JP2767620B2 - Manufacturing method of ultra-fine high-tensile steel wire with excellent toughness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application field] The present invention relates to a method for producing an ultrafine high-strength steel wire having a wire diameter of 0.4 mm or less and a tensile strength of 350 kg / mm ² or more excellent in toughness after drawing. Things.

[Conventional technology]

Fine steel wires used for reinforcing automobile tires, industrial belts, rubber hoses, etc. are manufactured by repeatedly patenting and drawing from hot-rolled wire. There is a strong need for ultra-fine steel wires and high tensile strength to reduce the weight of tires.
Japanese Patent Publication No. Sho 46-6702 discloses the highest strength of various component systems for ultrafine wires. However, in the invention described in the publication, patenting before drawing is performed at 500 ° C. or less in order to increase strength. In this component system, the temperature of the nose in the pearlite transformation is around 550 ° C, so that the bainite structure is very easy to appear. Therefore, stable production of high-strength steel wire is difficult, and there is a great risk of poor toughness. In addition, there is an expression that the material has high tensile strength and toughness, but there is no specific description of toughness in Examples. At that time, high tensile strength was probably due to the fact that only tensile strength was prioritized and that the applications were not as diverse as today. At present, it has not been used industrially due to the problem of toughness.

There is a strong need for high-strength ultra-fine steel wires with high toughness, but at present there is no ultra-fine high-tensile steel wire suitable for mass production with low wire cost and easy to patent and draw.

[Problems to be solved by the invention]

In the case of a high-tensile steel wire, high tensile strength is an essential condition, but at the same time, sufficient toughness is also required.

Conventionally, drawing and twisting characteristics have been used as toughness, but their evaluation is insufficient for recent diversified uses, and fatigue, twistability, and kink are important. Since the fatigue characteristics are factors that determine the design strength, it is important to increase the tensile strength and the fatigue strength for weight reduction.

Extra fine wires are often twisted rather than single wires, so it is industrially important to be able to twist them. In addition, since the ultrafine wire is deformed with a low load, it undergoes bending deformation during wire drawing, twisting, and embedding in rubber. At this time, if the bending radius is small or a knot is formed, it is not easy to break easily. Therefore, kink characteristics have recently been required. Therefore, these required properties are collectively referred to herein as toughness.

The present invention has been made to solve these problems, and provides a method for industrially stably producing an ultrafine high-tensile steel wire having excellent toughness.

[Means and actions for solving the problem]

The present inventor specified the composition of the steel wire rod and the pre-drawing amount before final patenting, thereby producing a very uniform fine pearlite structure with little variation at the time of final patenting, and by the subsequent final drawing, the toughness was determined. The present inventors have found the conditions under which a high-tensile ultrafine wire rich in iron can be produced, and have completed the invention.

That is, the gist of the present invention is a combination of the following steps.

C: 0.80 to 1.00%, Si: 0.40 to 1.10%, Mn: 0.20 to 0.60%, C
r: 0.20 to 0.60%, Co + Ni: 0.05 to 0.60%, Al: 0.0005 to 0.00
Use a steel wire consisting of 50% balance iron and unavoidable impurities.
Preliminary wire drawing of 3.0 Perform final patenting of the above pre-wired material, 0.04 to 0.10
A fine pearlite structure having a lamella spacing of μm The final patenting material is drawn strain 3.5 to 4.5 (drawing strain = l _n (d ₀ / d _n ) ² , d ₀ : patenting wire diameter, d _(n : wire diameter) is to produce a high-strength, high-toughness ultrafine wire having a tensile strength of 350 kg / mm ² or more by performing the final wire drawing.

 Reasons for limiting the above-mentioned components will be described.

First, C is the most important element for increasing the strength of steel. Therefore, use as much as possible. If C is not more than 0.80%, the tensile strength after patenting will not be more than 150 kg / mm ² , no matter how much other alloying elements are added. On the other hand, when the content exceeds 1.00%, the generation of network cementite cannot be suppressed, and it is not possible to suppress the disconnection of the cuppy during the wire drawing.

Si is known as a solid solution hardening element. In order to increase the tensile strength after patenting to 150 kg / mm ² or more, it is necessary to obtain solid solution hardening even if the pearlite lamellar interval is set to 0.04 to 0.10 μm. For that purpose, it is necessary to add Si 0.40% or more. When the Si content exceeds 1.10%, hard SiO ₂
Since the appearance of single inclusions cannot be prevented, the frequency of wire breakage in steel wires of 0.3 mm or less increases, and the fatigue characteristics deteriorate significantly.
10% or less.

Mn delays perlite transformation. The content is set to 0.60% or less so as not to generate an abnormal structure such as micro martensite in the center during the cooling process after the wire rod rolling. If Mn is less than 0.20%, it becomes impossible to prevent surface cracks during hot rolling.
20% or more. Since the effect of Mn on the strength of the patenting material is smaller than that of Si and Cr, the range of 0.20 to 0.60% is sufficient.

Cr is the most effective element for reducing the pearlite lamellar spacing. In order to industrially end patenting in a short time, it is necessary to suppress the pearlite transformation end time at the temperature of the nose within 30 seconds. For that, Cr should be 0.60
% Or less. On the other hand, to make the lamella interval 0.10 μm or less in the final patenting,
% Must be added.

It is well known that Ni exhibits a pearlite lamellar alignment effect when added simultaneously with Co. However, at the time of the final patenting after the preliminary drawing, a structure in which very fine cementite is precipitated in dots between the undeveloped lamellar pearlite appears in the case of carbon steel. This significantly impairs the drawability. For this reason, although it was known that the tensile strength after the final patenting was increased by the preliminary drawing, it could not be used effectively. The present inventor has found that Co and Ni are effective in preventing precipitation of this very fine point-like cementite, and the effects are the same. This very fine point-like cementite and 0.05% Co + Ni to prevent precipitation
% Is required. At 0.60%, the effect of preventing precipitation is saturated. Because Co and Ni are expensive, they restrict industrial use from the viewpoint of cost.

The hardest inclusion in steel is Al ₂ O ₃ alone. However, in the case of a composite oxide, it has the effect of melting into oxide-based inclusions, lowering the melting point and softening. Al is 0.0005
%, There is no softening effect of oxide-based inclusions, so 0.0005
% Or more. If the content is more than 0.0050%, a single inclusion of Al ₂ O ₃ is generated, so the content is restricted to 0.0050% or less.

Next, in pre-drawing, carbon steel shows a structure in which very fine cementite precipitates in dots between undeveloped lamellar pearlite at the time of final patenting, impairing drawability at the time of final drawing. Therefore, the effect of increasing the tensile strength of the final patenting material by the preliminary drawing could not be used effectively. By adding 0.05% to 0.50% of Co + Ni, the effect of increasing the tensile strength of the final patenting material by preliminary drawing can be used without impairing the drawability. If the drawing strain of the pre-drawing is less than 1.0, austenite crystal grains are not sufficiently refined at the time of final patenting, and the effect of increasing the tensile strength cannot be obtained. If the drawing strain exceeds 3.0, no matter how much Co + Ni is added, fine cementite dot-like precipitation cannot be prevented.

In the final patenting, the lamella interval is 0.10μm
Otherwise, the strength of the patenting material will not exceed 150 kg / mm ² and the tensile strength will not reach 350 kg / mm ² with the fine wire after drawing. On the other hand, when the lamellar spacing is less than 0.04 μm,
Since the transformation temperature is lower than the temperature of the nose, the bainite structure is partially mixed. In order to secure drawability, it is necessary to form a uniform fine pearlite structure on the entire surface. Therefore, the lamella interval is set to 0.04 μm or more.

Although it is the strain at the time of final drawing, 3.5 or more is necessary in order to make the wire diameter 0.4 mm or less and the tensile strength 350 kg / mm ² or more. However, if the drawing strain exceeds 4.5, toughness cannot be secured. Therefore, the drawing strain was set to 4.5 or less.

According to the present invention, it has become possible to stably produce an ultrafine high-tensile steel wire having a wire diameter of 0.4 mm or less and a high toughness of 350 kg / mm ² or more.

 Hereinafter, the present invention will be described with reference to examples.

〔Example〕

Using a 50 kg vacuum melting furnace, steel having the components shown in Table 1 was melted. After rolling these steels into 7mmφ wire rods, they were subjected to lead patenting and wire drawing to produce ultrafine wires as prototypes and their characteristics were grasped.

Table 2 shows the drawing conditions and the obtained ultrafine wire characteristics. No.
1,8,9,14 are the present invention. Both have a tensile strength of 350kg / mm ²
As described above, the twistability, fatigue life, and kink characteristics are excellent.

No.2 because C is low, since the tensile strength of the lead patenting material is less than 150 kg / mm ^2, tensile strength of 0.20 mm 350 kg
/ mm ² . In No. 3, since the C content was high, network cementite was precipitated, and the wire was cut off. In No.4, hard SiO ₂ inclusions were present due to the high Si content, which caused the disconnection of the cuppy. N
In the case of o.5, the transformation to pearlite did not complete at the time of patenting due to the high Cr content, micro-martensite was generated in the center, and the disconnection occurred during drawing. No.6 is Co + Ni
Because of the small amount of, a point-like precipitation of cementite occurred at the time of final patenting, which caused disconnection of the cuppy. In No. 7, since Al was as high as 0.0055%, Al ₂ O ₃ inclusions were generated, and the wire was broken during the wire drawing. In No. 10, the tensile strength of the final patenting material was increased because the drawing strain of the preliminary drawing exceeded 3 and the tensile effect of the final patenting material was increased, but the effect of preventing the precipitation of the cementite in the form of spots by Ni + Co was not obtained, and the wire was cut off. . No.11 tensile strength of the final patenting material to wire drawing strain preliminary drawing is small is less than 150 kg / mm ^2,
Even the final ultrafine wire has a tensile strength of less than 350 kg / mm ² and a low fatigue life. No. 12 has a small final wire drawing strain, so the final ultrafine wire also has a tensile strength of less than 350 kg / mm ² and a low fatigue life. No. 13 was overdrawn due to large final drawing strain, and the tensile strength was high but the toughness was poor.

The above examples also show how excellent the present invention is as a method for producing an ultrafine high-tensile steel wire having excellent toughness.

〔The invention's effect〕

As described above, according to the present invention, it is possible to industrially produce an ultrafine high-tensile steel wire having a low cost and excellent toughness and a tensile strength of 350 kg / mm ² or more.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21D 8/06 B21C 1/00-19/00

Claims (1)

(57) [Claims] [Claim 1] C: 0.80 to 1.00%, Si: 0.40 to 1.10% Mn: 0.20 to 0.60%, Cr: 0.20 to 0.60% Co + Ni: 0.05 to 0.60%, Al: 0.0005 to 0.0050% Balance iron and unavoidable impurities Before final patenting, a steel wire rod consisting of 1.0 to 3.0 (drawing strain = l
_{n (d 0 / d n)} 2, d 0: patenting wire diameter, d _n: Shinsen径) after the conducted preliminary drawing of performs final patenting, 0.04
A method for producing an ultra-fine high-tensile steel wire with excellent toughness and a tensile strength of 350 kg / mm ² or more, which has a fine pearlite structure with a lamellar interval of 0.10 μm and is subjected to final drawing with a drawing strain of 3.5 to 4.5.