[0001]The present disclosure is related to high strength steel wire.
BACKGROUND
[0002]Steel wire, for example, is applied rope wire, in civil engineering and building structures applications such as bridges wire. Rope wires and bridges wire, for example, after by patenting a piano wire to pearlite structure, the wire was drawn, are manufactured using an aging treatment was steel wire.
[0003]
　Patent Document 1, at least 1 / 10d of the surface steel wire (d steel wire radius) in the region of the depth of the high-strength steel wire an average aspect ratio of the plate-like cementite in the pearlite is set to 30 or less have been proposed ing.
[0004]
　In Patent Document 2, the wire diameter of the steel wire is D, the hardness of the area of ​​0.1D from the surface is high-strength steel wire which is below 1.1 times the internal hardness is proposed there.
[0005]
　Patent Document 1: JP 2004-360005 Patent Publication
　Patent Document 2: JP 2009-280836 JP
Summary of the Invention
Problems that the Invention is to Solve
[0006]
　Recently, steel wire, when applied to civil engineering and building construction applications, the reduction of construction costs, for the purpose of weight reduction of the structure, for example, high strength steel wire tensile strength is at least 1800MPa is obtained ing.
　However, steel wire, with the high strength, in some cases hydrogen embrittlement resistance is deteriorated. Therefore, the high strength steel wire, a further improvement of hydrogen embrittlement resistance has been demanded.
[0007]
　The present disclosure aims to provide a high-strength and high-strength steel wire excellent in hydrogen embrittlement resistance.
Means for Solving the Problems
[0008]
　The means for solving the above problems includes the following aspects.
(1) in mass%, C: 0.70 ~ 1.20% , Si: 0.10 ~ 2.00%, Mn: 0.20 ~ 1.00%, P: 0.030% or less, S: than 0.030%, N: 0.0010 ~ 0.0100%, Al: 0 ~ 0.100%, Cr: 0 ~ 2.00%, V: 0 ~ 0.30%, B: 0 ~ 0. 0050%, Ti: 0 ~ 0.050 %, Nb: 0 ~ 0.050%, Zr: 0 ~ 0.050%, Ni: 0 ~ 2.00%, Cu: 0 ~ 1.00%, Sn: 0 ~ 0.50%, Mg: 0 ~ 0.010%, Ca: 0 ~ 0.010%, and the balance: having a chemical composition consisting of Fe and impurities, the metal structure is 95% or more by area ratio der of consists pearlite structure, an average aspect ratio R of the pearlite blocks measured at the surface of an axial section containing an axis of the steel wire is 2.0 or more Ri, and when the diameter of the steel wire was as D, in axial cross-section containing the axis of the steel wire, (average aspect ratio of pearlite blocks measured at the surface layer) / (pearlite block measured at the position of 0.25D average aspect ratio) is not less than 1.1, and high strength steel wire tensile strength is not less than 1800MPa of.
(2) the chemical composition, in mass%, Al: 0.005 ~ 0.100% , Cr: 0.01 ~ 2.00%, V: 0.01 ~ 0.30%, B: 0.0001 ~ 0.0050%, Ti: 0.001 ~ 0.050%, Nb: 0.001 ~ 0.050%, Zr: 0.001 ~ 0.050%, and Ni: 0.01 ~ 2.00% high strength steel wire according to the containing one or more (1).
(3) the content of Al in the chemical composition, in mass%, high-strength steel wire according to the 0.005 ultrasonic to 0.100% (1) or (2).
(4) the diameter of 2.5 mm ~ 9.5 mm (1) ~ high strength steel wire according to any one of (3).
Effect of the invention
[0009]
　According to the present disclosure, high-strength and high-strength steel wire excellent in hydrogen embrittlement resistance is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010]
FIG. 1 is a schematic diagram showing a cross section perpendicular to the axial direction including the axis of the steel wire in high strength steel wire of the present disclosure.
Is a schematic diagram showing an axial cross-section including the axis of the steel wire in high strength steel wire [2] The present disclosure.
DESCRIPTION OF THE INVENTION
[0011]
　For tensile strength to suppress a decrease in the hydrogen embrittlement resistance of high strength steel wire is not less than 1800MPa, the metal structure of the steel wire and pearlite structure, and pearlite blocks in the axial direction (steel wire of the steel wire it is effective to tissue extending along the longitudinal direction). Pearlite structure has a layered structure of the cementite phase and a ferrite phase. The layered structure, the penetration resistance of the hydrogen (hydrogen embrittlement resistance) against crack propagation. If the pearlite block is extended along the axial direction of the steel wire, since the direction of the layered structure of the pearlite structure becomes uniform, reduction in hydrogen embrittlement resistance can be suppressed.
[0012]
　That is, the metal structure satisfies all of the following conditions, it is possible strength of the steel wire has a hydrogen embrittlement resistance excellent even more 1800 MPa.
　1) metal structure is 95% or more pearlite structure area ratio.
　2) the average aspect ratio R of the pearlite blocks measured at the surface of an axial section containing an axis of the steel wire of 2.0 or more.
　3) When the diameter of the steel wire was as D, in axial cross-section containing the axis of the steel wire, the average (average aspect ratio of pearlite blocks measured at the surface layer) / (pearlite block measured at the position of 0.25D aspect ratio) is not less than 1.1.
　Therefore, high-strength steel wire of the present disclosure, high strength and because it is excellent steel wire hydrogen embrittlement resistance, for example, a rope wire for use in civil engineering and building construction, application to bridges wire etc. it is useful to.
[0013]
　In the present specification, the term "cross-section in the axial direction including the axis of the steel wire", including the center axis of the steel wire, cut along the axial direction of the steel wire (longitudinal direction, i.e. the wire drawing direction), the center It shows an axial section parallel.
　In this specification, the term "central axis", passes through the center point of the cross section perpendicular to the axial direction of the steel wire (longitudinal direction) shows a virtual line extending in the axial direction.
　Referring now to FIG. 2, FIG. 2 is a schematic diagram showing an axial cross-section including the axis of the steel wire. In FIG. 2, S is the surface layer, Q is the central axis, D is representative of the diameter of the steel wire. As shown in FIG. 2, the cross section of the axial direction including the axis of the steel wire, the center axis Q direction, along the central axis Q of the steel wire represents a cut plane in the center axis Q parallel to the plane.
[0014]
　In the present specification, the term "surface", the surface of the steel wire, toward the central axis (toward the radial direction), showing the depth of the region of up to 100 [mu] m.
　In the present specification, the term "0.25D", when the diameter of the steel wire was D, from the surface of the steel wire, toward the central axis (toward the radial direction), 0.25 times the diameter D indicating the position of the depth.
　Referring now to FIG. 1, FIG. 1 is a schematic view showing a cross section perpendicular to the axial direction of the steel wire. In Figure 1, S is the surface layer, D is the diameter of the steel wire, 0.25 D represents a position of 0.25 D. As shown in FIG. 1, the surface layer S from the surface of the steel wire, toward the central axis, an area of up to 100μm deep. 0.25D from the surface of the steel wire, toward the central axis, a position of 0.25 times the depth of the diameter D.
[0015]
　In this specification, numerical ranges expressed using "to" means a range including numerical values described before and after "to" as the lower and upper limits. Further, numerical ranges when the numerical values set forth are "super" or "less than" are assigned before and after "to" means a range that does not include the lower limit or the upper limit value of these values.
　In the present specification, "%" indicating the content of the component (element) means "% by mass".
　In this specification, the content of C (carbon), may be referred to as "C content". It may be referred Similarly, the content of the other elements.
　In this specification, the term "process" not only separate steps, if a there also is achieved the intended purpose of the process that can not be clearly distinguished from other processes, this term included.
[0016]
　First, the reasons for limiting the scope of the elements contained in the high-strength steel wire in the present disclosure.
　The chemical composition of high-strength steel wire of the present disclosure, by mass%, C: 0.70 ~ 1.20% , Si: 0.10 ~ 2.00%, Mn: 0.20 ~ 1.00%, P 0.030% or less, S: 0.030% or less, N: 0.0010 ~ 0.0100%, Al: 0 ~ 0.100%, Cr: 0 ~ 2.00%, V: 0 ~ 0. 30%, B: 0 ~ 0.0050 %, Ti: 0 ~ 0.050%, Nb: 0 ~ 0.050%, Zr: 0 ~ 0.050%, Ni: 0 ~ 2.00%, Cu: 0 ~ 1.00%, Sn: 0 ~ 0.50%, Mg: 0 ~ 0.010%, Ca: 0 ~ 0.010%, and the balance having a chemical composition consisting of Fe and impurities.
[0017]
　C is added to secure the tensile strength of the steel wire. C amount is generated pro-eutectoid ferrite is less than 0.70%, it is difficult to secure a predetermined tensile strength. On the other hand, when the C content exceeds 1.20% pro-eutectoid cementite volume increases, wire drawability is deteriorated. For this reason, the C amount is from 0.70 to 1.20%. In that both high strength and drawability, C of the preferred range, 0.80 to 1.15%, more preferred range is 0.90 to 1.10%.
[0018]
　With Si enhances the relaxation characteristics, the effect of increasing the tensile strength by solid solution strengthening. The Si content is less than 0.10% such effects are insufficient. On the other hand, when the Si content exceeds 2.00%, these effects can be hot ductility deteriorate with saturated, manufacturability is lowered. Therefore, the amount of Si and 0.10 to 2.00%. Si content is preferably within a range from 0.20 to 1.80%, a more preferred range is 0.50 to 1.50%.
[0019]
　Mn has the effect of increasing the tensile strength of steel after the pearlite transformation. The Mn amount is less than 0.20%, the effect is insufficient. On the other hand, the effect is saturated when the Mn amount exceeds 1.00%. For this reason, the amount of Mn and 0.20 to 1.00%. Mn amount of the preferred range is 0.30 to 0.90%, a more preferred range is 0.40 to 0.80%.
[0020]
　P and S are contained as impurities. P and S, in order to degrade the hydrogen embrittlement resistance segregated in the grain boundary, P amount and S content had better suppressed. Therefore, the upper limit of the P content and S content 0.030%, respectively. A preferred range of the P content and S content is 0.020%, respectively, more preferable range is 0.015% or less. The lower limit of the P content and S-content is not particularly limited, may be 0%, such as from the viewpoint of dephosphorization cost reduction and desulfurization cost, may be respectively 0.0001% or more.
[0021]
　When the N content is excessive, degrading the hydrogen embrittlement resistance. Therefore, N content was set to 0.0100% or less. Meanwhile, N is the an effect of increasing the relaxation characteristics. Further, N represents, Al, Ti, to form a Nb, and V and nitrides, an effect of improving the grain refining ductile grain size. N amount is unlikely these effects are obtained is less than 0.0010%. Therefore, N amount was 0.0010 to 0.0100%. N amount is preferably from 0.0010 to 0.0080 percent, more preferably 0.0010 to 0.0050%.
[0022]
　Also, high-strength steel wire of the present disclosure, Al, Cr, V, B, Ti, Nb, may contain one or more of the elements of Zr, and Ni. If high strength steel wire of the present disclosure, containing these elements, by mass%, Al: 0.005 ~ 0.100%, Cr: 0.01 ~ 2.00%, V: 0.01 ~ 0. 30%, B: 0.0001 ~ 0.0050%, Ti: 0.001 ~ 0.050%, Nb: 0.001 ~ 0.050%, Zr: 0.001 ~ 0.050%, and Ni: it may contain one or more from 0.01 to 2.00%.
[0023]
　Al is an optional element. Therefore, Al content may be 0%.
　Al functions as a deoxidizing element. Further, Al has an effect of improving effect, and reduced by hydrogen embrittlement resistance of solute N to enhance the AlN was formed fine crystal grains ductility. In this regard, Al content may be 0 percent. Further, in order to obtain this effect sufficiently, Al amount may be preferably 0.005% or more. Further, Al content may be 0.005 percent, often is 0.008% or more, may be 0.010% or more, it is to be 0.020% or more. On the other hand, when the Al content exceeds 0.100%, the above effect is saturated, which may reduce the productivity. Therefore, Al content may be set to 0.100% or less, it is possible to 0.060 or less. Therefore, Al amount in the case of including Al may be 0.005 to 0.100% often from 0.005 ultrasonic to 0.100% A 0.008 to 0.060% it may be.
[0024]
　Cr is an optional element. Therefore, Cr content may be 0%.
　Cr is effective to increase the tensile strength of steel after the pearlite transformation. In this regard, Cr content may be 0 percent. Further, in order to obtain this effect sufficiently, Cr content should preferably be set to 0.01% or more. On the other hand, the alloy cost increases when the Cr content exceeds 2.00%. Furthermore, it is easy martensite structure occurs, which may cause deterioration in wire drawing workability and resistance to hydrogen embrittlement. Therefore, Cr amount when containing Cr should preferably be 0.01 to 2.00%. The preferred range is from 0.10 to 0.50%.
[0025]
　V is an arbitrary element. Therefore, V amount may be 0%.
　V is precipitated carbide VC, to increase the tensile strength, the effect of improving hydrogen embrittlement resistance. In this regard, V amount may be 0 percent. Further, in order to obtain this effect sufficiently, V amount may be preferably 0.01% or more. On the other hand, when the amount of V exceeds 0.30%, the alloy cost increases. Therefore, V amount in the case of including the V should preferably be 0.01 to 0.30%. The preferred range is from 0.02 to 0.10%.
[0026]
　B is any element. Therefore, B amount may be 0%.
　B has an effect of improving the effectiveness and hydrogen embrittlement resistance increase the tensile strength after pearlite transformation. In this regard, B amount may be 0 percent. Further, in order to obtain this effect sufficiently, B the amount may be preferably 0.0001% or more. On the other hand, B the amount of the effect is saturated if it exceeds 0.0050%. Therefore, B amount in the case of including B good be 0.0001 to 0.0050%. The preferred range is from 0.0005 to 0.0020 percent.
[0027]
　Ti is an optional element. Therefore, Ti amount may be 0%.
　Ti is functions as a deoxidizing element, is effective effect of increasing the tensile strength by precipitating carbides and nitrides, and that by fine crystal grains to improve the ductility. In this regard, Ti content may be 0 percent. Further, in order to obtain this effect sufficiently, Ti amount may be preferably 0.001% or more. On the other hand, Ti amount exceeds 0.050%, the these effects are saturated, which may cause deterioration in wire drawing workability by generating a coarse oxides. Therefore, Ti amount when containing Ti good be 0.001 to 0.050%. The preferred range is from 0.005 to 0.020 percent.
[0028]
　Nb is an optional element. Therefore, Nb amount may be 0%.
　Nb is effective effect of increasing the tensile strength by precipitating carbides and nitrides, and that by fine crystal grains to improve the ductility. In this regard, Nb amount may be 0 percent. Also, in the order to obtain these effects sufficiently, Nb amount may be preferably 0.001% or more. On the other hand, there are cases where the effect degrades the twisting characteristics as well as saturated when the Nb content exceeds 0.050%. Therefore, Nb amount in the case of including Nb good be 0.001 to 0.050%. The preferred range is from 0.005 to 0.020 percent.
[0029]
　Zr is an arbitrary element. Accordingly, Zr amount may be 0%.
　Zr functions as a deoxidizing element. Moreover, Zr reduces the solid solution S by forming a sulfide, has the effect of improving hydrogen embrittlement resistance. In this regard, Zr amount may be 0 percent. Further, in order to obtain this effect sufficiently, Zr amount may be preferably 0.001% or more. On the other hand, when the Zr amount is more than 0.050% produces coarse oxides together with the effect is saturated, causing deterioration in wire drawing workability. Therefore, Zr amount when containing Zr good be 0.001 to 0.050%. The preferred range is from 0.002 to 0.020%.
[0030]
　Ni is an optional element. Therefore, Ni amount may be 0%.
　Ni has the effect of suppressing the penetration of hydrogen. In this regard, Ni content may be 0 percent. Further, in order to obtain this effect sufficiently, Ni amount may be 0.01% or more. On the other hand, the alloy cost increases when the Ni content exceeds 2.00%. Furthermore, it is easy martensite structure occurs, which may cause deterioration in wire drawing workability and resistance to hydrogen embrittlement. Therefore, Ni amount in the case of containing Ni good from 0.01 to 2.00%. The preferred range is from 0.05 to 0.50 percent.
[0031]
　Further, as an optional component, Cu, Sn, may contain one or more of the elements of Mg, and Ca. Therefore, the content of these elements, by mass%, may be 0%. When containing these elements, in wt.%, Cu: 0 super ~ 1.00% Sn: 0 super ~ 0.50% Mg: 0 super ~ 0.010%, and Ca: 0 super ~ 0.010% it may be.
[0032]
　The balance being Fe and impurities. In the chemical composition of the high strength steel wire of the present disclosure, the balance excluding the respective elements described above is Fe and impurities.
　Here, the impurity components contained in the raw material, or a component mixed in the manufacturing process, intentionally refer to a component not intended to be contained in the steel.
　As the impurity, for example, O (oxygen) and the like.
　O is contained as an impurity in steel, Al, is present as an oxide, such as Ti. O amount is high, the coarse oxides are formed, causing breakage when subjected to wire drawing. Therefore, O content is preferably suppressed to 0.01% or less. Although the lower limit of the O content is not specified, for example, it may be 0 percent, may be 0.001% or more.
[0033]
　The high-strength steel wire of the present disclosure, the steel wire having the above-described components and specific metal structure described above. Next, a description will be given of reasons for limitation of the metal structure.
[0034]
　In the metal structure of the steel wire, the area ratio of the pearlite structure decreases and twisting characteristics of strength is degraded by less than 95%. Therefore, the lower limit of the area ratio of the pearlite structure was 95%. The area ratio of the pearlite structure may be 96% or more. The upper limit of the area ratio of pearlite may be 100% or less, may be 99% or less.
[0035]
　In the high strength steel wire of the present disclosure, region defining an average aspect ratio R of the pearlite block is the position of the depth 100μm from the surface of the steel wire (surface layer). In the high strength steel wire of the present disclosure defines a ratio of the average aspect ratio of pearlite blocks measured at the surface layer to the average aspect ratio of pearlite blocks measured at the position of 0.25 D.
[0036]
　The tensile strength of more high-strength steel wire 1800 MPa, in order to impart excellent hydrogen embrittlement resistance is a surface layer of pearlite blocks of steel wire, it is effective to elongate the drawing direction.
　Pearlite structure has a layered structure of the cementite phase and the ferrite phase. The layered structure, become resistance to hydrogen penetration from the surface layer (hydrogen embrittlement resistance). If pearlite blocks in the surface layer of the steel wire is extended along the wire drawing direction (longitudinal direction of the steel wire), the uniform orientation of the layered structure of the pearlite structure in the surface layer of the steel wire. Therefore, since the number of layers of the pearlite structure is laminated, drop in hydrogen embrittlement resistance can be suppressed.
　On the other hand, it was measured at the surface of the steel wire in the axial direction of the cross section including the axis of the steel wire, if the average aspect ratio R of the pearlite block is less than 2.0, no effect of the above can be obtained. Therefore, since the resistance to hydrogen penetration from the surface can not be sufficiently improved, hydrogen embrittlement resistance is deteriorated. Accordingly, the average aspect ratio R is 2.0 or more. Preferably 2.5 or more, still more preferably 3.0 or more. On the other hand, although the upper limit of the average aspect ratio R is not particularly limited, in terms of productivity, for example, may be a 15 or less may be 12 or less, or 10 or less.
[0037]
　Further, in order to effectively suppress deterioration of hydrogen embrittlement resistance of the steel wire, it is effective to concentrate the strain on the surface layer. In axial cross-section including the axis of the steel wire, when the diameter of the steel wire was as D, the ratio of the average aspect ratio represented by the following formula is less than 1.1, the internal strain becomes high, resistance to hydrogen embrittlement is deteriorated. The average aspect ratio of pearlite blocks measured at the surface layer has the same meaning as the average aspect ratio R described above.
(Formula) ratio of the average aspect ratio = (average aspect ratio of pearlite blocks measured at the surface layer) / (average aspect ratio of pearlite blocks measured at the position of 0.25 D)
[0038]
　In axial cross-section including the axis of the steel wire, when the ratio of the average aspect ratio of the above formula is small (less than 1.1) (i.e., elongation of the surface layer of the pearlite blocks for internal pearlite blocks are the same, or small time), the surface of the strain or of the same order as the strain of the inner or internal than the surface undergoing high strain. Therefore, the surface layer may for internal, not enough strain is applied. The surface layer of the strain is not sufficiently applied, when the internal strain is high, steel wire, the ductility is lowered, that cracking is likely to occur, hydrogen embrittlement resistance is deteriorated. Therefore, to concentrate the strain on the surface layer, and the ratio of the average aspect ratio of the formula 1.1 or more. In order to impart a high strain on both the surface and interior of the steel wire, for example, to increase the total area reduction rate in the drawing. As a result, the ratio of the average aspect ratio of the above formula is less than 1.1, prone to decrease in ductility and crack of the steel wire.
[0039]
　The ratio of the average aspect ratio represented by the above formula in that they further suppress the decrease in hydrogen embrittlement resistance, preferably, 1.2 or more, more preferably 1.3 or more. This upper limit of the ratio of the average aspect ratio is not particularly limited, in terms of productivity, for example, it may be 5 or less, may be 3 or less, may be two or less.
[0040]
　Method of measuring the metal structure was the following.
　Area ratio of pearlite steel wire was determined by the following procedure. First, the cross section perpendicular to the axis of the steel wire (hereinafter also referred to as "C section") was etched with picral, thereby revealing the metal structure. Then, when the diameter of the steel wire is D, the surface of the center position (depth 50μm positions from steel wire surface), and to observe the metal structure of the position of the depth of 0.25 D. Observation of metal structure is made by photographing with four positions rotated 90 ° intervals about the axis of the steel wire, one point at the center, a SEM at nine points. Photography metallic structure by SEM is the 90μm region of the 120μm and central direction in the circumferential direction, carried out in 1000-fold magnification.
　Referring now to FIG. 1, point for measuring the area ratio of pearlite of the steel wire, the center position (the depth is 50μm from steel wire surface position) of the surface layer S at four positions, 0 in four places. position of 25D, and a total of nine of the center C of the one place.
　Then, marking non-pearlite structure in the structural photograph obtained by photographing the (ferrite, bainite, martensite, and each tissue of pro-eutectoid cementite) visually determining the area ratio of the respective tissue by image analysis. The area ratio of the pearlite structure is obtained by subtracting the area of the non-pearlite structure from the entire observation field of view. This was measured for two samples, determine the average value thereof, and pearlite area ratio of the whole steel wire.
[0041]
　The average aspect ratio of the surface layer of the pearlite blocks was determined by the following procedure.
　First, in the axial direction including the axis of the steel wire cross-section (hereinafter, L section referred to as) against, EBSD: using (Electron Back Scatter Diffraction pattern electron backscatter diffraction method) apparatus, detects the pearlite block grain boundary to. In this case, per one L section, from the surface of the steel wire in the longitudinal direction to 500μm region of 100μm and steel wire in the central axis direction (radial direction) of the steel wire, each measurement point the measurement step as 0.3 [mu] m bcc measuring the crystal orientation of -fe, misorientation seeks 9 degrees or more boundary. The region surrounded by the boundary and pearlite block grain. In the obtained crystal orientation map, among the pearlite block group within the measurement region, selecting 20 pearlite blocks from those largest circle equivalent diameter in the order. Then each of the aspect ratio of the selected 20 pearlite blocks (long diameter ratio to the minor diameter of pearlite blocks, i.e., major axis / minor axis) sought to determine the average aspect ratio of 20 pearlite blocks. Then, two locations on both sides per one L cross the pearlite block further investigated for all 4 samples taken from different sites of the steel wire, the average pearlite block average value of the average aspect ratio of all eight of the surface layer and aspect ratio.
　Next, the sample as, when the diameter of the wire was as D, in the region of 500μm to 100μm and steel wire longitudinally central axis direction around the position of the depth of 0.25D from the steel wire surface similarly obtaining an average aspect ratio of pearlite blocks of all eight. Then, determine the ratio between the average aspect ratio of the surface layer of pearlite blocks, the (average aspect ratio of pearlite blocks measured at the surface layer) / (average aspect ratio of pearlite blocks measured at the position of 0.25 D).
　Referring now to FIG. 2, the portion for measuring the aspect ratio, the surface layer S, which is longitudinally 500μm region of 100μm and steel wire in the direction of the central axis of the steel wire from the surface. Further, in 0.25 D, about the position of the depth of 100 [mu] m (0.25 D in the central axis direction around the position of the depth of 0.25 D, to 50μm on the surface direction from the 0.25 D, and 0. 25D 100 [mu] m range of from to 50μm in the central axis direction) and a region of the steel wire longitudinally 500 [mu] m. Measurements, as shown in FIG. 2, performed for both sides of the surface and sides of 0.25D with respect to the central axis Q in L section.
[0042]
　Next, a description will be given tensile strength of the steel wire according to the embodiment. If it is less than the tensile strength of the steel wire is 1800 MPa, for example, when applied to the use of the civil engineering and building construction, the effect of reduction and weight reduction of construction cost is reduced. Therefore, in the high-strength steel wire of the present disclosure, the lower limit of the tensile strength was 1800 MPa.
　The upper limit of the tensile strength is not particularly limited, when the tensile strength is too high, ductility is reduced, there are cases where cracking when subjected to wire drawing occurs. In this regard, the tensile strength may be in the following 3000MPa, may be less than 2800MPa.
[0043]
　High-strength steel wire of the present disclosure, in view of the perspective and the aforementioned applications for manufacturing a steel wire having a metal structure and the tensile strength of the above, the steel wire diameter (wire diameter) is 2.5 mm ~ 9.5 mm it often is, well even 3.0mm ~ 9.0mm, may be 3.5mm ~ 8.5mm.
　The diameter of the steel wire has the same meaning as the wire diameter of the steel wire.
[0044]
　Next, an example of a preferred method of producing a high strength steel wire of the present disclosure. Method of producing a high strength steel wire of the present disclosure but is not particularly limited, for example, as an example of a preferred manufacturing methods include the following embodiments.
[0045]
　Step a first aspect, a steel slab having a specific chemical composition, to obtain a step of heating to 1000 ~ 1150 ° C., the steel strip, a wire by hot rolling at a finish rolling temperature of 800 ~ 950 ° C. When, the wire is 800 ~ 950 ° C., directly, a step of pearlite transformation treatment by immersing 50 seconds in a molten salt bath of 500 ~ 600 ° C., further step of water cooling from 400 ° C. or higher to 300 ° C. or less If, with a wire after pearlite transformation process, a step of drawing at a total reduction of area of ​​70 to 95%, and performing aging treatment at 450 ° C. or less to the wire after drawing, a.
[0046]
　Step a second aspect, the steel slab having a specific chemical composition, to obtain a step of heating to 1000 ~ 1150 ° C., the steel strip, a wire by hot rolling at a finish rolling temperature of 800 ~ 950 ° C. When, the wire is 800 ~ 950 ° C., a step of pearlitic transformation process by air blast cooling, the wire after pearlite transformation process, a step of drawing at a total reduction of area of ​​70 to 95%, Shin and a step of performing aging treatment at 450 ° C. or less to the wire after the wire.
[0047]
　Step as a third aspect, the steel slab having a specific chemical composition, to obtain a step of heating to 1000 ~ 1150 ° C., the steel strip, a wire by hot rolling at a finish rolling temperature of 800 ~ 950 ° C. When, the wire is 800 ~ 950 ° C. cooling, and reheating the cooled wire rod to a temperature range of not lower than 950 ° C., said wire after reheating is immersed in Pb bath or molten salt bath a step of pearlitic transformation process by holding the 500 ~ 600 ° C., the wire after pearlite transformation process, a step of drawing at a total reduction of area of ​​70 ~ 95%, 450 ℃ below the wire after drawing in and a step of performing an aging treatment, the.
[0048]
　In each embodiment described above, drawing is performed as follows. To the extent that the whole cross sectional reduction ratio is 70 to 95%, at least during the drawing in the final pass, using a die approach half angle 10 degrees or more (preferably 20 degrees or less), less 12% of the reduction in area (preferably 3% or more, 9% or less) the intensity is given as. In other words, this condition, the final pass not only may be employed by a plurality of paths including the last path and final pass.
[0049]
　In each embodiment described above, the chemical composition of the steel strip is similar to the chemical composition of the high strength steel wire mentioned above. The chemical composition of the steel strip are shown below.
　Chemical composition of the steel pieces, C: 0.70 ~ 1.20%, Si: 0.10 ~ 2.00%, Mn: 0.20 ~ 1.00%, P: 0.030% or less, S: than 0.030%, N: 0.0010 ~ 0.0100%, Al: 0 ~ 0.100%, Cr: 0 ~ 2.00%, V: 0 ~ 0.30%, B: 0 ~ 0. 0050%, Ti: 0 ~ 0.050 %, Nb: 0 ~ 0.050%, Zr: 0 ~ 0.050%, Ni: 0 ~ 2.00%, Cu: 0 ~ 1.00%, Sn: 0 ~ 0.50%, Mg: 0 ~ 0.010%, Ca: 0 ~ 0.010%, and the balance: is made of Fe and impurities.
[0050]
　Above, a preferred method of producing a high strength steel wire of the present disclosure has been described by way of the above embodiments as an example. According to the above aspect, excellent steel wire in high strength and resistance to hydrogen embrittlement, can be easily produced.
Example
[0051]
　The steel types A ~ L having the chemical compositions shown in Table 1, and heated under the conditions shown in Table 2, subjected to hot rolling, winding in a ring shape, the hot rolling line behind the molten salt bath at a temperature shown in Table 2 immersed in the make patenting treatment, to produce a wire. Also, for some, instead of performing the patenting treatment by dipping in a molten salt bath, by performing the blast cooling, to produce a wire. Thereafter, the wire was drawn and the resulting wire to wire diameter after drawing shown in Table 3, performs an aging treatment by heating after drawing, to produce a steel wire shown in Test Nos 1-22.
　Further, the wire cooling after hot rolling and reheating under the conditions shown in Table 4, performs a patenting treatment by dipping the Pb bath at the temperature shown in Table 4, were prepared wire. Thereafter, the wire was drawn and the resulting wire to wire diameter after drawing shown in Table 5, subjected to aging treatment by heating after drawing, to produce a steel wire shown in Test Nos 23-25.
[0052]
[Table 1]

[0053]
[Table 2]

[0054]
[table 3]

[0055]
[Table 4]

[0056]
[table 5]

[0057]
　Then, for these steel wires were subjected to the following tests.
　Tensile strength test, JIS Z 2241: comply with the 2011, it was carried out using the 9A No. 5 test piece. The results shown in Table 3, and Table 5.
[0058]
　The area ratio of the metal structure, measured by the ratio (surface layer with an average aspect ratio of at 0.25D position from the average aspect ratio and the surface layer of the average aspect ratio R, and pearlite block measured by the surface layer of the measured pearlite blocks in the surface layer perlite the average aspect ratio of pearlite blocks measured at the position of the average aspect ratio /0.25D block) was determined as described above. The results shown in Table 3, and Table 5.
[0059]
　Hydrogen embrittlement resistance was evaluated by FIP test. Specifically, the steel wire of the test numbers 1 to 25, a 20% strength NH of 50 ° C. 4 is immersed in SCN solution, loaded with 0.8 times the load breaking load was assessed rupture time. The specific liquid amount (amount of solution / test piece surface area) is 12 cc / cm 2 was. FIP test was evaluated by 12 per steel wire, and the average value was used as the hydrogen embrittlement time. Those hydrogen embrittlement time is 10 hours or more was judged hydrogen embrittlement resistance and good (represented by each table in G). Moreover, those that do not meet the above conditions, hydrogen embrittlement resistance is determined to be defective (denoted by the tables in NG). The results shown in Table 3, and Table 5.
[0060]
　Steel wire Test Nos. 1 to 11 and 20 to 25 meet all the requirements of high-strength steel wire of the present disclosure, the tensile strength becomes higher 1800 MPa, and has good resistance to hydrogen embrittlement.
　On the other hand, steel wire test No. 12 is hydrogen embrittlement resistance is excellent, the tensile strength is low. Furthermore, the area ratio of the pearlite structure, an average aspect ratio of pearlite blocks measured at the surface R and, (average aspect ratio of pearlite blocks measured at the surface layer) / (average aspect ratio of pearlite blocks measured at the position of 0.25 D) There outside the scope of this disclosure.
　Steel wire test No. 13 and 15 is less than the lower limit average aspect ratio R of the present disclosure pearlite blocks measured at the surface, hydrogen embrittlement resistance is poor.
　Steel wire test No. 14 is less than the lower limit area ratio of the present disclosure pearlite structure, hydrogen embrittlement resistance is poor.
　Steel wire test No. 16, the area ratio of the pearlite structure, and an average aspect ratio R of the measured pearlite blocks in the surface layer is less than the lower limit of the present disclosure, hydrogen embrittlement resistance is poor.
　Steel wire test No. 17, the average aspect ratio of pearlite blocks measured at the surface R and, (average aspect ratio of pearlite blocks measured at the surface layer) / (average aspect ratio of pearlite blocks measured at the position of 0.25 D) There is less than the lower limit of the present disclosure, hydrogen embrittlement resistance is poor.
　Steel wire Test No. 18, although the hydrogen embrittlement resistance is excellent, the tensile strength is less than the lower limit of the present disclosure. Furthermore, the area ratio of pearlite, and (the average aspect ratio of pearlite blocks measured at the surface layer) / (average aspect ratio of pearlite blocks measured at the position of 0.25 D) is less than the lower limit of the present disclosure.
　Steel wire Test No. 19, (average aspect ratio of pearlite blocks measured at the surface layer) / (average aspect ratio of pearlite blocks measured at the position of 0.25 D) is less than the lower limit of the present disclosure, the hydrogen embrittlement characteristic is bad.
[0061]
　Japanese disclosure of patent application 2016-150584 its entirety is incorporated herein by reference.
　All documents described herein, patent applications, and technical standards, each individual publication, patent application, and that the technical specification is incorporated by reference to the same extent as if marked specifically and individually, It incorporated by reference herein.

WE CLAIM

　By
mass%, C:
0.70
~ 1.20%, Si: 0.10 ~ 2.00%, Mn: 0.20
~ 1.00%, P: 0.030% or
less, S: 0.030 % or
less,
N:
0.0010 ~ 0.0100%,
Al: 0 ~ 0.100%, Cr: 0 ~ 2.00%,
V: 0 ~ 0.30%, B: 0 ~ 0.0050%, Ti:
0 ~ 0.050%, Nb: 0 ~ 0.050%, Zr: 0 ~ 0.050%, Ni: 0 ~ 2.00%, Cu: 0 ~ 1.00%, Sn: 0 ~ 0 % .50, Mg: 0 ~ 0.010%, Ca: 0 ~ 0.010%, and balance: having a chemical composition consisting of Fe and impurities, 　metallic structure, 95% or more pearlite structure at an area ratio becomes, 　the average aspect ratio R of the pearlite blocks measured at the surface of an axial section containing an axis of the steel wire is 2.0 or more Yes,

　And, when the diameter of the steel wire was as D, in axial cross-section containing the axis of the steel wire, the average (average aspect ratio of pearlite blocks measured at the surface layer) / (pearlite block measured at the position of 0.25D aspect ratio) is not less than 1.1,
　and a high strength steel wire tensile strength is at least 1800 MPa.
[Requested item 2]
　The chemical composition, in
mass%,
Al: 0.005 ~
0.100%, Cr: 0.01 ~ 2.00%, V: 0.01
~ 0.30%, B: 0.0001 ~ 0.
% 0050,
Ti: 0.001 ~
0.050%, Nb: 0.001 ~ 0.050%, Zr: 0.001 ~ 0.050%, and
Ni: 0.01 ~ 2.00%
of one or or high-strength steel wire according to claim 1 containing two or more.
[Requested item 3]
　The chemical content of Al in the composition, by mass%, 0.005 high strength steel wire according to claim 1 or claim 2 is an ultra to 0.100%.
[Requested item 4]
　High strength steel wire according to any one of claims 1 to 3 having a diameter of 2.5 mm ~ 9.5 mm.