This application is a Divisional application of U.S. patent application Ser. No. 13/142,473, filed Jun. 28, 2011, which is the U.S. National Phase of PCT/JP2010/068363, filed Oct. 19, 2010. Priority is claimed thereto under 35 U.S.C. Â§120. This application also claims priority under 35 U.S.C. Â§119(a) to Japanese Patent Application No. 2010-020185, filed in Japan on Feb. 1, 2010.

TECHNICAL FIELD

The present invention relates to a wire rod, a steel wire, and a manufacturing method thereof, and, more specifically, to a rolled wire rod preferable for use as a steel cord which is used as a reinforcement material in radial tires of automobiles or belts and hoses for a variety of industrial uses, a sawing wire, a PC steel wire, a zinc plated steel strand, a wire rod for springs, a cable for suspension bridges, or the like, a manufacturing method thereof, and a steel wire produced from the rolled wire rod.

BACKGROUND ART

Generally, a steel wire which is used for a sawing wire or a steel cord which is used as a reinforcement material for radial tires of automobiles, a variety of belts and hoses, or the like, is manufactured by subjecting a wire rod with a diameter of 5-6 mm, which has been hot-rolled and subjected to controlled-cooling, to a primary wire drawing so as to have a diameter of 3-4 mm, and subjecting the wire rod to a patenting treatment and a secondary wire drawing so as to have a diameter of 1-2 mm, and then subjecting the wire rod to a final patenting treatment, brass plating, and a final wet wire drawing process so as to have a diameter of 0.15-0.40 mm.

A steel cord is manufactured by twisting together a plurality of the ultrafine steel wires which obtained in the above manner in a twisting process so as to produce a twisted steel wire.

In general, if a wire is broken when processing a wire rod into a steel wire or twisting a steel wire, productivity and yield rate are significantly degraded. Therefore, there is a strong demand for wire rods or steel wires belonging to the above technical fields to not be broken during the wire drawing process or the twisting process. Among wire drawing processes, in the case of the final wet wire drawing process, since the diameter of a steel wire to be treated is extremely small, the steel wire is highly likely to be broken. Furthermore, in recent years, there has been a trend towards reducing the weight of steel cords or the like for a variety of purposes. As a result, there is a demand for a high strength in the variety of products described above.

In addition, a steel wire used as a PC steel wire, a PC twisted wire, a rope, a PWS wire for bridges, or the like is generally formed into a strand shape by subjecting a wire rod with a diameter of 5-16 mm, which has been subjected to hot rolling and then controlled cooling, to a wire drawing process so as to have a diameter of 2-8 mm, subjecting the rod to molten zinc plating after the wire drawing or in the middle of the wire drawing, according to necessity, and then stranding the rods with or without twisting them together.

Generally, if a wire is broken when processing a wire rod into a steel wire or longitudinal cracks (delamination) occur when twisting the steel wire, productivity and yield rate are significantly degraded. Therefore, there is a strong demand for wire rods or steel wires belonging to the above technical fields to not break during a wire drawing process or a stranding process.

With regard to such products, there was a demand in the past to secure a strength of 1600 MPa or higher as well as to secure sufficient performance in terms of toughness and ductility evaluated by a twisting test or the like, but, in recent years, there has been a trend in which the weight of wires has been reduced for a variety of purposes.

As a result, there is a demand for high strength in a variety of the above products, but it has become impossible to obtain the desired high strength in carbon steel wire rods with a C content of less than 0.9 mass %. Therefore, there has been an increasing demand for steel wires with a C content of 0.9 mass % or higher. However, if the amount of C is increased, since wire drawing properties or torsional properties (delamination resistance) are degraded due to generation of pro-eutectoid cementite (hereinafter, sometimes referred to as â€˜pro-eutectoid Î¸â€™), wires break more often. As a result, wire rods not only including high amount of C for obtaining high strength but also having excellent wire drawing properties are strongly demanded.

With respect to such recent demands from industries, manufacturing technologies of high carbon wire rods with an amount of C exceeding 1% have been suggested.

For example, Patent Document 1 discloses â€œa wire rod for high strength and high toughness ultrafine steel wires, a high strength and high toughness ultrafine steel wire, a twisted product using the ultrafine steel wire, and a manufacturing method of the ultrafine steel wireâ€ made of a steel material having a specific chemical composition, in which the average area ratio containing pro-eutectoid cementite is defined. However, since the wire rod suggested in the publication includes one or both of Ni and Co, which are high-priced elements, as essential components, the manufacturing costs are increased.

Patent Document 2 suggests a technology in which 0.6% or more of Al is added so as to suppress generation of pro-eutectoid cementite in a high carbon steel with a content of C exceeding 1%. However, since Al is a strong deoxidizing element, and the amount of hard inclusions that act as a cause of wire breakage during wire drawing is increased, it is difficult to apply the technology to wire rods for steel wires with a small diameter, such as steel cords.

On the other hand, Patent Document 3 suggests a technology in which a high carbon wire rod is heated to an austenite temperature zone, cooled to a temperature range of 823-1023 K, subjected to a deforming process with a degree of 15-80% in the above temperature zone, and then isothermally transformed in a temperature zone of 823-923 K so as to suppress pro-eutectoid cementite. However, since a large facility investment is required to perform a predetermined process in such a temperature zone, there is concern of an increase in manufacturing costs.

RELATED ART DOCUMENTPatent Document

[Patent Document 1] Japanese Patent No. 2609387
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2003-193129
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. H8-283867

DISCLOSURE OF THE INVENTIONProblems to be Solved by the Invention

The present invention has been made in consideration of the above circumstances, and the object of the invention is to provide, with high productivity as well as favorable yield rate at a low price, high strength wire rods that are preferable for use as a steel cord, a sawing wire, or use as a PC steel wire, a zinc plated steel strand, a steel wire for springs, a cable for suspension bridges, or the like, and are excellent in terms of wire drawing properties.

Means for Solving the Problems

In order to solve the above problems, the invention adopts the following configurations and methods.

(1) The first aspect of the invention is a wire rod with a composition including: C: 0.95-1.30 mass %; Si: 0.1-1.5 mass %; Mn: 0.1-1.0 mass %; Al: 0-0.1 mass %; Ti: 0-0.1 mass %; P: 0-0.02 mass %; S: 0-0.02 mass %; N: 10-50 ppm; O: 10-40 ppm; Cr: 0-0.5 mass %; Ni: 0-0.5 mass %; Co: 0-0.5 mass %; V: 0-0.5 mass %; Cu: 0-0.5 mass %; Nb: 0-0.1 mass %; Mo: 0-0.2 mass %; W: 0-0.2 mass %; B: 0-30 ppm; REM: 0-50 ppm; Ca: 0-50 ppm; Mg: 0-50 ppm; Zr: 0-100 ppm; and the balance including Fe and inevitable impurities, wherein 97% or more of an area in a cross-section perpendicular to the longitudinal direction of the wire rod is occupied by a pearlite, and 0.5% or less of an area in a central area in the cross-section and 0.5% or less of an area in a first surface layer area in the cross-section are occupied by a pro-eutectoid cementite.

(2) In the wire rod described in the above (1), the cross-section of the wire rod may be occupied by the pearlite, the pro-eutectoid cementite, a bainite, a pseudo pearlite, a ferrite, a grain boundary ferrite, and a martensite.

(3) The second aspect of the invention is a manufacturing method of the wire rod described in the above (1) or (2). The manufacturing method includes a process in which a billet having the above composition is hot-rolled so as to obtain a rolled wire rod; a process in which the rolled wire rod is coiled; and a process in which a patenting treatment is performed by immersing the rolled wire rod of 900Â° C. or higher into a molten salt at a temperature of 500Â° C.-600Â° C.

(4) The third aspect of the invention is a manufacturing method of the wire rod described in the above (1) or (2). The manufacturing method includes a process in which a billet having the above composition is hot-rolled so as to obtain a rolled wire rod; a process in which the rolled wire rod is coiled; and a process in which cooling is started with respect to the rolled wire rod of 900Â° C. or higher, cooling is performed in a controlled manner to make the cooling rate Y while cooling from 900Â° C. to 650Â° C. satisfy

Yâ‰§exp((C %âˆ’0.66)/0.12)â€ƒâ€ƒ(Formula 1)

and a patenting treatment is performed by finishing pearlite transformation at a temperature of 650Â° C.-500Â° C.

(5) The fourth aspect of the invention is a manufacturing method of the wire rod described in the above (1) or (2). The manufacturing method includes a process in which a rolled wire rod with the above composition and a diameter of 3-16 mm is prepared; a process in which the rod is reheated to 950Â° C.-1050Â° C.; and a process in which cooling is started with respect to the rolled wire rod of 900Â° C. or higher, and a patenting treatment is performed in a lead bath or a fluidized bed at a temperature of 500Â° C.-600Â° C.

(6) The fifth aspect of the invention is a steel wire obtained by performing at least once wire drawing and a reheating patenting treatment on a wire rod having the above composition with 97% or more of the area in cross-section perpendicular to the longitudinal direction of the wire rod occupied by a pearlite, and 0.5% or less of the area in the central area in cross-section and 0.5% or less of the area of a first surface layer area in cross-section occupied by a pro-eutectoid cementite, in which the steel wire has a diameter of 0.1-0.4 mm and a tensile strength of 4200 MPa or higher, and 0.5% or less of the area in the second surface layer area of the cross-section perpendicular to the longitudinal direction of the steel wire is occupied by pro-eutectoid cementite.

(7) The sixth aspect of the invention is a steel wire obtained by drawing a wire rod having the above composition with 97% or more of the area in cross-section perpendicular to the longitudinal direction of the wire rod occupied by a pearlite, and 0.5% or less of the area in the central area in cross-section and 0.5% or less of the area of a first surface layer area in cross-section occupied by a pro-eutectoid cementite, in which the steel wire has a diameter of 0.8-8 mm and a tensile strength of 1800 MPa or higher, and 0.5% or less of the area in the third surface layer area of the cross-section perpendicular to the longitudinal direction of the steel wire is occupied by pro-eutectoid cementite.

(8) The steel wire described in the above (7) may be obtained in a manner in which (a) the wire rod is drawn and then subjected to bluing, heat stretching, molten zinc plating, or molten zinc alloy plating, (b) the wire rod is molten zinc-plated or molten zinc alloy-plated and then drawn, or (c) the wire rod is drawn and then subjected to molten zinc plating or molten zinc alloy plating and, furthermore, is drawn.

(9) The seventh aspect of the invention is the manufacturing method of a steel wire described in the above (6) including a process in which a billet with the above composition is hot-rolled so as to manufacture a rolled wire rod, the rolled wire rod is coiled, a patenting treatment is performed by immersing the rolled wire rod of 900Â° C. or higher in a molten salt at a temperature of 500Â° C.-600Â° C. so as to manufacture a wire rod with a diameter of 3-7 mm; a process in which the wire rod is drawn; a process in which a second patenting treatment is performed by starting cooling by introducing the drawn rolled wire rod of 900Â° C. or higher to a lead bath or a fluidized bed at a temperature of 500Â° C.-600Â° C., and a process in which cold wire drawing is performed on the wire rod which has been subjected to the second patenting treatment.

(10) The eighth aspect of the invention is the manufacturing method of a steel wire described in the above (6) including a process in which a billet with the above composition is hot-rolled so as to manufacture a rolled wire rod, the rolled wire rod is coiled, cooling is started with respect to the rolled wire rod of 900Â° C. or higher, quenching is performed in a controlled manner to make the cooling rate Y while cooling from 900Â° C. to 650Â° C. satisfy

Yâ‰§exp((C %âˆ’0.66)/0.12)â€ƒâ€ƒ(Formula 1)

and a patenting treatment is performed by finishing pearlite transformation at a temperature of 650Â° C.-500Â° C. so as to manufacture a wire rod with a diameter of 3-7 mm; a process in which the wire rod is drawn; a process in which a second patenting treatment is performed by starting cooling by introducing the drawn rolled wire rod of 900Â° C. or higher to a lead bath or a fluidized bed of 500Â° C.-600Â° C., and a process in which cold wire drawing is performed on the wire rod which has been subjected to the second patenting treatment.

(11) The ninth aspect of the invention is the manufacturing method of a steel wire described in the above (6) including a process in which a wire rod with the above composition and a diameter of 3-7 mm is reheated to a temperature of 950Â° C.-1050Â° C., cooling is started with respect to the reheated wire rod of 900Â° C. or higher, and a patenting treatment is performed in a lead bath or a fluidized bed at a temperature of 500Â° C.-600Â° C. so as to manufacture a wire rod with a diameter of 3-7 mm; a process in which the wire rod is drawn; a process in which a second patenting treatment is performed by starting cooling by introducing the drawn wire rod of 900Â° C. or higher to a lead bath or a fluidized bed at a temperature of 500Â° C.-600Â° C., and a process in which cold wire drawing is performed on the wire rod which has been subjected to the second patenting treatment.

(12) The tenth aspect of the invention is the manufacturing method of a steel wire described in the above (7) including a process in which a billet having the above composition is hot-rolled so as to manufacture a rolled wire rod, the rolled wire rod is coiled, and a patenting treatment is performed by immersing the rolled wire rod of 900Â° C. or higher into a molten salt at a temperature of 500Â° C.-600Â° C. so as to manufacture a wire rod with a diameter of 5-16 mm; and a process in which the wire rod is drawn.

(13) The tenth aspect of the invention is the manufacturing method of a steel wire described in the above (7) including a process in which a billet having the above composition is hot-rolled so as to manufacture a rolled wire rod, the rolled wire rod is coiled, cooling is started with respect to the rolled wire rod of 900Â° C. or higher, quenching is performed in a controlled manner to make the cooling rate Y while cooling from 900Â° C. to 650Â° C. satisfy

Yâ‰§exp((C %âˆ’0.66)/0.12)â€ƒâ€ƒ(Formula 1)

and a patenting treatment is performed by finishing pearlite transformation at a temperature of 650Â° C.-500Â° C. so as to manufacture a wire rod with a diameter of 5-16 mm; and a process in which the wire rod is drawn.

(14) The tenth aspect of the invention is the manufacturing method of a steel wire described in the above (7) including a process in which a rolled wire rod with the above composition and a diameter of 5-16 mm is prepared and reheated to a temperature of 950Â° C.-1050Â° C., cooling is started with respect to the rolled wire rod of 900Â° C. or higher, and a patenting treatment is performed in a lead bath or a fluidized bed at a temperature of 500Â° C.-600Â° C. so as to manufacture a wire rod with a diameter of 5-16 mm; and a process in which the wire rod is drawn.

Effects of the Invention

According to the invention, it is possible to provide, with high productivity as well as favorable yield rate at a low price, high strength wire rods that are preferable for use as a steel cord, a sawing wire, a PC steel wire, a zinc plated steel strand, a steel wire for springs, a cable for suspension bridges, or the like, and are excellent in terms of wire drawing properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of pro-eutectoid cementite generated in the surface layer area of a wire rod.

FIG. 2 shows the relationship between the temperatures where cooling of wire rods is started and the area ratios of pro-eutectoid Î¸ in the first surface layer areas of the wire rods.

FIG. 3 shows the relationship between the amounts of C in wire rods and the area ratios of pro-eutectoid Î¸ in the first surface layer areas of the wire rods.

FIG. 4 shows the relationship between the amounts of C in wire rods and the area ratios of pro-eutectoid Î¸ in the central areas of the wire rods.

FIG. 5 shows the influence of the cooling rates from 900Â° C. to 650Â° C. and the amounts of C on the amounts of pro-eutectoid Î¸ precipitated in the central areas of the wire rods.

FIG. 6 shows the relationship between the temperatures where cooling of wire rods is started and the area ratios of pro-eutectoid Î¸ in the first surface layer areas of the wire rods.

FIG. 7 shows the relationship between the amounts of C in wire rods and the area ratios of pro-eutectoid Î¸ in the first surface layer areas of the wire rods.

FIG. 8 shows the relationship between the amounts of C in wire rods and the area ratios of pro-eutectoid Î¸ in the central areas of the wire rods.

FIG. 9 shows the influence of the cooling rates from 900Â° C. to 650Â° C. and the amounts of C on the amounts of pro-eutectoid Î¸ precipitated in the central areas of the wire rods.

EMBODIMENTS OF THE INVENTION

The inventors of the present invention carried out repeated investigations and studies on the influence of the chemical compositions and mechanical properties of wire rods on the wire drawing properties and consequently obtained the following findings.

(a) It is preferable to increase the content of alloy elements, such as C, Si, Mn, Cr, or the like, to increase tensile strength. Particularly, it is possible to increase strength while maintaining high ductility of a steel wire by increasing the amount of C to 1 mass % or higher and relatively decreasing work strain for obtaining target strength.

(b) If the amount of C is increased, pro-eutectoid cementite as shown by the arrow in FIG. 1 is liable to precipitate in overcooled austenite during the period from the start of cooling to the start of pearlite transformation in a cooling process from an austenite zone in a patenting treatment. This tendency becomes remarkable in the central area of a wire rod in which the cooling rate is decreased.

(c) It is possible to express, with a function of the C amount, the critical cooling rate at which the generation of pro-eutectoid cementite in the central area of a wire rod can be suppressed. It is possible to suppress generation of pro-eutectoid cementite in the central area of a wire rod at which the cooling rate is decreased, by cooling parent-phase austenite at a higher rate and subsequently performing an isothermal treatment.

(d) It is possible to obtain a cooling rate higher than the above critical cooling rate by immersing a wire rod with a content of C of 1.3 mass % or less and a diameter of 3-16 mm in molten salt after heating.

(e) In a general wire rod rolling line, a wire rod is coiled at a constant temperature after final rolling and then transported by a conveyor to a patenting treatment zone, such as a Stelmor or the like. In a reheating patenting line, there is no wire rod coiling process, but a certain amount of time is required to transport the wire rod from the exit side of a heating band to a cooling band for patenting. In a high C material with an amount of C exceeding 1 mass %, since the cementite precipitation temperature (a temperature where austenite becomes austenite+cementite) is high, in the conventional heating and transportation conditions, there are concern that the temperature in an area several tens of Î¼m deep in the outermost surface layer of a wire rod which comes into contact with the atmosphere during transportation may be lowered, and pro-eutectoid cementite may be generated in the outermost surface layer of the wire rod before cooling for a patenting treatment is started.

(f) FIG. 1 shows an example of pro-eutectoid cementite generated in the surface layer area of a wire rod. Since such cementite in the surface layer has a brittle structure, this acts as a cause of surface layer cracks during wire drawing and a cause of the occurrence of delamination in a steel wire obtained by wire drawing, or the like, the ductility of a steel wire is remarkably degraded.

(g) In order to suppress such pro-eutectoid cementite in the outermost surface layer of a wire rod, it is necessary to set the cooling starting temperature of a wire rod for patenting to 900Â° C. or higher. For this, it is necessary to perform final rolling at 980Â° C. or higher, to set the temperature for coiling or reheating to 925Â° C. or higher, which is higher than that in the related art, and preferably to higher than 950Â° C., and to shorten the transportation time as possible or suppress the lowering of temperature during transportation.

(h) If the final rolling temperature and the coiling temperature are too high, since the grain diameter of austenite in a wire rod becomes coarsened and ductility is degraded, there is an upper limit temperature at which ductility can be secured.

Hereinafter, embodiments of the invention, which is derived from the above findings will be described in detail.

First EmbodimentConfiguration of Wire Rods

The first embodiment of the invention is a wire rod in which 0.5% or less of the area in the central area in cross-section perpendicular to the longitudinal direction of the wire rod and 0.5% or less of the area of the surface layer area (the first surface layer area) in cross-section are occupied by a pro-eutectoid cementite.

According to studies by the inventors of the invention, there is a relationship between the ratio of pro-eutectoid cementite in the surface layer area of a wire rod and in the central area of the wire rod before wire drawing and the ductility of the steel wire obtained by drawing a wire rod, and, if it is possible to suppress the area ratio of cementite in the surface layer area of the wire rod, the ductility of the steel wire which can be obtained by drawing a wire rod is improved, and wire breakage during wire drawing can be suppressed by decreasing the area ratio of cementite in the central area of the wire rod to 0.5% or lower.

Here, the surface layer area (the first surface layer area) in the wire rod refers to an area corresponding to a depth of 50 Î¼m from the surface of the wire rod (the circumferential portion in cross-section) in cross-section perpendicular to the longitudinal direction of the wire rod.

The central area in the wire rod refers to an area with a radius of 100 Î¼m from the central point in cross-section perpendicular to the longitudinal direction of the wire rod.

The pro-eutectoid cementite refers to cementite with a small deformability, which is generated at the prior austenite grain boundary and has a thickness of 100 nm or larger.

In addition, the wire rod according to the present embodiment has 97% or more of the area in cross-section perpendicular to the longitudinal direction of the wire rod occupied by a pearlite. The remainder may be pro-eutectoid cementite, a bainite, a pseudo pearlite, a ferrite, a grain boundary ferrite, a martensite, or the like.

(Manufacturing Conditions of the Wire Rods)

In order to suppress pro-eutectoid cementite in the surface layer area of a rolled wire rod made of a material with a high C content of 0.95-1.3 mass % to the above area ratio, it is necessary to set the temperature of the wire rod to 900Â° C. or higher, and more preferably to 920Â° C. or higher, at the moment of starting cooling for patenting with a salt bath or a Stelmor when hot-rolling steel pieces (billets) to have a diameter of 3-16 mm. For that, it is desirable to perform final rolling at 980Â° C. or higher and to perform coiling at a temperature range higher than 925Â° C., and preferably higher than 950Â° C. If the temperature of final rolling and the temperature of coiling are too high, an austenite grain diameter in the wire rod becomes coarsened, and ductility (maximum drawable rate) is degraded. Therefore, it is desirable to set both the temperature of final rolling and the temperature of coiling to 1050Â° C. or lower.

The amount of pro-eutectoid cementitie generated in the central area of a wire rod is dependent on the cooling rate Y while cooling from 900Â° C. to 650Â° C. The inventors of the invention found that it is effective to quench a wire rod in a method in which the cooling rate Y [Â° C./s] and the amount of carbon in the wire rod C % [mass %] satisfy

Yâ‰§exp((C %âˆ’0.66)/0.12)â€ƒâ€ƒ(Formula 1)

and then to finish pearlite transformation at a temperature of 500Â° C.-650Â° C.

It is desirable to perform the same measure even in the process of reheating patenting, which is performed on a steel wire before wire drawing or during wire drawing. The reheating patenting refers to a patenting treatment performed after putting a subject into a state of 200Â° C. or lower once and reheating it. In order to suppress pro-eutectoid cementite in the surface layer area or the central area of a reheating patenting steel wire made of a material with a high C content of 0.95-1.3 mass % to the above area ratio, it is effective to set the reheating temperature to 950Â° C.-1050Â° C., and desirably to from the higher temperature of 975Â° C. or higher and C %Ã—450+450 (Â° C.) to 1050Â° C., to sufficiently form a solid solution of C and other alloy elements, to set the temperature of the steel wire when starting cooling for patenting to 900Â° C. or higher, and desirably to 920Â° C. or higher, and then to perform a patenting treatment in a lead bath or a fluidized bed at 500Â° C.-600Â° C.

(Basic Elements)

The wire rod according to the embodiment includes C, Si, Mn, Al, Ti, N, and O. Hereinafter, the amount of each component will be described.

C: 0.95-1.35 mass %

C is an effective element for increasing the strength of a wire rod, and, if the content is less than 0.95%, it is difficult to stabilize and supply high strength to a final product. On the other hand, if the content of C is too high, net-shaped pro-eutectoid cementite is generated in austenite grain boundaries so that the wire is liable to be broken during a wire drawing process and also the toughness and ductility of the ultrafine wire rod after final wire drawing is remarkably degraded. As a result, the amount of C is defined as 0.95-1.30 mass %. In order to obtain a high-strength steel wire, the amount is set preferably to 1.0 mass % or more, and more preferably to 1.1 mass % or more.

Si: 0.1-1.5 mass %

Si is an effective element for increasing the strength. In addition, Si is a useful element as a deoxidizing element and a necessary element when treating a steel wire rod including no Al. If the amount of Si is less than 0.1 mass %, a deoxidizing action is too low. On the other hand, if the amount of Si is too high, precipitation of pro-eutectoid ferrite is accelerated even in hypereutectoid steel, and the limit processibility in a wire drawing process is degraded. Furthermore, it becomes difficult to perform a wire drawing process by mechanical descaling. Accordingly, the amount of Si is defined as 0.1-1.5 mass %. More preferably, the amount of Si is defined as 1.0 mass % or less, and more preferably as 0.35 mass % or less.

Mn: 0.1-1.0 mass %

Similarly to Si, Mn is also a useful element as a deoxidizing agent. In addition, Mn is effective to improve hardenability and thus increase the strength of a wire rod. Furthermore, Mn is combined with S to form MnS, thereby preventing hot rolling brittleness. If the amount of Mn content is less than 0.1 mass %, it is difficult to obtain the above effects. On the other hand, Mn is an element liable to be segregated so that, if the Mn content exceeds 1.0 mass %, Mn is segregated particularly in the central area of a wire rod, and martensite or bainite is generated in the segregated portions, which leads to degradation of wire drawing processiblity. Accordingly, the amount of Mn is defined as 0.1-1.0 mass %.

Al: 0-0.1 mass %

The amount of Al is defined as a range of 0.1 mass % or less including 0 mass % (or exceeding 0 mass %) in order to prevent generation of hard unmodified alumina-based non-metallic inclusions, which causes degradation in the ductility and wire drawing properties of a steel wire. The amount of Al is preferably 0.05 mass % or less, and more preferably 0.01 mass % or less.

Ti: 0-0.1 mass %

The amount of Ti is defined as a range of 0.1 mass % or less including 0 mass % (or exceeding 0 mass) in order to prevent generation of hard unmodified oxides, which causes degradation in the ductility and wire drawing properties of a steel wire. The amount of Ti is preferably 0.05 mass % or less, and more preferably 0.01 mass % or less.

N: from 10 ppm to 50 ppm

N generates nitrides with Al, Ti, and B in a steel and has an action of preventing coarsening of the austenite grain size during heating, and the effect is effectively exhibited by including 10 ppm or more of N. However, if the N content is too high, the amount of nitrides increases excessively, and therefore the amount of solid-solute B in austenite is decreased. Furthermore, since there is concern that solid-solute N may accelerate aging during wire drawing, the upper limit is set to 50 ppm. More preferably, the amount of N is 30 ppm or less.

O: 10-40 ppm

O can form composite inclusions with Si and the like so as to form soft inclusions having no adverse effect on wire drawing properties. It is possible to finely disperse such soft inclusions after rolling, and thus there are effects of refining Î³ grain size by a pinning effect and of improving ductility of a patenting wire rod. Accordingly, the lower limit is defined as 10 ppm. However, if the O content is too high, since hard inclusions are formed, and wire drawing properties are degraded, the upper limit is defined as 40 ppm.

(Inevitable Impurities)

Further, although the contents of P and S which are included in the wire rod according to the embodiment as impurities are not particularly defined, from the viewpoint of securing ductility similar to that of an ultrafine steel wire in the related art, it is desirable to limit each to 0.02 mass % or less. Here, even when less than 0.0005 mass % of each of P and S are included, the effects are limited.

(Optional Elements)

In addition to the above elements, the wire rod according to the embodiment may further optionally include one kind or more of elements from Cr, Ni, Co, V, Cu, Nb, Mo, W, B, REM, Ca, Mg, and Zr for the purpose of improving mechanical properties, such as strength, toughness, ductility, or the like. Hereinafter, the amount of each component will be described.

Cr: 0-0.5 mass %

Cr is an element that refines the lamella interval in pearlite and is effective to improve the strength, wire drawing processibility or the like of a wire rod. In order to effectively exhibit such actions, it is preferable to add 0.1 mass % or more of Cr. On the other hand, if the amount of Cr is too high, since transformation completion time becomes long, there is concern that supercooled structures, such as martensite, bainite, or the like, may be generated in a hot-rolled wire rod, and mechanical descaling properties may deteriorate, thus, the upper limit is defined as 0.5 mass %.

Ni: 0-0.5 mass %

Ni is an element that contributes little to an increase in the strength of a wire rod, but increases the toughness of a drawn wire rod. In order to effectively exhibit such an action, it is preferable to add 0.1 mass % or more of Ni. On the other hand, if Ni is excessively added, transformation completion time becomes long, thus, the upper limit is defined as 0.5 mass %.

Co: 0-0.5 mass %

Co is an effective element that suppresses segregation of pro-eutectoid cementite in a rolled material. In order to effectively exhibit such an action, it is preferable to add 0.1 mass % or more of Co. On the other hand, even when Co is excessively added, the effect is saturated and thus no economic benefit is produced. Accordingly, the upper limit is defined as 0.5 mass %.

V: 0-0.5 mass %

V forms fine carbonitrides in ferrite so as to prevent coarsening of autenite grains during heating and contributes to an increase in strength after rolling. In order to effectively exhibit such an action, it is preferable to add 0.05 mass % or more of V. However, if V is excessively added, the amount of carbonitrides becomes too large, and the grain diameter of carbonitrides becomes large, thus, the upper limit is defined as 0.5 mass %.

Cu: 0-0.5 mass %

Cu has an effect of increasing the corrosion resistance of an ultrafine steel wire. In order to effectively exhibit such an action, it is preferable to add 0.1 mass % or more of Cu. However, if Cu is excessively added, Cu reacts with S so as to precipitate CuS, which causes defects in a steel ingot or a wire rod in the manufacturing process of a wire rod. In order to prevent such adverse effects, the upper limit is defined as 0.5 mass %.

Nb: 0-0.1 mass %

Nb has an effect of increasing the corrosion resistance of ultrafine steel wires. In order to effectively exhibit such an action, it is preferable to add 0.05 mass % or more of Nb. On the other hand, if Nb is excessivley added, the transformation completion time becomes long. Thus, the upper limit of Nb is defined as 0.1 mass %.

Mo: 0-0.2 mass %

Mo is concentrated in pearlite growth interfaces and has an effect of suppressing the growth of pearlite by a so-called solute drag effect. By adding an appropriate amount, it is possible to suppress the growth of pearlite only in a high temperature area of 600Â° C. or higher, and to suppress the generation of pearlite having coarse lamella spacing. In addition, Mo also has an effect of improving hardenability, with which the generation of ferrite is suppressed, and is also effective to reduce non-pearlite structures. If the amount of Mo is excessive, pearlite growth is suppressed across the entire temperature range so that a long time is required for patenting, which results in a decrease in productivity, and coarse Mo₂C carbides are precipitated, and thus wire drawing properties are degraded. Accordingly, the amount of Mo is defined as 0.2 mass % or less. The preferable amount of Mo is 0.005-0.06 mass %.

W: 0-0.2 mass %

Similarly to Mo, W is concentrated in pearlite growth interfaces and has an effect of suppressing the growth of pearlite by a so-called solute drag effect. By adding an appropriate amount, it is possible to suppress the growth of pearlite only in a high temperature area of 600Â° C. or higher, and to suppress the generation of pearlite in a coarse lamella spacing. In addition, W also has an effect of improving hardenability, with which the generation of ferrite is suppressed, and is also effective to reduce non-ferrite structures. If the amount of W is excessive, pearlite growth is suppressed across the entire temperature range so that a long time is required for patenting, which results in a decrease in productivity, and coarse W₂C carbides are precipitated, and thus wire drawing properties are degraded. Accordingly, the amount of W is defined as 0.2 mass % or lower. The preferable amount of W is 0.005-0.06 mass %.

B: 0-30 ppm

When present in a solid solution state in austenite, B is concentrated in grain boundaries so as to suppress the generation of non-pearlite structure, such as ferrite, pseudo pearlite, bainite, or the like. If the amount of B is 4 ppm or higher, it is possible to obtain this effect. On the other hand, if B is excessively added, precipitation of coarse Fe₂₃(CB)₆carbides in austenite is accelerated, and wire drawing properties are adversely affected. In order to satisfy the above, the upper limit of the amount of B is defined as 30 ppm. The amount of B is preferably 4-15 ppm, and more preferably 8-12 ppm.

REM: 0-50 ppm

REM (Rare Earth Metal) is effective for detoxifying of S, but an excessive addition generates oxides which becomes a cause of wire breakage, and therefore the upper limit of the REM content is defined as 50 ppm.

Ca: 0-50 ppm

Ca is effective to reduce hard alumina-based inclusions, but an excessive addition generates oxides which becomes a cause of wire breakage, and therefore the upper limit of the Ca content is defined as 50 ppm.

Mg: 0-50 ppm

Mg forms fine oxides so as to refine the structure of a steel and improve the ductility. If the content of Mg exceeds 50 ppm, breakage of the wire becomes apt to occur due to oxides, and therefore the upper limit of the Mg content is defined as 50 ppm.

Zr: 0-100 ppm

Since Zr forms the crystallization nuclei of austenite as ZrO, Zr increases the equiaxial crystal ratio of austenite and thus has an effect of reducing central segregation, but if the Zr content exceeds 100 ppm, breakage of the wire becomes apt to occur due to oxides, and therefore the upper limit of the Zr content is defined as 100 ppm.

Second EmbodimentConfiguration of Steel Wires

The second embodiment of the invention is a steel wire which is obtained by drawing the wire rod described in the first embodiment and has a diameter of from 0.1-0.4 mm and a tensile strength of 4200 MPa or higher. The steel wire has 0.5% or less of the area in the surface layer area (the second surface layer area) in cross-section perpendicular to the longitudinal direction of the steel wire occupied by pro-eutectoid cementite.

Here, the second surface layer area refers to an area to a depth of 10 Î¼m from the surface layer of the steel wire.

(Manufacturing Conditions of the Steel Wires)

The above steel wires can be obtained by drawing the wire rods described in the first embodiment, heating the rods to 900Â° C. or higher, performing patenting at least once, which starts cooling by introducing the heated wire rods to a lead bath or a fluidized bed at a temperature of 500Â° C.-600Â° C., and performing cold drawing.

Third EmbodimentConfiguration of Steel Wires

The third embodiment of the invention is a steel wire which is obtained by drawing the wire rod described in the first embodiment with a diameter of from 5-16 mm and has a diameter of from 0.8-8 mm and a tensile strength of 1800 MPa or higher. The steel wire has 0.5% or less of the area in the surface layer area (the third surface layer area) in cross-section perpendicular to the longitudinal direction of the steel wire occupied by pro-eutectoid cementite.

Here, the third surface layer area refers to an area to a depth of 20 Î¼m from the surface layer of the steel wire.

(Manufacturing Conditions of the Steel Wires)

The above steel wires can be obtained by performing cold drawing on the wire rods described in the first embodiment.

The steel wires obtained in the above manner may be used as they are after wire drawing, but treatments, such as (1) performing bluing, heat stretching, molten zinc plating, or molten zinc alloy plating after the wire drawing, (2) performing wire drawing after molten zinc plating or molten zinc alloy plating, or (3) performing another wire drawing after wire drawing and molten zinc plating or molten zinc alloy plating, or the like.

A wire rod, a steel wire, or a manufacturing method thereof having characteristics described in the above embodiments can be also expressed as follows:

That is, one aspect of the invention is a wire rod for high strength steel wire, including, by mass %, C: 0.95-1.30%; Si: 0.1-1.5%; Mn: 0.1-1.0%; Al: 0.1% or less; Ti: 0.1% or less; N: 10-50 ppm; and O: 10-40 ppm with the balance including Fe and inevitable impurities, the steel wire being composed of 97% or more of a pearlite by the area ratio with the remainder of bainite, pseudo pearlite, ferrite, grain boudary ferrite, and pro-eutectoid cementite, wherein the area ratio of pro-eutectoid cementite in an area with a radius of 100 Î¼m from the central portion of the wire rod is 0.5% or less, the area ratio of pro-eutectoid cementite in an area to 50 Î¼m depth of the wire rod from the surface layer is 0.5% or less.

In addition, the wire rod may further include, by % by mass, at least one kind or more selected from the group consisting of Cr: 0.5% or less (not including 0%), Ni: 0.5% or less (not including 0%), Co: 0.5% or less (not including 0%), V: 0.5% or less (not including 0%), Cu: 0.5% or less (not including 0%), Nb: 0.1% or less (not including 0%), Mo: 0.2% or less (not including 0%), W: 0.2% or less (not including 0%), B: 30 ppm or less (not including 0%).

In addition, another aspect of the invention is a high strength steel wire excellent in terms of ducility, obtained by drawing the above mentioned wire rod with a diameter of 3-7 mm, performing a patenting treatment, and again drawing the rod, in which the tensile strength is 4200 MPa or higher, and the area ratio of pro-eutectoid cementite in an area to 10 Î¼m depth from the surface layer is 0.5% or less.

In addition, another aspect of the invention is a high strength steel wire excellent in terms of ducility obtained by drawing the above-mentioned wire rod with a diameter of 5.0-16 mm and then performing bluing, heat stretching, molten zinc plating, or molten zinc alloy plating; a steel wire obtained by performing molten zinc plating or molten zinc alloy plating on the above mentioned wire rod with a diameter of 5.0-16 mm as above, and then performing wire drawing; or a steel wire obtained by drawing the above mentioned wire rod with a diameter of 5.0-16 mm, performing molten zinc plating or molten zinc alloy plating, and then again performing wire drawing, in which the tensile strength is 1800 MPa or higher, and the area ratio of pro-eutectoid cementite in an area to 20 Î¼m depth from the surface layer is 0.5% or less.

In addition, another aspect of the invention is a manufacturing method of a wire rod for high strength steel wires excellent in terms of ducility, in which when a billet with the above composition is hot-rolled so as to have a wire diameter of 3-16 mm, final rolling and coiling are performed, and then, when immersing into a molten salt, the temperature of the wire rod is set to 900Â° C. or higher, and, subsequently, a patenting treatment is performed by directly immersing into molten salt at a temperature of 500Â° C.-600Â° C.

In addition, another aspect of the invention is a manufacturing method of a wire rod for high strength steel wires excellent in terms of ductility, in which, when a billet with the above composition is hot-rolled so as to have a wire diameter of 3-16 mm, final rolling and coiling is performed, and then, when starting cooling of a Stelmor or the like for patenting, the temperature of the wire rod is set to 900Â° C. or higher, and, in the subsequent patenting treatment, quenching is performed in a manner in which the cooling rate Y while cooling from 900Â° C. to 650Â° C. satisfies Formula 1

Yâ‰§exp((C %âˆ’0.66)/0.12)â€ƒâ€ƒ(Formula 1)

and then pearlite transformation is finished at a temperature of from 500Â° C.-650Â° C.

In addition, another aspect of the invention is a manufacturing method of a high strength steel wire excellent in terms of ductility, in which, when performing reheating patenting on a wire rod having the above-described composition and a wire diameter of 3-16 mm, the heating temperature of the wire rod is set to 950Â° C.-1050Â° C., the temperature of the wire rod when starting cooling for the patenting is set to 900Â° C. or higher, and a patenting treatment is immediately performed in lead or a fluidizied bed of 500Â° C.-600Â° C.

In addition, another aspect of the invention is a manufacturing method of a high strength steel wire excellent in terms of ductility, in which a wire rod with a diameter of 3-7 mm manufactured by the above manufacturing method is drawn, cold wire drawing is furthermore performed after patenting, the heating temperature of the steel wire during the patenting is set to 950Â° C.-1050Â° C., the temperature of the steel wire when starting cooling for patenting is set to 900Â° C. or higher, that is a steel wire, on which a patenting treatment has been performed in a lead bath or a fluidized bed at a temperature of 500Â° C.-600Â° C., is drawn.

Example

Next, the invention will be described in more detail with examples, but the invention is not limited only to the following examples and can be appropriately modified and carried out within a scope not departing from the gist of the invention, and all of such modifications are included in the technical scope of the invention.

First Example

Tables 1 to 4 show the chemical components of A-1 steel, B-1 steel, C-1 steel, D-1 steel, E steel, F steel, G-1 steel, H steel, I steel, J steel, K steel, L-1 steel, M steel, N steel, 0 steel, P steel, Q-1 steel, Q-2 steel, and Q-3 steel, all of which are used in Examples Î±1 to Î±19 of the invention, and the chemical components of A-2 steel, A-3 steel, B-2 steel, B-3 steel, B-4 steel, C-2 steel, D-2 steel, G-2 steel, G-3 steel, G-4 steel, L-2 steel, R steel, S steel, T steel, U steel, V steel, W steel, and X steel, all of which are used in Comparative Examples Î±1 to Î±18. Further, in Tables 1 to 8, numeric values, disadvantageous results, and the like, not included in an appropriate scope are underlined.

Billets of steels containing the chemical components shown in Tables 1 to 4 were heated and then hot-rolled so as to become wire rods with a diameter of 3-7 mm, and then were subjected to final rolling at a predetermined temperature, coiling, and a patenting treatment.

After being coiled into a ring shape, the rolled wires were subjected to a patenting treatment by a Stelmor or a molten salt immersion patenting (DLP). Here, DLP refers to a direct in-line patenting facility with which rolled wire rods were directly immersed in molten salt so as to be patenting-treated. In the case of the Stelmor, the cooling rate Y from 900Â° C. to 650Â° C. was obtained from (900-650)/t[Â° C./s] by measuring the temperatures of overlapped ring portions on the Stelmor conveyor every 0.5 m with a non-contact type thermometer and measuring a necessary time t [s] for cooling from 900Â° C. to 650Â° C.

In order to measure the area ratios of pearlite and the area ratios of pro-eutectoid cementite in the rolled wire rods, one ring-shaped wire rod ring with a diameter of 1.0 m to 1.5 m was equally divided into 8 pieces, and two portions with the highest and lowest TSs were identified. 10 mm-long samples were taken out from the portions with the highest and lowest TSs in the continuous ring and implanted in a resin to make it possible to observe the cross-sections (C cross-section) perpendicular to the longitudinal direction. Then, the samples were alumina-polished and corroded with saturated picral, and then were subjected to SEM observation.

The area ratio of the pearlite was obtained from the average value of area ratios measured at four places in a 200 Î¼mÃ—200 Î¼m square area, which is in Â¼ depth from the surface at the above two portions (the portions with the highest and lowest TSs), every 90 degrees in the circumferential direction at a magnification of 3000 times by image analysis with an assumption that an area ratio excluding pseudo-pearlite portions in which cementite was granularly dispersed, bainite portions in which plate-shaped cementite was dispersed at a lamella spacing three or more times coarser than the surroundings, intergranular ferrite portions precipitated along austenite, and pro-eutectoid cementite portions was considered as the area ratio of pearlite.

Places where the SEM photos were taken for measurement of the area ratio of pro-eutectoid cementite will be described.

As the central area of a wire rod, an area with a radius of 100 Î¼M from the central point in cross-section of the portion with the lowest TS was selected.

As the surface layer area of a wire rod, 4 places in a 50 Î¼mÃ—50 Î¼m area in the vicinity of the circumferential portion in cross-section of the portion with the highest TS were selected every 90 degrees in the circumferential direction.

The selected areas were measured at a magnification of 5000 times, and the area ratio of pro-eutectoid cementite with a thickness of 100 nm or larger was measured by image analysis.

Further, with regard to the surface layer area, the maximum value of the measurement results of the four places was used.

For the wire drawing properties of a wire rod, a high strength wire rod was obtained in a manner in which, after scales were removed by pickling from a rolled wire rod, a 10 m-long wire rod provided with a zinc phosphate layer by a bonding treatment was prepared, and then subjected to single head-type wire drawing with an area reduction ratio per pass of 16% to 20% with intermediate lead patenting or fluidized bed patenting performed and then subjected to wet continuous wire drawing so as to have a diameter of 0.18 mm to 0.22 mm.

In order to measure the area ratio of pro-eutectoid cementite in the drawn steel wire, a 10 mm-long sample was taken out from the steel wire with a diameter of 0.18 m to 0.22 m and then implanted in a resin to make it possible to observe the cross-section (C cross-section) thereof perpendicular to the longitudinal direction. Then, the sample was alumina-polished and corroded with saturated picral, and then subjected to SEM observation.

As a place selected for the SEM observation, a 10 Î¼mÃ—50 Î¼m rectangular area in the vicinity of the circumferential portion in cross-section of the steel wire was selected.

The selected place was measured at a magnification of 10000 times, and the area ratio of pro-eutectoid cementite with a thickness of 100 nm or larger was measured by image analysis.

Tables 5 to 8 show the manufacturing conditions and the measurement results of the wire rods and the steel wires in Examples Î±1 to Î±19 and Comparative Examples Î±1 to Î±18. In the tables, the FBP refers to a patenting treatment by a fluidized bed.

As is clear from Examples Î±1 to Î±19 shown in Tables 1 to 8, when the amounts of elements included in the wire rods were appropriately controlled so that the fractions of pro-eutectoid cementite in the surface layers and central portions of the rolled wire rods were suppressed, it was possible to suppress the occurrence of delamination and wire breakage during the wire drawing in the steel wires after the wire drawing.

In Comparative Examples Î±1, Î±5, Î±6, Î±7, Î±17, and Î±18, it was not possible to suppress the generation of surface layer pro-eutectoid cementite in the rolled wire rods due to the low temperature of the wire rods when starting the cooling, which is designed for the patenting. As a result, the area ratios of the pro-eutectoid cementite at the surface layer of the rolled wire rods exceeded 0.5%, and therefore delamination occurred in the steel wires after the final wire drawing.

Here, as data reflecting the results of Examples Î±1 to Î±19 and the results of Comparative Examples Î±1, Î±5, Î±6, Î±7, Î±17, and Î±18, for which the temperatures of the wire rods when starting the cooling were set to less than 900Â° C., FIG. 2 shows the relationship between the temperatures of the rolled wire rods when starting the cooling and the area ratios of surface layer cementite. From the drawing, it can be confirmed that, when the temperatures of the wire rods when starting the cooling were set to 900Â° C. or higher, it was possible to suppress pro-eutectoid cementite at the surface layer of the wire rods to 0.5% or lower.

In Comparative Example Î±2, since the coiling temperature was high, the ductility of the rolled wire rod was low, and thus the rolled wire rod broke in the primary wire drawing.

In Comparative Example Î±3, since the heating temperature was low during the final patenting, it was not possible to suppress cementite at the surface layer and central area of the steel wire after the final wire drawing, and thus delamination occurred.

In Comparative Examples Î±4, Î±11, and Î±15, since the patenting treatments of the rolled wire rods were performed in a Stelmor, and the cooling rate Y from 900Â° C. to 650Â° C. did not satisfy Formula 1, a large amount of pro-eutectoid cementite was generated in the central areas of the wire rods, and the wire rods broke in the primary wire drawing.

Yâ‰§exp((C %âˆ’0.66)/0.12)â€ƒâ€ƒ(Formula 1)

FIG. 3 shows the relationship between the amounts of C in the wire rods and the area ratios of pre-eutectoid cementite in the surface layer area of the wire rods in Examples Î±1 to Î±19 and Comparative Examples Î±1, Î±5, Î±6, Î±7, Î±9, Î±17, and Î±18, for which the component ranges were appropriate, but the final temperature or the temperature when starting the cooling for the patenting, which is an important index that suppresses pro-eutectoid cementite in the surface layers, was low.

FIG. 4 shows the relationship between the amounts of C in the wire rods and the area ratios of pre-eutectoid cementite in the central area of the wire rods in Examples Î±1 to Î±19 and Comparative Examples Î±4 and Î±11, for which the component ranges were appropriate, but the cooling rate Y from 900Â° C. to 650Â° C. did not satisfy (Formula 1).

FIG. 5 shows the influence of the cooling rate Y from 900Â° C. to 650Â° C. and the amounts of C on the amounts of pro-eutectoid cementite precipitated in the central areas of the wire rods in Examples Î±4, Î±8, Î±12, Î±17, Î±18, and Î±19 and Comparative Examples Î±4, Î±11, and Î±15, in which the wire rods were cooled in a Stelmor during the rolling of wire rods. From FIG. 5, it can be confirmed that, when the cooling rate Y satisfied (Formula 1), it was possible to suppress pro-eutectoid cementite in the central area of the wire rods to 0.5% or lower.

In Comparative Example Î±8, since the temperature of the molten salt was low, the ductility was lowered due to generation of upper bainite, and thus the wire rod broke in the primary wire drawing.

In Comparative Example Î±9, since the temperature of the final rolling was too low, pro-eutectoid cementite was generated in the surface layer of the wire rod during the final rolling. As a result, the area ratio of pro-eutetoid Î¸ in the surface layer of the rolled wire rods exceeded 0.5%, and thus delamination occurred in the steel wire after the final wire drawing.

In Comparative Example Î±10, since the temperature of the final rolling was too high, the ductility of the wire rod was lowered, and thus the wire rod broke in the primary wire drawing.

In Comparative Example Î±12, since the amount of C was large, the strength of the wire rod was high, and the ductility was too low so that the wire rod broke in the primary wire drawing.

In Comparative Example Î±13, since the amount of C was low, it was not possible to obtain a steel wire with a predetermined TS.

In Comparative Example Î±14, since the amount of Mn was large, bainite or micro martensite was generated so that it was not possible to satisfy a predetermined pearlite fraction. As a result, the wire rod broke in the primary wire drawing.

In Comparative Example Î±16, since the amount of Si was large, bainite or micro martensite was generated so that it was not possible to satisfy a predetermined pearlite fraction. As a result, the wire rod broke in the primary wire drawing.

In Comparative Example Î±17, since the coiling temperature was a general condition, a large amount of surface layer pro-eutectoid Î¸ was present, and thus delamination occurred in the steel wire after the final wire drawing.

In Comparative Example Î±18, since the coiling temperature was low, a large amount of surface layer pro-eutectoid Î¸ was present, and thus delamination occurred in the steel wire after the final wire drawing.

TABLE 1ElementsSteelCSiMnPSAlTiNOTypemass %mass %mass %mass %mass %mass %mass %ppmppmExample Î±1A-11.070.180.30.0160.0250.0000.0002021Example Î±2B-11.170.200.320.0080.0070.0030.0002623Example Î±3C-11.120.200.480.0150.0200.0010.0002523Example Î±4D-11.060.340.30.0080.0080.0000.0002626Example Î±5E1.150.200.30.0100.0080.0040.0002538Example Î±6F1.210.200.50.0080.0080.0000.0012521Example Î±7G-11.220.200.50.0080.0080.0000.0012624Example Î±8H1.050.200.30.0150.0130.0000.0002231Example Î±9I1.100.200.30.0080.0080.0010.0002521Example Î±10J1.280.220.490.0100.0090.0000.0002424Example Î±11K1.120.200.340.0090.0100.0000.0032123Example Î±12L-11.080.200.40.0100.0070.0000.0002028Example Î±13M1.120.200.30.0190.0150.0000.0002725Example Î±14N1.170.300.30.0080.0080.0000.0002721Example Î±15O1.160.580.30.0080.0100.0000.0002722Example Î±16P1.120.700.510.0080.0080.0010.0042735Example Î±17Q-11.020.200.30.0080.0080.0010.0022725Example Î±18Q-21.020.200.30.0080.0080.0010.0022725Example Î±19Q-31.020.200.30.0080.0080.0010.0022725

TABLE 2ElementsSteelCrNiCuVCoNbMoWBREMCaMgZrTypemass %mass %mass %mass %mass %mass %mass %mass %ppmppmppmppmppmExample Î±1A-10.200.000.000.000.000.000.0000.00000000Example Î±2B-10.220.000.000.000.000.000.0000.00000000Example Î±3C-10.200.000.000.040.000.000.0000.00090000Example Î±4D-10.180.000.000.000.000.000.0300.00080000Example Î±5E0.050.000.000.000.100.000.0000.00000000Example Î±6F0.000.000.000.060.000.000.0000.00000000Example Î±7G-10.200.000.200.000.000.020.0000.00000000Example Î±8H0.200.000.000.000.000.000.0000.00080000Example Î±9I0.210.000.000.000.000.000.0600.000100000Example Î±10J0.000.000.100.000.000.000.0000.00000000Example Î±11K0.190.000.000.000.000.000.0000.00000000Example Î±12L-10.000.100.000.000.000.000.0000.00000000Example Î±13M0.180.000.000.000.000.000.0000.00080000Example Î±14N0.230.000.000.000.000.000.0000.00090000Example Î±15O0.200.000.000.000.000.000.0000.05000000Example Î±16P0.000.000.000.000.000.000.0000.00000000Example Î±17Q-10.200.000.000.000.000.000.0000.00000000Example Î±18Q-20.200.000.000.000.000.000.0000.00000000Example Î±19Q-30.200.000.000.000.000.000.0000.00000000

TABLE 3ElementsSteelCSiMnPSAlTiNOTypemass %mass %mass %mass %mass %mass %mass %ppmppmComparative Example Î±1A-21.070.180.30.0160.0150.0000.0002021Comparative Example Î±2A-31.070.180.30.0160.0150.0000.0002021Comparative Example Î±3B-21.170.20â€‚0.320.0080.0070.0030.0002623Comparative Example Î±4B-31.170.20â€‚0.320.0080.0070.0030.0002623Comparative Example Î±5B-41.170.20â€‚0.320.0080.0070.0030.0002623Comparative Example Î±6C-21.120.20â€‚0.480.0150.0200.0010.0002523Comparative Example Î±7D-21.060.340.30.0080.0080.0000.0002626Comparative Example Î±8G-21.220.200.50.0080.0080.0000.0012624Comparative Example Î±9G-31.220.200.50.0080.0080.0000.0012624Comparative Example Î±10G-41.220.200.50.0080.0080.0000.0012624Comparative Example Î±11L-21.080.200.40.0100.0070.0000.0002028Comparative Example Î±12R1.350.200.30.0150.0130.0000.0002231Comparative Example Î±13S0.920.200.50.0100.0090.0000.0102523Comparative Example Î±14T1.120.201.20.0090.0100.0000.0032123Comparative Example Î±15U0.980.200.50.0090.0100.0000.0032123Comparative Example Î±16V1.121.600.20.0090.0100.0000.0032123Comparative Example Î±17W1.040.210.40.0080.0050.0010.0013511Comparative Example Î±18X1.050.18â€‚0.490.0060.0050.0010.0002510

TABLE 4ElementsSteelCrNiCuVCoNbMoWBREMCaMgZrTypemass %mass %mass %mass %mass %mass %mass %mass %ppmppmppmppmppmComparative Example Î±1A-20.200.000.000.000.000.000.0000.00000000Comparative Example Î±2A-30.200.000.000.000.000.000.0000.00000000Comparative Example Î±3B-20.220.000.000.000.000.000.0000.00000000Comparative Example Î±4B-30.220.000.000.000.000.000.0000.00000000Comparative Example Î±5B-40.220.000.000.000.000.000.0000.00000000Comparative Example Î±6C-20.200.000.000.040.000.000.0000.00090000Comparative Example Î±7D-20.180.000.000.000.000.000.0300.00080000Comparative Example Î±8G-20.200.000.200.000.000.020.0000.00000000Comparative Example Î±9G-30.200.000.200.000.000.020.0000.00000000Comparative Example Î±10G-40.200.000.200.000.000.020.0000.00000000Comparative Example Î±11L-20.000.100.000.000.000.000.0000.00000000Comparative Example Î±12R0.200.000.000.000.000.000.0000.00080000Comparative Example Î±13S0.210.000.000.100.000.000.0000.00000000Comparative Example Î±14T0.190.000.000.000.000.000.0000.00000000Comparative Example Î±15U0.190.000.000.000.000.000.0000.00000000Comparative Example Î±16V0.190.000.000.000.000.000.0000.00000000Comparative Example Î±17W0.490.000.000.000.000.000.0000.00000000Comparative Example Î±18X0.220.010.110.000.000.000.0000.000100000

TABLE 5Temp. of wireWireFinalCoilingrod whenSaltSteeldiametertemperaturetemperaturestarting coolingCoolingtemperature(Formula 1)TypemmÂ° C.Â° C.Â° C.methodÂ° C.Right sideExample Î±1A-15.51010970930DLP550â€”Example Î±2B-15.51020985940DLP545â€”Example Î±3C-15.51025960920DLP555â€”Example Î±4D-13.81005960925Stelmorâ€”28.0â€‚Example Î±5E5.51000975930DLP570â€”Example Î±6F5.51020970925DLP580â€”Example Î±7G-15.510301010970DLP600â€”Example Î±8H5.01010955920Stelmorâ€”25.8â€‚Example Î±9I5.51015955925DLP540â€”Example Î±10J5.51020990960DLP600â€”Example Î±11K5.51005960930DLP550â€”Example Î±12L-15.51050965935Stelmorâ€”33.1â€‚Example Î±13M5.01010960925DLP575â€”Example Î±14N5.51030950925DLP575â€”Example Î±15O6.81020980945DLP540â€”Example Î±16P5.51035975935DLP530â€”Example Î±17Q-15.51010950920Stelmorâ€”20.09Example Î±18Q-25.51020960930Stelmorâ€”20.09Example Î±19Q-35.51005955920Stelmorâ€”20.09Area ratio of pro-Area ratio of pro-Strength ofeutectoid Î¸ in theeutectoid Î¸ in theCooling rate YrolledArea ratio ofsurface layer area ofcentral area of wire900â†’650Â°materialpearlitewire rodrodÂ° C./sMPa%%%Example Î±1â€”150098.50.050.00Example Î±2â€”160099.00.220.40Example Î±3â€”157097.20.280.22Example Î±429.0141098.60.250.15Example Î±5â€”156099.20.220.28Example Î±6â€”163099.10.460.40Example Î±7â€”161097.50.370.42Example Î±827.0140098.20.150.19Example Î±9â€”154098.40.450.17Example Î±10â€”169097.90.480.49Example Î±11â€”156099.10.250.10Example Î±1234.0155099.50.120.10Example Î±13â€”153097.10.260.22Example Î±14â€”158098.20.470.39Example Î±15â€”162098.30.250.30Example Î±16â€”166099.00.180.15Example Î±1723.0134097.50.050.08Example Î±1830.0135598.50.000.00Example Î±1925.0135598.50.010.01

TABLE 6Temp. ofDiameterHeatingsteel wireStrength ofof finalDiameter of finaltemp. of finalwhen startingPatentingpatenteddrawnSteelpatented wirepatentingcoolingPatentingtemperaturematerialwireTypemmÂ° C.Â° C.methodÂ° C.MPammExample Î±1A-11.46950930LP57515600.20Example Î±2B-11.27980960LP57516700.20Example Î±3C-11.27960940LP58016400.20Example Î±4D-11.46950925FBP57515300.20Example Î±5E1.27970950LP55016400.20Example Î±6F1.09995970LP59016900.20Example Î±7G-11.181000980FBP57517200.20Example Î±8H1.46950935LP55015600.20Example Î±9I1.27955930LP57516000.18Example Î±10J1.2710301000LP60017200.20Example Î±11K1.27960930FBP57516300.20Example Î±12L-11.46950935LP57515900.22Example Î±13M1.27960940LP60016300.20Example Î±14N1.27980945LP57516900.20Example Î±15O1.27975955LP57517100.20Example Î±16P1.27975955LP57517200.22Example Î±17Q-11.53960930FBP55014700.18Example Î±18Q-21.53960930FBP55014750.18Example Î±19Q-31.53960930FBP55014650.18Area ratio of pro-Area ratio of pro-TS ofeutectoid Î¸ in theeutectoid Î¸ in theWireFinal drawnsurface layer area ofcentral area of steelbreakagewiresteel wirewireduring wireMPa%%drawingDelaminationExample Î±143310.000.00Not occurNot occurExample Î±243500.140.21Not occurNot occurExample Î±342530.090.08Not occurNot occurExample Î±442440.080.00Not occurNot occurExample Î±542650.120.15Not occurNot occurExample Î±640520.120.21Not occurNot occurExample Î±743200.150.18Not occurNot occurExample Î±843230.020.04Not occurNot occurExample Î±943780.080.00Not occurNot occurExample Î±1045210.250.24Not occurNot occurExample Î±1142270.090.05Not occurNot occurExample Î±1242070.050.03Not occurNot occurExample Î±1342270.070.06Not occurNot occurExample Î±1444020.130.14Not occurNot occurExample Î±1544500.150.13Not occurNot occurExample Î±1642310.100.06Not occurNot occurExample Î±1743730.040.06Not occurNot occurExample Î±1844050.000.00Not occurNot occurExample Î±1943600.000.01Not occurNot occur

TABLE 7ArearatioAreaof pro-ratioTemp.eutectoidof pro-ofÎ¸ in theeutectoidwiresurfaceÎ¸ in theFinalCoilingrodlayercentralWiretem-tem-whenCoolingStrengthAreaareaareadiam-pera-pera-startingSalt(Formularate Yof rolledratio ofof wireof wireSteeletertureturecoolingCoolingtemperature1)900â†’650Â°materialpearliterodrodTypemmÂ° C.Â° C.Â° C.methodÂ° C.Right sideÂ° C./sMPa%%%ComparativeA-25.51030910880DLP550â€”â€”149098.20.700.00Example Î±1ComparativeA-35.510801060â€‚1030â€‚DLP550â€”â€”151097.30.030.00Example Î±2ComparativeB-25.51030985945DLP540â€”â€”161099.30.220.42Example Î±3ComparativeB-35.51035985940Stelmorâ€”70.125.0151099.10.211.60Example Î±4ComparativeB-45.51035900860DLP550â€”â€”161097.51.320.41Example Î±5ComparativeC-25.51025880845DLP550â€”â€”156097.60.950.15Example Î±6ComparativeD-23.81050880840Stelmorâ€”28.030.0140098.21.100.25Example Î±7ComparativeG-25.51020980945DLP480â€”â€”162085.90.350.45Example Î±8ComparativeG-35.5â€‚960940930DLP560â€”â€”167097.81.200.46Example Î±9ComparativeG-45.51090990950DLP540â€”â€”165098.60.420.42Example Î±10ComparativeL-25.51050965935Stelmorâ€”33.125.0144099.10.120.90Example Î±11ComparativeR5.51020980940DLP560â€”â€”173099.20.660.71Example Î±12ComparativeS5.51030950925DLP550â€”â€”141097.30.000.00Example Î±13ComparativeT5.51030960930DLP550â€”â€”164095.20.300.28Example Î±14ComparativeU5.51030960920Stelmorâ€”14.413.0125097.30.000.60Example Î±15ComparativeV5.51030960930DLP540â€”â€”165091.60.000.36Example Î±16ComparativeW5.5â€‚980880850Stelmorâ€”23.725.0130098.00.550.15Example Î±17ComparativeX5.51037915880Stelmorâ€”25.845.0132097.50.670.01Example Î±18

TABLE 8Arearatio ofAreaTemp.pro-ratio ofofeutectoidpro-Diam-HeatingsteelPat-Diam-Î¸ in theeutectoidetertemp. ofwireentingStrengtheterTS ofsurfaceÎ¸ in theWireof finalfinalwhentem-ofof finalFinallayercentralbreakageDe-patentedpat-startingPat-pera-patenteddrawndrawnarea ofarea ofduringlam-Steelwireentingcoolingentingturematerialwirewiresteel wiresteel wirewireina-TypemmÂ° C.Â° C.methodÂ° C.MPammMPa%%drawingtionComparativeA-21.27955920LP57515650.2040400.000.00Not occurOccurExample Î±1ComparativeA-3Wireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Example Î±2break-ageduringprimarywiredrawingComparativeB-21.27920880LP60016500.2042980.850.18Not occurOccurExample Î±3ComparativeB-3Wireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Example Î±4break-ageduringprimarywiredrawingComparativeB-41.27960940LP57516600.2043240.210.31Not occurOccurExample Î±5ComparativeC-21.27960945LP57016500.2042790.090.08Not occurOccurExample Î±6ComparativeD-21.46950930FBP57515350.2042580.030.00Not occurOccurExample Î±7ComparativeG-2Wireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Example Î±8break-ageduringprimarywiredrawingComparativeG-31.27980960LP57517200.2044990.480.46Not occurOccurExample Î±9ComparativeG-4Wireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Examplebreak-Î±10ageduringprimarywiredrawingComparativeL-2Wireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Examplebreak-Î±11ageduringprimarywiredrawingComparativeRWireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Examplebreak-Î±12ageduringprimarywiredrawingComparativeS1.46950930LP57514300.2039110.000.00Not occurNot occurExampleÎ±13ComparativeTWireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Examplebreak-Î±14ageduringprimarywiredrawingComparativeUWireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Examplebreak-Î±15ageduringprimarywiredrawingComparativeVWireâ€”â€”â€”â€”â€”â€”â€”â€”â€”â€”â€”Examplebreak-Î±16ageduringprimarywiredrawingComparativeW1.50960945LP57514100.2039570.020.00Not occurOccurExampleÎ±17ComparativeX1.46970955LP57514200.2039350.000.00Not occurOccurExampleÎ±18

Second Example

Tables 9 to 12 show the chemical components of a-1 steel, b-1 steel, c steel, d steel, e steel, f-2 steel, g-1 steel, h steel, i steel, j-1 steel, k steel, l steel, m steel, n steel, o steel, and p steel, all of which are used in Examples Î²1 to Î²16 of the invention, and the chemical components of j-2 steel, b-2 steel, f-2 steel, a-2 steel, g-2 steel, q steel, and r steel, all of which are used in Comparative Examples Î²1 to Î²7. Further, in Tables 9 to 16, numeric values, disadvantageous results, and the like, not included in an appropriate scope, are underlined.

Billets of steels containing the chemical components shown in Tables 9 to 12 were heated and then hot-rolled so as to become wire rods with a diameter of 5.0 mm to 16 mm, and then subjected to final rolling at a predetermined temperature, coiling, and a patenting treatment or reheating patenting.

After being coiled into a ring shape, the rolled wire rods were subjected to a patenting treatment by a Stelmor or a direct in-line patenting (DLP). In the case of the Stelmor, the cooling rate Y from 900Â° C. to 650Â° C. was obtained from (900-650)/t[Â° C./s] by measuring the temperatures of overlapped ring portions on the Stelmor conveyor every 0.5 m with a non-contact type thermometer and measuring a necessary time t [t] for cooling from 900Â° C. to 650Â° C.

In order to measure the area ratios of pearlite and the area ratios of pro-eutectoid cementite in the rolled wire rods, one ring-shaped wire rod ring with a diameter of 1.0 m to 1.5 m was equally divided into 8 pieces, and the portions with the highest and lowest TSs were identified. 10 mm-long samples were taken out from two portions with the highest and lowest TSs in the continuous ring and implanted in a resin to make it possible to observe the cross-sections (C cross-sections) perpendicular to the longitudinal direction. Then, the samples were alumina-polished and corroded with saturated picral, and then were subjected to SEM observation.

The area ratio of the pearlite was obtained from the average value of area ratios measured at four places in a 200 Î¼mÃ—200 Î¼m square area, which is in Â¼ depth portion (D=diameter) from the surface layer at the above two portions (the portions with the highest and lowest TSs), every 90 degrees in a circumferential direction at a magnification of 3000 times by image analysis with an assumption that an area ratio excluding pseudo-pearlite portions in which cementite was granularly dispersed, bainite portions in which plate-shaped cementite was dispersed at a lamella spacing three or more times coarser than the surroundings, intergranular ferrite portions precipitated alongside, and pro-eutectoid cementite portions was considered as the area ratio of pearlite.

Places where the SEM photos were taken for measurement of the area ratio of pro-eutectoid cementite will be described.

As the central area of a wire rod, an area with a radius of 100 Î¼m from the central point in cross-section of the portion with the lowest TS was selected.

As the surface layer area of a wire rod, 4 places in a 50 Î¼mÃ—50 Î¼m square area in the vicinity of the circumferential portion in cross-section of the portion with the highest TS were selected every 90 degrees in the circumferential direction.

The selected areas were measured at a magnification of 5000 times, and the area ratio of pro-eutectoid cementite with a thickness of 100 nm or larger was measured by image analysis.

Further, with regard to the surface layer area, the maximum value of the measurement results of the four places was used.

For the wire drawing properties of a wire rod, a target high strength steel wire was obtained in any of the following methods and then evaluated by performing a tensile strength test and a twist test.

(1) After scales were removed by pickling from a rolled wire rod, a 20 m-long wire rod provided with a zinc phosphate layer by a bonding treatment was prepared, and then subjected to single head-type wire drawing with an area reduction ratio per pass of 16% to 20% so as to obtain a high strength steel wire with a diameter of 0.8 mm to 7 mm. The steel wire was subjected to any of molten zinc plating, molten zinc alloy plating, bluing, and heat stretching.

(2) After scales were removed by pickling from a rolled wire rod, a 20 m-long wire rod on which molten zinc plating or molten zinc alloy plating had been performed was prepared, and then subjected to single head-type wire drawing with an area reduction ratio per pass of 16% to 20% so as to obtain a high strength steel wire with a diameter of 0.8 mm to 7 mm.

(3) After scales were removed by pickling from a rolled wire rod, a 20 m-long wire rod provided with a zinc phosphate layer by a bonding treatment was prepared, then subjected to single head-type wire drawing with an area reduction ratio per pass of 16% to 20%, and then subjected to molten zinc plating or molten zinc alloy plating, and, furthermore, wire drawing so as to obtain a high strength steel wire with a diameter of 0.8 mm to 7 mm.

In order to measure the area ratio of pro-eutectoid cementite in the drawn wire rod, a 10 mm-long sample was taken out from the steel wire and then implanted in a resin to make it possible to observe the cross-section (C cross-section) perpendicular to the longitudinal direction. Then, the sample was alumina-polished and corroded with saturated picral, and then was subjected to SEM observation.

As a place selected for the SEM phototaking, a 20 Î¼mÃ—50 Î¼m rectangular area in the vicinity of the circumferential portion in cross-section of the steel wire was selected.

The selected place was measured at a magnification of 10000 times, and the area ratio of pro-eutectoid cementite with a thickness of 100 nm or larger was measured by image analysis.

Tables 13 to 16 show the manufacturing conditions and the measurement results of the wire rods and the steel wires in Examples Î²1 to Î²16 and Comparative Examples Î²1 to Î²7.

As is clear from Examples Î²1 to Î²16 shown in Tables 9 to 16, when the amounts of elements included in the wire rods were appropriately controlled so that the fractions of pro-eutectoid cementite in the surface layers and central portions of the rolled wire rods were suppressed, it was possible to suppress the occurrence of delamination and wire breakage in the steel wires after the wire drawing.

In Comparative Examples Î²1 and Î²5, it was not possible to suppress the generation of surface layer pro-eutectoid cementite in the rolled wire rods due to the low temperature of the wire rods when starting the cooling, which is designed for the patenting.

Here, as data reflecting the results of Examples Î²1 to Î²16 and the results of Comparative Examples Î²1, Î²5, and Î²7, for which the temperatures of the wire rods when starting the cooling were set to less than 900Â° C., FIG. 6 shows the relationship between the temperatures of the rolled wire rods when starting the cooling and the area ratios of surface layer cementite. From the drawing, it can be confirmed that, when the temperatures of the wire rods when starting the cooling were set to 900Â° C. or higher, it was possible to suppress pro-eutectoid cementite at the surface layer of the wire rods to 0.5% or lower.

In Comparative Example Î²2 and Î²7, since the final rolling temperature was too low, pro-eutectoid cementite was generated in the surface layer of the wire rod during the final rolling.

In Comparative Examples Î²3 and Î²4, since the patenting treatments of the rolled wire rods were performed in a Stelmor, and the cooling rate Y from 900Â° C. to 650Â° C. did not satisfy Formula 1, a predetermined cooling rate in accordance with the amount of C could not be obtained, and a large amount of pro-eutectoid cementite was generated in the central areas of the wire rods so that the wire rods were broken during the wire drawing.

Yâ‰§exp((C %âˆ’0.66)/0.12)â€ƒâ€ƒ(Formula 1)

In Comparative Example Î²6, since the q steel containing more than the regulated amount of B was used, a large amount of cementite was generated in the surface layer.

FIG. 7 shows the relationship between the amounts of C in the wire rods and the area ratios of pre-eutectoid cementite in the surface layer area of the wire rods in Examples Î²1 to Î²16 and Comparative Examples Î²1, Î²2, and Î²5, for which the component ranges were appropriate, but the final temperature or the temperature when starting the cooling for the patenting, which is *an important index that suppresses pro-eutectoid cementite in the surface layers, was low.

FIG. 8 shows the relationship between the amounts of C in the wire rods and the area ratios of pre-eutectoid cementite in the central area of the wire rods in Examples Î²1 to Î²16 and Comparative Examples Î²3 and Î²4, for which the component ranges were appropriate, but the cooling rate Y from 900Â° C. to 650Â° C. did not satisfy (Formula 1).

FIG. 9 shows the influence of the cooling rate Y from 900Â° C. to 650Â° C. and the amounts of C on the amounts of pro-eutectoid cementite precipitated in the central areas of the wire rods in Examples Î²6 and Î²9 and Comparative Examples Î²3 and Î²4. From the drawing, it can be confirmed that, when the cooling rate Y satisfied (Formula 1), it was possible to suppress pro-eutectoid cementite in the central area of the wire rods to 0.5% or lower.

TABLE 9ElementsSteelCSiMnPSAlTiNOTypemass %mass %mass %mass %mass %mass %mass %ppmppmExample Î²1a-10.970.200.750.0080.0090.0300.0003521Example Î²2b-11.120.200.730.0100.0080.0320.0003423Example Î²3c0.981.200.330.0100.0080.0290.0002538Example Î²4d0.981.000.350.0150.0080.0300.0003638Example Î²5e0.970.900.740.0110.0120.0310.0113524Example Î²6f-21.020.910.740.0090.0100.0310.0093524Example Î²7g-11.020.200.30.0080.0080.0010.0002521Example Î²8h1.120.220.730.0100.0090.0300.0002424Example Î²9i1.120.220.510.0100.0090.0010.0002424Example Î²10j-11.080.200.750.0100.0070.0300.0003128Example Î²11k1.120.200.30.0190.0250.0000.0002725Example Î²12l0.981.000.350.0150.0080.0300.0003638Example Î²13m1.020.910.740.0090.0100.0310.0093524Example Î²14n0.970.900.70.0120.0090.0800.0003626Example Î²15o0.970.950.30.0010.0010.0310.0123626Example Î²16p0.970.920.750.0090.0100.0300.0123626

TABLE 10ElementsSteelCrNiCuVCoNbMoWBTypemass %mass %mass %mass %mass %mass %mass %mass %ppmREMCaMgZrExample Î²1a-10.000.000.000.000.000.000.0000.00000000Example Î²2b-10.000.000.000.000.000.000.0000.00000000Example Î²3c0.190.000.000.000.000.000.0000.00000000Example Î²4d0.200.000.000.070.000.000.0000.00000000Example Î²5e0.000.000.000.000.000.000.0000.000100000Example Î²6f-20.000.000.000.000.000.000.0000.00080000Example Î²7g-10.210.000.000.000.000.000.0000.00000000Example Î²8h0.000.000.100.000.000.000.0000.00000000Example Î²9i0.000.100.000.000.000.050.0000.00000000Example Î²10j-10.000.000.000.000.000.000.0000.00000000Example Î²11k0.000.000.000.000.100.000.0080.00000000Example Î²12l0.200.000.000.070.000.000.0000.00080000Example Î²13m0.000.000.000.000.000.000.0000.05090000Example Î²14n0.000.000.000.000.000.000.0000.000050000Example Î²15o0.210.000.000.000.000.000.0000.000003000Example Î²16p0.210.000.000.000.000.000.0000.0009002050

TABLE 11ElementsSteelCSiMnPSAlTiNOTypemass %mass %mass %mass %mass %mass %mass %ppmppmComparative Example Î²1j-21.120.220.510.0100.0090.0010.0002424Comparative Example Î²2b-21.120.200.730.0100.0080.0320.0003423Comparative Example Î²3f-21.020.910.740.0090.0100.0310.0093524Comparative Example Î²4a-20.970.200.750.0080.0090.0300.0003521Comparative Example Î²5g-21.020.200.30.0080.0080.0010.0002521Comparative Example Î²6o1.000.900.60.0700.0700.0430.0103522Comparative Example Î²7r0.950.910.490.0060.0030.0320.0004020

TABLE 12ElementsSteelCrNiCuVCoNbMoWBREMCaMgZrTypemass %mass %mass %mass %mass %mass %mass %mass %ppmppmppmppmppmComparativej-20.000.100.000.000.000.050.0000.00000000Example Î²1Comparativeb-20.000.000.000.000.000.000.0000.00000000Example Î²2Comparativef-20.000.000.000.000.000.000.0000.00080000Example Î²3Comparativea-20.000.000.000.000.000.000.0000.00000000Example Î²4Comparativeg-20.210.000.000.000.000.000.0000.00000000Example Î²5Comparativeo0.000.200.000.000.000.100.0000.00070â€‚0000Example Î²6Comparativer0.000.000.000.000.000.000.0000.00000000Example Î²7

TABLE 13Final temperature(heating temperatureTemp. of wire rodWirein the case ofCoilingwhen startingTemperatureSteeldiameterreheating patenting)temperaturecoolingof salt or leadTypemmÂ° C.Â° C.Â° C.Cooling methodÂ° C.Example Î²1a-113.01010970930DLP510Example Î²2b-110.01020960940DLP540Example Î²3c16.01000950905DLP500Example Î²4d12.51020970925DLP545Example Î²5e10.01030985970DLP560Example Î²6f-28.01010â€”920Reheating LP600Example Î²7g-18.01015955925DLP540Example Î²8h10.01020950920DLP530Example Î²9i12.01020â€”920Reheating LP550Example Î²10j-17.01050965935DLP550Example Î²11k5.51010960925DLP575Example Î²12l12.51020925905DLP550Example Î²13m5.51030950925DLP550Example Î²14n12.01010955925DLP560Example Î²15o12.01015960930DLP550Example Î²16p12.01010955930DLP570Area ratio of pro-Area ratio of pro-Strength ofeutectoid Î¸ in theeutectoid Î¸ in the(FormulaCooling raterolledArea ratiosurface layer areacentral area of1)900â†’650Â° C.materialof pearliteof wire rodwire rodRight sideÂ° C./sMPa%%%Example Î²1â€”â€”139498.10.050.20Example Î²2â€”â€”154998.50.160.40Example Î²3â€”â€”159999.10.120.28Example Î²4â€”â€”153098.60.110.38Example Î²5â€”â€”154497.30.220.35Example Î²620.130.0162098.30.150.39Example Î²7â€”â€”142698.20.120.26Example Î²8â€”â€”156297.30.480.49Example Î²946.255.0151198.60.420.48Example Î²10â€”â€”155999.10.350.29Example Î²11â€”â€”155997.20.260.36Example Î²12â€”â€”152697.50.050.28Example Î²13â€”â€”169897.30.310.42Example Î²14â€”â€”162097.10.030.01Example Î²15â€”â€”159198.20.000.00Example Î²16â€”â€”162197.60.020.01

TABLE 14DiameterTS ofArea ratio of pro-Area ratio of pro-Wireof FinalFinaleutectoid Î¸ in theeutectoid Î¸ in thebreakagedrawndrawnsurface layer areacentral area ofduringSteelwirewireof steel wiresteel wirewireTypemmMPa%%drawingDelaminationRemarkExample Î²1a-15.421200.000.12Not occurNot occurBluing after wire drawingExample Î²2b-14.222860.140.35Not occurNot occurHeat stretching after wire drawingExample Î²3c6.721260.100.22Not occurNot occurHeat stretching after wire drawingExample Î²4d5.222570.090.30Not occurNot occurHeat stretching after wire drawingExample Î²5e4.222700.150.28Not occurNot occurAfter wire drawing, molten 5% Alâ€”Znplating and another wire drawingExample Î²6f-23.323510.100.30Not occurNot occurBluing after wire drawingExample Î²7g-13.321560.050.19Not occurNot occurWire drawing after molten 10%Alâ€”Zn platingExample Î²8h4.222990.430.41Not occurNot occurAs the drawn wire isExample Î²9i5.022480.390.42Not occurNot occurAfter wire drawing, molten zinc platingand another wire drawingExample Î²10j-12.922940.260.21Not occurNot occurWire drawing after molten zinc platingExample Î²11k2.322960.190.29Not occurNot occurWire drawing after molten zinc platingExample Î²12l5.222540.030.25Not occurNot occurHeat stretching after wire drawingExample Î²13m2.324280.220.36Not occurNot occurWire drawing after molten zinc platingExample Î²14n5.021960.010.00Not occurNot occurMolten lead plating and heatstretching after wire drawingExample Î²15o5.021680.000.00Not occurNot occurMolten zinc plating after wire drawingExample Î²16p5.121810.010.00Not occurNot occurMolten zinc plating after wire drawing

TABLE 15Final temperature(heatingtemperature in theTemp. of wire rodWirecase of reheatingCoilingwhen startingTemperatureSteeldiameterpatenting)temperaturecoolingof salt or leadTypemmÂ° C.Â° C.Â° C.Cooling methodÂ° C.Comparative Example Î²1j-211.01030875850DLP550Comparative Example Î²2b-211.0â€‚960930910DLP550Comparative Example Î²3f-212.01030985945Stelmorâ€”Comparative Example Î²4a-213.01035985940Stelmorâ€”Comparative Example Î²5g-2â€‚8.01035825800DLP550Comparative Example Î²6o12.01035950900DLP550Comparative Example Î²7r11.0â€‚950â€”890Reheating LP540Area ratio ofArea ratio ofpro-eutectoid Î¸pro-eutectoid Î¸Strength ofin the surfacein the central(FormulaCooling raterolledArea ratiolayer area ofarea of wire1)900â†’650Â° C.materialof pearlitewire rodrodRight sideÂ° C./sMPa%%%Comparative Example Î²1â€”â€”151598.20.700.02Comparative Example Î²2â€”â€”153197.30.620.04Comparative Example Î²320.115.0145099.30.601.60Comparative Example Î²413.2â€‚8.0124099.10.401.20Comparative Example Î²5â€”â€”142097.51.320.05Comparative Example Î²6â€”â€”146097.21.560.40Comparative Example Î²7â€”â€”144097.20.650.30

TABLE 16Area ratio of pro-Area ratio ofDiameterTS ofeutectoid Î¸ inpro-eutectoidof FinalFinalthe surface layerÎ¸ in the centralWiredrawndrawnarea of steelarea of steelbreakageSteelwirewirewirewireduring wireTypemmMPa%%drawingDelaminationRemarkComparativej-24.622520.620.00Not occurOccurHeat stretching after wire drawingExample Î²1Comparativeb-24.622680.520.00Not occurOccurBluing after wire drawingExample Î²2Comparativef-2Wireâ€”â€”â€”Occurâ€”Wire drawing after molten zinc platingExample Î²3breakageoccursComparativea-2Wireâ€”â€”â€”Occurâ€”Wire drawing after molten zinc platingExample Î²4breakageoccursComparativeg-23.321501.200.00Not occurOccurWire drawing after molten zinc platingExample Î²5Comparativeo5.320301.430.00Not occurOccurMolten zinc plating after wire drawingExample Î²6Comparativer5.020400.520.25Not occurOccurAs the drawn wire isExample Î²7

INDUSTRIAL APPLICABILITY

According to the invention, it is possible to provide with high productivity and favorable yield rate at a low price high strength wire rods that are preferable for use as a steel cord, a sewing wire, a PC steel wire, a zinc plated steel strand, a steel wire for springs, a cable for suspension bridges, or the like, and are excellent in terms of wire drawing properties, which makes the invention have broad industrial applicability.