Group B. <5> The wire diameter is 0.050 mm to 0.400 mm, and the tensile strength is 2000 MPa or more. The steel wire according to any one of <1> to <4>. <6> The steel wire according to any one of <1> to <5>, which is plated. <7> A stranded wire containing the steel wire according to any one of <1> to <6>.

Advantages of the Invention

[0012] According to the present disclosure, a steel wire excellent in twisting characteristics and fatigue characteristics and a stranded wire using the same are provided.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Mode for Carrying Out the Invention

[0014] An embodiment which is an example of the present disclosure will be described. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. Further, when "more than" or "less than" is attached to the numerical values described before and after "~", the numerical range means a range not including these numerical values as the lower limit value or the upper limit value. In the numerical ranges described stepwise in this specification, the upper limit value of a certain stepwise numerical range may be replaced with the upper limit value of the numerical range described in other stepwise descriptions, or may be replaced with the value shown in the examples. Further, in the numerical ranges described stepwise in this specification, the lower limit value of a certain stepwise numerical range may be replaced with the lower limit value of the numerical range described in other stepwise descriptions, or may be replaced with the value shown in the examples. Further, the content of the element of the steel composition may be expressed as the amount of the element (for example, the amount of C, the amount of Si, etc.). Further, regarding the content of the element of the steel composition, unless otherwise specified, "%" means "mass%". Further, the "surface of the steel wire" means the outer peripheral surface of the steel wire. In addition, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0015] <Steel composition> The steel wire according to the present disclosure contains, by mass%, C: 0.30 to 2.00%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, Al: 0.100% or less, P: 0.050% or less, S: 0.050% or less, N: 0.015% or less, O: 0.0100% or less, and the balance is Fe and impurities. In addition, the steel wire according to the present disclosure may contain, as optional elements, one or more selected from the group consisting of the following Group A and Group B in place of a part of Fe. The steel wire according to the present disclosure may contain one or more elements selected from Group A, one or more elements selected from Group B, or two or more elements selected from Group A and Group B, respectively. [Group A] Cr: 1.00% or less Mo: 0.50% or less Ti: 0.100% or less Nb: 0.100% or less V: 0.30% or less B: 0.0100% or less Cu: 0.50% or less Ni: 0.50% or less Sn: 0.10% or less [Group B] Ca: 0.0050% or less Mg: 0.0050% or less Sb: 0.050% or less As: 0.050% or less Hereinafter, each component (element) constituting the steel wire according to the present disclosure will be described.

[0016] C: 0.30% to 2.00% C is an element that improves the strength of wire rods and steel wires. When the C content is less than 0.30%, grain boundary ferrite is generated and the tensile strength decreases. On the other hand, when the C content exceeds 2.00%, primary cementite is produced excessively and the workability deteriorates. Therefore, the C content is limited to the range of 0.30% to 2.00%. The C content is preferably 0.40 to 1.50%, more preferably 0.60 to 1.20%.

[0017] Si: 0.01 - 2.00% Si is also an element effective for deoxidizing steel. It strengthens the ferrite phase and segregates at the interface between the ferrite phase and the cementite phase, suppressing the spheroidization of cementite during heat treatment and suppressing the decrease in strength. However, if the Si content is less than 0.01%, the above effects cannot be expected, and if the Si content exceeds 2.00%, the effects saturate and the work hardening characteristics deteriorate. Therefore, the Si content is limited to the range of 0.01 to 2.00%. The Si content is preferably 0.50 to 1.70%, more preferably 0.70 to 1.50%.

[0018] Mn: 0.01 - 1.00% Mn is an element necessary for deoxidation and desulfurization and is also an element that improves hardenability. However, if the Mn content is less than 0.01%, sufficient hardenability cannot be obtained. On the other hand, if the Mn content exceeds 1.00%, martensite is likely to occur and the workability and ductility of the steel material deteriorate. Therefore, the Mn content is limited to the range of 0.01 to 1.00%. The Mn content is preferably 0.20 to 0.90%, more preferably 0.40 to 0.80%.

[0019] Al: 0.100% or less Al is effective as a deoxidizing element, forms nitrides to suppress the coarsening of the ferrite phase, and ensures the ductility of wire rods and steel wires. It also has the effect of enhancing corrosion resistance. However, if the Al content exceeds 0.100%, alumina-based non-metallic inclusions are generated and the cold workability decreases. Therefore, the Al content is 0.100% or less, preferably 0.080% or less.

[0020] P: 0.050% or less P is an element that significantly strengthens the ferrite phase in steel and embrittles the steel, so it should be 0.050% or less to reduce the twisting characteristics of the steel wire. Although it is preferable that the amount of P is as small as possible, approaching 0% increases the refining time and cost. Therefore, the lower limit of the amount of P may be 0.001%.

[0021] S: 0.050% or less S is a segregation element and reduces the ductility of steel, so it should be 0.050% or less. Although it is preferable that the amount of S is as small as possible, approaching 0% increases the refining time and cost. Therefore, the lower limit of the amount of S may be 0.001%.

[0022] N: 0.015% or less N is an element that adheres to dislocations during cold working, improving the strength of the steel and reducing the ductility of the steel wire. In particular, when it exceeds 0.015%, the decrease in deformability becomes significant. Therefore, the amount of N should be 0.015% or less, and preferably 0.010% or less. Although approaching 0% for the amount of N increases the refining time and cost, the lower limit of the amount of N may be 0.001%.

[0023] O: 0.0100% or less O exists as oxides such as Al and Ti in the steel wire. When the amount of O is high, coarse oxides may be formed, which can cause a decrease in cold workability. Therefore, the amount of O should be 0.0100% or less, and it is preferably suppressed to 0.0020% or less. Although approaching 0% for the amount of O increases the refining time and cost, the preferable lower limit may be 0.0010%.

[0024] Cr: 1.00% or less Cr is an element effective in refining the ferrite phase and cementite phase and improving the strength of wire rods and steel wires. On the other hand, if the Cr content is too high, the transformation end time becomes long, and there is a risk of the formation of supercooled structures such as micro martensite in the segregation part of the hot-rolled wire rod. Therefore, when the steel wire according to the present disclosure contains Cr, the Cr content is set to 1.00% or less. From the viewpoint of exerting the effect of Cr, the lower limit value of the Cr content is preferably 0.01% or more, and more preferably 0.08% or more.

[0025] Mo: 0.50% or less Mo is effective in suppressing grain boundary ferrite. If Mo is excessive, coarse Mo2C carbides precipitate and the cold workability deteriorates. Therefore, when the steel wire according to the present disclosure contains Mo, the Mo content is set to 0.50% or less. From the viewpoint of exerting the effect of Mo, the lower limit value of the Mo content is preferably 0.01% or more, and more preferably 0.05% or more.

[0026] Ti: 0.100% or less Ti precipitates as TiN and contributes to preventing the coarsening of austenite grains. If the Ti content exceeds 0.100%, coarse carbides are formed and the cold workability deteriorates. Therefore, when the steel wire according to the present disclosure contains Ti, the Ti content is set to 0.100% or less, preferably 0.080%. From the viewpoint of exerting the effect of Ti, the lower limit value of the Ti content is preferably 0.005% or more, and more preferably 0.008% or more.

[0027] Nb: 0.100% or less Nb has the effect of suppressing the coarsening of austenite grains during heating by generating carbonitrides. On the other hand, if Nb is added in excess, the transformation end time becomes long. Therefore, when the steel wire according to the present disclosure contains Nb, the Nb content is set to 0.100% or less, preferably 0.050% or less. From the viewpoint of exerting the effect of Nb, the lower limit value of the Nb content is preferably 0.003% or more, and more preferably 0.010% or more.

[0028] V: 0.30% or less V prevents the coarsening of austenite grains during heating and contributes to the increase in strength after rolling by forming fine carbonitrides in the ferrite phase. On the other hand, if added in excess, the amount of carbonitride formed becomes too large and the ductility decreases. Therefore, when the steel wire according to the present disclosure contains V, the amount of V is 0.30% or less. From the viewpoint of exerting the effect of V, the lower limit of the amount of V is preferably 0.005% or more, more preferably 0.050% or more.

[0029] B: 0.0100% or less B is effective in suppressing the decrease in ductility of the steel wire caused by N being fixed to dislocations by binding with N. On the other hand, if too much B is added, coarse Fe 23 (CB)6 carbide precipitation is promoted and the cold workability is reduced. Therefore, when the steel wire according to the present disclosure contains B, the amount of B is 0.0100% or less, preferably 0.0050% or less, more preferably 0.0040%. From the viewpoint of exerting the effect of B, the lower limit of the amount of B is preferably 0.0001% or more, more preferably 0.0002% or more.

[0030] Cu: 0.50% or less Cu has the effect of enhancing the corrosion resistance of the steel wire. On the other hand, if Cu is added in excess, it reacts with S and CuS segregates at the grain boundaries, causing defects in the wire rod and reducing the cold workability. Therefore, when the steel wire according to the present disclosure contains Cu, the amount of Cu is 0.50% or less, preferably 0.20% or less. From the viewpoint of exerting the effect of Cu, the lower limit of the amount of Cu is preferably 0.005% or more, more preferably 0.020% or more.

[0031] Ni: 0.50% or less Ni is an element that enhances the toughness of the steel wire. On the other hand, if Ni is added in excess, the transformation end time becomes long. Therefore, when the steel wire according to the present disclosure contains Ni, the amount of Ni is 0.50% or less, preferably 0.30% or less. From the viewpoint of exerting the effect of Ni, the lower limit of the amount of Ni is preferably 0.005% or more, more preferably 0.02% or more.

[0032] Sn: 0.10% or less Sn is an element that improves corrosion resistance. However, if Sn is added in excess, it will increase the cost and impair the cold workability. Therefore, when the steel wire according to the present disclosure contains Sn, the amount of Sn is 0.10% or less. From the viewpoint of exerting the effect of Sn, the lower limit value of the amount of Sn is preferably 0.002% or more, and more preferably 0.01% or more.

[0033] Ca: 0.0050% or less Ca is an element effective for deoxidizing steel. On the other hand, if added in excess, the amount of inclusions in the steel will increase, which may cause wire breakage during cold working. When the steel wire according to the present disclosure contains Ca, the amount of Ca is 0.0050% or less, preferably 0.0025% or less. From the viewpoint of exerting the effect of Ca, the lower limit value of the amount of Ca is preferably 0.0002% or more, and more preferably 0.0005% or more.

[0034] Mg: 0.0050% or less Mg is an element effective for deoxidizing steel. However, if Mg is added in excess, the inclusions in the steel will increase and the cold workability will be reduced. When the steel wire according to the present disclosure contains Mg, the amount of Mg is 0.0050% or less. From the viewpoint of exerting the effect of Mg, the lower limit value of the amount of Mg is preferably 0.0002% or more, and more preferably 0.0005% or more.

[0035] Sb: 0.050% or less Sb is an element that improves corrosion resistance. However, if added in excess, it will impair the cold workability. Therefore, when the steel wire according to the present disclosure contains Sb, the amount of Sb is 0.050% or less, preferably 0.015% or less. From the viewpoint of exerting the effect of Sb, the lower limit value of the amount of Sb is preferably 0.002% or more, and more preferably 0.005% or more.

[0036] As: 0.050% or less As is an element that improves corrosion resistance. On the other hand, when added in excess, it deteriorates cold workability. Therefore, when the steel wire according to the present disclosure contains As, the amount of As is 0.050% or less, preferably 0.025% or less. From the viewpoint of exerting the effect of As, the lower limit of the amount of As is preferably 0.001% or more, more preferably 0.005% or more.

[0037] Balance: Fe and impurity elements In the steel composition of the steel wire according to the present disclosure, the balance is Fe and impurity elements. Here, the impurity elements refer to components contained in the raw materials or components inadvertently mixed in the manufacturing process, and are not components intentionally contained. Further, the impurity elements also include components that are intentionally contained but are contained in an amount that does not affect the performance of the steel wire. Examples of other impurities include Co, Zr, W, REM (elements with atomic numbers from 57 to 71), Hf, Ta, La, Ce, In, Pb, Bi, Te, and Zn. It is desirable to regulate them to Co: 0.1% or less, (total of W, REM, Hf, Ta, La, and Ce): 0.01% or less, and (total of Zr, Te, Bi, Pb, and Zn): 0.01% or less, respectively.

[0038] <Metallographic structure> Next, the metallographic structure of the steel wire according to the present disclosure will be described. The metallographic structure of the steel wire according to the present disclosure consists of a ferrite phase and a cementite phase. Examples of the metallographic structure composed of the ferrite phase and the cementite phase include a pearlite structure and a bainite structure. The steel wire according to the present disclosure may be composed of a pearlite structure, may be composed of a bainite structure, or may have a mixture of a pearlite structure and a bainite structure. Further, a ferrite structure composed of a ferrite phase or a cementite structure composed of a cementite phase may be included. The method for measuring the metallographic structure of the steel wire according to the present disclosure will be described in the examples.

[0039] <Aggregate structure> The steel wire according to the present disclosure has an aggregation degree of ferrite {111} texture in the steel wire surface layer of 2.0 or more. According to the experiments of the inventors of the present disclosure, in the steel wire according to the present disclosure, the site where ferrite {111} accumulates in the steel wire surface layer (which may be referred to as the "{111} accumulation part" in the present disclosure) is considered to contribute to the improvement of the twisting property. When the aggregation degree of the {111} accumulation part in the surface layer region is less than 2.0, delamination is likely to occur. Therefore, the aggregation degree of the {111} accumulation part in the surface layer region is set to 2.0 or more. When the aggregation degree of the {111} in the surface layer region is 2.0 or more, the non-uniformity of the ferrite crystals in the steel wire is alleviated, so that the slip system responsible for torsional deformation becomes active and the twisting property is improved. From the viewpoint of improving the twisting property, the aggregation degree of the {111} texture in the surface layer of the steel wire according to the present disclosure is preferably 2.2 or more, and more preferably 2.5 or more.

[0040] The aggregation degree of {111} in the surface layer region is determined by measuring the crystal orientation. Specifically, it is as follows. Measure the crystal orientation on the surface layer of the steel wire. As shown in FIG. 1, the position for measuring the crystal orientation on the surface layer of the steel wire is the outer peripheral surface (S1) of the steel wire surface layer. Calculate the number of measurement points that become {111} (which may be referred to as "{111} measurement points" in the present disclosure) among the ferrite crystals on the outer peripheral surface (S1) of the steel wire surface layer of the steel wire 10. Then, calculate the ratio of the number of {111} measurement points to the total number of measurement points of the ferrite crystals on the outer peripheral surface (S1), and this ratio is defined as the aggregation degree of {111}.

[0041] Also, the method for measuring the crystal orientation is as follows. The crystal orientation is obtained using a DigiviewIV camera and an EBSD (Electron Backscattering Diffraction) device from TSL installed in the chamber of a scanning electron microscope (SEM), and OIM-DC (Data Collection), software for controlling them. As the SEM, for example, a scanning electron microscope JSM7100F manufactured by JEOL Ltd. can be used. EBSD irradiates an electron probe step by step on the observation sample surface to obtain a diffraction pattern, and based on that pattern, obtains the plane orientation of the iron cubic crystal. Then, by connecting these, a crystal orientation map of the scan area is obtained. The crystal orientation map is obtained such that the area of a square with a diameter D / 4 or less has 50,000 or more analysis points (number of pixels). By setting the measurement area to a square with a diameter D / 4 or less, the influence of the curvature of the outer peripheral surface can be minimized for measurement. For example, when the wire diameter D is 0.2 mm, since 0.2 mm / 4 = 50 μm, the measurement area is set to 30 μm × 30 μm so that it is 50 μm or less, and the measurement interval is 0.1 μm, resulting in 90,000 pixels. At this time, it is important to obtain the crystal orientation map such that the confidence index (CI) value is 0.2 or more. The CI value is an indicator of whether the crystal orientation has been appropriately obtained. From the obtained crystal orientation map, information on how many points where the {111} crystal plane enters (the aforementioned {111} measurement points) are included in the total number of measurement points can be tabulated using TSL's OIM-Analysis (crystal orientation analysis software). The above is the method for measuring the {111} integration degree in the surface layer region of the steel wire according to the present disclosure.

[0042] <Residual stress> Next, the residual stress of the steel wire according to the present disclosure will be described. The steel wire according to the present disclosure has an average residual stress in the axial direction on the surface layer of the steel wire of 100 MPa or less. When the average residual stress is 100 MPa or less, the fatigue strength is improved. From the viewpoint of improving the fatigue strength, the average residual stress in the axial direction on the surface layer of the steel wire according to the present disclosure is preferably 50 MPa or less, and more preferably -50 MPa or less.

[0043] The residual stress is measured using an X-ray residual stress measuring device. The measurement is performed using a Co tube target. As shown in Figure 2, the obtained steel wire 10 is cut into pieces about 10 mm in length, and they are arranged in parallel without gaps to form a surface of about 10 mm × 10 mm. The X-ray irradiation area is set to φ2 mm, and the residual stress in the longitudinal direction (axial direction) on the surface layer of the steel wire 10 is measured. At that time, two points are measured in the longitudinal direction, the surface is turned over, and two points are similarly measured, for a total of four points, and the average value is obtained. Note that the surface layer of the steel wire for measuring the residual stress does not necessarily have to be at the same position as the surface layer for measuring the aggregate structure. The above is the method for measuring the average residual stress in the axial direction on the surface layer of the steel wire according to the present disclosure.

[0044] <Wire diameter> The wire diameter of the steel wire according to the present disclosure is not particularly limited, but it is preferably 0.050 mm to 0.400 mm. By having a wire diameter within this range, the function as a steel element wire for forming a structure such as a stranded wire like a steel cord can be preferably exhibited.

[0045] <Usage> The usage of the steel wire according to the present disclosure is not particularly limited, but since it has excellent twisting characteristics and fatigue characteristics, it is particularly suitable for use as a steel cord made by twisting a plurality of steel wires.

[0046] <Manufacturing method of steel wire and stranded wire> Next, the manufacturing method of the steel wire according to the present disclosure and the manufacturing method of the stranded wire using this steel wire will be described. In the following description, the case of manufacturing a filament and a steel cord will be described as representative examples of the steel wire and the stranded wire according to the present disclosure.

[0047] A method for manufacturing a steel cord, which is an example of a steel wire according to the present disclosure, includes a descaling step (descaling step) of descaling a wire rod to remove oxide scale on the surface of the wire rod, a rough drawing step (rough drawing step) of rough drawing the descaled wire rod to obtain an intermediate steel wire, a patenting step (patenting step) of performing a patenting treatment on the roughly drawn intermediate steel wire, a brass plating step (brass plating step) of brass plating the patented intermediate steel wire, a finishing drawing step (finishing drawing step) of obtaining a steel wire (filament) by finishing drawing the brass-plated intermediate steel wire, and a stranding step (stranding step) of performing stranding using a plurality of filaments.

[0048] (Descaling step) In the method for manufacturing a steel wire according to the present disclosure, a wire rod having the above-described component composition is used as a raw material. The type of the wire rod is not particularly limited, but it is preferably a hot-rolled wire rod. The diameter of the wire rod is not particularly limited, but it is preferably about 4.0 to 5.5 mm. The oxide scale formed on the surface of this wire rod is removed by chemical treatment such as pickling or mechanical treatment. Such treatment is called descaling. The method of descaling is not particularly limited.

[0049] (Rough drawing step) Next, the wire rod from which the oxide scale has been removed is roughly drawn to form an intermediate steel wire having a wire diameter of 0.50 mm or more and 4.00 mm or less (rough drawing step). The method of rough drawing is not particularly limited, but rough drawing is preferably performed by dry drawing. In this specification, in order to distinguish the steel wire after the rough drawing step from the steel wire after the finishing drawing step, the steel wire before the finishing drawing step after the rough drawing step may be referred to as an intermediate steel wire.

[0050] (Patenting step) Next, the intermediate steel wire obtained by the rough drawing step is subjected to a patenting treatment using a molten lead bath, a molten salt bath, or a fluidized bed (patenting step). From the viewpoint of obtaining a metal structure composed of a ferrite phase and a cementite phase, the treatment temperature is preferably 530°C or higher and 650°C or lower.

[0051] (Brass Plating Process) In the patenting process, brass plating is applied to the surface of the intermediate steel wire that has been patented (brass plating process). Due to the characteristics of its use, the steel cord is drawn to an ultra-fine diameter of 0.400 mm or less and then used. Brass plating has a lubricating effect when drawing to an ultra-fine diameter. In addition, brass plating has the effect of enhancing the adhesion between the rubber and the steel cord.

[0052] (Final Drawing Process) Wet drawing is performed on the intermediate steel wire that has been brass plated in the brass plating process to form a steel wire with a wire diameter of 0.05 - 0.40 mm (final drawing process). As a means of increasing the ferrite {111} aggregation degree on the steel wire surface, in the final finishing process, for example, shaped drawing is performed. Shaped drawing is a process in which the intermediate steel wire, which is the workpiece, is drawn through a shaped die using a die.

[0053] (Shaped Drawing) Figure 3 schematically shows an example of a cross-section in the traveling direction X of the workpiece of die 20. As shown in Figure 3, generally, die 20 has a structure that includes a bell portion 21, an approach portion 22, and a bearing portion 24 in sequence in the traveling direction X of the workpiece. FIG. 4 shows the entrance shape of the approach portion 22 and the shape of the bearing portion 24 of various dies when viewed from the advancing direction X of the workpiece. FIG. 4(A) shows a general die, and FIGS. 4(B) to (F) show non-circular dies 22B to 22F that can be used in the production of steel wires according to the present disclosure. FIG. 4(G) shows a non-circular die 22G modeled after the die disclosed in Patent Document 4 for reference. As shown in FIG. 4(A), in a die (hereinafter, "ordinary die") 20A used for normal wire drawing, the shape of the approach portion (drawing portion) 22A is circular. On the other hand, as shown in FIGS. 4(B) to (F), in the non-circular dies 22B to 22F that can be used in the production of steel wires according to the present disclosure, the shape of the approach portion 22 is a polygonal shape such as an ellipse (FIG. 4(B)), a triangle (FIG. 4(C)), a quadrilateral (FIG. 4(D)), a pentagon (FIG. 4(E)), or a hexagon (FIG. 4(F)). Note that the shape of the bearing portion (shaping portion) 24 is circular in both the ordinary die (FIG. 4(A)) and the non-circular dies (FIGS. 4(B) to (F)). Although not shown, the bell portion also has a non-circular shape that is similar to the approach shape. Also, with respect to the wire diameter D, for example, the approach length is 1.5D and the bearing length is 0.3D. The outermost point of the approach shape is inscribed in the shape (circular shape) one pass before. The circular broken lines in each die in FIGS. 4(B) to (F) indicate the wire diameter one pass before. The wire diameter one pass before can be calculated from the reduction ratio described below. Such non-circular wire drawing using such a non-circular die is performed in the final finishing process of the steel wire. The non-circular wire drawing is performed in the final pass, but it may be continuously performed one pass before and two passes before the final pass. Also, ordinary wire drawing using an ordinary die may be performed for one pass after the non-circular wire drawing. The reduction ratio per pass of the non-circular wire drawing is preferably 5% or more in order to improve the {111} orientation density. The reduction ratio per pass is the area of the cross section perpendicular to the longitudinal direction of the steel wire before and after one-pass wire drawing, respectively, S n-1 , S n and is a value calculated by the following formula. Reduction ratio per pass (%) = (S n-1 - S n ) / S n-1 × 100 Note that in the die 20G shown in Fig. 4(G) that imitates the die shape disclosed in Patent Document 4 for reference, the shape of the approach portion 22G is a circle and the shape of the bearing portion 24G is an ellipse, and it is a die in which both the approach shape and the bearing shape are different from those in Fig. 4(B).

[0054] Through the above steps, the steel wire according to the present disclosure can be preferably manufactured.

[0055] (Stranding process) In the method for producing a steel cord using the steel wire according to the present disclosure, stranding is performed using a plurality of steel wires manufactured through the above steps (stranding process). The number and arrangement of the steel wires constituting the stranded wire are not particularly limited and can be selected according to the strength, wire diameter, etc. required for the steel cord. Thereby, a steel cord having a stranded wire structure is manufactured.

[0056] Through the above steps, the stranded wire according to the present disclosure can be preferably manufactured. Note that the method for manufacturing the steel wire and the stranded wire according to the present disclosure is not limited to the above method, and they may be manufactured by other manufacturing methods.

Examples

[0057] Hereinafter, the steel wire according to the embodiments of the present disclosure and their manufacturing methods will be specifically described while showing examples. Note that the examples shown below are merely examples, and the steel wire and their manufacturing methods according to the present disclosure are not limited to the following examples.

[0058] A rolled wire rod (wire diameter: 5.5 mm) obtained by hot rolling a steel slab having the chemical components (steel composition) shown in Table 1 was subjected to rough drawing, patenting treatment, brass plating treatment, and finish drawing. Ordinary drawing and shaped drawing were used for the finish drawing. Note that the remainder excluding the components (elements) shown in Table 1 is Fe and impurities, and "-" in Table 1 means that the element is not intentionally added.

[0059]

Table 1

[0060] Specimens were taken from the steel wires obtained by the above manufacturing method, and measurements of the metallographic structure, acquisition of a crystal orientation map in the surface layer region and measurement of the {111} integration degree, measurement of the average residual stress in the surface layer region, a tensile test for evaluating the tensile strength, a twist test for evaluating the presence or absence of delamination, a fatigue test, and a stranded wire test were conducted. Each evaluation method will be described below.

[0061] (Measurement of Metallographic Structure) Observation is carried out using a transmission electron microscope (TEM) on the central part of a cross-section (L cross-section) that includes the central axis of the steel wire and is parallel to the axial direction. For sample preparation, samples from three regions are collected and prepared from the central part of the L cross-section using a focused ion beam (FIB). The area per region shall be 5 μm × 5 μm to 10 μm × 10 μm. The observation is carried out at 100,000 to 200,000 times magnification with three fields of view per region. By observation, it is confirmed that the metallographic structure has a pearlite structure or a bainite structure having a lamellar structure composed of a ferrite phase and a cementite phase, and a structure in which they are mixed. At that time, grain boundary ferrite, primary cementite, or spheroidized cementite may be present. Also, it is confirmed that there is no retained austenite or martensite. Since retained austenite and martensite have a contrast different from that of pearlite structure, bainite structure, grain boundary ferrite, primary cementite, or spheroidized cementite, the confirmation is easy.

[0062] (Measurement of {111} Integration Degree in the Surface Layer Region) The observation surface is the outer peripheral surface of the steel wire surface layer. For obtaining the crystal orientation map, a specimen with a mirror surface and little polishing distortion is used for the observation surface. The surface layer of the obtained steel wire is electrolytically polished to finish the observation surface into a mirror surface. Electrolytic polishing is performed by applying a voltage using nitric acid or sulfuric acid. Polishing is carried out so that the wire diameter after polishing is D - (4 to 10 μm), where D is the wire diameter before polishing. The observation and analysis of the obtained test pieces are performed using SEM and EBSD, and the measurement of the {111} integration degree is carried out by the method described above.

[0063] (Measurement of the average residual stress in the surface layer region) The measurement of the axial average residual stress in the surface layer region is carried out by the method described above.

[0064] (Tensile test) The tensile test is carried out in accordance with JIS Z 2241:2011. At that time, the number of N is set to 3, and the average value is used.

[0065] (Twisting test) In the twisting test, the steel wire is cut to a length of 100×D, twisted in one direction at a speed of 20 rotations per minute, and the twisting characteristics are evaluated based on whether delamination occurs. The presence or absence of delamination is confirmed by the presence or absence of a sharp drop in the torque value. If there is a sharp drop in the torque value, it is determined that delamination occurs.

[0066] (Fatigue test) The fatigue test is carried out by rotating bending. Both ends of the steel wire are fixed to the rotating shafts (chucks), one of the chucks is rotated by a motor, and the other chuck is allowed to rotate freely. The chucks at both ends of the steel wire are set in parallel so as to face the same direction, and bending stress is applied to the steel wire. The bending stress is adjusted by changing the curvature of the steel wire according to the length of the steel wire and the distance between the chucks. For example, when the distance between the chucks is narrowed, the curvature of the steel wire increases and the bending stress increases. The rotation speed is set to 3000 rotations per minute, and it is rotated in one direction to evaluate the fracture life. Among the levels reached when the number of repetitions reaches 10 7 cycles, the highest stress is taken as the fatigue strength.

[0067] (Stranding test) Using a tubular stranding machine, stranding is carried out under the conditions of a stranding pitch of 10 mm and a speed of 2 m / min in the 1+6 seven-strand configuration shown in FIGS. 5A and 5B. When a wire break occurs in the steel wire with a stranding length of less than 100 m, it is determined as "wire break".

[0068] Table 2 shows the wire diameter of the intermediate steel wire, the patenting treatment temperature, the wire drawing method of the finishing wire drawing, the area reduction rate in the final process, the die shape in the final process, the diameter of the steel wire after the finishing wire drawing (final wire diameter D), and Table 3 shows the average residual stress in the axial direction on the steel wire surface, the ferrite {111} integration degree on the steel wire surface, the tensile strength, the fatigue strength, the presence or absence of delamination, and the presence or absence of strand breakage. The underlined parts in Tables 2 and 3 mean that they are outside the scope of the present disclosure.

[0069]

Table 2

[0070]

Table 3

[0071] The twisting characteristics indicate the presence or absence of delamination. When delamination occurs, it is indicated as "Yes", and when it does not occur, it is indicated as "No". The {111} integration degree of the microstructure is the integration degree of ferrite {111} on the steel wire surface. When it is 2.0 or more, delamination did not occur. The residual stress is the average residual stress in the axial direction on the steel wire surface. When it is 100 MPa or less, the fatigue strength is improved. The characteristics (criteria) that the steel wire should satisfy are set as follows: the tensile strength is 2000 MPa or more, the average residual stress is 100 MPa or less, and the {111} integration degree is 2.0 or more.

[0072] No.1 to 19 are examples of the steel wire and stranded wire according to the present disclosure and satisfy the above criteria.

[0073] No.20 to 38 are examples of the same steel type and wire diameter as No.1 to 19, but the final wire drawing is normal wire drawing, and the average residual stress is higher than 100 MPa, or the {111} integration degree is less than 2.0, or both. For example, No.20 has the same steel type and wire diameter as No.1, but since the average residual stress is higher than 100 MPa, the fatigue strength is lower than that of No.1. No. 21 has the same steel type and wire diameter as No. 2, but its average residual stress is higher than 100 MPa, so its fatigue strength is lower than that of No. 2. No. 22 has the same steel type and wire diameter as No. 3, but its average residual stress is higher than 100 MPa, so its fatigue strength is lower than that of No. 3. No. 23 has the same steel type and wire diameter as No. 4, but since the {111} integration degree is less than 2.0, strand breakage occurred. No. 24 has the same steel type and wire diameter as No. 5, but its average residual stress is higher than 100 MPa, so its fatigue strength is lower than that of No. 5, and since the {111} integration degree is less than 2.0, strand breakage occurred. No. 25 - 38 have the same steel type and wire diameter as No. 6 - 19 respectively, but since the {111} integration degree is less than 2.0, strand breakage occurred. Also, since the average residual stress of No. 25 - 38 is higher than 100 MPa, their fatigue strengths are lower than those of No. 6 - 19 respectively.

[0074] For No. 39 - 46, since any one of C, Si, Mn, Al, P, S, N, O exceeds the upper limit, wire breakage occurred during wire drawing due to segregation, etc. For No. 47 - 49, since any one of C, Si, Mn is below the lower limit, the tensile strength has not reached 2000 MPa and the fatigue strength is low.

[0075] No. 50 and 51 are reference examples in which products with the same steel type and wire diameter as No. 8 were manufactured according to the manufacturing methods of Patent Document 3 and Patent Document 4 respectively. Both No. 50 and 51 have an average residual stress higher than 100 MPa and a {111} integration degree less than 2.0, which are different technologies from the invention of the present disclosure.

[0076] As described above in detail with respect to the embodiments and examples of the present disclosure, the present disclosure is not limited to such embodiments and examples. It is obvious that those having ordinary knowledge in the technical field to which the present disclosure pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and these also naturally belong to the technical scope of the present disclosure.

Description of Reference Numerals

[0077] 10 Steel wire 20 Die 22 Approach portion 24 Bearing portion 100 Twisted wire

Claims

1. The steel composition is in mass %, C: 0.30 to 2.00%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, Al: 0.100% or less, P: 0.050% or less, S: 0.050% or less, N: 0.015% or less, and O: 0.0100% or less, comprising, with the balance being composed of Fe and impurities, the metallographic structure being composed of a ferrite phase and a cementite phase, the average residual stress in the axial direction on the surface layer being 100 MPa or less, and the degree of aggregation of the ferrite {111} texture on the surface layer being 2.0 or more. A steel wire.

2. The steel composition is in mass %, C: 0.30 to 2.00%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, Al: 0.100% or less, P: 0.050% or less, S: 0.050% or less, N: 0.015% or less, and O: 0.0100% or less, comprising, further containing one or more selected from the group consisting of the following Group A and Group B, with the balance being composed of Fe and impurities, [Group A] Cr: 1.00% or less, Mo: 0.50% or less, Ti: 0.100% or less, Nb: 0.100% or less, V: 0.30% or less, B: 0.0100% or less, Cu: 0.50% or less, Ni: 0.50% or less, and Sn: 0.10% or less, one or more selected from the group consisting thereof [Group B] Ca: 0.0050% or less, Mg: 0.0050% or less, Sb: 0.050% or less, and As: 0.050% or less, one or more selected from the group consisting thereof The metallographic structure is composed of a ferrite phase and a cementite phase, the average residual stress in the axial direction on the surface layer being 100 MPa or less, and the degree of aggregation of the ferrite {111} texture on the surface layer being 2.0 or more. A steel wire.

3. The steel wire according to Claim 2, having a steel composition containing the Group A in mass %.

4. The steel wire according to Claim 2, having a steel composition containing the Group B in mass %.

5. The steel wire according to Claim 1 or Claim 2, having a wire diameter of 0.050 mm to 0.400 mm and a tensile strength of 2000 MPa or more.

6. The steel wire according to Claim 1 or Claim 2, which is plated.

7. A stranded wire containing the steel wire according to Claim 1 or Claim 2.

8. A stranded wire containing the steel wire according to Claim 6.

Images