KR100928783B1 - Wire rod for high strength tire cord with excellent freshness - Google Patents

Abstract

The present invention relates to a steel for high-strength tire record (Tirecord) with excellent drawability, while providing a high strength to the steel, easy refining work, preventing segregation of chemical components in the steel sheet and at the same time excellent in freshness The purpose is to provide a wire rod for high strength tire cords.

In the present invention, by weight%, C: 0.9-1.5%, Si: 0.2-0.4%, Mn: 0.1-0.6%, Al: 1.0-2.5%, Cr: 0.1-1.0%, and V: 0.05-0.30% A high-strength tire cord wire having excellent freshness, comprising a balance Fe and other unavoidable impurities, and wherein the C and Al content ratio (C / Al) is in the range of 0.5 to 1.0.

According to the present invention, it is possible to easily obtain a steel wire having excellent tensile strength and excellent cross-sectional reduction rate, and also excellent in refining work of steel and freshness of wire, which is very effective for producing tire cord wire.

Drawing, high strength, tire cord, wire rod, cross section reduction rate

Description

Wire Rod for High-Strength Tirecord with Advanced Drawability}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire rod for high strength tire records having excellent drawability. More specifically, the reduction ratio of the wire rod is high, and the strength after drawing of the wire rod can be greatly improved. To a wire rod for a tire cord.

The tire cord refers to a reinforcement or member that enters the rubber to increase durability, running and stability of a tire in a vehicle such as an automobile. The tire cord material is made of polymer synthetic fiber such as polyester or nylon and steel steel. In recent years, steel cords are widely used because of their high strength and excellent heat resistance.

The tire cord should have high strength. The method of increasing the strength of the steel tire cord is to add an alloy component to iron (Fe), to increase the work hardening rate of the tire cord, and to increase the fresh strain of the material. And the like, and among these, a method of adding an alloying element is widely used.

An example of the prior art for manufacturing steel tire cords is Japanese Patent Application No. 195-002938, where iron (Fe) is carbon (C), silicon (Si), manganese (Mn) and phosphorus (P). It is characterized by improving the corrosion resistance by the addition, the tensile strength is less than 320 megapascals (hereinafter referred to as MPa) is a steel material having a relatively low tensile strength.

Another example is home patent application 1993-6868512, where Fe is C, Si, Mn, chromium (Cr), boron (B), nitrogen (N) and molybdenum (Mo) or vanadium (V). However, this technique has a disadvantage in that segregation of alloy components occurs in steel slabs during continuous casting by adding a large amount of expensive alloy iron such as Mo and V.

Another example is Japanese Patent Laid-Open No. 1987-077441, where Fe is C, Si, Mn, P, S, N, Cr, Mo, tungsten (W), copper (Cu), nickel (Ni ) And cobalt (Co), etc., but when 10 or more alloying elements are added, not only refining is actually easy in the steelmaking process, but when Cu is added, the steel is heated in a heating furnace. Due to the occurrence of Cu brittleness, wire rod rolling is difficult.

Another example is Korean Patent Publication No. 2006-0028080, which is characterized by improving the freshness of the wire rod by controlling the chemical composition of the non-metallic inclusions in the steel by adding Ca-Si in the molten steel stage.

However, while the technology described in the Republic of Korea Patent Publication can improve the divinity, it is difficult to significantly increase the strength.

The present invention has been completed in a series of research processes to overcome the technical limitations of the prior art, it is easy to refine the work while giving a high strength to the wire rod, while preventing segregation of chemical components in the steel sheet and at the same time freshness The purpose is to provide an excellent high strength tire cord wire.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is in weight%, C: 0.9-1.5%, Si: 0.2-0.4%, Mn: 0.1-0.6%, Al: 1.0-2.5%, Cr: 0.1-1.0%, V: 0.05-0.30%, S : Contains less than 0.030%, and P: less than 0.030%, and is composed of the balance Fe and other unavoidable impurities, the freshness characterized in that the C and Al content ratio (C / Al) is in the range of 0.5 ~ 1.0 An excellent high strength tire cord wire rod.

At this time, the physical properties of the wire for the tire cord is preferably at least 1380MPa tensile strength, 30% or more of the maximum cross-sectional reduction.

In addition, it is effective that the wire rod for tire cords contains P and S as impurities at 0.030% by weight or less, respectively.

As described above, according to the present invention, it is possible to easily obtain a steel wire rod having excellent tensile strength and excellent cross-sectional reduction rate, that is, ductility, and also excellent in refining work and freshness of the wire rod. It is very effective to manufacture.

Hereinafter, the present invention will be described in detail.

The inventors of the present invention have come to the following conclusions as a result of a careful examination of the relationship between the carbon content and the strength of the tire cords, which were generally added in large amounts to improve the strength of the tire cords.

That is, in general, as the strength of the tire cord is increased to 3000 MPa or less, 4000 MPa or less, and 4000 MPa or more, it is a general trend that the carbon content is increased from the suba pore region to the super pore region.

However, according to the research results of the present inventors, it is difficult to expect additional strength increase when the carbon content is increased by a certain level or more, and the amount of fresh processing is reduced so that the overall strength of the wire rod is reduced or reaches a certain limit value. do.

The addition of a certain amount of Al to the C content suppresses the precipitation of the cornerstone ferrite at the base, which further increases the strength of the material and increases the amount of drawing, which is effective in securing high strength and excellent elongation. lost.

The present invention is derived based on the above research results.

Hereinafter, the reason for limiting the alloying elements in the present invention will be described.

Carbon (C): 0.9-1.5 wt%

Carbon is an essential element added to form a graphite phase on a metal matrix and is an important element for obtaining wire strength. However, when the carbon content is less than 0.9% by weight, it is difficult to secure a desired wire strength and also ferrite + residue. It is difficult to secure the strength and to control the ferrite structure fraction during the heat treatment for manufacturing austenitic composite steel.

On the other hand, when the carbon content exceeds 1.5% by weight, a large amount of cornerstone ferrite is precipitated on the substrate, so that the cross-sectional reduction rate (RA) is lowered, and eventually, it is difficult to increase the strength by drawing.

In addition, the carbon content is limited to 0.9 to 1.5% by weight since mechanical properties such as elongation and impact toughness are reduced after heat treatment, and further, such as segregation of carbon components and intensification of surface decarburization during charging by heating occurs. do.

Silicon (Si): 0.2-0.4 wt%

Silicon contributes to the deoxidation of molten steel in the refining process and increases the strength of the wire rod, so an appropriate amount is added. Si is an element that plays a very important role in the present invention together with Al and Cr to be described later. When Si is added with Cr, a certain amount contributes to simultaneously increasing the strength and ductility of the wire rod.

When the Si content is added less than 0.2% by weight, it is difficult to obtain the desired strength increase effect. When the Si content is added more than 0.4% by weight, the strength and ductility increase effect reaches saturation due to insufficient solidification of ferrite. The amount of addition is preferably limited to 0.2 to 0.4% by weight.

Manganese (Mn): 0.1-0.6 wt%

Manganese is an element that is useful for securing the strength of steel, but its content is less than 0.1% by weight, and if it exceeds 0.6% by weight, Mn component segregation is generated in the steel sheet during continuous casting. In the present invention, since the low-temperature tissue is generated to inhibit the freshness, the Si content is limited to 0.1 to 0.6% by weight.

Aluminum (Al): 1.0-2.5 wt%

Aluminum is a powerful molten deoxidation element that not only contributes to deoxidation but also suppresses the phenomenon of precipitation of cornerstone ferrite at the base.

Typically, when the carbon content exceeds the vacancy point, that is, when the temperature is lowered on the super-vacanite, the formation of the cornerstone ferrite carbide forms, which lowers the strength and elongation.

In the present invention, carbon is added in an amount of 0.9 to 1.5% by weight as described above in order to greatly increase the strength. According to the researches of the present inventors, despite the relatively high carbon content, it is found that the addition of Al does not produce cornerstone ferrite at the base after heat treatment, and can increase the strength and elongation of the wire rod to a desired range.

When the Al content is less than 1.0% by weight, it is difficult to obtain the desired effect because the cornerstone ferrite is produced at the base, and when it exceeds 2.5% by weight, continuous casting of molten steel is not easy. Therefore, in the present invention, the Al content is limited to 1.0 to 2.5% by weight.

Chromium (Cr): 0.1-1.0 wt%

Cr plays a role of simultaneously increasing the strength and elongation of the wire rod of the present invention similarly to the Si addition effect within the range of 0.1 to 1.0% by weight.

This is because the addition of Cr expands the austenite region and combines with carbon to form carbides that do not embrittle the matrix.

When the amount of Cr added is less than 0.1% by weight, the effect of increasing the strength and elongation is small. If the amount of Cr is more than 1.0% by weight, the effect of increasing the strength and elongation reaches a saturation value.

Vanadium (V): 0.05-0.3 wt%

When V is added to the steel, the surface structure is finely formed and reacts with carbon to form carbides, thereby increasing the known strength and impact toughness. In general, V has a large carbide formation ability, thereby forming fine carbides, thereby having excellent softening resistance after tempering and greatly improving high temperature strength.

In the present invention, when the amount of V is less than 0.05%, it is difficult to improve mechanical properties such as impact toughness, and when the amount of V is more than 0.3% by weight, the amount of V oxide, that is, V ₂ O ₅ , is increased due to the high vapor pressure of V ₂ O ₅ in the refining step. In the present invention, the V content is limited to 0.05 to 0.30% by weight because it is difficult to make.

Other impurities

The remaining impurity elements can be included within the range inevitably included in the steelmaking process. In particular, P and S are not preferably contained in the wire rods because they hinder the toughness of the steel, but considering the workload, manufacturing cost, and process efficiency in the steelmaking refining process, it is preferable to include 0.030% by weight or less.

Relationship between carbon and aluminum: C / Al ratio = 0.5 ~ 1.0

According to the present invention, in order to manufacture a tire cord wire having excellent strength and stretchability, it is important to suppress formation of cornerstone ferrite.

It is very important to properly control the ratio of carbon to aluminum in the alloy components in order to increase the strength and elongation of the wire rod to the desired target after the tire cord wire is heat-treated and the foundation ferrite is not produced. 0.5 to 1.0 was found to be preferable.

When the C / Al weight ratio is less than 0.5, Al is added to the required amount or more, thereby increasing the manufacturing cost. On the other hand, when the C / Al weight ratio is more than 1.0, the strength and elongation are due to precipitation of the cornerstone at the base. It is difficult to obtain the simultaneous increase of sex.

The steel wire of the present invention is produced by a conventional production method, and is not particularly limited to the method.

The steel strip having the composition of the present invention as described above is rolled to produce a billet, and then heated to finish rolling with a wire rod and cooled.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

Figure 1 schematically shows the steel sheet and wire rod rolling process experimented by the present inventors for the purpose of implementing the present invention.

First, molten steel was refined in a 10 ton atmosphere furnace, and a steel strip of 1,000 mm in width and 100 mm in thickness was manufactured using a test cycle. Subsequently, the width was cut to 270 mm while maintaining the thickness of the slab at 100 mm, and the cut steel piece was rolled in a test mill to produce 160 mm x 160 mm billets. Subsequently, the steel sheets were heated under normal process conditions, subjected to finish rolling and cooling with a wire diameter of 5.5 mm, and then measured for tensile strength and a rate of reduction in section (RA), and the results are shown in Table 1 below. Table 1 shows the chemical composition of the steel sheet prepared in this experiment.

division C Si Mn P S Al Cr V C / Al ratio TS (MPa) RA (%) Invention 1 0.95 0.2 0.4 0.02 0.013 1.0 0.5 0.25 0.95 1396 35 Invention 2 1.15 0.2 0.2 0.02 0.011 1.75 0.3 0.25 0.68 1405 40 Invention 3 1.25 0.3 0.2 0.01 0.012 2.0 0.3 0.20 0.63 1415 43 Invention 4 1.35 0.4 0.3 0.01 0.010 2.5 0.2 0.15 0.68 1430 41 Comparative Material 1 0.85 0.2 0.3 0.02 0.013 0.80 0.3 0.25 1.06 1365 41 Comparative Material 2 1.00 0.2 0.4 0.02 0.011 - 0.3 0.25 - 1370 11 Comparative Material 3 1.15 0.3 0.4 0.03 0.012 2.5 0.3 0.20 0.46 1430 27 Comparative Material 4 1.35 0.5 0.2 0.03 0.010 - 0.3 0.15 - 1435 8 Comparative Material 5 1.55 0.3 0.4 0.01 0.04 1.75 0.3 0.25 0.89 1447 16

In the above Table 1, the inventive material (1) to the inventive material (4) are included in the C, Si, Mn, P, S, Al, Cr and V content within the range defined by the present invention, and the C / Al ratio is also the present invention. It falls within 0.5-1.0 which is a limit of.

As shown in Table 1, the invention material (1) to invention material (4) is all of the tensile strength (TS, Tensile Strength) of the wire rod is more than 1380MPa, the reduction ratio (RA, Reduction of Area) exceeds 30% It can be seen that the wire rod satisfies all the physical properties of the present invention.

On the other hand, the comparative material (1) has a carbon content of 0.85% by weight, which is less than the range of the present invention, and the C / Al ratio is 1.06, which exceeds the limited range of 0.5 to 1.0 of the present invention. It is good, but the tensile strength (TS) of about 1365 MPa is less than 1380 MPa pursued by the present invention can be seen that it is difficult to obtain the desired physical properties.

Comparative material (2) is an alloy component such as C, Si, Mn, P, S, Cr, V, but belongs to the scope of the present invention, it does not add aluminum (Al) like a tire cord steel commonly used, Since aluminum (Al) is not added, the C / Al ratio is infinite and is beyond the scope of the present invention, and the tensile strength is less than the desired target value, and the cross-sectional reduction rate is about 11%. It can be seen that it is significantly less.

As a result of observing the microstructure of Comparative Material 2 using the present inventors as an optical microscope, it was confirmed that a large amount of cornerstone ferrite was deposited at the austenite grain boundary.

Therefore, the lowering of tensile strength and cross-sectional reduction rate compared to the target value may be attributed to the precipitation of ferrite.

Comparative material (3) is the content of all alloying components, such as C, Si, Mn, P, S, Al, Cr, V is within the scope of the present invention, but the C / Al ratio of 0.46 and the scope of the present invention 0.5 ~ 1.0 As it is less than, the tensile strength exceeds 1380MPa while the section reduction rate is about 27%, it can be seen that the target value pursued by the present invention.

According to the optical microscope observation of the comparative material (3), it was confirmed that some of the cornerstone ferrite was precipitated at the austenite grain boundary.

The comparative material 4 does not add Al like the comparative material 2, and the Si content is 0.5% by weight, which exceeds the limited range of 0.2 to 0.4% by weight of the present invention, while the tensile strength is good at 1435 MPa. It can be seen that the cross-sectional reduction rate is about 8%, which is far below 30% pursued by the present invention. Also in the comparative material (4), it was observed that a large amount of cornerstone ferrite precipitated at the austenite grain boundary.

Comparative material 5 has a carbon content of 1.55% by weight, exceeding the limited range of 0.9 to 1.5% by weight of the present invention, the remaining chemical components and C / Al ratio to satisfy the present invention, the tensile strength is sufficient On the other hand, it can be seen that the section reduction rate is significantly less than 30%.

Through this embodiment, according to the present invention it was confirmed that the target tensile strength and the rate of cross-sectional reduction can be obtained.

1 is a schematic view showing a process for producing a tire cord wire of the present invention.

Claims (2)

By weight%, C: 0.9-1.5%, Si: 0.2-0.4%, Mn: 0.1-0.6%, Al: 1.0-2.5%, Cr: 0.1-1.0%, V: 0.05-0.30%, S: 0.030% Or less, and P: 0.030% or less, consisting of the balance Fe and other unavoidable impurities, the C and Al content ratio (C / Al) is a high-strength excellent tire, characterized in that it falls in the range of 0.5 ~ 1.0 Wire rod for cord The wire rod for excellent high strength tire cord according to claim 1, wherein the tensile strength and the maximum cross-sectional reduction rate of the wire rod are 1380 MPa or more and 30% or more, respectively.

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