Abstract: The present invention relates to a high strength steel sheet having a tensile strength of 700 to 1,300 Mpa and an elongation of 12% or more, and having a tempered martensite single phase structure. The steel sheet of the present invention is manufactured through the steps of: rapidly heating a material steel sheet for 3 to 60 seconds to an Ac3 transformation point or higher and maintaining the material steel sheet, the material steel sheet containing 0.08 to 0.30 wt % of C, 0.01 to 2.0 wt % of Si, 0.30 to 3.0 wt % of Mn, 0.05 wt % or less of P and 0.05 wt % or less of S and the remainder being Fe and other unavoidable impurities; rapidly cooling the heated steel sheet to 100° C./s or higher with water or oil; and rapidly tempering to 500° C. to A1 transformation point for 3 to 60 seconds including heating and maintaining time.

Abstract: A method of manufacturing high strength steel wire for cold forging containing 0.15-0.40 wt % of C, less than 1.5 wt % of Si, 0.30-2.0 wt % of Mn, less than 0.03 wt % of P, and less than 0.03 wt % of S. After initial cold-drawing, the wire rod is heated in a series of high frequency induction heating devices over the Ac3 transformation point for 30-90 seconds. The wire rod is then rapidly cooled and tempered at a temperature of from 500° C. to the A1 transformation point for 30-90 seconds. The wire rod is then cooled to achieve a tensile strength of 1,100-1, 400 MPa. The wire rod is then cold-drawn at an area reduction rate in excess of 25% and up to 40% to yield a tensile strength of 1,200-1,600 MPa, with improved service life of the mold.

Abstract: Disclosed herein is a method of preparing a MgB2 superconducting wire and the MgB2 superconducting wire prepared thereby. The method comprising rolling a raw powder by using a powder rolling method. According to the method of the present invention has an effect of increasing an effective area where superconducting current can flow by improvement of the connectivity of a MgB2 superconducting powder and achievement of high density through a powder rolling process, and maintaining an uniform current value even in a large length because of the improvement of the connectivity.

Abstract: The present invention relates to a pre-heat treatment steel wire with high strength for a cold forging which is used as a material for an engine, chassy and parts (bolts and shafts) of a steering device. The method includes: cold drawing of a wire rod containing 0.15-0.40 wt % of C, less than 1.5 wt % of Si, 0.30-2.0 wt % of Mn, less than 0.03 wt % of P, less than 0.03 wt % of S and the remainder including Fe and unavoidable impurities; rapidly heating the cold drawn wire rod in a series of high frequency induction heating devices over Ac3 transformation point for 30-90 seconds and maintaining such a heated state; rapidly cooling the wire rod in the heated state by water or oil; executing a tempering process by heating the wire rod to 500° C.

Abstract: Disclosed herein is a method of preparing a MgB2 superconducting wire and the MgB2 superconducting wire prepared thereby. The method comprising rolling a raw powder by using a powder rolling method. According to the method of the present invention has an effect of increasing an effective area where superconducting current can flow by improvement of the connectivity of a MgB2 superconducting powder and achievement of high density through a powder rolling process, and maintaining an uniform current value even in a large length because of the improvement of the connectivity.

Abstract: Disclosed is a steel wire for cold forging, which has excellent low temperature impact properties, and a method of producing the same. The steel wire consists of 0.10-0.40 wt % C, 1.0 wt % or less of Si, 0.30 - 2.0 wt % Mn, 0.03 wt % or less of P, 0.03 wt % or less of S, and the balance of Fe and impurities. The steel wire has an austenite grain size of 5-20 ?m, impact absorption energy of 60 J/cm2 or more at ?40° C., and tensile strength of 70-130 kgf/mm2. A steel material for cold forming according present invention has impact toughness that is greatly superior to a conventional spheroidized material or non-heat treated steel at a low temperature of ?40° C.

Abstract: Disclosed is a steel wire for cold forging, which has excellent low temperature impact properties, and a method of producing the same. The steel wire consists of 0.10-0.40 wt % C, 1.0 wt % or less of Si, 0.30-2.0 wt % Mn, 0.03 wt % or less of P, 0.03 wt % or less of S, and the balance of Fe and impurities. The steel wire has an austenite grain size of 5-20 ?m, impact absorption energy of 60 J/cm2 or more at ?40° C., and tensile strength of 70-130 kgf/mm2. A steel material for cold forming according to the present invention has impact toughness that is greatly superior to a conventional spheroidized material or non-heat treated steel at a low temperature of ?40° C.

Abstract: Disclosed is a quenched and tempered steel wire with superior cold forging characteristics, consisting essentially of 0.1-0.5 wt % of C, 1.0 wt % or less of Si, 0.2-2.5 wt % of Mn, 0.03 wt % or less of P, and 0.03 wt % of S, with the balance being Fe and inevitable impurities, which has tensile strength of 700-1300 Mpa and percent spheroidization of carbides of at least 30%. Such quenched and tempered steel wire, which is subjected to a quenching and tempering processes by high frequency induction heating in a short period, without a spheroidizing annealing process needing a long period, has forging characteristics equal or superior to those of spheroidizing annealed steel wire, thus increasing productivity. Therefore, the quenched and tempered steel wire is applicable to make various bolts and shafts as parts for machine structures requiring high strengths.

Abstract: Steel wires and steel rods with excellent cold forging properties and used in a manufacture of various machine components, which have relatively high strengths, are disclosed. The steel wires are produced by maintaining a product (n×YS) of a yield strength (YS) and a work hardening coefficient (n) obtained by a tensile test of the steel wire within a range of 4.0-11.0 kgf/mm2, without a need of additional quenching and tempering treatments after cold forging. There is no need to perform heating for spheroidizing annealing for a long time, and it is possible to produce quenched and tempered steel wires having excellent cold forging properties by quenching and tempering treatments in a short period of time.

Abstract: Steel wires and steel rods with excellent cold forging properties and used in a manufacture of various machine components, which have relatively high strengths, are disclosed. The steel wires are produced by maintaining a product (n×YS) of a yield strength (YS) and a work hardening coefficient (n) obtained by a tensile test of the steel wire within a range of 4.0-11.0 kgf/2, without a need of additional quenching and tempering treatments after cold forging. There is no need to perform heating for spheroidizing annealing for a long time, and it is possible to produce quenched and tempered steel wires having excellent cold forging properties by quenching and tempering treatments in a short period of time.

Abstract: Steel wires and steel rods with excellent cold forging properties and used in a manufacture of various machine components, which have relatively high strengths, are disclosed. The steel wires are produced by maintaining a product (n×YS) of a yield strength (YS) and a work hardening coefficient (n) obtained by a tensile test of the steel wire within a range of 4.0-11.0 kgf/mm2, without a need of additional quenching or tempering treatments after cold forging. There is no need to perform heating for spheroidizing annealing for a long time, and it is possible to produce quenched and tempered steel wires having excellent cold forging properties by quenching and tempering treatments in a short period of time.