JPH08295931A - Wire rod excellent in wire drawability - Google Patents

Abstract

PURPOSE: To produce a wire rod excellent in wire drawability by specifying the characteristics of the curve of true stress-true strain of a high carbon steel wire rod with a specified dimension obtd. by hot rolling. CONSTITUTION: A steel having a compsn. contg., by weight, >=0.6%, preferably, 0.6 to 1.5% C, 0.1 to 2.0% Si and 0.1 to 2.0% Mn, if required, furthermore added with one or more kinds among 0.1 to 2.0% Cr, Ni, Cu and Mo, 0.01 to 2.0% Co, 0.005 to 0.03% Ti, Nb, V and Al and 0.0001 to 0.003% B, and in which the contents of P and S are regulated to <=0.02% is subjected to hot rolling to form into a steel wire rod of 5 to 16mm. The curve of true stress-true strain in a tensile test of this wire rod has the following characteristics: (1) the maximum deformation stress is regulated to 800 to 1200MPa, (2) the total elongation is regulated to >=20%, (3) the total yield ratio σ0.2 /σu .t .s is regulated to >=0.5 (σ0.2 denotes 0.2% proof stress and σu .t .s denotes the maximum deformation stress). Thus, the wire rod of >=3.0mmϕ having workability of >=3.7 true strain can be obtd. by wire drawing with a drawing die.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is used for producing a high strength and high ductility hard steel wire such as a steel cord, a valve spring, and a rope used for reinforcing rubber and organic materials such as tires and belt cords. It relates to wire rods.

[0002]

2. Description of the Related Art Wire rods made of high carbon steel are generally processed by hot rolling to a wire diameter of 4.0 mmφ to 16 mmφ, and then subjected to adjustment cooling in order to adjust the mechanical properties of the wire rod to become the wire rod. .

Thereafter, the adjusted and cooled wire is processed into a finer wire diameter by repeating drawing by cold drawing and intermediate heat treatment. For example, in the case of a valve spring, it is formed into a spiral shape and then quenched. It is used by tempering it into the final product, or by performing final patenting treatment and then wire drawing to obtain a high-strength wire.

Therefore, in manufacturing the final product,
The better the workability of the wire rod after hot rolling, the easier the production cost can be reduced.

Conventionally, as a method for adjusting the mechanical properties of a hot rolled wire rod, there are a Stelmore method by blast cooling and a DLP method using a molten salt as a cooling medium. There is Japanese Patent Publication No. 59-37725 in which molten salt is used, but it is a direct heat treatment method which can obtain high strength equivalent to lead patenting by improving workability.

[0006] Japanese Patent Application Laid-Open Nos. 6-17190, 6-17191, and 6-1 disclose methods using bainite.
Although 7192 and the like are disclosed, these are steel wire rods excellent in workability characterized by adjusting the bainite structure to 80% or more and adjusting to a predetermined strength and ductility. However, there is a problem that it is extremely difficult to set the bainite ratio shown in this publication to 80% or more with a wire diameter of 5.0 mmφ or more.

Further, as a technique utilizing the high carbon bainite structure, Japanese Patent Laid-Open No. 62-241136 has been disclosed. This is a method in which a wire material having a diameter of 1.2 mm or less is made into an upper bainite structure by a lead patenting treatment and then drawn. The wire has excellent fatigue characteristics of 0.3 mmφ or less.

In recent years, in order to reduce the manufacturing cost of the final product wire, it has been required to develop a high carbon steel wire rod which is excellent in workability and can be processed up to the final heat treatment step as easily as possible.

[0009]

[Problems to be Solved by the Invention] C content is 0.6 by weight%
%, Wire rods with excellent workability in the field of high carbon steel, more specifically, in wire drawing using a drawing die, workability of 3.7 or more in true strain at wire diameters of 3.0 mmφ or more A wire rod is provided.

[0010]

According to the present invention, (1) a steel wire having a C content of 5 mm or more and 16 mm or less and a C content of 0.6% or more obtained by hot rolling has a true stress-true strain curve in a tensile test. A wire rod with excellent drawability that has the following characteristics. Maximum deformation stress 800MPa or more 1200MPa or less total elongation of 20% or more yield ratio σ _{0. 2} / σ _uts is here 0.5 or more, σ _{0. 2} 0.2% proof stress, sigma _uts is the maximum deformation stress .

(2) Steel composition in% by weight: C: 0.6% or more and 1.5% or less Si: 0.1% or more and 2.0% or less Mn: 0.1% or more and 2.0% or less A wire rod having excellent wire drawability according to the above (1), which is made of steel.

(3) The wire according to the above (2), wherein one or more of the following components are added. Cr: 0.1% or more and 2.0% or less Ni: 0.1% or more and 2.0% or less Cu: 0.1% or more and 2.0% or less Mo: 0.1% or more and 2.0% or less Co: 0.01% or more and 2.0% or less.

(4) The wire according to the above (2) or (3), wherein one or more of the following components are added. Ti: 0.005% or more and 0.03% or less Nb: 0.005% or more and 0.03% or less V: 0.005% or more and 0.03% or less Al: 0.005% or more and 0.03% or less B: 0.0001% or more and 0.003% or less.

(5) P: 0.02% or less S: 0.02% or less The wire according to the above (2), (3) or (4).

[0015]

[Operation] In order to improve the workability of the wire, the workability of the wire can be improved by adjusting the stress-strain curve obtained from the tensile test.

The maximum deformation stress in the stress-strain curve corresponds to the degree of refinement of the material structure. Therefore, at least 800 MPa or more of strength is required for uniform and stable deformation, and 1200 MPa for work hardening to be small.
It should be adjusted to a or less. The relationship between tensile strength and wire drawing limit is shown in FIG. However, the wire drawing limit is true strain.

The total elongation in the stress-strain curve is an index of the uniformity of the material, and it is necessary to secure a workability of at least 20% in order to secure a true strain of 3.8 or more. The relationship between total elongation and wire drawing limit is shown in FIG.

The yield ratio in the stress-strain curve depends on the shape of cementite, and the more the cementite is divided, the smaller the yield ratio becomes. In order to reduce the work hardening rate, it is better that the cementite is divided, so it is necessary to adjust the yield ratio to at least 0.5 or more. Fig. 3 shows the relationship between the yield ratio and the wire drawing limit. However, the yield ratio is shown by σ _{0. 2} / σ _uts.

As a method for achieving such characteristics of the stress-strain curve, any of a pearlite structure, a bainite structure and a mixed structure thereof obtained by controlled cooling after rolling may be used.

The structure obtained by performing controlled cooling after rolling may be tempered and annealed to satisfy the characteristics of the stress-strain curve.

Next, the reasons for limiting the constituent elements in steel will be described. C is an economical and effective strengthening element. C is at least 0.6 in order to secure the necessary strength as a steel wire.
It is necessary to be at least%. If it is too high, the ductility decreases, so the upper limit is made 1.5%.

Si is an element necessary for deoxidizing steel. Therefore, when the content is too small, the deoxidizing effect becomes insufficient, so the lower limit is made 0.1%. Further, Si dissolves in the ferrite phase in the pearlite formed after heat treatment to increase the strength after patenting, but on the other hand, it reduces the ductility of the ferrite, so it does not adversely affect the post-drawability. And

Mn is added in an amount of 0.1% or more in order to secure the hardenability of steel. However, addition of a large amount of Mn causes segregation and causes a supercooled structure such as bainite and martensite during patenting, which impairs the subsequent wire drawability, so the content is made 2.0% or less.

If a large amount of S is contained, the ductility of the wire is impaired, so its content is preferably 0.02% or less.
Like P, P also impairs the ductility of the wire, so its content is preferably 0.02% or less.

Cr has the effect of suppressing the appearance of such abnormal portions of cementite and further making fine pearlite. However, addition of a large amount increases the dislocation density in the ferrite after heat treatment, and therefore significantly impairs the ductility of the ultrafine wire after drawing. Therefore, the addition amount of Cr is set to 0.1% or more, which is expected to have the effect, without increasing the dislocation density in ferrite and impairing ductility.
It is 0% or less.

Since Ni has the same effect as Cr, if necessary, 0.1% or more is added so that the effect is exhibited. If Ni is added too much, the ductility of the ferrite phase deteriorates, so the upper limit is made 2.0%.

Since Cu is an element that improves the corrosion fatigue characteristics of the wire, 0.1% to exert its effect if necessary.
It is desirable to add the above. If Cu is added too much, the ductility of the ferrite phase will be reduced, so the upper limit is made 2.0%.

Mo is an element added in order to improve the hardenability of the wire rod, and it exerts its effect if necessary.
% Or more is desirable. If Mo is added too much, the hardenability is improved and micro martensite is likely to precipitate in the segregated portion, so the upper limit is made 2.0%.

Co is an element added to improve the ductility of the wire, and it is desirable to add 0.01% or more so as to exert its effect if necessary. Since Co is an expensive element, it is added at 2.0% or less so as not to impair economic efficiency.

Ti, Nb, V, and Al are effective in improving the toughness value by making the γ grain size fine and the structural unit formed thereafter fine. 0.005%
The above is added to make it 0.03% or less so as not to adversely affect other characteristics.

B is added to improve the hardenability, and is added in an amount of 0.0001% or more where the effect is recognized. The hardenability becomes too high and the treatment becomes difficult.
% Or less.

[0032]

[Examples] Using the steels having the components shown in Table 1, wire rods were manufactured by a method of adjusting the stress-strain curve by separately producing a bainite structure, a pearlite structure, and a mixed structure thereof by adjusting cooling after rolling.

A 122 mm square sample billet was hot-rolled to 5.0 to 16.0 mmφ and subjected to controlled cooling to obtain a wire rod having the structure shown in Table 2. These wire rods after hot rolling were G. L. = 200 mm, the stress-strain curve was obtained. Table 2 shows the maximum deformation stress, total elongation, and yield ratio obtained from this stress-strain curve. Invention Steels 1 to 4
According to the present invention, No. 5 satisfies all the conditions described in claim 1 in terms of maximum deformation stress, total elongation and yield ratio. A typical example of the stress-strain curve is shown in FIG.

[0034]

[Table 1]

[0035]

[Table 2]

Comparative steel 46 differs from the steels of the present invention in that the maximum deformation stress is high and the total elongation is low. Comparative steel 47 is different from the steels of the present invention in that the maximum deformation stress is high and the total elongation is low. Comparative steel 48 differs from the steel of the present invention in that the total elongation is low. Comparative steel 49
Is different from the steel of the present invention in that the yield ratio is lower than that of the present invention. Comparative steel 50 is tempered, but differs from the steel of the present invention in that the total elongation is low due to inappropriate treatment conditions.

The pullability test of these test steels was carried out using dry drawing. The wire drawing has a reduction rate of 1 in each pass.
The wire drawing process was performed so as to be between 5% and 20%. The raw drawability is indicated by ◯ when processing was performed up to the wire drawing limit and when true strain of 3.8 or more was possible, and by x when it was not possible.

The steels 1 to 45 of the present invention are adjusted so that the stress-strain curve satisfies the steel of the present invention, and thus exhibit excellent drawability. On the contrary, the comparative steels 46 to 50 are inferior in raw drawability due to the difference described above from the present invention.

[0039]

EFFECTS OF THE INVENTION It is possible to obtain a wire rod having a wire drawability of 5 mm to 16 mm, which is more excellent in wire drawability than conventional steel.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between tensile strength and wire drawing limit.

FIG. 2 is a diagram showing the relationship between total elongation and wire drawing limit.

FIG. 3 is a diagram showing a relationship between a yield ratio and a wire drawing limit.

FIG. 4 is a diagram showing a typical example of a stress-strain curve.

Claims (5)

[Claims] Claims: 1. Not less than 5 mm obtained by hot rolling 16
A steel wire rod having a C content of not more than mm of 0.6% or more, and having a true stress-true strain curve in a tensile test having the following characteristics, having excellent wire drawability. Maximum deformation stress 800MPa or more 1200MPa or less total elongation of 20% or more yield ratio σ _{0. 2} / σ _uts is 0.5 or more, however, sigma _{0. 2} 0.2% proof stress, sigma _uts is the maximum deformation stress. 2. Steel in which the weight percentage of steel is C: 0.6% or more and 1.5% or less Si: 0.1% or more and 2.0% or less Mn: 0.1% or more and 2.0% or less 2. A wire rod having excellent wire drawing workability according to claim 1. 3. A wire rod having excellent wire drawability according to claim 2, wherein one or more of the following components are added. Cr: 0.1% or more and 2.0% or less Ni: 0.1% or more and 2.0% or less Cu: 0.1% or more and 2.0% or less Mo: 0.1% or more and 2.0% or less Co: 0.01% or more and 2.0% or less 4. A wire rod having excellent wire drawability according to claim 2, wherein one or more of the following components are added. Ti: 0.005% or more and 0.03% or less Nb: 0.005% or more and 0.03% or less V: 0.005% or more and 0.03% or less Al: 0.005% or more and 0.03% or less B: 0.0001% or more and 0.003% or less 5. A wire rod having excellent wire drawability according to claim 2 or 3 or 4, wherein P: 0.02% or less and S: 0.02% or less.