WO2023191027A1 - Plated steel wire - Google Patents

Abstract

This plated steel wire comprises a plating layer that is arranged on the surface of a steel wire; the plating layer comprises an Fe-Al interfacial alloy layer that is arranged on the steel wire side and a Zn-Al-Mg alloy layer that is arranged on the Fe-Al interfacial alloy layer; the Fe-Al interfacial alloy layer contains one or more substances selected from among Fe4Al13, Fe2Al5 and Fe2Al5Zn0.4, while having an average thickness of 0.2 µm to 5 µm; the Zn-Al-Mg alloy layer is formed of Al, Mg, Cr and the balance made up of Zn and impurities, while having an average thickness of 10 µm to 150 µm and a structure that contains 0.1% by area to 40.0% by area of MgZn2 phase.

Description

plated steel wire

The present invention relates to a plated steel wire.
This application claims priority based on Japanese Patent Application No. 2022-058885 filed in Japan on March 31, 2022, the contents of which are incorporated herein.

Galvanized steel wire is widely used, for example, as a reinforcing wire for overhead power transmission lines. One type of overhead power transmission line is steel core aluminum stranded wire (ACSR). The steel-core aluminum stranded wire is composed of a steel stranded wire made of a plurality of galvanized steel wires and an aluminum stranded wire arranged on the outer peripheral side of the steel stranded wire. As described above, galvanized steel wires used for overhead power transmission lines are required to have excellent corrosion resistance since they are installed outdoors. In addition, since overhead power transmission lines are installed at high places between steel towers, they are susceptible to repeated tensile stress or compressive stress due to being blown by the wind. For this reason, galvanized steel wire is required to have excellent fatigue properties. Furthermore, since the galvanized wire is subjected to twisting processing, it is required to have excellent workability.

Furthermore, galvanized steel wires have uses such as supporting not only power lines but also signal lines, bridge wires, wire meshes, and other exposed steel wires used outdoors. Even in these applications, galvanized steel wire is required to have corrosion resistance, fatigue properties, and workability.
Furthermore, as a technique related to galvanizing, there is a technique in which galvanizing is applied to steel sheets. However, the knowledge in the technology of applying galvanization to steel sheets cannot be applied to the technology related to steel wires because the manufacturing conditions, such as annealing temperature and atmosphere, are significantly different from those of steel wires. For example, in the manufacturing method shown in Patent Document 4, the Sendzimer method is used for treatment before immersion in a plating bath, and the steel plate is heated to 600° C. and subjected to reduction treatment. Reductive heating as described above cannot be used with steel wires because it degrades fatigue properties.

As conventional galvanized steel wires, for example, those described in Patent Documents 1 to 3 below are known.
Patent Document 1 has a steel material and a plating layer formed on the surface of the steel material, and the plating layer is formed by sequentially forming an interfacial alloy layer, an intermediate alloy layer, and a surface plating layer from the steel material side, The interfacial alloy layer consists of Fe: 20 to 60% by mass, Al: 10 to 44% by mass, and the remainder substantially consists of Zn and impurities, and the intermediate alloy layer contains Fe: 20 to 60% by mass, Al: 10 to 44%. Mass%, Cr: 0.001 to 3.0% by mass, the remainder substantially consisting of Zn and impurities, and the surface plating layer has an average concentration of Al: 5% by mass or less, the remainder substantially consisting of Zn and impurities. A plated steel material is described in which the total thickness of the interfacial alloy layer and the intermediate alloy layer is 30 μm or more.

Patent Document 2 discloses that a Fe-Zn-Al-Mg quaternary intermetallic compound is present at the interface between the plated base metal and has a thickness of 2 to 20 μm, and a residual strain of 0.01% or more is present in the intermetallic compound layer. Plating with fatigue resistance and excellent corrosion resistance in which a Zn-Al-Mg alloy layer of 5 μm or more is present on the outside, consisting of Al: 8 to 15%, Mg: 0.1 to 3%, and the balance Zn in mass%. Steel wire is listed.

Patent Document 3 discloses a steel wire for bridges, which includes a steel wire, a plated main body layer, and a Zn-Al plating having a Fe-Al alloy forming layer formed at the interface between the surface layer of the steel wire and the plated main body layer. A strength Zn-Al plated steel wire, in which the composition of the matrix of the steel wire is, in mass%, 0.70% or more and 1.2% or less of C, and 0.01% or more and 2.5% or less of Si. , contains Mn from 0.01% to 0.9%, limits P to 0.02% or less, S to 0.02% or less, and N to 0.01% or less, with the balance being Fe and unavoidable In the metallographic structure of the matrix of steel wire, drawn pearlite structure is the type of structure that contains the most amount of impurities, and the average component composition of Zn-Al plating is 3.5% by mass of Al. 0 to 15.0%, Fe is limited to 3.0% or less, the thickness of the Fe-Al alloying layer is 5 μm or less, and the Fe-Al alloying layer is on the steel wire side. The multi-layer structure consists of a layer containing the most Al _3.2 Fe columnar crystals, and a layer containing the most Al ₅ Fe ₂ columnar crystals on the Zn-Al plating side, which has excellent corrosion resistance and fatigue properties. An excellent high-strength Zn-Al plated steel wire for bridges is described.

Japanese Patent No. 6772724 Japanese Patent Application Publication No. 2003-328101 Japanese Patent No. 4782246 Japanese Patent Application Publication No. 10-226865

Although the plated steel materials and plated steel wires described in Patent Documents 1 to 3 have excellent corrosion resistance, there is still room for further improvement in corrosion resistance, fatigue properties, and workability.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a plated steel wire with excellent corrosion resistance, fatigue properties, and workability.

In order to solve the above problems, the present invention employs the following configuration.
[1] Steel wire and
a plating layer disposed on the surface of the steel wire,
The plating layer includes an Fe-Al-based interfacial alloy layer disposed on the steel wire side, and a Zn-Al-Mg alloy layer disposed on the Fe-Al-based interfacial alloy layer,
The chemical composition of the steel wire is in mass%,
C: 0.030% or more and 1.20% or less,
Si: 0.05% or more and 2.00% or less,
Mn: 0.10% or more and 0.90% or less,
P: 0.030% or less,
S: 0.030% or less,
Contains N: 0.010% or less,
The remainder consists of Fe and impurities,
The average composition of the plating layer is in mass%,
Fe: 15.0% or less,
Al: 3.0% or more and 15.0% or less,
Mg: 0.3% or more and 3.5% or less,
Cr: Contains 0.003% or more and 0.500% or less,
The remainder: consists of Zn and impurities,
The Fe--Al interface alloy layer contains one or more of Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , Fe ₂ Al ₅ Zn _0.4 , and has an average thickness of 0.2 μm or more.5. 0 μm or less,
The Zn-Al-Mg alloy layer contains Al, Mg, Cr, balance Zn and impurities, contains 0.1 to 40.0 area% MgZn _two phase in the structure, and has an average thickness of 10 μm or more and 150 μm. A plated steel wire characterized by:
[2] The average composition of the plating layer is in mass%,
Fe: 2% or less,
Al: 3.0% or more and 8.0% or less,
Mg: 0.3% or more and 3.5% or less,
Cr: Contains 0.003% or more and 0.5% or less,
The remainder: consists of Zn and impurities,
The plated steel wire according to [1], wherein the average thickness of the Zn-Al-Mg alloy layer is 30 μm or more and 100 μm or less.
[3] The plating layer further has an average composition of one or more of Ni, Ti, Zr, Sr, Sn, Ca, Co, Mn, B, REM, and Hf in a total of 0. The plated steel wire according to [1] or [2], containing 0001 to 2% by mass.
[4] The chemical composition of the steel wire is C: 0.40% or more and 1.20% or less in mass %,
Si: 0.3% or more and 2.00% or less,
Mn: 0.10% or more and 0.90% or less,
P: 0.030% or less,
S: 0.030% or less,
Contains N: 0.010% or less,
The plated steel wire according to any one of [1] to [3], wherein the remainder consists of Fe and impurities.
[5] The steel wire according to any one of [1] to [4], characterized in that the chemical composition further contains 0.1% or more and 0.5% or less of Cr in mass %. plated steel wire.
[6] The chemical composition of the steel wire is further expressed in mass%,
Ni: more than 0% and less than 1.00%,
Cu: more than 0% and 0.50% or less,
Mo: more than 0% and less than 0.50%,
V: more than 0% and less than 0.50%,
B: more than 0% and less than 0.0070%,
Al: more than 0% and less than 0.100%,
Ti: more than 0% and less than 0.10%,
Nb: more than 0% and less than 0.10%,
Zr: more than 0% and less than 0.10%,
Ca: more than 0% and less than 0.005%,
Mg: more than 0% and less than 0.005%,
REM: more than 0% and less than 0.02%,
Co: more than 0% and less than 0.5%,
Sb: more than 0% and less than 0.05%,
As: more than 0% and less than 0.05%,
Sn: more than 0% and less than 0.05%,
The plated steel wire according to any one of [1] to [5], characterized in that it contains one or more of O: more than 0% and 0.0100% or less.

According to the present invention, a plated steel wire with excellent corrosion resistance, fatigue properties, and workability can be provided.

FIG. 1 is a schematic diagram of a cross-sectional structure of a plating layer of a plated steel wire according to an embodiment of the present invention.

The present inventors have conducted extensive studies in order to realize a plated steel wire with excellent corrosion resistance, fatigue properties, and workability.

Galvanized steel wire is required to have corrosion resistance and fatigue properties. When high corrosion resistance is required for hot-dip galvanized steel wire, Zn alloy plating is mainly used. However, conventional Zn alloy plated steel wires are mainly manufactured by two-step plating, which is easy to plate, due to the restriction that they are manufactured using the flux method. In some cases, the fatigue properties were insufficient due to the thick formation.

To make the Fe-containing interfacial alloy layer thinner when manufacturing Zn alloy-plated steel wire using a two-stage plating method, the composition of the plating layer must be changed from the normal plating composition in the first stage plating, or the composition of the plating layer in the first stage must be It is necessary to separately prepare a plating bath and a second plating bath to perform plating. However, these lead to a decrease in productivity. Therefore, in applications where fatigue characteristics are important, pure Zn-plated steel wire or Al-clad steel wire, which have relatively low corrosion resistance, must be used instead of Zn alloy-plated steel wire.

However, although Al-clad wire has superior corrosion resistance compared to pure Zn-plated wire, it has the drawback of high manufacturing cost. Therefore, there is a need for a Zn alloy plated wire that has excellent fatigue properties and better corrosion resistance than pure Zn plating.

Therefore, the present inventors considered adopting a one-stage continuous hot-dip plating method in order to thin the Fe-containing interfacial alloy layer. The present inventors also aimed to improve corrosion resistance by using a Zn-Al-Mg alloy plating layer as the plating layer. Zn-Al-Mg plating using the flux method was difficult to manufacture using the one-step plating method because Mg inhibits the plating reaction, but by adding a small amount of Cr to the plating bath, the reaction between the steel and the plating bath can be improved. The present inventors have found that the properties are improved and one-step plating becomes possible.

However, when Cr is added to a Zn-Al-Mg alloy plating bath, the reactivity becomes too high, and depending on the conditions, a thick Fe-Al interfacial alloy layer is formed, making it difficult to improve fatigue properties. A problem arose.

Therefore, in order to suppress the growth of the Fe-Al-based interfacial alloy layer, the present inventors have considered utilizing the components in steel. Usually, Si in steel exists in the form of Si oxide on the steel surface, and therefore, during hot-dip plating, it greatly reduces plating wettability and causes plating defects such as no plating. On the other hand, in steel wires that have been cold drawn before hot-dip plating, the amount of Si oxide on the surface is reduced, so the Fe-Al interfacial alloy layer, which is a characteristic of metallic Si, can be formed without impairing the plating wettability. The present inventors have discovered that growth can be suppressed.

Additionally, the present inventors have discovered that Cr in the plating bath promotes the initial reaction of Fe-Al alloying, but Cr in steel conversely suppresses Fe-Al alloy growth. Therefore, by increasing the content of Si and Cr in steel and making use of the alloy growth suppressing effects of both elements to thin the Fe-Al interface alloy layer, fatigue properties and corrosion resistance can be improved even with the same plating thickness. The Zn--Al--Mg alloy layer, which is advantageous for this purpose, can be relatively increased.

Furthermore, by using a Zn-Al-Mg alloy layer that is advantageous in corrosion resistance, it is possible to reduce the plating thickness while maintaining corrosion resistance, and therefore workability can also be improved.

Based on the above findings, the present inventors completed the present invention. Hereinafter, a plated steel wire that is an embodiment of the present invention will be described.

The plated steel wire of this embodiment includes a steel wire and a plating layer disposed on the surface of the steel wire, and the plating layer includes an Fe-Al interface alloy layer disposed on the steel wire side and a Fe-Al based interfacial alloy layer disposed on the steel wire side. - Zn-Al-Mg alloy layer disposed on the Al-based interfacial alloy layer, and the chemical composition of the steel wire is, in mass %, C: 0.030% or more and 1.20% or less, Si: 0. 05% or more and 2.00% or less, Mn: 0.10% or more and 0.90% or less, P: 0.030% or less, S: 0.030% or less, N: 0.010% or less, The remainder consists of Fe and impurities, and the average composition of the plating layer is, in mass%, Fe: 15.0% or less, Al: 3.0% or more and 15.0% or less, Mg: 0.3% or more and 3.5%. % or less, Cr: 0.003% or more and 0.500% or less, the remainder: Zn and impurities, and the Fe-Al interface alloy layer contains Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , Fe ₂ Al ₅ Zn _0.4 and has an average thickness of 0.2 μm or more and 5.0 μm or less, and the Zn-Al-Mg alloy layer contains Al, Mg, Cr, the balance being Zn and It contains impurities, contains 0.1 to 40.0 area % MgZn _two- phase in its structure, and has an average thickness of 10 μm or more and 150 μm or less.

In the following description, the content of each element in the chemical composition expressed as "%" means "mass%". Furthermore, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as lower and upper limits. In addition, a numerical range in which "more than" or "less than" is attached to the numerical value written before and after "~" means a range that does not include these numerical values as the lower limit or upper limit.

The reason for limiting the chemical composition of steel wire will be explained.

C: C is an effective element for increasing the tensile strength of steel wire and increasing the work hardening rate during wire drawing. The inclusion of C makes it possible to increase the strength of the steel wire with less wire drawing strain, and also contributes to improving fatigue properties. In this embodiment, the amount of C is set in a range of 0.030% or more and 1.20% or less. The lower limit of the amount of C may be set to 0.40% or more. If the C content of the steel wire is at least the lower limit of the above range, sufficient tensile strength is ensured in the plated steel wire, and the wire drawing work hardening rate is also sufficiently large, making it possible to obtain a steel wire with the desired strength. can. On the other hand, if the amount of C is below the upper limit of the above range, the processing cost for reducing center segregation will be within an allowable range.

The amount of C is determined by the mechanical properties of the steel wire, but it also affects the plating. C is an element that basically suppresses the Fe-Al reaction, and when the content is high, it causes poor adhesion and non-plating, and when the content is low, it becomes difficult to control the alloy layer to be thin, resulting in poor workability. , reduce fatigue properties. Therefore, also from the viewpoint of plating properties, the C content needs to be in the range of 0.030% or more and 1.20% or less.

Si: In this embodiment, the amount of Si is set to 0.05% or more and 2.00% or less. In order to increase the hardness of the steel wire, the lower limit of the amount of Si may be set to 0.30% or more. Since Si is a deoxidizing agent and an element effective in strengthening ferrite in pearlite, the amount of Si is set to be at least the lower limit of the above range. On the other hand, even if Si exceeding the upper limit of the above range is contained, the effect is saturated. Since Si is also effective in suppressing the growth of the Fe--Al based interfacial alloy layer when immersed in a plating bath, it is contained in an amount of 0.05% or more.

Note that in this embodiment, Si oxide on the steel surface is removed and shredded after cold wire drawing, so it does not interfere with plating. However, if the Si content exceeds 2.00%, an adverse effect may appear on the plating.

Mn: In this embodiment, the amount of Mn is set to 0.10 to 0.90%. Since Mn is an effective element for deoxidation and desulfurization, it is contained in an amount equal to or higher than the lower limit of the above range. In order to improve the hardenability of the steel and increase the tensile strength of the plated steel wire, it is contained in an amount of 0.10% or more. On the other hand, if the amount of Mn is below the upper limit of the above range, the degree of segregation will not increase and the generation of bainite that reduces the number of twists during patenting treatment will be suppressed.

P: P is set to 0.030% or less in order to suppress a decrease in ductility. Note that the upper limit of the amount of P is preferably 0.025% or less. Since excessive reduction of P increases refining cost, P may be 0.0005% or more.

S: S is set to 0.030% or less in order to suppress deterioration of hot workability. The upper limit of the amount of S is preferably 0.025% or less. Since excessive reduction of S increases refining cost, the S content may be 0.0005% or more.

N: If N is contained excessively, ductility decreases, so it is set to 0.010% or less. A preferable upper limit of the amount of N is 0.007% or less. The lower limit of the N content may be, for example, 0.001% or more.

Cr: Cr is an optionally added element and has the effect of increasing the strength of the steel wire by affecting the pearlite structure of the steel wire, so it may be included as necessary. Also, like Si, it is effective in suppressing the growth of the Fe--Al based interfacial alloy layer when immersed in a plating bath. Therefore, 0.10% or more of Cr may be contained in the steel wire. By containing Cr together with Si, the growth of the Fe--Al based interfacial alloy layer can be further suppressed and fatigue properties can be improved. The upper limit of the Cr amount is 0.50% or less. It is meaningless for the amount of Cr to exceed this upper limit due to the influence on the plating and the influence of the material, and if it exceeds 0.5%, the effect of suppressing the plating reaction becomes excessive and poor plating adhesion is likely to occur.

In this embodiment, in order to increase the strength, improve the strength, refine the crystal grain size, in particular, refine the prior austenite grain size, and improve the cold wire drawability. contains more than 0% of one or more of Ni, Cu, Mo, V, B, Al, Ti, Nb, Zr, Ca, Mg, REM, Co, Sb, As, Sn, Sb, and O. You may.

Ni: Ni is an element that improves hardenability and is an effective element for improving strength after patenting treatment. However, even if more than 1.00% of Ni is contained, the effect is saturated, so it is preferable that the upper limit is 1.00% or less. Note that Ni is also effective in improving wire drawability, and is preferably contained in an amount of 0.01% or more.

Cu: Like Ni, Cu is an element effective in improving strength after patenting treatment. In order to obtain this effect, it is preferable to contain Cu in an amount of 0.01% or more. However, even if more than 0.50% of Cu is contained, the effect is saturated, so it is preferable that the upper limit is 0.5% or less.

Mo: Mo is an element that improves hardenability. The content of Mo is effective in improving the tensile strength after the patenting treatment, and the content is preferably 0.01% or more. On the other hand, even if more than 0.50% of Mo is contained, the effect is saturated, so it is preferable that the upper limit is 0.5% or less.

V: V is an element that increases the tensile strength after patenting treatment by precipitation strengthening. Further, the inclusion of V is also effective in suppressing a decrease in strength during hot-dip plating, and it is preferable that the amount of V is 0.01% or more. On the other hand, if more than 0.50% of V is contained, the ductility may decrease, so the upper limit is preferably 0.50% or less.

B: B is an element that increases the tensile strength after patenting treatment due to its hardenability improving effect. In order to improve hardenability, the content is preferably 0.0001% or more. On the other hand, even if B is contained in an amount exceeding 0.0070%, an effect commensurate with the content will not be exhibited, so it is preferable to set the upper limit of the B amount to 0.0070% or less.

Al: Al is an effective element for deoxidation, and also contributes to preventing coarsening of crystal grains by forming nitrides. However, even if Al exceeds 0.100%, the effect is saturated, so it is preferable to set the upper limit to 0.100% or less. In addition, in order to refine the prior austenite grain size and improve the wire drawability of the steel wire after pearlite transformation, the Al content is preferably 0.001% or more.

Ti: Ti is an effective element for deoxidation, and contributes to improving strength and preventing coarsening of crystal grains by forming carbides and nitrides. In order to refine the prior austenite grain size, improve the wire drawability of the steel wire, and improve the ductility of the steel wire, it is preferable to contain 0.001% or more of Ti. On the other hand, if more than 0.10% of Ti is contained, Ti carbonitrides may become coarse and may deteriorate wire drawability and fatigue properties, so it is preferable that the upper limit is 0.10% or less. .

Nb: Like Ti, Nb is an element that forms carbides and nitrides. It is an effective element for refining austenite grains by forming Nb carbides and nitrides. In particular, in order to refine the prior austenite grain size, improve the wire drawability of the steel wire, and improve the ductility of the steel wire, Nb content of 0.001% or more is preferable. On the other hand, even if more than 0.10% of Nb is contained, the effect is saturated, so it is preferable that the upper limit of the amount of Nb is 0.10% or less. More preferably, it is 0.05% or less.

Zr: Like Ti and Nb, Zr is an element that forms carbides and nitrides, and is contained in an amount of 0.001% or more in order to improve the wire drawability of the steel wire and the ductility of the steel wire. It is preferable to do so. On the other hand, even if more than 0.10% of Zr is contained, the effect is saturated, so the upper limit is preferably 0.10% or less.

Ca: Ca is effective in reducing hard alumina-based inclusions and improving wire drawability. In order to reliably obtain this effect, the Ca content is preferably 0.0002% or more. However, when Ca is contained excessively, oxides are generated, causing wire breakage. Therefore, the Ca content is preferably 0.005% or less.

Mg: Mg becomes a fine oxide that refines the structure of steel and improves its ductility. In order to reliably obtain this effect, it is preferable that the Mg content is 0.0002% or more. However, when the Mg content exceeds 0.005%, wire breakage tends to occur starting from the oxide. Therefore, the Mg content is preferably 0.005% or less.

REM: REM is effective in rendering S harmless. In order to reliably obtain this effect, it is preferable that the REM content is 0.0002% or more. However, when REM is contained excessively, oxides are generated, which causes wire breakage. Therefore, the REM content is preferably 0.02% or less.
In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the content of REM refers to the total content of these elements.

Co: Co enhances the orientation of lamellar cementite of pearlite and improves wire drawability. In order to reliably obtain this effect, it is preferable that the Co content be 0.05% or more. However, even if Co is contained excessively, the effect is saturated, resulting in a large economic loss. Therefore, the Co content is preferably 0.5% or less.

Sb, As, and Sn: Sb, As, and Sn are elements that do not adversely affect the plated steel wire according to this embodiment even if they are contained in trace amounts. Therefore, these elements may be contained as necessary. However, when these elements are contained excessively, manufacturability deteriorates due to a decrease in hot ductility and the like. Therefore, it is preferable that the contents of Sb, As, and Sn are each 0.05% or less.

O: Since O forms an oxide, if it is contained in excess, it may cause wire breakage or decrease in fatigue strength. Therefore, the O content is preferably 0.0100% or less. On the other hand, since deoxidation is costly, reducing the O concentration to less than 0.0010% results in a large economic loss. Therefore, the concentration of O is preferably 0.0010% or more and 0.0100% or less.

The chemical composition of the steel wire is identified by the following method.
The plating layer is removed by peeling and dissolving it with an acid containing an inhibitor that suppresses corrosion of the steel wire. Next, the chemical composition of the steel wire is analyzed using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) or Optical Emission Spectroscopy (OES). Note that C and S may be measured using a combustion-infrared absorption method, N using an inert gas melting-thermal conductivity method, and O using an inert gas melting-non-dispersive infrared absorption method.

Next, the average composition of the plating layer will be explained. The plating layer of this embodiment includes a Fe--Al based interfacial alloy layer and a Zn--Al--Mg alloy layer. The Fe--Al based interfacial alloy layer is mainly formed by the reaction between Al in the plating bath and the base iron of the steel wire during hot-dip plating. The average composition of the plating layer described below is the average composition of the Fe--Al interfacial alloy layer and the Zn--Al--Mg alloy layer.

Fe: Fe diffuses from the surface of the steel wire and forms an Fe--Al based interfacial alloy layer mainly containing Fe and Al at the interface between the plating and the steel wire. Therefore, the amount of Fe in the plating layer changes with the thickness of the Fe--Al based interfacial alloy layer and the Fe--Al--Mg alloy layer. If the amount of Fe in the plating layer exceeds 15.0%, it means that the Fe-Al interfacial alloy layer is too thick or the Zn-Al-Mg alloy layer is too thin. This results in a decrease in properties or corrosion resistance. Therefore, in order to satisfy the desired fatigue properties, workability, and corrosion resistance of the plated steel wire, the amount of Fe in the plated layer should be 15.0% or less. In order to satisfy various properties of the plated steel wire, it is desirable to reduce the thickness of the Fe--Al based interfacial alloy layer, and for this purpose, the Fe content is preferably 2.0% or less.

Al: Al is an element that improves corrosion resistance mainly by forming a dense oxide film on the surface of the plating, rather than having a sacrificial corrosion protection effect like Zn. In order to improve the corrosion resistance of the plating layer, it is preferable to contain 3.0% or more of Al. Increasing the amount of Al increases the effect of improving corrosion resistance, but if the amount of Al exceeds 15.0%, the effect is saturated and the melting point of the plating bath becomes high, which is disadvantageous in terms of operation. Therefore, the upper limit of the Al amount is set to 15.0% or less. More preferably it is 8.0% or less.

Mg: Mg is an essential element for improving the corrosion resistance of the plating layer. However, when the amount of Mg becomes excessive, the plating layer becomes hard and cracks are likely to occur, and workability and fatigue properties are reduced. It also interferes with flux reactions and significantly reduces plating properties. Therefore, the Mg amount is set in the range of 0.3 to 3.5%. Preferably it is 0.5 to 3.0%. More preferably, the amount of Mg may be greater than 1.0%. Further, the Mg amount may be less than 2.5%. By including Mg, a MgZn _two phase can be included in the Zn--Al--Mg alloy layer, thereby further improving corrosion resistance.
It is preferable that the plating layer of this embodiment does not contain Si. If Si is contained, Mg ₂ Si will be formed preferentially over the MgZn _two -phase, and the fatigue resistance and corrosion resistance of the plating layer will deteriorate.

Cr: Cr is an element contained in the plating bath to promote the initial reaction during the formation of the Fe-Al interfacial alloy layer (hereinafter referred to as Fe-Al initial reaction), so it is included in the plating layer. It becomes like this. In order to promote the Fe--Al initial reaction, the plating layer preferably contains 0.003% or more of Cr. However, if the amount of Cr becomes excessive, the corrosion resistance of the plating layer decreases, so the upper limit is set to 0.5% or less. The preferred amount of Cr is 0.005 to 0.40%, more preferably 0.008 to 0.05%. However, since Cr is easily lost through oxidation and concentrated in the Fe--Al interfacial alloy layer, the concentration in the plating bath tends to fluctuate. Care must be taken regarding the scope of management.

There are methods to accelerate the Fe-Al initial reaction, such as increasing the bath temperature and increasing the Al concentration in the plating bath. However, when the reaction is promoted by these methods, the mechanical properties of the wire are affected. There are problems such as deterioration and non-uniform formation of interfacial alloys. To address these problems, reaction acceleration using Cr allows the plating bath to be lowered in temperature, and has the effect of making interfacial alloy formation uniform.

The remainder in the average composition of the plating layer is Zn and impurities. Impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but not intentionally included. For example, trace amounts of components other than Fe contained in the steel may be mixed into the plating layer as impurities due to mutual atomic diffusion between the steel material (base iron) and the plating bath.

In addition, the plating layer further contains one or more of Ni, Ti, Zr, Sr, Sn, Ca, Co, Mn, B, REM, and Hf in a total average composition of 0.0001 to 2 It may be contained in an amount of .0% by mass. By containing these elements, the corrosion resistance of the plating layer can be further improved.
Note that REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the content of REM refers to the total content of these elements.

To identify the average composition of the plating layer, obtain an acid solution by removing and dissolving the plating layer with an acid containing an inhibitor that suppresses corrosion of the base iron (steel wire). Next, the chemical composition can be obtained by measuring the obtained acid solution by ICP emission spectrometry or the like. The acid species is not particularly limited as long as it can dissolve the plating layer.

Next, the Fe--Al based interfacial alloy layer will be explained. The Fe--Al based interfacial alloy layer of this embodiment contains one or more of Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , and Fe ₂ Al ₅ Zn _0.4 . The Fe--Al interfacial alloy layer is a layer that is formed when the steel wire comes into contact with the plating bath, mainly due to the reaction between Al contained in the plating bath and Fe contained in the steel wire. According to electron beam diffraction, the Fe-Al-based interfacial alloy layer of this embodiment has a composition mainly composed of Fe-Al-based alloys such as Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , and Fe ₂ Al ₅ Zn _0.4 . Confirmed by. These alloys have low so-called sacrificial corrosion protection ability, but in the present invention, it is easy to increase the thickness of the Zn-Al-Mg alloy layer, which has greater corrosion protection ability than conventional plated steel wire, so the plating layer The ability to protect steel wire from corrosion is improved. Confirmation of these Fe-Al alloys is that when the structure of the Fe-Al interface alloy layer is analyzed by electron beam diffraction, Laue spots can be clearly attributed to Fe-Al alloys of any of the three types mentioned above. If the material is a Fe-Al alloy, it is confirmed that the Fe-Al alloy is included.
A method for identifying Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , and Fe ₂ Al ₅ Zn _0.4 in the Fe--Al interfacial alloy layer will be specifically described below.
A field emission transmission electron microscope (FE-TEM) is used to identify the Fe-Al alloy. Specifically, a sample was cut out using FIB processing to include the alloy layer in an arbitrary cross section to create an analysis sample, and the alloy layer was irradiated with an electron beam with a beam diameter of 5 nm using FE-TEM. Identify the intermetallic compound from the diffraction pattern.

When the elements constituting the Fe-Al interfacial alloy layer are measured using an energy dispersive X-ray spectrometer (EDS) attached to a field emission scanning electron microscope (FE-SEM), in addition to Fe and Al, 20 atoms are found. % Zn, less than 5 atomic % each of elements such as Mg, Cr, Si, etc., although the invention is not limited to this chemical composition.

In addition to these elements, elements derived from steel components such as Mn and elements derived from impurities in the plating bath may be detected, but these components are not important in the present invention.

It has been confirmed that Zn is present in an amount of about 0 to 20 atomic % in the Fe--Al based interfacial alloy layer. From the viewpoint of red rust resistance, it is desirable that a certain amount of Zn exist in the Fe--Al based interfacial alloy layer, but it is difficult to actively control this amount.

If the plating bath has a low Cr concentration, Cr will be concentrated in the Fe-Al-based interfacial alloy layer to a level higher than the plating bath concentration. Therefore, the concentration is about 1 to 100 times the Cr concentration in the bath.

Mg is generally rarely included in Fe-Al alloys. However, in some examples of plated steel wires according to the present invention, which will be described later, the presence of Mg was observed in the Fe--Al interface alloy layer. This is thought to be due to the fact that Mg is also taken in at the same time as Zn enters the Fe--Al based interfacial alloy layer.

Since Si significantly affects the thickness of the Fe--Al interfacial alloy layer, it is considered that it exists as Fe ₂ Al ₈ Si. It is thought that Si enters the Fe-Al-based interfacial alloy layer from the steel.
The average composition of the Fe--Al based interfacial alloy layer is measured using EDS attached to the FE-SEM. There are no restrictions on the measurement conditions as long as the composition of the Fe-Al interfacial alloy layer can be measured, but for example, SEM-EDS spot analysis can be used. An example of this is to set a spot at the center of the sample, set an accelerating voltage of 15.0 KV, an irradiation current of 7.5 nA, and an irradiation time of 60 s.

With the exception of Zn, these elements are analyzed at a concentration of 1 element % or less in most cases, and at a maximum of about 5 element %.

The average thickness of the Fe-Al-based interfacial alloy layer is 0.2 μm or more and 5.0 μm or less. If the average thickness is less than 0.2 μm, barrier properties and plating adhesion cannot be ensured. Furthermore, if the average thickness of the Fe--Al interfacial alloy layer exceeds 5.0 μm, the fatigue properties of the plated steel wire will deteriorate. The thickness of the Fe--Al based interfacial alloy layer is more preferably 0.2 μm or more and 2.0 μm or less.

To accurately measure the average thickness of the Fe-Al interfacial alloy layer, a plated steel wire was horizontally embedded in resin and polished so that its cross section could be observed, and the polished width of the wire was made equal to the diameter of the wire. At this stage, a backscattered electron image of the cross section of the plating layer is taken using a field emission scanning electron microscope (FE-SEM).

A Fe-Al-based interfacial alloy layer with a large proportion of Al, a light element, appears as a black image in a backscattered electron image. On the other hand, since the steel part and pure Zn structure have a high proportion of heavy elements, they appear white in the backscattered electron image. Therefore, we used commercially available image processing software to binarize the pixels contained in the Fe-Al interfacial alloy layer, which is a black image, and the pixels contained in the steel part and pure Zn structure, which are white images. , set the threshold. After removing noise, the average thickness of the Fe--Al interface alloy layer is calculated by counting the number of black pixels. Specifically, the total number of pixels counted is divided by the number of pixels in the measured length to calculate the average number of pixels in the thickness, and the average number of pixels in the thickness is converted to the actual length to calculate the thickness of the Fe-Al interface alloy layer. Derive the average thickness. Note that since the thickness of the interfacial alloy layer is not uniform, it is desirable to calculate it by processing image data of 100 μm or more in the longitudinal direction.

Next, the Zn-Al-Mg alloy layer will be explained. The Zn--Al--Mg alloy layer is a layer containing Al, Mg, Cr, balance Zn, and impurities, and is formed on the Fe--Al based interfacial alloy layer. The Zn--Al--Mg alloy layer is a Zn alloy plating layer containing Zn, Al, and Mg as main components, and exhibits superior corrosion resistance compared to pure Zn plating. The Fe-Al interfacial alloy layer provided in the plating layer has a high content of Fe, so it is relatively prone to red rust, and even if there is no problem with corrosion protection of the steel wire, it may cause aesthetic problems. . By forming a Zn-Al-Mg alloy layer with excellent corrosion resistance so as to cover such a Fe-Al-based interfacial alloy layer, the overall corrosion resistance of the plated steel wire can be improved. Note that the Zn-Al-Mg alloy layer may contain a small amount of Fe in addition to Al, Mg, Cr, the balance Zn, and impurities, and may contain Ni, Ti, Zr, Sr, Sn, Ca, Co. , Mn, B, REM, and Hf.

The average thickness of the Zn-Al-Mg alloy layer is 10 μm or more and 150 μm or less. Further, the average thickness of the Zn-Al-Mg alloy layer may be 30 μm or more and 100 μm or less. If the average thickness of the Zn-Al-Mg alloy layer is less than 10 μm, the corrosion resistance of the entire plating layer will be insufficient. Furthermore, if the average thickness exceeds 150 μm, the Zn--Al--Mg alloy layer becomes susceptible to cracking, and workability and fatigue properties may deteriorate, which is not preferable.

To measure the average thickness of the Zn-Al-Mg alloy layer, first, a backscattered electron image of the cross section is taken using an FE-SEM in the same manner as the method for measuring the average thickness of the Fe-Al interface alloy layer. . Although the Zn--Al--Mg plating layer has a complex structure, since the main component is Zn, which is a heavy element, it can be easily distinguished from the Fe--Al based interfacial alloy layer, which has a large proportion of Al, which is a light element. In the same manner as the method for measuring the average thickness of the Fe--Al interfacial alloy layer, the captured image is subjected to binarization image processing using commercially available image processing software. At this time, the white area located in the center is considered to be the steel part, the black layer above it is considered to be the Fe-Al interfacial alloy layer, and the layer with white and black parts above it is considered to be the Zn-Al-Mg alloy. Considered as a layer. After noise removal, the average thickness of the Zn-Al-Mg alloy layer is calculated by counting the number of pixels of the Zn-Al-Mg alloy layer. Note that since the variation in the thickness of the Zn-Al-Mg alloy layer is larger than the variation in the thickness of the Fe-Al-based interfacial alloy layer, it is desirable to calculate by processing image data of 300 μm or more in the longitudinal direction.

The Zn--Al--Mg alloy layer contains 0.1 to 40.0 area % of MgZn _two phases as a metal structure. In addition to the MgZn _two phases, a Zn phase and Al primary crystals may be included. FIG. 1 shows a schematic diagram of a Zn-Al-Mg alloy layer. The MgZn ₂ phase is included as a ternary eutectic structure of Zn/Al/MgZn ₂ . Note that FIG. 1 shows a plating layer plated in a plating bath containing Zn-5% Al-0.5% Mg-0.01% Cr. The Zn phase or Al primary crystal is a primary phase that crystallizes at the early stage of the solidification process of hot-dip plating. More specifically, the Al primary crystal contains about 45 atomic % or less of Zn and has a mixed structure of a fine Al phase and a fine Zn phase. The crystallization of MgZn _two phases is influenced by the Mg concentration in the plating bath.

In single-component/single-structure plating such as pure Zn plating, the entire plating layer exhibits approximately the same potential. For this reason, corrosion in a certain portion may progress in the depth direction. In this case, when the corrosion reaches the steel, the exposed steel acts as an efficient cathode, rapidly anodic dissolution of the plating, and the plating is quickly consumed. Red rust also develops quickly.

On the other hand, the plating layer according to the present embodiment has a structure that includes 0.1 to 40.0 area % of MgZn _two phases and may also include other Al primary crystals and Zn phase. Each phase or structure has a different corrosion potential, so under wet conditions, until one phase is corroded away, other phases are less likely to corrode. Therefore, localized corrosion, where corrosion progresses only in the depth direction and exposes the steel, is less likely to occur.

In the plated steel wire of this embodiment, in an environment exposed to the atmosphere, Zn in the Al primary corrodes first, then MgZn ₂ corrodes, and then, if a Zn phase exists, the Zn phase corrodes, and the Al primary corrodes. Al in the crystal corrodes last. In addition, when a plated steel wire is buried in concrete as a wire mesh, the Al in the Al primary crystals, which is weak against alkali, corrodes first, and after the Al is completely corroded, the _MgZn2 corrodes, and if a Zn phase is present. For example, the Zn phase that reacts with Ca in the cement to form a protective film corrodes. In this way, a plating layer consisting of multiple structures can behave like sacrificial corrosion within the plating layer if the combination of each structure is suitable, that is, if the potential difference is clear and the electrochemical connection is good. and each tissue corrodes in turn. Therefore, the plating layer is less likely to cause local corrosion and has excellent corrosion resistance. Furthermore, the eluted Mg ²⁺ ions are said to have the effect of preventing Zn corrosion products from changing into ZnO, which can easily conduct electricity, and in this respect also contributes to improving corrosion resistance.

The Al primary crystals have a dendrite-like morphology, and the MgZn _two- phase has a lamellar morphology. In these continuous structures, corrosion tends to spread within each structure, making it easier for sacrificial corrosion protection to function and promoting uniform corrosion. When Mg atoms are dispersed as a solid solution in the plating layer, such as when the Mg content is small, there is no electrochemical connection between each Mg atom, resulting in a sacrificial corrosion protection effect and promotion of uniform corrosion. The effect is small.

In order to clearly form _two MgZn phases with a constant corrosion potential, it is desirable to slowly cool the plate after plating. In hot-dip plating of steel wire, in most cases, the wire is water-cooled immediately after plating. When the main plating is rapidly cooled, the existence form and structure may change, such as Mg entering a solid solution state or Mg ₂ Zn ₁₁ being generated. When dissolved in solid solution, the effect of improving corrosion resistance is small as described above. Furthermore, when Mg ₂ Zn ₁₁ is generated, a large amount of intermetallic compounds are precipitated from the same amount of Mg, which causes deterioration in workability and fatigue properties. Since wire rods have a small heat capacity, the cooling rate tends to be high. However, due to the small heat capacity, it is difficult to directly and accurately measure the temperature, and the small area and curved surface make it difficult to measure the temperature without contact. Speed cannot be measured in numbers. However, water cooling immediately after plating has a large effect on the structure, and tends to deteriorate not only corrosion resistance but also other properties such as workability.

Furthermore, when the plating is water-cooled in a molten state, the formation of Mg ₂ Zn ₁₁ is promoted, which causes a decrease in the amount of MgZn _two- phase formation. Therefore, until the plating solidifies, it is preferable to let it cool naturally, and if necessary, it is preferable to cool it by blowing air. Furthermore, even after the plating has solidified, it is desirable to avoid water cooling as much as possible and use only air cooling if possible.

In order to stably form _two MgZn phases, the Mg content in the plating bath must be 0.3% by mass or more. Furthermore, if Mg is present in an amount of 1.0% by mass or more or more than 1.0% by mass, the continuity of the MgZn _two -phase in the plating layer increases and the effect of improving corrosion resistance becomes stable. The content of the MgZn _two phase in the Zn-Al-Mg alloy layer is 0.1 to 40.0 area %, preferably 3.0 to 20.0 area %, more preferably 8. It is 0 to 15.0 area%.
This area % is identified by the same method as the identification method of Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , Fe ₂ Al ₅ Zn _0.4 of the Fe-Al interfacial alloy layer, and the area ratio is calculated. Obtainable. Examples of phases or structures other than MgZn ₂ include Al primary crystal and Zn phase.
Specifically, the area ratio of the MgZn _two- phase in the Zn--Al--Mg alloy layer is measured by the following method.
The area ratio of the MgZn _two- phase in the Zn--Al--Mg alloy layer is determined by first taking a backscattered electron image of a cross section using an FE-SEM. Similar to the method for measuring the average thickness of the Zn-Al-Mg alloy layer, the captured images are subjected to binarized image processing using commercially available image processing software, and the pixels of the Zn-Al-Mg alloy layer are By counting the number, the number of pixels in the Zn--Al--Mg alloy layer is calculated. Note that the measurement of the area ratio of the MgZn _two- phase in the Zn--Al--Mg alloy layer is preferably calculated by processing image data of 300 μm or more in the longitudinal direction in order to eliminate local deviations in the structure ratio.
Since the MgZn _two phase contains Mg, which is a light element, it becomes a black image next to the Al primary crystal in the backscattered electron image of the Zn-Al-Mg alloy layer. Therefore, a threshold value is set for the Zn--Al--Mg alloy layer using commercially available image processing software so that the MgZn _two phase and other phases can be binarized. Furthermore, component analysis by SEM-EDS may be used in conjunction with phase identification to assist in phase identification; in this case, the MgZn ₂ phase corresponds to a phase containing 16 mass% (±5%) of Mg and 84 mass% (±5%) of Zn. By counting the number of MgZn _two- phase pixels obtained by binarization, the number of MgZn _two- phase pixels is calculated, and by calculating the ratio to the Zn-Al-Mg alloy layer, the area of the MgZn _two- phase can be calculated. The rate can be derived.
Since Mg ₂ Zn ₁₁ has a larger proportion of Zn than the MgZn ₂ phase, it is reflected in the backscattered electron image as a whiter image than the MgZn ₂ phase, and can be distinguished from the MgZn ₂ phase.
Since the Al primary crystal contains a large amount of the light element Al, it has a blacker image than Mg ₂ Zn ₁₁ or MgZn ₂ , so it can be distinguished from the above phases.

The plated steel wire of this embodiment described above can exhibit excellent corrosion resistance, fatigue properties, and workability.
The corrosion resistance is evaluated, for example, by using the plated steel wire of this embodiment cut into a length of 150 mm as a sample and performing a salt spray test (JIS Z 2371:2015, SST).

Fatigue properties are evaluated using a Nakamura rotary fatigue tester. The stress amplitude that did not break after ¹⁰⁷ rotations was taken as the fatigue limit, and the difference in fatigue limit depending on the type of plating and the presence or absence of plating was investigated.

Regarding workability, the plated steel wire of this embodiment was wound six times around a steel wire of a predetermined diameter, and the presence or absence of cracks was determined by visually observing the surface.

Next, a method for manufacturing the plated steel wire of this embodiment will be explained. The plated steel wire of this embodiment is made into a steel wire by subjecting a hot-rolled wire rod having chemical components within the range of the present invention to a patenting treatment as necessary, and then subjecting it to cold wire drawing. Next, after cleaning the surface of the steel wire, it is subjected to flux treatment, and manufactured by a so-called one-stage immersion plating method in which the steel wire is immersed in one type of plating bath and then pulled out.

There are no particular restrictions on the hot rolling process and patenting treatment. Patenting processing may or may not be performed.

In cold wire drawing, the total area reduction rate is preferably 50 to 95%, for example. In cold wire drawing, drawing or roll processing using a die is performed at least once or twice or more. By performing such drawing processing or rolling processing, the oxide film that had adhered to the surface of the wire rod in the pre-process stage of cold wire drawing is removed or fragmented, and the steel wire after drawing is A new surface appears on the surface. Therefore, there are few oxides such as Si on the surface of the steel wire after cold drawing. By performing hot-dip plating on the steel wire after wire drawing, the effect of suppressing the growth of the Fe--Al interfacial alloy layer, which is a characteristic of metal Si, can be exerted without impairing the plating wettability.

In the flux treatment, for example, the drawn steel wire is immersed in an aqueous flux solution at 60° C. for 20 seconds, and then dried. As the flux, a solution in which various salts such as NaCl, KCl, NaF, SnCl ₂ , SnCl _{4 ,} BiCl ₃ , surfactants, etc. are dissolved based on ZnCl ₂ and acidified with hydrochloric acid as necessary is used. By applying flux to the steel wire before plating, oxides on the surface of the steel wire are removed and the plating reaction is stabilized. Examples of the flux include fluxes dissolved in water such that the concentration of NaCl is 30 to 100 g/L, KCl is 30 to 100 g/L, SnCl ₂ is 0 to 20 g/L, and ZnCl ₂ is 100 to 300 g/L. can be exemplified. Furthermore, a commercially available surfactant for plating flux may be added.

The plating bath is a plating bath based on Zn and further containing Al, Mg, and Cr. The Al concentration in the plating bath is 3.0 to 15.0% by mass. If the Al concentration is less than 3.0% by mass, sufficient corrosion resistance cannot be imparted to the plating layer. Furthermore, if the Al concentration exceeds 15.0% by mass, the FeAl alloying reaction becomes intense, making it difficult to control the thickness of the Fe-Al interfacial alloy layer, and increasing Al primary crystals, which tends to reduce fatigue properties. It is in. Preferably it is 8.0% by mass or less. Considering that in the immersion plating method, it is difficult to maintain the bath components at a constant value, the Al concentration is preferably 4.0 to 7.0% by mass.

The Cr concentration in the plating bath is 0.003 to 0.5% by mass. If the Cr concentration is 0.003% by mass or more, the FeAl reaction is clearly promoted, and the effect is almost saturated at 0.5% by mass. Since Cr is concentrated in the Fe--Al interfacial alloy layer and has a large loss as dross, the bath concentration tends to decrease. Therefore, it is necessary to maintain a high plating bath concentration.
If Cr is not added, the formation and subsequent growth of the Fe--Al interfacial alloy layer will be non-uniform due to the influence of the steel structure of the hard wire, resulting in particularly poor workability and fatigue properties. Further, in a plating bath to which Mg is added as in the present invention, stable plating at a low bath temperature is difficult. However, the existence form of Cr in the plating layer cannot be confirmed by X-ray diffraction or the like.
Note that when Cr is included in the plating bath, Cr is an element that is easily lost through oxidation. In order to ensure a desired amount of Cr in the plating layer of the finally obtained plated steel wire, it is important to intentionally add Cr to the plating bath to maintain the Cr concentration. That is, the plated steel wire of the present invention cannot be realized with a level of Cr contained as an impurity in the plating bath.

Mg is added to the plating bath to improve the corrosion resistance of the plating layer. The Mg concentration is 0.3 to 3.5% by mass. Mg in the plating layer has an effect of improving corrosion resistance when it is 0.3% by mass or more, and is almost saturated at 3.5% by mass. When Mg exceeds 3.5% by mass, operational problems such as generation of dross in the plating bath become serious. Further, although Mg clearly improves corrosion resistance, it tends to reduce the workability and fatigue properties of the plating layer. In this way, Mg greatly affects plating quality. Furthermore, Mg has a large influence on the plating reaction, and obstructs the initial flux reaction, making plating defects more likely to occur. Therefore, addition of Cr is essential for stable production. Furthermore, since the subsequent FeAl alloying reaction is suppressed and the Fe--Al interfacial alloy layer is thinned, it also has the effect of improving workability and fatigue properties. As described above, since Mg has a large influence on quality and manufacturing, the amount of Mg added should be determined depending on the required quality and use.

The bath temperature of the plating bath is 440°C to 500°C, preferably 460°C to 490°C. If the bath temperature is high, the growth of the Fe-Al interfacial alloy layer will be faster and the threading speed can be increased, resulting in excellent productivity, but the Fe-Al alloying reaction will become uncontrollable, especially if the thickness is There is a risk that a Fe--Al based interfacial alloy layer will be formed, and the plating equipment will be worn out. Further, in the case of hard steel wire, mechanical properties (particularly strength) may deteriorate at temperatures exceeding 500°C. When the bath temperature is low, plating defects such as non-plating and foreign matter adhesion are more likely to occur, and in particular, when the Mg concentration is high, plating defects are more likely to occur. In this embodiment, by intentionally adding Cr to the plating bath, compared to the case where no Cr is added, the plating bath promotes the FeAl alloying reaction even at a low temperature of 500°C or less, and in particular, the thickness is A uniform Fe--Al based interfacial alloy layer can be produced.

The immersion time of the steel wire in the plating bath is 10 seconds or more and 100 seconds or less, preferably 10 seconds or more and 30 seconds or less. Particularly when plating hard steel wires, care must be taken as prolonged immersion deteriorates mechanical properties in the same way as high bath temperatures.

After taking it out of the plating bath, adjust the amount of plating by using an air knife, wiping with an aramid nonwoven fabric, etc., if necessary. Further, if necessary, cooling treatment is performed immediately after plating.

In the cooling treatment, after wiping, the plating layer may be left in the air to cool (natural cooling) until it solidifies, or may be air cooling. If rapid cooling such as water cooling or mist cooling is performed after wiping, MgZn ₂ becomes difficult to generate, which is not preferable. In terms of performance, corrosion resistance and fatigue resistance may be improved, but this does not significantly affect the present invention.
Note that the cooling rates for natural cooling, air cooling, and water cooling differ depending on the wire diameter, and are as follows.
<Natural cooling>
Wire diameter: 0.5 to 2.0 mm, 10°C/s or less Wire diameter: 2.0 to 10 mm, 5°C/s or less <Blow cooling>
Wire diameter: 20-40℃/s for 0.5-2.0mm
Wire diameter: 10-20℃/s for 2.0-10mm
<Water cooling>
Wire diameter: 300-500℃/s for 0.5-2.0mm
Wire diameter: 100-300℃/s for 2.0-10mm
As described above, the plated steel wire of this embodiment can be manufactured.

EXAMPLES Hereinafter, the effects of the present invention will be specifically explained with reference to Examples.
Contains C: 0.62%, Si: 0.18%, Mn: 0.55%, P: 0.006%, S: 0.008%, N 0.007%, Al 0.031%, and the remainder is A steel material consisting of Fe and impurities was hot rolled into a wire rod with a wire diameter of 5.5 mm, and after patenting treatment, this wire rod was cold drawn to produce a steel wire with a wire diameter of 2.0 mm. After degreasing and pickling, the steel wire was immersed in an aqueous flux solution at 60° C. for 20 seconds, dried, and then hot-dipped.
Note that the O content of the steel material was 0.0010 to 0.0100%.

The flux was a 60° C. aqueous solution containing 210 g/L of ZnCl ₂ , 25 g/L of NaCl, and 6 g/L of SnCl ₂ , and a commercially available surfactant for plating flux was added. No pH adjustment was performed, leaving the solution in a cloudy white state. During operation, the wire rod was immersed with sufficient stirring.

The plating bath contained Al: 0 to 15% by mass, Mg: 0 to 4.0% by mass, and Cr: 0 to 0.5%, with the balance being Zn and impurities. The bath temperature was 440 to 490°C, and the immersion time was in the range of 25 to 40 seconds. However, No. The plating immersion time in No. 7 was 110 seconds. The thickness of the plating layer is No. Except for Nos. 4, 13, 15, and 18, the target was 50 μm by gas wiping. In addition, natural cooling was performed until the plating layer solidified.

However, No. Nos. 2 and 3 were produced by a two-step plating method in which pure zinc plating was applied to the steel wire as a first-step plating, and then the steel wire was immersed in a plating bath having the above-mentioned component range as a second-step plating. Also, No. Samples Nos. 11 and 13 were water-cooled while the plating was in a molten state about 2 seconds after being removed from the plating bath.

In this way, as shown in Tables 1A and 1B, No. Plated steel wires Nos. 1 to 20 and 101 to 115 were manufactured.

In addition, the steel wire Nos. 3A and 3B shown in Table 3A and 3B were prepared in the same manner as above except that the chemical composition of the steel wire was changed to the steels A to b shown in Table 2. Plated steel wires 201-205, 301-315 and 401-415 were manufactured.
Note that in all steels, the O content was 0.0010 to 0.0100%.

To identify the average composition of the plating layer, an acid solution was obtained by peeling and dissolving the plating layer with a 5% by volume HCl solution containing an inhibitor that suppresses corrosion of the base iron (steel wire). Next, the chemical composition of the obtained acid solution was measured by ICP emission spectrometry.

The average composition of the Fe--Al interfacial alloy layer was determined using EDS spot analysis attached to the FE-SEM, as described above. However, although characteristic X-rays were confirmed, if it was less than 0.1 atomic %, it was written as "less than 0.1."
The measurement conditions for FE-SEM-EDS were: acceleration voltage of 15.0 KV, irradiation current of 7.5 nA, irradiation time of 60 s, measurement position at the center in the thickness direction, and the average composition was obtained by measuring 5 points.

As described above, the crystal structure of the alloy constituting the Fe--Al interface alloy layer was identified by electron beam diffraction using a transmission electron microscope. Specifically, a sample cut out by FIB processing to include an alloy layer was subjected to FE-TEM analysis, and three arbitrary locations in the alloy layer with different crystal grains were irradiated with an electron beam with a beam diameter of 5 nm. , the obtained electron diffraction images were identified.

The average thickness of the Fe-Al-based interfacial alloy layer and the Zn-Al-Mg alloy layer was measured using a field emission scanning electron microscope (FE-SEM). A backscattered electron image of the cross section was taken, and the average thickness was calculated using the method described above.
Furthermore, the chemical composition of the Zn--Al--Mg alloy layer was analyzed using the method described above.

Corrosion resistance was tested by using a plated steel wire cut to a length of 150 mm as a sample, masking the cut end with paint, and then conducting a salt spray test (JIS Z 2371:2015) for over 360 hours. The time from the start of the test until the appearance of red rust was measured. Then, evaluation was made according to the following evaluation criteria. A and B were passed.

A: Time until red rust appears is 360 hours or more.
B: Time until red rust occurs is 180 hours or more and less than 360 hours.
X: Time until red rust occurs is less than 180 hours.

The fatigue properties were evaluated using a Nakamura rotary fatigue tester. When the stress amplitude that did not break after ¹⁰⁷ rotations was taken as the fatigue limit, the amount of decrease in the fatigue limit of the plated steel wire with respect to the fatigue limit of the unplated steel wire was determined. Then, evaluation was made according to the following evaluation criteria. A and B were passed.

A: Fatigue limit reduction amount is less than 100 MPa.
B: Fatigue limit reduction amount is 100 to 200 MPa.
X: Fatigue limit reduction amount exceeds 200 MPa.

Regarding workability, a plated steel wire was wound six times around a steel wire with a diameter of 2 mm (self-diameter winding), and the presence or absence of cracks was determined by visually observing the surface. Then, evaluation was made according to the following evaluation criteria. A and B were passed.

A: There were no cracks or they were minute.
B: Crack length is 0.5 mm or more and less than 1.0 mm.
X: The crack length was 1.0 mm or more, the crack width was large, or the plating was partially peeled off.

As is clear from the results in Tables 1A to 3B, the plated steel wires (No. ~415), it was excellent in workability, fatigue properties, and corrosion resistance. Note that the Zn--Al--Mg alloy layers in these examples contained Al, Mg, Cr, the remainder Zn, and impurities. Further, the Zn--Al--Mg alloy layers of these examples contained Al primary crystals and a Zn phase.

No. In No. 1, in the average composition of the plating layer, the amount of Al, the amount of Mg, and the amount of Cr were out of the invention range, an Fe--Al interface alloy layer was not formed, and an FeZn alloy was present at the corresponding position. Further, no Zn--Al--Mg alloy layer was formed, and an almost pure Zn layer was formed. This resulted in a decrease in corrosion resistance.
No. In No. 2, in the average composition of the plating layer, the Mg amount and Cr amount were out of the invention range, and the average thickness of the Fe-Al based interfacial alloy layer was out of the invention range. This resulted in a decrease in corrosion resistance.
No. In No. 3, in terms of the average composition of the plating layer, the Cr content was outside the invention range, and the average thickness of the Fe--Al interfacial alloy layer was outside the invention range. This resulted in poor workability and fatigue properties.

No. In No. 4, the thickness of the Zn--Al--Mg alloy layer was out of the invention range because the amount of plating was increased. This resulted in poor workability and fatigue properties.
No. In No. 5, the Mg amount was outside the invention range in the average composition of the plating layer. This resulted in a decrease in corrosion resistance.

No. In No. 6, in terms of the average composition of the plating layer, the Cr content was out of the invention range, and the average thickness of the Fe--Al interfacial alloy layer was out of the invention range. This resulted in poor workability and fatigue properties.
No. In No. 7, the immersion time in the plating bath was as long as 110 seconds, so the average thickness of the Fe--Al interfacial alloy layer was outside the range of the invention. This resulted in poor workability and fatigue properties.

No. In No. 8, the Mg amount was outside the invention range in the average composition of the plating layer. This resulted in poor workability and fatigue properties.
No. In No. 9, the average composition of the plating layer had both Mg content and Cr content of 0%, which was outside the scope of the invention. This resulted in a decrease in corrosion resistance.
No. In No. 10, the average composition of the plating layer had a Cr content outside the invention range, resulting in poor plating.

No. In No. 11, in the average composition of the plating layer, the amount of Al was outside the invention range. This resulted in reduced workability. Furthermore, since the plating was water-cooled in a molten state about 2 seconds after being pulled out of the plating bath, _two MgZn phases were not generated.

No. In No. 12, in terms of the average composition of the plating layer, the amount of Al was outside the invention range, and the average thickness of the Fe-Al interfacial alloy layer was outside the invention range. This resulted in poor workability and fatigue properties.
No. In No. 13, the average thickness of the Zn--Al--Mg alloy layer was out of the invention range because the amount of plating deposited was reduced. This resulted in a decrease in corrosion resistance. Furthermore, since the plating was water-cooled in a molten state about 2 seconds after being pulled out of the plating bath, _two MgZn phases were not generated.

No. In No. 301, the Fe--Al interfacial alloy layer grew too much due to the small amount of C in the steel, and the average thickness of the Fe--Al interfacial alloy layer was out of the invention range. This resulted in poor workability and fatigue properties.
No. In No. 304 and No. 308, non-plating occurred because C and Si in the steel were out of the invention range, respectively. In addition, it became difficult to appropriately measure the composition of the plating layer.
No. In No. 305, the amount of Si in the steel was small and the Fe--Al interface alloy layer was thick. This resulted in poor workability and fatigue properties.

No. In No. 401, in the average composition of the plating layer, the amount of Al, the amount of Mg, and the amount of Cr were out of the invention range, an Fe--Al interfacial alloy layer was not formed, and an FeZn alloy was present at the corresponding position. Further, no Zn--Al--Mg alloy layer was formed, and an almost pure Zn layer was formed. This resulted in a decrease in corrosion resistance.

No. In No. 402, the Mg amount was outside the invention range in the average composition of the plating layer. This resulted in a decrease in corrosion resistance.

No. In No. 403, the Cr amount was outside the invention range in the average composition of the plating layer. Furthermore, the relatively high Mg content resulted in poor plating.
Further, in an example in which the average composition of the plating layer had a Cr content outside the inventive range and the thickness of the Fe--Al interfacial alloy layer was within the inventive range, the thickness of the plating layer was non-uniform.

Claims (11)

1. steel wire and
   a plating layer disposed on the surface of the steel wire,
   The plating layer includes an Fe-Al-based interfacial alloy layer disposed on the steel wire side, and a Zn-Al-Mg alloy layer disposed on the Fe-Al-based interfacial alloy layer,
   The chemical composition of the steel wire is in mass%,
   C: 0.030% or more and 1.20% or less,
   Si: 0.05% or more and 2.00% or less,
   Mn: 0.10% or more and 0.90% or less,
   P: 0.030% or less,
   S: 0.030% or less,
   Contains N: 0.010% or less,
   The remainder consists of Fe and impurities,
   The average composition of the plating layer is in mass%,
   Fe: 15.0% or less,
   Al: 3.0% or more and 15.0% or less,
   Mg: 0.3% or more and 3.5% or less,
   Contains Cr: 0.003% or more and 0.500% or less,
   The remainder: consists of Zn and impurities,
   The Fe--Al interface alloy layer contains one or more of Fe ₄ Al ₁₃ , Fe ₂ Al ₅ , Fe ₂ Al ₅ Zn _0.4 , and has an average thickness of 0.2 μm or more.5. 0 μm or less,
   The Zn-Al-Mg alloy layer contains Al, Mg, Cr, balance Zn and impurities, contains 0.1 to 40.0 area% MgZn _two phase in the structure, and has an average thickness of 10 μm or more and 150 μm. A plated steel wire characterized by:
2. The average composition of the plating layer is in mass%,
   Fe: 2.0% or less,
   Al: 3.0% or more and 8.0% or less,
   Mg: 0.3% or more and 3.5% or less,
   Cr: Contains 0.003% or more and 0.500% or less,
   The remainder: consists of Zn and impurities,
   The plated steel wire according to claim 1, wherein the average thickness of the Zn-Al-Mg alloy layer is 30 μm or more and 100 μm or less.
3. The plating layer further has an average composition of one or more of Ni, Ti, Zr, Sr, Sn, Ca, Co, Mn, B, REM, and Hf in a total of 0.0001 to 2. The plated steel wire according to claim 1, containing .0% by mass.
4. The plating layer further has an average composition of one or more of Ni, Ti, Zr, Sr, Sn, Ca, Co, Mn, B, REM, and Hf in a total of 0.0001 to 2. The plated steel wire according to claim 2, containing .0% by mass.
5. The chemical composition of the steel wire is C: 0.40% or more and 1.20% or less in mass %,
   Si: 0.30% or more and 2.00% or less,
   Mn: 0.10% or more and 0.90% or less,
   P: 0.030% or less,
   S: 0.030% or less,
   Contains N: 0.010% or less,
   The plated steel wire according to any one of claims 1 to 4, wherein the remainder consists of Fe and impurities.
6. The plated steel according to any one of claims 1 to 4, wherein the chemical composition of the steel wire further contains 0.10% or more and 0.50% or less of Cr in mass%. line.
7. The plated steel wire according to claim 5, wherein the chemical composition of the steel wire further contains 0.10% or more and 0.50% or less Cr in mass %.
8. The chemical composition of the steel wire further includes, in mass %,
   Ni: more than 0% and less than 1.00%,
   Cu: more than 0% and 0.50% or less,
   Mo: more than 0% and less than 0.50%,
   V: more than 0% and less than 0.50%,
   B: more than 0% and less than 0.0070%,
   Al: more than 0% and less than 0.100%,
   Ti: more than 0% and less than 0.10%,
   Nb: more than 0% and less than 0.10%,
   Zr: more than 0% and less than 0.10%,
   Ca: more than 0% and less than 0.005%,
   Mg: more than 0% and less than 0.005%,
   REM: more than 0% and less than 0.02%,
   Co: more than 0% and less than 0.5%,
   Sb: more than 0% and less than 0.05%,
   As: more than 0% and less than 0.05%,
   Sn: more than 0% and less than 0.05%,
   The plated steel wire according to any one of claims 1 to 4, characterized in that it contains one or more of O: more than 0% and 0.0100% or less.
9. The chemical composition of the steel wire further includes, in mass %,
   Ni: more than 0% and less than 1.00%,
   Cu: more than 0% and 0.50% or less,
   Mo: more than 0% and less than 0.50%,
   V: more than 0% and less than 0.50%,
   B: more than 0% and less than 0.0070%,
   Al: more than 0% and less than 0.100%,
   Ti: more than 0% and less than 0.10%,
   Nb: more than 0% and less than 0.10%,
   Zr: more than 0% and less than 0.10%,
   Ca: more than 0% and less than 0.005%,
   Mg: more than 0% and less than 0.005%,
   REM: more than 0% and less than 0.02%,
   Co: more than 0% and less than 0.5%,
   Sb: more than 0% and less than 0.05%,
   As: more than 0% and less than 0.05%,
   Sn: more than 0% and less than 0.05%,
   The plated steel wire according to claim 5, characterized in that it contains one or more of O: more than 0% and 0.0100% or less.
10. The chemical composition of the steel wire further includes, in mass %,
    Ni: more than 0% and less than 1.00%,
    Cu: more than 0% and 0.50% or less,
    Mo: more than 0% and less than 0.50%,
    V: more than 0% and less than 0.50%,
    B: more than 0% and less than 0.0070%,
    Al: more than 0% and less than 0.100%,
    Ti: more than 0% and less than 0.10%,
    Nb: more than 0% and less than 0.10%,
    Zr: more than 0% and less than 0.10%,
    Ca: more than 0% and less than 0.005%,
    Mg: more than 0% and less than 0.005%,
    REM: more than 0% and less than 0.02%,
    Co: more than 0% and less than 0.5%,
    Sb: more than 0% and less than 0.05%,
    As: more than 0% and less than 0.05%,
    Sn: more than 0% and less than 0.05%,
    The plated steel wire according to claim 6, characterized in that it contains one or more of O: more than 0% and 0.0100% or less.
11. The chemical composition of the steel wire further includes, in mass %,
    Ni: more than 0% and less than 1.00%,
    Cu: more than 0% and 0.50% or less,
    Mo: more than 0% and less than 0.50%,
    V: more than 0% and less than 0.50%,
    B: more than 0% and less than 0.0070%,
    Al: more than 0% and less than 0.100%,
    Ti: more than 0% and less than 0.10%,
    Nb: more than 0% and less than 0.10%,
    Zr: more than 0% and less than 0.10%,
    Ca: more than 0% and less than 0.005%,
    Mg: more than 0% and less than 0.005%,
    REM: more than 0% and less than 0.02%,
    Co: more than 0% and less than 0.5%,
    Sb: more than 0% and less than 0.05%,
    As: more than 0% and less than 0.05%,
    Sn: more than 0% and less than 0.05%,
    The plated steel wire according to claim 7, characterized in that it contains one or more of O: more than 0% and 0.0100% or less.

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