KR20150061281A

KR20150061281A - Ultra high strength steel wire having excellent dtawability and mothod for manufacturing the same

Info

Publication number: KR20150061281A
Application number: KR1020130145187A
Authority: KR
Inventors: 이충열
Original assignee: 주식회사 포스코
Priority date: 2013-11-27
Filing date: 2013-11-27
Publication date: 2015-06-04

Abstract

The present invention relates to an ultrahigh strength steel wire having excellent drawability to be used for a steel wire for a bridge and a wire rope to support high loads and a method for manufacturing the same. More specifically, the present invention relates to an ultrahigh strength steel wire having excellent drawability and torsional characteristics without delamination during strand processing and a method for manufacturing the same. According to an embodiment of the present invention, provided are an ultrahigh strength steel wire having excellent drawability, which is composed of 0.95-1.05 wt% of C, 0.3-0.8 wt% of Mn, 1.0-1.6 wt% of Si (excluding 1.0 wt%), 0.5-1.0 wt% of Cr (excluding 0.5 wt%), remaining amount of Fe, and impurities and is twisted for more than thirteen times and a method for manufacturing the same. According to the present invention, provided is a steel wire which inhibits delamination interrupting the strengthening of the steel wire and has excellent torsional characteristics, drawability, and ultrahigh strength.

Description

TECHNICAL FIELD [0001] The present invention relates to an ultra-high strength steel wire having excellent workability,

The present invention relates to an ultra-high strength steel wire having excellent drawability which can be used for supporting a heavy load such as a steel wire for a bridge and a wire rope and a method for manufacturing the same. More specifically, the present invention relates to a super high strength steel wire having delamination High strength steel wire having excellent warpage characteristic and excellent drafting property, and a method for producing the same.

Since the steel wire for a bridge and the tire cord are reinforcing materials for supporting a force applied to a structure or a tire, a steel wire for a bridge and a steel wire for a tire cord require high strength.

The following methods are known for obtaining a high strength steel wire.

1) How to increase the strength of the material itself

As a method for obtaining a high strength steel wire, a method of increasing the strength of the material itself by adding a large amount of reinforcing elements that increase the strength of the steel can be mentioned. A representative example of such a strengthening element is carbon. As the strength of the tire cord gradually increased, the carbon content gradually increased from the vacant area to the vacant area, from the vacant area to the overtone area. If the carbon content is increased as described above, the proportion of cementite, which is a hard phase, increases in the wire material, and the lamella interval of the pearlite structure becomes dense, thereby improving the strength of the material. As described above, techniques for adding various alloying elements other than carbon have been proposed.

2) How to increase the work hardening rate

Steel wire for tire cord is manufactured by drawing and annealing the rolled wire. By increasing the work hardening rate during drawing of the wire rod, the strength can be greatly improved. That is, when the work hardening rate is increased in the drawing process, the lamellar spacing becomes finer, the work hardening coefficient increases, and the integration degree of dislocation increases, so that the strength of the steel wire increases.

3) Separately from the above, the strength can be improved by increasing the drawing strain of the material for the tire cord. In this case, the fresh deformation rate of the material is closely related to the ductility of the material, and it is advantageous to increase the strength as the material itself is easily processed without causing disconnection in the drawing process.

However, all of these methods do not work independently but mutually change the strength of the steel wire, so there is a limit to improve the strength of the steel wire by controlling them independently.

For example, when a large amount of an alloying element is simply added to improve the strength of the wire rod, there may arise a problem such that the wire rod is poorly ducted in the steel wire making process subsequent to the wire rod rolling, resulting in disconnection. Therefore, in order to improve the strength of the steel wire for a tire cord, various factors need to be taken into account in various aspects.

The present invention relates to an ultra high strength steel wire having excellent drawability which suppresses the occurrence of delamination by restoring the ductility of the steel material through stress relieving heat treatment, And a manufacturing method thereof.

An embodiment of the present invention is a steel sheet comprising, by weight%, 0.95 to 1.05% of C, 0.3 to 0.8% of Mn, more than 1.0 to 1.6% of Si, more than 0.5 to 1.0% of Cr, the balance Fe and other unavoidable impurities , And an ultra-high strength steel wire having excellent drawing processability with twist number of 13 or more.

Another embodiment of the present invention is a ferritic stainless steel comprising, by weight%, 0.95 to 1.05% of C, 0.3 to 0.8% of Mn, more than 1.0 to 1.6% of Si, more than 0.5 to 1.0% of Cr, the balance Fe and other inevitable impurities A step of drawing the wire material to a wire drawing ratio of 80 to 90% to obtain a steel wire; And heat treating the steel wire at a temperature of 450 to 550 ° C. The present invention also provides a method of manufacturing an ultra-high strength steel wire having excellent wire drawing workability.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to suppress the occurrence of delamination which acts as a stumbling block for high strength, to have an excellent torsional characteristic as well as to increase the freshness limit, and ultimately to provide a steel wire having ultra high strength.

An embodiment of the present invention is a steel sheet comprising, by weight%, 0.95 to 1.05% of C, 0.3 to 0.8% of Mn, more than 1.0 to 1.6% of Si, more than 0.5 to 1.0% of Cr, the balance Fe and other unavoidable impurities , And an ultra-high strength steel wire having twist number of 13 or more.

Hereinafter, the present invention will be described in detail. (% Is% by weight)

C: 0.95 to 1.05%

C is the most economical element for improving the strength of the steel wire. When the content is less than 0.95%, the effect of improving the strength is insufficient. When the content exceeds 1.05%, the strength is improved but the ductility is decreased. Is preferably in the range of 0.95 to 1.05%.

Mn: 0.3 to 0.8%

Mn is an effective element for increasing the incombustibility or an element having a strong center-segregation. If it exceeds 0.8%, it is highly likely to induce a low-temperature structure, and if it is added below 0.3%, the effect of addition can not be sufficiently achieved. Therefore, the content of Mn is preferably in the range of 0.3 to 0.8%.

Si: more than 1.0 to 1.6%

Si is a component which stabilizes the pearlite layer phase together with the solid solution strengthening effect and increases the strength and ductility. In order to obtain the above effect, Si preferably has a range exceeding 1.0%. However, when it exceeds 1.6%, the ductility is drastically reduced to deteriorate the drawability. Therefore, it is preferable that the content of Si is in the range of more than 1.0 to 1.6%.

Cr: more than 0.5 to 1.0%

Cr is a component that improves strength and ductility by making the layer structure of pearlite fine, and when it is added in an amount of 0.5% or less, the effect of improving the strength and ductility is insufficient because of insufficient effect of finely dividing the layered structure. On the other hand, It slows the transformation speed and deteriorates the productivity. Therefore, it is preferable that the content of Cr is in the range of more than 0.5 to 1.0%.

Hereinafter, the production method of the present invention will be described in detail.

First, in order to make the wire having the above composition suitable for drawing, it is preferable that the wire is LP heat-treated before the drawing. The LP heat treatment refers to a process of transforming a wire material subjected to heat treatment at a high temperature into a structure suitable for drawing processing by quenching the wire material.

Thereafter, in order to increase the strength of the wire rod, a steel wire is obtained by drawing. When the cross-sectional reduction ratio is less than 80%, the strength to be achieved by the present invention can not be obtained. When the cross-sectional reduction ratio is more than 90%, excessive work hardening The disconnection of the steel wire occurs well.

After the drawing, the steel wire is subjected to heat treatment in a temperature range of 400 to 450 占 폚. Generally, during drawing processing, the strength of the steel wire is increased by the work hardening, but the delamination occurs at a constant reduction rate or more, and the twisting characteristic of the steel wire is remarkably deteriorated, so that the commercial property as a product is lost. However, in the present invention, after the wire drawing process, it is left in the wire material through the drawing process through the heat treatment, thereby removing the residual stress which causes delamination of the steel wire during the wire drawing process. When the heat treatment temperature is less than 400 ° C, the steel wire is aged to increase the strength, but the ductility is sharply lowered. When the temperature exceeds 450 ° C, the plate cementite contained in the pearlite structure is changed into a spherical shape, . Therefore, the heat treatment temperature is preferably in the range of 400 to 450 ° C.

In addition, the heat treatment is performed for 20 to 60 seconds. If the curing time is less than 20 seconds, it may be difficult to effectively remove the residual stress. If the curing time exceeds 60 seconds, the cementite may be sphericalized and the cementite may be broken .

As described above, according to the present invention, heat treatment is performed after the drawing process, thereby suppressing the occurrence of delamination and drastically improving the torsional characteristics. More specifically, it is possible to make the number of twistings 13 times or more, to prevent delamination from occurring in wire processing, and to secure a very high level of tensile strength of 2200 to 2600 MPa, Wire rope and wire rope.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are only illustrative of the present invention in detail and do not limit the scope of the present invention.

(Example)

The ingots having the composition ranges shown in the following Table 1 were hot rolled at 1000 ° C to produce wire rods, and then subjected to drawing and heat treatment under the conditions shown in Table 2 to prepare steel wires. Inventive Examples 1 to 6 and Comparative Examples 1, 2, 4, and 5 were heat-treated at 440 ° C for 40 seconds after drawing, and Comparative Material 5 was not subjected to heat treatment after drawing. The mechanical properties of Inventive materials 1 to 6 and comparative materials 1 to 5 prepared as described above were measured, and the results are shown in Table 2 below.

division Component (% by weight) C Si Mn Cr Grade 1 0.98 1.3 0.5 0.6 Gangjong 2 1.02 1.3 0.5 0.6

Steel grade Wire Rod No. Manufacture process Mechanical properties Cross section reduction rate in drafting
(%) Heat treatment
Implementation The tensile strength
(MPa) Torsion number
(time) Whether or not the delamination occurred Grade 1 Comparative Example 1 77 ○ 2066 26 Not occurring Inventory 1 82 ○ 2204 25 Not occurring Inventory 2 85 ○ 2283 22 Not occurring Inventory 3 89 ○ 2418 17 Not occurring Comparative Example 2 93 ○ 2571 7 Occur Comparative Example 3 85 × 2412 2 Occur Gangjong 2 Comparative Example 4 77 ○ 2186 21 Not occurring Honorable 4 81 ○ 2339 19 Not occurring Inventory 5 85 ○ 2467 15 Not occurring Inventory 6 89 ○ 2594 13 Not occurring Comparative Example 5 93 ○ 2748 5 Occur Comparative Example 6 85 × 2593 3 Occur

As shown in Table 2, the inventive materials 1 to 6 prepared according to the composition range and the manufacturing conditions in accordance with the present invention not only have excellent strength but also excellent torsional characteristics, and in particular, no delamination occurred Able to know. It is considered that the increase of the drawing amount compared to the conventional manufacturing method, but the stress in the pearlite structure which is severely deformed by the heat treatment is removed, and the carbon fixed to the potential is separated into the base to improve the plastic deformation.

However, in the case of Comparative Examples 1 and 3 in which the composition range of the present invention was satisfied, but were freshly processed at a section reduction ratio lower than the range of the drawing amount proposed by the present invention, it was found that the tensile strength was lower than that of Inventive Materials 1 to 6 there was. The comparative materials 2 and 4 exhibited excellent tensile strength owing to excessive drafting, but showed a tendency that the number of twists (the number of rotations until breakage in the torsion test) significantly decreased, and it was also found that delamination occurred . In addition, in the case of the comparative materials 3 and 6, the heat treatment was not performed after the drawing process, the torsional characteristics were remarkably lowered, and it was found that the delamination occurred.

Claims

The steel sheet contains 0.95 to 1.05% of C, 0.3 to 0.8% of Si, more than 1.0 to 1.6% of Si, more than 0.5 to 1.0% of Cr, the balance Fe and other unavoidable impurities, Ultra high tensile steel wire with draftability.

The method according to claim 1,
Wherein the steel wire has a tensile strength of 2200 to 2600 MPa.

The steel sheet according to any one of claims 1 to 3, wherein the wire material containing 0.95 to 1.05% of C, 0.3 to 0.8% of C, more than 1.0 to 1.6% of Si, more than 0.5 to 1.0% of Cr, balance Fe and other unavoidable impurities, % To obtain a steel wire; And
And heat treating the steel wire at 450 to 550 占 폚.

The method of claim 3,
Further comprising the step of LP heat-treating the wire material before the drawing process, to thereby obtain a super high strength steel wire.

The method of claim 3,
Wherein the heat treatment is performed for 20 to 60 seconds.