JP3487957B2 - Wire with excellent wire drawing processability - Google Patents

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 capable of obtaining 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, Japanese Patent Laid-Open No. 62-241136 has been disclosed as a technique for utilizing a high carbon bainite structure. This is a wire rod having a diameter of 1.2 mm or less 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]

The present invention SUMMARY OF] is a (1) C amount obtained by hot rolling to 0.6% by weight, base
Inite structure, pearlite structure or a mixture of these
In woven steel wire rods, cementite present in the cross section of the wire rod has the following characteristics and has excellent wire drawability. i. The average cementite length is 0.7 μm or less. ii . The average cementite interval is 900Å or more.

(2) Steel composition in wt% 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): A wire rod having excellent wire drawability as described in (2) above, which is characterized by adding one or more of the following components. 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 the above (2) or (3), characterized in that 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, wherein the wire rod has excellent wire drawability according to (2), (3) or (4).

[0015]

[Function] The workability of the wire is greatly affected by the form of cementite in the wire. The shorter the length of cementite observed in the cross section of the wire, the more the growth of dislocations introduced during processing is suppressed. Therefore, it is necessary to set the average length of cementite to 0.7 μm or less. The relationship between the average cementite length and the wire drawability is shown in FIG.

Similarly, the larger the average spacing of cementites observed in the cross section of the wire, the more the growth of dislocations introduced during processing is suppressed. Therefore, the average spacing of cementites must be at least 900Å or more. Fig. 2 shows the relationship between the average cementite spacing and wire drawability.

If the cementite can be adjusted to the above-mentioned form, the initial strength of the wire can be lowered and the work hardening rate can be lowered, so that the wire having excellent workability can be obtained.

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, if its 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 an effect of suppressing the appearance of such an abnormal portion of cementite and further refining 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 also has the same effect as Cr, if necessary, 0.1% or more is added to exhibit the effect. If Ni is added too much, the ductility of the ferrite phase deteriorates, so the upper limit is made 2.0%.

Cu is an element that improves the corrosion fatigue properties of the wire, so if necessary, 0.1% to exert its effect.
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 if necessary, it is desirable to add 0.01% or more so as to exert its effect. 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 making the microstructure 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, at which the effect is recognized, and the hardenability becomes too high.
% Or less.

[0029]

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

A 122 mm square sample billet was hot-rolled to 4.5 to 16.0 mmφ and subjected to controlled cooling to obtain a wire rod having the structure shown in Table 2.

According to the present invention, all of the maximum deformation stress, the total elongation and the yield ratio of the steels 1 to 45 of the present invention satisfy the conditions described in claim 1.

The comparative steels 46, 47 and 48 differ from the steels of the present invention in that the cementite length is as long as more than 0.7 μm. Comparative steels 49, 50 and 51 have cementite spacing of 900
It is different from the present invention in that it is as small as less than Å.

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%. For raw drawability, the wire is processed to the wire drawing limit and the true strain is 3.8.
Table 2 shows the case where the above processing was possible, and x when it could not be processed.

The steels 1 to 45 according to the present invention have excellent cementability because the shape of cementite is adjusted according to the present invention. On the contrary, the comparative steels 46 to 51 are inferior in the drawability because they have the above-mentioned difference from the present invention.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

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 a relationship between an average cementite length and wire drawability.

FIG. 2 is a diagram showing a relationship between an average interval of cementite and critical strain of wire drawing.

Claims (5)

(57) [Claims] 1. A C amount obtained by hot rolling 0.6%
Above , bainite structure, pearlite structure or this
In the steel wire rods of these mixed structures , the shape of the cementite existing in the cross section of the wire rod has the following characteristics and is excellent in wire drawing workability. i. The average cementite length is 0.7 μm or less. ii . The average cementite interval is 900Å or more. 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 A wire rod having excellent wire drawability according to claim 1. 3. A wire rod excellent in 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% to 2.0% 4. A wire rod excellent in wire drawability according to claim 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. A wire rod excellent in wire drawability according to claim 2, 3 or 4, wherein P: 0.02% or less and S: 0.02% or less.