JPH0765096B2 - Method for producing ultra high strength steel wire with excellent ductility - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an ultra high strength steel wire having excellent ductility.

(Prior Art) Piano wire and its equivalent steel wire are used in a wide range of fields such as PWS wire, spring, hose wire, and tire cord, but in recent years, there is a demand for the development of steel wire having a strength level of JIS or higher. Is high.

Hereinafter, the "ultra" high-strength steel wire in the present invention is usually referred to as a high-strength steel wire, because it is customary to indicate a steel wire having a strength equivalent to JIS G 3522 piano wire, and therefore, a higher strength. It was called an ultra high-strength steel wire in the sense of a steel wire having.

JIS G 3522 specifies the tensile strength of steel wire with a diameter of 6 mm to 0.08 mm, but the tensile strength depends on the wire diameter, and the thinner the wire diameter, the easier it is to achieve high strength. JIS also has a system based on this, and the upper limit of tensile strength can be roughly expressed by the following formula.

TS = 250-100logD (kgf / mm ² ) (1) where D is the diameter (mm) of the steel wire.

The formula (1) is obtained for a steel wire of 6 to 0.08 mm, but it is appropriate in the range of about 10 to 0.05 mm. The cross-sectional shape of the steel wire is often circular, but square, trapezoidal,
It may be a trapezoid or the like. In this case, the diameter of a circle having the same cross section is used as D.

For the piano wire and the steel wire equivalent to this, after using a wire material equivalent to the piano wire material and applying patenting treatment to this,
It is generally manufactured by drawing a wire at room temperature.

In addition, cold rolling may be performed instead of wire drawing. For cold rolling of steel wire, see Wire J.16 (1983),
Examples are given in 7,64, but it is difficult to achieve ultra-high tension levels with ordinary carbon steel as illustrated.

In cold rolling and roller die drawing, the processing limit is larger than that of ordinary wire drawing for the reasons described later, but the work hardening rate is smaller than that of ordinary wire drawing. This is because it is necessary to remarkably increase the workability in order to achieve the above, and this leads to a decrease in ductility.

Further, Japanese Patent Publication No. 59-33175 discloses a case where a medium carbon steel is made into martensite and is wire-drawn by a roller die, which relates to a tempered martensite-based high-tensile wire.

Furthermore, when an attempt is made to manufacture an ultra-high-strength steel wire having a strength level higher than that of the formula (1) by the conventional wire drawing method, the following problems occur.

That is, in order to increase the strength, there are a method of increasing the strength during the patenting treatment and a method of increasing the wire drawing area reduction rate. In either method, the strength is increased as long as the ordinary wire drawing method is used for production. Even though it is possible, the ductility, which is an important property for ultra-high-strength steel wire, especially the deterioration of the twisting property is remarkable, and troubles such as cracking and disconnection are likely to occur in the processes such as twisting and coiling. Become.

Further, piano wires are often used after being plated or bluing-treated, but by these treatments, age hardening occurs and ductility decreases, and it is difficult to achieve an ultrahigh tension level.

(Problems to be Solved by the Invention) The present invention is to provide a method for producing a steel wire rod having a steel composition for achieving ultra-high tensile strength without causing such a decrease in ductility.

(Means for Solving Problems) In the present invention, a high carbon steel wire rod containing C, Si, Mn, Cr, V, and Nb as main components is cold-roller-die drawn or cold-rolled, or , At least the cross-section reduction rate after the processing
By making wire with 40% or less hole die, 250-100logD
(Kgf / mm ² ) (where D is the diameter of the steel wire in mm) or more and the tensile strength of the steel wire is excellent.

When a steel wire is drawn, the strength increases due to work hardening as the workability increases, but if the workability exceeds a certain workability, a reduction in ductility, represented by a drawing value or a twist value, occurs. The strength at that time is the limit of practically usable strength, and the working degree at that time is the practical working limit.

The working limit is essentially caused by a decrease in the ductility of the material due to work hardening, but it also changes depending on the working conditions. It is well known that, in the wire drawing process using a normal hole die, a tensile residual stress is generated in the vicinity of the surface of the steel wire, strain age hardening is caused by heat generated during wire drawing, and a deformation texture is generated. However, all of the factors inherent in the wire drawing work result in a decrease in ductility.

At normal strength levels, sufficient ductility peculiar to the material remains, so these factors resulting from wire drawing have no noticeable effect, but as the strength level increases, wire drawing Factors have come to have a significant influence, which leads to lower machining limits. Therefore, it is difficult to manufacture an ultrahigh-strength steel wire having a strength level equal to or higher than that represented by the formula (1) by the wire drawing method.

As a result of various studies on the method for producing an ultra high strength steel wire, the present inventors have obtained the following findings. In normal wire drawing, a steel wire is passed through a hole die (hereinafter simply referred to as "wire drawing") and drawing is performed. Therefore, the friction force between the die and the steel wire, the compression force from the die, and the drawing force are combined. The strain in the cross section of the steel wire rod at right angles to the longitudinal direction is non-uniform because it is processed in a complicated stress field.

In particular, since the ratio of the pulling force is larger than that of the compressive force, minute cracks are likely to occur around the non-metallic inclusions in the material, which causes the ductility to decrease.

Further, since frictional work is large, heat generation on the surface is large, and aging embrittlement due to temperature rise near the surface layer is large. Embrittlement of the surface layer is particularly harmful to the twisting property.

All of the above problems are derived from the drawing of the hole die, and as a result of studying a machining method that is an alternative,
It has been found that cold rolling and roller die drawing are effective.

In cold rolling and roller die drawing, the friction work between the roll and the steel wire is smaller than that of the hole die, the drawing force is almost zero in the rolling method, and even in the roller die, compared to the hole die. Since it is small, and therefore the main deformation stress is the compressive stress from the roll, the deformation is uniform, and it is difficult for minute cracks around non-metallic inclusions to occur, and embrittlement due to aging does not easily occur. ,
It is possible to prevent a decrease in ductility.

The excellent ductility of such rolled and roller die processed materials is not continuously lost even when performing hole die wire drawing, and the wire drawing amount is within 40% of the cross-section reduction rate, The effect was recognized.

Ordinary rolling and roller die processing, since the cross-sectional shape accuracy and dimensional accuracy of the steel wire is inferior to that of the hole die wire drawing, it may be inconvenient depending on the application. By performing the wire drawing process after the roller die process, it is possible to obtain an ultra high tensile strength steel wire having high ductility and excellent size and shape.

Furthermore, since the work hardening rate can be increased in wire drawing, there is also an advantage that the strength up can be easily achieved by combining rolling and wire drawing as compared with the case of only rolling (or roller die). Therefore, the wire drawing after rolling (or roller die) has a positive significance.

As a result of investigating the influence of the steel composition, in order to achieve high strength and improvement of ductility, the present inventors have found that the following component systems are suitable.

C is an economical and effective strengthening element, but 0.85% is required to achieve the strength of the formula (1) or higher without adding a special alloy.
(Weight ratio, the same applies hereinafter) or more, and when adding an alloying element as described later, 0.6% or more is required.

On the other hand, if it exceeds 1.0%, proeutectoid menthite is generated during patenting, which is not suitable for cold working. However, in order to obtain more excellent ductility in the strength of the formula (1) or higher, it is desirable to contain an alloying element as described below.

Si needs 0.1% or more for deoxidation. Si is also effective as a solid solution hardening element for strengthening, but if 0.35% or less, the effect is small, and if it exceeds 2%, ductility deteriorates, which is not suitable.

The drawing of the steel wire is closely related to the pearlite lamellar spacing, and it becomes maximum at about 280 A, but Si hardly strengthens the ferrite layer without changing the pearlite lamellar spacing of the material, so there is almost no decrease in ductility. Effective in increasing the strength of steel wire.

Therefore, for the purpose of deoxidation, the minimum value of Si should be 0.1
%, The minimum value is 0.35% for solid solution hardening.
And

Mn is required to be 0.1% or more in order to remove deoxidation and damage of S. Mn is a hardenability-improving element, and is particularly effective in increasing the patenting strength of thick wire rods. 0.9%
With the above addition, the effect is remarkable, but if it exceeds 2%, the ductility is deteriorated, which is not suitable.

Therefore, depending on the purpose, the minimum value of Mn can be selected from 0.1% and 0.9%.

Cr is an element effective in making the pearlite lamellar spacing fine, and is effective in strengthening the wire rod from a thin size to a thick size, but if it exceeds 1%, it is difficult to sufficiently exert the effect.

V is a hardenability-improving element and is effective for increasing the patenting strength of a wire having a particularly large size. Further, it is effective in reducing the austenite grain size and improving the ductility. If it is less than 0.002%, its effect is small, and if it exceeds 0.5%, the ductility is deteriorated, which is not suitable.

Nb is effective for refining the austenite grain size and improving the ductility, but if it is less than 0.002%, it has no effect, and if it exceeds 0.5%, the ductility deteriorates, which is not suitable.

For Al, 0.01 to 0 if fine-grained steel is desired.
If about 1% is added and softening of coarse-grained steel or inclusions is necessary, 0.01% or less. In any of these cases, the Al content is not specified.

By cold rolling or drawing with a roller die, a material with increased strength during patenting with the above components can be used to obtain an ultra-high strength steel wire having strength of (1) or more without causing deterioration in ductility. It can be easily manufactured.

(Example) A steel wire rod was subjected to pickling after lead patenting, the scale was removed, and then a zinc phosphate coating treatment was performed. At the time of wire drawing, wire drawing was performed using a wire drawing lubricant, and at the time of cold rolling and roller die drawing, rolling or roller die drawing was performed while lubricating with rolling oil.

The processed steel wire was subjected to a blueing treatment for 45 seconds at the as-processed condition and 450 ° C., and the material was evaluated by a tensile test and a twisting test.

Table 1 shows the results of production with various steel components.

No. 1 to 14 increase C, Si, Mn, or Cr, V, Nb
Although the strength at the time of patenting was further increased by adding, the conventional wire-drawing method had a particularly large decrease in the twist value, and it was not possible to obtain sufficient performance.
However, according to the rolling or roller die method of the present invention, the drawing and twist values were high and excellent ductility was obtained.

Table 2 shows the results of wire drawing using a hole die after working with a rolling or roller die, but it was found that sufficient ductility remained in wire drawing within 40% of the present invention.

(Effect of the invention) The present invention, as described above, a steel wire rod having a specific component, by cold working with a rolling or roller die, or by performing wire drawing within 40% after the working, It has made it possible to manufacture ultra high strength steel wire without deterioration.
According to the present invention, breakage during wire drawing and twisting, work cracking during molding, and breakage during use can be significantly reduced.

Claims (4)

[Claims] 1. A high carbon steel wire rod whose basic component is C: 0.60 / 1.0% Si: 0.1 / 2.0% Mn: 0.1 / 2.0% by weight, is cold rolled or drawn by a roller die, or After cold rolling or drawing the roller die, draw a hole die with a cross-section reduction rate of 40% or less to obtain 250-100logD (kg
/ mm) (however, D is the diameter of the steel wire, mm) or more and the tensile strength is excellent. 2. The high carbon steel wire rod is C: 0.85 / 1.0%, Si: 0.1 /
The method for producing an ultrahigh-strength steel wire with excellent ductility according to claim 1, comprising 2.0% and Mn: 0.1 / 2.0%, and the balance iron and unavoidable impurities. 3. The high carbon steel wire rod is C: 0.60 / 1.0%, Si: 0.35 /
The method for producing an ultrahigh-strength steel wire with excellent ductility according to claim 1, comprising 2.0% and Mn: 0.1 / 2.0%, and the balance iron and unavoidable impurities. 4. The high carbon steel wire rod is C: 60 / 1.0%, Si: 0.1 / 2.0.
%, Mn: 0.1 / 2.0%, Cr: 0.1 / 1.0%, V: 0.
The method for producing an ultrahigh-strength steel wire with excellent ductility according to claim 1, comprising at least one of 002 / 0.5% and Nb: 0.002 / 0.50%, and the balance being iron and unavoidable impurities.