JP2013204133A - Wire rod and steel wire using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire rod with a pearlitic structure as the main phase in which deterioration in delayed fracture resistance associated with the increase in strength is suppressed, and usable for a high strength PC steel wire, a wire rope or the like having delayed fracture resistance suited to the building standards.SOLUTION: A wire rod includes prescribed amounts of C, Si, Mn, N, Al, P and S, and the balance iron with inevitable impurities, and in which the Al content and the N content satisfy the relation in inequality (1): [Al]≤-2.1×10×[N]+0.255 (1) (wherein, [Al] and [N] denote the contents (mass%) of Al and N, respectively) and has a structure with pearlite as the main phase, and in which the content of AlN is ≥0.005%, and also, in the maximum value extreme value distribution of the diameter of AlN dexpressed as the geometric mean (ab)of the length a and the thickness b, the ratio of AlN in which dis 10 to 20 μm is ≥50% on the basis of numbers.

Description

  The present invention relates to a wire used for a PC steel wire, a wire rope, and the like and a steel wire using the same.

  In the field of civil engineering and construction, there is a strong need for high strength and light weight of concrete members, and as a method of strengthening concrete members, prestressed concrete (hereinafter referred to as PC) that applies compressive stress to concrete using steel wires is well known. It has been. The steel wire used for PC, that is, the PC steel wire, can contribute to higher strength and lighter weight of PC as the strength is higher. At present, as defined in JIS G3536, for example, seven strands of φ15.2 mm Thus, the one having a maximum test force of about 261 kN is known.

  In addition, various standards and recommended tests are defined for PC steel wires in addition to the JIS standard from the viewpoint of building safety and the like. In particular, when applying high strength PC steel wire, it is important to consider delayed fracture resistance. Delayed fracture means that when steel is used for a long time with stress applied, hydrogen that has penetrated into the steel concentrates on fine scratches on the surface of the steel, embrittles the structure around the scratch, and causes brittle fracture. It is a phenomenon that causes Since the PC steel wire is always used in a tensioned state, there is a possibility of causing delayed fracture, and strict standards are provided. In particular, it is well known that delayed fracture is likely to occur as the strength increases, and there is a demand for the development of a steel material that can suppress delayed fracture even when the strength is increased.

  For example, in Patent Document 1, in a PC steel wire having a carbon content of 0.6 to 1.1%, the plate-like cementite on the surface of the wire material is spheroidized by performing bluing at a temperature of 450 ° C. or higher after wire drawing, A technique for improving delayed fracture resistance is disclosed. However, Patent Document 1 has a problem that the strength of the steel wire decreases due to the spheroidization of the plate-like cementite, and there is a limit to the improvement of the strength.

  Patent Document 2 discloses a technique for improving delayed fracture resistance by forming a processed pearlite structure in which a compressive residual stress is applied to a surface layer portion in a PC steel wire having a carbon content of 0.6 to 1.3%. ing. However, Patent Document 2 is a technology for wire strength up to about 1600 MPa, and this technology sufficiently secures delayed fracture resistance due to hydrogen diffusion in a higher region where the wire strength is, for example, 2000 MPa or more. It seems difficult to do.

  Although it is not a PC steel wire, Patent Document 3 traps hydrogen by dispersing a Ti-based or Al-based nitride of 50 to 300 nm or more in a bearing steel having a carbon content of 0.65 to 1.20%. In addition, a technique for improving delayed fracture resistance in a tempered martensite structure is disclosed. However, since the diffusion behavior of hydrogen is different for different structures and the size and amount of precipitates suitable as trap sites are different, it is not possible to apply this technology as it is to PC steel wires whose main phase is a pearlite structure. Can not. Also, the manufacturing process of bearing steel that performs quenching and tempering after the wire drawing process and the manufacturing process of PC steel wire that performs the wire drawing process after the patenting process are greatly different. Different.

JP 2004-360005 A JP 2004-131797 A Japanese Patent No. 3591236

  The present invention provides a high-strength PC steel wire, wire rope, etc. that has a delayed fracture resistance property that conforms to building standards, in a wire rod whose main phase is a pearlite structure, suppressing a decrease in the delayed fracture resistance property with increasing strength. It aims at providing the wire which can be used.

The present inventors examined inclusions having a hydrogen trap effect in a wire having a pearlite structure as a main phase. As a result, the AlN content was ensured to be a predetermined amount or more, and AlN having a size of 10 to 20 μm was predetermined among AlN. We found that it is important to secure the above. That is, the wire rod of the present invention has C: 0.8 to 1.2% (meaning mass%, hereinafter the same for the component composition), Si: 0.1 to 2.0%, Mn: 0.1 to 0.1%. 2.0%, N: 0.002 to 0.010%, Al: 0.04 to 0.15%, P: 0.02% or less (including 0%), S: 0.02% or less (0 And the balance is iron and inevitable impurities, the amount of Al and the amount of N satisfy the relationship of the following formula (1),
[Al] ≦ −2.1 × 10 × [N] +0.255 (1)
(However, in the formula (1), [Al] and [N] are the contents (mass%) of Al and N, respectively.)
Maximum main phase of tissue with a pearlite, and the amount of AlN is 0.005% or more and the diameter d _GM of AlN represented by geometric mean (ab) ^1/2 of the length a and the thickness b in value extreme value distribution, the ratio of AlN d _GM is 10~20μm, characterized in that a number basis of 50% or more. The wire rod preferably has a solid solution N content of 0.003% or less.

  Further, the present invention further includes (a) Cr: 1.0% or less (excluding 0%), Ni: 1.0% or less (not including 0%), Co: 1.0% or less (0% At least one selected from the group consisting of Mo: 1.0% or less (not including 0%) and Cu: 0.5% or less (not including 0%), (b) B : Selected from the group consisting of 0.005% or less (not including 0%), Nb: 0.5% or less (not including 0%), and V: 0.5% or less (not including 0%) It is also preferable to contain at least one kind.

  The present invention also includes a steel wire obtained from the wire.

According to the present invention, the amount of Al and the amount of N are appropriately adjusted, and the total amount of AlN and AlN having a predetermined size (d _GM is 10 to 20 μm) are appropriately present. Wire can be provided. Moreover, in the preferable aspect of this invention, the twist characteristic of a steel wire can be improved by adjusting the amount of solute N below predetermined.

  As a result of studies by the present inventors, it is effective to secure a predetermined amount of AlN as a hydrogen trap site and a predetermined amount or more of AlN having a size of 10 to 20 μm in a wire having a pearlite structure as a main phase. I found out.

  Since the amount of AlN increases as the hydrogen trapping effect increases, it is determined to be 0.005% or more. The amount of AlN is preferably 0.006% or more, more preferably 0.007% or more (particularly 0.01% or more). The upper limit of the amount of AlN is not particularly limited, but is usually about 0.04%.

In the present invention, the maximum value extreme value distribution is used as an index for securing the number of AlN having a size of 10 to 20 μm. First, as the size of AlN, the geometric mean (ab) ^1/2 of the length a and the thickness b of AlN is used, and this is expressed as d _GM (μm). In the present invention, the length “a” of AlN means the length of AlN in the longitudinal direction of the wire, and the thickness “b” of AlN means the length of AlN in the direction perpendicular to the longitudinal direction of the wire.

d _GM The maximum extreme value distribution, to measure the maximum value d _GM (max) of d _GM of AlN present in a given area, which is repeated for multiple viewing, measured more d _GM (max) This means that statistical processing was performed on. In the present invention, in the extreme value distribution, the ratio of AlN having d _GM (max) of 10 to 20 μm is set to 50% or more on the number basis. When the d _GM is there are many AlN more than 20μm, the total number of AlN is reduced, the hydrogen trapping effect can not be sufficiently exhibited. Further, d _GM is less than 10 [mu] m AlN is less hydrogen trapping effect. Therefore, in the extreme value distribution, by setting the ratio of AlN having d _GM (max) of 10 to 20 μm to 50% or more based on the number, AlN effective for hydrogen trap can be sufficiently secured.

  In the present invention, the main phase being pearlite means that 95% by area or more of the structure is a pearlite structure. The area ratio of the pearlite structure is preferably 97% or more, and more preferably 100%.

  Next, the chemical components of the wire of the present invention will be described.

C: 0.8 to 1.2%
C is an element effective for increasing the strength, and the strength of the wire rod and the steel wire after cold working is improved as the C content increases. Therefore, the C amount is set to 0.8% or more. The amount of C is preferably 0.85% or more, more preferably 0.90% or more. However, if the amount of C is excessive, aging embrittlement is caused during cold drawing, so that the toughness of the steel wire is lowered, and there is a problem that cracks occur during wire processing. Therefore, the C amount is set to 1.2% or less. The amount of C is preferably 1.1% or less, more preferably 1.05% or less.

Si: 0.1 to 2.0%
Si has an action of a deoxidizer, but is an effective element because it has an action of improving the strength of the wire and an action of improving relaxation characteristics. In addition, when hot dip galvanization is used, Si also has an action of suppressing strength reduction that occurs during plating. In order to exhibit these effects effectively, the Si amount was determined to be 0.1% or more. The amount of Si is preferably 0.2% or more, and more preferably 0.4% or more. On the other hand, when the amount of Si becomes excessive, the cold drawing property is deteriorated and the disconnection rate is increased. Therefore, the Si amount is set to 2.0% or less. The amount of Si is preferably 1.8% or less, and more preferably 1.5% or less.

Mn: 0.1 to 2.0%
Mn has a deoxidizing action similar to Si, but has an effect of increasing the toughness and ductility of steel by fixing S in steel as MnS. In order to effectively exhibit these actions, the amount of Mn is set to 0.1% or more. The amount of Mn is preferably 0.15% or more, more preferably 0.2% or more. However, Mn is an element that easily segregates, and if added excessively, the hardenability of the Mn segregated part is excessively increased, and a supercooled structure such as martensite may be generated. Therefore, the amount of Mn is set to 2.0% or less. The amount of Mn is preferably 1.8% or less, more preferably 1.5% or less.

N: 0.002 to 0.010%
N is an important element for forming AlN, which is a feature of the present invention, and needs to be contained in an amount of 0.002% or more. The amount of N is preferably 0.0025% or more, more preferably 0.0030% or more (particularly 0.0040% or more). However, N dissolves in steel as an interstitial element in the same manner as C and causes embrittlement due to strain aging. Therefore, when added excessively, the twisting characteristic is reduced due to an increase in the amount of dissolved N. Therefore, the N amount is determined to be 0.010% or less. The amount of N is preferably 0.0090% or less, and more preferably 0.0080% or less.

Solid solution N amount: 0.003% or less As described above, since the solid solution N causes a decrease in twisting characteristics, the smaller the amount, the better. Therefore, the amount of solute N is preferably 0.003% or less. The amount of solute N is more preferably 0.002% or less, and further preferably 0.001% or less. The amount of solute N can be controlled by adjusting the amount of nitride-forming elements such as Al, B, and Nb and the amount of N.

Al: 0.04-0.15% and [Al] ≦ −2.1 × 10 × [N] +0.255
In addition to the deoxidizing action, Al is an important element for bonding with N to form AlN and trapping hydrogen to improve delayed fracture resistance in the present invention. The AlN also has an effect of refining crystal grains by a pinning effect. In order to exhibit such an effect effectively, the amount of Al is made 0.04% or more. The amount of Al is preferably 0.05% or more, more preferably 0.055% or more. On the other hand, when the amount of Al becomes excessive, particularly when the amount of Al is excessive in a region where the amount of N is large, coarse AlN is generated, and the hydrogen trap effect by AlN is reduced. Therefore, the upper limit of the Al amount is set to 0.15% and satisfies the relationship of the following formula (1).
[Al] ≦ −2.1 × 10 × [N] +0.255 (1)
In the above formula (1), [Al] and [N] represent the contents (mass%) of Al and N, respectively. Expression (1) is an expression derived from a number of experimental examples in which the delayed fracture resistance characteristics when the N content and the Al content are changed in various ways. When the Al amount satisfies the relationship of the formula (1), the upper limit of the Al amount is more strictly controlled in a region where the N amount is large, and formation of coarse AlN can be suppressed. The upper limit of the amount of Al is preferably 0.14% or less, and more preferably 0.12% or less.

P: 0.02% or less (including 0%)
P segregates at the prior austenite grain boundaries, embrittles the grain boundaries, and lowers fatigue characteristics. Therefore, the smaller the content, the better. Therefore, the P content is 0.02% or less. The amount of P is preferably 0.015% or less, more preferably 0.010% or less.

S: 0.02% or less (including 0%)
S, like P, segregates at the prior austenite grain boundaries, embrittles the grain boundaries, and lowers fatigue characteristics. Therefore, the smaller the content, the better. Therefore, the S amount is 0.02% or less. The amount of S is preferably 0.015% or less, more preferably 0.010% or less.

  The basic components of the wire of the present invention are as described above, and the balance is substantially iron. However, it is naturally allowed that inevitable impurities brought into the steel depending on the situation of raw materials, materials, manufacturing equipment, etc. are contained in the steel. Furthermore, the wire rod of the present invention may further contain the following elements as necessary in order to further improve properties such as strength, toughness and ductility.

Cr: 1.0% or less (not including 0%), Ni: 1.0% or less (not including 0%),
Selected from the group consisting of Co: 1.0% or less (excluding 0%), Mo: 1.0% or less (not including 0%), and Cu: 0.5% or less (not including 0%) At least one kind of Cr that has a function of reducing the lamella spacing of pearlite and increasing the strength and toughness of the wire. In order to effectively exhibit such action, the Cr content is preferably 0.05% or more. The amount of Cr is more preferably 0.1% or more, and further preferably 0.2% or more. On the other hand, if the amount of Cr becomes excessive, the hardenability is improved and the risk of generating a supercooled structure during hot rolling increases, so the Cr amount is preferably 1.0% or less. The amount of Cr is more preferably 0.6% or less, and further preferably 0.5% or less.

  Ni is an element that increases the toughness of the steel wire after wire drawing. In order to effectively exhibit such an action, the Ni content is preferably 0.05% or more, more preferably 0.1% or more, and further preferably 0.2% or more. However, even if Ni is added excessively, the effect is saturated and it is economically wasteful. Therefore, the Ni content is preferably 1.0% or less, more preferably 0.7% or less, and still more preferably 0.6% or less.

  Co has the effect of reducing pro-eutectoid cementite (especially when the amount of C is high) and making it easy to control the structure to a uniform pearlite structure. In order to effectively exhibit this action, the Co content is preferably 0.05% or more, more preferably 0.1% or more, and further preferably 0.2% or more. However, even if Co is added excessively, the effect is saturated and it is economically wasteful. Therefore, the Co content is preferably 1.0% or less, more preferably 0.8% or less, and still more preferably 0.6% or less.

  Mo is an element that improves the corrosion resistance of the steel wire. In order to effectively exhibit such an action, the Mo amount is preferably 0.05% or more, more preferably 0.1% or more. However, when the amount of Mo becomes excessive, a supercooled structure is likely to occur during hot rolling, and ductility also deteriorates. Therefore, the Mo amount is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.3% or less.

  Cu is an element that improves the corrosion resistance of the steel wire. In order to effectively exhibit such action, the amount of Cu is preferably 0.05% or more, more preferably 0.08% or more. On the other hand, when the amount of Cu becomes excessive, it reacts with S to segregate CuS at the grain boundary part and generate soot in the wire manufacturing process. In order to avoid such influence, the amount of Cu is preferably 0.5% or less, more preferably 0.2% or less, and further preferably 0.18% or less.

B: selected from the group consisting of 0.005% or less (not including 0%), Nb: 0.5% or less (not including 0%), and V: 0.5% or less (not including 0%) At least one type B has an effect of preventing the formation of pro-eutectoid ferrite and pro-eutectoid cementite and making it easy to control the structure to a uniform pearlite structure. Moreover, by fixing the excess solid solution N after precipitation of AlN with BN, the strain aging due to the solid solution N can be suppressed and the toughness can be improved, and the solid solution B itself also has the effect of improving the toughness. In order to exhibit such an action effectively, the amount of B is preferably 0.0003% or more, more preferably 0.0005% or more, and further preferably 0.001% or more. On the other hand, when the amount of B becomes excessive, an Fe—B compound (for example, FeB ₂ ) that is a compound with Fe precipitates and causes cracking during hot rolling, so the amount of B is preferably 0.005% or less. The amount of B is more preferably 0.004% or less, and still more preferably 0.003% or less.

  Nb forms an excessive solid solution N and nitride after AlN is precipitated, contributes to refinement of crystal grains, and also has an effect of suppressing aging embrittlement by fixing the solid solution N. In order to effectively exhibit such an action, the Nb content is preferably 0.01% or more, more preferably 0.03% or more, and still more preferably 0.05% or more. However, even if the Nb amount is excessive, the effect is saturated and economically useless, so the Nb amount is preferably 0.5% or less, more preferably 0.4% or less, and still more preferably 0.2%. % Or less.

  V forms an excessive solid solution N and nitride after precipitation of AlN, like Nb, and contributes to refinement of crystal grains, and also has an effect of suppressing aging embrittlement by fixing the solid solution N. In order to effectively exhibit such an action, the V amount is preferably 0.01% or more, more preferably 0.02% or more, and further preferably 0.03% or more. However, even if the amount of V is excessive, the effect is saturated and economically useless, so the amount of V is preferably 0.5% or less, more preferably 0.4% or less, and still more preferably 0.2%. % Or less.

Wire rods (meaning those before cold drawing) are usually obtained by melting, split-rolling, and hot-rolling (and patenting as necessary) steel with appropriately controlled chemical components. can be produced, (in maximum extreme value distribution d _GM of AlN, the ratio of AlN d _GM is 10~20μm is, more than 50% on a particle number basis) the amount and particle size distribution of the AlN in the wire rod of the present invention the appropriate Therefore, it is important to appropriately control the heat history in the temperature range in which AlN precipitates, while appropriately controlling the contents of Al and N within the above-described range.

  AlN starts to precipitate at about 1300 ° C. or less in steel, and the precipitation amount increases as the temperature decreases, and it completely precipitates at about 900 ° C. Therefore, it is necessary to appropriately control the conditions of the block rolling and the hot rolling, in which the steel is exposed to these temperature ranges in the production process and greatly affects the precipitation behavior of AlN. Usually, since the cooling rate after the block rolling is slow, the precipitated AlN tends to be coarsened. On the other hand, the cooling rate after the hot rolling is relatively fast, so that the precipitated AlN can be made fine.

  Specifically, the heating temperature in the ingot rolling is set to 1230 to 1280 ° C, and the cooling rate is set to 0.2 ° C / second or more. Precipitation and coarsening of AlN can be prevented by heating at a high temperature during block rolling and increasing the cooling rate. Therefore, the batch rolling temperature is preferably 1230 ° C or higher, more preferably 1240 ° C or higher. On the other hand, if the partial rolling temperature is too high, firing cracks occur, so the upper limit is preferably 1280 ° C. or less, more preferably 1270 ° C. or less. The cooling rate is preferably 0.2 ° C./second or more, more preferably 0.4 ° C./second or more, and further preferably 0.5 ° C./second or more. Although the upper limit of a cooling rate is not specifically limited, For example, it is 1.5 degrees C / sec or less (preferably 1.2 degrees C / sec or less).

Furthermore, the billet obtained by the partial rolling is hot-rolled, then cooled to 850 to 950 ° C. by water cooling or the like, and placed in a coil shape. By the lower the placing置温of the coiled wire described above, fine (d _GM is 10 to 20 [mu] m) can deposit an AlN. Therefore, the mounting temperature is preferably 950 ° C. or lower, more preferably 940 ° C. or lower, and further preferably 920 ° C. or lower. On the other hand, if the mounting temperature is too low, many very fine AlNs that do not contribute to the hydrogen trap are deposited. Therefore, the mounting temperature is preferably 850 ° C. or higher, more preferably 870 ° C. or higher, and further preferably 890 ° C. or higher.

  In addition, if the amount and distribution of AlN cannot be controlled properly because at least a part of the conditions of the above-described block rolling and hot rolling are removed, a patent in the appropriate temperature range is obtained after hot rolling. It is also effective to perform the processing. The reheating temperature during the patenting treatment is preferably 880 to 1000 ° C, and the patenting temperature is preferably 530 to 620 ° C. When the amount of AlN after hot rolling is small, the amount of precipitation can be increased by setting the reheating temperature lower (for example, about 880 to 940 ° C.). In addition, when AlN after hot rolling is coarsened, the reheating temperature is set high (for example, 940 to 1000 ° C.), and the coarsened AlN is once dissolved in steel and then precipitated again. Just do it.

  Since the wire rod of the present invention sufficiently secures AlN that can effectively act as a hydrogen trap site, a steel wire such as a wire rope or PC steel wire using this has excellent delayed fracture resistance and is useful. It is. The present invention also includes such a steel wire.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and can of course be implemented with appropriate modifications within a range that can be adapted to the above-described gist. Included in the range.

  Steel ingots having the components shown in Table 1 were subjected to split rolling and hot rolling under the conditions shown in Table 2 to process into wire coils, and in some cases, patenting was further performed. The total amount of AlN was evaluated from the extraction residue measurement of the collected samples, and the distribution state of AlN was evaluated from observation of the cross-sectional area.

1. Measurement of the total amount of AlN and the amount of dissolved N In extraction residue measurement, electrolytic extraction residue measurement using a 10% acetylacetone solution is performed, a mesh of 0.1 μm is used, and the amount of AlN in the residue is determined by the bromester method. It was measured. Moreover, the amount of nitrogen compounds including AlN was measured using the indophenol absorption spectrophotometry method, and the amount of dissolved N was determined by subtracting from the total amount of N in the steel. The sample weight used for the bromoester method was 3 g, and the sample weight used for the absorption spectroscopy was 0.5 g.

2. Measurement of AlN distribution state In this measurement, the total area (two locations) from the surface layer to D / 4 (D is the diameter of the wire) is 140 mm ^{2 in the} cross section including the axis of the wire and parallel to the longitudinal direction. The sample is cut out so that the length L of the sample is determined so that L × D / 4 + L × D / 4 = L × D / 2 is 140 mm ^2, and the cross section is observed according to JIS G0555 The maximum AlN size was measured in the field of view and this was done for any 20 fields of view. In the measurement, the D-based and DS-based inclusions defined in JIS G0551 are regarded as AlN, and the size of AlN is the geometric mean (ab) ¹ of the length (a) and thickness (b) of AlN. ^{/ 2} was adopted.

  Next, the obtained wire coil is drawn to produce a steel wire, and the tensile strength (strand strength) of the steel wire is measured. Delayed fracture characteristics and twist characteristics were measured.

3. Measurement of tensile strength (strand strength) of steel wire The tensile strength of the steel wire was measured according to JIS Z2241.

4). Measurement of Rope Strength Rope strength was measured according to JIS G3536 by measuring the maximum test force of a tensile test.

5. Measurement of delayed fracture resistance Delayed fracture characteristics are based on the description in Reference 1 (fib bullten 30: Acceptance of stay cable systems using prestressing steels, January.2005). Under a load of u (0.8 p.u means 80% of the breaking load), it was immersed in an ammonium thiocyanate solution at 20% by mass and 50 ° C., and the time until breaking of 12 samples was measured. A case where the minimum breaking time was 2 hours or more and the median breaking time was 5 hours or more was regarded as acceptable.

6). Measurement of twisting characteristics The twisting characteristics were determined to be acceptable when the twisting value of 3 times or more was achieved based on the FKK HTS-26 standard of the FKK Frenessy method.

  Test No. 1-3, 5, 9, 10, 13-20, and 28, the component, the structure, the amount of AlN, and the distribution state of AlN all satisfied the requirements of the present invention. 2100 MPa or higher), and satisfying the high wire strength satisfying the standard specified in JIS G3536, the delayed fracture resistance was also good, and the wire was obtained with high strength that can withstand practical use. Furthermore, since these test examples also satisfy the requirements for the solid solution N amount, which is a preferable requirement, they are excellent in twisting characteristics. For example, test No. Nos. 15 to 18 are examples in which the amount of solid solution N was particularly reduced among the inventive examples, and as a result, the twisting characteristics were also very excellent, while the test number having the largest amount of solid solution N in the invention examples. . No. 9 had the smallest twist value in the invention examples.

  In addition, Test No. For 10, 15, and 17, the hot rolling placement temperature deviates from the preferable requirement, but since appropriate patenting treatment is performed thereafter, a wire rod satisfying the requirements of the present invention is obtained.

  On the other hand, test no. 4, 6-8, 11, 12, 21-27 are examples in which any of the requirements of the present invention was not satisfied.

  No. No. 4 was the same because No. 4 was heated at the time of ingot rolling. No. 6 had a slow cooling rate after the partial rolling, so that coarse AlN precipitated in all cases, the AlN particle size distribution did not satisfy the requirements of the present invention, and the delayed fracture resistance deteriorated.

  No. No. 7, the mounting temperature after hot rolling is high, precipitation of AlN during mounting becomes insufficient, the amount of AlN and the particle size distribution of AlN do not satisfy the requirements of the present invention, and delayed fracture resistance Deteriorated. No. In No. 8, since the mounting temperature after hot rolling was low and AlN was excessively refined, the particle size distribution of AlN did not satisfy the requirements of the present invention, and the delayed fracture resistance deteriorated.

  No. No. 11 caused a burning crack because the heating temperature at the time of the block rolling was too high.

  No. In No. 12, since the patenting treatment temperature was too low, a mixed structure of bainite and pearlite was formed, and the drawability was lowered. In addition, the fraction of bainite was about 20 area%.

  No. No. 21 is an example in which the amount of C was large, aging embrittlement during wire drawing was remarkable, and wire breakage occurred frequently. No. No. 22 is an example in which the amount of C was small, and the strength of the type B strand specified in JIS G3536 could not be achieved.

  No. No. 23 is an example in which the amount of Al was small, and since the amount of AlN could not be secured sufficiently, the delayed fracture resistance was deteriorated. No. No. 24 is an example in which the N content is within the range of the present invention, but less, and the Al content is large. A large amount of Al-based oxide was generated, and breakage during wire drawing occurred frequently.

  No. No. 25 was an example in which the amount of N was small, and a sufficient amount of AlN could not be secured, and the particle size distribution of AlN could not satisfy the requirements of the present invention, and the delayed fracture resistance was deteriorated. No. No. 26 is an example in which the amount of N was large, and the delayed fracture resistance deteriorated because coarse AlN precipitated. No. In No. 26, since the amount of solute N does not satisfy the preferable requirements of the present invention, the twist value is the smallest compared to other test examples.

  No. No. 27 is an example in which the amount of N is larger than the range specified in the present invention, and the amount of Al does not satisfy the requirement of formula (1), and is large. Delayed fracture characteristics deteriorated.

Claims (5)

C: 0.8 to 1.2% (meaning mass%, hereinafter the same for the component composition),
Si: 0.1 to 2.0%,
Mn: 0.1 to 2.0%,
N: 0.002 to 0.010%,
Al: 0.04 to 0.15%,
P: 0.02% or less (including 0%),
S: 0.02% or less (including 0%), the balance being iron and inevitable impurities,
The amount of Al and the amount of N satisfy the relationship of the following formula (1),
[Al] ≦ −2.1 × 10 × [N] +0.255 (1)
(However, in the formula (1), [Al] and [N] are the contents (mass%) of Al and N, respectively.)
The main phase of the organization is perlite,
And the amount of AlN is 0.005% or more and, in the maximum extreme value distribution in the radial d _GM of AlN represented by geometric mean (ab) ^1/2 of the length a and the thickness b, d _GM 10 A wire rod characterized in that the proportion of AlN of ˜20 μm is 50% or more based on the number.   The wire according to claim 1, wherein the solid solution N amount is 0.003% or less. Furthermore,
Cr: 1.0% or less (excluding 0%),
Ni: 1.0% or less (excluding 0%),
Co: 1.0% or less (excluding 0%),
3. The composition according to claim 1, comprising at least one selected from the group consisting of Mo: 1.0% or less (not including 0%) and Cu: 0.5% or less (not including 0%). Wire rod. Furthermore,
B: 0.005% or less (excluding 0%),
Nb: 0.5% or less (not including 0%), and V: 0.5% or less (not including 0%), at least one selected from the group consisting of any one of claims 1 to 3 Crab wire.   The steel wire obtained from the wire in any one of Claims 1-4.