JP5882827B2 - Steel wire, method for manufacturing steel wire, and method for evaluating steel wire - Google Patents

Description

  The present invention relates to a steel wire, a method for manufacturing a steel wire, and a method for evaluating a steel wire, and more particularly to a steel wire excellent in corrosion fatigue resistance, a method for manufacturing a steel wire, and a method for evaluating a steel wire.

  In rubber products such as pneumatic tires and industrial belts, high tensile strength and excellent fatigue resistance are required for steel cords used as reinforcing materials in order to reduce the weight and improve durability. Also, today, in order to reduce the amount of steel cords used and achieve the same tire strength as the current situation, it is required to increase the tensile strength of each steel wire of the steel cord as a reinforcing material. Yes.

  In order to meet such demands, many studies and reports have been made from various viewpoints, and it is known that it is important to increase the ductility of steel wire rods in order to achieve high tensile strength. Therefore, in order to achieve high tensile strength, the properties such as the ductility of the steel wire are evaluated. For example, in the case of evaluating the properties such as the ductility of the carbon steel wire by hardness, the conventional method uses the width direction of the steel wire. A method of evaluating using the hardness distribution in the cross section (cross section) of the above has been adopted.

For example, Patent Document 1 discloses that the hardness distribution in a steel wire of a high-carbon steel wire is 0.960 ≦ Hv ≦ 1.030 when R = 0, R = 0.8, and R = 0.95 ( R is _{r 0} the radius of the steel wire, if the distance between the arbitrary position and the center of the steel wire was r, R = _{r /} r 0, Hv is _{Hv 0.5} the hardness at a position R = 0.5 and then, if the hardness of the position R was Hv _R, steel wire of high strength is disclosed which can achieve high strength by satisfying _{Hv = Hv R / Hv 0.5)} . Further, in Patent Document 2, the Vickers hardness distribution in the wire cross section of the high carbon steel wire rod is substantially flat from the surface to the inside excluding the central portion within one-fourth of the wire diameter, thereby achieving ultrahigh strength and high strength. It has been reported that toughness can be obtained.

  Various production methods for realizing high ductility and high fatigue resistance in the final wet wire drawing process have also been proposed. For example, in Patent Document 3, for the purpose of obtaining a high quality steel wire even by using a general-purpose steel cord wire rod, each area reduction rate in the final wire drawing process is determined by the processing strain applied to the raw material wire rod of the steel cord. It has been proposed to adjust within a predetermined range. Further, in Patent Document 4, in order to obtain a high tensile strength steel wire having high torsion ductility, in the final wet drawing process, the area reduction rate of each die is about 15% to about 18%. It has been proposed to draw at a rate.

JP-A-8-156514 (Claims etc.) JP-A-8-311788 (Claims etc.) JP-A-7-305285 (Claims etc.) JP-A-5-200428 (Claims etc.)

  According to Patent Documents 1 and 2, although a steel wire having a high tensile strength can be obtained, the corrosion fatigue resistance may be lowered when the steel wire has a high tensile strength. Also, as in Patent Document 3 and Patent Document 4, in order to obtain high ductility, high fatigue resistance, etc. in the final wire drawing process, it is not sufficient to adjust the area reduction rate of the entire die, and high ductility. However, it was not always sufficient as a method for producing a steel cord having high fatigue resistance. That is, it is necessary to clarify the wire drawing conditions in the vicinity of the final die in the final wire drawing process that particularly affects the characteristics of the steel wire.

  Therefore, an object of the present invention is to clarify the wire drawing conditions in the vicinity of the final die in the final wire drawing process, which easily affects the properties of the steel wire, and to provide a steel wire excellent in corrosion fatigue resistance, a method of manufacturing a steel wire, and a steel It is in providing the evaluation method of a wire.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has a case where the corrosion fatigue resistance deteriorates when the strength of the steel wire is increased. The layered structure of ferrite and cementite in the inside) was found to be non-uniform. As a result of further intensive studies based on such knowledge, the lamellar structure is a nano-order structure, and thus it is difficult to observe the structure. However, the Vickers hardness in the longitudinal section (long section) of the steel wire is the lamellar spacing. Since there is a certain correlation, it has been found that the lamellar spacing can be easily evaluated by measuring the Vickers hardness of the steel wire before the straightening process, and the present invention has been completed.

That is, the steel wire of the present invention is a steel wire having a carbon content of 0.50 to 1.10% by mass, and is a surface layer portion of a longitudinal section (long section) of the steel wire before the straightening process. The Vickers hardness Hv _LS and the Vickers hardness Hv _{LC at} the center of the long cross section are expressed by the following formula (1),
0.95 <Hv _LS / Hv _LC <1.10 (1)
And a tensile strength of 3000 to 5000 MPa is satisfied.

In the steel wire of the present invention, the ratio between the hardness Hv _CS in the surface layer portion of the cross section (cross cross section) orthogonal to the longitudinal direction after the straightening and the hardness Hv _LS in the surface layer portion of the cross section in the longitudinal direction (long cross section), The coefficient X (Hv _CS / Hv _LS ), the ratio of the hardness Hv _{CC at} the center of the cross section to the hardness Hv _{LC at} the center of the long section, and the coefficient X (Hv _CC / Hv _LC ) are as follows: Formula (2),
0.9 <coefficient X ≦ 1.10 (2)
It is preferable to satisfy the relationship represented by these.

Moreover, the manufacturing method of the steel wire of this invention is carbon content 0.50-1.10 mass%, and manufactures the steel wire which has the final wire drawing process which wet-draws the steel wire material which has a pearlite structure | tissue. In the method
Of the 10 dies before the final die in the final wire drawing step, 3 or less dies with a surface reduction rate of 10% or less are set, and the processing strain of the 10 dies before the final die is 2.5 or more. It is characterized by that.

In the steel wire manufacturing method of the present invention, the following formula (3) is obtained from the die resistance (N) in each drawing pass of the final drawing step and the outlet wire diameter (mm ² ) of the die.
Coefficient A = Die resistance (N) / Die outlet wire diameter (mm ² ) (3)
It is preferable that the number of dies whose coefficient A represented by

Furthermore, the steel wire evaluation method according to the present invention provides the Vickers hardness Hv _LS of the surface layer portion of the steel wire in the longitudinal direction before the straightening process and the longitudinal section in evaluating the corrosion fatigue resistance of the steel wire. Vickers hardness Hv _{LC at} the center of the following formula (1),
0.95 <Hv _LS / Hv _LC <1.10 (1)
The corrosion fatigue resistance is evaluated based on whether or not the relationship expressed by the above is satisfied.

  ADVANTAGE OF THE INVENTION According to this invention, the steel wire excellent in corrosion fatigue resistance, its manufacturing method, and the evaluation method of a steel wire can be provided.

It is explanatory drawing which shows the hardness measurement location in the long cross section of a steel wire. It is explanatory drawing which shows the density distribution of the lamellar space | interval of the surface layer part and center part in the long cross section of a steel wire. It is explanatory drawing which shows the hardness measurement location in the cross section of a steel wire. It is a graph which shows the relationship with Hv _LS and Hv _LC of an Example and a comparative example.

Hereinafter, the steel wire of this invention is demonstrated in detail using drawing.
The steel wire of the present invention contains 0.50 to 1.10 mass%, preferably 0.80 to 1.10 mass% of carbon. When the carbon content is less than 0.50% by mass, pro-eutectoid ferrite is likely to precipitate, resulting in non-uniform metal structure, and the total amount of wire drawing for obtaining high strength is increased. On the other hand, when the carbon content exceeds 1.10% by mass, pro-eutectoid cementite is likely to be precipitated at the grain boundaries, resulting in non-uniform metallographic structure.

FIG. 1 is an explanatory view showing hardness measurement points of a long cross section of a steel wire. In the steel wire 1 of the present invention, the hardness Hv _LS in the surface layer part 3 of the long cross section 2 and the hardness Hv _LC in the center part 4 of the long cross section 2 before the straightening process are expressed by the following formula (1),
0.95 <Hv _LS / Hv _LC <1.10 (1)
It satisfies the relationship represented by Generally, when a steel wire material is drawn, different processing strains are applied to the surface layer portion and the center portion. Due to this processing difference, a sparse and dense distribution of lamellar spacing occurs between the surface layer portion 3 and the central portion 4 in the long cross section 2 of the steel wire 1.

  FIG. 2 is an explanatory diagram showing a sparse / dense distribution of the lamellar 5 interval between the surface layer portion 3 and the center portion 4 in the long cross section 2 of the steel wire 1. The ferrite and cementite in the pearlite form a local battery. However, as shown in FIG. 2, when the distance between the surface layer portion 3 of the long cross section 2 of the steel wire 1 and the lamellar 5 between the center portions 4 becomes uneven, It is thought that the progress of corrosion changes. Therefore, in order to improve the corrosion fatigue resistance of the steel wire, it is important to reduce the density distribution of the lamellar spacing in the long cross section 2 of the steel wire 1.

As described above, since there is a certain correlation between the hardness (Hv _LS and Hv _LC ) in the long cross section of the steel filament and the lamellar interval, the hardness (Hv _LS and Hv _LC ) of the surface layer portion 3 and the central portion 4 of the steel wire 1. Can be used to evaluate the lamellar spacing. The steel wire of the present invention satisfies the relationship represented by the above formula (1). However, the steel wire has a substantially uniform lamellar spacing in its long cross section and is excellent in corrosion fatigue resistance. It will be. Preferably 0.95 <Hv _LS / Hv _LC <1.05
Satisfies the relationship expressed by

In the steel wire of the present invention, the hardness Hv _CS in the surface layer portion of the cross section (cross cross section) orthogonal to the longitudinal direction after the straightening process and the hardness Hv _LS in the surface layer portion of the cross section in the longitudinal direction (long cross section). Ratio, coefficient X (Hv _CS / Hv _LS ), ratio of hardness Hv _{CC at} the center of the cross section to hardness Hv _{LC at} the center of the long section, and coefficient X (Hv _CC / Hv _LC ) Is the following formula (2),
0.9 <coefficient X ≦ 1.10 (2)
It is preferable to satisfy the relationship represented by these. Here, the cross section hardness is measured at the surface layer portion 3 and the central portion 4 in the cross section 2 of the steel wire 1 shown in FIG.

  In the drawn steel wire, the long section hardness is not affected by the curled grain, and the hardness is determined by the arrangement of the lamellar, so that the evaluation can be performed without variation. Therefore, based on the hardness of the long section, the ratio of the cross section hardness and the evaluation of the coefficient X are considered to enable more appropriate characteristic value evaluation. When the hardness ratio and the coefficient X are larger than 0.90, it was confirmed that a product having good ductility was obtained. Therefore, the lower limit was set to 0.90. On the other hand, with respect to the upper limit value, as a result of the evaluation test, when the hardness ratio of the steel wire surface layer portion and the coefficient X are 1.04, the best ductility is obtained. As a result, 1.10 was set as the upper limit.

  In the steel wire of the present invention, the tensile strength is set to 3000 to 5000 MPa, preferably 4000 MPa or more. By setting the tensile strength of the steel wire in the range of 3000 to 5000 MPa, it is possible to achieve the same tire strength as the current situation while reducing the amount of steel cord used.

Next, the manufacturing method of the steel wire of this invention is demonstrated.
In the steel wire manufacturing method of the present invention, the carbon content is 0.50 to 1.10% by mass, preferably 0.80 to 1.10% by mass, and a pearlite structure in the final wet drawing step. When the steel wire material having a thickness of 10 is subjected to the final wire drawing, among the 10 dies before the final die, the number of die having an area reduction rate of 10% or less is set to 3 or less, preferably 0. At this time, the processing strain in 10 dies before the final die is set to 2.5 or more. By satisfying such conditions, the processing difference between the surface layer portion and the center portion of the steel wire can be reduced. As a result, the Vickers hardness Hv _LS of the surface layer portion of the long cross section of the steel wire before the straightening process and the Vickers hardness Hv _LC of the central portion of the long cross section satisfy the relationship represented by the above formula (1). it can. Here, the processing strain is ε = 2 · ln (d ₀ / d ₁ ) (d ₀ is the diameter (mm) of the steel wire material before processing, and d ₁ is the diameter (mm) of the steel wire after processing. And ln is a natural logarithm).

In the steel wire manufacturing method of the present invention, the following formula (3) is obtained from the die drag (N) in each wire drawing pass in the final wire drawing step and the outlet wire diameter (mm ² ) of the die.
Coefficient A = Die resistance (N) / Die outlet wire diameter (mm ² ) (3)
It is preferable that the number of dies whose coefficient A represented by the formula is 95 or less is 2 or less, and preferably the coefficient A of all dies is 90 or less. By satisfying such requirements, it is possible to prevent the metal structure of the steel wire from being destroyed. As a result, after the straightening process applied to the steel wire after the final wire drawing step, the steel wire satisfies the above formula (2), and the steel wire is not only corrosion resistant but also excellent. Ductility can also be imparted.

  In the steel wire manufacturing method of the present invention, it is only important to satisfy the above requirements, and there are no particular restrictions on other conditions. For example, as a die shape, a shape generally used for steel wire drawing can be applied. For example, an approach angle is 8 ° to 12 °, and a bearing length is about 0.3D to 0.6D. Things can be used. The material of the die is not limited to a sintered diamond die or the like, and an inexpensive cemented carbide die can be used. Moreover, there is no restriction | limiting in particular also about the correction process after the final wire drawing, For example, it can carry out by letting a steel wire pass between several rollers arrange | positioned in zigzag form.

Next, a method for evaluating the corrosion fatigue resistance of the steel wire of the present invention will be described.
The method for evaluating the corrosion fatigue resistance of the steel wire according to the present invention includes the Vickers hardness Hv _LS of the surface portion of the long cross section and the Vickers hardness of the center portion of the long cross section in the state before the correction processing of the steel wire to be evaluated. Hv _LC is the following formula:
0.95 <Hv _LS / Hv _LC <1.10 (1)
The evaluation is performed based on whether the relationship expressed by is satisfied. By selecting a steel wire Hv _LC and Hv _LS satisfying the above relationship, a steel wire excellent in corrosion fatigue resistance can be reliably obtained.

Hereinafter, the steel wire of this invention is demonstrated in detail using an Example.
<Examples and Comparative Examples>
The steel wire materials of the type shown in Table 1 below were dry-drawn until the diameters shown in the same table were obtained. The obtained steel wire material was subjected to patenting heat treatment and brass plating to produce a brass-plated steel wire material. The obtained brass-plated steel wire material was wet-drawn according to the pass schedule shown in Table 1 to produce steel wires having the diameters shown in the same table.

The obtained steel wire was evaluated for tensile strength, Hv _LS , Hv _LC , and corrosion fatigue resistance according to the following procedure. The obtained results are shown in Table 2. Moreover, FIG. 4 is a graph which shows the relationship with Hv _LS and Hv _LC of an Example and a comparative example. For wet wire drawing, a slip-type wet continuous wire drawing machine was used, and a die of the wire drawing machine was a cemented carbide die having an approach angle of about 12 ° and a bearing length of about 0.5D.

<Tension>
Based on the tensile test of JIS G3510, the tensile strength of each steel wire was measured.

<Vickers hardness>
The hardness of the surface layer part and the center part of the long cross section of each steel wire was measured using a Mitsutyo Vickers hardness tester (model: HM-211).

<Corrosion fatigue resistance>
The corrosion fatigue resistance was evaluated by immersing a steel wire cut to 100 mm in a neutral aqueous solution containing a small amount of nitrate ions and sulfate ions, and applying a repeated bending stress of 300 N / mm ² at a speed of 1000 revolutions per minute. The number of revolutions until the steel wire was broken was determined. In Table 2, the body corrosion fatigue resistance is expressed as an index with the number of rotations until the fracture of the comparative example is taken as 100. It shows that it is excellent in corrosion fatigue resistance, so that this figure is large.

※１：最終ダイスより前１０個のダイスのうち減面率１０％以下のダイスの個数
※２：最終ダイスより前１０個のダイスにおける加工歪

* 1: Number of dies with a surface area reduction of 10% or less among the 10 dies before the final die * 2: Machining distortion in the 10 dies before the final die

  From Table 2 and FIG. 4, it can be seen that the steel wire of the present invention is excellent in corrosion fatigue resistance.

1 Steel Wire 2 Long Section 3 Surface Layer 4 Center 5 Lamella 6 Cross Section 21 Steel Wire 22 Grip

Claims (5)

A steel wire having a carbon content of 0.50 to 1.10% by mass, the Vickers hardness Hv _LS of the surface layer portion of the longitudinal section (long section) of the steel wire before the straightening process, and a long section The Vickers hardness Hv _{LC at the} center is the following formula (1),
0.95 <Hv _LS / Hv _LC <1.10 (1)
The steel wire characterized by satisfying the relationship represented by the above and having a tensile strength of 3000 to 5000 MPa. Ratio of hardness Hv _CS in the surface layer portion of the cross section (cross cross section) orthogonal to the longitudinal direction after the straightening processing and hardness Hv _LS in the surface layer portion of the cross section in the longitudinal direction (long cross section), coefficient X (Hv _CS / Hv _LS) ), And the ratio of the hardness Hv _{CC at} the center of the cross section to the hardness Hv _{LC at} the center of the long section, the coefficient X (Hv _CC / Hv _LC ) is the following formula (2),
0.9 <coefficient X ≦ 1.10 (2)
The steel wire of Claim 1 which satisfies the relationship represented by these. In the method for producing a steel wire having a carbon wire content of 0.50 to 1.10% by mass and having a final wire drawing step of performing wet wire drawing on a steel wire material having a pearlite structure,
Of the 10 dies before the final die in the final wire drawing step, 3 or less dies with a surface reduction rate of 10% or less are set, and the processing strain of the 10 dies before the final die is 2.5 or more. A method for producing steel wire, characterized in that From the die resistance (N) in each wire drawing pass in the final wire drawing step and the die outlet wire diameter (mm ² ), the following formula (3),
Coefficient A = Die resistance (N) / Die outlet wire diameter (mm ² ) (3)
The method of manufacturing a steel wire according to claim 3, wherein the number of dies whose coefficient A represented by In evaluating the corrosion fatigue resistance of the steel wire, the Vickers hardness Hv _LS of the surface layer portion of the cross section in the longitudinal direction of the steel wire and the Vickers hardness Hv _LC of the central portion of the cross section in the longitudinal direction before the straightening are as follows: Formula (1),
0.95 <Hv _LS / Hv _LC <1.10 (1)
Corrosion fatigue resistance evaluation method for steel wire, characterized in that corrosion fatigue resistance is evaluated based on whether or not the relationship expressed by

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