KR101403267B1 - High strength wire rod having execellent drawability and steel wire and method for manufacturing thereof - Google Patents

Abstract

In the present invention, it is intended to provide a high strength wire rod and a steel wire excellent in freshness without adding expensive alloying elements.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength wire rod,

The present invention relates to a high-strength wire rod and a steel wire excellent in freshness and a method of manufacturing the same.

Anchor ropes and bridges for bridges are reinforcing materials for seismic and structural stability. Anchor ropes and bridges for bridges are required to have excellent strength and freshness to secure the above strength.

As one of methods for obtaining excellent strength, there is a method of increasing the strength of the material itself by adding a large amount of strengthening elements for increasing the strength of the steel. As a representative example of such reinforcing elements, a sufficient amount of drawing work can be secured not only by improving the strength but also by increasing the amount of drawing, increasing pearlite and improving the strength of wire, depending on the appropriate contents of C, Si, Mn, Cr and the like.

Among them, Cr is present in front of or at the interface of the cementite in the region below or at the transformation temperature to suppress the growth thereof, thereby making the thickness of the cementite small and making the interval between the pearlite layers small. . Therefore, in the case of the anchor rope and the steel wire for bridges, Cr addition is an essential element in fresh materials, and Cr has been conventionally added in a large amount. However, if the amount is excessively high, Cr carbide is formed to lengthen the transformation time to deteriorate the productivity and form coarse pearlite in some areas.

As a method for obtaining another excellent strength, there is a method of increasing the work hardening rate.

Anchor ropes and bridges for bridges are manufactured by drawing and annealing the rolled wire. By increasing the work hardening rate during the drawing process 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.

Although the above method effectively increases the strength, there is a problem that the wire rod material is low in ductility and the drawing limit is low, so that the freshman can not give the drawing amount as much as desired.

That is, the limit of the drawing process is an important characteristic that determines the amount by which the strength can be increased by the work hardening, and the twisting characteristic of the steel wire should be considered, not simply the amount of drawing process that can be given until fracture. The torsional characteristics of the steel wire are classified according to the number of torsions and the shape of the fracture surface until fracture because the steel wire is used as a bundle of twisted strands. Generally, when the processing amount is increased, the ductility of the material is rapidly lowered, and the torsional characteristics are deteriorated. Therefore, it is known that it is excellent in terms of twisting to attain the target strength by securing the maximum strength before the drawing process and minimizing the amount of drawing process.

Therefore, although a method of increasing the amount of drawing processing in order to greatly increase the strength is preferable, there is a problem that the limit of the amount of drawing processing that can be applied to the present processing technology is almost fixed.

In the present invention, it is intended to provide a high strength wire rod and a steel wire excellent in freshness without adding expensive alloying elements.

In one aspect of the present invention, there is provided a high strength wire rod excellent in freshness, comprising 0.1-0.3% of C, 0.5-1.0% of Si, 0.5-1.0% of Mn, 0.003-0.005% of B, , The balance Fe and other unavoidable impurities, and the microstructure includes ferrite and martensite.

Another aspect of the present invention is a high strength steel wire excellent in freshness, comprising 0.1-0.3% of C, 0.5-1.0% of Si, 0.5-1.0% of Mn, 0.003-0.005% of B, 0.003-0.005% of Nb, %, The balance Fe and other unavoidable impurities, and the microstructure includes ferrite and martensite.

Another aspect of the present invention is to provide a method of manufacturing a high strength wire rod excellent in freshness, which comprises 0.1-0.3% of C, 0.5-1.0% of Si, 0.5-1.0% of Mn, 0.003-0.005% of B, 0.003 to 0.005%, and the balance Fe and other unavoidable impurities to obtain a wire rod; subjecting the cooled wire rod to a primary heat treatment at 850 to 950 캜 for 5 to 15 minutes; And subjecting the heat-treated wire to a secondary heat treatment at 760 to 800 ° C for 3 to 7 minutes.

A method for manufacturing a high strength steel wire excellent in freshness, which is another aspect of the present invention, comprises the steps of: 0.1-0.3% of C, 0.5-1.0% of Si, 0.5-1.0% of Mn, 0.003-0.005% of B, 0.003 to 0.005%, and the balance Fe and other unavoidable impurities to obtain a wire rod; subjecting the cooled wire rod to a primary heat treatment at 850 to 950 캜 for 5 to 15 minutes; Treating the heat-treated wire material at 760 to 800 ° C for 3 to 7 minutes, and drawing the heat-treated wire material.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof will be more fully understood by reference to the following specific embodiments.

According to the present invention, there is provided a wire rod having sufficient drawability without adding an expensive alloying element, and a wire rod having a high strength of the steel wire after final drawing, by suitably controlling the alloy component and the manufacturing conditions. Further, it is possible to provide a wire having excellent strength and having a drawing amount equal to or higher than that of Cr-added steel material. In addition, it is possible to provide a high-strength steel wire having an excellent torsional characteristic, suppressing the occurrence of delamination which acts as a stumbling block for high-strength steel wire, and to provide a steel wire with increased drawing limit of steel wire for drawing. Further, by performing the two-step heat treatment additionally, the LP heat treatment which is harmful to the human body can be omitted.

1 is a schematic diagram showing the process and thermal history of the present invention.
2 is a photograph showing the microstructure of Inventive Example 1. Fig.
3 is a graph showing changes in hardness at the end faces of Inventive Example 1 and Conventional Example 1. Fig.

The inventors of the present invention have conducted studies to derive wire rods and wires excellent in freshness. As a result, it has been found that it is preferable to omit Cr added to secure conventional high-strength wire rods, and to perform B- and Nb- The present invention has been completed. Through this, it is confirmed that by controlling the microstructure of the steel with ferrite and martensitic structure (dual phase), it has excellent strength and freshness simultaneously, and it is possible to omit LP heat treatment additionally, and it is possible to produce environmentally friendly wire rod I could.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a high strength wire excellent in freshness, which is one aspect of the present invention, will be described in detail.

In one aspect of the present invention, there is provided a high-strength wire rod excellent in freshness, comprising 0.1 to 0.3% of C, 0.5 to 1.0% of Si, 0.5 to 1.0% of Mn, 0.003 to 0.005% of B, 0.003 to 0.005% of Nb, %, The balance Fe and other unavoidable impurities, and the microstructure includes ferrite and martensite.

Carbon (C): 0.1 to 0.3 wt%

C is the most effective element for strengthening the river. Carbon is present in the untransformed state of the austenite remaining in martensite during the two-step heat treatment. When the content of carbon is less than 0.1% by weight, it is difficult to realize the target strength intended in the present invention, and it is not economical because a large amount of expensive alloying elements such as Mo and Ni must be added in order to increase the strength. On the other hand, when the content of C exceeds 0.3% by weight, a large number of martensite is formed in the ferrite grain boundaries to decrease the ductility, thereby causing disconnection at the time of freshness. Therefore, it is preferable that the carbon content is 0.1 to 0.3 wt%.

Silicon (Si): 0.5 to 1.0 wt%

Si is an effective element that is solidified in a ferrite base to improve the strength by employment strengthening effect. In order to exhibit such an effect in the present invention, it is preferable that it is contained in an amount of 0.5 wt% or more. On the other hand, when the content of silicon exceeds 1.0% by weight, loss due to surface decarburization and scale formation occurs. Therefore, it is preferable that the silicon is contained in an amount of 0.5 to 1.5% by weight.

Manganese (Mn): 0.5 to 1.0 wt%

Mn is an effective element for strengthening the strength of the steel. In order to exhibit such an effect in the present invention, it is preferable that it is contained in an amount of 0.5 wt% or more. On the other hand, when the content of manganese exceeds 1.0 wt%, the material becomes weak and the freshness limit occurs early. Therefore, it is preferable that the manganese is contained in an amount of 0.5 to 1.0 wt%.

Boron (B): 0.0030 to 0.0050 wt%

B is a component that delays the transformation of austenite into pearlite during cooling in annealing, and is an element capable of inhibiting the formation of a cubic cementite and being segregated in grain boundaries to improve the incombustibility. When the content of B is less than 0.0030% by weight, the above-mentioned effect can not be exhibited. On the other hand, if the content is more than 0.0050 wt%, not only the effect is saturated due to grain boundary segregation of B but also plating defects can be caused by formation of excessive surface contaminants. Therefore, the content of B is preferably controlled to 0.0030 to 0.0050% by weight.

Niobium (Nb): 0.003 to 0.005% by weight

Nb is an effective element for refining the austenite grains during hot rolling. In order to exhibit such an effect in the present invention, it is preferable that it is contained in an amount of 0.003% by weight or more. On the other hand, when it exceeds 0.005% by weight, it binds with C in the steel and exists as NbC to deteriorate the freshness. Therefore, it is preferable that the niobium is contained in an amount of 0.003 to 0.005% by weight.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, since they can be known by any ordinary person skilled in the art.

According to an aspect of the present invention, it is possible to provide a wire rod excellent in drawability and excellent in strength by satisfying the above-mentioned component system. The microstructure of the wire is preferably a dual phase consisting of ferrite and martensite.

The ferrite is preferably 80 to 85% in area fraction. It is preferable to set the martensite area fraction at maximum to 15 to 20% in order to secure the strength. In order to secure ductility, it is desirable to secure a ferrite area fraction of 80 to 85%.

The high strength steel wire excellent in freshness, which is another aspect of the present invention, will be described in detail.

The steel wire satisfying the above-mentioned composition and microstructure can be drawn and processed to produce a steel wire. The steel wire thus obtained preferably has 15 or more twists without delamination. At this time, the number of twists means the number of twists per 100 x D length (D: 5.34 mm).

It is more preferable to have a hardness of 480 Hv or more at a point 1.2 mm away from the center portion to the surface portion in the section of the steel wire.

A method of manufacturing a high-strength wire rod excellent in freshness, which is another aspect of the present invention, will be described in detail.

Another aspect of the present invention is to provide a method of manufacturing a high strength wire rod excellent in freshness, which comprises 0.1-0.3% of C, 0.5-1.0% of Si, 0.5-1.0% of Mn, 0.003-0.005% of B, 0.003 to 0.005%, and the balance Fe and other unavoidable impurities to obtain a wire rod; subjecting the cooled wire rod to a primary heat treatment at 850 to 950 캜 for 5 to 15 minutes; And subjecting the heat-treated wire to a secondary heat treatment at 760 to 800 ° C for 3 to 7 minutes. Hereinafter, this will be described in detail.

First, a step of hot-rolling a slab satisfying the above-mentioned component system precedes. The hot rolling may be carried out according to a conventional method, and is not particularly limited in the present invention. However, in the present invention, since pro-eutectoid ferrite is not produced, rolling at the austenite temperature should be terminated at least. The wire rod obtained by the hot rolling can be cooled by a subsequent cooling process.

Since the cooling may be performed by a conventional method, it is not particularly limited. However, in one embodiment of the present invention, the L / H (laying head) can be cooled by passing through as shown in FIG. By the above process, the wire rod can be cooled to 400 to 500 ° C at a cooling rate of 1 to 5 ° C / sec.

Primary heat treatment

It is preferable to perform the first heating of the wire material cooled as described above. Such a heat treatment is preferably carried out at an appropriate temperature for a suitable period of time in order to completely remove the pearlite phase of the wire by forming the entire structure of the wire into austenite. It is more preferable that the cooled wire rod is subjected to the first heat treatment at A3 to 950 DEG C for 5 to 15 minutes.

In order to fully austenitize, it is preferable to perform the primary heating at A3 DEG C or higher. Further, in order to form fine austenite, it is necessary to firstly heat to 950 占 폚 or less. In addition, when the heating is performed for less than 5 minutes, the austenite phase is not sufficiently formed, and when the primary heating is performed for more than 15 minutes, the austenite coarsening occurs. Therefore, it is preferable to conduct the first heating at A3 to 950 DEG C for 5 to 15 minutes. It is preferable to perform the primary cooling at a rate of 40 to 60 ° C / sec after the primary heating. When cooled at a cooling rate of less than 40 DEG C / sec, there is a pearlite phase, making it difficult to obtain the microstructure to which the present invention is intended. The upper limit does not have to be particularly limited, but the upper limit can be controlled at 60 ° C / sec in consideration of the effect and the manufacturing cost. More preferably, water cooling is performed. It is preferable to form the martensite structure through the primary cooling. Therefore, in order to form the microstructure to be secured in the present invention, it is preferable to perform the primary heat treatment including the primary heating and the primary cooling.

2nd heat treatment

It is preferable to perform the secondary heating of the wire material cooled as described above. The heating heat treatment is preferably carried out at an appropriate temperature for a suitable time, in order to constitute the strand of martensite and ferrite which are ideal structures to be secured in the present invention. It is more preferable that the cooled wire rod is subjected to a secondary heat treatment at A1 to A3 占 폚 for 3 to 7 minutes.

In order to constitute the abnormal structure as described above, it is necessary to perform secondary heating at a temperature of Al or higher. In addition, it is necessary to perform secondary heating at A3 ℃ or lower in consideration of the cost compared to the effect. In addition, when secondary heating is performed for 3 minutes or more, a sufficient amount of austenite and ferrite can be formed, and if it exceeds 7 minutes, there is a problem of coarsening of austenite and ferrite grains. Therefore, it is preferable to carry out secondary heating for 3 to 7 minutes at A1 to A3 占 폚. It is preferable that austenite and ferrite are formed through the secondary heating. And then secondary cooling at a rate of 40 to 60 ° C / sec. When cooled at a cooling rate of less than 40 DEG C / second, a sufficient martensite phase is not formed. The upper limit is not particularly limited, but the upper limit can be controlled to 60 占 폚 / sec in consideration of the effect and the manufacturing cost. More preferably, water cooling is performed. It is preferable to form the austenite into martensite through the secondary cooling to form the final ferrite and martensite.

A method of manufacturing a high strength steel wire having excellent freshness, which is another aspect of the present invention, will be described in detail.

The wire rod is manufactured by the above-described method, and then the step of drawing the heat-treated wire rod is performed to produce a high-strength steel wire having excellent freshness.

As described above, when the wire rod is drawn to produce the steel wire, it is preferable that the wire rod is drawn and processed in the range of 15 to 25% in the section reduction rate per pass. In order to obtain a high strength per pass, it is preferable that the reduction rate of the cross section per pass is not less than 15%. In order to prevent surface deterioration due to the material and the dice friction, it is desirable to control the reduction rate of the cross section per pass to 25% or less.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

Steels having the composition shown in Table 1 below were cast. Thereafter, hot rolled by a conventional method to produce a wire having a diameter of 13 mmf. Thereafter, as shown in Fig. 1, the hot-rolled 13 mm wire was cooled at a cooling rate of 1 DEG C / sec in a L / H (laying head), and then the two batch furnaces were sequentially Followed by a second heat treatment.

The thermal history in the two batches is as shown in Fig. That is, in the first batch, after maintaining at A3 or more at 900 ° C for 10 minutes, water-cooled martensite structure was obtained. Thereafter, in the secondary batch furnace, martensite and austenite were formed by keeping the temperature between A1 temperature and A3 at 780 DEG C for 5 minutes. Thereafter, austenite was made into ferrite by water cooling to form an abnormal structure of the final ferrite and martensite.

The microstructure of the wire (Inventive Example 1) formed through such a manufacturing process is shown in Fig. As shown in FIG. 2, observation of the microstructure of Inventive Example 1 revealed that the abnormal structure of ferrite and martensite was secured as shown in Table 2. [

In addition, Comparative Examples 1 to 6 were also produced by the same method as described above.

C Si Mn B Nb Cr Inventory 1 0.2 1.0 1.0 0.005 0.005 - Comparative Example 1 0.2 1.5 1.0 0.005 0.005 - Comparative Example 2 0.2 2.0 1.0 0.005 0.005 - Comparative Example 3 0.2 1.0 1.5 0.005 0.005 - Comparative Example 4 0.2 1.0 2.0 0.005 0.005 - Comparative Example 5 0.2 1.0 1.0 0.005 - Comparative Example 6 0.2 1.0 1.0 0.005 - Conventional Example 1 0.92 1.3 0.5 - - 0.3

Ferrite (area%) Martensite (area%) Inventory 1 80 20 Comparative Example 1 75 25 Comparative Example 2 70 30 Comparative Example 3 72 28 Comparative Example 4 67 33 Comparative Example 5 81 19 Comparative Example 6 79 21 Conventional Example 1 0 0

The wire rod produced under the above conditions was subjected to drawing at a reduction ratio of 20% per pass and a total reduction ratio of 83.2%, and then the hardness at a position 1.2 mm away from the center to the surface, the possibility of freshness to 5.32 mm and the number of twists Are shown in Table 3 below.

Hardness (Hv)
5.32 mm in diameter and 1.2 mm from the center 5.32 mm freshness available Torsion frequency Inventory 1 487.4 O 15 Comparative Example 1 510.3 X 0 Comparative Example 2 525.2 X 0 Comparative Example 3 490 X 0 Comparative Example 4 512.4 X 0 Comparative Example 5 486.7 X 0 Comparative Example 6 489.5 X 0 Conventional Example 1 463.3 O 12

For Inventive Example 1, a drawing die was used to cut the reduction rate by 20% per pass, to a total of 83.2% using a fresh die, and a specimen of the steel wire was taken for each pass.

As mentioned above, FIG. 3 is a graph showing changes in hardness at the end faces of Inventive Example 1 and Conventional Example 1. FIG. (RA: 36%), 8.32 mm (RA: 59%), 6.66 (RA: 73.8%) and 5.32 mm (RA: 83.2% And the hardness along the position away from the center to the surface. In the case of Conventional Example 1, only the hardness value of 5.32 mm (RA: 83.2%) is shown in the graph.

As shown in FIG. 3, it can be seen that the hardness value increases with the increase or decrease of the freshness reduction ratio.

As can be seen from FIG. 3 and Table 3, the hardness of Inventive Example 1 (5.32 mm in diameter, 1.2 mm away from the center in the surface direction) was 487.4 Hv, which was equal to or higher than that of Conventional Example 1. In addition, in the case of the twist test, it can be confirmed that the twist frequency is 15 times (twist test frequency: 30 times) in the state where the delamination does not occur. I could confirm.

On the other hand, as in Comparative Examples 1 and 2, when Si exceeded the range proposed in the present invention, it was confirmed that the hardness was higher than that of Inventive Example 1 but the drawing was impossible at 5.32 mm, .

As in Comparative Examples 3 and 4, when Mn exceeded the range proposed in the present invention, the hardness was higher than in Inventive Example 1, but it was impossible to draw at 5.32 mm similarly to Comparative Examples 1 and 2, It is possible to confirm that the organization is not secured.

In Comparative Examples 5 and 6, it was confirmed that Nb and B were not added and that the microstructure fraction and hardness similar to that of Inventive Example 1 could be secured, but not to 5.32 mm.

Therefore, it can be confirmed that the composite addition of B and Nb improves the ductility of the wire without influencing the hardness or strength, thereby enabling the wire to be drawn.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (10)

And the balance Fe and other unavoidable impurities. The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.1 to 0.3% of C, 0.5 to 1.0% of Si, 0.5 to 1.0% of Mn, 0.003 to 0.005% of B, 0.003 to 0.005% of B, Is a high strength wire having excellent freshness including an area fraction of 80 to 85% of ferrite and 15 to 20% of martensite.
delete And the balance Fe and other unavoidable impurities. The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.1 to 0.3% of C, 0.5 to 1.0% of Si, 0.5 to 1.0% of Mn, 0.003 to 0.005% of B, 0.003 to 0.005% of B, A high strength steel wire including ferrite and martensite and having excellent twistability of 15 times or more without delamination.
delete The method of claim 3,
And a hardness of 480 Hv or more at a point 1.2 mm away from the center portion to the surface portion in the section of the steel wire.
The steel sheet including 0.1 to 0.3% of C, 0.5 to 1.0% of Si, 0.5 to 1.0% of Mn, 0.003 to 0.005% of B, 0.003 to 0.005% of Nb and Fe and other unavoidable impurities in a weight% Rolling to obtain a wire rod;
A primary heat treatment including primary heating and primary cooling in which the wire rod is maintained at A3 to 900 占 폚 for 5 to 15 minutes; And
And subjecting the primary heat-treated wire rod to a secondary heat treatment including a secondary heating and a secondary cooling at A1 to A3 占 폚 for 3 to 7 minutes.
The method according to claim 6,
Wherein the primary cooling and the secondary cooling are excellent in freshness at a cooling rate of 40 to 60 DEG C / sec.
The steel sheet comprising 0.1 to 0.3% of C, 0.5 to 1.0% of Si, 0.5 to 1.0% of Mn, 0.003 to 0.005% of B, 0.003 to 0.005% of Nb and Fe and other unavoidable impurities in a weight% Rolling to obtain a wire rod;
A primary heat treatment including primary heating and primary cooling in which the wire rod is maintained at A3 to 900 占 폚 for 5 to 15 minutes;
Subjecting the primary heat-treated wire rod to a secondary heat treatment including a secondary heating and a secondary cooling for 3 to 7 minutes at A1 to A3 占 폚; And
And a step of drawing the second heat-treated wire material.
9. The method of claim 8,
Wherein the primary cooling and the secondary cooling are excellent in the freshness at a cooling rate of 40 to 60 DEG C / second.
9. The method of claim 8,
Characterized in that the drawing step is a drawing process in which the wire material is drawn to a reduction ratio of 15 to 25% per sectional area per pass.

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