JP3237305B2 - High carbon steel wire for high strength and high ductility steel wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high carbon steel wire which can be used as a material for a steel wire used as a reinforcing cord wire of a steel tire for automobiles, for example.
Particularly, the present invention relates to a high carbon steel wire capable of providing a steel wire having higher strength and higher ductility than before.

[0002]

2. Description of the Related Art Conventionally, steel wires such as cord wires and bead wires used as reinforcing materials for rubber products such as steel tires for automobiles, conveyor belts and high-pressure hoses generally have a diameter of about 0.2 mm. High-carbon steel filament, that is, a strand obtained by twisting a cord wire. At present, the strength of the filament is about 310 kgf / mm ² .

[0003] For example, code wires are generally

[0004]

(Equation 1)

[0005] It is manufactured in the process described above. The numbers in the above table represent dimensions (mm).

[0006] Eutectoid carbon steel typified by AISI standard-C1080 has been used as a steel wire material for the cord wire. Table 1 shows a typical composition example.

[0007]

[Table 1]

That is, to a steel wire having such a composition,
After the intensity subjected to patenting treatment in 115~125kgf / mm ^2, from the final subjected to brass plating for adhesion securing the rubber, by a wet method in order to avoid the adhesion of the lubricant to the surface as much as possible The wire was drawn to produce, for example, a steel wire having a strength of 310 kgf / mm ² and a wire diameter of 0.2 mm.

[0009] As a part of recent weight reduction of automobiles, automobile tires are also required to be reduced in weight, and in order to meet the demand for such reduction in weight, steel wires having higher strength such as 370 kgf / mm ² or more are required. It has become However, when a conventional steel wire having the steel composition shown in Table 1 was used, only a strength of about 350 to 360 kgf / mm ² was practically obtained even if the manufacturing conditions were optimally set.

Furthermore, in order to obtain this strength, the degree of working in drawing: In (cross-sectional area of base material / cross-sectional area after drawing) is at least 4.
0 is necessary, but at present, the working degree: 3.6 (processing of a 1.2 mm diameter drawn wire into a 0.2 mm diameter steel wire) is commonly used, and in order to obtain a working degree of 4.0 or more, wet drawing is required. The machine had to be modified to increase the number of dice passes.

On the other hand, FIG. 2 shows the strength TS and the reduction RA of the steel wire obtained by drawing a steel wire having the composition shown in Table 1.
FIG. 2 is a graph showing the relationship between the maximum workability ln (A ₀ / A _n ) at the time of wire drawing. As is clear from FIG.
If the wire is drawn with a degree of processing, the strength obtained is 300k
It was about gf / mm ² . Therefore, various techniques for increasing the strength of the steel wire have been conventionally proposed.

In the technique proposed in Japanese Patent Application Laid-Open No. 2-194147, the content of Cr is 0.10 to 0.30% (hereinafter, "%" means "% by weight" unless otherwise specified. ) Use added steel wire.

JP-A-3-271329 discloses that the C content is
0.90-1.25% and Cr content 0.1-1.0
% And, if necessary, a steel wire having a B content of 0.1% or less, and a heat treatment with a limited cooling rate according to the C content to prevent the formation of proeutectoid cementite. There has been proposed a technique of manufacturing a high-strength steel wire by enabling wire drawing at a reduced area.

Further, the present inventor has disclosed in Japanese Patent Laid-Open Publication No.
According to Japanese Patent Publication No. 19, in brief, C content: 0.7 to 0.9%
We proposed a technology to produce high-strength steel wire by drawing a wire with a workability of about 4.8 on the steel wire rod.

[0015]

According to the technique proposed in Japanese Patent Application Laid-Open No. 2-194147, although the wire is drawn with a workability of about 3.6, only a strength of about 360 kgf / mm ² is obtained.
In addition, the torsion value, which is an indicator of ductility, is a normal level of around 25 turns, and a desired high-strength and high-ductility steel wire cannot be produced. Furthermore, since no mention is made of the fatigue properties, which is one of the most important properties as a steel wire,
Its practicality is not clear.

According to the technique proposed in Japanese Patent Application Laid-Open No. 3-271329, even if the formation of proeutectoid cementite can be suppressed, the amount of cementite in pearlite increases, and micro defects that deteriorate the fatigue characteristics during processing are reduced. It occurs at the interface between ferrite and cementite. Since this point is not mentioned at all, its practicality is not clear.

Further, according to the technique proposed in Japanese Patent Application Laid-Open No. 3-240919, it is certain that a wire having a workability of 4.8 can be used to obtain 40
A steel wire having a strength exceeding 0 kgf / mm ² is provided. However, even with this technology, wire drawing with a working ratio of 3.6: the same level as the current situation can only achieve a strength of about 300 kgf / mm ² , and the high strength required unless a special method is required for heat treatment. I can't get it.

As described above, in order to increase the strength of a steel wire obtained by drawing, it is basically important to increase the strength before drawing and to increase the workability. . FIG. 3 is a graph showing the relationship between the strength or lamella spacing of the drawn wire before drawing and the degree of drawing or the ultimate strength of the steel wire. The steel wire made of eutectoid carbon steel containing no alloying element is shown in FIG. If the strength before wire drawing is too high, the working degree cannot be increased, so that the strength of the steel wire does not improve. On the other hand, if the strength before drawing is reduced, the workability can be increased, but the ultimate strength of the steel wire does not increase.

In order to solve these problems, alloying elements such as Cr are usually added to eutectoid carbon steel. However, it takes a long time for transformation or ductility due to insufficient growth of cementite in the pearlite structure. In addition, there is a problem that the steel wire cannot be used as a steel wire due to deterioration of the steel wire and fatigue characteristics.

Here, the object of the present invention is to provide a conventional manufacturing condition.
(Working degree), especially under the condition of working degree Inε = 3.6,
Ferrite - performing wire drawing while suppressing the occurrence of minute defects in the cementite interfacial strength 370kgf / mm ² or more, has a twisting value 30 times or more properties, and durability ratio (fatigue strength / tensile strength) is An object of the present invention is to provide a steel wire material which is a material of a steel wire having good fatigue characteristics of about 1/3.

[0021]

Means for Solving the Problems The present inventor has proposed that C: 0.88
%, Si: 0.30%, Mn: 0.50%, and the Cr content is 0,0.
Eight kinds of steel wires having compositions changed to eight levels of 40, 0.55, 0.75, 1.00, 1.10, 1.30 and 1.50% were repeatedly subjected to wire drawing (workability: 3.6) and heat treatment to produce steel wires. The ultimate strength and workability of this steel wire were measured.
FIG. 4 is a graph showing the results in relation to the Cr content.

As is apparent from FIG.
In the range of ~ 1.0%, the ultimate strength is extremely large, but the lamella spacing is 0.12μm (LP material TS 135 kgf / mm
² ) The case was relatively rough. If the lamella spacing is reduced, the strength before drawing (LP material TS) naturally increases. But,
In the region where the Cr content is less than 0.5%, the growth of cementite in pearlite is insufficient, the ductility is low, and the critical workability ln (A ₀
/ A _n ) is rather reduced, so that a finer structure cannot be obtained, and the ultimate strength is reduced.

Therefore, the present inventors have conducted intensive studies to improve the strength before drawing, the limit workability, and the strength after drawing by reducing the lamella spacing in the region where the Cr content is less than 0.5%. Continued.

As a result, as shown in the graph of FIG.
Is added in a certain amount defined by the Cr content, so that the Cr content is in the range of 0.15% to 0.35%,
Because it can promote the growth of cementite in pearlite,
It has been found that the ductility and drawability of the steel wire can be improved by making the lamella spacing finer, and that the strength can be further increased by drawing the steel wire, and further studies have been completed to complete the present invention.

Here, the gist of the present invention is as follows: C: 0.80 to 1.10%, Si ≦ 0.25%, Mn ≦ 0.45%, P ≦ 0.01
0%, S ≦ 0.010%, Cr: 0.15 to 0.35%, N ≦ 0.0040%, B: 0.0005 to 0.01 ×
Is Cr [%] +0.001% balance Fe and incidental impurities Tona Ri lamellar spacing and wherein <br/> have a finer structure than 0.12μm high strength and high ductility steel wire for high-carbon steel wire rod .

As described above, the present invention particularly determines the lower limit of the Cr content in order to increase the work hardening and increase the strength, and the heat treatment (patenting) conditions are almost free from conventional alloy elements. To determine the upper limit of Cr content so that it can be processed in the same manner as in the case of eutectoid steel, and to compensate for the lack of growth of cementite in the pearlite structure, which is a drawback of Cr-containing steel, and to secure ductility and drawability. It is characterized in that an appropriate amount of B is added according to the Cr content.

The high-carbon steel wire for high-strength and high-ductility steel wire according to the present invention can be used as a steel wire for reinforcing rubber products such as steel tires for automobiles, conveyor belts and high-pressure hoses.

[0028]

Hereinafter, the present invention will be described in detail together with the function and effect.
First, the reason for limiting the composition of the steel wire rod as described above in the present invention will be described.

C: C is an element necessary for securing the strength of the steel wire. The lower limit is set to 0.80% because a steel wire having a strength exceeding 370 kgf / mm ² cannot be obtained with a target C of 3.6 with a target working ratio of 3.6 if the C content is lower than this. On the other hand, the upper limit is set to 1.1% in order to suppress precipitation of proeutectoid cement. In general, at a cooling rate of about air cooling, when the C content exceeds 0.95%, ductility deterioration in the drawing process due to proeutectoid cementite becomes remarkable, but by making the cooling rate equal to or more than that of lead patenting, 1.
Up to 1% can be controlled. Therefore, the upper limit is 1.
1%, preferably less than 0.95%. Therefore, the C content is 0.80% or more and 1.1% or less, preferably 0.80% or more and 0.1% or less.
It shall be less than 95%.

FIG. 5 shows the relationship between the C content and the reduction RA (%) in terms of Si: 0.25%, Mn: 0.43%, P: 0.010%, and S: 0.010%.
%, Cr: 0.25%, N: 0.0040%, B: 0.0025% Diameter 1.
It is a graph shown about a 2 mm steel wire rod. As is clear from the figure, in the case of air cooling, when the C content exceeds 0.95%, RA
(%) Is remarkably deteriorated, but is improved when the C content is 0.90 to 0.95%. In the case of lead patenting, RA (%) deteriorates remarkably when it exceeds 1.1%.

Si: Si has the effect of increasing the strength of steel by forming a solid solution with ferrite, but also has the property of particularly deteriorating ductility when added to eutectoid steel. However, since Si is indispensable as a deoxidizing agent, in the present invention, the upper limit is set to 0.25% to prevent a decrease in ductility while maintaining the deoxidizing effect. Therefore, the Si content is limited to 0.25% or less.

[0032] Mn: Mn has the property of lowering the A ₁ transformation point, when the eutectoid steel is to lower the ductility roughened tissue (pearlite). Further, Mn causes segregation together with P and lowers ductility. Therefore, it is desirable that the Mn content be low, but it is not easy to completely reduce Mn since Mn is inevitably mixed in the hot metal stage. Therefore, the Mn content is limited to 0.45% or less, at which no harmful effect is recognized in practical use.

P, S: P and S are desirably small as both P and S degrade the drawability of the steel wire rod made of eutectoid steel and the ductility of the steel wire after drawing. Especially the content of each is 0.
If the content exceeds 010%, the content is significantly deteriorated. Therefore, the contents of P and S are each limited to 0.010% or less.

Cr: Cr is added to increase the strength of the drawn steel wire. By adding a certain amount of B, which will be described later, in combination with Cr, when the Cr content is in the range of 0.15% to 0.35%, the strength can be increased by reducing the lamella spacing. That is, if the Cr content is less than 0.15%, the target strength of 370 kgf / mm ² at the workability of 3.6 cannot be achieved, while the Cr content is less than 0.15%.
If it exceeds 35%, the growth of cementite in the pearlite having a lamella spacing of 0.1 μm becomes insufficient and ductility is reduced, and the critical working degree is rather lowered. Therefore, the Cr content is 0.
Limited to 15% or more and 0.35% or less.

N: N forms a solid solution in ferrite in pearlite and causes strain aging during and after wire drawing. Therefore, if a certain amount or more is contained, ductility such as drawing and twist value which are important for the steel wire is deteriorated. Therefore, in order to ensure ductility, the N content is limited to 0.0040% or less.

B: In general, the growth of cementite in pearlite is slow in Cr-added steel, and only pearlite consisting of cementite having a short length can be obtained. The strength of pearlite is determined by the spacing between cementite layers. The length of cementite affects ductility and drawability, and the longer the length, the better the ductility and drawability. Therefore, in order to increase the strength of the product obtained by drawing the Cr-added steel,
Increasing the length of cementite is also effective.

By adding an appropriate amount of B, the strength of the Cr-added steel can be increased. That is, as shown in the graph of FIG. 1, even if the same Cr content and the same lamella spacing (0.10 μm in the example shown in FIG. 1), when B is not added, the critical working degree is low, and The ultimate strength is 350 kgf / mm ² or less. This is because even when the lamella spacing is the same, when B is not added, the length of cementite is short, and the ductility and drawability are insufficient.

On the other hand, when B is added, the cementite grows sufficiently long, so that the drawability is improved and the target strength: 370 kgf / mm ² or more can be achieved in the range of Cr content: 0.15 to 0.35%. Thus, in the present invention, by adding B, the growth of cementite in pearlite is promoted,
It improves the ductility and drawability of a steel wire, and further improves the ductility, fatigue characteristics, and the like of a steel wire obtained by drawing.

In the present invention, the most remarkable effect of the addition of B is that cementite in pearlite grows for a sufficiently long time, so that micro defects generated in the wire drawing process are reduced, and fatigue properties are reduced.
(Durability ratio, fatigue strength). That is, as described above, by adding B in accordance with the added amount of Cr to overcome the shortcoming of cementite, which is a disadvantage of Cr-added steel, the growth of cementite in pearlite is promoted, and ferrite and cementite are drawn during wire drawing. The generation of micro defects generated at the interface with
Fatigue strength) is improved.

The amount of B added is determined according to the Cr content by B [%]: 0.00
The reason for limiting to the range expressed by not less than 05% and {0.01 × Cr [%] + 0.001%} is that if the amount of B added falls below the lower limit, cementite cannot be grown to a required level.
Further, even if B is added beyond the upper limit, the effect of not less than a certain level cannot be expected, but the amount of B existing at the grain boundary cannot be neglected, and the drawability is lowered. Therefore, the amount of B added is limited to the range of B [%]: 0.0005% or more {0.01 × Cr [%] + 0.001%} or less. Compositions other than the above are Fe and unavoidable impurities. Examples of the inevitable impurities include Al ₂ O ₃ and SiO ₂ .

The high-carbon steel wire for high-strength and high-ductility steel wire according to the present invention having the above composition is formed into a steel wire by ordinary heat treatment and wire drawing, and it is not necessary to go through any special process. Absent. For example, heat treatment (patenting treatment) and wire drawing are repeatedly performed on steel
After the 150 kgf / mm ^2, performs final drawing after applying brass plating, a conventional 3.6 about working ratio, for example, intensity 37
A steel wire of 0 kgf / mm ² or more and a wire diameter of 0.2 mm may be used. Further, the present invention will be described in detail with reference to examples, but this is an exemplification of the present invention, and the present invention is not limited thereto.

[0042]

EXAMPLES Each of the steels having the chemical compositions shown in Table 2 was melted in a 150 kg vacuum melting furnace, and hot-rolled into a wire having a diameter of 5.5 mm.

[0043]

[Table 2]

[0044]

[Table 3]

The wire drawing this line repeatedly performs diameter 1.2mm and heat treatment cold drawing the material, after the lead patenting as the final patenting treatment, subjected to pickling and lubricating treatment with 20% sulfuric acid After that, wire drawing was performed using a wet continuous wire drawing machine to produce sample Nos. 1 to 27, which are cord wires having a diameter of 0.20 to 0.26 mm. In addition, lead patenting was performed by adjusting the temperature of the lead bath so that the lamella spacing became 0.1 μm by a usual method. The manufacturing process of the sample is shown below.

[0046]

(Equation 2)

With respect to these samples, the strength TS, the drawing RA, and the lamella spacing after the patenting before drawing were measured, and the strength TS, drawing RA, and the twist value TN after drawing (distance between chucks: 100 × diameter) dmm) was measured. The rotary bending fatigue strength (strength not broken ¹⁰⁷ times repeated) was determined for each sample was determined endurance ratio. The results are summarized in Tables 2 and 3.

Of the samples shown in Tables 2 and 3, in each of the examples of the present invention, the critical working degree In (A ₀ /An)=3.6.
It had a strength exceeding the target strength of 370 kgf / mm ² , and the twist value also showed a high value exceeding 33 times. Furthermore, the fatigue property, which is one of the most important properties of the steel wire, has a durability ratio (fatigue strength / tensile strength) of about 0.25 in the comparative example, but the present invention example has a high value of about 0.33. Is shown. The fatigue strength of the comparative example was about 70 to 100 kgf / mm ² , whereas the fatigue strength of the inventive example was as high as 125 to 135 kgf / mm ² .

On the other hand, in Sample No. 1, since the C content was lower than the lower limit of the range of the present invention, the strength of the steel wire was insufficient. In Sample No. 6, since the C content exceeded the upper limit of the range of the present invention, the ductility of the steel wire was deteriorated.

In sample No. 9, the ductility of the steel wire was deteriorated because the Si content exceeded the upper limit of the range of the present invention. Sample N
In o.12, the ductility of the steel wire was deteriorated because the Mn content exceeded the upper limit of the present invention.

In Sample No. 13, since the P content exceeded the upper limit of the range of the present invention, the ductility of the steel wire was deteriorated. sample
In No. 14, the S content exceeded the upper limit of the range of the present invention, so that the ductility of the steel wire was deteriorated.

In Sample No. 15, the Cr content was below the lower limit of the range of the present invention, so that the strength of the steel wire was insufficient. sample
In No. 18, since the Cr content exceeded the upper limit of the range of the present invention, the ductility of the steel wire was deteriorated and the strength was insufficient.

In sample No. 19, since the N content exceeded the upper limit of the range of the present invention, the ductility of the steel wire was deteriorated. sample
In No. 20, since the B content was below the lower limit of the range of the present invention, the fatigue strength of the steel wire was deteriorated.

In sample No. 23, since the B content exceeded the upper limit of the range of the present invention, the fatigue strength of the steel wire was deteriorated.
In sample No. 24, since the B content was lower than the lower limit of the range of the present invention, the strength of the steel wire was deteriorated.

In sample No. 27, since the B content exceeded the upper limit of the range of the present invention, the fatigue strength of the steel wire was deteriorated.
Thus, by using a steel wire having a steel composition that satisfies the scope of the present invention, even when performing a patenting process under normal conditions and a wire drawing with a conventional working ratio of Inε = 3.6,
A steel wire having a strength of 370 kgf / mm ² or more and a torsion value of 35 times or more and a fatigue strength of 124 to 133 kgf / mm ² , which is higher than the conventional value, can be manufactured.

[0056]

As described above in detail, according to the present invention, even if the wire is drawn at a workability of 3.6, which is the same as the conventional one, the strength: 370
kgf / mm ² or more, torsion value: 30 times or more, fatigue strength 120 kgf / mm
It became possible to manufacture ^two or more high-strength, high-ductility steel wires. By using a high-strength and high-ductility steel wire manufactured by using the present invention as a reinforcing cord wire of a steel tire for an automobile, it is possible to significantly contribute to weight reduction of the automobile.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the amount of Cr on the working ratio and the ultimate strength of a steel wire when Cr and B are added in combination according to the present invention.

FIG. 2 is a graph showing the relationship between the strength and drawing of a steel wire obtained by drawing a steel wire having the composition shown in Table 1 as a conventional method, and the degree of work during drawing.

FIG. 3 is a graph showing the relationship between the strength or lamella spacing of a drawn wire before drawing and the workability or the ultimate strength of a steel wire in a conventional method.

FIG. 4 shows a Cr content of 0 to 1.50% as a preliminary test of the present invention.
The results obtained by repeatedly drawing and heat-treating eight types of steel wires having compositions changed to eight levels in the range of to produce steel wires and measuring the ultimate strength and workability of the steel wires at this time are shown. It is a graph.

FIG. 5 is a graph showing the relationship between the C content and the reduction RA (%) in the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Terutaka Tsumura 4-33 Kitahama, Chuo-ku, Osaka City Inside Sumitomo Metal Industries, Ltd. (56) References JP-A-3-271329 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (1)

(57) [Claims] C .: 0.80-1.10%, Si ≦ 0.25%, Mn ≦ 0.45%, P ≦ 0.01 by weight%.
0%, S ≦ 0.010%, Cr: 0.15 to 0.35%, N ≦ 0.0040%, B: 0.0005 to 0.01 ×
Cr [%] +0.001% balance Fe and incidental impurities Tona Ri lamellar spacing and wherein <br/> have a finer structure than 0.12μm high strength and high ductility steel wire for high-carbon steel wire rod.