JPH04289148A - Wire for wire drawing and wire made of steel - Google Patents

Abstract

PURPOSE:To offer a high strength and high ductility wire made of steel provided with mechanical properties of >=500kgf/mm<2> strength and >=40% reduction of area. CONSTITUTION:A wire material for wire drawing having a structure in which carbide and ferrite are alternately arranged with a space and the direction of the arrangement has an angle of <=45 deg.C in the longitudinal direction of the wire rod and having 0.7 to 0.9 wt.% carbon content is subjected to wire drawing.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel wire, typified by a steel cord wire used, for example, for reinforcing automobile tires, and a drawing wire therefor. More specifically, the present invention relates to a high-strength and high-ductility steel wire that is made to have high strength and high ductility, and a wire for wire drawing therefor.

0002

[Prior Art] Steel cord wire, which is the most typical example of the use of ultra-fine steel wire, has conventionally been produced by patenting eutectoid carbon steel represented by AISI standard C1080, that is, heating it to about 1000°C. It was produced by austenitizing, rapidly cooling in a lead bath at 450 to 600°C, and then wire drawing.

The structure obtained by the patenting process is fine pearlite, and as shown in FIG. 3, the crystal grain structure is carbide (Fe3C, cementite).
The structure consisted of layered layers of ferrite and ferrite, which were arranged in various directions. Within each crystal grain, black lines indicate cementite, and white lines indicate ferrite. By drawing a wire for wire drawing having such a structure, work hardening has been utilized to increase the strength of the resulting steel wire.

By the way, as is clear from FIG. 4, which schematically shows the crystal grain structure during drawing of this steel wire, when drawing using a die, a layered structure consisting of carbide (cementite) and ferrite is formed. A phenomenon occurs in which a part of the wire rotates so that it is aligned with the longitudinal direction of the wire, which is the drawing direction, or bends. In other words, the crystal grains rotate in the direction of the arrow in the figure, or the crystal grains are crushed, and the layered structure of cementite/ferrite within the same crystal grain is bent. Such rotation and bending of the layered structure ultimately causes defects (microvoids) in the internal structure of the steel wire product, deteriorating the ductility of the steel wire and increasing the degree of wire drawing. If such rotation or buckling occurs, it becomes impossible to increase the strength of the steel wire.

FIG. 5 shows the results of experimental confirmation of the above points by the present inventors, showing that steel having the composition shown in Table 1 and having the crystal grain structure exhibiting rotation and buckling as shown in FIG. A conventional patenting process is applied to increase the strength to 11.
The degree of workability (InAo/An) when drawing a wire for wire drawing (herein also referred to as wire rod for wire drawing) maintained at about 5 to 125 kgf/mm2 and the mechanical properties of the obtained steel wire The solid line shows the correlation with

[0006]

[Table 1]

As is clear from FIG. 5, the above-mentioned rotation and bending of the layered structure in the wire drawing direction occur during the wire drawing, so that the work hardening is reduced once and the high strength of the resulting wire is inhibited. I know it will happen. In this experiment, wire drawing was carried out under conditions that were carefully selected in the laboratory, but the strength obtained when ductility was maintained at a certain level was about 380 to 400 kgf/mm2 at most. .

On the other hand, for example, Japanese Patent Application No. 2-34525 discloses that in the patenting treatment before the final wire drawing, after heating to the austenite region temperature, the temperature is reduced to Ae 1 point or less at a cooling rate within a range that does not fall below the pearlite transformation start temperature. , a technology has been proposed to obtain a steel wire with a strength of over 400 kgf/mm2 by drawing a wire that has been cooled to a temperature range above the Ms point and subjected to plastic working with a working degree of 20% or higher to undergo pearlite transformation. has been done. However, even with this technique, the strength that can be obtained is about 410 kgf/mm2, and a special method is required for heat treatment, so it is difficult to say that it is a desirable technique from the viewpoint of manufacturing cost.

[0009]

[Problems to be Solved by the Invention] In order to improve the strength of steel wire obtained by wire drawing, such as steel cord, it is necessary to make the strength of the wire material for wire drawing as high as possible and to A means of setting the degree of wire drawing as high as possible is generally used. However, if the strength of the wire rod for wire drawing is simply set high, it becomes difficult to increase the degree of wire drawing, and the strength of the resulting steel wire does not improve. On the other hand, although the degree of wire drawing can be increased by lowering the strength of the wire rod for wire drawing, the strength of the steel wire still does not improve much.

[0010] In any case, improving the strength of the steel wire while maintaining the ductility value indicated by the reduction of area and torsion value is achieved by the rotation of the layered structure mentioned above during wire drawing. There is a limit due to the occurrence of bending and buckling, and in particular, work hardening becomes small due to the rotation of the layered structure, making it impossible to achieve high strength. In this way, depending on the conventional steel type and heat treatment method, for example, the reduction of area: 40% or more and the strength: about 390 kgf/mm2, or the reduction of area:
With 30% or more, only a steel wire with a strength of about 410 kgf/mm2 could be obtained. SUMMARY OF THE INVENTION An object of the present invention is to provide a high-strength and high-ductility steel wire that solves the problems of the above-mentioned conventional techniques and can achieve even higher strength and ductility, and for wire drawing therefor. Providing wire, specifically strength: 500kgf
The object of the present invention is to provide a high-strength and high-ductility steel wire having mechanical properties of 40% or more and a drawing wire therefor.

[0011]

[Means for Solving the Problems] Even with the conventional technique of drawing a wire rod having a pearlite structure in which carbide and ferrite are layered and arranged in various directions, it is possible to draw a wire of 380 to 400 kgf at most. The reason why a strength of only about /mm2 could be obtained is that, as mentioned above, part of the layered structure of carbide and ferrite rotates or bends, resulting in deterioration of ductility, which limits the wire drawing process. This is thought to be due to the following reasons: (1) Rotation of the layered structure occurs and work hardening becomes small.

[0012] Therefore, in order to solve the above-mentioned problem, the inventors of the present invention thought that it would be best not to cause rotation and buckling of the layered structure during wire drawing, and conducted further studies. As a result, the present inventors obtained a 45° longitudinal direction as shown in FIG.
A layered structure of carbides and ferrite arranged within (
It has been discovered that a material having a "unidirectional pearlite structure" (hereinafter referred to as "unidirectional pearlite structure" in this specification) is useful as a wire rod for wire drawing, and by drawing this wire rod for wire drawing, it is possible to eliminate the problems that occur during conventional wire drawing. It is possible to eliminate factors that inhibit high strength, such as the occurrence of internal defects and a decrease in work hardening, which previously existed, as well as to prevent the decrease in work hardening during wire drawing as described above, and to reduce the wire drawing limit during wire drawing. The present invention was completed based on the finding that a steel wire with high strength and high ductility, which did not previously exist, and a wire for wire drawing therefor could be obtained.

[0013] The gist of the present invention is that the carbide and the ferrite are arranged alternately at intervals, and the direction of the arrangement is at an angle of 45° or less with respect to the longitudinal direction. and the carbon content is 0.7~
It is a wire for wire drawing of 0.9% by weight. From another perspective, the TS obtained by drawing the above-mentioned wire for wire drawing≧
It is a high strength and high ductility steel wire with 500 kgf/mm2 and RA≧40%.

In a preferred embodiment of the present invention, the arrangement direction of the layered structure of pearlite/ferrite is preferably within 40 degrees for all crystal grains. Also, although not limited to this, TS≧500kgf/mm2,
Generally 10-20% as long as RA≧40% is ensured
Orientations beyond 45 degrees may be acceptable.

[0015]

[Function] The present invention will be explained in detail below along with its functions and effects. In the following description of the present invention, "%" means "% by weight" unless otherwise specified. First, in the steel wire according to the present invention and the drawing wire therefor, the carbon content is set to 0.7 to 0.9%.
Explain the reason for this limitation. This is because if the carbon content is less than 0.7%, the ferrite structure will precipitate alone in the pearlite structure consisting of carbide and ferrite, which will inhibit high strength.On the other hand, if the carbon content is 0.9% This is because if the wire is exceeded, carbide (cementite) will precipitate on its own, causing internal defects in the subsequent wire drawing process and significantly inhibiting the ductility of the steel wire. Therefore, in the present invention, the carbon content is 0.7%
Limit it to 0.9% or less.

The composition other than carbon is not particularly limited and may be the same as the composition of ordinary wires of this type. For example, Si: 0.3 to 0.6%, Mn:
0.4-0.7%, P: 0.010-0.015
%, S: 0.010 to 0.015%, balance Fe and unavoidable impurities. Next, the reason for using a unidirectional pearlite structure in the present invention will be explained.

This structure is schematically shown in FIG. As shown in Figure 4, in the conventional structure, the layered structure formed by carbide (Fe3C) and ferrite is arranged so as to be oriented in multiple directions, so when this is drawn, each structure is oriented in the drawing direction. As the tissues try to rotate so that they are aligned, tissues that cannot rotate will bend. This rotation phenomenon causes a decrease in work hardening during wire drawing, as seen from the workability curve shown in FIG. Furthermore, the bent part is ductile (drawing).
Since it is not possible to increase the degree of wire drawing as it also causes a decrease in the strength of the obtained wire, the strength of the obtained wire cannot be sufficiently improved.

Accordingly, in the present invention, in order to prevent the occurrence of the rotation and buckling, the pearlite structure of the wire for wire drawing is aligned in substantially one direction, and then the wire is drawn. By doing so, a steel wire with unprecedented high strength and high ductility can be obtained. In the unidirectional pearlite structure, the angle of inclination of the layered structure with respect to the longitudinal direction is limited to within 45°, but this indicates the range in one direction; if the angle of inclination exceeds 45°, the rotation and The suppressive effect of sitting music is weakened.

Many methods can be used to form such a unidirectional pearlite structure, but from a practical point of view, a simple method is to heat it to Ac1 point or higher, and then
Provide a temperature gradient in the longitudinal direction of the wire 150 to 250
It is conceivable that the unidirectional pearlite structure thus precipitated is grown by cooling at a cooling rate of °C/sec and heating it to 550 to 600 °C. Note that there are no limitations on the diameter of the drawing wire and the obtained steel wire. Wire drawing may also be performed by conventional means. Generally, TS≧500kgf/mm2, RA≧
To achieve 40%, the wire can be made by dry and wet wire drawing. Further, the present invention will be described in detail with reference to Examples, but these are merely illustrative of the present invention and are not intended to limit the present invention.

[0020]

[Example] Steel types A to D having the compositions shown in Table 2 were prepared by 15
After melting in a 0kg vacuum melting furnace, hot rolling is performed to obtain a diameter:
The wire rod was rolled to a diameter of 5.5 mm and further cold-drawn to a diameter of 2.0 mm, and then heat treated using the apparatus shown in FIG. 2(a) or FIG. 2(b).

[0021]

[Table 2]

FIG. 2 is a schematic diagram schematically showing the structure of an apparatus for performing the heat treatment. First, Figure 2(a)
is a schematic explanatory diagram showing an example of an apparatus for obtaining a unidirectional pearlite structure. The material is heated to a temperature range of A1 point or higher using the heater 1 and the heating furnace 3 to form austenite, and then cooled to a supercooled austenite state using the induction heater 2 and the rapid cooling device 4 at a cooling rate of 150 to 250 °C/sec. 550～
This is a device that aims at unidirectional growth of pearlite by heating to a temperature range of 600°C.

FIG. 2(b) is a schematic explanatory diagram showing the configuration of a conventional lead patenting apparatus comprising a heating furnace 7 and a lead bath furnace 8. As shown in FIG. Since this device is a conventionally known device for changing the structure of the wire to a sorbite structure (fine pearlite structure), further explanation will be omitted. Heat-treating the wire using such a device,
After measuring the tensile properties (TS, RA) of the heat-treated materials, they were each pickled (H2SO4
20°C x 5 minutes), lubrication (film forming) treatment using the Bonderite method and Bonda Lube method, and cold wire drawing were performed, and the wire drawing limit and TS and RA of the wire drawn material were measured. The results are summarized in Table 3.

[0024]

[Table 3]

In the same table, sample No. 1 is test steel A
It can be seen that since the C content is below the lower limit of the range of the present invention, free ferrite is precipitated in the pearlite structure, resulting in insufficient strength. Sample No. 2 and sample no. 3, in order for all conditions to satisfy the range of the present invention, TS = 515 to 520 kgf/mm2, R
A steel wire (drawn wire material) with high strength and high ductility with A=41 to 44% was obtained.

Sample No. In No. 4, it can be seen that the strength did not increase because the C content of the test steel exceeded the upper limit of the range of the present invention, and cementite precipitated alone and sufficient wire drawing could not be performed. . Sample No. 5 to sample no. No. 8 has a multi-directional pearlite structure, which is different from the scope of the present invention, and therefore the strength is insufficient.

Next, sample No. When looking at the changes in TS and RA when the working degree was changed for No. 2, the results shown by the broken line in FIG. 5 were obtained. It can be seen that by creating a unidirectional structure, as the degree of processing increases, the TS can be significantly improved while maintaining the RA approximately constant.

As described above, by satisfying the scope of the present invention, a steel wire with high strength (TS≧500 kgf/mm2) and high ductility (RA≧40%) and a wire for wire drawing therefor can be obtained. That is clear.

[0029]

Effects of the Invention The present invention provides a steel wire with high strength and high ductility and a wire for wire drawing therefor, specifically, a strength of 500 kgf/mm2 or more,
Drawing: We were able to provide a high strength and high ductility steel wire with mechanical properties of 40% or more. The practical significance of the present invention having such effects is extremely significant.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram schematically showing the structure of a drawing wire for obtaining a high-strength and high-ductility steel wire according to the present invention.

FIG. 2 is a schematic explanatory diagram schematically showing the configuration of an apparatus for heat-treating a wire for wire drawing, and FIG. 2(a) shows an example of an apparatus for obtaining a unidirectional pearlite structure; b)
1 and 2 show examples of devices that perform conventional lead patenting processing, respectively.

FIG. 3 is a schematic explanatory diagram showing the structure of a wire for wire drawing obtained by a patenting process.

FIG. 4 is a schematic diagram schematically showing the structure of a wire for wire drawing during wire drawing.

FIG. 5 is a graph showing a workability curve obtained from a confirmation experiment under specific conditions.

Claims (2)

[Claims] 1. A structure in which carbides and ferrite are arranged alternately at intervals, the direction of the arrangement is at an angle of 45° or less with respect to the longitudinal direction of the wire, and the carbon content is 0. 7 to 0.9% by weight wire for wire drawing. 2. TS≧500 kgf/mm2, RA obtained by drawing the wire for wire drawing according to claim 1.
≧40% high strength and high ductility steel wire.