JP4374357B2 - High-strength wire rod excellent in wire drawing characteristics, manufacturing method thereof, and high-strength steel wire excellent in wire drawing properties - Google Patents

Description

  The present invention relates to a high-strength wire having excellent wire drawing characteristics used for drawing to a PC steel wire, galvanized steel stranded wire, spring steel wire, suspension bridge cable, etc., a method for producing the same, and wire drawing properties It relates to high-strength steel wires with excellent resistance.

  Conventional high carbon hard steel wires, for example, have a limit of 1600 MPa in strength, even for bridge wires. However, with the recent increase in size of bridges, higher strength of wires has been required. Further, other steel wires such as PC steel wires are also required to have high strength.

  When producing high carbon hard steel wire, it is usually necessary to perform a patenting treatment on the hot-rolled wire, and then draw it into a steel wire with a predetermined wire diameter. Such treatment ensures a strength of 1600 MPa or more. At the same time, it is required to ensure sufficient performance with respect to toughness evaluated by the fracture drawing value.

In response to the above-described requirements, attempts have been made to improve the drawing workability of high carbon wire by controlling segregation and microstructure or by containing specific elements.
The drawing value of the patenting wire depends on the austenite particle size, and the drawing value is improved by making the austenite particle size finer. Therefore, by using carbides and nitrides such as Nb, Ti, and B as pinning particles, austenite is obtained. Attempts have also been made to reduce the particle size.

  The group consisting of Nb: 0.01 to 0.1% by weight, Zr: 0.05 to 0.1% by weight, Mo: 0.02 to 0.5% by weight as component elements in the high carbon wire Has proposed a wire rod containing at least one kind (see, for example, Patent Document 1).

Moreover, the wire which refine | miniaturized the austenite particle size by making NbC contain in a high carbon wire is proposed (for example, refer patent document 2).
Japanese Patent No. 2609387 JP 2001-131697 A

  The wire described in Patent Document 1 has a component composition in which the ductility of the steel wire is increased by including the above-described component elements. However, in the wire described in Patent Document 1, since the component elements to be added are all expensive, the manufacturing cost may increase.

  In the wire described in Patent Document 2, the wire drawing workability is improved by using NbC as pinning particles. However, in the wire described in Patent Document 2, since the contained component elements are all expensive, the manufacturing cost may increase. In addition, Nb forms coarse carbides and nitrides, and Ti forms coarse oxides, so that these become starting points for destruction, and there is a possibility that the wire drawing property is lowered.

  By the way, it has been confirmed that increasing the amount of C and the amount of Si in the steel material component is the most economical and effective means for increasing the strength of the high carbon steel wire. However, since the precipitation of ferrite is promoted with the increase of Si and the precipitation of cementite is suppressed, even when the hypereutectoid composition is such that the C content exceeds 0.8%, the patenting process is performed. When cooling from the austenite region, proeutectoid ferrite tends to precipitate in a plate shape along the austenite grain boundary. For this reason, there has been a problem that the fracture drawing value of the wire after the patenting treatment is reduced, the ductility is deteriorated, the frequency of disconnection during the wire drawing process is increased, and productivity and yield are reduced.

  Therefore, the present invention has been made in view of the above circumstances, and has a low-cost configuration, a high yield, a high aperture value, a high-strength wire excellent in wire drawing characteristics, a manufacturing method thereof, and wire drawing characteristics. The object is to provide an excellent high-strength steel wire.

  As a result of intensive studies to achieve the above object, the present inventors have made solid solution B in an amount corresponding to the amount of C and Si present in the austenite before the patenting treatment, thereby allowing cementite precipitation and ferrite. Balanced the driving force of precipitation, a high carbon pearlite wire with a small amount of pro-eutectoid ferrite was obtained, and it was found that it was possible to achieve both workability and high strength due to excellent wire drawing characteristics, and the present invention was completed. .

That is, the gist of the present invention is as follows.
[1] By mass%
C: 0.7 to 1.2%
Si: 0.6 to 1.5%
Mn: 0.1 to 1.0%,
N: 0.001 to 0.006%,
Al: 0.005 to 0.1% is contained,
Further, B is contained in a range given by 0.0009 to 0.0060%, and the amount of solid solution B is 0.0002% or more, and the balance consists of Fe and inevitable impurities,
The tensile strength TS [MPa] is represented by the following formula (1):
TS> (1000 × C [%] − 10 × wire diameter [mm] +320) (1)
A high-strength wire excellent in wire drawing characteristics, wherein the area ratio of pro-eutectoid ferrite is 3% or less and the area ratio of pearlite structure is 90% or more.
[2] Further, in mass%, Cr: 0.5% or less (excluding 0%), Ni: 0.5% or less (excluding 0%), Co: 0.5% or less (0% V: 0.5% or less (not including 0%), Cu: 0.2% or less (not including 0%), Mo: 0.2% or less (not including 0%), W : 0.2% or less (not including 0%), Nb: containing at least one selected from the group consisting of 0.1% or less (not including 0%) [ 1 ] High-strength wire with excellent wire drawing characteristics as described in 1.
[3] By mass%,
C: 0.7 to 1.2%
Si: 0.6 to 1.5%
Mn: 0.1 to 1.0%,
N: 0.001 to 0.006%,
Ti: 0.005 to 0.1%,
Al: containing 0.1% or less,
Further, Cr: 0.5% or less (not including 0%), Ni: 0.5% or less (not including 0%), Co: 0.5% or less (not including 0%), V: 0 0.5% or less (not including 0%), Cu: 0.2% or less (not including 0%), Mo: 0.2% or less (not including 0%), W: 0.2% or less ( 0% not included), Nb: containing at least one selected from the group consisting of 0.1% or less (not including 0%),
Furthermore, B is contained in a range given by 0.0009 to 0.0060%, and the amount of solid solution B is 0.0002% or more, and the balance consists of Fe and inevitable impurities,
The tensile strength TS [MPa] is represented by the following formula (1):
TS> (1000 × C [%] − 10 × wire diameter [mm] +320) (1)
A high-strength wire excellent in wire drawing characteristics, wherein the area ratio of pro-eutectoid ferrite is 3% or less and the area ratio of pearlite structure is 90% or more.
[4] A steel slab having the chemical composition according to any one of [1] to [3] is hot-rolled, wound at a temperature of Tr = 800 to 950 ° C., and then hot-rolled. After the subsequent cooling and winding process, cooling is started within the time t1 shown by the following formula (2), the cooling rate at the temperature from the cooling start temperature to 700 ° C. is set to 5 ° C./sec or more, and the patenting process A method for producing a high-strength wire rod having excellent wire drawing characteristics.
t1 = 0.0008 × (Tr−815) ² + 4 × (B−0.0003) / ((N−Ti / 3.41) × 0.71−B + 0.0003) (2)
However, when 4 × (B−0.0003) / ((N−Ti / 3.41) × 0.71−B + 0.0003) is 0 or less, or when t1 is larger than 40 s, t1 = 40 s To do.
[5] The composition of the high-strength wire excellent in wire drawing characteristics according to any one of [1] to [3], having a tensile strength TS of 1600 MPa or more, and an area ratio of pro-eutectoid ferrite Is a high-strength steel wire characterized by having an area ratio of pearlite structure of 90% or more.

According to the high-strength wire rod excellent in drawability of the present invention, C: 0.7-1.2%, Si: 0.6-1.5%, Mn: 0.1-1.0 in mass%. %, N: 0.001 to 0.006%, Al: 0.005 to 0.1%, and B in a range given by 0.0009 to 0.0060%, and solid solution The amount of B is 0.0002% or more, the balance is made of Fe and inevitable impurities, and the tensile strength TS [MPa] is expressed by the formula {TS> (1000 × C [%] − 10 × wire diameter [mm] +320)} The area ratio of pro-eutectoid ferrite is 3% or less, and the area ratio of the pearlite structure is 90% or more.
With the relationship of each component composition as described above, the solid solution B in an amount corresponding to the amount of C and Si is present in the austenite before the patenting treatment, thereby balancing the driving force of cementite precipitation and ferrite precipitation, By suppressing ferrite, ductility can be improved and disconnection in wire drawing can be prevented, and productivity and yield can be improved.
Moreover, a hard steel wire having a structure mainly composed of pearlite and having an average value of proeutectoid ferrite area ratio of 3% or less can be obtained. PC steel wire, galvanized steel wire, spring steel wire, The performance as a cable for a suspension bridge can be improved.

Hereinafter, embodiments of a high-strength wire rod excellent in wire drawing characteristics and a manufacturing method thereof and a high-strength steel wire excellent in wire drawing properties according to the present invention will be described with reference to the drawings.
Note that this embodiment is described in detail for better understanding of the gist of the invention, and thus does not limit the present invention unless otherwise specified.

[High-strength wire]
The high-strength steel wire having excellent wire drawing characteristics according to the present embodiment is mass%, C: 0.7 to 1.2%, Si: 0.6 to 1.5%, Mn: 0.1 to 1. 0%, N: 0.001 to 0.006%, Al: 0.005 to 0.1%, further containing B in a range given by 0.0009 to 0.0060%, and The amount of dissolved B is 0.0002% or more, and the balance consists of Fe and inevitable impurities,
The tensile strength TS [MPa] is represented by the following formula (1):
TS> (1000 × C [%] − 10 × wire diameter [mm] +320) (1)
The area ratio of pro-eutectoid ferrite is 3% or less, and the area ratio of the pearlite structure is 90% or more.

  Further, in the high-strength wire rod having excellent wire drawing characteristics according to the present embodiment, B is 0 when Ti is contained in the range of 0.005 to 0.1% by mass instead of Al of the above-described components. A component composition that is contained within a range given by .0009 to 0.0060% and that the amount of solid solution B is 0.0002% or more, and further contains Al in an amount of 0.1% or less. Can do.

  Furthermore, in the high-strength wire rod having excellent wire drawing characteristics according to the present embodiment, in addition to the above-described components, Cr: 0.5% or less (not including 0%), Ni: 0.5% or less (inclusive) ( Co: 0.5% or less (not including 0%), V: 0.5% or less (not including 0%), Cu: 0.2% or less (not including 0%) ), Mo: 0.2% or less (not including 0%), W: 0.2% or less (not including 0%), Nb: 0.1% or less (not including 0%) It can be set as the structure containing at least 1 or more types selected.

  In this embodiment, the component composition of the wire is limited for reasons described later, and the pearlite transformation is performed by limiting the winding temperature during rolling, the time from winding to patenting, and the cooling rate during the patenting process. It suppresses precipitation of pro-eutectoid ferrite at the time, and has excellent strength characteristics and wire drawing characteristics.

(Component composition)
Below, the reason for limitation of each component composition of the high intensity | strength wire rod excellent in the wire drawing characteristic of this embodiment is demonstrated.
(C: 0.7-1.2%)
C is an element effective for increasing the strength of the wire. When the C content is less than 0.7%, it is difficult to stably give the final product the high strength specified in the above formula (1), and at the same time, precipitation of pro-eutectoid ferrite at the austenite grain boundaries. Is promoted, and it becomes difficult to obtain a uniform pearlite structure. On the other hand, if the content of C is too large, not only is the net-form pro-eutectoid cementite generated at the austenite grain boundaries and breakage is likely to occur during wire drawing, but the toughness and ductility of the ultrafine wire after the final wire drawing is increased. Deteriorate significantly. Therefore, the C content is within a range of 0.7 to 1.2% by mass.

(Si: 0.6-1.5%)
Si is an element effective for increasing the strength. Furthermore, it is an element useful as a deoxidizer, and is also an element necessary when targeting a steel wire containing no Al. On the other hand, when the amount of Si is too large, precipitation of pro-eutectoid ferrite is promoted even in eutectoid steel, and the limit working degree in wire drawing decreases. Furthermore, the wire drawing process by mechanical descaling (hereinafter abbreviated as MD) becomes difficult. Therefore, the content of Si is set in the range of 0.6 to 1.5% by mass.

(Mn: 0.1 to 1.0%)
Mn is an element useful as a deoxidizer like Si. It is also effective in improving the hardenability and increasing the strength of the wire. Furthermore, Mn has the effect | action which fixes S in steel as MnS and prevents hot brittleness. If the content is less than 0.1% by mass, it is difficult to obtain the above effect. On the other hand, Mn is an element that easily segregates, and when it exceeds 1.0 mass%, segregation occurs particularly in the center of the wire, and martensite and bainite are generated in the segregated portion, so that the wire drawing workability decreases. Therefore, the content of Mn is set within a range of 0.1 to 1.0% by mass.

(Al: 0.005 to 0.1%)
Al is effective as a deoxidizing material. Moreover, it has the effect of fixing N and suppressing aging and increasing the solid solution B. The Al content is preferably in the range of 0.005 to 0.1%. If the Al content is less than 0.005%, it is difficult to obtain an effect of fixing N. If the Al content exceeds 0.1%, a large amount of hard non-deformation alumina-based non-metallic inclusions are generated, and the ductility and drawability of the steel wire are lowered. In addition, when Ti described later is added, the above effect can be obtained without adding Al by fixing Ti to Ti, so there is no need to define the lower limit of Al, and the content of Al is 0 may be sufficient.

(Ti: 0.005 to 0.1%)
Ti is effective as a deoxidizer. Moreover, it precipitates as TiN, contributes to preventing the coarsening of the austenite grain size, and is an effective element effective for securing the amount of dissolved B in the austenite by fixing N. When the Ti content is less than 0.005%, the above-described effects are hardly obtained. If the Ti content exceeds 0.1%, coarse carbides are formed in austenite, and the drawability may be reduced. Therefore, the Ti content is within the range of 0.005 to 0.1% by mass.

(N: 0.001 to 0.006%)
N produces Al, B or Ti and nitride in steel and has the effect of preventing coarsening of the austenite grain size during heating, and the effect is effectively exhibited by containing 0.001% or more. . However, if the content becomes too large, the amount of nitride increases too much, and the amount of dissolved B in austenite is reduced. Further, solute N may promote aging during wire drawing. Therefore, the N content is set in a range of 0.001 to 0.006% by mass%.

(B: 0.0009 to 0.0060%)
When B is present in austenite in a solid solution state, B has an effect of concentrating at the grain boundary to suppress precipitation of pro-eutectoid ferrite and promote precipitation of pro-eutectoid cementite. Therefore, it is possible to suppress the formation of pro-eutectoid ferrite by adding an appropriate amount according to the balance between the amounts of C and Si. Since B forms a nitride, it is necessary to consider the balance with the N amount in addition to C and Si in order to secure the B amount in a solid solution state. On the other hand, when B is added too much, not only the precipitation of pro-eutectoid cementite is promoted, but also coarse Fe3 (CB) 6 carbides are formed in austenite, and the drawability may be reduced. About these relationships, the present inventors repeated experiments, and set it as 0.0009 to 0.0060% as the optimal range of B content. In addition, B needs to exist in a solid solution state before a patenting process, and needs to be 0.0002% or more as a solid solution B amount in the wire after rolling.

  The impurities P and S are not particularly defined, but are each preferably 0.02% or less from the viewpoint of ensuring ductility as in the case of conventional ultra fine steel wires.

  The high-strength steel wire rod described in the present embodiment has the above-mentioned components as a basic composition, but for the purpose of further improving mechanical properties such as strength, toughness, ductility, etc., the selective tolerance described below It is good also as a component composition which contained the additive element 1 type (s) or 2 or more types positively.

(Cr: 0.5% or less)
Cr is an element effective for reducing the lamella spacing of pearlite and improving the strength of the wire and the wire drawing workability. Addition of 0.1% or more is preferable for effectively exhibiting such an action. On the other hand, if the amount of Cr is too large, the transformation end time becomes long, and there is a possibility that a supercooled structure such as martensite and bainite is formed in the hot-rolled wire, and the mechanical descaling property is also deteriorated. 0.5%.

(Ni: 0.5% or less)
Ni is an element that does not contribute much to increasing the strength of the wire, but increases the toughness of the wire. Addition of 0.1% or more is preferable for effectively exhibiting such an action. On the other hand, if Ni is added excessively, the transformation end time becomes longer, so the upper limit was made 0.5%.

(Co: 0.5% or less)
Co is an element effective for suppressing precipitation of pro-eutectoid cementite in the rolled material. Addition of 0.1% or more is preferable for effectively exhibiting such an action. On the other hand, even if Co is added excessively, the effect is saturated and the excess content is wasted, and the manufacturing cost may increase, so the upper limit was set to 0.5%.

(V: 0.5% or less)
V forms fine carbonitrides in the ferrite, thereby preventing austenite grains from coarsening during heating and contributing to an increase in strength after rolling. Addition of 0.05% or more is preferable for effectively exhibiting such an action. However, if the amount is excessively added, the amount of carbonitride formed becomes too large and the particle size of the carbonitride increases, so the upper limit was made 0.5%.

(Cu: 0.2% or less)
Cu has the effect of increasing the corrosion resistance of the ultrafine steel wire. Addition of 0.1% or more is preferable for effectively exhibiting such an action. However, if added excessively, it reacts with S and segregates CuS in the grain boundaries, so that flaws are generated in the steel ingot, wire, etc. during the wire manufacturing process. In order to prevent such adverse effects, the upper limit was made 0.2%.

(Mo: 0.2% or less)
Mo has the effect of increasing the corrosion resistance of the ultrafine steel wire. Addition of 0.1% or more is preferable for effectively exhibiting such an action. On the other hand, if Mo is added excessively, the transformation end time becomes long, so the upper limit was made 0.2%.

(W: 0.2% or less)
W has the effect of increasing the corrosion resistance of the ultrafine steel wire. Addition of 0.1% or more is preferable for effectively exhibiting such an action. On the other hand, if W is added excessively, the transformation end time becomes longer, so the upper limit was made 0.2%.

(Nb: 0.1% or less)
Nb has the effect of increasing the corrosion resistance of the ultrafine steel wire. Addition of 0.05% or more is preferable for effectively exhibiting such an action. On the other hand, if Nb is added excessively, the transformation end time becomes longer, so the upper limit was made 0.1%.

(Structure of wire rod)
According to various studies conducted by the present inventors, it was precipitated at the prior austenite grain boundaries of the wire that particularly affects the wire drawing workability of the wire having an Si content of 0.6% or more. It is clear that it is proeutectoid ferrite. Therefore, it was confirmed that the occurrence of delamination can be suppressed by setting the area ratio of pro-eutectoid ferrite in the cross section to 3% or less as in the wire of the present embodiment.

  In the present embodiment, a wire steel satisfying the requirements of the above component composition is used, and this is hot-rolled and then directly patented, whereby the main structure is made of pearlite and the pro-eutectoid ferrite area ratio is 3%. The following wire or steel wire can be obtained. Further, the pearlite structure is a structure having a high strength due to a lamellar structure and the most excellent wire drawing characteristics. However, when the area ratio of the pearlite structure is less than 90%, the strength of the wire and the ductility at the time of wire drawing decrease. Therefore, the area ratio of the pearlite structure is preferably 90% or more.

[Method for producing high-strength wire]
In order to obtain a wire having the structure and tensile strength defined in the present embodiment by using the steel having the component composition defined in the present embodiment, during the conveyance from winding after rolling to patenting treatment, B It is necessary not to form carbides or nitrides and to cool at a rate higher than a certain value during the patenting process. According to the study by the present inventors, the structure of the wire material and the amount of solute B that were heated to 1050 ° C., rapidly cooled to a temperature of 750 to 950 ° C. within 1 sec, subsequently kept at this temperature for a certain time, and then blast-cooled. As a result of measurement, the limit holding time containing 0.0002% or more of solute B becomes a C curve determined by the combination of B amount and N amount as shown in FIG. 1, and the time t1 is expressed by the following equation: Made it clear that
t1 = 0.0008 × (Tr−815) ² + 4 × (B−0.0003) / ( ( N-Ti / 3.41 ) × 0.71− B + 0.0003) (2)

In the formula (2), Tr is a winding temperature, and ( ( N−Ti / 3.41 ) × 0.71− B + 0.0003) is effective in a component range larger than 0 (zero). If it is (zero) or less, there is no limit on the holding time. In actual rolling, it hardly takes 40 seconds or more after winding up to start the patenting process, and the upper limit is 40 seconds.

  Based on the above, the wire rolled at 1050 ° C. or higher is water-cooled, wound at a temperature of 800 ° C. or higher, preferably 850 ° C. or higher and 950 ° C. or lower, and the time from winding to the start of patenting treatment is It is necessary to make it within the formula (2). When the temperature at the time of winding is less than 800 ° C., B precipitates as a carbide and the effect of suppressing the non-pearlite structure as solid solution B becomes insufficient. When the temperature at the time of winding exceeds 950 ° C., the γ particle size becomes coarse and the aperture value decreases.

  After winding the wire, a patenting process is then performed. The patenting process for the wire material needs to be performed at a cooling rate of 5 ° C./sec or more at least in the temperature range from the cooling start temperature to 700 ° C. by blast cooling or other cooling methods. When the cooling rate is less than 5 ° C./sec, a predetermined strength cannot be obtained.

By the above-described patenting treatment, the area ratio of pro-eutectoid ferrite can be suppressed to 3% or less, and a tensile strength TS greater than that represented by the above formula (1) can be secured.
In addition, in this embodiment, the outstanding wire drawing characteristic and high intensity | strength can be stably obtained by making the diameter of a wire into the range of 5.5-18 mm.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and is implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

<Sample preparation method>
The test steel of each component shown in Table 1 and Table 3 was made into a slab having a cross-sectional size of 300 × 500 mm by a continuous casting facility, and a steel slab having a 122 mm square cross section was produced by split rolling. Thereafter, the wire is rolled into a wire having a predetermined diameter under the conditions shown in Tables 2 and 4, wound at a predetermined temperature, and subjected to blast patenting (DP: Direct Pateting) within a predetermined time. No. 2 1-15 and no. Nos. 31 to 44 and Nos. 16-30 and no. Each sample shown in 45-55 was obtained. These sample Nos. The following evaluation tests were conducted for 1 to 55.

<Evaluation test method>
The solid solution B was obtained by measuring the amount of B present as a compound in the electrolytic extraction residue of the patenting wire by the curcumin spectrophotometry and determining the difference from the total amount of B.
As for the pro-eutectoid ferrite structure fraction, in the cross section (L cross section) parallel to the length direction of the wire by SEM observation after embedding and polishing the patenting wire and the drawn wire and conducting chemical corrosion using picric acid. The pro-eutectoid ferrite area ratio was determined.
The pro-eutectoid ferrite area ratio of the rolled wire rod is cut and polished at a location ± 5% of the radius from the center of the wire rod, and the L cross section appears, and the wire diameter (radial direction) × double the wire diameter (length direction) The area of pro-eutectoid ferrite was measured by image analysis to obtain the pro-eutectoid ferrite area ratio.
As for the pearlite area ratio, in the surface layer, 1 / 4D, and 1 / 2D portions of the L cross section of the wire rod, 5 micrographs of the structure photograph of the region of 100 μm × 100 μm were taken at a magnification of 2000 by SEM observation, and image analysis was performed. The average value of the area ratio was measured. At that time, pseudo pearlite or bainite in which cementite was dispersed in a point sequence was excluded.
As for the pro-eutectoid ferrite area ratio of the wire drawing material, an L cross-section appears by cutting and polishing at a location ± 5% of the radius from the center of the wire, and an area of 40 μm depth × 40 μm width at a magnification of 4000 by SEM observation The tissue photographs were taken for 5 fields of view, and the average value of the area ratio was measured by image analysis.
By this measurement, it was confirmed that the pro-eutectoid ferrite area ratio before wire drawing and the pro-eutectoid ferrite area ratio after wire drawing almost coincided.
In addition, when the decarburization layer existed in the surface layer, all the decarburization parts prescribed | regulated by 4 of JISG0558 were excluded from the measurement site | part.
Regarding the tensile strength TS, the gauge length was 200 mm, a tensile test was performed at a speed of 10 mm / min, and an average value of n = 3 was measured.

  Hereinafter, No. in Table 1 1-15 and no. Table 2 shows a list of evaluation test conditions and results for each sample shown in 31-43.

  In Tables 1 and 2, no. Each sample shown in 1 to 15 is a high-strength wire (invented steel) having excellent wire drawing characteristics according to the present invention. Each sample shown to 31-44 is the conventional wire (comparison steel).

As shown in Table 2, no. The wire rods of the samples (invention steels) shown in 1 to 15 all satisfy the range in which the B content is given by 0.0009 to 0.0060%, and the time until the start of patenting after winding is t1 = 0.0008 × (Tr−815) ² + 4 × (B−0.0003) / ( ( N−Ti / 3.41 ) × 0.71− B + 0.0003) or less. For this reason, in all cases, the amount of solute B was 0.0002% or more, and the pro-eutectoid ferrite area ratio in the cross section from the surface of the wire to the center was 3% or less. In addition, the strength of any patenting material exceeds the strength (TS threshold value) represented by TS = (1000 × C [%] − 10 × wire diameter [mm] +320).

In contrast, no. In the wire rod of the sample (comparative steel) shown in No. 31, since the coiling temperature was as low as 750 ° C., B carbide precipitated before the patenting treatment, and the pro-eutectoid ferrite could not be suppressed.
No. In the sample (comparative steel) wires shown in 37, 38 and 43, the time from winding to the start of patenting is t1 = 0.0008 × (Tr−815) ² + 4 × (B−0.0003) / ( Since it was longer than ( N—Ti / 3.41 ) × 0.71− B + 0.0003), solid solution B could not be secured and pro-eutectoid ferrite could not be suppressed.
No. In the wires of the samples (comparative steel) shown in Nos. 33 and 42, the B content was more than the predetermined amount, and B carbide and proeutectoid cementite were precipitated.
No. In the sample (comparative steel) shown in No. 34, since the Si content was excessive at 1.6%, the generation of pro-eutectoid ferrite could not be suppressed.
No. In the wire of the sample (comparative steel) shown in 35, since the C content was excessive as 1.3%, it was not possible to suppress the precipitation of proeutectoid cementite.
No. In the wire of the sample (comparative steel) shown in 36, since the Mn content is excessive at 1.5%, the generation of micromartensite could not be suppressed.
No. In the wire samples of 39 and 40 (comparative steel), the cooling speed during the patenting process was smaller than the specified cooling speed, so that the tensile strength with the specified LP material and the tensile strength after wire drawing can be satisfied. There wasn't.
No. In the wires of the samples (comparative steels) shown in 32, 41, and 44, since the B content did not reach the specified amount, the formation of pro-eutectoid ferrite could not be suppressed, and it was 3% or more.

  Next, No. in Table 3 16-30 and no. Table 4 shows a list of evaluation test conditions and results for each sample shown in 45-55.

  In Tables 3 and 4, no. Each sample shown to 16-30 is the high intensity | strength wire rod (this invention steel) excellent in the wire drawing characteristic which concerns on this invention, and No.1. Each sample shown to 45-55 is a conventional wire (comparison steel).

As shown in Table 4, no. The wires of the samples (invention steels) shown in 16 to 30 satisfy the range in which the B content is given by 0.0009 to 0.0060%, and the time from winding to the start of patenting is t1 = 0.0008 × (Tr−815) ² + 4 × (B−0.0003) / ( ( N−Ti / 3.41 ) × 0.71− B + 0.0003) or less. For this reason, in all cases, the amount of solute B was 0.0002% or more, and the pro-eutectoid ferrite area ratio in the cross section from the surface of the wire to the center was 3% or less. In addition, the strength of any patenting material exceeds the strength (TS threshold value) represented by TS = (1000 × C [%] − 10 × wire diameter [mm] +320).

In contrast, no. In the wire rod of the sample (comparative steel) shown in 45, since the coiling temperature was as low as 750 ° C., B carbide precipitated before the patenting treatment, and generation of proeutectoid ferrite could not be suppressed.
No. In the sample (comparative steel) wires shown in 50, 52, 53, and 54, the time from winding to the start of patenting is t1 = 0.0008 × (Tr−815) ² + 4 × (B−0.0003) / ((N-Ti / 3.41 ) × 0.71 -B + 0.0003) for longer than can not be ensured solid solution B, it was not able to suppress the formation of pro-eutectoid ferrite.
No. In the wire rod of the sample (comparative steel) shown in 46, the B content was more than the predetermined amount, and B carbide and pro-eutectoid cementite were precipitated.
No. In the wire of the sample (comparative steel) shown in 47, since the Si content was excessive at 1.6%, generation of proeutectoid ferrite could not be suppressed.
No. In the wire of the sample (comparative steel) shown in FIG. 48, the Mn content was excessive at 1.5%, and therefore generation of micromartensite could not be suppressed.
No. In the wire materials of the samples (comparative steels) shown in 49, 51, and 55, the B content was less than the prescribed amount, so the formation of proeutectoid ferrite could not be suppressed and the content was 3% or more.

  In addition, No. A steel wire for PWS with a diameter of φ5.2 mm was made using 19, 21, 26 (steel of the present invention), and a steel wire that had a tensile strength TS of 1932 MPa, 1930 MPa, and 1910 MPa and did not cause delamination was obtained. We were able to make it. On the other hand, no. When a similar trial production was carried out using a 54 (comparative steel) wire, delamination occurred with a tensile strength TS of 2010 MPa.

FIG. 2 is a graph showing the relationship between the wire diameter of the wire after the patenting treatment and the area ratio of pro-eutectoid ferrite in the cross section from the surface of the wire to the center. Note that in FIG. Samples 1 to 15 (steel of the present invention) are shown. Each sample (comparative steel) of 31-44 is shown. In addition, ● indicates no. Samples 16 to 30 (present invention steel) are shown. Each sample (comparative steel) of 45-55 is shown.
From the graph shown in FIG. 2, in the high-strength wire rod (◆, ●) according to the present invention, the pro-eutectoid ferrite is stably 3% or less regardless of the wire diameter, whereas the conventional wire rod of the comparative example (◇ , ○), the area ratio of proeutectoid ferrite is a value exceeding 3%.

FIG. 3 is a graph showing the relationship between the tensile strength TS and the drawing value of the wire after the patenting process. Note that in FIG. Samples 1 to 15 (steel of the present invention) are shown. Each sample (comparative steel) of 31-44 is shown. In addition, ● indicates no. Samples 16 to 30 (present invention steel) are shown. Each sample (comparative steel) of 45-55 is shown.
From the graph shown in FIG. 3, when the tensile strength TS is the same, the aperture value of the high-strength wire (◆, ●) according to the present invention is superior to the conventional wire (◇, ○) of the comparative example. Obviously.

FIG. 1 is a graph showing precipitation curves of BN when the amounts of B and N are different. FIG. 2 is a graph showing the relationship between the wire diameter and the proeutectoid ferrite area ratio in the wire after the patenting treatment. FIG. 3 is a graph showing the relationship between the tensile strength and the drawing value of the wire after the patenting process.

Claims (5)

% By mass
C: 0.7 to 1.2%
Si: 0.6 to 1.5%
Mn: 0.1 to 1.0%,
N: 0.001 to 0.006%,
Al: 0.005 to 0.1% is contained,
Further, B is contained in a range given by 0.0009 to 0.0060%, and the amount of solid solution B is 0.0002% or more, and the balance consists of Fe and inevitable impurities,
The tensile strength TS [MPa] is represented by the following formula (1):
TS> (1000 × C [%] − 10 × wire diameter [mm] +320) (1)
A high-strength wire excellent in wire drawing characteristics, wherein the area ratio of pro-eutectoid ferrite is 3% or less and the area ratio of pearlite structure is 90% or more. Further, in mass%, Cr: 0.5% or less (excluding 0%), Ni: 0.5% or less (not including 0%), Co: 0.5% or less (not including 0%) V: 0.5% or less (not including 0%), Cu: 0.2% or less (not including 0%), Mo: 0.2% or less (not including 0%), W: 0.0. 2. The composition according to claim 1 , comprising at least one selected from the group consisting of 2% or less (not including 0%), Nb: 0.1% or less (not including 0%). High-strength wire with excellent wire drawing characteristics. % By mass
C: 0.7 to 1.2%
Si: 0.6 to 1.5%
Mn: 0.1 to 1.0%,
N: 0.001 to 0.006%,
Ti: 0.005 to 0.1%,
Al: containing 0.1% or less,
Further, Cr: 0.5% or less (not including 0%), Ni: 0.5% or less (not including 0%), Co: 0.5% or less (not including 0%), V: 0 0.5% or less (not including 0%), Cu: 0.2% or less (not including 0%), Mo: 0.2% or less (not including 0%), W: 0.2% or less ( 0% not included), Nb: containing at least one selected from the group consisting of 0.1% or less (not including 0%),
Furthermore, B is contained in a range given by 0.0009 to 0.0060%, and the amount of solid solution B is 0.0002% or more, and the balance consists of Fe and inevitable impurities,
The tensile strength TS [MPa] is represented by the following formula (1):
TS> (1000 × C [%] − 10 × wire diameter [mm] +320) (1)
A high-strength wire excellent in wire drawing characteristics, wherein the area ratio of pro-eutectoid ferrite is 3% or less and the area ratio of pearlite structure is 90% or more. The steel slab having the chemical composition according to any one of claims 1 to 3 is rolled up at a temperature of Tr = 800 to 950 ° C after hot rolling, and then cooled and wound after hot rolling. The cooling is started within the time t1 represented by the following formula (2) after the taking step, the cooling rate at the temperature from the cooling start temperature to 700 ° C. is set to 5 ° C./sec or more, and patenting is performed. A method for producing a high-strength wire rod having excellent wire drawing characteristics.
t1 = 0.0008 × (Tr−815) ² + 4 × (B−0.0003) / ((N−Ti / 3.41) × 0.71−B + 0.0003) (2)
However, when 4 × (B−0.0003) / ((N−Ti / 3.41) × 0.71−B + 0.0003) is 0 or less, or when t1 is larger than 40 s, t1 = 40 s To do.   It has the component composition of the high strength wire rod excellent in the wire drawing characteristics according to any one of claims 1 to 3, the tensile strength TS is 1600 MPa or more, and the area ratio of proeutectoid ferrite is 3% or less. And a high-strength steel wire having an area ratio of pearlite structure of 90% or more.

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