Steel wire

Abstract

A steel wire according to the present invention is formed of a steel that contains 1.0% by mass to 1.1% by mass of C, 0.15% by mass to 0.25% by mass of Si, 0.25% by mass to 0.35% by mass of Mn and 0.15% by mass to 0.25% by mass of Cr, with the balance being made up of Fe and unavoidable impurities. A steel wire 1 has a wire diameter D of 0.15 mm to 0.42 mm. The steel has a pearlite structure. The dislocation density of the steel is 2.4 × 1016 m-2 to 5.0 × 1016 m-2. The half width of a Debye ring of the Fe (211) plane of the steel in the circumferential direction at the maximum peak intensity is 42° or more.

Description

[Technical Field]

[0001] The present disclosure relates to steel wire.

[0002] This application claims priority from Japanese Application No. 2022-25608, filed February 22, 2022, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0003] A steel wire containing a pearlite structure can be used, for example, as a steel wire constituting a steel cord. In the production of a steel cord, a plurality of steel wires are twisted together. Therefore, steel wires used for such applications are required to have not only tensile strength but also toughness in order to prevent wire breakage during twisting. Technology relating to steel wires that aims to achieve both tensile strength and toughness has been proposed (see, for example, JP 2019-56162 A (Patent Document 1)). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-56162 Summary of the Invention

[0005] The steel wire according to the present disclosure contains 1.0 mass % or more and 1.1 mass % or less of C (carbon), 0.15 mass % or more and 0.25 mass % or less of Si (silicon), and 0.25 mass % or more and 0.3 5 quality Mn (manganese) 0.15 mass% or more and 0.2 mass% or more 5 quality The steel wire of the present disclosure is made of a steel containing 0.15 mm or more and 0.42 mm or less of Cr (chromium), with the balance being Fe (iron) and unavoidable impurities. The steel has a pearlite structure. The dislocation density of the steel is 2.4 × 10 16 m -2 Over 5.0 x 10 16 m -2The half-width in the circumferential direction at the maximum peak intensity of the Debye rings on the Fe(211) plane of the above steel is 42° or more. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic perspective view showing the structure of a steel wire. [Figure 2] FIG. 2 is a flowchart showing an outline of the method for manufacturing a steel wire. [Figure 3] FIG. 3 is a graph showing the relationship between dislocation density and tensile strength. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Problem to be solved by this disclosure] As described above, there are cases where a steel wire is required to have both high tensile strength and high toughness. One of the objects of the present disclosure is to provide a steel wire that can have both high tensile strength and high toughness.

[0008] [Effects of this disclosure] The steel wire of the present disclosure can achieve both high tensile strength and high toughness.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. The steel wire of the present disclosure contains 1.0 mass % or more and 1.1 mass % or less of C, 0.15 mass % or more and 0.25 mass % or less of Si, and 0.25 mass % or more and 0.3 5 quality % or less of Mn and 0.15% or more of Mn and 0.2% or more of Mn. 5 quality The steel wire of the present disclosure is made of a steel containing 0.15 mm or more and 0.42 mm or less of Cr, with the balance being Fe and unavoidable impurities. The steel has a pearlite structure. The dislocation density of the steel is 2.4 × 10 16 m -2 Over 5.0 x 10 16 m -2 The half-width in the circumferential direction at the maximum peak intensity of the Debye rings on the Fe(211) plane of the above steel is 42° or more.

[0010] Increasing the degree of processing (area reduction rate) in the wire drawing process when manufacturing a steel wire can improve the strength of the steel wire, but this also reduces the toughness of the steel wire.

[0011] According to the investigations of the present inventors, in the production of a steel wire made of steel having a pearlite structure, even if the degree of processing in the wiredrawing step is increased to increase the dislocation density and thereby increase the tensile strength, high toughness can be ensured by suppressing an increase in the crystal orientation in the steel constituting the steel wire. Specifically, in the steel wire of the present disclosure, the dislocation density is 2.4 × 10 16 m -2 Over 5.0 x 10 16 m -2 Despite the high value of 0.01 or less, the circumferential half-width at the maximum peak intensity of the Debye rings on the Fe(211) plane of the steel constituting the steel wire is 42° or more. As a result, the steel wire of the present disclosure can ensure excellent toughness despite its high tensile strength. In this way, the steel wire of the present disclosure can achieve both high tensile strength and high toughness.

[0012] In this application, "wire diameter" means the diameter of a circle having the same area as the area of ​​a cross section perpendicular to the longitudinal direction of the steel wire. The shape of the cross section perpendicular to the longitudinal direction of the steel wire is not particularly limited, and any shape can be adopted. The shape of the cross section perpendicular to the longitudinal direction of the steel wire is, for example, a circle. In this case, "wire diameter" means the diameter of the cross section perpendicular to the longitudinal direction of the steel wire.

[0013] In the steel wire, the half-value width may be 60° or more and 90° or less. By making the half-value width 60° or more, it becomes easier to ensure high toughness. By making the half-value width 90° or less, a high dislocation density is tolerated, making it easier to obtain high tensile strength.

[0014] In the above steel wire, the dislocation density is 3.0 × 10 16 m -2 Over 5.0 x 10 16 m -2The dislocation density may be 3.0×10 or less. 16 m -2 By making the dislocation density 5.0×10 or more, it becomes easier to ensure high tensile strength. 16 m -2 By making it the following, it becomes easy to suppress the crystal orientation and ensure high toughness.

[0015] The steel wire may have a wire diameter of 0.15 mm or more and 0.18 mm or less, and a tensile strength of 4240 MPa or more and 4900 MPa or less.

[0016] The steel wire may have a wire diameter of 0.18 mm or more and 0.21 mm or less, and a tensile strength of 4180 MPa or more and 4740 MPa or less.

[0017] The steel wire may have a wire diameter of 0.21 mm or more and 0.30 mm or less, and a tensile strength of 4000 MPa or more and 4580 MPa or less.

[0018] The above combination of wire diameter and tensile strength makes it possible to achieve a sufficient tensile strength for each wire diameter. The tensile strength can be measured, for example, in accordance with JIS (Japanese Industrial Standards) Z 2241.

[0019] Here, the reason why the composition of the steel constituting the steel wire is limited to the above range will be explained.

[0020] C: 1.0% by mass or more and 1.1% by mass or less C is an element that has a significant effect on the strength of a steel wire having a pearlite structure. From the viewpoint of obtaining sufficient tensile strength as a steel wire, the C content must be 1.0 mass% or more. As the C content increases, toughness decreases. From the viewpoint of ensuring sufficient toughness, the C content must be 1.1 mass% or less. From the viewpoint of improving toughness, the C content is preferably 1.05 mass% or less.

[0021] Si: 0.15 mass% or more and 0.25 mass% or less Silicon is an element that functions as a deoxidizer during steel refining. Si also increases the strength of ferrite in pearlite structures. To ensure high tensile strength, the silicon content must be 0.15 mass% or more. If the silicon content is too high, toughness may decrease. To ensure sufficient toughness, the silicon content must be 0.25 mass% or less.

[0022] Mn: 0.25 mass% or more and 0.35 mass% or less Mn, like Si, is an element that functions as a deoxidizer during steel smelting. To fully exert its effect as a deoxidizer, the manganese content must be 0.25% by mass or more. If the amount of Mn added is large, when patenting is performed before the wiredrawing process, a martensite structure is more likely to form during cooling after heating. The martensite structure thus formed reduces workability during wiredrawing. Therefore, the Mn content must be 0.35% by mass or less.

[0023] Cr: 0.15 mass% or more and 0.25 mass% or less Cr contributes to increasing the tensile strength of steel wire. From the viewpoint of ensuring high tensile strength, the Cr content must be 0.15 mass% or more. Addition of Cr leads to an increase in raw material costs. From the viewpoint of reducing raw material costs, the Cr content must be 0.25 mass% or less.

[0024] Inevitable impurities During the manufacturing process of steel wire, unavoidable impurities such as P (phosphorus) and S (sulfur) are inevitably mixed into the steel constituting the steel wire. If excessive amounts of P and S are present, they cause grain boundary segregation and the formation of inclusions, thereby deteriorating the properties of the steel. Therefore, the P and S contents are preferably 0.025 mass% or less, respectively. Furthermore, the total content of unavoidable impurities, including P and S, is preferably 0.3 mass% or less.

[0025] [Details of the embodiments of the present disclosure] Next, embodiments of the steel wire according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0026] FIG. 1 is a schematic perspective view showing the structure of a steel wire. In FIG. 1, a cross section perpendicular to the longitudinal direction of the steel wire is also shown. Referring to FIG. 1, a steel wire 1 in this embodiment is a steel wire having a circular cross section perpendicular to the longitudinal direction and an outer circumferential surface 11 in the shape of a cylindrical surface. The wire diameter D of the steel wire 1 is 0.15 mm or more and 0.42 mm or less. The cross section perpendicular to the longitudinal direction of the steel wire 1 may be other than circular, and may be, for example, elliptical.

[0027] The steel wire 1 contains 1.0 mass % or more and 1.1 mass % or less of C, 0.15 mass % or more and 0.25 mass % or less of Si, and 0.25 mass % or more and 0.3 5 quality % or less of Mn and 0.15% or more of Mn and 0.2% or more of Mn. 5 quality % or less of Cr, and the balance being Fe and unavoidable impurities. The steel constituting the steel wire 1 has a pearlite structure. The dislocation density of the steel constituting the steel wire 1 is 2.4 × 10 16 m -2 Over 5.0 x 10 16 m -2 The half-width in the circumferential direction at the maximum peak intensity of the Debye rings on the Fe(211) plane of the steel constituting the steel wire 1 is 42° or more.

[0028] The dislocation density of the steel constituting the steel wire 1 can be measured, for example, using a synchrotron XRD (X-ray diffractometer). The half-width in the circumferential direction at the maximum peak intensity of the Debye rings on the Fe(211) plane of the steel constituting the steel wire 1 can be obtained, for example, by two-dimensionally acquiring the entire circumference of the Debye rings on the Fe(211) plane using XRD and calculating the half-width in the circumferential direction at the maximum peak intensity.

[0029] Next, an example of a method for manufacturing the steel wire 1 will be described. Referring to Fig. 2, in the method for manufacturing the steel wire 1 according to the present embodiment, a raw wire rod preparation step is first carried out as step S10. In step S10, a raw wire rod containing 1.0 mass % or more and 1.1 mass % or less of C, 0.15 mass % or more and 0.25 mass % or less of Si, and 0.25 mass % or more and 0.3 mass % or less of Si is prepared. 5 quality % or less of Mn and 0.15% or more of Mn and 0.2% or more of Mn. 5 quality A raw wire rod is prepared, which is made of steel containing 0.01% or less of Cr, and the balance being Fe and unavoidable impurities. The diameter of the raw wire rod can be, for example, 4 mm or more and 6 mm or less.

[0030] Next, a first wiredrawing step is carried out as step S20. In step S20, the raw material wire prepared in step S10 is drawn. In this embodiment, in step S20, the raw material wire is drawn so that the wire diameter is, for example, 1 mm or more and 2 mm or less.

[0031] Next, a patenting step is performed as step S30. In this step S30, patenting is performed on the raw wire material that has been drawn in step S20. Specifically, the raw wire material is first heated to a temperature range above the temperature at which the steel constituting the wire material is austenitized (a temperature range above the Acm point), for example, a temperature range of 950°C to 1000°C, and held for 5 to 10 seconds (austenitizing treatment). Thereafter, the raw wire material is rapidly cooled to a temperature range above the temperature at which the steel begins to martensite (a temperature range above the MS point), for example, a temperature range of 500°C to 600°C, and held in that temperature range (isothermal transformation treatment). This results in the metal structure of the raw wire material becoming a fine pearlite structure. In the austenitizing treatment, the raw wire material may be heated in an inert gas atmosphere to suppress decarburization.

[0032] Next, an orientation reduction step is carried out as step S40. In this step S40, a heat treatment is carried out on the raw wire rod that has been drawn in step S20 and patented in step S30. Specifically, in step S40, the raw wire rod is heated to a temperature range of 600°C to 665°C and held for 5 seconds to 10 seconds. This heat treatment reduces the orientation of the steel.

[0033] Next, a second wiredrawing step is carried out as step S50. In this step S50, wiredrawing is carried out on the raw wire rod that has been patented in step S30 and has been subjected to orientation reduction treatment in step S40. In this embodiment, wiredrawing is carried out in step S50 so that the wire diameter of the raw wire rod becomes 0.15 mm or more and 0.42 mm or less. Through these steps, the steel wire of this embodiment is completed.

[0034] In the steel wire manufacturing method of this embodiment, heat treatment is performed in step S40, thereby reducing the orientation of the steel. In step S40, an appropriate temperature and holding time are adopted, thereby reducing the orientation of the steel while suppressing a decrease in dislocation density. Then, wire drawing is performed in step S50, thereby increasing the dislocation density and achieving high tensile strength. At this time, although the orientation of the steel also increases due to the wire drawing in step S50, the orientation of the steel is lower than when step S40 is not performed, due to the reduction in orientation in step S40. As a result, 2.4 × 10 16 m -2 Over 5.0 x 10 16 m -2 It is possible to achieve a dislocation density of 42° or more in the circumferential direction at half maximum of the maximum peak intensity of the Debye rings on the Fe(211) plane while achieving the following:

[0035] In the steel wire 1 of this embodiment, the dislocation density is 2.4 × 10 16 m -2 Over 5.0 x 10 16 m -2Despite the high value of 0.01 or less, the half-width in the circumferential direction at the maximum peak intensity of the Debye rings on the Fe(211) plane of the steel constituting the steel wire is 42° or more. This makes the steel wire 1 a steel wire that combines high tensile strength and high toughness. Because this steel wire 1 has high toughness, it can suppress wire breakage during twisting processing. Therefore, the steel wire 1 is suitable as a steel wire for constituting a high-strength steel cord.

[0036] In this embodiment, the half-value width is preferably 60° or more and 90° or less. By making the half-value width 60° or more, it becomes easier to ensure high toughness. By making the half-value width 90° or less, a high dislocation density is tolerated, making it easier to obtain high tensile strength.

[0037] In this embodiment, the dislocation density is 3.0×10 16 m -2 Over 5.0 x 10 16 m -2 It is preferable that the dislocation density is 3.0 × 10 or less. 16 m -2 By making the dislocation density 5.0×10 or more, it becomes easier to ensure high tensile strength. 16 m -2 By making it the following, it becomes easy to suppress the crystal orientation and ensure high toughness.

[0038] In this embodiment, the wire diameter D may be 0.15 mm or more and 0.18 mm or less, and the tensile strength may be 4240 MPa or more and 4900 MPa or less. The wire diameter D may be 0.18 mm or more and 0.21 mm or less, and the tensile strength may be 4180 MPa or more and 4740 MPa or less. The wire diameter D may be 0.21 mm or more and 0.30 mm or less, and the tensile strength may be 4000 MPa or more and 4580 MPa or less. By combining the wire diameter D and tensile strength as described above, a sufficient tensile strength can be achieved for each wire diameter D. [Example]

[0039] An experiment was conducted to confirm that the steel wire 1 of the present disclosure can achieve both high tensile strength and high toughness. The procedure of the experiment is as follows.

[0040] (1) Relationship between dislocation density and tensile strength Two types of raw wire rods (raw wire rods A and B) made of steel with different carbon contents were prepared, and steel wires were produced using the same procedure as in the above embodiment. Table 1 shows the chemical compositions of the steel constituting each raw wire rod. Raw wire rods with circular cross sections and wire diameters of 4.0 mm and 5.5 mm were prepared and wiredrawn in the first wiredrawing process to wire diameters of 1.3 mm and 1.5 mm. Next, the wires were heated to 980°C and held there for 8 seconds, then rapidly cooled to 580°C and patented. Next, to reduce orientation, heat treatment was performed by heating to 640°C and holding there for 8 seconds. After that, copper plating and zinc plating were performed, and the copper and zinc were mutually diffused to form a brass plating layer with a thickness of 2 μm. Finally, wiredrawing was performed in the second wiredrawing process to obtain steel wires (element wires) with a wire diameter of 0.21 mm. The area reduction rates at this time were 97% and 98%. The different area reduction rates resulted in steel wires with different dislocation densities. Here, the area reduction rate r is defined by the following formula (1), where the cross-sectional area before drawing is S0 and the cross-sectional area after drawing is S1 in a cross section perpendicular to the longitudinal direction of the wire rod (steel wire).

[0041] r={(S0-S1) / S0}×100 (%)...(1)

[0042] [Table 1]

[0043] The dislocation density of the steel wire thus obtained was measured, and the tensile strength was investigated. The dislocation density was measured as follows. First, approximately 20 of the steel wires prepared as described above were arranged in a row to widen the X-ray irradiation area, and this sample was irradiated with X-rays. Then, line profiles of the diffraction peaks of the iron (110), (200), (211), (220), and (310) planes were obtained. The dislocation density was calculated by analyzing this line profile using the modified Williamson-Hall method and the modified Warren-Averbach method. The modified Williamson-Hall method and the modified Warren-Averbach method are well known, and their details are described, for example, in T. Ungar and A. Borbely, "The effect of dislocation contrast on x-ray line broadening: A new approach to line profile analysis," Appl. Phys. Lett., vol. 69, no. 21, p. 3173, 1996, and T. Ungar, S. Ott, P. Sanders, A. Borbely, and J. Weertman, "Dislocations, grain size, and planar faults in nanostructured copper determined by high-resolution X-ray diffraction and a new procedure of peak profile analysis," Acta Mater., vol. 46, no. 10, pp. 3693-3699, 1998. Synchrotron radiation was used as the X-ray source. A Si(111) double-crystal monochromator and a Pt (platinum)-coated mirror were used. The X-ray incident angle was 2.5 mrad, the X-ray wavelength was 0.0689 nm (energy: 18.0 keV), and the detector was a NaI scintillation counter. The scanning method was 2θ-θ scan. The entrance slit was 4 mm wide and 0.5 mm high, and the receiving slit was a double slit (4 mm wide and 0.5 mm high).The measurement conditions were set so that there were nine or more measurement points within the half-width of each diffraction peak, the peak intensity was 2000 counts or more, and the measurement range was about 10 times the half-width.

[0044] The tensile test was carried out in accordance with JIS Z 2241. Figure 3 shows the relationship between dislocation density and tensile strength obtained from the experiment.

[0045] In Figure 3, the horizontal axis corresponds to dislocation density. The vertical axis corresponds to tensile strength. Solid circles represent data points for steel wires made from raw wire rod A. Hollow circles represent data points for steel wires made from raw wire rod B. The solid and dashed lines represent the relationship between dislocation density and tensile strength for raw wire rod A and raw wire rod B, respectively.

[0046] 3, it can be seen that the tensile strength increases as the dislocation density increases. 16 m -2 It is clear that by setting the above, a high tensile strength of 4000 MPa or more can be achieved.

[0047] (2) Relationship between half-width and toughness Steel wires were produced using raw wire rod A using the same procedure as in (1) above. Sample 1 was produced by setting the heating temperature at 665°C and the holding time at 10 seconds in step S40, Sample 2 was produced by setting the heating temperature at 600°C and the holding time at 5 seconds, and Sample 3 was produced by omitting step S40. In addition, Sample 4 was also produced by setting the area reduction rate in the first wiredrawing step to be smaller than those of Samples 1 to 3 and omitting step S40. Then, the half-width was measured and the toughness was evaluated for each sample.

[0048] The half-width measurements were performed using a Pulstec X-ray residual stress measurement system (model number: μ-X360s). A Cr tube was used as the X-ray source. The longitudinal direction of the steel wire was aligned with the incident direction, and the angle between the steel wire surface and the X-ray incident direction was 35° (incident angle 35°). The half-width was calculated in the circumferential direction at the maximum peak intensity of the Debye rings on the Fe(211) surface. Specifically, the half-width was calculated using the following procedure. First, the point of maximum peak intensity was identified for the Debye rings on the Fe(211) surface obtained under the above conditions. Next, the peak intensity was counted in the circumferential direction of a circle that passes through this point and is concentric with the Debye rings. The half-width (angle) was then calculated as the angle between the two points where the peak intensity was half of the maximum peak intensity. The toughness was evaluated by bundling four brass-plated steel wires with a diameter of 0.30 mm and twisting them together under the same conditions using a buncher twisting machine, and then counting the number of times the steel wires broke per ton of steel wire. The results of the experiment are shown in Table 2.

[0049] [Table 2]

[0050] In the toughness evaluation in Table 2, taking into consideration the yield in mass production of steel cords, the number of broken steel wires was evaluated as A if it was preferable, B if it was acceptable, and C if it required improvement. As shown in Table 2, the dislocation density of samples 1 to 3 was 3.8 × 10 16 m -2 ~4.3×10 16 m -2 is.

[0051] Referring to Table 2, it can be seen that although Samples 1 to 3 have the same dislocation density, there is a difference in the number of wire breakages due to differences in the half-width in the circumferential direction at the maximum peak intensity of the Debye rings on the Fe (211) plane. It is confirmed that high toughness can be obtained in Samples 1 and 2, where the half-width is 42° or more. Furthermore, it is confirmed that even higher toughness can be obtained in Sample 1, where the half-width is 60° or more. On the other hand, as in Sample 4, it is easy to increase the half-width by decreasing the area reduction rate in the first wiredrawing step, but this results in a dislocation density of 1.9 × 10 16 m -2 As a result, as shown in Figure 3, it becomes difficult to obtain a high tensile strength of, for example, 4000 MPa or more.

[0052] As described above, the steel wire of the present disclosure is capable of achieving both high tensile strength and high toughness, and is therefore suitable as a steel wire for constituting, for example, a steel cord. The applications of the steel wire of the present disclosure are not limited to steel cords, but can also be used as a conveyor cord, a handrail cord, or a rubber reinforcing wire.

[0053] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0054] 1 Steel wire, 11 Outer surface, D Wire diameter, S10, S20, S30, S40, S50 process.

Claims

1. 1.0 mass% or more and 1.1 mass% or less of C; 0.15% by mass or more and 0.25% by mass or less of Si; 0.25% by mass or more and 0.35% by mass or less of Mn; 0.15% by mass or more and 0.25% by mass or less of Cr; the balance being Fe and unavoidable impurities; The wire diameter is 0.15 mm or more and 0.42 mm or less, The steel is It has a pearlite structure, Dislocation density is 2.4 × 10 １６ m －２ Above 5.0 x 10 １６ m －２ is as follows: A steel wire having a circumferential half-width of the maximum peak intensity of the Debye rings on the Fe(211) plane of 42° or more.

2. The steel wire according to claim 1, wherein the half width is 60° or more and 90° or less.

3. The dislocation density is 3.0×10 １６ m －２ Above 5.0 x 10 １６ m －２ 3. The steel wire according to claim 1 or claim 2, wherein:

4. The wire diameter is 0.15 mm or more and 0.18 mm or less, The steel wire according to claim 1 or 2, wherein the tensile strength of the steel wire is 4240 MPa or more and 4900 MPa or less.

5. The wire diameter is 0.18 mm or more and 0.21 mm or less, The steel wire according to claim 1 or 2, wherein the tensile strength of the steel wire is 4180 MPa or more and 4740 MPa or less.

6. The wire diameter is 0.21 mm or more and 0.30 mm or less, The steel wire according to claim 1 or 2, wherein the tensile strength of the steel wire is 4000 MPa or more and 4580 MPa or less.

7. The wire diameter is 0.15 mm or more and 0.18 mm or less, The steel wire according to claim 3, wherein the tensile strength of the steel wire is 4240 MPa or more and 4900 MPa or less.

8. The wire diameter is 0.18 mm or more and 0.21 mm or less, The steel wire according to claim 3, wherein the tensile strength of the steel wire is 4180 MPa or more and 4740 MPa or less.

9. The wire diameter is 0.21 mm or more and 0.30 mm or less, The steel wire according to claim 3, wherein the tensile strength of the steel wire is 4000 MPa or more and 4580 MPa or less.

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