The present invention, wire, steel wire, and a method for manufacturing a steel wire.
The present application, on May 18, 2017, claiming priority based on Japanese Patent Application No. 2017-099227, filed in Japan, the contents of which are incorporated here.
BACKGROUND
[0002]
　The present invention is a wire and a reinforcing material of a tire of an automobile or the like, reinforcing wires, such as aluminum transmission lines, PC steel wire, widely as a material for high strength steel wire, such as those used in the rope wire for use in bridges, etc. it relates wire used. Further, the present invention is the steel wire obtained from the wire, and a process for producing a steel wire using the wire.
[0003]
　Wire is manufactured by hot rolling, by drawing to a predetermined wire diameter, are processed into wires. Subjected once or twice a patenting treatment in the course of drawing, because they are drawn to have a thin steel wire, to have a high drawability is required for wire.
[0004]
　For example, the reinforcement of the above diameter 0.5mm, such as those used in tires for large motor vehicles, so that productivity improvement is required. From a stable hot wire diameter 3.5mm or more wires that can be manufactured by rolling, wire can be manufactured of steel wire having a diameter of 0.5 mm ~ 1.5 mm stably at a low cost has been demanded. Therefore, a wire drawability can be omitted intermediate patenting steps performed during drawing process, and the development of the wire rod capable of exerting a stable torsional properties after wire drawing has been promoted.
[0005]
　However, the wire produced by a process of drawing up KoShinsen working ratio, breakage of the middle drawing has become more prone situation. Furthermore, drawing the steel wire to KoShinsen working ratio tends to twist characteristics are deteriorated. Furthermore, it wire diameter of the wire which is a material of the steel wire is thick is disadvantageous for torsional properties of the steel wire.
[0006]
　To prevent disconnection during wire drawing of the wire rod, improvement technique of tissue of the wire rod have been proposed. As such technology, for example, Patent Document 1 (JP 2014-055316), lamellar cementite which the aspect ratio is 10 or more, high strength steel wire which is present more than 50% on a particle number basis to the total number of lamellar cementite a use wire, high strength steel wire for wire to prevent drawability deterioration has been proposed by such a lamellar cementite.
[0007]
　Further, Patent Document 2 (JP 2000-119756), the rest in the fraction of pro-eutectoid ferrite is 10% or less encompass cementite (Cementite) is discontinuously formed perlite (pearlite) by construction, high strength steel wire for wire to prevent drawability deterioration are proposed.
[0008]
　These techniques, by improving the drawability of the wire by controlling the form of cementite of any wire, wire drawing process for obtaining a steel wire having a diameter of 0.1 ~ 0.4 mm in which Kappi disconnection or the like so as not to occur in. However, only by controlling the form of cementite can not suppress the variations in strength in the cross-section of the steel wire. Therefore, the case of producing the above steel wire wire diameter 0.5mm by Patent Documents technique disclosed, both the deterioration prevention of torsional and suppressing the occurrence of breakage properties is not effectively made, above problems there may be generated.
[0009]
　For these reasons, disconnection in step hardly occurs, such as to produce a steel wire drawing to a large diameter (e.g. over a wire diameter 0.5 mm) to KoShinsen working ratio, the torsional characteristics after drawing realization of wire becomes good is desired.
CITATION
Patent Document
[0010]
Patent Document 1: Japanese Patent 2014-055316 JP
Patent Document 2: Japanese Patent 2000-119756 JP
Summary of the Invention
Problems that the Invention is to Solve
[0011]
　The present invention has been made in view of the above circumstances, even suitable as a material for wires or the like of the large diameter, a steel wire having a superior torsional characteristics high strength, reduced disconnections in the drawing and to provide a stable wire may be prepared by. Further, the present invention is a steel wire having a torsional characteristics and excellent high strength, and it is an object to provide a manufacturing method thereof.
Means for Solving the Problems
[0012]
　The present inventors have conducted various studies to solve the problems described above. As a result, we obtained the following findings.
[0013]
　(I) a wire diameter 5.5mm or more wires, to wire drawing to wire diameter 0.5mm level, wire drawing strain becomes 4.5 or more. When performing drawing in such a KoShinsen working ratio in drawing workability is poor eutectoid steel or over eutectoid steel, patenting in the course drawing is essential. On the other hand, by using a small hypo-eutectoid steel of cementite fraction as a material of the wire, it is possible to improve the drawability of the wire rod, subjecting the wire to drawing the wire drawing strain becomes 4.5 or more it was found that is possible.
[0014]
　(II) On the other hand, if hypoeutectic cross section of the wire of the eutectoid steel (i.e. the wire in the longitudinal direction perpendicular cut surface) ferrite area ratio of the central portion of becomes 45 percent, the ferrite structure to become a lump and coarse, drawability was found that insufficient even wire of hypoeutectoid steel. Also, if the crystal grain size becomes coarse (i.e. if high angle grain boundary density is small), since the aperture of the wire is ductile low poor, likely coarse Without crack inside the wire during drawing is formed drawability is lowered. Further, in the cross section of the wire of hypoeutectoid steel, if the area ratio of ferrite in the surface layer portion was 45 percent, the torsional characteristics after wire drawing has been found to decrease. This is, deformation in the ferrite structure is considered to concentrate.
[0015]
　After (III) pearlite transformation, layered ferrite pearlite structure in (hereinafter referred to as lamellar ferrite) sub-boundaries are introduced in a large amount in. The present inventors have investigated a sub-grain boundary density of the wire, twist characteristics after drawing of the wire rod the relationship between (hereinafter simply twisting may be abbreviated as characteristics). As a result, basically, it was found that more favorable torsional characteristics is large sub-grain boundary density of pearlite structure in is obtained. This much is often sub-grain boundaries, uniformly plastic strain during drawing is introduced, the intensity variation in the cross section of the steel wire is considered to reduce.
[0016]
　(IV) The present inventors have investigated the means of improving the sub-grain boundary density. Sub-grain boundaries, layered cementite of lamellar ferrite and pearlite in the time of pearlite transformation (hereinafter referred to as lamellar cementite) and is in growing the cooperative, it is believed to be introduced in order to eliminate the misfit of both phases. Sub-grain boundary density is pearlite transformation temperature, and the present inventors to be able to adjust with the content of alloying elements (e.g., Si) forming a solid solution in the lamella ferrite was knowledge.
[0017]
　Specifically explaining the relationship between the pearlite transformation temperature and sub-grain boundary density, pearlite transformation temperature in the 550 ° C. or less, more pearlite transformation temperature is low, sub-grain boundary density in the lamellar ferrite was found to be reduced. This is considered to increase the portion where the growth of the lamellar cementite is divided. On the other hand, in the high temperature region than pearlite transformation temperature 550 ° C., sub-grain boundary density in accordance with a high temperature tended to decrease gradually. This is because, when pearlite transformation temperature is higher than 550 ℃, the lamellar spacing as the high temperature will continue to coarse, because it reduces the total amount of misfit number of lamellar cementite is reduced, reducing sub-grain boundary density in the lamellar ferrite It is considered to continue to. From these results, when the pearlite transformation temperature were controlled cooling conditions such that the 550 ° C. vicinity, it was found that the most abundant sub-grain boundaries are introduced.
[0018]
　Further, concretely describing the relationship between the alloy element content and the sub-grain boundary density, by increasing the content of alloying elements, as represented by Si, increased misfit at the interface between the lamellar ferrite and lamellar cementite and it is believed that sub-grain boundary density is increased.
[0019]
　(V), however, was repeated experiments to enhance the sub-grain boundary density of pearlite structure in the basis of the above findings, the torsional characteristics after high despite drawing subgrain boundaries density is observed lower wire It was. The cause is not clear, in the case of increasing the sub-grain boundary density by pearlite transformation is less than 600 ° C., twist number after wire drawing tended to decrease. Thus, instead of 550 ° C. vicinity to maximize the sub-grain boundary density, by pearlite transformation at 600 ° C. ~ 620 ° C., by not excessively increase the sub-grain boundary density in the lamellar ferrite, wire drawability and drawing it is considered possible to obtain a wire rod to achieve both torsional characteristics after machining.
[0020]
　From the above findings (I) ~ (V), a steel wire having a torsional properties excellent and suitable high strength as a material of the wire or the like of the large diameter, stably by suppressing breakage during wire drawing production to realize the wire rod may be, it is necessary to use a hypoeutectoid steel as the material of the wire. Further, by adjusting the adjusting cooling conditions after the content and the hot rolling of the alloy elements, by adjusting the pearlite transformation temperature within an appropriate range, ferrite fraction of wires, large angle grain boundary density, and sub-grain boundary density the is also necessary to control the proper range. Thus, by adjusting the adjusting cooling conditions after the content and the hot rolling of the alloy elements, large angle grain boundary density, wire obtained by increasing the sub-grain boundary density is the same other wire strength levels and this the better the torsional characteristics after drawability and drawing present inventors have found than.
[0021]
　The present invention has been completed based on the above findings and has as its gist is as follows.
(1) wire according to one embodiment of the present invention, the chemical composition, in mass%, C: 0.30 ~ 0.75% , Si: 0.80 ~ 2.00%, Mn: 0.30 ~ 1 .00%, N: 0.0080% or less, P: 0.030% or less, S: 0.020% or less, O: 0.0070% or less, Al: 0 ~ 0.050%, Cr: 0 ~ 1 .00%, V: 0 ~ 0.15 %, Ti: 0 ~ 0.050%, Nb: 0 ~ 0.050%, B: 0 ~ 0.0040%, Ca: 0 ~ 0.0050%, and mg: 0 contained ~ 0.0040%, the balance being Fe and impurities, and the surface layer portion is in the range of depth 0.99 - 400 [mu] m from the surface of the wire, from the central axis of the wire diameter of the wire 1 in both the central portion is in the range of / 10, primary tissue is pearlite structure, perpendicular transverse to the length direction of the wire Or less 45% area ratio of the ferrite structure in the surface, the non-pearlite and non-ferrite area ratio of the cross section is not more than 5%, the pearlite structure in the angular difference 2 ° of the crystal orientation of the lamellae ferrite more than 15 less than ° sub-grain boundaries density .rho.1 is 70 / mm ≦ ρ1 ≦ 600 / mm, in all the tissues, a density ρ2 of the large angle grain boundary serving as a ferrite crystal orientation angle difference 15 ° or more is 200 / mm or more.
(2) In the wire according to the above (1), the chemical composition, in mass%, Al: may contain 0.010 to 0.050%.
(3) In the wire according to the above (1) or (2), the chemical composition, in mass%, Cr: may contain 0.05 to 1.00%.
(4) above (1) to (3) wire according to any one of the chemical composition, in mass%, V: 0.005 ~ 0.15% , Ti: 0.002 ~ 0. 050%, and Nb: it may contain one or more selected from the group consisting of 0.002 to 0.050 percent.
(5) In the wire rod according to any one of the above (1) to (4), the chemical composition, by mass%, B: may contain from 0.0001 to 0.0040 percent.
(6) In the wire rod according to any one of the above (1) to (5), the chemical composition, by mass%, Ca: 0.0002 ~ 0.0050% , and Mg: 0.0002 ~ 0 one or two selected from the group consisting of .0040% may contain.
(7) In the wire rod according to any one of the above (1) to (6), in the surface layer portion and the central portion of the wire material, said density ρ1 of the sub-grain boundaries, satisfies the following formula 1 it may be.
　220 × (C) +100 <ρ1 <220 × (C) +300: Formula 1
　in Formula 1 (C) is a C content by mass% in the chemical composition of the wire.
(8) In the wire rod according to any one of the above (1) to (7), the diameter of the wire may be 3.5 ~ 7.0 mm.
(9) above (1) to wire according to any one of (8) may be used as the material of the steel wire.
(10) steel wire according to another aspect of the present invention, the above (1) is produced by drawing a wire rod according to any one of - (9), a diameter of 0.5 to 1. it is 5mm.
(11) A method of manufacturing a steel wire according to another aspect of the present invention includes a step of obtaining a steel wire by drawing the wire rod according to any one of the above (1) to (9), wherein the diameter of the steel wire is 0.5 ~ 1.5 mm.
The invention's effect
[0022]
　According to the wire in accordance with one embodiment of the present invention, a steel wire having a torsional properties and excellent suitable high strength as a material such as a wire, can be produced stably by suppressing breakage during wire drawing, industrial it is extremely useful. Steel wire according to one embodiment of the present invention has a high strength and excellent torsional properties, for example, suitable as a material of the wire or the like, it is extremely useful industrially. The method of manufacturing a steel wire according to one embodiment of the present invention, a steel wire having a torsional properties and excellent suitable high strength as a material of the wire, can be manufactured stably by suppressing breakage during wire drawing, industry on is very useful.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023]
It is a schematic view showing a surface layer portion and the center portion of the wire according to FIG. 1 embodiment.
Is an explanatory diagram showing an example of FIG. 2 pearlite structure.
DESCRIPTION OF THE INVENTION
[0024]
　Will be described in detail below in embodiments wherein an example of a wire according to the present invention.
　Incidentally, as shown in FIG. 1, in the wire rod 1 according to the present embodiment, for convenience, the range of depth 0.99 ~ 400 [mu] m from the surface of the wire is defined between the surface layer portion 11, from the central axis of the wire of the wire diameter d It is defined as a center 12 a range of 1/10 of. In the present specification, the numerical range expressed using "to" means a range including numerical values described before and after "to" as the lower and upper limits.
[0025]
　Wire of this embodiment, a wire or a reinforcing material of a tire of an automobile or the like, of aluminum transmission line reinforcement wires, such as, PC steel wire, suitable steel wire as a material for such a rope wires used in bridges or the like material a wire that can be used as a.
　Here, the wire drawability of the wire rod, in obtaining a steel wire a wire by wire drawing, is an index showing the resulting difficulty in disconnection. The torsional characteristics after drawing of the wire, when the wire was subjected to torsion test steel wire obtained by drawing, delamination occurred difficulty, and generation of twisting disconnected difficulty etc. a is an index showing. Wire according to the present embodiment preferably has a with 50kg preparing a wire having a diameter of 6.0 mm, wire drawability, such as number of wire breakage when the wire drawing becomes zero so far 0.5mm diameter . Moreover, steel wire after drawing, it is preferable tensile strength is not less than 2800 MPa. Moreover, steel wire used in the wire is de-even if ten the torsion test lamination does not occur once, and the average value of the twist number is preferably has a twist properties such that more than 23 times. Number torsion 23 times or more steel wires, it can be determined that there is sufficient ductility not only broken at handling such straightening after wire drawing.
[0026]
　Next, the chemical composition and microstructure of the wire rod of the present embodiment (metal structure) will be described in detail. Incidentally, "%" for the content of each element means "mass%".
[0027]
　(A) Chemical Composition
　first described the chemical composition of the wire rod of the present embodiment. Hereinafter, the unit of the content of chemical compositions are by weight.
[0028]
　C: 0.30 ~ 0.75%
　C is an element to strengthen steel. To obtain this effect must contain a C or above 0.30%. On the other hand, when the content of C is 0.75%, the cementite fraction is increased, and wire drawability is reduced. Accordingly, the content of the appropriate C is less 0.75% 0.30%. Further, it is preferable that the crack formation inhibition aspect C content of 0.35% or more from, and further preferably 0.40% or more. On the other hand, in view of less than 0.75% of C content from drawability improved, or it is preferable that 0.70% or less, and more preferably set to 0.65% or less. C content 0.42% or more, or 0.45% or more. The C content of 0.60% or less, or may be 0.55% or less.
[0029]
　Si: 0.80 ~
　2.00% Si is a component that contributes to an increase in the sub-grain boundary density not only enhances the strength of the wire. However, the Si content of the wire is less than 0.80%, is not sufficiently obtained effect of sub-grain boundary density increased by containing Si. On the other hand, when the Si content of the wire is more than 2.00%, the fraction of ferrite is increased, wire drawability is reduced. Therefore, the content of Si in the wire rod was determined in the range of 0.80 to 2.00%. Further, in order to obtain a wire rod having a stable desired microstructure, the Si content of the wire 1.00% or more, 1.15% or more, 1.30% or more, or it may be 1.50% or more . The Si content of the wire 1.90% or less, 1.80% or less, 1.75% or less, or may be 1.70% or less.
[0030]
　Mn: 0.30 ~
　1.00% Mn, in addition to the effect of improving the strength of the steel wire, an element having an effect of securing the S in the steel as MnS to prevent the hot shortness of the steel wire. However, Mn content above effect is not sufficient at less than 0.30%. Therefore, the lower limit of the Mn content is 0.30% or more. Furthermore, in order to realize the prevention of ensuring the strength and hot brittleness of the steel wire at a higher level, it is preferable that the content of Mn 0.35% or more, more preferably 0.40% or more . Mn content of 0.50% or more, or may be 0.55% or more.
　On the other hand, Mn is easily segregated elements. The inclusion of Mn beyond 1.00%, Mn is concentrated in the particular heart, martensite and bainite is generated in the center, wire drawability is reduced. Also, contributing to reduction of drawability be coarse MnS is formed. Mn is preferably set to less 0.90%, still more preferably not more than 0.80%. The Mn content of 0.75% or less, or may be 0.70% or less.
[0031]
　N: 0.0080% or less
　N is, while increasing the strength of the wire by fixing the dislocations during drawing of the cold, it is thus to reduce the torsional properties element. When the N content of the wire is more than 0.0080% decrease in torsional characteristics becomes remarkable. Therefore, the N content of the wire was decided to regulate below 0.0080%. The preferable upper limit of the N content is 0.0060% or less, or 0.0050%. N content, the better low, N is the may not contain the wire. The N content of 0.0045% or less, or 0.0040% may be the following. N content 0.0010% or more, or may be 0.0025% or more.
[0032]
　P: 0.030% or less
　P is an element which would reduce the segregated torsion characteristics in the grain boundary of the wire. When the P content of the wire is more than 0.030% decrease in torsional characteristics becomes remarkable. Therefore, the P content of the wire was decided to regulate the 0.030% or less. The upper limit of the P content is preferably not more than 0.025%. P content is preferably as low, P is may not contain the wire. The P content more than 0.020%, 0.015% or less, or may be 0.010% or less. P content of 0.002% or more, 0.005% or more, or may be 0.008% or more.
[0033]
　S: 0.020% or less
　S is to form MnS, which is an element which would reduce the wire drawability. When the S content of the wire is more than 0.020% decrease in wire drawability is markedly. Therefore, the S content of the wire was decided to regulate the 0.020% or less. The preferable upper limit of the S content is 0.010% or less. S content is preferably as low, S is may not contain the wire. The S content of 0.015% or less, 0.008% or less, or may be 0.005% or less. S content of 0.001% or more, 0.002% or more, or may be 0.005% or more.
[0034]
　O: 0.0070% or less
　O is an element which would reduce the ductility of the wire by forming an oxide. When O content of the wire is more than 0.0070% decrease in torsional characteristics becomes remarkable. Therefore, the O content of the wire was decided to regulate below 0.0070%. The upper limit of the O content is preferably 0.0050% or less. O content, the better low, O may not contain the wire. O content of 0.0005% or more, or may be 0.0010% or more. O content 0.0045% or less, or may be 0.0040% or less.
[0035]
　(B) for the organization of wire
　will now be described metal structure of the wire according to the present embodiment. Note that the requirements on the metal structure of the wire rod to be described below, must be satisfied at both surface portions 11 and the central portion 12 of the wire rod 1.
[0036]
　The surface layer portion and the center portion of the wire, the primary tissue is pearlite structure, 45% or less ferrite structure with an area ratio in a cross section of the wire, the non-pearlite and non-ferrite structure is 5% or less in area ratio, pearlite a lamellar ferrite crystal orientation angle difference 2 ° or 15 ° than to become sub-grain boundary density .rho.1 is 70 / mm ≦ ρ1 ≦ 600 / mm of being, and the total tissue of the ferrite crystal orientation angle difference 15 ° or more It becomes large angle grain boundary density ρ2 is required to have a metal structure made of a 200 / mm or more. Note that "main tissue" means tissue that occupies the largest area ratio in the metal structure. The "area ratio" means the area ratio measured in perpendicular cross-section in the longitudinal direction of the wire, the measurement method is described below. In other words the above-mentioned requirements regarding the amount of pearlite, the surface layer portion and the center portion of the wire according to the present embodiment includes 50% or more pearlite structure at an area ratio.
[0037]
　Such wire rod metallographic having the surface layer portion and the center portion, the aperture value of the tensile test is high, excellent wire drawability. Further, according to such a metal structure in the wire rod having the surface layer portion and the center portion, which was drawing the following steel wire diameter 1 mm, when the this tensile strength 2800MPa or more, excellent torsional properties steel wire having is obtained. Note that in the metal structure of the wire, the ferrite structure, the main structure of the balance, except for pearlite structure (non-pearlite and non-ferrite structure) is bainite, and martensite and the like.
[0038]
　Here, a supplementary explanation for the grain boundaries of the pearlite structure.
　In normal technical knowledge, perlite, lamellar ferrite and lamellar cementite by eutectoid reactions resulting from austenite exhibits a lamellar structure arranged in a layered, inside thereof is described as a hierarchical infrastructure is formed. Large angle called block region surrounded by the grain boundaries, the alignment of the lamellae is referred to the same region as colonies within that block. In other words, tissue cementite plates is dispersed while having some orientation within each grain of ferrite structure is recognized as pearlite.
[0039]
　However, the actual pearlite structure is not believed to be so simple. Shows a schematic diagram of an example of simplified pearlite structure in FIG. In the metal structure shown in Figure 2, starting from the old γ grain boundaries 21 (prior austenite grain boundaries), surrounded by a curved high angle grain boundary 22 blocks are generated, the sub-grain boundaries 23 in the block It is formed. Crystal orientation in the block is changed to a number of random orientation, the total length of the chain line shows the sub-grain boundaries 23 in the tissue 2 can recognition total length of sub-grain boundaries 23. Also, the total length of the high angle grain boundary 22 that constitutes the outer periphery of the block or the like in the schematic diagram of FIG. 2 (the length of the thick solid line surrounding the block), it recognition lengths of high angle grain boundary 22. Incidentally, in FIG. 2, previously enlarged to the layered structure of the lamellar cementite 31 and lamellar ferrite 32 of the lamellar structure.
[0040]
　Incidentally, "pearlite" of the wire according to the present embodiment is a so-called pseudo-pearlite structure is intended to include (lamellar cementite 31 pearlite structure produced without growing the plate-shaped). Pseudo pearlite structure is lamellar cementite 31 when observed by SEM is the point to be observed state that is divided in the block, the usual pearlite structure differs. However, in the present embodiment deals with the pearlite structure and the pseudo pearlite structure as identical.
[0041]
　In the actual steel in addition to the pearlite structure other tissues also coexist, since the complicated tissue much than tissue 2, in the wire according to the present embodiment, sub-grain boundaries, a high-angle grain boundaries It is defined to the following. Pearlite structure during the crystal orientation of adjacent lamellae ferrite angular difference boundary surface is less than 15 ° 2 ° or more is referred to as a sub-grain boundaries, the sub-grain boundaries length per unit area of ​​the perlite in test field total referred to as sub-grain boundary density <ρ1> a. Further, in all tissues, the interface where the angular difference between adjacent ferrite crystal orientation is 15 ° or more is referred to as a large-angle grain boundaries, high-angle grain boundaries of the large angle grain boundary density of total length per unit area of ​​the test field It referred to as <ρ2>. The ferrite used in a particular large angle grain boundaries, to a normal ferrite structure, is intended to include both the lamellar ferrite constituting the pearlite structure. Note that for each of the measurement method will be described later.
[0042]
　
　area ratio of ferrite structure in the cross section of the wire rod, wire center, is required to be 45% or less in a surface portion both. If 45 percent by wire center, wire drawability is deteriorated because the ferrite is precipitated lump and coarse. Also, when the area ratio of the ferrite structure in the wire surface layer part is 45 percent, twist number after drawing is lowered. This is considered to concentrate deformation in the ferrite portion of the surface layer portion. It is not particularly necessary to define the lower limit of the area ratio of the ferrite structure. In the central portion or the surface layer portion of the wire, the area ratio of the ferrite structure may be 0%. In the central portion or the surface layer portion of the wire, the area of 43% of the ferrite or less, 40% or less, 35% or less, or as a 30% or less. In the central portion or the surface layer portion of the wire, the area ratio of ferrite of 10% or more, 15% or more, 20% or more, or may be 27% or more.
[0043]
　The area ratio of the non-ferrite and non-pearlite structure is required to be 5% or less. In other words, it is necessary total area ratio of the ferrite structure and pearlite structure is 95%. If a non-ferrite, non-pearlite structure became more than 5%, the non-ferrite and non-pearlite structures easily the crack as a starting point is formed wire drawability during wire drawing is reduced. It is not particularly necessary to define the lower limit of the area ratio of the non-ferrite and non-pearlite structures. In the central portion or the surface layer portion of the wire, the non-ferrite and non-pearlite structure area ratio of may be 0%. That is, the total area ratio of the ferrite structure and pearlite structure may be 100%. The area ratio of 4% of the non-ferrite and non-pearlite structures below, 3%, 2%, or 1% or less (i.e., the total area ratio of the ferrite structure and pearlite structure than 96%, more than 97%, 98% ultra, or 99 percent) may be. Non ferrite and the area fraction of non-pearlite structures more than 1%, or 2% or more (i.e., the total area ratio of the ferrite structure and pearlite structure than 99%, or less than 98%) may be.
[0044]
　
　at the center and the surface layer portion of the wire, the crystal lamellae ferrite sub-grain boundary density .rho.1 (pearlite in density of angular difference 2 ° or 15 ° than to become sub-grain boundaries orientation) must be 70 / mm ~ 600 / mm. By such a wire having a metal structure, and the later tensile strength 2800MPa or drawing, and steel wire excellent in torsional characteristics can be stably obtained. In the central part and the surface layer portion of the wire, by the sub-grain boundary density and 70 / mm or more, it is possible to suppress variations in the strength of the steel wire after drawing, it is possible to reduce the localization of deformation during torsion test Therefore, it is possible to be a steel wire of a high strength obtain good twist properties. When sub-grain boundary density in the center portion and surface layer portion of the wire on the contrary is less than 70 / mm, tensile strength of the steel wire obtained after wire drawing is not improved torsional characteristics at least 2800 MPa. Also, if the pearlite transformation temperature is below 600 ° C., tends to twist properties deteriorate as described above, for sub-grain boundary density in the central portion and surface layer portion of the wire at this time was 600 / mm greater, which it is preferable to set the upper limit and 600 / mm. Therefore, at the center portion and surface layer portion of the wire, the density of the sub-grain boundaries as the angular difference 2 ° or less than 15 ° of the crystal orientation of the lamellae ferrite pearlite structure in the a range of 70 / mm ~ 600 / mm to. In the surface layer portion or the central portion of the wire, sub-grain boundary density is preferably set to 100 / mm or higher, more preferably 120 / mm or more. In the surface layer portion or the central portion of the wire, a sub-grain boundary density 0.99 / mm or more, or may be more than 180 / mm. In the surface layer portion or the central portion of the wire, a sub-grain boundary density 550 / mm or less, 500 / mm or less, 400 / mm or less, or 350 / mm may be less.
[0045]
　In the surface layer portion and the center portion of the wire, sub-grain boundary density ρ1 preferably satisfies the following formula 1. In Formula 1 (C) is, in the chemical composition of the wire rod, a C content in the unit mass%.
　　220 × (C) +100 <ρ1 <220 × (C) +300: Equation 1
　the larger the C content in the chemical composition of the wire rod, the area ratio of the ferrite structure in the surface layer and the center portion of the wire is reduced, the pearlite structure area ratio increases. The larger the area ratio of the pearlite structure, the growth distance of cementite increases, considered sub-grain boundaries during pearlite structure tends to be introduced. Therefore the present inventors have found that the preferred range of sub-grain boundary density is considered to depend on the C content in the chemical composition of the wire rod. According to the findings of the present inventors, when the sub-grain boundary density satisfies the above formula 1 in the surface layer portion and the center portion of the wire, by variations in the twisting value of the wire is reduced, the torsional characteristics further improved It is.
[0046]
　
　in the surface layer portion and the center portion of the wire, the large angle grain boundary density [rho] 2 (ferrite crystal orientation angle difference 15 ° or more the density of high-angle grain boundaries) is required to be 200 / mm or more. If large angle grain boundary density is sufficiently large, the ductility of the wire is high, it is possible to suppress the formation of coarse Without crack during wire drawing, thereby improving drawability. When high-angle grain boundary density in the surface layer portion and the center portion of the wire on the contrary is less than 200 / mm, wire drawability is reduced. Therefore, the surface layer portion and the center portion of the wire, the density of the large angle grain boundary serving as a ferrite crystal orientation angle difference 15 ° or more is in a range of more than 200 / mm. In the surface layer portion or the central portion of the wire, large angle grain boundary density, preferably 230 / mm or more. The upper limit of the high angle grain boundary density is not particularly defined in the surface layer or central wire, for making the large angle grain boundary density 500 / mm or more is difficult manufacturing, large angle grain in the surface layer or central wire the upper limit of the field density is preferably set to 500 / mm. The high angle grain boundary density in the surface layer or central wire 220 / mm or more, 250 / mm or more, or may be 280 / mm or more. The high angle grain boundary density in the surface layer or central wire 400 / mm or less, 380 / mm or less, or 350 / mm may be less.
[0047]
　(C) Evaluation Method
　Next, for each condition of the metal structure of the wire according to the present embodiment will be described measurement method.
[0048]
　
　After the cross-section of wire (i.e. perpendicular cut surface in the longitudinal direction of the wire) was mirror polished, corroded with picral, using a field emission scanning electron microscope (FE-SEM) magnification respectively observed 10 places at an arbitrary position of the surface portion and the central portion 2000 times and photographed. Area per field of view, 2.7 × 10 -3 mm 2 to (vertical 0.045 mm, horizontal 0.060 mm).
[0049]
　Then, overlapping transparent to each photograph obtained sheet (eg OHP (Over Head Projector) sheet). In this state, paint color to "ferrite structure" in each of the transparent sheet. Then, it determined by image analysis software to area ratio of the "areas painted color" in the transparent sheet, and calculates the average value as the average value of the area ratio of the ferrite structure. In this way it is possible to obtain a ferrite area ratio. Then, in a separate transparent sheet painted color "than pearlite structure, a region overlapping with the tissue is other than ferrite structure" and calculate the area ratio. It can be obtained area ratio of non-pearlite and non ferrite structure by the above method. Note that ferrite structure and pearlite structure is because it is isotropic tissue, the area of ​​the tissue in the cross section of the wire is the same as the volume of the tissue of the wire rod. The area ratio of the pearlite structure is a ferrite area ratio, the sum of the non-pearlite and non-ferrite area ratio can be calculated by subtracting from 100% by area.
[0050]
　
　After the cross-section of wire (i.e. perpendicular cut surface in the length direction) mirror polished, polishing with colloidal silica, a field emission scanning by type electron microscope to observe the 4-field in (FE-SEM) wire surface portion at a magnification of 400 times using a (range of depth 0.99 ~ 400 [mu] m from the surface) and a central portion, EBSD measurement (electron backscatter diffraction method the measurement) is carried out. Area per field of view, 0.0324Mm 2 and (vertical 0.18 mm, horizontal 0.18 mm), the step at the time of measurement is set to 0.3 [mu] m.
[0051]
　Then, the results of each measurement field of view obtained, the total length of the line with the sub-grain boundaries less than 15 ° 2 ° or more, and the total length of the line with a 15 ° or more high-angle grain boundaries measured. For example, OIM analysis (OIM: Orientation Imaging Microscopy) be used in sub-grain boundaries of having total length of the line, and can be obtained the total length of the line with the large angle grain boundaries. Since sub-grain boundaries are present only in a portion of the pearlite structure, the total length of the line with the sub-grain boundaries obtained in each measurement field, the value obtained by dividing by the perlite area included in each measurement field, nitrous at each measurement field It is defined as a grain boundary density ρ1.
[0052]
　Since high-angle grain boundaries are also present in the boundary of ferrite structure and pearlite structure, the total length of the line with the large angle grain boundaries obtained in each measurement field, the value obtained by dividing an area of each measurement field, large angular in each measurement field of view It is defined as a grain boundary density ρ2.
　The surface layer portion and the center portion of the average value of each analysis result, the surface layer portion and the center portion of the sub-grain boundary density of angular difference less 2 ° or 15 ° of the ferrite crystal orientation of the pearlite structure in .rho.1, as well as the surface layer portion and the center portion the large angle grain boundary density ρ2 of the total tissue ferrite crystal orientation angle difference 15 ° or more of the. Since EBSD result depends heavily on the noise, average CI (confidence index) is set to be used 0.60 above results, also CI is to be those of 0.10 or less to be removed as noise. Incidentally, 0.10 following removal of CI is possible within OIM analysis.
[0053]
　As described above, the value of the sub-grain boundary density ρ1 and the large angle grain boundary density ρ2 is not only the aforementioned range in the wire surface portion (range of depth 0.99 ~ 400 [mu] m from the surface), the same also in the wire center it is necessary in the range. Sub-grain boundary density ρ1 is 70 / mm ~ 600 / mm in the wire center, or if the surface layer portion be in the range high angle grain boundary density ρ2 is more than 200 / mm is not in the range described above, the wire surface layer portion described above ranged in the center even if no characteristic required by the object is obtained as the wire if not in the range described above. .rho.1 the wire surface layer part, [rho] 2, and the wire center of .rho.1, if it is confirmed that [rho] 2 is within the above range, the entire wire .rho.1 and [rho] 2 can be recognized that within the range described above.
[0054]
　For (D) production process
　by the production method of the wire according to the present embodiment, in order to improve the torsional properties of the wire, optimizing various conditions during pearlite transformation, to control tissue.
　Wire that meets the above requirements of the wire according to the present embodiment, regardless of the manufacturing method, it is possible to obtain the effect of the wire according to the present embodiment, for example, by a manufacturing method described below, according to this embodiment the wire may be produced. The manufacturing process described below is an example, even if the chemical composition and other requirements by a process other than the following is obtained a wire in a range of wire according to the present embodiment, on the wire by the present invention is it is needless to say that included.
[0055]
　First, after Steels so that the above components, to produce a steel strip by continuous casting, performing hot rolling. It should be noted that, after casting, may be subjected to slabbing. The resulting steel slab during hot rolling is heated as slab is 1000 ~ 1250 ° C., it is hot rolled to φ5.5 ~ 7.0mm finishing temperature of 900 ~ 1000 ° C..
　The heating temperature of the billet before hot rolling is 1000 ° C. or more and 1250 ° C. or less. The heating temperature is less than 1000 ° C. billet increases and the reaction force at the time of hot rolling, at the 1250 ° C. than the heating temperature of the steel strip is because decarburization proceeds.
　Finish rolling temperature of the hot rolling is made 900 ° C. or higher. The finish rolling temperature is lower than 900 ° C. This is because the shape precision increases and the reaction force of the finish rolling deteriorates. On the other hand, the finish rolling temperature is set to 1000 ° C. or less. Austenite grain size Doing hot rolling is increased at 1000 ° C. greater than high-angle grain boundary density after pearlite transformation is lowered.
[0056]
　After hot rolling, subjected to cooling in the following 4 stages, to adjust the ferrite area ratio and sub-grain boundary density, a large angle grain boundary density. In one primary cooling, be cooled at a high cooling rate suppresses the grain growth of austenite, and its object is to produce a fine austenitic structure. The secondary cooling aims to perform Johiya to a uniform temperature from the wire surface portion to the center in order to reduce the temperature difference existing wire surface portion and the central portion when the primary cooling. The tertiary cooling, can as far as possible uniformly cooled from the wire surface portion to the center portion, and at a cooling rate which can suppress the ferrite transformation, it is an object of cooling to pearlite transformation temperature of aim. The quaternary cooling, to perform Johiya in order to as far as possible uniform pearlite transformation from wire surface portion to the center, sub-grain boundary density, thereby advancing the pearlite transformation so that the range of the purpose of high-angle grain boundary density With the goal. Details are shown below. Note that the primary-average cooling rate of the four primary cooling described below, the amount of decrease in wire temperature from the start to the end of the primary-quaternary cooling, the time from the start to the end of the primary-quaternary cooling it is divided by the value. And the arrival temperature of the primary-quaternary cooling is the temperature at the end of the wire of the primary-quaternary cooling.
[0057]
　After hot rolling, by a water-cooled, in the range of the average cooling rate 50 ~ 200 ° C. / sec, perform primary cooling to 830 ~ 870 ° C.. Note that the start and end of the primary cooling, is that the spraying of the start and end of the refrigerant (water).
　The average cooling rate at 870 ° C. or higher temperature range large grain growth rate is less than 50 ° C. / sec, when the time present in this temperature range is long, since grain growth of the austenite is promoted, after pearlite transformation high angle grain boundary density is reduced. No upper limit of the average cooling rate in the primary cooling but, on the manufacturing equipment constraints, the average cooling rate of 200 ° C. / sec greater is difficult, a 200 ° C. / sec or less and the upper limit of the average cooling rate in the primary cooling.
　If it is less than temperature reached 830 ° C. in the primary cooling, there is a possibility to proceed large amount of ferrite transformation only in the surface layer portion, an increased ferrite area ratio of the surface layer portion, it is difficult to control 45% or less. Therefore, the arrival temperature of the primary cooling 830 ° C. or higher. If you stop the cooling at a temperature exceeding 870 ° C., austenite grains grow larger, large angle grain boundary density after pearlite transformation is decreased. For this reason, the temperature reached in the primary cooling and 870 ° C. or less.
[0058]
　Thereafter, the air cooling by air, less than the average cooling rate 5 ° C. / sec, performing secondary cooling to within 790 ° C. or higher 820 ° C. or less. Incidentally, at the start of secondary cooling is equal to the time of termination of the spraying of the coolant in the primary cooling, the time of the termination of the secondary cooling is equal to the time of the start of spraying of the refrigerant in the tertiary cooling. Secondary cooling is a cooling for the small difference in temperature between the surface portion and the central portion of the wire occurs during the primary cooling, the pearlite transformation temperature from the wire surface portion to the center portion uniform.
　If it is a 5 ° C. / sec or more average cooling rate in the secondary cooling, would be a temperature difference remains between the surface layer portion and the center portion, the surface layer of the large angle grain boundary density and sub-grain boundary density of the wire after pearlite transformation even can control the door, the large angle grain boundary density at the central portion of the wire decreases. Therefore, the average cooling rate in the secondary cooling is lower than 5 ° C. / sec.
　Is less than the secondary cooling temperature reached 790 ° C., there is a possibility that ferrite transformation is improved ferrite area ratio occurs. Therefore, reaching a temperature of the secondary cooling to 790 ° C. or higher. On the other hand, when stopping the secondary cooling at 820 ° C. greater than the temperature difference of up to pearlite transformation temperature between the surface portion and the central portion of the wire is increased, again the temperature difference between the surface portion and the central portion when the tertiary cooling It occurs. Therefore, reaching a temperature of the secondary cooling was 820 ° C. or less. The Si steels containing large amounts of, the Ac1 temperature is shifted to the high temperature side, reaching temperature in the secondary cooling is particularly important.
　Incidentally, it is preferable to be within 12 seconds 5 seconds or more (time elapsed between the start and end of the secondary cooling) secondary cooling time. A secondary cooling takes time of 12 seconds more than is because grain growth of the austenite grains is promoted. On the other hand, in the secondary cooling time within 5 seconds, there is a possibility that the temperature difference in the wire remains.
[0059]
　Thereafter, the air blast cooling, the average cooling rate 20 ° C. / sec ultra 30 ° C. / sec or less, perform tertiary cooling to within 600 ° C. or higher 620 ° C. or less. Incidentally, tertiary cooling of the start and end, is that the start and end of the blowing of air. At a cooling rate which can suppress ferrite transformation in tertiary cooling, the optimal sub-grain boundary density, provide cooling to pearlite transformation temperature obtained a high angle grain boundary density.
　At an average cooling rate of tertiary cooling 20 ° C. / sec or less, the ferrite area ratio becomes excessive occurs ferrite transformation. Therefore, the average cooling rate is set to 20 ° C. / sec greater. On the other hand, when subjected to tertiary cooling at an average cooling rate of 30 ° C. / sec greater, only the wire surface layer portion is cooled to a temperature of aim, the temperature of the wire center resulting in the quaternary cooled in excess state is initiated . Therefore, the average cooling rate is set to 30 ° C. / sec or less.
　When temperature reached in three primary cooling is less than 600 ° C., properties deteriorate pearlite structure twisting excessively high strength. Therefore, temperature reached tertiary cooling to 600 ° C. or higher. On the other hand, if the ultimate temperature of the tertiary cooling is 620 ° C. greater than pearlite transformation temperature is high, also decreases the tensile strength after pearlite transformation with high angle grain boundary density and the subgrain boundaries density decreases. Therefore, it reaches the temperature of the three primary cooling was 620 ° C. or less.
[0060]
　Thereafter, the average cooling rate 10 ° C. / sec quaternary cooled to 550 ° C. or less in the following by air cooling by air. Incidentally, at the start of the four primary cooling it is equal to the time of termination of blowing of air at the tertiary cooling. The time of termination of the four primary cooling is a time when the time was discontinued air, i.e. reheating the wire, or spraying of the refrigerant is started. However, when the temperature of the wire is carried out cooling until 550 ° C. or less, the time when the temperature of the wire became 550 ° C. regarded as the time of completion of the four primary cooling. The quaternary cooling, by reducing the temperature difference between the wire rod in the cross section in the pearlite transformation, and to obtain uniform high angle grain boundary density from the surface layer portion to the center portion, a wire having a sub-grain boundary density.
　If the average cooling rate in the quaternary cooling of 10 ° C. / sec greater than the temperature change of the surface layer is large, sub-grain boundary density is reduced. Therefore, the average cooling rate in the quaternary cooling to 10 ° C. / sec or less. The lower limit of the average cooling rate in the quaternary cooling include, but are not limited to, the cooling rate in the case of cooling the wire may be a 2 ° C. / sec or more is usually. Therefore, 2 ° C. / sec or lower limit of the average cooling rate in the quaternary cooling.
　When temperature reached quaternary cooling of 550 ° C. greater, there is a possibility that pearlite transformation is not completed. Therefore, temperature reached quaternary cooling to 550 ° C. or less. Since the effect of cooling rate in the temperature range of 550 ° C. or less gives the tissue a minor, may be carried out accelerated cooling such as water cooling after carrying quaternary cooled to a temperature of 550 ° C. or less. In Examples described later, an example the invention has been cooled to room temperature cool after cooling to 550 ° C. or less by the four primary cooling, the same even when cooled by another cooling means after the completion of the four primary cooling tissue is formed.
[0061]
　(E) for any component:
　wire material of the present embodiment, instead of a part of the remainder of Fe, optionally, it is selected Al, Cr, V, Ti, Nb, B, Ca, from the group consisting of Mg at least one or more elements that may be contained. However, the wire according to the present embodiment without including these optional elements since it is possible to solve the problem, the lower limit of these optional elements is 0%. Or less, Al is any element, Cr, V, Ti, Nb , B, Ca, and effects of the Mg, reasons for limiting the content will be described. % Are by weight of optional ingredients.
[0062]
　Al: 0 ~ 0.050%
　Al in the wire rod of the present embodiment may not be contained. Al is precipitated as a AlN, is an element which can increase the high angle grain boundary density above angle difference 15 ° of ferrite crystal orientation. If you want reliably obtain the effect it is preferable to contain Al of 0.010% or more. On the other hand, Al are the easily forms an element of the hard oxide inclusions, the Al content of wire is more than 0.050% likely to be significantly formed coarse oxide inclusions, decrease in torsional characteristics becomes remarkable. Therefore, the upper limit of the content of Al of the wire is 0.050%. The preferable upper limit of the Al content is at 0.040% or less, and more preferable upper limit is not more than 0.035%, still more preferred upper limit is 0.030% or less.
[0063]
　Cr: 0 ~ 1.00%
　Cr in the wire rod of the present embodiment may not be contained. Cr, like Mn, increases the hardenability of steel, is an element strengthening the steel. In order to obtain this effect reliably, it is preferable to contain 0.05% or more Cr. On the other hand, when the content of Cr exceeds 1.00%, the torsional characteristics deteriorate. Therefore, the content of Cr is 1.00% or less. In the case of increasing the hardenability of steel, Cr is preferably be contained 0.10% or more, more preferably it is contained 0.30% or more. The upper limit of Cr is preferably set to 0.90% or less, still more preferably not more than 0.80%.
[0064]
　V: 0 ~ 0.15%
　V in the wire of the present embodiment may not be contained. V combines with N, C, or carbide, to form a nitride or carbo-nitrides, has the effect of refining the austenite grains during hot rolling by their pinning effect, improving the torsional properties of the steel effects there is. In order to obtain this effect reliably it is preferably contained the V of 0.005% or more. From the viewpoint of improving the torsional characteristics, the may preferably be 0.02% or more the content and V, more preferably contained 0.03% or more. On the other hand, if the content of V exceeds 0.15%, not only the effect is saturated, production of steel, such as cracks in the slab results in a steel ingot or slab in the step of slabbing steel strip since an adverse effect on, V content is 0.15% or less. The content of V is preferably 0.10% or less, more and still more preferably not more than 0.07%.
[0065]
　Ti: 0 ~ 0.050%
　Ti in the wire rod of the present embodiment may not be contained. Ti combines with N, C, or carbide, to form a nitride or carbo-nitrides, has the effect of refining the austenite grains during hot rolling by their pinning effect, improving the torsional properties of the steel effects there is. In order to obtain this effect reliably, Ti is preferably contained more than 0.002%. From the viewpoint of improving the torsional characteristics, it is preferable the content of Ti to 0.005% or more, it is more preferable to contain 0.010% or more of Ti. On the other hand, if the content of Ti exceeds 0.050%, not only the effect is saturated, production of steel, such as cracks in the slab results in a steel ingot or slab in the step of slabbing steel strip adversely affect the. Thus, the content of Ti is set to 0.050% or less. The content of Ti is more preferably 0.025% or less.
[0066]
　Nb: 0 ~ 0.050%
　Nb at a linear material of the present embodiment may not be contained. Nb combines with N, C, or carbide, to form a nitride or carbo-nitrides, has the effect of refining the austenite grains during hot rolling by their pinning effect, improving the torsional properties of the steel effects there is. In order to obtain this effect reliably, Nb is preferably contained more than 0.002%. From the viewpoint of improving the torsional properties, more preferably to a content of Nb 0.003% or more, and even more preferably it contained at least 0.004% Nb. On the other hand, if the content of Nb exceeds 0.050%, not only the effect is saturated, production of steel, such as cracks in the slab results in a steel ingot or slab in the step of slabbing steel strip since a negative impact on the content of Nb is set to 0.050% or less. The content of Nb, it is more preferably 0.030% or less.
[0067]
　B: 0 ~ 0.0040%
　B at a linear material of the present embodiment may not be contained. B has the effect of reducing the ferrite structure of the steel by being contained trace amounts, when it is desired to obtain with certainty the effect it is preferably contained 0.0001% or more of B. Be contained 0.0040% of B, the effect is not only saturated, so coarse nitrides are produced, torsional characteristics are deteriorated. Accordingly, the content of B in the case of containing the to 0.0040%. If you want to increase the area ratio of the pearlite structure is preferably that the content of B 0.0004% or more, and still more preferably equal to or greater than 0.0007%. Incidentally, the content of B for improving torsional characteristics preferably be less 0.0035%, still more preferably not more than 0.0030% or.
[0068]
　Ca: 0 ~ 0.0050%
　Ca in the wire rod of the present embodiment may not be contained. Ca is a solid solution in MnS, the effect of dispersing the MnS finely. MnS to be to finely dispersed, it can be reduced disconnections in drawing you due to MnS. In order to obtain the effect of Ca surely it is, Ca is preferably contained 0.0002% or more. For obtaining a better effect, it is sufficient to contain 0.0005% or more Ca. However, the content of Ca exceeds 0.0050%, the effect is saturated. Further, the content of Ca exceeds 0.0050% oxide reacts with oxygen in the steel becomes coarse, rather deteriorate wire drawing workability. Therefore, the content proper of Ca case of incorporating is 0.0050%. The content of Ca is preferably not more than 0.0030% or, more preferably in the range from 0.0025% or less.
[0069]
　Mg: 0 ~ 0.0040%
　Mg in the wire rod of the present embodiment may not be contained. Mg is a deoxidizing element, but to produce an oxide, an element having a mutual relationship between MnS by generating also sulfide, has the effect of dispersing MnS finely. Breakage during drawing due to MnS This effect can be suppressed. In order to ensure the effect of Mg is, Mg is preferably contained 0.0002% or more. For obtaining a better effect, it is sufficient to contain 0.0005% or more Mg. However, when the content of Mg exceeds 0.0040% to the effect is saturated, large amounts generates MgS, rather deteriorate wire drawing workability. Accordingly, the content of the proper Mg when to be contained is 0.0040%. The content of Mg is preferably not more than 0.0035%, more preferably not more than 0.0030% or.
[0070]
　The remainder of the chemical composition includes a "Fe and impurities". The term "impurities", when the industrial production of steel material, refers to those mixed ores as raw material, scrap, or the like manufacturing environment in steel.
[0071]
　The diameter of the wire according to the present embodiment is not particularly limited, the diameter of the current wire that circulates in the market that are 3.5 ~ 7.0 mm is usual, the diameter of the wire of this in the present embodiment it may be used as the upper and lower limits of the. If the diameter of the wire was above 3.5 mm, preferably it is able to reduce the burden of the hot rolling during the wire production. If the diameter of the wire is less 7.0 mm, it is possible to suppress the drawing strain amount during drawing of the wire preferred.
[0072]
　Steel wire according to another aspect of the present invention, the wire according to the present embodiment is obtained by drawing. The diameter of the steel wire, considering applications, it is usual that is 0.5 ~ 1.5 mm. Steel wire according to the present embodiment, the chemical composition of the wire according to the present embodiment is a raw material, construction of the metal structure, sub-grain boundary density .rho.1, and since large angle grain boundary density ρ2 is within the above range, It has excellent tensile strength and torsional properties.
[0073]
　Incidentally, the steel wire according to the present embodiment, since the amount of strain is produced through a very large drawing, the metal structure is undergoing significant deformation. For example, looking at the enlarged photograph of a section of the steel wire according to the present embodiment, the phase surrounded by the grain boundaries is crushed considerably, its type can not be determined. It is also extremely difficult to identify the presence of sub-grain boundaries and large angle grain boundaries. That is, normal tissue specific manner (e.g., taking a metal structure photograph, and EBSD by crystal structure analysis, etc.) by the metal structure of the steel wire according to the present embodiment, it is extremely difficult to a certain other configurations. Or a metal structure of the steel wire according to the present embodiment it is not possible to identify directly by its structure, or characteristic, or not about practical.
[0074]
　Method for manufacturing a steel wire according to another aspect of the present invention, the wire according to the present embodiment comprises the step of drawing. Wire drawing, the diameter of the finally obtained steel wire is carried out at reduction rate such that 0.5 ~ 1.5 mm. The chemical composition of the wire according to the present embodiment, the configuration of the metal structure, sub-grain boundary density .rho.1, and since large angle grain boundary density ρ2 is within the above range, production of the steel wire according to the present embodiment using this the method can suppress disconnection count to extremely low levels, also, it is possible to obtain a steel wire having excellent tensile strength and torsional properties.
Example
[0075]
　Will be specifically described below by way of examples the invention, the invention is not intended to be limited by the following examples.
[0076]
　Table 1, and Steels having chemical compositions shown in Table 2, to prepare a wire in the following manner. Incidentally, Table 1, in Table 2, "-" notation, the content of the element is an impurity level, indicating that it can be determined not to be substantially contained. Table 1 and the remainder of the chemical composition of the steel shown in Table 2 is iron and impurities.
[0077]
　First, after melting by a converter steel A having a chemical composition shown in Table 1, the slabbing in the usual manner to obtain a billet of 122mm square. Next, after the steel strip is heated so that the 1050 ~ 1150 ° C., in a range of finishing temperature 900 ~ 1000 ° C., and hot rolled to 6mm.
[0078]
　Adjust cooling after the finish rolling, cooling was effected under the conditions shown in shown in Table 3-1 through Table 3-3 (A1) ~ (A21) .
　Specifically, (A1) ~ within the range of the average cooling rate 50 ~ 200 ° C. / sec by water cooling with respect to (A7), after cooling (primary cooling) in 830 ~ 870 ° C., then air-cooled by air was air-cooled (secondary cooling) to within 790 ° C. or higher 820 ° C. or less in less than an average cooling rate of 5 ° C. / sec by. Thereafter, 20 ° C. / sec subjected to cooling to 600 ~ 620 ° C. or less super 30 ° C. / sec (cubic cooling), and cooled (quaternary cooling) at 550 ° C. or less 10 ° C. / sec to below, then, at room temperature by cooling until it was cooling.
　(A8) with respect to the ~ (A17), performs four types of adjustment cooled with different conditions and cooling conditions described above to obtain a wire. Incidentally, underline in Table 3-1 is attached values are incorrect value in the production conditions of the wire according to the present invention.
[0079]
　(A18) with respect to the - (A21), without performing four types of adjustments cooling, cooling was effected under the conditions shown in Table 3-2 through Table 3-4. Incidentally, the term "primary cooling" or the like in these tables are merely to distinguish cooling phase, different from the primary cooling-quaternary cooling involved in the preparation process of the present invention.
　Specifically, (A18) with respect to the place of tertiary cooling and quaternary cooling in the production process of the present invention, was performed immersion in salt bath at 550 ° C..
　With respect to (A19), with respect to the end of hot rolling after the wire of the above, conducted reheating and 60 seconds the temperature holding to 950 ° C., immersion in 550 ° C. Salt bath immediately after the temperature holding ends It was carried out.
　(A20) with respect to subjects cooling at blowing after performing a primary cooling, was subjected to cooling to an average 1.0 ° C. / sec 550 ° C. by switching to cool after cooling to 680 ° C. or less.
　With respect to (A21), it cooled the wire to 700 ° C. at 10 ° C. / sec subjected to air blast cooling after carrying out the primary cooling were subjected to subsequent cooling to below 550 ° C. at 5 ° C. / sec at air.
[0080]
　Furthermore, from the steel a ~ z of chemical compositions shown in Table 2 to prepare a hot-rolled wire rod in the same manner as in Table 3-1 (A1). Thereafter, dry wire drawing, plating, to implement wet wire drawing, to obtain a steel wire having a diameter of 0.5 mm. Values ​​underline is attached in Table 2, a desirable range of the present invention.

WE claims

[Requested item 1]
A wire,
　the chemical composition, in
　mass%,
　C: 0.30% ~
　0.75%, Si: 0.80 ~ 2.00%, Mn: 0.30 ~
　1.00%, N: 0 .0080% or
　less, P: 0.030% or
　less, S: 0.020% or
　less, O: 0.0070% or
　less,
　Al: 0 ~ 0.050%, Cr: 0 ~
　1.00%, V: 0
　0.15%

　Ti:~, 0 ~ 0.050%, Nb: 0 ~ 0.050%,
　B: 0 ~ 0.0040%, Ca: 0 ~ 0.0050%, and
　Mg: 0 ~ 0.0040 %
　containing the balance being Fe and impurities,
　A surface layer portion in a range of depth 0.99 ~ 400 [mu] m from the surface of the wire, both in the central portion is in the range of 1/10 of the diameter of the wire from the central axis of the wire, the principal organization be pearlite structure , or less area ratio of 45% ferrite structure in perpendicular cross-section in the longitudinal direction of the wire, the non-pearlite and non-ferrite area ratio of the said cross section is not more than 5%, of the pearlite structure in , the density of the sub-grain boundaries as the angular difference 2 ° or less than 15 ° of the crystal orientation of the lamellar ferrite .rho.1 a is 70 / mm ≦ ρ1 ≦ 600 / mm, in all the tissues, angle difference 15 ° of ferrite crystal orientation large angle grain boundary density ρ2 of the above is 200 / mm or more
wires, characterized in that.
[Requested item 2]
　The chemical composition, in
　mass%, Al: 0.010 ~ 0.050%
wire according to claim 1, characterized in that it contains.
[Requested item 3]
　The chemical composition, in
　mass%, Cr: 0.05 ~ 1.00%
wire of claim 1 or claim 2, characterized in that it contains.
[Requested item 4]
　The chemical composition, in
　mass%,
　V: 0.005 ~ 0.15%, Ti: 0.002 ~ 0.050%, and
　Nb: 0.002 ~ 0.050%
1 kind selected from the group consisting of or wire according to any one of claims 1 to 3, characterized in that it contains two or more.
[Requested item 5]
　The chemical composition, by
　mass%, B: 0.0001 ~ 0.0040%
, characterized in that it contains the claims 1 to wire according to any one of claims 4.
[Requested item 6]
　The chemical composition, by
　mass%, Ca: 0.0002 ~ 0.0050%, and
　Mg: 0.0002 ~ 0.0040%
, characterized in that it contains one or two elements selected from the group consisting of wire according to any one of claims 1 to 5.
[Requested item 7]
　In the surface layer portion and the central portion of the wire material, wherein the density ρ1 of the sub-grain boundaries, the wire according to any one of claims 1 to 6, characterized in that satisfy the following formula 1.
　　220 × (C) +100 <ρ1 <220 × (C) +300: Formula 1
　in Formula 1 (C) is a C content by mass% in the chemical composition of the wire.
[Requested item 8]
　Wire according to any one of claims 1 to 7, wherein the diameter of the wire is 3.5 ~ 7.0 mm.
[Requested item 9]
　Wire according to any one of claims 1 to 8, characterized in that used as the material of the steel wire.
[Requested item 10]
　Produced by drawing a wire rod according to any one of claims 1 to 9,
　having a diameter of 0.5 ~ 1.5 mm
steel wire, characterized in that.
[Requested item 11]
　The wire of any one of claims 1 to 9 and drawing comprises a step of obtaining a steel wire, the
　diameter of the steel wire is 0.5 ~ 1.5 mm
, characterized in that method of manufacturing a steel wire.