ES2743735T3 - Wire rod and steel cable using the same - Google Patents

Abstract

A wire rod consisting of: by mass percentage, hereinafter referred to in this document as the same for chemical composition; C in a content of 0.8% to 1.2%, Si in a content of 0.1% to 2.0%; Mn in a content of 0.1% to 2.0%; N in a content of 0.002% to 0.010%; Al in a content of 0.04% to 0.15%; P in a content of 0.02% or less; and S in a content of 0.02% or less; and optionally at least one element selected from the group consisting of: Cr in a content of 1.0% or less, excluding 0%; Ni in a content of 1.0% or less, excluding 0%; Co in a content of 1.0% or less, excluding 0%; Mo in a content of 1.0% or less, excluding 0%; and Cu in a content of 0.5% or less, excluding 0%; and optionally at least one element selected from the group consisting of: B in a content of 0.005% or less, excluding 0%; Nb in a content of 0.5% or less, excluding 0%; and V in a content of 0.5% or less, excluding 0%; the remainder being iron and unavoidable impurities; the Al content and the N content satisfying a condition specified by Expression (1) given as follows: [Al] <= -2.1 × 10 × [N] + 0.255 (1) where [Al] and [N] are the mass percent contents of Al and N, respectively; the wire rod having a microstructure comprising 95 percent by area or more of pearlite; the wire rod having an AlN content of 0.005% or more; and 35 having a percentage of AlN particles a dGM diameter of 10 to 20 μm being 50% or more in percentage number in a distribution of extreme values of maximum values of the dGM diameters of AlN particles, wherein the dGM diameter is represented by a geometric mean (ab)1/2 of a length "a" and a thickness "b" of an AlN particle, wherein the term "length "a"" of an AlN particle refers to the length (dimension) of the AlN particle in the longitudinal direction of the wire rod; The term "thickness "b" of the AlN particle refers to a dimension of the AlN particle in a direction perpendicular to the longitudinal direction of the wire rod, and the size of an AlN particle that has the maximum size in a field of view of observation in the cross section is measured in accordance with JIS G0555, wherein the measurement is made in twenty arbitrary fields of view and wherein Group D and Group DS inclusions as specified in JIS G0551 are considered to be AlN particles in the measurement.

Description

DESCRIPTION

Wire rod and steel cable using the same

Technical field

The present invention relates to a wire rod and a steel cable using the same each of which is used for or as prestressed steel wires and wire ropes.

Prior art

There are strong demands for concrete members to have greater strength and lighter weight in the areas of civil engineering and construction. Prestressed concrete (hereinafter also referred to as "PC") is well known as a way to strengthen said concrete members. In prestressed concrete, the compression stress is applied to the concrete material through the use of steel wires. Such a PC steel cable, namely a prestressing steel cable (PC steel cable), when it has a greater force, can contribute more satisfactorily to a higher strength and a lighter PC weight. A prestressing chain is now known which includes 7 wires with a diameter of 15.2 mm and having a maximum force of approximately 261 kN, as prescribed in the Japanese Industrial Standard (JIS) G3536. In addition to Japanese industrial standards, several standards (specifications) and recommended tests for prestressing steel wires from the point of view of architectural safety are prescribed. In particular, it is important to take into account delayed fracture resistance when applying a high-strength prestressing steel cable. Delayed fracture is a phenomenon where, when a steel is used for a long time under the application of an effort, hydrogen migrated to the steel typically accumulates in a fine fault on the surface of the steel, causing a microstructure around the defect to become fragile and, therefore, induces a fragile fracture. Prestressing steel wires are used while they are always strained and can possibly undergo a delayed fracture. To avoid this, strict rules about them are prescribed. In particular, it is well known that prestressing steel wires become more susceptible to delayed fracture with increasing resistance. Therefore, demands are made to develop steels that may suffer less delayed fractures even when they have greater resistance.

Typically, Patent Bibliography 1 discloses a technique for improving the delayed fracture resistance of a prestressing steel cable having a carbon content of 0.6% to 1.1%. In accordance with the technique, a wire rod after drawing is subjected to a bluish at a temperature of 450 ° C or higher to spheroidize the plate-like cementite to thereby improve delayed fracture resistance. The technique in Patent Bibliography 1, however, causes the steel cable to have a low resistance due to the spheroidization of the plate type cementite, therefore it has limitations in the improvement of the resistance and, disadvantageously, it does not It helps the steel cable have a wire resistance of 2000 MPa or more.

Patent Bibliography 2 discloses a technique for improving the delayed fracture resistance of a prestressing steel cable having a carbon content of 0.6% to 1.3%. The improvement is achieved by imparting a residual compression stress to a surface layer of the steel cable and thus forming a deformed perlite in the surface layer. The technique in Patent Bibliography 2, however, is applied to prestressing steel wires that have a wire strength of up to about 1600 MPa and probably cannot sufficiently guarantee the delayed fracture resistance caused by hydrogen diffusion to higher wire resistors of typically 2000 MPa or more.

Patent Bibliography 3 describes a technique to improve delayed fracture resistance in a tempered martensite phase of a non-prestressed steel cable, but a bearing steel with a carbon content of 0.65% to 1.20% . The improvement is achieved by dispersing typically nitride particles containing Ti or Al having a particle size of 50 to 300 nm in a predetermined amount or greater to trap hydrogen. However, hydrogen behaves differently in different microstructures and dimensions, quantities and other precipitate factors that act as appropriate capture sites also differ in different microstructures. This prevents the application of the technique in Patent Bibliography 3 typically to a prestressing steel cable without modification, where the prestressing steel cable includes a perlite as the main phase. A manufacturing process for such a steel bearing performs a quench-quench treatment after wire drawing; while a manufacturing process for a prestressing steel cable performs wire drawing after a patented treatment. In this way, the two manufacturing processes differ significantly from each other and employ different procedures to control the precipitation typically of nitrides.

EP 1897964 A1 discloses a high strength wire rod that stands out in the drawing performance and a process to produce it.

Appointment List

Patent Bibliography

Patent Bibliography 1: Japanese Patent Application Publication Unexamined (JP-A) No. 2004-360005 Patent Bibliography 2: JP-A Document No. 2004-131797

Patent Bibliography 3: Japanese Patent No. 3591236

Summary of the invention

Technical problem

An object of the present invention is to provide a wire rod that includes a perlite as the main phase, where the wire rod suffers less reduction in delayed fracture resistance even when it has high strength and can typically be used as a high prestressing steel cable. resistance and a wire cable that has a fracture resistance so late that it complies with construction regulations.

Solution to the problem

The invention is defined in the claims.

The present inventors conducted investigations on inclusions that have a hydrogen trap effect on a wire rod that includes a perlite as the main phase. As a result, they have discovered that it is important to ensure that the AlN particles in an amount at a predetermined or higher level and ensure, of such AlN particles, AlN particles having a size of 10 to 20 pm in an amount at a level Default or higher. Specifically, the present invention provides, in one aspect, a wire rod that includes C in a content of 0.8% to 1.2% (in mass percentage, hereinafter the same for the chemical composition) ; If in a content of 0.1% to 2.0%; Mn in a content of 0.1% to 2.0%; N in a content of 0.002% to 0.010%; Al in a content of 0.04% to 0.15%; P in a content of 0.02% or less (including 0%); and S in a content of 0.02% or less (including 0%), the rest being iron and unavoidable impurities, in which the content of Al and the content of N meet a condition specified by the given Expression (1) as follows:

[Al] <-2.1 x 10 x [N] 0.255 (1)

where [Al] and [N] are contained (in mass percentage) of Al and N, respectively; the wire rod has a microstructure that includes 95 percent in area or more than one perlite; the wire rod has an AlN content of 0.005% or more; and a percentage of AlN particles having a dGM diameter of 10 to 20 pm is 50% or more in percentage in number in a distribution of extreme values of maximum values of the dGM diameters of AlN particles, where the dGM diameter is represented by a geometric mean (ab) 1/2 of a length "a" and a thickness "b" of a particle of AlN. In a preferred embodiment, the wire rod may have a solute nitrogen content of 0.003% or less.

In the present invention, the wire rod may further contain any of (a) at least one element selected from the group consisting of Cr in a content of 1.0% or less (excluding 0%), nor in a content of 1, 0% or less (excluding 0%), Co in a content of 1.0% or less (excluding 0%), Mo in a content of 1.0% or less (excluding 0%) and Cu in a content of 0.5% or less (excluding 0%); and (b) at least one element selected from the group consisting of B in a content of 0.005% or less (excluding 0%), Nb in a content of 0.5% or less (excluding 0%) and V in a content of 0.5% or less (excluding 0%). The present invention also includes a steel cable obtained from the wire rod.

Advantageous effects of the invention

The present invention adjusts the contents of Al and N appropriately and controls the total content of AlN particles and the content of AlN particles having a predetermined size (dGM from 10 to 20 pm) in an appropriate manner. Therefore the present invention can provide a wire rod that has excellent resistance to delayed fracture. The present invention, in the preferred embodiment, adjusts the nitrogen content of the solute to a predetermined or higher level and, therefore, can help the steel cable to have better torsion properties.

Description of the realizations

After intensive research, the present inventors have discovered that, in a wire rod that includes a perlite as the main phase, it is effective to ensure AlN (particles) in a predetermined content as a hydrogen trap site and to ensure that AlN particles have a size from 10 to 20 pm in a content at a predetermined level or higher.

The AlN content is specified at 0.005 % or more, because the wire rod offers an increasing hydrogen trap effect with an increasing AlN content. The AlN content is preferably 0.006% or more, more preferably 0.007% or more and in particular preferably 0.01% or more. Although not critical, the upper limit of the AlN content is generally about 0.04%.

A distribution of extreme values of maximum values is used herein as an index to ensure that the AlN particles are sized from 10 to 20 pm in a number at a predetermined level or greater. Initially, a geometric mean (ab) 1/2 of the length "a" and the thickness "b" of an AlN particle is used as a size of the AlN particle and is indicated as dGM (pm). As used herein, the term "length" to "" of an AlN particle refers to the length (dimension) of the AlN particle in the longitudinal direction of the wire rod; and the term "thickness" b "of the AlN particle refers to a dimension of the AlN particle in a direction perpendicular to the longitudinal direction of the wire rod.

The phrase "distribution of extreme values of maximum values of dGM" refers to a distribution determined by measuring a maximum dGM (max) between the dGM values of AlN particles present in a predetermined area; repeating this procedure in two or more fields of view; and subjecting the two or more measured dGM (max) values to statistical processing. The percentage of AlN particles having a dGM (max) of 10 to 20 pm is 50% or more (in percentage by number) in the distribution of the extreme value in the embodiment of the present invention. If AlN particles having a dGM size greater than 20 pm are present in a large percentage, the AlN particles are present in a smaller total number and may not exhibit the hydrogen trap effect sufficiently. In addition, such AlN particles having a dGM size of less than 10 pm exhibit a lower hydrogen trap effect. Therefore, the AlN particles that are effective for the hydrogen trap can be sufficiently secured by controlling the AlN particles having a dGM (max) of 10 to 20 pm to be present in a numerical percentage of 50% or more in The extreme value distribution.

The wire rod according to the embodiment of the present invention includes a perlite that occupies 95 percent in area or more of the main phase. The percentage of perlite area is preferably 97% or more, and more preferably 100%.

Next, the chemical compositions of the wire rod according to the embodiment of the present invention will be illustrated below.

Carbon content (C): 0.8% to 1.2%

The element carbon (C) effectively contributes to greater resistance. the wire rod and a steel cable after cold treatment have higher resistance with an increasing carbon content. Therefore, the carbon content is specified at 0.8% or more. The carbon content is preferably 0.85% or more and more preferably 0.90% or more. However, carbon, if present in an excessively high content, can cause frailty due to aging during cold drawing, thus causing the steel cable to have a lower toughness and, disadvantageously, invites cracking during stranded. To avoid this, the carbon content is specified at 1.2% or less. The carbon content is preferably 1.1% or less and more preferably 1.05% or less.

Silicon content (Si): from 0.1% to 2.0%

The silicon element (Si) not only acts as a deoxidant, but also has effective actions to help the wire rod to have greater resistance and offer better relaxation properties. When hot-dip galvanized is applied to the wire rod, the silicon element also offers a suppressing action to reduce the resistance that occurs when galvanizing. To exhibit these actions effectively, the Si content is specified at 0.1% or more. The Si content is preferably 0.2% or more and more preferably 0.4% or more. On the other hand, Yes, if it is present in excessively high content, it can cause the wire rod to have a lower stretching capacity of the cold wire and suffer a greater breaking ratio. To avoid this, the content of Si is specified at 2.0% or less. The Si content is preferably 1.8% or less and more preferably 1.5% or less.

Manganese content (Mn): from 0.1% to 2.0%

The manganese element (Mn) not only acts as a deoxidant as with Si, but also has a particular action of fixing sulfur (S) in steel as MnS and helping the steel to have a better toughness and ductility. To exhibit these actions effectively, the Mn content is specified at 0.1% or more. The content of Mn is preferably 0.15% or more, and more preferably 0.2% or more. However, the manganese element is easily segregated and, if added in excess, can cause the formation of supercooled phases such as martensite, due to the excessively high hardening capacity of a region where the Mn is segregated. To avoid this, the content of Mn is specified at 2.0% or less. The content of Mn is preferably 1.8% or less and more preferably 1.5% or less.

Nitrogen content (N): from 0.002 % to 0.010 %

The nitrogen element (N) is important for the formation of AlN which presents the embodiment of the present invention and is contained in a content of 0.002% or more. The nitrogen content is preferably 0.0025% or more, more preferably 0.0030% or more and in particular preferably 0.0040% or more. However, nitrogen, if added in excess, can cause the wire rod to have lower torsion properties due to a higher nitrogen content in solute. This is because nitrogen dissolves as an interstitial element in steel as with carbon and causes fragility due to deformation aging. To avoid this, the nitrogen content is specified at 0.010% or less. The nitrogen content is preferably 0.0090% or less and more preferably 0.0080% or less.

Nitrogen content in solute: 0.003% or less

Nitrogen in solute causes lower torsion properties and is preferably minimized in quantity. Therefore, the nitrogen content in solute is preferably 0.003% or less, more preferably 0.002% or less and also preferably 0.001% or less. The nitrogen content in solute can typically be controlled by adjusting the contents of nitride forming elements such as Al, B and Nb; and the nitrogen content.

Aluminum content (Al): 0.04% to 0.15% and [Al] <-2.1 * 10 * [N] 0.255

The aluminum element (Al) acts as a deoxidant and is important herein, because aluminum combines with nitrogen to form AlN, thus trapping hydrogen and helping the wire rod to have a better resistance to delayed fracture. . AlN aluminum nitride also effectively contributes to grain refinement through a fixing effect. To exhibit these effects effectively, the Al content is specified at 0.04% or more. The Al content is preferably 0.05% or more, and more preferably 0.055% or more. On the other hand, Al, if present in an excessively high content, particularly at a high nitrogen content range, can form thick AlN particles and this can reduce the AlN hydrogen trap effect. To avoid this, the Al content is specified at 0.15% in terms of its upper limit and is adapted to meet a condition specified by Expression (1) given as follows.

[Forum math one]

[Al] <-2.1 * 10 * [N] 0.255 (1)

In the expression (1), [Al] and [N] denote contents (in mass percentage) of Al and N, respectively. Expression (1) is an expression that has been derived from many experimental examples in which delayed fracture resistance to different nitrogen and aluminum contents was examined. When the Al content meets the condition specified by Expression (1), the upper limit of the Al content is more strictly controlled in a range of high nitrogen contents to suppress the formation of thick AlN particles. The Al content is preferably 0.14% or less and more preferably 0.12% or less in terms of its upper limit.

Phosphorus content (P): 0.02% or less

The phosphorus element (P) is segregated in a previous austenite grain limit, makes the grain limit fragile and causes the wire rod to have lower fatigue properties. To avoid this, the phosphorus content is preferably minimized and 0.02% or less specified herein. The phosphorus content is preferably 0.015% or less and more preferably 0.010% or less.

Sulfur content (S): 0.02% or less

The sulfur element (S) is segregated into an anterior austenite grain limit, makes the grain limit fragile and causes the wire rod to have lower fatigue properties, as with phosphorus. To avoid this, the sulfur content is preferably minimized and 0.02% or less specified herein. The sulfur content is preferably 0.015% or less and more preferably 0.010% or less.

The wire rod according to the embodiment of the present invention has a basic chemical composition as before, the remainder being substantially iron. However, unavoidable impurities are naturally acceptable, where unavoidable impurities are introduced into steel under conditions typically of raw materials, installation materials and manufacturing facilities and are contained in steel. In accordance with the need to have better properties such as strength, hardness and ductility, the wire rod according to the embodiment of the present invention may further contain any of the elements as follows.

At least one element selected from the group consisting of Cr in a content of 1.0% or less (excluding 0%), Nor in a content of 1.0% or less (excluding 0%), Co in a content 1.0% or less (excluding 0%), Mo in a content of 1.0 % or less (excluding 0%) and Cu in a content of 0.5 % or less (excluding 0%).

The chrome element (Cr) has actions to reduce the perlite laminar space and help the wire rod to have greater strength and better toughness. To exhibit these actions efficiently, the Cr content is preferably 0.05% or more, more preferably 0.1% or more and also preferably 0.2% or more. On the other hand, Cr, if present in an excessively high content, can cause the wire rod to have a greater hardening capacity and, therefore, increase the risk of forming a supercooled phase during hot rolling. To avoid this, the Cr content is preferably 1.0% or less, more preferably 0.6% or less and also preferably 0.5% or less.

The nickel element (Ni) helps the steel wire after wire drawing to have a higher tenacity. To exhibit such actions efficiently, the Ni content is preferably 0.05% or more, more preferably 0.1% or more and also preferably 0.2% or more. However, Ni, if added in excess, can exhibit saturated effects, thus being economically useless. To avoid this, the Ni content is preferably 1.0% or less, more preferably 0.7% or less and also preferably 0.6% or less.

The Cobalt (Co) element has actions to reduce pro-eutectoid cementite (particularly with a high carbon content) and help the wire rod to more easily control its microstructure to be a homogeneous perlite. To exhibit these actions effectively, the Co content is preferably 0.05% or more, more preferably 0.1% or more and also preferably 0.2% or more. However, Co, if added in excess, can exhibit saturated effects, thus being economically useless. To avoid this, the Co content is preferably 1.0% or less, more preferably 0.8% or less and also preferably 0.6% or less.

The molybdenum element (Mo) helps the steel cable to have a better corrosion resistance. To exhibit such actions efficiently, the Mo content is preferably 0.05% or more and more preferably 0.1% or more. However, Mo, if present in an excessively high content, can cause the formation of a supercooled phase more easily during hot rolling and cause the wire rod to have a lower ductility. To avoid this, the Mo content is preferably 1.0% or less, more preferably 0.5% or less and also preferably 0.3% or less.

The copper element (Cu) helps the steel cable to have a better corrosion resistance. To exhibit such actions efficiently, the Cu content is preferably 0.05% or more and more preferably 0.08% or more. On the other hand, the Cu, if present in an excessively high content, can react with the sulfur to segregate as CuS in a grain boundary region and, therefore, generate a defect during the manufacture of the wire rod. To avoid such an influence, the Cu content is preferably 0.5% or less, more preferably 0.2% or less and also preferably 0.18% or less.

At least one element selected from the group consisting of B in a content of 0.005% or less (excluding 0%), Nb in a content of 0.5% or less (excluding 0%) and V in a content of 0 , 5% or less (excluding 0%).

The boron element (B) has actions to prevent the formation of pro-eutectoid ferrite and pro-eutectoid cementite and helps the wire rod easily control its microstructure to be a homogeneous perlite. Boron also has binding actions, such as boron nitride (BN), of excess nitrogen in solute after AlN precipitation, suppresses deformation aging caused by solute nitrogen and helps the wire rod to have a higher tenacity. In addition, the solute boron itself has the action of helping the wire rod to have a greater tenacity. To exhibit such actions efficiently, the boron content is preferably 0.0003% or more, more preferably 0.0005% or more and also preferably 0.001% or more. On the other hand, boron, if present in an excessively high content, can cause precipitation of a compound with iron, that is, a Fe-B compound such as FeB2 and causes cracks after hot rolling. To avoid this, the boron content is preferably 0.005% or less, more preferably 0.004% or less and also preferably 0.003% or less.

The niobium element (Nb) forms a nitride with excess solute nitrogen after AlN precipitation and contributes to grain refinement. In addition, the element also advantageously fixes the nitrogen of the solute and, therefore, suppresses fragility by aging. To exhibit such actions efficiently, the Nb content is preferably 0.01% or more, more preferably 0.03% or more, and also preferably 0.05% or more. However, Nb, if present in excessively high content, can exhibit saturated effects, thus being economically useless. To avoid this, the Nb content is preferably 0.5% or less, more preferably 0.4% or less and also preferably 0.2% or less.

The vanadium element (V) forms a nitride with excess solute nitrogen after AlN precipitation and contributes to grain refinement, as with Nb. In addition, vanadium also fixes solute nitrogen and therefore suppresses frailty by aging. To exhibit such actions effectively, vanadium content it is preferably 0.01 % or more, more preferably 0.02 % or more and also preferably 0.03 % or more. However, vanadium, if present in excessively high content, may exhibit saturated effects, thus being economically useless. To avoid this, the vanadium content is preferably 0.5% or less, more preferably 0.4% or less and also preferably 0.2% or less.

In general, a regular wire rod (referring to one before cold drawing) can be made by preparing a steel ingot with chemical compositions suitably controlled by manufacturing ingots, and subjecting the ingot to roughing and hot rolling (when necessary , in addition to a patented treatment). It should be noted, however, that the wire rod according to the embodiment of the present invention is intended to control the content and particle size distribution of AlN particles appropriately, where the particle size distribution is controlled so that the percentage of AlN particles having a dGM size of 10 to 20 pm be 50% or more (in percentage by number) in the distribution of extreme dGM values of maximum AlN particle values. For this purpose, it is important to adequately control the contents of Al and N within the ranges specified above and adequately control a thermal hysteresis in a temperature range in which AlN precipitates.

In steel, AlN begins to precipitate at approximately 1300 ° C or less, precipitated in a greater amount with a falling temperature, and completely precipitated at approximately 900 ° C. During manufacturing processes, hot-rolled and hot-rolled processes significantly affect the precipitation behavior of AlN because the steel is exposed to temperatures within the ranges mentioned above in these processes. Consequently, roughing and hot rolling conditions must be properly controlled. In general, cooling after roughing is performed at a low cooling rate and, therefore, often causes the precipitated AlN particle to become thick. In contrast, cooling after hot rolling is carried out at a relatively high cooling rate and, therefore, allows precipitated AlN particles to be fine.

Specifically, roughing can be performed at a heating temperature of 1230 ° C to 1280 ° C and a cooling rate of 0.2 ° C / second or more. Roughing, when performed at a high heating temperature and at a high cooling rate, can prevent precipitation and thickening of AlN particles. For this reason, the grinding temperature is preferably 1230 ° C or higher and more preferably 1240 ° C or higher. On the other hand, roughing, if performed at an excessively high heating temperature, can cause cooling cracks. To avoid this, the roughing temperature is preferably 1280 ° C or lower, and more preferably 1270 ° C or lower in terms of its upper limit. The cooling rate is preferably 0.2 ° C / second or more, more preferably 0.4 ° C / second or more and also preferably 0.5 ° C / second or more. The cooling rate is not limited at its upper limit, but is typically 1.5 ° C / second or less and preferably 1.2 ° C / second or less.

A square section obtained by roughing is hot rolled, cooled to 850 ° C to 950 ° C typically by cooling with water and placed in the form of a coil. AlN fine particles (which have a dGM of 10 to 20 pm) can be precipitated by placing the wire rod in the form of a coil at a relatively low temperature. For this reason, the placement temperature is preferably 950 ° C or less, more preferably 940 ° C or less and also preferably 920 ° C or less. Instead, placement, if performed at an excessively low temperature, can cause very fine AlN particles to precipitate in a large number, where such very fine AlN particles do not contribute to the hydrogen trap. To avoid this, the placement temperature is preferably 850 ° C or higher, more preferably 870 ° C or more and more preferably 890 ° C or higher.

The content and particle size distribution of AlN particles may not be adequately controlled, generally when at least part of the flowering and hot rolling conditions do not meet the conditions specified above. In this case, it is also effective to perform a patented treatment at an appropriate temperature range after hot rolling. The patented treatment is preferably performed at an overheating temperature of 880 ° C to 1000 ° C and a patented temperature of 530 ° C to 620 ° C. If the treatment after hot rolling has a low AlN content, the reheating temperature may be adjusted to be relatively low (for example, about 880 ° C to about 940 ° C) to increase the amount of AlN precipitation. If the work after hot rolling includes thick AlN particles, the reheating temperature can be set to relatively high (for example, 940 ° C to 1000 ° C) to allow the thick AlN particles to dissolve once in the steel and rush again.

The wire rod according to the embodiment of the present invention sufficiently includes AlN particles capable of acting effectively as hydrogen trap sites, thereby providing steel wires such as prestressing steel wires and cables that have excellent resistance to Delayed fracture, and they are useful. The present invention, in another aspect, also includes such steel wires.

Examples

The present invention will be illustrated in further detail with reference to several working examples below. It should be noted, however, that the examples should not be construed as limiting the scope of the invention; that various changes and modifications may naturally be made therein without departing from the spirit and scope of the invention as described herein; and all such changes and modifications should be considered within the scope of the invention.

Steel ingots having chemical compositions given in Table 1 were subjected to roughing, hot rolling and processing in wire rod coils, and some of them were subjected to a patented treatment under the conditions given in Table 2. Samples Samples of the resulting works were taken and subjected to a measurement of extraction residues to determine the total AlN particle content and a cross-sectional observation to evaluate the distribution of AlN particles. The results are indicated in Table 2.

1. Total AlN content and measurements of nitrogen content in solute

A measurement of electrolytic extraction residues was performed with a 10% acetylacetone solution using a 0.1 pm mesh as a measurement of extraction residues, where the amount of AlN particles in the residue was measured by the bromoester method. . Independently, the nitrogen content in solute was determined by measuring the content of nitrogen compounds including AlN by indophenol absorption spectrophotometry and subtracting the content of the total nitrogen content in the steel. The sample weights were 3 g in the bromoester method and 0.5 g in the absorption spectrophotometry.

2. AlN distribution measurement

The measurement was performed as follows. A sample of each wire rod was cut in a cross section that includes the wire rod axis and is parallel to the longitudinal direction of the wire rod so that the total area of two areas from the surface layer to a quarter position (D / 4) the diameter D of the wire rod is 140 mm2 Specifically, the length L of the sample was determined so that L * D / 4 + LxD / 4 = L * D / 2 is 140 mm2 The size of an AlN particle having the maximum size in an observation field of view in the cross section was measured in accordance with JIS G0555 and this measurement was performed in twenty (20) arbitrary fields of view. In the measurement, the inclusions of Group D and Group DS specified in JIS G0551 were considered as AlN particles and the geometric mean (ab) 1/2 of the length (a) and thickness (b) of each AlN particle It was used as the particle size of AlN.

Next, the wire rod coils obtained above were subjected to a wire stretch to give steel cables and the tensile strength (cable resistance) of each steel cable was measured. The steel cables were additionally subjected to stranding and hot stretching to give wires that had filament diameters and filament structures as indicated in Table 2, and the cable resistance, delayed fracture resistance and twisting properties They were measured from each strand. The results are indicated in Table 3.

3. Measurement of tensile strength of the steel cable (cable resistance)

The tensile strength of each steel cable was measured in accordance with JIS Z2241.

4. Measurement of rope resistance

For the strength of the rope, the maximum strength of a sample in a tensile test was measured in accordance with JIS G3536.

5. Measurement of delayed fracture resistance

The property of delayed fracture (resistance to delayed fracture) was measured as follows. Each of the twelve (12) samples was immersed in a solution of 20 percent mass ammonium thiocyanate at 50 ° C under a load of 0.8 pu according to the description in Bibliography 1 (Bulletin fib N. 30: Acceptance of stay cable systems using prestressing steels, January 2005) and a period of time was measured until the sample was broken. The term "0.8 p.u" refers to an 80% load of a breaking load. In this document, a test sample with a minimum break time of 2 hours or more and an average break time of 5 hours or more was accepted.

6. Measurement of torsion properties

For torsion properties, a test sample having a torsion number of 3 or more (capable of twisting three times or more) in accordance with FKK HTS-26 of the FKK Freynessit system was accepted herein.

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Tests No. 1 to 3, 5, 9, 10 and 13 to 20 had chemical compositions, microstructures, AlN contents and AlN distributions that respectively meet the conditions specified in the present invention, thus achieving a cable resistance of 2000 MPa or more (preferably 2100 MPa or more), offered a strand strength as high as to meet the criteria prescribed in JIS G3536, still had good resistance to delayed fracture, and could give high strength strands that are practically viable. In addition, these test samples also fulfilled the condition of nitrogen content in solute and, therefore, offered excellent torsion properties. Of the samples according to the embodiment of the present invention, tests No. 15 to 18 were samples that had a particularly reduced nitrogen content in solute and, therefore, offered very excellent torsion properties; while test No. 9 had a higher solute nitrogen content and offered a smaller number of torsion between the samples according to the embodiment of the present invention.

Tests No. 10, 15 and 17 were subjected to hot rolling at a placement temperature outside the range of preferred conditions, but was subjected to an appropriate patent treatment thereafter, and could give wire rod that meets the conditions specified in the present invention.

In contrast, tests No. 4, 6 to 8, 11, 12 and 21 to 27 were samples that did not meet any of the conditions specified in the present invention or were manufactured under a condition that did not meet the manufacturing conditions required to obtain steels in accordance with the embodiment of the present invention. Test No. 4 experienced roughing performed at low heating temperature; and test No. 6 was subjected to cooling performed at a low cooling rate after roughing. These samples underwent precipitation of thick AlN particles, had a particle size distribution of AlN that did not meet the condition specified in the present invention, and offered inferior resistance to delayed fracture. Test No. 7 was placed at an excessively high temperature after hot rolling, suffered insufficient precipitation of AlN particles during placement, had an AlN content and an AlN particle size distribution that did not It fulfilled the conditions specified in the present invention and offered a lower resistance to delayed fracture. Test No. 8 was subjected to placement carried out at an excessively low temperature after hot rolling, underwent an excessive refinement of AlN particles, therefore it had an AlN particle size distribution that did not meet the condition specified in the present invention and offered inferior resistance to delayed fracture.

Test No. 11 was subjected to roughing performed at an excessively high heating temperature and suffered cooling cracks.

Test No. 12 was subjected to a patented treatment carried out at an excessively low temperature, therefore, it had a microstructure that included a mixture (P + B) of bainite (B) and perlite (P) phases and offered a lower tensile capacity of the cable. This sample had a bainite fraction of approximately 20 percent in area.

Test No. 21 was a sample that had an excessively high carbon content, suffered significant frailty due to aging during drawing and suffered numerous tears. Test No. 22 was a sample that had an excessively low carbon content and could not offer a resistance corresponding to the type of B chain as prescribed in JIS G3536.

Test No. 23 was a sample with an excessively low Al content, could not include AlN particles in a sufficient amount and offered inferior resistance to delayed fracture. Test No. 24 was a sample that had a nitrogen content within the range specified in the present invention but was relatively low and had an excessively high Al content, underwent the formation of Al-containing oxides in large quantities, and suffered numerous breaks in the wire drawing.

Test No. 25 was a sample that had an excessively low nitrogen content, could not include AlN particles in a sufficient amount, had an AlN particle size distribution that did not meet the condition specified in the present invention, and it offered inferior resistance to delayed fracture. Test No. 26 was a sample that had an excessively high nitrogen content, suffered the precipitation of thick AlN particles and, therefore, offered a lower resistance to delayed fracture. Test No. 26 had a nitrogen content in solute that did not meet the preferred condition in the present invention and had a smaller torsion number among all test samples.

Test No. 27 was a sample that had a nitrogen content within the range specified in the present invention, but being relatively high and having an Al content that does not meet the condition specified by Expression (1), suffered the precipitation of thick particles of AlN and offered a lower resistance to delayed fracture.

Claims (5)

1. A wire rod consisting of: in mass percentage, hereinafter the same for the chemical composition; C in a content of 0.8% to 1.2%, If in a content of 0.1% to 2.0%; Mn in a content of 0.1% to 2.0%; N in a content of 0.002% to 0.010%; Al in a content of 0.04% to 0.15%; P in a content of 0.02% or less; Y S in a content of 0.02% or less; and optionally at least one element selected from the group consisting of: Cr in a content of 1.0% or less, excluding 0%; Nor in a content of 1.0% or less, excluding 0%; Co in a content of 1.0% or less, excluding 0%; Mo in a content of 1.0% or less, excluding 0%; Y Cu in a content of 0.5% or less, excluding 0%; and optionally at least one element selected from the group consisting of: B in a content of 0.005% or less, excluding 0%; Nb in a content of 0.5% or less, excluding 0%; Y V in a content of 0.5% or less, excluding 0%; the rest being iron and inevitable impurities; the content of Al and the content of N meet a condition specified by Expression (1) given as follows: [Al] <-2.1 x 10 x [N] 0.255 (1) where [Al] and [N] are contained in mass percentage of Al and N, respectively; the wire rod having a microstructure comprising 95 percent in area or more than one perlite; the wire rod having an AlN content of 0.005% or more; Y having a percentage of AlN particles with a dGM diameter of 10 to 20 pm, 50% or more in percentage by number in a distribution of extreme values of maximum values of the dGM diameters of AlN particles, where the dGM diameter is represented by a geometric mean (ab) 1/2 of a length "a" and a thickness "b" of an AlN particle, where the term "length" a "" of an AlN particle refers to the length (dimension) of the AlN particle in the longitudinal direction of the wire rod; the term "thickness" b "" of the AlN particle refers to a dimension of the AlN particle in a direction perpendicular to the longitudinal direction of the wire rod and The size of an AlN particle that has the maximum size in an observation field of view in the cross section is measured in accordance with JIS G0555, where the measurement is made in twenty arbitrary fields of view and where the Group's inclusions D and Group DS as specified in JIS G0551 are considered AlN particles in the measurement. 2. The wire rod according to claim 1, which has a solute nitrogen content of 0.003% or less. 3. The wire rod according to claim 1, further comprising at least one element selected from the group consisting of: Cr in a content of 0.05% to 1.0%; Nor in a content of 0.05% to 1.0%; Co in a content of 0.05% to 1.0%; Mo in a content of 0.05% to 1.0%; Y Cu in a content of 0.05% to 0.5%. 4. The wire rod according to claim 1, further comprising at least one element selected from the group consisting of: B in a content of 0.0003% to 0.005%; Nb in a content of 0.01% to 0.5%; Y V in a content of 0.01% to 0.5%. 5. A steel cable obtained from the wire rod of any one of claims 1 to 4.