Galvanized steel wire, coated galvanized steel wire, wire mesh and rockfall protection works

Abstract

To provide a plated steel wire and a clad plated steel wire having high absorption energy performance, and a wire mesh having high absorption energy when receiving a falling rock, and a small overhang of the wire mesh when receiving the falling rock, and a rock fall protection work.SOLUTION: Provided is a plated steel wire having a predetermined steel composition, wherein a metal structure in a central region of a longitudinal section has a total area ratio of ferrite and pearlite to an entire structure of 90.0% or more, and an area ratio of pearlite to the entire structure of 47.5% or more, and when the total area ratio of ferrite and pearlite to the entire structure is less than 100%, a remainder is composed of at least one of cementite and bainite, and when a tensile test is performed, the tensile strength is 850 to 2,000 MPa. a uniform elongation of 4.0 to 8.0%. Also provided are a wire mesh using the same and a rock fall protection work.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a galvanized steel wire, a coated galvanized steel wire, a wire mesh, and a rockfall protection structure. [Background technology]

[0002] In mountainous areas, rockfall protection works are installed to prevent disasters caused by falling rocks on roads. Examples of rockfall protection works include waiting-type rockfall protection nets and wire net rockfall protection works that secure natural slopes. These rockfall protection works use wire mesh, and the material used for this wire mesh is generally galvanized steel wire, which is made by drawing, annealing, and plating zinc (Zn) from a steel wire with a composition that contains almost no carbon (C). The material required for wire mesh used in rockfall protection works is high energy absorption performance to absorb the energy of falling rocks. In addition, in the case of rockfall protection works installed near roads, if the wire mesh extends out into the road when a falling rock is caught, there is a risk of it hitting pedestrians or moving vehicles, so steel wire with low elongation and high energy absorption is desirable. In addition, wire mesh is used in urban areas to protect against flying objects, and similar capabilities are required.

[0003] For rockfall protection works, methods have been proposed for improving their energy absorption by improving their structure. Also proposed is improving the energy absorption of rockfall protection works by improving the mechanical properties of the wire mesh that makes up the work. For example, Patent Documents 1 and 2 disclose lightweight protection works that have high energy absorption and little overhang when catching falling rocks, achieved by increasing the tensile strength of the wire used as the material for the wire mesh compared to conventional works. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication 2001-522422 [Patent Document 2] Japanese Patent Application Publication No. 2019-190183 Summary of the Invention [Problem to be solved by the invention]

[0005] The wire mesh used in rockfall protection works requires steel wire with high energy absorption. Generally, methods for increasing energy absorption include increasing the tensile strength or elongation of the steel wire. However, if the tensile strength of the steel wire increases excessively, the ductility decreases and the energy absorption decreases. In addition, if the elongation of the steel wire is excessively large, there is a problem in that the wire mesh will overhang to a large extent when the rockfall protection work receives a falling object.

[0006] The present disclosure aims to provide plated steel wire and coated plated steel wire with high energy absorption performance, as well as wire mesh and rockfall protection work that absorbs large amounts of energy when catching falling rocks and has a small amount of protrusion when catching falling rocks. [Means for solving the problem]

[0007] The above object can be achieved by the following means. <1> A plated steel wire having a plating layer on the surface of the steel wire, The steel composition of the steel wire is, in mass%, C: 0.30~1.20%, Si: 0.10 to 1.50% Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, N: 0.0150% or less, and O: 0.0070% or less and the balance being Fe and impurities, When the radius of the steel wire is R, in a cross section that is parallel to the longitudinal direction of the steel wire and includes the central axis of the steel wire, a metal structure observed in a central region at a distance from the central axis of 0.2 × R or more and 0.8 × R or less has a total area ratio of ferrite and pearlite to the entire metal structure of 90.0% or more, an area ratio of the pearlite to the entire metal structure of 47.5% or more, and when the total area ratio of the ferrite and pearlite to the entire metal structure is less than 100%, the remainder consists of at least one of cementite and bainite, When subjected to a tensile test, the tensile strength is 850 to 2000 MPa and the uniform elongation is 4.0 to 8.0%. Plated steel wire. <2> The steel composition contains, in mass%, replacing a part of the Fe, Cr: 1.50% or less, B: 0.0050% or less, Ti: 0.040% or less, Mo: 0.40% or less V: 0.30% or less, Cu: 0.50% or less, Al: 0.080% or less, Ni: 0.50% or less, and Nb: 0.10% or less, One or more selected from the group consisting of <1> The plated steel wire according to claim 1. <3> The steel composition contains, in mass%, replacing a part of the Fe, Mg: 0.010% or less, Zr: 0.010% or less, Sb: 0.015% or less, W: 0.010% or less, REM (elements with atomic numbers 57 to 71): 0.005% or less Hf: 0.005% or less, Ta: 0.050% or less, Ca: 0.005% or less, Sn: 0.050% or less, Bi: 0.050% or less, Te: 0.050% or less, Zn: 0.050% or less, and Co:0.10% or less One or more selected from the group consisting of <1> or <2> The plated steel wire according to claim 1. <4> The breaking elongation when the tensile test is performed is 5.0% to 10.0%, The number of twists until breakage when performing a torsion test is 25 or more. <1> ~ <3> 10. The plated steel wire according to any one of the above items. <5> When the radius of the steel wire is R, in a metallographic structure observed at a position at a depth of R / 2 from the surface of the steel wire in the cross section of the steel wire, the grain size of crystal grains identified as body-centered cubic by electron backscatter diffraction (EBSD) is 5 μm or less, and the area ratio of the crystal grains having a grain size ratio X / Y of less than 2.0, where X is the grain size in a direction parallel to the longitudinal direction of the steel wire and Y is the grain size in a direction perpendicular to the longitudinal direction, is 10% or less with respect to the entire metallographic structure, The yield ratio when the tensile test is performed is 70.0 to 90.0%. <1> ~ <4> 10. The plated steel wire according to any one of the above items. <6> When the radius of the steel wire is R, in a metal structure observed at a position at a depth of R / 2 from the surface of the steel wire in the cross section of the steel wire, crystal grains identified as body-centered cubic by electron backscatter diffraction (EBSD) have a particle size ratio X / Y of 2.0 to 10.0, where X is the particle size in a direction parallel to the longitudinal direction of the steel wire and Y is the particle size in a direction perpendicular to the longitudinal direction, and the area ratio of pearlite in which the length of cementite in lamellar cementite constituting the pearlite is 0.1 μm or less is 20.0% or less with respect to the entire metal structure. <1> ~ <5> 10. The plated steel wire according to any one of the above items. <7> For wire mesh <1> ~ <6> 10. The plated steel wire according to any one of the above items. <8> <1> ~ <7> 1. A coated plated steel wire, the surface of which is coated with resin or painted, according to any one of the above. <9> <1> ~ <7> or <8> A wire mesh produced by weaving the coated plated steel wire according to claim 1. <10> the wire mesh includes at least one of a bending point and a welding point, and when the plated steel wire or the coated-plated steel wire including one or more of the bending points or the welding points is taken out and subjected to a tensile test, the tensile strength is 800 to 2000 MPa, and the elongation from half the maximum tensile load to the maximum load point is 3.5 to 7.0%; <9> The wire mesh described in <11> A diamond-shaped wire mesh having a thickness 5.0 to 12.0 times the wire diameter of the plated steel wire. <9> or <10> The wire mesh described in <12> <9> ~ <11> A rockfall protection work including a wire mesh described in any one of the above. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide plated steel wire and coated plated steel wire with high energy absorption performance, as well as wire mesh and rockfall protection works that absorb large amounts of energy when catching falling rocks and have a small amount of protrusion of the wire mesh when catching falling rocks. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram showing a central region for observing the metal structure in a longitudinal cross section of a steel wire. [Figure 2] FIG. 2 is a diagram illustrating an intersection and the vicinity of the intersection when measuring the area ratio of lamellar cementite. [Figure 3] FIG. 2 is a schematic diagram illustrating the position at which the shape of body-centered cubic crystal grains is measured in the longitudinal cross section of the steel wire. [Figure 4] FIG. 2 is a schematic diagram showing the grain size ratio X / Y of body-centered cubic crystal grains. [Figure 5] FIG. 1 is a front view showing an example of a diamond-shaped wire mesh. [Figure 6] FIG. 1 is a side view showing an example of a diamond-shaped wire mesh. [Figure 7] FIG. 1 is a schematic diagram illustrating a tensile test of a plated steel wire including a bending point taken from a wire mesh. [Figure 8]FIG. 1 is a schematic diagram showing the relationship between the stroke between chucks and the load when a tensile test is performed to measure the elongation of a plated steel wire including a bending point sampled from a wire mesh. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment that is an example of the present disclosure will be described in detail. In this specification, the "%" designation for the content of each element in the chemical composition means "% by mass." The content of each element in the chemical composition is sometimes expressed as "amount." For example, the carbon content is sometimes expressed as the carbon amount. A numerical range expressed using "to" means a range that includes the numbers written before and after "to" as the lower and upper limits. However, when the numbers written before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numbers as the lower or upper limits. In the present specification, the upper limit of a numerical range described in stages may be replaced with the upper limit of another numerical range described in stages or with a numerical value shown in an Example, and the lower limit of a numerical range may be replaced with the lower limit of another numerical range described in stages or with a numerical value shown in an Example. In addition, the upper or lower limit may be replaced with a value shown in an Example. In this specification, the term "steel wire" refers to a steel material in an as-drawn state without a plating layer, and the steel material portion of a plated steel wire excluding the plating layer, and the term "plated steel wire" refers to a steel wire in which a plating layer made of one type of metal or alloy, or a plating layer made of two or more types of metals or alloys laminated on the outer surface of the steel wire is provided. The "central axis" means an imaginary line that passes through the center point of a cross section (transverse cross section) perpendicular to the axial direction (longitudinal direction) of a steel wire and extends in the axial direction. The term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0011] <Plated steel wire> The plated steel wire according to the present disclosure is a plated steel wire having a plating layer on the surface of the steel wire, wherein the steel composition of the steel wire is, in mass%, C: 0.30~1.20%, Si: 0.10 to 1.50% Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, N: 0.0150% or less, and O: 0.0070% or less and the balance being Fe and impurities, When the radius of the steel wire is R, in a cross section that is parallel to the longitudinal direction of the steel wire and includes the central axis of the steel wire, a metal structure observed in a central region at a distance from the central axis of 0.2 × R or more and 0.8 × R or less has a total area ratio of ferrite and pearlite to the entire metal structure of 90.0% or more, an area ratio of the pearlite to the entire metal structure of 47.5% or more, and when the total area ratio of the ferrite and pearlite to the entire metal structure is less than 100%, the remainder consists of at least one of cementite and bainite, When a tensile test was carried out, the tensile strength was 850 to 2000 MPa and the uniform elongation was 4.0 to 8.0%.

[0012] [Steel composition] The steel composition of the steel wire in the plated steel wire according to the present disclosure (sometimes referred to as the "steel composition of the plated steel wire," the "steel composition of the steel wire," or simply the "steel composition") will be described. The steel composition of the plated steel wire according to the present disclosure contains, as basic components (essential components), in mass %: C: 0.30~1.20%, Si: 0.10 to 0.50% Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, N: 0.0150% or less, and O: 0.0070% or less The term "mainly composed of Fe" means that the balance other than the basic components is Fe and impurities, or Fe, impurities, and optional components.

[0013] (C: 0.30% to 1.20%) Carbon (C) is an essential element for imparting the necessary strength to steel wire. If the C content is less than 0.30%, the tensile strength of the steel wire will decrease, resulting in a decrease in the energy absorption capacity. Therefore, the C content is set to 0.30% or more. On the other hand, if the C content exceeds 1.20%, the tensile strength of the steel wire will be excessively high, resulting in a decrease in mesh-making properties. In addition, the uniform elongation and ductility after mesh-making will decrease, resulting in a decrease in the energy absorption capacity when catching falling rocks. Therefore, the upper limit of the C content is set to 1.20%. The C content is preferably 0.50% or more and 1.00% or less, and more preferably 0.60% or more and 0.90% or less.

[0014] (Si: 0.10 to 1.50%) Silicon (Si) is an element effective in deoxidizing steel, and also has the effects of suppressing the formation of pro-eutectoid cementite and strengthening ferrite. To achieve these effects, a Si content of 0.10% or more is required. However, if Si is contained in excess, these effects become saturated, so the upper limit of the Si content is set at 1.50%. The Si content is preferably 0.15% or more and 1.00% or less.

[0015] (Mn: 0.10 to 1.00%) Manganese (Mn) is useful for deoxidation and desulfurization, and also has the effect of delaying the transformation from austenite to proeutectoid cementite and grain boundary ferrite. Therefore, Mn is a useful element for making the structure of the wire rod before wiredrawing to obtain the steel wire of the present disclosure mainly pearlite. To exert such effects, the Mn content must be 0.10% or more, preferably 0.20% or more, and more preferably 0.40% or more. On the other hand, even if Mn is contained in excess, the above effects saturate and there is a possibility that workability may be reduced due to segregation. Therefore, the upper limit of the Mn content is 1.00%, preferably 0.80% or less, and more preferably 0.60% or less.

[0016] (P:0.030% or less) Since P (phosphorus) is an impurity element that segregates at grain boundaries and embrittles steel, the upper limit of its content is limited to 0.030%, preferably 0.020% or less, and more preferably 0.010% or less. Although the smaller the P content, the better, from the viewpoint of reducing the dephosphorization cost, the lower limit of the P content may be 0.003% or 0.005%.

[0017] (S:0.030% or less) S (sulfur) is an impurity element that segregates at grain boundaries and embrittles steel, so the upper limit of its content is limited to 0.030%, preferably 0.020% or less, and more preferably 0.010% or less. Although the smaller the S content, the more preferable, from the viewpoint of reducing the desulfurization cost, the lower limit of the S content may be 0.003% or 0.005%.

[0018] (N:0.0150% or less) N (nitrogen) is an impurity element that dissolves in the ferrite matrix and embrittles the steel, and the upper limit is set to 0.0150%. The N content is preferably 0.0080% or less, and more preferably 0.0050% or less. The lower limit of the N content is not limited, but from the viewpoint of reducing the denitrification cost, the lower limit of the N content may be 0.0010% or 0.0020%.

[0019] (O:0.0070% or less) O (oxygen) is an impurity element that affects the amount of oxide-based inclusions in a steel wire. By keeping the O content at 0.0070% or less, it is possible to suppress a decrease in the energy absorption capacity of the steel wire caused by coarse oxides. The O content is preferably 0.0050% or less, and more preferably 0.0040% or less. The lower limit of the O content is not limited, but from the viewpoint of reducing the cost of deoxidization, the lower limit of the O content may be 0.0005% or 0.0010%.

[0020] The steel wire of the present disclosure has the above elements as its basic steel components, with the remainder being primarily Fe (iron). Here, "primarily Fe" means that the remainder other than the basic steel components is Fe and impurities, or Fe, impurities, and optional components. That is, the steel composition of the steel wire of the present disclosure may be composed of the above basic components, Fe, and impurities, or may actively contain one or more of the following optional elements (optional elements) in place of a portion of the Fe, for the purpose of further improving strength, mesh-making properties, etc. However, the following optional elements are not essential, and the effects of the plated steel wire of the present disclosure can be obtained even if they are not contained (i.e., even if the content is 0%). The term "impurities" refers to substances that are mixed in from raw materials such as ore and scrap, or the manufacturing environment, during industrial production of steel wire, and are acceptable within a range that does not adversely affect the plated steel wire according to the present disclosure (i.e., does not hinder the effects).

[0021] (Al: 0.080% or less) Although Al (aluminum) is not an essential component, it may be contained because it is useful as a deoxidizing element during steelmaking. When Al is contained, it precipitates AlN, which has the effect of refining the ferrite matrix. However, excessive Al content exceeding 0.080% can generate coarse Al inclusions, which can reduce ductility. Therefore, the upper limit of Al content is set to 0.080%. It is more preferably 0.050% or less, and even more preferably 0.030% or less. There is no particular lower limit for the Al content, but when Al is actively used as a deoxidizing element, it is preferably 0.005% or more, and more preferably 0.010% or more. When Al is not utilized as a deoxidizing element, Al is contained within the range of being contained as an impurity, and the upper limit of the Al content may be less than 0.010%.

[0022] (Cr:1.50% or less) Like Mn, Cr (chromium) has the effect of delaying the transformation from austenite to pro-eutectoid cementite and grain boundary ferrite, making it a useful element for obtaining a pearlite-based structure in the rolled wire rod before wiredrawing to obtain the steel wire of the present disclosure. Furthermore, Cr stabilizes cementite, and is expected to moderately assist spheroidization during annealing. However, if the Cr content exceeds 1.50%, these effects saturate, and the hardenability increases, making it easier for supercooled structures such as bainite and martensite to form during the cooling process during hot rolling, and lengthening the time until transformation completion, leading to reduced productivity and increased equipment costs. The Cr content is preferably 0.05% or more and 0.30% or less, and more preferably 0.10% or more and 0.25% or less.

[0023] (B:0.0050% or less) A small amount of B (boron) strengthens the grain boundary and suppresses the precipitation of grain boundary ferrite. However, if the B content exceeds 0.0050%, the Fe 23B forms carbides such as (CB)6, which inhibits grain boundary bonding. Therefore, when B is added, the B content is preferably 0.0050% or less. The B content is more preferably 0.0005 to 0.0030%, and even more preferably 0.0008 to 0.0020%.

[0024] (Ti:0.040% or less) Ti (titanium) forms TiN in steel, immobilizing N and preventing strain aging. However, if the Ti content exceeds 0.040%, coarse TiN may form in the steel, adversely affecting the material properties. Therefore, it is effective to contain 0.040% or less of Ti. The Ti content is more preferably 0.005 to 0.030%, and even more preferably 0.008 to 0.020%.

[0025] (Mo: 0.40% or less) An appropriate amount of Mo (molybdenum) improves hardenability, reduces the ferrite fraction, and promotes the grain boundary strengthening effect of B. However, if the Mo content exceeds 0.40%, the hardenability of the steel becomes too high, and supercooled structures such as martensite are formed in the steel during the cooling process during hot rolling, adversely affecting wire drawability. Therefore, it is effective to include Mo in an amount of 0.40% or less. The Mo content is more preferably 0.05 to 0.20%, and even more preferably 0.07 to 0.10%.

[0026] (V:0.30% or less) V (vanadium) has the effect of increasing the strength of ferrite, but if its content exceeds 0.30%, it becomes embrittled. Therefore, when V is added, it is effective to set the upper limit of the V content to 0.30%. The V content is more preferably 0.05 to 0.30%, and even more preferably 0.07 to 0.15%.

[0027] (Cu:0.50% or less) Although copper (Cu) has the effect of strengthening steel by dissolving in ferrite, if the content exceeds 0.50%, it concentrates at the grain boundaries during heating of the slab, embrittling the steel. Therefore, when Cu is contained, it is effective to set the upper limit of the Cu content to 0.50%. The Cu content is more preferably 0.02 to 0.30%, and even more preferably 0.03 to 0.20%.

[0028] (Ni:0.50% or less) Ni (nickel) has a solid solution strengthening effect, but this effect tends to saturate at 0.50%. Therefore, when Ni is contained, it is effective to set the upper limit to 0.50%. The Ni content is more preferably 0.01 to 0.30%, and even more preferably 0.03 to 0.20%.

[0029] (Nb:0.10% or less) Niobium (Nb) precipitates in steel as fine carbides and has the effect of strengthening ferrite, but if the content exceeds 0.10%, it embrittles the steel. Therefore, it is effective to set the upper limit of the Nb content to 0.10%. The Nb content is more preferably 0.02 to 0.07%, and even more preferably 0.03 to 0.05%.

[0030] (balance: Fe and impurities) The steel wire in the present disclosure is composed of the above-mentioned basic components and optional elements, with the remainder of the chemical composition consisting of Fe and impurities. Here, the impurities refer to elements that are mixed in from ores or scraps used as raw materials for the steel, the environment during the manufacturing process, etc.

[0031] [Metal structure of steel wire] Next, the metal structure of the plated steel wire according to the present disclosure will be described. The present inventors manufactured various steel wires by changing the amount of cold wire drawing and annealing conditions using the above-mentioned steel material having a C content of 0.30% or more, and conducted a detailed study on the relationship between the structure and mechanical properties of the steel wires, and obtained the following findings. In order to obtain a steel wire that has the ability to be formed into wire mesh and also has high energy absorption capacity, it is effective to use steel with the above-mentioned components and to control the area ratios of ferrite and pearlite in particular, and preferably, the shape of the ferrite grain size and the morphology of lamellar cementite can be controlled to obtain more desirable performance as desired.

[0032] The plated steel wire according to the present disclosure is manufactured by using a rolled wire rod as a raw material through a wiredrawing-plating process. The metal structure of the steel wire according to the present disclosure is preferably composed of ferrite and pearlite, and may further contain cementite and / or bainite. The above "ferrite" excludes the ferrite phase contained in pearlite and bainite. The above-mentioned "cementite" refers to cementite other than the cementite phase contained in pearlite or bainite, such as cementite that remains in the steel wire and originates from pro-eutectoid cementite present in the wire rod before wiredrawing. In the present disclosure, "pearlite" refers to a layered structure (lamellar structure) of cementite and ferrite. "Bainite" is a mixed structure of ferrite and cementite that contains more dislocations than normal ferrite and does not belong to either lamellar pearlite or a structure in which spheroidal cementite is dispersed in a ferrite matrix.

[0033] Fig. 1 shows a central region for observing the metal structure in a longitudinal cross section of a plated steel wire. Note that the plating layer is omitted in Fig. 1. Regarding the plated steel wire according to the present disclosure, the metal structure observed in a central region 12 at a distance of 0.2 × R or more and 0.8 × R or less from the central axis C in a cross section (longitudinal cross section) that is parallel to the longitudinal direction of the steel wire 10 and passes through the central axis C, where R is the radius of the steel wire 10, will be described.

[0034] (Inner Sphere Organization) In the central region 12 of a cross section (longitudinal cross section) parallel to the longitudinal direction of the steel wire 10 and passing through the central axis C, the total area ratio of ferrite and pearlite to the entire structure is 90.0% or more. If the total area ratio of ferrite and pearlite is less than 90.0%, the elongation and torsion properties of the steel wire will be reduced, and the energy absorption capacity will be reduced. The total area ratio of ferrite and pearlite to the entire structure is preferably 95.0% or more, and more preferably 97.0% or more. In addition, when the total area ratio of ferrite and pearlite to the entire structure in the central region 12 is less than 100%, the remainder is made up of at least one of cementite and bainite. When cementite and / or bainite are present as the remainder, the area ratio of these structures is 10% or less.

[0035] Furthermore, the area ratio of pearlite to the entire structure is 47.5% or more. With an area ratio of pearlite of 47.5% or more, the tensile strength increases, the absorbed energy of the wire mesh increases, and the amount of protrusion of the wire mesh when catching falling rocks decreases. The area ratio of pearlite to the entire structure is preferably 50% or more, more preferably 60.0% or more, and even more preferably 80.0% or more.

[0036] (Body-centered cubic crystal grain shape) In the steel wire of the present disclosure, it is preferable to control the grain size of the body-centered cubic crystal grains in order to achieve a high level of balance between plastic deformability (ductility) and strength (in the present disclosure, the body-centered cubic crystal grains are referred to as bcc grains). When bcc grains become coarse due to recrystallization caused by heating during plating, the tensile strength decreases, and an increase in the number of fine recrystallized bcc grains increases the yield ratio and reduces the mesh-making ability. Therefore, in a cross section parallel to the longitudinal direction of the steel wire (longitudinal cross section), it is preferable that the grain size of the bcc grains is 5 μm or less, and the area fraction of fine ferrite, in which the grain size ratio X / Y of the bcc grains in the direction parallel to the longitudinal direction of the steel wire to the grain size Y in the direction perpendicular to the longitudinal direction is less than 2.0, is 10% or less of the entire structure.

[0037] If the particle size ratio X / Y of the bcc grains is less than 2.0, the recrystallization proceeds, resulting in a decrease in tensile strength and a large elongation, resulting in a large amount of protrusion of the wire mesh during rockfall. On the other hand, if the bcc particle size ratio exceeds 10.0, the amount of strain within the bcc grains is large, resulting in insufficient elongation of the plated steel wire and a decrease in absorbed energy during rockfall. Therefore, the particle size ratio of the bcc grains is preferably 2.0 to 10.0, and more preferably 3.0 to 8.0. On the other hand, if the area fraction of fine recrystallized bcc grains with a bcc grain size of 5 μm or less and a grain size ratio of less than 2.0 exceeds 10% of the entire structure, the yield strength increases. If the area fraction of such bcc grains is 10% or less, the effect on the absorbed energy and the amount of overhang of the wire mesh when catching a rockfall is small.

[0038] (lamellar cementite morphology) When lamellar cementite constituting pearlite is split by heating during the plating process, the tensile strength is insufficient and the torsional properties deteriorate. Therefore, in the lamellar cementite of pearlite, the region of pearlite where the length of the cementite is 0.1 μm or less preferably accounts for 20.0% or less of the entire structure, and more preferably 10.0% or less. In the present disclosure, when the length of lamellar cementite constituting pearlite is 0.1 μm or less, it may be referred to as "split lamellar cementite." The area ratio of the region that is divided into lamellar cementite may also be referred to as the "area ratio of divided lamellar cementite."

[0039] (Method for measuring metal structure) Observation of the metal structure of the steel wire and measurement of the area ratio of the structure can be carried out as follows. To enable observation of a cross section parallel to the longitudinal direction of the steel wire (longitudinal cross section), a galvanized steel wire is cut, embedded in resin, and then polished with abrasive paper and alumina abrasive grains to a mirror finish. This mirror-finished section is corroded for 5 seconds in a 3% picral solution at room temperature (25°C), and then immediately washed with alcohol to prepare an observation sample. If the boundary between ferrite and carbide (cementite) is unclear after corrosion, an additional 5-second corrosion may be performed.

[0040] (Measurement of area ratio of ferrite and pearlite) The specimen was observed and photographed using a field-emission scanning electron microscope (FE-SEM). The photographs were taken at a magnification of 2000x, centered on a line passing through the central axis of the steel wire at positions 0.2×R, 0.4×R, 0.6×R, and 0.8×R (R is the radius of the steel wire) from the center, with two fields of view of at least 60 μm × 60 μm each, for a total of eight fields of view. Five lines were drawn vertically and horizontally at 10 μm intervals on the SEM photograph in a grid pattern, dividing the photograph into 25 intersections. The structure at each intersection was then identified, and the area ratios of ferrite and pearlite were measured. The same procedure was repeated for each photograph. In other words, a total of 200 intersections were measured. For example, the area ratio of ferrite (%) was calculated as (total number of intersections determined to be ferrite / 200) × 100. Similarly, the area ratio (%) of pearlite is (total number of intersections determined to be pearlite / 200)×100.

[0041] (Measurement of area ratio of fragmented lamellar cementite) The corroded portion of the specimen is observed and photographed using a field emission scanning electron microscope (FE-SEM). Photographs are taken at a magnification of 5000x, with two fields of view each covering an area of at least 12 μm × 12 μm, for a total of eight fields of view, centered on a line passing through the central axis of the steel wire at positions 0.2 × R, 0.4 × R, 0.6 × R, and 0.8 × R (R is the radius of the steel wire) from the central axis.

[0042] Using the SEM photograph, five lines are drawn vertically and horizontally at 2 μm intervals to form a grid, dividing the area into 25 intersections. The length of cementite on or near each intersection is measured, and the number of cementite particles with a length of 0.1 μm or less is counted. If no cementite is present near an intersection, the area is considered to be free of cementite and is included in the parameter. Here, "near the intersection" refers to area A within a square with sides of 2 μm and centered on the target intersection a, as shown in Figure 2. In other words, if the length (linear distance between both ends) of the cementite closest to intersection a among the cementite present in area A is 0.1 μm or less, the length of the cementite at intersection a is determined to be 0.1 μm or less. If no cementite is present in area A, intersection a is considered to be an intersection without cementite. The total number of intersections in the eight visual fields where the cementite has a length of 0.1 μm or less is divided by the total number of intersections in the visual fields observed, 200, to obtain the area ratio of cementite having a length of 0.1 μm or less (divided lamellar cementite).

[0043] (Measurement of the morphology of body-centered cubic crystal grains) To determine the grain size, grain size ratio, and area ratio of bcc grains, i.e., body-centered cubic crystal grains, in the metal structure of a steel wire, a longitudinal cross section including the central axis of the steel wire is embedded in resin, polished with alumina, and then polished with colloidal silica, and then subjected to electron backscatter diffraction (EBSD) measurement. Note that polishing can also be electrolytic polishing. As shown in Figure 3, the measurement location is a vertical cross section parallel to the longitudinal direction of the steel wire 10, with the radius of the steel wire 10 being R, and photographs are taken in a field of view centered on a line at a depth of R / 2 from the surface (outer surface) of the steel wire 10. To minimize variations in the structure depending on the location, photographs are taken at five locations on the line at depth R / 2 so that the photographed areas do not overlap. The measurements are taken at a magnification of 500x, and a bcc crystal orientation data map is collected from the photographed area at 0.4 μm / step. Grains with a crystal orientation difference of within 15° and connected by 10 or more pixels are considered to be the same bcc grain, and the grain boundaries are determined. The measurement area (area) at each location to evaluate the shape (grain size and grain size ratio) of the bcc grains is a measurement field area of 43,200 μm.2 (180 μm in the radial direction of the steel wire × 240 μm in the longitudinal direction of the steel wire).

[0044] After defining and revealing the bcc grain boundaries using the above method, eight lines are drawn vertically and horizontally at 20 μm intervals on a diagram tracing the bcc grain boundaries, and the grain size and grain size ratio of the bcc grains at each intersection are determined. Figure 4 is a diagram explaining the grain size ratio of bcc grains 16. In this measurement, the length X of the bcc grain 16 at each intersection in the wiredrawing direction is defined as the bcc grain size, and the grain size ratio X / Y is determined using the length X in the wiredrawing direction as the numerator and the length Y in the direction perpendicular to the wiredrawing direction (i.e., the radial direction) as the denominator. Note that if the wiredrawing strain is small and the maximum diameter is not in the wiredrawing direction, bcc grains with a grain size ratio of approximately 1 or less (i.e., the length X in the wiredrawing direction of the steel wire < the length Y in the radial direction of the steel wire) may exist, but bcc grains with a grain size ratio of 1 or less may also exist. Furthermore, if there are multiple intersections within the same grain, measurement shall be made at only one point, and not at other intersections within the same grain.

[0045] Using this method, the area ratio of fine bcc grains is determined by dividing the number of intersections among 64 intersections in each observation region where the bcc grain size is 5 μm or less and where the grain size ratio of the bcc grains in the direction parallel to the longitudinal direction of the steel wire to the grain size in the direction perpendicular to the longitudinal direction is less than 2.0 (sometimes referred to as "fine bcc grains" in this disclosure) by the total number of intersections in the observation region, 64. The area ratio of fine bcc grains is calculated for each of the five observation regions, and the arithmetic average value can be used as the area ratio of fine bcc grains for that steel wire.

[0046] The steel wire according to the present disclosure is plated, i.e., the plated steel wire according to the present disclosure has a plating layer that coats the surface of the steel wire. The plating type may be, for example, zinc plating or zinc alloy plating (hereinafter referred to as zinc-based plating), as well as tin plating, aluminum plating, or the like. As the plating method, either hot dip plating or electroplating can be used. Zinc-based plating is generally used for wire mesh used in rockfall protection works. The following explains zinc-based plating. The amount of zinc-based plating is not particularly limited, but the amount of plating is preferably 30 g / m 2 If the thickness is less than 30g / m, the sacrificial corrosion protection effect may be insufficient. 2 On the other hand, the coating weight of the plating is 400 g / m 2 Even if the thickness is increased to more than 400 g / m, stable production is difficult and uneconomical. 2 Therefore, the coating weight is 30 g / m 2 More than 400g / m 2 The following ranges are desirable: Zinc-based plating is a plating mainly composed of Zn, but it may also be an alloy plating containing other components. Examples of other components include Al and Mg. The preferred range of Al content is 0 to 25%, and the preferred range of Mg content is 0 to 3%.

[0047] Furthermore, the plated steel wire according to the present disclosure may be a coated plated steel wire in which the surface of the plated steel wire is coated with a resin or painted.

[0048] [Mechanical properties] The plated steel wire according to the present disclosure has mechanical properties of a tensile strength of 850 to 2000 MPa and a uniform elongation of 4.0 to 8.0% in a tensile test. Such mechanical properties make it suitable for mesh production, and when used in wire mesh, it is possible to reduce the amount of overhang when falling rocks are caught. The plated steel wire according to the present disclosure preferably has mechanical properties such that a breaking elongation in a tensile test is 5.0 to 10.0% and a yield ratio is 70.0 to 90.0%. Furthermore, the plated steel wire according to the present disclosure preferably has mechanical properties such that no delamination occurs in a torsion test and the number of revolutions until fracture is 25 or more. Each mechanical property and its measurement method will be described below.

[0049] (tensile strength) The plated steel wire according to the present disclosure has a tensile strength of 850 to 2000 MPa. If the tensile strength is less than 850 MPa, the strength is low, so elongation is required to increase the absorbed energy, and when a wire mesh is used to protect against falling rocks, the amount of protrusion when the falling rock is received increases. On the other hand, if the tensile strength exceeds 2000 MPa, embrittlement progresses, and the energy absorption capacity of the wire mesh decreases. The tensile strength is preferably 900 to 1800 MPa, and more preferably 1000 to 1600 MPa.

[0050] (uniform elongation) The plated steel wire according to the present disclosure has a uniform elongation of 4.0 to 8.0% in a tensile test. If the uniform elongation is 4.0% or more, the energy absorption capacity is high. On the other hand, if the breaking elongation is 8.0% or less, when a wire mesh is used to protect against falling rocks, the amount of protrusion when the falling rock is received is small. More preferably, it is 4.2% or more and 7.0% or less. It is considered that the uniform elongation is largely influenced by dislocations in the steel wire. The elongation of the plated steel wire according to the present disclosure is measured in a tensile test described below by placing a test specimen, marking it at two or more points between the chucks, and measuring the movement of the marks while photographing the relative positions of the marks with a camera during the tensile test. The uniform elongation is calculated from the displacement from before tension to the maximum load point during the tensile test, and is calculated by the following formula: Uniform elongation (%) = (D2-D1) / D1 x 100 D1: Distance between two marks before tensioning D2: Distance between two marks at the maximum load point during tensile test

[0051] (Elongation at break) The plated steel wire according to the present disclosure preferably has a breaking elongation of 5.0 to 10.0% in a tensile test. If the breaking elongation is 5.0% or more, the energy absorption capacity is high. On the other hand, if the breaking elongation is 10.0% or less, when a wire mesh is used to protect against falling rocks, the amount of protrusion when the falling rock is received is small. The breaking elongation is more preferably 5.2% or more and 9.0% or less. The breaking elongation is also determined in the tensile test described below. After placing the test piece, marks are made in two or more places between the chucks, and the relative positions of the marks are photographed with a camera during the tensile test. The breaking elongation is calculated from the displacement before tension and at the time of break during the tensile test.

[0052] (yield ratio) The plated steel wire according to the present disclosure preferably has a yield ratio in a tensile test of 70.0 to 90.0%. If the yield ratio is 70.0% or more, the wire mesh is less likely to deform under small loads and elongation is suppressed, so that the amount of protrusion when a wire mesh made from the plated steel wire according to the present disclosure receives a falling rock is small. On the other hand, if the yield ratio is 90.0% or less, the load during plastic deformation is small, improving workability during mesh making and improving energy absorption during impact. The yield ratio is more preferably 75.0% to 85.0%. The yield ratio (%) is a value calculated by yield strength / tensile strength × 100 (%), where yield strength is 0.2% proof stress.

[0053] (Number of twists) In a torsion test, the plated steel wire of the present disclosure is preferably twisted 25 times or more without longitudinal cracks occurring before breaking. If the number of twists until breaking without longitudinal cracks is 25 or more, a decrease in absorbed energy during wire mesh formation can be effectively suppressed. In a torsion test, the number of twists until breaking without longitudinal cracks is preferably 28 times or more, and more preferably 30 times or more. On the other hand, there is no upper limit to the number of twists until breaking, but approximately 60 times is considered to be the upper limit.

[0054] (Mechanical property measurement method) The above mechanical properties other than the number of twists of the plated steel wire according to the present disclosure can be determined by a tensile test. A 200mm long sample is taken from the steel wire to be measured, excluding any unsteady sections, and subjected to a tensile test. The tensile test is performed with a chuck distance of 100mm, a strain rate of 10 / s, and an 80mm interval between marks for measuring elongation. The same test is performed three times, and the average is used as each measurement value. If the fracture during the tensile test is outside the area marked for measuring elongation, the test results are not included and the measurement is performed again. The tensile strength, uniform elongation, elongation at break, and yield ratio are also determined by the above tensile test.

[0055] (Torsion test method) In measuring the mechanical properties of the plated steel wire according to the present disclosure, the torsion test is performed using the method described in JIS G 3548:2011. Specifically, a sample of a length sufficient to provide a gripping distance of 100 times the diameter of the steel wire is taken from the steel wire to be measured, excluding the non-steady-state portion, and used for the test. The sample is straightened using a roll or other tool to avoid scratching the surface, and then both ends of the sample are gripped at a distance of 100 times the diameter of the steel wire. A load of 1% of the tensile strength is applied to the sample, and one end is rotated in the same direction while tensioning the sample until it breaks. The number of rotations at which the sample breaks is defined as the number of twisting rotations until fracture. The presence or absence of longitudinal cracks is determined by observing the fracture surface after fracture and determining whether or not there are any cracks perpendicular to the wire axis. If multiple fractures occur, all fracture surfaces are observed. If at least one fracture surface is free of longitudinal cracks, the sample is deemed to have broken without longitudinal cracks.

[0056] <Wire mesh> The wire mesh according to the present disclosure is a wire mesh manufactured from the plated steel wire according to the present disclosure described above. Note that the wire mesh may also be manufactured from a coated plated steel wire, which is a plated steel wire having a surface coated with paint or resin, as described below. Fig. 5 shows an example of the mesh of the wire mesh according to the present disclosure. The wire mesh according to the present disclosure is preferably a diamond-shaped mesh as shown in Fig. 5, i.e., a diamond-shaped wire mesh, but may also be a welded wire mesh or a ring wire mesh. Fig. 6 is a view of a wire mesh having diamond-shaped mesh as shown in Fig. 5, viewed from the direction of arrow E. The wire diameter of the plated steel wires 20 constituting the wire mesh 30 is 2.0 to 5.0 mm, and it is preferable that the thickness t of the diamond-shaped wire mesh 30 is 5.0 to 12.0 times the wire diameter of the plated steel wires 20. If the wire diameter of the galvanized steel wire 20 is less than 2.0 mm, the absorbed energy during impact with a falling rock decreases, while if it exceeds 5.0 mm, the weight of the wire mesh increases, reducing workability. By making the thickness t of the wire mesh 30 5.0 times or more the wire diameter of the galvanized steel wire 20, the absorbed energy of the wire mesh 30 increases. However, if the thickness of the wire mesh 30 exceeds 12.0 times the wire diameter of the galvanized steel wire 20, the weight of the wire mesh 30 increases and the space required for transportation increases, reducing workability.

[0057] [Mechanical properties of wire mesh] After a wire mesh is made using the plated steel wire and coated plated steel wire according to the present disclosure, when a steel wire having one or more bending or welding points is removed from the wire mesh and subjected to a tensile test, it is preferable that the tensile strength is 800 to 2000 MPa and the elongation from a load half the maximum tensile load to the maximum load point is 3.5 to 7.0%. By having such mechanical properties, the wire mesh can absorb a large amount of energy when it receives a falling rock, and the amount of overhang can be reduced.

[0058] When using plated steel wire to make mesh, this includes bends in the case of diamond-shaped wire mesh, and welds in the case of welded wire mesh. These points can be the starting points of fracture, and therefore the mechanical properties may be lower than those of the plated steel wire used as the base material. On the other hand, if the mechanical properties are significantly reduced, this leads to a decrease in the energy absorption capacity when catching falling rocks, so it is preferable for the mesh to have the above properties.

[0059] (Tensile strength of wire mesh) In the present disclosure, the tensile strength of the plated steel wire after mesh-making is preferably 800 to 2000 MPa. If the tensile strength of the steel wire after mesh-making is less than 800 MPa, the strength is low, resulting in a decrease in the energy absorption capacity of the rockfall protection work when it receives a falling rock, or elongation is required to increase the energy absorption capacity, which tends to result in a large amount of overhang when the rockfall protection work receives a falling rock. On the other hand, if the tensile strength exceeds 2000 MPa, embrittlement progresses, making it difficult to ensure the energy absorption capacity of the wire mesh. More preferably, the tensile strength is 850 MPa or more and 1800 MPa or less, and even more preferably, the tensile strength is 900 MPa or more and 1600 MPa or less.

[0060] (Stretching of wire mesh) The elongation of the plated steel wire after mesh-making in the wire mesh according to the present disclosure is preferably 3.5% to 7.0%. If the elongation of the plated steel wire after mesh-making is 3.5% or more, a decrease in ductility can be prevented, thereby preventing a decrease in the energy absorption capacity of the rockfall protection work when it receives a falling rock. On the other hand, if the elongation of the plated steel wire after mesh-making is 7.0% or less, the amount of overhang when the rockfall protection work receives a falling rock can be reduced. The elongation of the plated steel wire after mesh-making is more preferably 3.7% or more and 6.5% or less.

[0061] (Method for measuring mechanical properties of wire mesh) The above mechanical properties of the wire mesh according to the present disclosure can be determined by tensile testing.

[0062] (Measurement of tensile strength of plated steel wire that composes wire mesh) Figure 7 is a schematic diagram showing a method for measuring the mechanical properties of the galvanized steel wire that constitutes the wire mesh by a tensile test. The ends are removed from the wire mesh to be measured to obtain a galvanized steel wire 20 that includes one or more bending or welding points (Figure 7(A)). Both ends are straightened (Figure 7(B)), and both ends are gripped with chucks 40 for the tensile test (Figure 7(C)). The tensile test is performed at a strain rate of 10 / s. The maximum load strength at break is defined as the tensile strength.

[0063] (Measurement of elongation of plated steel wires that make up the wire mesh) Regarding the elongation of plated steel wire after mesh-making, the test material is straightened during the tensile test to eliminate the effects of bending during mesh-making, and the change in elongation until breakage is measured. Figure 8 is a schematic diagram showing the relationship between the stroke between chucks and the load during a tensile test. In this disclosure, in the stress-strain curve due to the applied load and the movement of the chuck, the point where half of the maximum load is applied is set as the starting point. The distance the chuck moves from the point where half of the maximum applied load is applied until breakage is measured. This value is divided by the distance between chucks at the starting point to determine the elongation of the steel wire after mesh-making. Similar tests are performed three times, and the average is used as each measurement value. Note that if the breakage during the tensile test occurs outside the chucks, such as within the chuck, the test results are not included and the measurement is performed again.

[0064] <Method of manufacturing plated steel wire> Next, a method for manufacturing a plated steel wire according to the present disclosure will be described. Note that the manufacturing method described below is an example, and is not limited to the following procedure and method. Any method may be adopted as long as it can realize the configuration of the plated steel wire according to the present disclosure. The plated steel wire according to the present disclosure can be obtained by forming a steel billet, the steel having the composition adjusted to the above-described steel composition, into a wire rod by hot rolling or the like, and then performing wiredrawing and plating under conditions that result in the above-described metallographic structure and mechanical properties.

[0065] [Wire rod manufacturing] The wire rod is produced, for example, by casting steel having the above-described components and blooming the cast piece to produce a steel piece of a size suitable for wire rod rolling (a steel piece before wire rod rolling called a billet), which is then subjected to hot rolling. When rolling the wire rod, the steel billet is heated to 950 to 1150° C., and the finish rolling start temperature is controlled to 800° C. or more and 950° C. or less. The rolling temperature of the wire rod is measured with a radiation thermometer and means the surface temperature of the steel material.

[0066] The structure of the wire rod is preferably mainly pearlite in wire rods with a carbon content equal to or greater than that of eutectoid steel, and mainly ferrite-pearlite in wire rods with a carbon content less than that of eutectoid steel. A high pearlite area fraction is also desirable, and for wire rods with a carbon content less than 0.7%, the pearlite area fraction is preferably (C content: mass% + 0.2) × 100% or more. For wire rods with a carbon content equal to or greater than that of eutectoid steel, the pearlite area fraction is preferably 90% or more, and the total area fraction of pro-eutectoid cementite, bainite, and martensite is preferably 10% or less.

[0067] To obtain these structures, the finish rolling start temperature of the rolled wire rod is set to 800°C or higher, and the average cooling rate from finish rolling (after coiling into a ring) to 650°C is set to 5.0°C / s or higher. Thereafter, the cooling rate from 650 to 550°C is preferably set to 3.0 to 10.0°C / s. If the cooling rate from 650 to 550°C exceeds 10.0°C / s, a supercooled structure will form, and if it is less than 3.0°C / s, the cementite will be severed and sufficient tensile strength will not be obtained.

[0068] [Wire drawing] The wire rod is dry-drawn to a predetermined wire diameter. In this case, the area reduction rate in one pass is preferably 30% or less, and the total strain amount is preferably in the range of 0.4 to 2.0 in true strain. If the area reduction rate in one pass exceeds 30%, the possibility of wire breakage during drawing increases. Furthermore, if the total true strain during wiredrawing is less than 0.4, it is difficult to obtain bcc grains with desirable properties during subsequent annealing, resulting in a decrease in tensile strength, and a decrease in absorbed energy capacity or protrusion amount. On the other hand, if the total true strain during wiredrawing exceeds 2.0, the tensile strength of the steel wire after wiredrawing is high, and it is difficult to obtain the desirable mechanical properties and structure of the present disclosure even after plating. The total strain amount during wiredrawing is more preferably in the range of 0.5 to 1.6 true strain. The true strain can be calculated using the formula -2 x ln (wire diameter of drawn wire material / wire diameter of wire material), where "ln" is the natural logarithm.

[0069] By using the steel composition of the present disclosure and adjusting the manufacturing conditions as described above, the metal structure and mechanical properties of the steel wire can be within the ranges of the present disclosure.

[0070] [Plating] For example, when the plating is zinc plating, the zinc plating can be performed by a normal industrial method. For example, the lubricant used during wire drawing is removed, and the surface is activated by pickling. Next, flux is applied, and then hot-dip galvanization is performed. The mechanical properties and structure of the zinc-plated steel wire are controlled by the zinc plating temperature and the immersion time in the plating bath. The temperature of the plating bath is preferably 450 to 490°C, and the immersion time is 20 to 60 seconds.

[0071] (coated steel wire) The plated steel wire according to the present disclosure may be a coated plated steel wire in which the plated surface is further coated with paint, resin, or the like. The coating material or resin to be used for coating is not particularly limited and can be selected depending on the application. For example, when used for wire mesh, a coating material or resin that is used as a coating material for known plated steel wire for wire mesh can be used. In the case of a coated plated steel wire, the mechanical properties of the plated steel wire after the mesh-making process may be measured by a tensile test in the painted or resin-coated state. However, when measuring the tensile strength of the plated steel wire, the measurement should be based on the wire diameter of the plated steel wire that serves as the core material.

[0072] <Application> The uses of the plated steel wire and coated plated steel wire according to the present disclosure are not particularly limited. For example, if a wire mesh manufactured using the plated steel wire or coated plated steel wire according to the present disclosure is used as a wire mesh for rockfall protection work, when a falling rock is received, the wire mesh will have little elongation and high energy absorption performance, and will be prevented from protruding toward the road. Furthermore, the plated steel wire and coated plated steel wire according to the present disclosure are suitable for wire mesh used in rockfall protection works and for preventing flying objects, but are not limited thereto. The plated steel wire and coated plated steel wire according to the present disclosure can be used as materials for, for example, bridge wire, concrete reinforcing wire, and guard wire used to prevent highways and bridge girders from falling. [Example]

[0073] The plated steel wires and the like according to the present disclosure will be described in more detail below by way of examples of galvanized steel wires. The present disclosure is not limited to the following examples, and modifications can be made within the scope of the above and below-described aims, and all such modifications are within the technical scope of the present disclosure.

[0074] [Manufacturing and evaluation of hot-dip galvanized steel wire] (Wire rod manufacturing) In both the Examples and Comparative Examples, hot rolling was performed by first heating the billet to 1000 to 1100°C, rolling it, and coiling it into a ring. The finish rolling start temperature, the cooling rate after coiling into a ring to 650°C (cooling rate A1), and the cooling rate from 650°C to 550°C (cooling rate A2) were the values shown in Tables 2A and 2B.

[0075] (Wire drawing process) The wire rod obtained as described above was subjected to wire drawing (dry wire drawing) and heat treatment under the conditions shown in Tables 2A and 2B to obtain steel wires. Note that, in the dry wire drawing, as pretreatment, scale removal was performed by pickling or bending, and lime coating treatment was performed, followed by wire drawing at an area reduction rate of 12 to 30% per pass. The wire diameters of the steel wires are shown in Tables 2A and 2B.

[0076] (Zinc plating) To clean and activate the surface of the steel wire (removing scale and lubricant), the wire was dissolved in 50°C hot water and 60°C 17% hydrochloric acid, then rinsed with water, and then passed through a mixed solution of ammonium chloride and zinc chloride, which is a flux, to apply the flux. After the applied flux was dried, the wire was passed through molten zinc and pulled out to produce a hot-dip galvanized steel wire. Note that the zinc-based alloy plating was produced by immersing the wire in the alloy plating after zinc plating. In this case, the immersion time was measured as the total time for each immersion.

[0077] The thus obtained galvanized steel wire was subjected to microstructural evaluation and tensile testing, and the metallographic structure and mechanical properties were measured by the methods described above.

[0078] [Evaluation of wire mesh] Next, the method for evaluating the energy absorption capacity of wire mesh will be described. First, the hot-dip galvanized steel wire was formed into a diamond-shaped wire mesh measuring 3 m x 3 m and having a mesh size of 50 mm x 50 mm.

[0079] The wire mesh fabricated as described above was fixed to a fixed frame with bolts at a specified interval on both sides along two of the four opposing sides, and after passing a rope through the mesh on the remaining two sides and fixing the end of the rope to the fixed frame, a spherical weight with a diameter of 0.7 m and a weight of 1.6 t was dropped from various heights. The energy (kJ) that the wire mesh could absorb was calculated from the maximum height at which the weight did not penetrate the wire mesh, and the absorbed energy of the wire mesh (kJ / mm) was calculated by dividing this energy by the cross-sectional area of the galvanized steel wire used in the wire mesh. 2 The amount of overhang (overhang distance) is the distance traveled from the initial position to the final position of the wire mesh when the falling weight reaches the maximum height without penetrating the wire mesh. The criterion for determining high energy absorption wire mesh is the absorbed energy (kJ / mm 2 ) is 4.5kJ / mm 2 The overhang amount is considered to be good if it is 1,350 mm or less.

[0080] Tables 1A and 1B show the steel compositions, Tables 2A and 2B show the hot rolling conditions, the structural evaluation of the wire rod, and the wire drawing and plating conditions, and Tables 3A and 3B show the structural evaluation of the steel wire and the mechanical properties of the galvanized steel wire and wire mesh. The cooling rate A1, the cooling rate A2 and the formula (A) shown in Tables 2A and 2B are defined as follows. Cooling rate A1: Average cooling rate up to 650°C after finish rolling (after coiling) Cooling rate A2: Average cooling rate from 650℃ to 550℃ T: Temperature of plating bath (℃) S: Immersion time in plating bath (seconds)

[0081] [Table 1A]

[0082] [Table 1B]

[0083] [Table 2A]

[0084] [Table 2B]

[0085] [Table 3A]

[0086] [Table 3B]

[0087] Levels A1 to A40 are all examples of the present disclosure, and as wire mesh, they are able to achieve high energy absorption capacity while suppressing the amount of protrusion. B1 is a steel composition used in current normal galvanized wires, and is an example of low absorbed energy due to a low C content and low tensile strength. B2 is an example in which the amount of C was excessive, resulting in reduced uniform elongation and elongation at break, vertical cracking in the torsion test, and reduced absorbed energy. B3 is an example in which the absorbed energy was reduced due to the low tensile strength of the plated steel wire. B4 and B5 are samples that were annealed at 750°C for 80 seconds after drawing and before plating. These are examples where the absorbed energy decreased and the amount of protrusion increased due to a decrease in tensile strength and an increase in uniform elongation. B6 is an example in which the tensile strength of the steel wire is excessively high, uniform elongation is not obtained, and the absorbed energy is reduced. B7, 8, and 9 are examples where the absorbed energy decreased due to low uniform elongation of the plated steel wire. The reason for the low uniform elongation of these plated steel wires is unclear, but it is thought that inappropriate manufacturing conditions and dislocations in the steel wire are the cause. B7 was immersed in the plating bath for a short time, and B8 had a low plating bath temperature, so it is presumed that there was little recovery of the structure due to the plating bath, resulting in a difference in dislocation density. It is also presumed that B9 had a different dislocation density due to excessive strain during wire drawing. In addition, the uniform elongation and twisting properties of B3 and B4 were reduced, which resulted in breakage during net making.

Claims

1. A plated steel wire having a plating layer on the surface of the steel wire, The steel composition of the steel wire is, in mass%, C: 0.30-1.20%, Si: 0.10 to 1.50%, Mn: 0.10-1.00%, P: 0.030% or less, S: 0.030% or less, N: 0.0150% or less, and O: 0.0070% or less and the balance being Fe and impurities, When the radius of the steel wire is R, in a cross section that is parallel to the longitudinal direction of the steel wire and includes the central axis of the steel wire, a metal structure observed in a central region at a distance from the central axis of 0.2 × R or more and 0.8 × R or less has a total area ratio of ferrite and pearlite to the entire metal structure of 90.0% or more, an area ratio of the pearlite to the entire metal structure of 47.5% or more, and when the total area ratio of the ferrite and pearlite to the entire metal structure is less than 100%, the remainder consists of at least one of cementite and bainite, When subjected to a tensile test, the tensile strength is 850 to 2000 MPa and the uniform elongation is 4.0 to 8.0%. Plated steel wire.

2. The steel composition contains, in mass%, replacing a portion of the Fe, Cr: 1.50% or less, B: 0.0050% or less, Ti: 0.040% or less, Mo: 0.40% or less, V: 0.30% or less, Cu: 0.50% or less, Al: 0.080% or less, Ni: 0.50% or less, and Nb: 0.10% or less, The plated steel wire according to claim 1, comprising one or more selected from the group consisting of:

3. The steel composition contains, in mass%, replacing a portion of the Fe, Mg: 0.010% or less, Zr: 0.010% or less, Sb: 0.015% or less, W: 0.010% or less, REM (elements with atomic numbers 57 to 71): 0.005% or less, Hf: 0.005% or less, Ta: 0.050% or less, Ca: 0.005% or less, Sn: 0.050% or less, Bi: 0.050% or less, Te: 0.050% or less, Zn: 0.050% or less, and Co: 0.10% or less The plated steel wire according to claim 1 or claim 2, comprising one or more selected from the group consisting of:

4. The breaking elongation when the tensile test was carried out is 5.0% to 10.0%; The plated steel wire according to any one of claims 1 to 3, which can be twisted 25 times or more until breakage occurs in a torsion test.

5. When the radius of the steel wire is R, in a metallographic structure observed in the cross section of the steel wire at a position at a depth of R / 2 from the surface of the steel wire, the grain size of crystal grains identified as body-centered cubic by electron backscatter diffraction (EBSD) is 5 μm or less, and the area ratio of the crystal grains having a grain size ratio X / Y of less than 2.0, where X is the grain size in a direction parallel to the longitudinal direction of the steel wire and Y is the grain size in a direction perpendicular to the longitudinal direction, is 10% or less with respect to the entire metallographic structure observed at a position at a depth of R / 2 from the surface of the steel wire, The yield ratio when the tensile test is performed is 70.0 to 90.0%. The plated steel wire according to any one of claims 1 to 4.

6. 6. The plated steel wire according to claim 1, wherein, in a metallographic structure observed in the cross section of the steel wire at a depth of R / 2 from the surface of the steel wire, where R is a radius of the steel wire, crystal grains identified as body-centered cubic by electron backscatter diffraction (EBSD) have a grain size ratio X / Y of 2.0 to 10.0, where X is a grain size in a direction parallel to the longitudinal direction of the steel wire and Y is a grain size in a direction perpendicular to the longitudinal direction, and the metallographic structure observed in the central region has an area ratio of 20.0% or less of regions in which the lamellar cementite constituting the pearlite is segmented lamellar cementite, in which the cementite has a length of 0.1 μm or less, with respect to the entire metallographic structure observed in the central region.

7. The plated steel wire according to any one of claims 1 to 6, which is for use in wire mesh.

8. A coated plated steel wire, the surface of which is coated with a resin or painted, according to any one of claims 1 to 7.

9. A wire mesh produced by weaving the plated steel wire according to any one of claims 1 to 7 or the coated plated steel wire according to claim 8.

10. The wire mesh according to claim 9, wherein the wire mesh includes at least one of bending points and welding points, and when the plated steel wire or the coated plated steel wire including one or more of the bending points or welding points is taken out and subjected to a tensile test, the tensile strength is 800 to 2000 MPa, and the elongation from a load half the maximum tensile load to the maximum load point is 3.5 to 7.0%.

11. The wire mesh according to claim 9 or claim 10, which is a diamond-shaped wire mesh having a thickness 5.0 to 12.0 times the wire diameter of the plated steel wire.

12. A rockfall protection work comprising the wire mesh according to any one of claims 9 to 11.

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