KR20130053084A

KR20130053084A - Steel wire rod having good drawability and drawing method using the same

Info

Publication number: KR20130053084A
Application number: KR1020110118608A
Authority: KR
Inventors: 이유환; 김동현
Original assignee: 주식회사 포스코
Priority date: 2011-11-15
Filing date: 2011-11-15
Publication date: 2013-05-23

Abstract

PURPOSE: A wire for wire drawing which has an excellent wire drawing property with high surface lubrication is provided to form a self-lubrication layer without any special coating on the surface of a steel material by including antimony. CONSTITUTION: A wire for wire drawing which has an excellent wire drawing property is composed of, in wt%: C: 0.25-0.45; Si: 0.1-0.2; Mn: 0.1-0.7; Sb: 0.005-0.02; and the remainder Fe and inevitable impurities. The wire for wire drawing includes Sb oxide inside. The internal structure of the wire for wire drawing is composed of ferrite and pearlite, and the grain size of the ferrite is 20μm or less. A wire drawing method comprises the following steps of: preparing the wire for wire drawing; heating the wire at the temperature of 300-400°C; and drawing the wire.

Description

Wire rod for excellent drawing and drawing method using same {STEEL WIRE ROD HAVING GOOD DRAWABILITY AND DRAWING METHOD USING THE SAME}

The present invention relates to a drawing wire having excellent drawability and a drawing method using the same, and more particularly, a drawing wire for drawing and a drawing method using the same, in which drawability is improved by a simple heat treatment of drawing. It is about.

The wire rod is processed into a material having high strength and ductility through subsequent drawing, as described, for example, in Japanese Patent Laid-Open No. 2004-307929. In particular, drawing is a major process that increases the utilization of wire rods, as it gives the structure to the steel and improves the strength of the steel through work hardening.

By the way, since the wire work is performed while passing the wire rod through a predetermined die for drawing, friction occurs between the wire rod and the die. This friction may not only cause wire breakage, but also cause wear of the die. Therefore, in the conventional drawing, it is necessary to coat the surface with a lubricant.

However, such a lubricant may not only increase the cost of drawing by itself, but also may cause a cost increase in many ways because it requires an additional process of coating the surface of the wire for the drawing. In particular, typical lubricants include lubricants containing butyric acid. These lubricants are not only hazardous substances but also very expensive. However, as described above, as well as improving the physical properties of materials such as cold forging and the like (referred to as steel wire after being drawn), and also plays an important role in controlling the size of the steel wire, the steel is subjected to the drawing process It is hard to think about omitting the process.

That is, in the case of cold forging wire rod, low-medium carbon steel is used as a material, and is produced as CHQ parts of 800-1000MPa grade through a manufacturing process including drawing, cold forging, and the like. In order to manufacture such CHQ parts, the ferrite fraction and size to increase the ductility are very important. In other words, if the ductility is not added, the yield is lowered due to defects or breakage of the heading part after the forging and failing to forge the load during cold forging. In order to solve the above problems, the addition of alloying elements to increase the ferrite fraction and reduce the ferrite size by suppressing the initial austenite grain size through high temperature carbonitride precipitation, and rolling and rolling at low temperature during wire rolling and cooling The ongoing TMCP (Thermo-mechanical controlled process) process is being introduced, but it is indispensable to invest in equipment to increase the load of equipment, and also has the disadvantage of adjusting the load during rolling and cooling during the investment of equipment.

In addition, by increasing the speed of drawing as a means to increase the productivity to promote the drawing process under the harsh conditions, for this reason, the situation that the materials used in the past without problems have caused many problems in the drawing process. Accordingly, there is a demand for wire rods having excellent strength that can withstand harsh drawing even with the same ductility.

According to one embodiment of the present invention, there is provided a wire rod for wire drawing having improved surface workability and having a high surface lubricity and a manufacturing method thereof.

In addition, according to another embodiment of the present invention, the ductility is improved, suitable for production of parts such as CHQ, or by drawing the wire under severe conditions, the drawing wire rod for improved drawing productivity and its manufacturing method are provided.

The wire rod for drawing according to one embodiment of the present invention is C: 0.25-0.45% by weight, Si: 0.1-0.2% by weight, Mn: 0.1-0.7% by weight, Sb: 0.005-0.02% by weight, balance Fe and unavoidable impurities Wire rod for drawing excellent in freshness.

At this time, it is preferable that the wire rod contains Sb oxide therein.

In addition, the internal structure of the wire rod is made of ferrite and pearlite and the grain size of the ferrite is advantageously 25㎛ or less.

The drawing method according to another embodiment of the present invention is C: 0.25-0.45% by weight, Si: 0.1-0.2% by weight, Mn: 0.1-0.7% by weight, Sb: 0.005-0.02% by weight, balance Fe and unavoidable impurities Preparing a wire rod for drawing; Heating the wire rod to a temperature of 300 to 400 ° C .; And drawing the wire rod.

At this time, it is preferable that the wire rod contains Sb oxide therein.

In addition, the holding time of the heating step is preferably 30 minutes to 1 hour.

In addition, it is advantageous that the iron oxide having a thickness of 50 to 150 μm is formed on the surface of the wire rod after the heating step, so that the lubrication coating process may be omitted.

As a result, the fresh lubricating film may not be applied.

As described above, according to one embodiment of the present invention, the steel for drawing may include antimony, thereby providing a wire that can form a self-lubricating layer without a special coating on the surface of the steel, and thus, the cost required for the formation of the lubricating layer. According to another embodiment, the internal structure of the wire rod may be made of fine ferrite and pearlite, and thus the freshness of the material itself may be greatly improved.

1 is a micrograph of a wire rod internal structure (a) when the wire rod of the composition shown in Table 1 contains 0.015% by weight, and a cross section (b) after heating the wire rod to 350 ° C.
2 is a result of observing the surface state after heating the general material of Table 1 under the same conditions as the result (b) of the surface condition after heating the wire of Figure 1 (a),
3 is a graph showing the change of the surface scale amount when the heating temperature of the wire rod containing 0.015% by weight of Sb among the wire rod of Table 1;
4 is a result of observing the surface oxide shape according to the Sb content of the steel having a composition of Table 1, and
5 is a result of observing the formation of Sb oxide in the interior of the wire having a composition according to the present invention.

Hereinafter, the present invention will be described in detail.

The inventors of the present invention have studied the improvement of the freshness of the wire rod, and as a result, when a component capable of replacing the conventional lubricant is generated on the wire rod surface by simple heat treatment, a complicated and expensive procedure of lubricant coating is performed. It has been found that the invention can be omitted and has led to the present invention.

That is, according to the exemplary embodiment of the present invention, by forming a self-lubricating layer on the surface of the wire rod by simple heat treatment of the wire, it is possible to have a lubricating layer having a function similar to that of a conventional butyric acid-based lubricant without a separate coating process.

For this purpose, it is preferable to control the composition of the wire rod as follows. That is, the wire rod according to one embodiment of the present invention, in addition to Fe and unavoidable impurities, C: 0.25-0.45% by weight, Si: 0.1-0.2% by weight, Mn: 0.1-0.7% by weight and Sb: 0.005-0.02% by weight It is characterized by including one. The reason for addition of each additional element and the reason for limiting its content are explained below.

C: 0.25 ~ 0.45 wt%

C is an essential element added to secure the strength of the steel. When the content of C is less than 0.25% by weight, sufficient strength is not secured, so it is impossible to secure the strength of the non-coarse high strength steel, and when the content of C is more than 0.45%, the carbon content is high, so that cracking or It may cause breakage.

Si: 0.1-0.2 wt%

Si has the effect of solidifying in the ferrite to strengthen the base material strength. If the Si content is less than 0.1, the strength increase effect through solid solution is insufficient, and should be limited to 0.1% by weight. On the contrary, when the content is added in excess of 0.2% by weight, the work hardening effect may be increased during cold forging, leading to a decrease in toughness. It may be limited to 0.2% or less because it can be.

Mn: 0.1-0.7 wt%

Mn is an alloying element that increases the strength of the steel and affects the impact characteristics, and has an effect of increasing the rolling rolling property and reducing the brittleness. When added in an amount of less than 0.1% by weight, the strength compensation effect is insignificant, and when it is added in excess of 0.7% by weight, it is preferable to limit the curing phenomenon due to the increase in strength.

Sb: 0.005 ~ 0.02 wt%

Sb, a key element of the present invention, forms Sb2O5 in the austenite matrix to suppress austenite grain growth and suppresses excessive iron oxide formation in the wire rod state to make the final surface of the wire rod beautiful. In addition, when heating the wire rod at a predetermined temperature before wire drawing, a spherical iron oxide is formed on the wire rod surface to enhance the lubrication effect. When Sb is added less than 0.005%, there is a problem that insufficient Sb2O5 is difficult to form thermodynamically due to insufficient reaction amount with oxygen, and it is also difficult to form a solid solution in the metal state of Sb capable of forming such an oxide. When added in excess of 0.02% by weight, Sb having an oxygen affinity or higher is added and eluted in the austenite matrix in the form of a solute atom.

Therefore, according to the present embodiment, it is preferable that the wire rod of the present invention includes C, Si, Mn, and Sb in the aforementioned ranges. Of course, it should be noted that in addition to the active additive elements described above, unavoidable impurities incorporated in the steel manufacturing process may be added up to a normal level.

However, it is preferable not to add elements such as Ti, Nb and V among the elements added to the wire rod as much as possible, and even if it is unavoidably added, the sum of the contents is preferably added in less than 0.01% by weight. This is because these elements may not only react with oxygen in molten steel to prevent Sb oxide from forming, but also cause wire rod prices to increase.

In addition, according to still another embodiment of the present invention, the wire rod of the present invention preferably includes an Sb-based oxide (eg, Sb 2 O 5) therein. As described above, the Sb-based oxides suppress the formation of oxides on the surface in the wire rod state, and when heated to a predetermined temperature, the self-lubricating coating having excellent lubricity serves to be formed on the wire rod surface. In addition, it plays a role in suppressing grain growth of the wire internal tissue to increase the ductility of the material. Increased ductility can also contribute to improving the drawability of wire rods.

According to another embodiment of the present invention, the wire rod having the above-described composition preferably has an internal structure composed of ferrite and pearlite in order to omit spheroidizing heat treatment. The internal structure composed of the ferrite and pearlite is necessary to secure the ductility of the steel. At this time, other structures other than the ferrite and pearlite are not preferably included because they impair the processability of the wire rod.

In addition, the ferrite is preferably contained in more than 60 area%. This is because a sufficient amount of ferrite is required to secure the ductility of the wire rod. The remaining tissues other than the ferrite and inevitably contained impurity tissues are preferably pearlite.

In addition, in order to ensure the workability of the wire rod, it is more advantageous that the grain size of the ferrite is 25 µm or less.

Hereinafter, a drawing method according to one embodiment of the present invention will be described. For drawing, it is necessary to prepare a wire rod having the above-mentioned advantageous composition. As described above, the wire rod of the present invention is suppressed so that oxide formation on the surface is not excessive in the wire rod state, but when the wire rod is heated to a predetermined temperature, iron oxides close to the spherical shape having excellent lubricity are formed on the surface. These iron oxides perform a rolling lubrication function on the surface of the wire rod, thus reducing friction between the die and the wire rod. In addition, in some cases, the iron oxides may also serve as a protective coating of fresh steel wire. In order to have sufficient lubricity, the thickness of the iron oxide is preferably 50 µm or more. However, when too thick, the material loss is severe, so the thickness is preferably 150 μm or less.

More preferably, the heating temperature at which the above-described advantageous iron oxide is formed is 300 to 400 ° C. That is, the heating temperature needs to be 300 ° C. or higher to obtain a sufficient iron oxide forming effect. However, since excessive heating may cause aging in the wire rod, the heating temperature is preferably controlled to 400 ° C. or lower.

In addition, even within the preferred temperature range can be divided into low-temperature heating of 300 ~ 350 ℃ and high temperature heating of 350 ~ 400 ℃, the effect may be slightly different for each embodiment. Specifically, an oxide having a thickness of about 50 to 200 μm may be formed on the surface during low temperature heating, and they perform a lubricating role of suppressing fresh heat generation in place of all or part of the butyric acid added as a lubricant when fresh. do. In addition, when heated to a high temperature, the oxide is formed in a thicker range of 150 to 400 μm, preferably 200 to 300 μm. In this case, lubrication is performed during drawing, and the coating process for storage remains after storage. This can be omitted since it is effective. In addition, the self-lubricating film is effective because it is less harmful to the environment than conventional lubricants such as butyric acid. Moreover, it is preferable that the said heating time is 30 minutes-1 hour. In other words, in order to obtain a sufficient heating effect, the heating time is preferably 30 minutes or more, and when heated excessively, it is preferable to heat it to 1 hour or less because there is a possibility that an undesirable strength increase may occur due to an aging effect or the like.

After heating as described above, a drawing process follows, and any drawing process may be included in the scope of the present invention. At this time, according to one more preferred embodiment of the present invention, when the wire is drawn, the lubricant coating is not substantially applied.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it should be noted that the following embodiments are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. And the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

(Example)

C: 0.25% by weight, Si: 0.15% by weight, Mn: 0.6% by weight, and Sb and the balance of the contents shown in Table 1 below were obtained wires having a composition that is substantially Fe and inevitable impurities. The wire rod was heated to 250 ° C. for 30 minutes and cooled, and then drawn under the conditions of the fresh dose shown in Table 1. However, in Table 1, the general material shows the case where Sb is not contained.

Tensile strength and elongation of the wire rod obtained as a result of drawing is shown in Table 1 below. As can be seen in the drawings, according to a preferred embodiment of the present invention, when the appropriate amount of Sb was added, it was confirmed that the tensile strength is high in all the fresh dose range compared to the general material not added.

Fresh dose Tensile Strength [Mpa] Elongation Sb 0.015% Sb 0.005% Sb 0.02% General Sb 0.015% Sb 0.005% Sb 0.02% General 10 629.7 613 607.9 550 31.2 30.3 28.9 27.2 20 702.1 655.3 642.9 578.5 29.9 29.6 27.5 26.5 30 742.2 714.4 687.7 620.3 29.1 28.5 27.2 25.4 40 778.6 742.2 715.5 638.9 28.6 28.6 26.3 24.9 50 836.9 789.6 762.2 655.8 27.9 27.5 26.1 23.1 60 887.5 826.4 796.4 666.8 27.5 27.1 25.5 22.8 70 925.3 866.6 825.2 675.2 27.5 26.8 25.3 20.1 80 936.8 897.2 856.4 683.3 26.8 26.5 25.1 19.2

In FIG. 1, the wire internal structure (a) and the cross section photograph (b) after heating the wire at 250 ° C in the case of containing 0.015% by weight of Sb in the wire of the composition shown in Table 1 are shown. As can be seen from the figure, it can be seen that a structure in which ferrite and pearlite of 20 µm or less are mixed is formed inside the wire rod. In addition, after the wire was heated, it was confirmed that Fe 3 O 4 oxide was stably formed on the surface with a thickness of about 100 μm.

In FIG. 2, the surface state of the wire rod of FIG. 1 is observed after heating the general material of Table 1 under the same conditions as the result of the heating (b). As can be seen in the drawings, since the general material does not contain Sb, iron oxides are not smoothly formed on the surface, and thus have a relatively fine and smooth surface. However, according to one preferred embodiment of the present invention, iron oxides are formed on the surface. This large amount was found to be suitable for lubrication.

3 shows the change in the scale amount of the surface layer when the wire rod containing 0.015% by weight of Sb in Table 1 was heated for 1 hour while varying the heating temperature. As can be seen from the drawings, it can be seen that the scale thickness can be stably controlled in the range of 50 to 200 μm in the temperature range of 300 to 400 ° C., which is a more preferable range of the present invention.

Figure 4 shows the results of observing the surface oxide shape according to the Sb content of the steel having a composition of Table 1 above. As can be seen in the picture of the figure, it was confirmed that the particle shape of the surface scale is very different depending on the amount of Sb added. That is, in the case of the general material without Sb, it can be confirmed that the iron particles are uniformly distributed because no scale is formed on the surface, and the amount of Sb added is 0.005 (b), 0.01 (c), and 0.015, respectively. It can be seen that the surface scale grows as it increases to (d), 0.02 (e), and 0.025 (f). As shown in the drawing, it can be seen that the (d) steel species added with Sb 0.015 exhibits the scale shape and particle size of the most uniform size, which can prevent surface cracking during drawing, and thus can be used for high strength drawing and high speed drawing. Indicates that it can be created.

In addition, Sb oxide of the wire rod added with 0.015% by weight of Sb was observed and shown in FIG. 5. As shown in the figure, it can be seen that the Sb oxide forms a nano-sized oxide. In addition, it can be seen that 50 to 100 Sb oxides are distributed per unit area. In the present invention, the fine Sb oxide is distributed in an appropriate number as described above, and the grain growth of the initial austenite grains is suppressed due to the pinning effect of the grain boundary, so that the grain size of the ferrite is reduced, and the high strength and the fine ferrite are increased. It can be seen that the toughness can be secured.

Claims

C: 0.25 to 0.45% by weight, Si: 0.1 to 0.2% by weight, Mn: 0.1 to 0.7% by weight, Sb: 0.005 to 0.02% by weight, the drawing wire having excellent freshness including the balance Fe and unavoidable impurities.

The wire rod for wire drawing of Claim 1 excellent in the freshness containing Sb oxide inside.

The wire rod for wire drawing according to claim 1, wherein the internal structure is made of ferrite and pearlite and the grain size of the ferrite is 20 µm or less.

C: 0.25-0.45% by weight, Si: 0.1-0.2% by weight, Mn: 0.1-0.7% by weight, Sb: 0.005-0.02% by weight, preparing a wire for drawing comprising a balance Fe and unavoidable impurities;
Heating the wire rod to a temperature of 300 to 400 ° C .; And
Drawing method comprising the step of drawing the wire.

The drawing method according to claim 4, wherein Sb oxide is contained in the drawing wire.

The method of claim 4, wherein the holding time of the heating step is 30 to 60 minutes.

The drawing method according to claim 4, wherein an iron oxide having a thickness of 50-150 μm is formed on the wire surface after the heating.

The drawing method according to claim 4, wherein the lubricating film is not applied when drawing.