KR101018054B1 - High-ductility high-carbon steel wire - Google Patents

Abstract

The present invention provides a high ductility high carbon steel wire rod such as for steel cord with less disconnection for drawing, so that at least 95% is a pearlite structure in a high carbon steel wire rod having a carbon content of 0.7% or more produced by hot rolling. The high-ductility high carbon steel wire rod which the maximum value of the pearlite block particle diameter of the pearlite of the center part of a hot rolled wire rod is 65 micrometers or less. A high ductility high carbon steel wire rod having a tensile strength in the range of {248 + 980 × (C mass%)} ± 40 MPa and having a cross sectional reduction rate of {72.8-40 × (C mass%)}% or more. A high ductility high carbon steel wire rod having an average value of a pearlite block particle diameter composed of a ferrite grain boundary composed of an azimuth difference of 9 degrees or more measured by an EBSP apparatus at the center of a hot rolled wire rod, wherein the average diameter is 10 µm or more and 30 µm or less.

High Ductile High Carbon Steel Wire, Steel Cord, Pearlite Block

Description

High-ductility, high carbon steel wire {HIGH-DUCTILITY HIGH-CARBON STEEL WIRE}

The present invention relates to a high ductility high carbon steel wire rod after hot rolling whose main structure is made of pearlite. More specifically, it relates to a piano wire or a high carbon steel wire in the JIS standard, the thin wire having a wire diameter of about 0.1 to 2 mm in the final product, for example, steel cord, saw wire ), Hot-rolled wire rod of high carbon steel used for hose wire, narrow rope, and the like.

Reinforcement wires, such as steel cords used for reinforcement of rubber products such as tires, conveyor belts and pressure resistant hoses, are made of high carbon steel wire. These high carbon steel wire rods are manufactured by hot rolling, and then subjected to borax treatment or bond treatment, which becomes a carrier coat after descaling, followed by intermediate patterning treatment, if necessary, with a wire diameter of 0.8 to 1.2 mm. Is processed into steel wire. In addition, in this invention, a hot rolled material is described as a wire rod, and steel steel of diameter smaller than the hot rolled material produced by the subsequent process is described as a steel wire, and these are distinguished.

After the patterning process, these steel wires are subjected to brass plating in the case of steel cords, and then drawn and processed again into steel wires having a diameter of 0.15 to 0.35 mm, followed by stranded wires, and covered with rubber. have. In order to improve the workability in such a secondary processing process, the wear property of the drawing die | dye, etc., continuous research is made.

For example, Japanese Laid-Open Patent Publication No. 3-60900 has a C amount of 0.59 to 0.86%, a tensile strength of 87.5 x C equivalent + 27 ± 2 (kg / mm 2) (C equivalent = C + Mn / 5), Moreover, the wire rod which the coarse pearlite which occupies in a wire structure is measured under the microscope of 500 times, and whose occupation area is adjusted to -60 * C equivalent +69.5 +/- 3 (%) is disclosed. This wire rod is intended to improve the life of the die, and to improve the die life by defining the tensile strength and adjusting the volume fraction of the coarse pearlite structure to a certain range. Although this patent document 1 aims at improving the lifetime of a drawing die by focusing on a rough pearlite structure, the relationship with the cause of the disconnection after direct drawing like the objective of this invention is not disclosed at all.

Japanese Unexamined Patent Publication No. 2000-6810 discloses a high-carbon steel wire having excellent drawability, wherein at least 90% of the structure is a pearlite structure, an average lamellar spacing of pearlite is 0.1 to 0.4 µm, and an average colony diameter is 150 µm or less. Is disclosed. The colony diameter obtained by general hot rolling is smaller than 150 micrometers, and the ductility obtained even if it adjusts to 150 micrometers or less is not constant, and the improvement of disconnection is not necessarily expected.

Patent No. 3681712 discloses that at least 95% of the wire structure is a pearlite structure, and the average nodule diameter P of the pearlite is 30 µm or less, the average lamellar spacing S is 100 nm or more, and P is the µm and S. A high carbon steel wire rod having excellent freshness in which F formula (F = 350.3 / √S + 130.3 / √P-51.7) is expressed as F> 0 when expressed in nm is disclosed. Invention described in this Patent Document 3 is to adjust the lamellar spacing and nodule size by inserting a cooling step of isothermal holding during air-cooling cooling in hot rolling. In general air-cooling cooling, since continuous cooling is performed, the width of the value of the lamellar spacing The larger the width of the nodule size is. In such a case, even if the average value is small, good workability cannot be obtained, and on the contrary, there is a problem that it involves an internal defect. In addition, by changing the cooling conditions after wire rod rolling, it is said that wire rods excellent in high-speed wire workability can be obtained by adjusting the structure in the range described in the above formula (F). There is a problem that heat treatment is required.

In recent years, from the viewpoint of improving the economics in secondary processing, even in the case of wire rods in which internal defects are hardly generated in the primary wire drawing or the primary wire drawing, in which the target amount of processing is relatively large, the subsequent wire break does not increase. Development is required.

Accordingly, the present invention relates to a high carbon steel wire used for piano wire, hard steel wire, etc. used for thin wires such as steel cords, belt cords, rubber hose wires, rope wires, and the like. It provides a high ductility high carbon steel wire which is hard to generate internal defects during machining and can omit intermediate patterning treatment.

The present inventors earnestly studied and studied the pearlite structure in the hot rolling wire which does not affect subsequent secondary workability even if the intermediate patterning process is omitted. The gist of the present invention is as follows.

 (1) A high carbon steel wire having a carbon content of 0.7% by mass or more, wherein the metal structure of the wire consists of 95% by volume or more of pearlite structure, and the pearlite pearlite block particle diameter at the center of the cross section perpendicular to the axial direction of the wire. The high carbon steel wire rod, characterized in that the maximum value of 65 ㎛ or less.

 (2) The tensile strength of the wire rod is in the range of {248 + 980 × (C mass%)} ± 40 MPa, and the cross-sectional reduction rate is {72.8-40 × (C mass%)}% or more, The high ductility high carbon steel wire rod of 1).

 (3) The high-ductility high carbon steel wire rod according to (1) or (2), wherein the average value of the pearlite block particle diameters of the pearlite central portion of the cross section perpendicular to the axial direction of the wire rod is 10 µm or more and 30 µm or less.

 (4) The high-ductility high carbon steel wire rod according to any one of (1) to (3), wherein the metal structure of the wire rod contains a cornerstone ferrite having a volume fraction of 2% or less.

 (5) The components of the wire rod contain, in mass%, C: 0.7 to 1.1%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, P: 0.02% or less, S: 0.02% or less, and the balance Fe and The high-ductility high carbon steel wire rod in any one of (1)-(4) characterized by consisting of inevitable impurities.

 (6) The components of the wire rod are, in mass%, Cr: 0.05 to 1.0%, Mo: 0.05 to 1.0%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0%, V: 0.001 to 0.1%, Nb: 0.001 to 0.1%, Ti: 0.005 to 0.1%, B: 0.0005 to 0.006%, O: 18 to 30 ppm, N: 0 to 40 ppm. High ductility high carbon steel wire rod.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the correspondence relationship of the crack (a) and the pearlite block particle diameter (b) which generate | occur | produced in the fresh wire at the time of carrying out the general stelmor process.

It is a figure which shows the change of the pearlite block particle diameter reaching the center from the surface layer of a rolled wire rod.

** Best Mode for Carrying Out the Invention **

When the present inventors process the steel wire of the wire diameter of the final patterning from the wire rod without the intermediate patterning treatment, when the amount of processing increases, defects occur inside even when the ductility of the steel wire does not decrease at a glance, and the subsequent pattern In the coating process and subsequent drawing processing, defects were promoted and it was found that the disconnection may be reached.

Even in the case of severe processing in the primary drawing process (processing amount of two or more in true deformation), in order not to affect the process after the subsequent patterning treatment, to prevent excessive internal defects in the primary drawing process It is necessary to carry out the restructuring of the wire rod and to perform the primary drawing which is hard to cause defects.

Therefore, the present inventors observe the internal defect site after the primary drawing, and the center of the wire rod as a feature of the tissue which is likely to cause internal defects in a state in which mechanical properties, processing conditions, and numerous factors of the wire structure are complicated. It was found that the pearlite block particle diameter measured by the EBSP (Electron Back Scatter Pattern) device of the pearlite structure was large. This method cannot measure a pearlite block particle diameter correctly by the method of measuring with a general optical microscope, and cannot determine the tissue state which impairs workability. Therefore, it is necessary to use an EBSP apparatus for measuring the pearlite block particle diameter.

The particle size of the pearlite block was measured using a device in which a FE-SEM (S4300SE) manufactured by Hitachi, Inc., and an EBSP device, manufactured by TSL, were combined. The definition of the pearlite block was obtained by the EBSP apparatus as an area in which the crystal directions of ferrite described in Takahashi et al., 42 (1978), p. 702, were the same. Since the measurement was extremely difficult with the structure observed by the optical microscope or the secondary electron image obtained by SEM observation, the pearlite block particle diameter was obtained from the measurement result by the EBSP apparatus which can obtain the crystal orientation map of ferrite. In addition, unlike the case of the ferrite single phase of low carbon steel, the ferrite crystal grains in a pearlite steel have a small diameter angle boundary even if it is a patterning material.

For this reason, an appropriate inverted angle (limit angle) is examined so that the grain boundary, which is an orientation difference of 15 degrees or more, which can be recognized as a general grain boundary, is almost 90% or more. Good results were obtained. The unit comprised by the boundary which has an orientation difference of 9 degree or more was made into the pearlite block particle.

MEANS TO SOLVE THE PROBLEM As a result of earnestly investigating the control method of the pearlite block particle diameter, the present inventors stealmo-cooled by adjusting the amount of oxygen and the finishing rolling temperature after rolling, sizing the gamma particle diameter at the finish-rolling exit side to the state of being sized. We have found that it can prevent the appearance of coarse pearlite blocks. In the case where the? particles are mixed, the pearlite transformation easily occurs at a portion having a small? particle diameter, and since the metamorphic nucleus of the pearlite exists unevenly, the pearlite block is likely to grow and the particle diameter becomes large.

In order to reduce the γ particle diameter after finish rolling, the amount of oxygen in the steel is at least 18 ppm or more, preferably 20 ppm or more. On the other hand, when the amount of oxygen is increased, the amount of inclusions increases and coarse inclusions are generated. As a result, ductility decreases, so the upper limit is 30 ppm.

In the case of using normal continuous cooling, the pearlite block particle diameter changes while reaching the center from the surface layer of the wire rod, and as shown in FIG. 2, the pearlite block particle diameter at the position from the center is changed even when a general stealmo treatment is performed. Change. In addition, in FIG. 2, the pearlite block particle diameter is the average value in each case measured at eight places. Even though the average value was the same, the pearlite block particle diameters present in the center were greatly different. The present inventors have found that a portion having a large diameter of the central pearlite block is coarse with the pearlite lamellae, and this coarse pearlite portion is a breakpoint in the drawing process. Therefore, in order not to leave a defect after primary drawing, it is necessary to adjust the maximum value of a pearlite block particle diameter to 65 micrometers or less. As a result of investigating the relationship between the pearlite block particle diameter and the disconnection index in final drawing, when the pearlite block particle diameter at the center is 65 µm or less, the wire workability is improved, and the disconnection in the subsequent drawing process can be reduced. Turned out.

Next, the reason for defining the average value of the pearlite block particle diameter will be described. Since the measured pearlite block particle diameter uses continuous cooling, the pearlite block particles are mixed, and even if the average pearlite block particle diameter is simply averaged in this mixed state, the value is too small because many small pearlite blocks exist. It is not possible to reflect the disconnection characteristics. For this reason, Johnson-Saltykov measurement method ("measurement morphology" Uchidarogakuhosa, published July 30, 1972), which is a method for obtaining the average particle diameter of a known particle population premised on incorporation, The average value of the pearlite block particle diameters obtained using RT DeHoff.FN Rbiness.P189) is obtained by totaling 24 parts of 8 parts at each position of the surface layer, 1/4 part, and center part (1/2 part) of the wire rod. The average was calculated.
The Johnson-Soltikov measurement method is a method of obtaining the distribution of particle size from the distribution of the measured cross-sectional area of a particle. The measured cross-sectional area is divided into groups based on the linear logarithmic scale of diameter according to the size. It is a method of dividing into and calculating the cross-sectional area and particle volume for each group, obtaining the average diameter of a group, and calculating | requiring the diameter of the whole particle from the result.

When the obtained average value becomes 10 micrometers or less, it is difficult to adjust a pearlite structure to 95% or more, and the volume fraction of ferrite becomes high in 2% or more in a pearlite structure. For this reason, an average particle diameter needs to be 10 micrometers or more. In addition, when the average value exceeds 30 micrometers, in the case of continuous cooling, since the probability that coarse particle is contained becomes extremely high, it is necessary to adjust to 30 micrometers or less.

If the tensile strength is less than {248 + 980 × (C mass%)}-40 MPa, the pearlite lamellar gap structure becomes too large, and the good tensile strength is 248 + 980 × (C mass%)}- It is necessary to adjust to 40 MPa or more. Further, when the tensile strength exceeds 248 + 980 × (C mass%)} + 40 MPa, the work hardening is large, and the strength after wire drawing increases, so that the ductility decreases, so it is 248 + 980 × (C mass%)} + 40 MPa or less You need to adjust it.

In addition, it is good to adjust a cross-sectional reduction rate more than {72.8-40x (C mass%)}. When the cross-sectional reduction rate is less than 40%, internal defects are likely to occur at the time of drawing. In addition, in order to suppress that the cross-sectional reduction rate is less than 40%, the volume ratio of the cornerstone ferrite observed inside the wire rod obtained by stealmo cooling is adjusted to 2% or less. If it exceeds 2%, the cornerstone ferrite is likely to be the starting point of internal defects during the drawing process or the starting point of the internal defects in the tensile test. The problem that the cornerstone ferrite is a problem is less than 0.85% by mass of carbon. In the region where the amount of carbon is 0.85% by mass or more, since the amount of C is large, the cornerstone ferrite is generally adjusted to 2% or less.

Hereinafter, the reason for limitation of the steel component of the high carbon steel wire rod by this invention is demonstrated. All components are in weight percent.

C is an effective element for reinforcement, and in order to obtain a high strength steel wire, the amount of C needs to be 0.7% or more, but if it is too high, the cornerstone cementite easily precipitates and the ductility tends to decrease, so the upper limit is 1.1%. .

Si is an element necessary for deoxidation of steel, and when the content thereof is too small, 0.1% or more is added because the deoxidation effect is insufficient. In addition, Si is dissolved in the ferrite in the pearlite formed after the heat treatment to increase the strength after the patterning, while Si is 1.0% or less because it inhibits the heat treatment.

P tends to cause segregation, and the segregation portion is concentrated to 0.02% or less since P is concentrated and dissolved in ferrite to lower workability.

If S is in a large amount, MnS is formed in a large amount and the ductility of the steel is lowered, so it is adjusted to 0.02% or less.

Mn adds 0.1% or more of Mn to secure hardenability of the steel. However, addition of a large amount of Mn makes the transformation time during patterning too long, so it is 1.0% or less.

Cr is added to increase the strength of the steel. When it adds, it adds 0.05% or more which the effect is exhibited, and sets it as 1.0% or less which does not produce ductility of steel wire.

Mo is added to increase the strength of the steel. When it adds, it adds 0.05% or more which the effect is exhibited, and sets it as 1.0% or less which does not produce ductility of steel wire.

Cu is added to improve corrosion resistance and corrosion fatigue properties. When adding, it adds 0.05% of the addition effect. However, when a large amount is added, it is easy to embrittle at the time of hot rolling, and therefore an upper limit is made into 1.0%.

Ni has the effect of increasing the strength of the steel. When adding, 0.05% or more which adds the effect is added. However, when the amount added is too large, ductility is lowered, so it is 1.0% or less.

V has the effect of increasing the strength of the steel. When adding, it adds 0.001% or more of the addition effect. However, if the amount added is too large, the ductility decreases, so the upper limit is made 0.1%.

Nb has the effect of increasing the strength of the steel. When adding, it adds 0.001% or more of the addition effect. However, when the amount added is too large, the ductility decreases, so the upper limit is made 0.1%.

B has the effect of reducing the γ particle diameter when austenitized. This improves ductility, such as drawing. For this reason, when it adds, it adds 0.0005% or more which has the effect. However, if it is added beyond 0.006%, the transformation time at the time of transformation by heat treatment becomes too long, so the upper limit is made 0.006%.

Moreover, as a manufacturing method of obtaining the high ductility high carbon steel wire rod which concerns on this invention, in the hot rolling of the billet containing the above-mentioned component composition, after coiling at 850-900 degreeC within 10 second after hot rolling finishing, Stelmor It is preferable to perform direct patterning treatment which is cooled or immersed in the molten salt at 500 to 570 ° C.

Table 1 shows the chemical components of the test steels used for the start. No. 1 to No. 18, the composition of the steel is adjusted according to the present invention. No. 19, No. 20 is a river for comparison. Comparative steel 19 is a steel with less oxygen than present invention steel, and comparative steel 20 has a higher oxygen content than present invention steel.

These steels were melted in a furnace so as to be steels of the components shown in Table 1, and a bloom of 500 × 300 mm in cross-sectional dimension was produced by continuous casting. Then, it reheated and it was set as the billet of 120x122 mm cross section by the pulverization rolling process. Then, it heated to gamma region again, it was made into the wire rod of 5.5 mm diameter by hot rolling, and after finishing rolling, the winding temperature was adjusted to 850-900 degreeC for 10 second, and the stylo cooling divided into 4 zones was performed continuously. Table 2 shows the conditions for producing the wire rods. In addition, the mechanical properties of the wire rod obtained under the production conditions shown in Table 2 and the measured maximum and average values of the pearlite block are shown.

No. of Table 2 1, No. 2, No. 6 to no. 21 is prepared according to the present invention, No. 3 to No. 5, No. 22, no. 23 was prepared for comparison.

In Table 2, the die approach angle is set to 20 degrees to show the primary freshness, the drawing process is performed from 5.5 mm diameter to 1.0 mm diameter, and the disconnection and tensile tests in each pass are conducted. Indicated. In addition, after wire drawing was performed from 5.5 mm diameter to 1.56 mm diameter, brass plating was performed to process from 1.56 mm diameter to 0.2 mm diameter. Was obtained. The case where this disconnection index is favorable is shown by (circle).

No. of the present invention 1, No. 2, No. 6 to no. 21 shows good results for both primary freshness and secondary freshness.

No. by comparative steel Since 3 had a high finishing temperature, the maximum value of the pearlite block exceeded 65 micrometers, and both the primary freshness and the secondary freshness had a bad result.

Comparative Steel No. Since 4 had a high winding temperature, the maximum value of a pearlite block exceeded 65 micrometers, and both the primary freshness and the secondary freshness had a bad result.

Comparative Steel No. 5 is a case where the TS is lower than that of the present invention due to the change of the Stallmore cooling conditions. Also in this, 1st freshness and 2nd freshness had a bad result.

Comparative Steel No. 22 is a case where the amount of oxygen in the steel component is lower than the present invention. In this case, the maximum value of the pearlite block at the center is larger than the present invention.

Comparative Steel No. 23 is a case where the amount of oxygen in the component of steel is higher than this invention. In this case, although the maximum value of the pearlite block of the center part is the same as this invention, since the oxygen amount is high and the total amount of inclusions is large, secondary freshness fell.

According to the present invention, it is possible to produce an ultrafine wire having a higher fatigue strength than the conventional high carbon steel wire, and it is possible to reduce the weight and the life of the rubber product.

Claims (6)

By mass%, C: 0.7-1.1%, Si: 0.1-1.0%, Mn: 0.1-1.0%, P: 0.02% or less, S: 0.02% or less, O: 18-30 ppm, N: 0-40 ppm A high carbon steel wire rod comprising a residual Fe and unavoidable impurities, wherein the metal structure of the wire rod is composed of a pearlite structure of 95% by volume or more, and ranges from a center of a cross section perpendicular to the axis direction of the wire rod to a radius of 78 µm. The maximum value of the pearlite block particle diameter of pearlite in the center of the film is 65 µm or less, the tensile strength of the wire rod is in the range of {248 + 980 × (C mass%)} ± 40 MPa, and the reduction ratio of the cross section is {72.8-40 A high ductility high carbon steel wire rod, characterized by not less than x (% by mass)}%. The method of claim 1, wherein the wire is, in mass%, Cr: 0.05 to 0.22%, Mo: 0.05 to 1.0%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0%, V: 0.001 to 0.1%, Nb : 0.001 to 0.1%, Ti: 0.005 to 0.1%, B: 0.0005 to 0.006% of the high ductility high carbon steel wire, characterized in that it contains. The high-ductility high carbon steel wire rod according to claim 1 or 2, wherein an average value of the pearlite block particle diameters of the pearlite in the center of the cross section perpendicular to the axial direction of the wire rod is 10 µm or more and 30 µm or less. 3. The high ductility high carbon steel wire rod according to claim 1 or 2, wherein the metal structure of the wire rod includes a cornerstone ferrite having a volume fraction of 2% or less. delete delete

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