Wire rod having good superior surface properties, high strength, and high toughness, and a method for manufacturing same

Abstract

Provided is a wire rod having high strength and high toughness, which suppresses the generation of surface oxide and has superior surface properties through uniform oxide formation, and to a method for manufacturing same. For this purpose, a wire rod comprising 0.005˜ to 0.02 wt. % of Sb, having superior surface properties, high strength and high toughness, and a method for manufacturing same are provided.

Description

TECHNICAL FIELD[0001]The present invention relates to a wire rod used in a structural steel, in particular, used in automobile components such as bolts, tie-rods and the like, requiring cold forging, and a method for manufacturing the same.BACKGROUND ART[0002]Most structural steels may be heat treated steels formed by reheating, quenching and tempering steel after hot processing to increase the strength and toughness thereof. On the contrary, non-heat treated steel refers to steel having degrees of strength and toughness almost similar to those of a heat treated steel material, even without a heat treatment being performed thereon after hot processing. The term ‘non-heat treated steel’ is used in Korea and Japan and is also known as ‘microalloyed steel’ because a material thereof is formed by adding a small amount of an alloying element.[0003]Meanwhile, since high strength steel is manufactured through tempering and thus, has a tensile strength of 900 MPa or more and excellent ducti...

AI Technical Summary

Benefits of technology

The present invention provides a method for manufacturing a wire rod that has high strength, high toughness, and suppressed surface defects. The method includes adding a small amount of antimony to form oxides, which increases the tensile strength and ductility of the wire rod while refining grains. The final scale thickness is reduced by forming uniform iron oxide at high temperatures during hot rolling. This method is cost-competitive and does not have process condition limitations, making it a useful technology for manufacturing high-quality wire rod.

Problems solved by technology

However, in most steels, since when strength thereof is increased, ductility thereof may be lowered, the application thereof may be restricted.

In addition, an iron oxide unavoidably generated at the time of rolling wire rods may cause surface defects in the wire rod during wire drawing after the manufacturing of the wire rod to deteriorate quality thereof.

Thus, there has been a process defect in which an iron oxide (scale) layer on the surface of the wire rod needs to be removed through post-processing such as pickling or the like, after the manufacturing of the wire rod.

Thus, an increase in processing costs due to the removal of scale using water spraying or hot-scarfing in order to control the scale before hot rolling of the wire rod, during the manufacturing of the wire rod, has not been solved.

However, the controlled rolling and cooling processes may inevitably increase processing costs in accordance with an increase in the price of alloying elements and multiple process variations, and thus, the application thereof may be restricted.

However, the technology has limitations in that processing costs are increased and a cooling device is further required.

In addition, in Japanese Patent Laid-Open Publication No. 2010-222680, a non-heat treated wire rod having high strength may be manufactured through controlled rolling and cooling processes by adding Al, Cu, Ni, Mo, V or the like thereto, in order to control an initial austenite microstructure, but processing costs may inevitably be increased due to the necessity of further equipment installations.

Further, Japanese Patent Laid-Open Publication No. 1998-008209 discloses that an alloying element such as Cr, V or the like is essentially added at the time of manufacturing a high strength and high toughness wire rod configured of ferrite and pearlite, but the effectiveness thereof is degraded due to the addition of an expensive alloying element in order to improve cold workability.

Thus, as described above, the limitations in increasing tensile strength and the solution to reducing a surface scale for manufacturing a high strength and high toughness wire rod are not overcome.

A small number of patent applications relating to non-heat treated wire rods were filed in Japan, but in the patent applications, the addition of an expensive alloying element and controlled rolling and cooling are still essentially required, leading to an inability to secure a competitive price, and in particular, the removal of the surface scale is restricted.

However, since most elements capable of forming oxides may be expensive and further, may be added in the same amount as that of a ferroalloy, the development of technologies thereof has been slow to progress.

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