Steel wire and rope

Abstract

To provide a steel wire excellent in fatigue characteristics, and a rope using the same.SOLUTION: A steel wire including C:0.30-1.50%, 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. A difference ΔHV between the maximum and minimum hardnesses in the cross section of the steel wire and the average hardness HVave satisfy the formula 1; and a difference between the absolute value|σ(θ)| of the residual stress in the axis direction at a first position on the surface layer and the absolute value |σ(θ+180°)| of the residual stress in the axis direction at a second position having 180 degrees in the circumferential direction to the first position satisfy the formula 2. A rope includes the steel wire. ΔHV≤0.1×HVave... the formula 1, and |{|σ(θ)|-|σ(θ+180°)|}|≤200 MPa... the formula 2.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] For ropes such as elevator ropes and crane ropes to which repeated bending stress is applied, the bending fatigue characteristics of the steel wires greatly affect the life of the ropes. In recent years, due to the improvement of maintainability, the need for extending the life of ropes has increased, and steel wires with excellent bending fatigue characteristics for realizing this have been demanded. In addition, steel wires with excellent bending fatigue characteristics are also useful as ropes for bridges and PC steel wires.

[0003] For example, Patent Document 1 discloses a technique for improving fatigue characteristics by finely precipitating inclusions in steel. In addition, Patent Document 2 discloses a technique for obtaining high-strength wire rods by controlling the wire rod structure through salt patenting treatment after hot rolling.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the techniques disclosed in Patent Document 1 or Patent Document 2, control at the wire rod stage is required, and it is difficult to improve the characteristics by secondary processing alone.

[0006] An object of the present disclosure is to provide a steel wire having excellent fatigue characteristics and a rope using the same.

Means for Solving the Problems

[0007] According to the present disclosure, there are provided steel wires having excellent fatigue characteristics and ropes using the same. <1> The steel composition is, by mass%, C: 0.30 to 1.50%, 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, contains the above, and the balance consists of Fe and impurities, the metallographic structure consists of a ferrite phase and a cementite phase, in a cross-section perpendicular to the axial direction of the steel wire, the difference ΔHV between the maximum hardness and the minimum hardness and the average hardness HVave satisfy the following formula 1 In the surface layer, the difference between the absolute value |σ(θ)| of the axial residual stress at the first position and the absolute value |σ(θ + 180°)| of the axial residual stress at the second position 180 degrees in the circumferential direction with respect to the first position satisfies the following formula 2, a steel wire. ΔHV ≦ 0.1 × HVave ··· Formula 1 |{|σ(θ)| ― |σ(θ + 180°)|}| ≦ 200 MPa ··· Formula 2 <2> The steel composition is, by mass%, C: 0.30 to 1.50%, 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, contains the above, further contains one or more selected from the group consisting of the following Group A and Group B, and the balance consists of Fe and impurities, [Group A] Cr: 1.00% or less, Mo: 0.50% or less, Ti: less than 0.100%, Nb: less than 0.100%, V: less than 0.30%, B: less than 0.0100%, Cu: less than 0.50%, Ni: less than 0.50%, and Sn: one or more selected from the group consisting of less than 0.10% [Group B] Ca: less than 0.0050%, Mg: less than 0.0050%, Sb: less than 0.050%, and As: one or more selected from the group consisting of less than 0.050% The metallographic structure consists of a ferrite phase and a cementite phase, The difference ΔHV between the maximum hardness and the minimum hardness in a cross-section perpendicular to the axial direction of the steel wire, and the average hardness HVave satisfy the following formula 1 In the surface layer, the difference between the absolute value |σ(θ)| of the axial residual stress at the first position and the absolute value |σ(θ + 180°)| of the axial residual stress at the second position 180 degrees circumferentially with respect to the first position satisfies the following formula 2, steel wire. ΔHV ≦ 0.1 × HVave ··· Formula 1 |{|σ(θ)| ― |σ(θ + 180°)|}| ≦ 200 MPa ··· Formula 2 <3> The steel wire according to <2>, having a steel composition containing the Group A in mass%. <4> The steel wire according to <2> or <3>, having a steel composition containing the Group B in mass%. <5> The steel wire according to any one of <1> to <4>, having a wire diameter of 0.41 mm to 8.00 mm and a tensile strength of 1000 MPa or more. <6> The steel wire according to any one of <1> to <5>, which is for ropes. <7> A rope including the steel wire according to any one of <1> to <6>.

Advantages of the Invention

[0008] According to the present disclosure, a steel wire having excellent fatigue characteristics and a rope using the same are provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Modes for Carrying Out the Invention

[0010] 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. Also, 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 step by step 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 of other stepwise descriptions, or may be replaced with the value shown in the examples. Also, in the numerical ranges described step by step 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 of other stepwise descriptions, or may be replaced with the value shown in the examples. Also, the content of the elements of the steel composition may be expressed as the amount of the element (for example, the amount of C, the amount of Si, etc.). Also, regarding the content of the elements of the steel composition, unless otherwise specified, "%" means "mass%". Also, "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.

[0011] <Steel composition> The steel wire according to the present disclosure contains, by mass%, C: 0.30 to 1.50%, 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, or 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.

[0012] C: 0.30% to 1.50% 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 formed and the tensile strength decreases. On the other hand, when the C content exceeds 1.50%, primary cementite is produced excessively and the workability deteriorates. Therefore, the C content is limited to the range of 0.30% to 1.50%. The C content is preferably 0.35 to 1.20%, more preferably 0.40 to 1.10%.

[0013] 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%.

[0014] 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 form 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%.

[0015] 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 set to 0.100% or less, preferably 0.080% or less.

[0016] P: 0.050% or less P is an element that significantly strengthens the ferrite phase in steel and embrittles the steel, and thus 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%.

[0017] S: 0.050% or less S is a segregation element and reduces the ductility of steel, and thus 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%.

[0018] 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 reduction 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%.

[0019] 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 reduction 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%.

[0020] Cr: 1.00% or less Cr is an element effective in refining the ferrite phase and the 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 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, more preferably 0.08% or more.

[0021] 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, more preferably 0.05% or more.

[0022] 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. From the viewpoint of exerting the effect of Ti, the lower limit value of the Ti content is preferably 0.005% or more, more preferably 0.008% or more.

[0023] Nb: 0.100% or less Nb has the effect of suppressing the coarsening of austenite grains during heating by forming 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, more preferably 0.010% or more.

[0024] 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 V content is set to 0.30% or less. From the viewpoint of exerting the effect of V, the lower limit value of the V content is preferably 0.005% or more, more preferably 0.050% or more.

[0025] 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 B content is set to 0.0100% or less, preferably 0.0050% or less. From the viewpoint of exerting the effect of B, the lower limit value of the B content is preferably 0.0001% or more, more preferably 0.0002% or more.

[0026] 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 Cu content is set to 0.50% or less, preferably 0.20% or less. From the viewpoint of exerting the effect of Cu, the lower limit value of the Cu content is preferably 0.005% or more, more preferably 0.020% or more.

[0027] 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 completion time becomes long. Therefore, when the steel wire according to the present disclosure contains Ni, the Ni content is set to 0.50% or less, preferably 0.30% or less. From the viewpoint of exerting the effect of Ni, the lower limit value of the Ni content is preferably 0.005% or more, more preferably 0.02% or more.

[0028] 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 Sn content should be 0.10% or less. From the perspective of exerting the effect of Sn, the lower limit of the Sn content is preferably 0.002% or more, and more preferably 0.01% or more.

[0029] Ca: 0.0050% or less Ca is an element effective for deoxidizing steel. On the other hand, if Ca is 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 Ca content should be 0.0050% or less, preferably 0.0020% or less. From the perspective of exerting the effect of Ca, the lower limit of the Ca content is preferably 0.0002% or more, and more preferably 0.0005% or more.

[0030] Mg: 0.0050% or less Mg is an element effective for deoxidizing steel. However, if 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 Mg content should be 0.0050% or less, preferably 0.0040% or less. From the perspective of exerting the effect of Mg, the lower limit of the Mg content is preferably 0.0002% or more, and more preferably 0.0005% or more.

[0031] 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 Sb content should be 0.050% or less, preferably 0.015% or less. From the perspective of exerting the effect of Sb, the lower limit of the Sb content is preferably 0.002% or more, and more preferably 0.005% or more.

[0032] As: 0.050% or less As is an element that improves corrosion resistance. On the other hand, if added in excess, it will deteriorate the 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 value of the amount of As is preferably 0.001% or more, more preferably 0.005% or more.

[0033] 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 unintentionally 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. 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, etc. 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, (total of Zr, Te, Bi, Pb and Zn): 0.01% or less, respectively.

[0034] <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 a ferrite phase and a 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 a pearlite structure and a bainite structure may be mixed. Further, a ferrite structure composed of a ferrite phase or a cementite structure composed of a cementite phase may be included. The measurement method of the metallographic structure of the steel wire according to the present disclosure will be described in the examples.

[0035] <Hardness> The steel wire according to the present disclosure satisfies the formula 1 in that the difference ΔHV between the maximum hardness and the minimum hardness of the Vickers hardness HV in the cross-section perpendicular to the axial direction of the steel wire (which may be referred to as the C cross-section) is within 10% of the average hardness HV(ave), that is, satisfies the formula 1. ΔHV≦0.1×HVave ··· Formula 1 According to the experiments of the present inventors, when the difference (ΔHV) between the maximum value and the minimum value of the hardness from the surface layer to the center in the C cross-section of the steel wire according to the present disclosure is within 10% of the average value (HVave) of the hardness from the surface layer to the center, that is, satisfies the formula 1, the hardness difference within the steel wire cross-section is reduced, and uniform deformation is performed against repeated fatigue, so that the fatigue characteristics are improved. From the viewpoint of improving the fatigue characteristics, ΔHV is preferably within 8% of HVave, and more preferably within 5% of HVave.

[0036] <Residual stress> Next, the residual stress of the steel wire according to the present disclosure will be described. In the steel wire according to the present disclosure, on the surface layer of the steel wire, the difference between the absolute value (|σ(θ)|) of the axial residual stress σ(θ) at the first position and the absolute value (|σ(θ + 180°)|) of the residual stress σ(θ + 180°) at the second position 180 degrees in the circumferential direction with respect to the first position is 200 MPa or less, that is, satisfies the formula 2. |{|σ(θ)|―|σ(θ+180°)|}|≦200MPa ··· Formula 2

[0037] According to the experiments of the present inventors, when the difference between the absolute value of the axial residual stress σ(θ) on the surface layer of the steel wire according to the present disclosure and the absolute value of the axial residual stress σ(θ + 180°) at a position 180 degrees in the circumferential direction of the steel wire with respect to the measurement position of σ(θ) (that is, the surface layer position targeted with respect to the central axis of the steel wire) is 200 MPa or less, the variation in the residual stress on the surface layer of the steel wire is reduced, and the fatigue characteristics are improved by reducing the site that preferentially undergoes fatigue failure. From the viewpoint of improving the fatigue strength, the difference between |σ(θ)| and |σ(θ + 180°)| is preferably 150 MPa or less, and more preferably 120 MPa or less.

[0038] <Tensile strength> The tensile strength of the steel wire according to the present disclosure is not particularly limited, but is preferably 1000 MPa or more, and more preferably 1200 MPa or more. The measurement methods of Vickers hardness, residual stress, and tensile strength of the steel wire according to the present disclosure will be described in the examples.

[0039] <Wire diameter> The wire diameter of the steel wire according to the present disclosure is not particularly limited, but is preferably 0.41 mm to 8.00 mm. By having a wire diameter within this range, the function as a steel element wire for forming a structure such as a rope can be preferably exhibited.

[0040] <Manufacturing method of steel wire and rope> Next, the manufacturing method of the steel wire according to the present disclosure and the manufacturing method of the rope using this steel wire will be described.

[0041] The manufacturing method of the steel wire according to the present disclosure includes a step of descaling the wire rod to remove the oxide scale on the surface of the wire rod (descaling step), a step of rough drawing the descaled wire rod to obtain an intermediate steel wire (rough drawing step), a step of patenting the rough drawn intermediate steel wire (patenting step), a step of obtaining a steel wire by finish drawing the patented intermediate steel wire (finish drawing step), and a step of performing rope processing using a plurality of steel wires (rope processing step).

[0042] (Descaling step) In the manufacturing method of the 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 a hot-rolled wire rod is preferable. The diameter of the wire rod is not particularly limited, but is preferably about 4.0 to 14.0 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.

[0043] (Rough drawing) Next, wire drawing may be performed on the wire rod from which the oxide scale has been removed, and plastic working may be performed to elongate the steel wire rod in the longitudinal direction. The method of wire drawing is not particularly limited, but it is preferably performed by dry wire drawing. For example, wire drawing is performed to a wire diameter of 0.70 mm or more and 13.50 mm or less. In this specification, in order to distinguish between the steel wire after the rough wire drawing process and the steel wire after the finish wire drawing process, the steel wire after the rough wire drawing process and before the finish wire drawing process may be referred to as an intermediate steel wire.

[0044] (Patenting treatment) The intermediate steel wire obtained by wire drawing may be subjected to a patenting treatment using a molten lead bath or a molten salt bath. 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 more and 650°C or less. After the patenting treatment, wire drawing may be performed again. In this specification, the steel wire that has been subjected to rough wire drawing and patenting treatment may sometimes be referred to as an intermediate steel wire.

[0045] (Finish wire drawing) For the wire rod that has passed through the descaling process or the intermediate steel wire that has been subjected to wire drawing and patenting treatment, as a means of reducing the hardness difference from the surface layer to the center of the cross-section of the steel wire and reducing the variation in residual stress, in the final finishing process, for example, shaped wire drawing is performed.

[0046] (Shaped wire drawing) Figure 1 schematically shows an example of a cross-section parallel to the traveling direction X of the workpiece of the die 20. As shown in Figure 1, generally, the die 20 has a structure including a bell portion 21, an approach portion 22, and a bearing portion 24 in order 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. 2(A) shows a general die, and FIGS. 2(B) to 2(F) show the profiled dies 22B to 22F that can be used in the production of steel wires according to the present disclosure. As shown in FIG. 2(A), the die (hereinafter, "ordinary die") 20A used for normal wire drawing has a circular shape of the approach portion (drawing portion) 22A. On the other hand, as shown in FIGS. 2(B) to 2(F), the profiled dies 22B to 22F that can be used in the production of steel wires according to the present disclosure have an approach portion 22 with a shape that is an ellipse (FIG. 2(B)), or a triangular shape (FIG. 2(C)), a quadrangular shape (FIG. 2(D)), a pentagonal shape (FIG. 2(E)), or a hexagonal shape (FIG. 2(F)). Note that the shape of the bearing portion (shaping portion) 24 is circular for both the ordinary die (FIG. 2(A)) and the profiled dies (FIGS. 2(B) to 2(F)). Also, with respect to the wire diameter D, for example, the approach length is 1.2D 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 dashed lines in each die in FIGS. 2(B) to 2(F) indicate the wire diameter one pass before. The wire diameter one pass before can be calculated from the reduction rate described below. Such profiled wire drawing using such a profiled die is performed in the final finishing process of the steel wire. The profiled 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 profiled wire drawing. The reduction rate per pass of the profiled wire drawing is preferably 5% or more in order to obtain the above-described effects. Note that the reduction rate per pass is the value calculated by the following formula when the cross-sectional areas perpendicular to the longitudinal direction of the steel wire before and after one-pass wire drawing are S n-1 and S n respectively. Reduction rate per pass (%) = (S n-1 - S n ) / S n-1 × 100

[0047] (Heat treatment) The steel wire obtained as described above may be subjected to heat treatment such as hot dip plating, bluing, heat stretching, etc. as necessary. For example, in the hot dip galvanizing process, the steel wire is immersed in a zinc bath at 450°C for about 30 seconds. For example, in the bluing process, while applying a tension of 0 to 20% of the tensile strength of the obtained steel wire, the surface layer of the steel wire is heated at 380°C for several tens of seconds using an induction heating device and then air-cooled.

[0048] Through the above steps, the steel wire according to the present disclosure can be preferably manufactured.

[0049] (Rope processing step) In the method of manufacturing a rope using the steel wire according to the present disclosure, rope processing is performed on a plurality of steel wires including the steel wire according to the present disclosure. In the rope processing, for example, a twisted wire obtained by twisting steel wires or a parallel wire strand (PWS) obtained by combining steel wires in parallel is manufactured. The number and arrangement of the steel wires constituting the rope are not particularly limited and can be selected according to the strength, wire diameter, etc. required for the rope. Thereby, a rope is manufactured. The rope includes not only twisted wires but also parallel wire strands (PWS).

[0050] Through the above steps, the rope according to the present disclosure can be preferably manufactured. Note that the method for manufacturing the steel wire and rope according to the present disclosure is not limited to the above method, and they may be manufactured by other manufacturing methods.

[0051] <Applications> The applications of the steel wire according to the present disclosure are not particularly limited, but due to its excellent fatigue characteristics, it is particularly suitable as a rope application such as an elevator rope, a crane rope, a bridge rope, and a PC steel wire.

Examples

[0052] 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 just examples, and the steel wire and their manufacturing methods according to the present disclosure are not limited to the following examples.

[0053] Various cold working processes were performed on the rolled wire rod obtained by hot rolling a steel sheet having the chemical composition (steel composition) shown in Table 1. The balance excluding the components (elements) shown in Table 1 is Fe and impurities, and "-" in Table 1 means that the element was not intentionally added.

[0054]

Table 1

[0055] Using the steel wire obtained by the above manufacturing method, the metallographic structure, residual stress, hardness, tensile strength, and fatigue strength were evaluated by the methods described below. Each evaluation method will be described below.

[0056] (Measurement of Metallographic Structure) After mirror-polishing a cross-section (L cross-section) that includes the central axis of the steel wire and is parallel to the axial direction, the metallographic structure is revealed using a 3% nital solution. Then, using a field emission scanning electron microscope (FE-SEM), the structure is observed at magnifications of 5,000 to 20,000 times. The observation regions are two regions at positions D / 4 and D / 2 in the direction perpendicular to the central axis from the central axis when the wire diameter is D. At that time, two fields of view are observed for each region, and the observed area per field of view is 30 μm × 30 μm to 100 μm × 100 μm. It is confirmed by observation that the metallographic structure has a pearlite structure or bainite structure having a lamellar structure composed of ferrite phase and 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 retained austenite and martensite do not exist. Since retained austenite and martensite have a different contrast from the above-mentioned pearlite structure, bainite structure, grain boundary ferrite, primary cementite, or spheroidized cementite, the confirmation is easy.

[0057] (Measurement of Residual Stress in the Surface Layer Region) The residual stress in the surface region is measured using an X-ray residual stress measuring device. The measurement is performed using a Co tube target. As shown in Fig. 3, with the axis C of the steel wire 10 as the center, the residual stress in the axial direction is measured at three locations (N3) each at the 0-degree position and the 180-degree position in the circumferential direction. The collimator diameter is set to 0.3 mm. The N3 average value at the 0-degree position and the N3 average value at the 180-degree position are obtained respectively, and their average values are further used for the determination in Equation 2.

[0058] (Hardness measurement) The hardness measurement is performed in accordance with JIS Z 2244:2009. The Vickers hardness is measured from the surface to the center in a cross-section (C cross-section) perpendicular to the axial direction of the steel wire. With the wire diameter as D, a total of 7 points are measured at intervals of D / 8 from the surface to the center. The measurement load is 100 gf. As shown in Fig. 4, a total of 7 points are measured at 3 points each from 2 directions at 180-degree intervals in the circumferential direction of the steel wire 10 and 1 point at the center. The average value, maximum value, and minimum value of the 7 measured points are used for the determination in Equation 1.

[0059] (Tensile test) The tensile test is performed in accordance with JIS Z 2241:2011. At that time, the number of N is set to 3, and its average value is used.

[0060] (Fatigue test) The fatigue test is performed 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 revolutions 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 times, the highest stress is taken as the fatigue strength.

[0061] (Twisted wire test) Using a general wire twisting machine for steel wires, a 7-strand twisted configuration as shown in FIGS. 5A and 5B is used to twist the wire under the conditions of a twist pitch of 50D (wire diameter D) and a speed of 2 m / min. When a wire break occurred in the steel wire with a twisted wire length of less than 100 m, it was judged as "wire break".

[0062] Table 2 shows the wire diameter of the intermediate steel wire, the patenting conditions (processing temperature), the wire drawing method of the finishing wire drawing, the area reduction rate of the final process, and the die shape of the final process. In addition, the wire drawing method of the process before the final process in the finishing wire drawing was normal wire drawing, and wire drawing was performed with an area reduction rate of 10 - 20% for each pass. Table 3 shows the metallographic structure, the diameter of the steel wire after finishing wire drawing (final wire diameter) D, the tensile strength, the difference ΔHV between the maximum hardness and the minimum hardness of the cross section of the steel wire, and 10% of the average hardness HV(ave) in the cross section, the determination of Formula 1, the absolute value of the axial residual stress σ(θ) on the steel wire surface layer, and the difference between the absolute value of the residual stress σ(θ + 180°) at a position 180 degrees in the radial direction with respect to σ(θ), that is, the left side of Formula 2, the determination of Formula 2, and the feasibility of twisting the wire. Note that the underlined parts in Table 2 and Table 3 mean that they are outside the scope of the present disclosure. Regarding the determination of Formula 1 and Formula 2, when the following formula is satisfied, it is marked as "〇", and when it is not satisfied, it is marked as "×". ΔHV ≦ 0.1 × HVave ··· Formula 1 |{|σ(θ)| - |σ(θ + 180°)|}| ≦ 200 MPa ··· Formula 2

Table 2

[0063]

Table 3

[0064] No.1 to 19 are examples of the steel wire and the twisted wire according to the present disclosure, and satisfy the above criteria.

[0065] No.20 to 38 are examples of the same steel type × wire diameter as No.1 to 19, but the final wire drawing is normal wire drawing and does not satisfy Formula 1 and Formula 2, or either one of the formulas. For example, No. 20 has the same steel type × wire diameter as No. 1, but since the left side of Equation 2 is higher than 200 MPa, its fatigue strength is low. Similarly, No. 21 corresponds to No. 2 and has a low fatigue strength for the same reason. No. 22 has the same steel type × wire diameter as No. 3, but does not satisfy Equation 1, so its fatigue strength is low. Similarly, Nos. 24 to 38 correspond to Nos. 5 to 19 and have low fatigue strengths because they do not satisfy Equation 1 and Equation 2.

[0066] For Nos. 39 to 46, since the content of any one of C, Si, Mn, Al, P, S, N, and O exceeds the upper limit, wire breakage occurred during wire drawing due to segregation or the like. For Nos. 47 to 49, since the content of any one of C, Si, and Mn is below the lower limit, the tensile strength has not reached 1000 MPa and the fatigue strength is low.

[0067] As described above in detail for 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.

Explanation of Reference Numerals

[0068] 10 Steel wire 20 Die 22 Approach section 24 Bearing section 100 Rope

Claims

1. The steel composition is by mass%, C: 0.30 to 1.50%, 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, and the balance consists of Fe and impurities, the metallographic structure consists of a ferrite phase and a cementite phase, the difference ΔHV between the maximum hardness and the minimum hardness in a cross-section perpendicular to the axial direction of the steel wire, and the average hardness HVave satisfy the following formula 1 In the surface layer, the difference between the absolute value |σ(θ)| of the axial residual stress at the first position and the absolute value |σ(θ + 180°)| of the axial residual stress at the second position 180 degrees circumferentially from the first position satisfies the following formula 2, a steel wire. ΔHV ≦ 0.1 × HVave... Formula 1 |{|σ(θ)| - |σ(θ + 180°)|}| ≦ 200 MPa... Formula 2

2. The steel composition is by mass%, C: 0.30 to 1.50%, 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, and further contains one or more selected from the group consisting of the following Group A and Group B, and the balance consists 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 difference ΔHV between the maximum hardness and the minimum hardness in a cross-section perpendicular to the axial direction of the steel wire, and the average hardness HVave satisfy the following formula 1 In the surface layer, the difference between the absolute value |σ(θ)| of the axial residual stress at the first position and the absolute value |σ(θ + 180°)| of the axial residual stress at the second position 180 degrees circumferentially from the first position satisfies the following formula 2, a steel wire. ΔHV ≦ 0.1 × HVave... Formula 1 |{|σ(θ)| - |σ(θ + 180°)|}| ≦ 200 MPa... Formula 2

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 0.41 mm to 8.00 mm and a tensile strength of 1000 MPa or more.

6. The steel wire according to claim 1 or claim 2, which is for a rope.

7. A rope comprising the steel wire according to claim 1 or claim 2.

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