Steel wire and method of manufacturing the same

A method of manufacturing a steel wire comprising;

• a wire diameter ranging from 0.10 mm to 0.40 mm obtained by subjecting a high-carbon steel wire material having a carbon content ranging from 0.70% to 0.90% in weight to heat treatment and wire drawing, characterized in;
• a tensile strength TS (N/mm2) of the steel wire satisfies following formula,
• TS≧2250−1450 log D
• wherein D is the diameter of the steel wire in mm and log means common logarithm,
• and that repeated torsion value RT (turns/100D) of the steel wire, which is defined as sum of forward twisting and reverse twisting given until a crack is formed on a steel wire in a test wherein a steel wire is subjected to a repetition of forward twisting equivalent to 3 turns per 100D and reverse twisting to the original state with the axis of the steel wire kept straight, satisfies following formula log RT≧2−0.001 {TS−(2250−1450 log D)},
• said method comprising the steps of heat treating drawing a high-carbon steel wire material after heat treatment, wherein the step of drawing is carried out according to following conditions;
• 1. reduction per die is set from (22.67 ε+3)% to 29% for dies at which ε is less than 0.75,
• 2. reduction per die is set from 20% to 29% for dies at which ε is not less than 0.75 and not more than 2.25,
• 3. reduction per dies is set from (−5.56 ε32.5)% to (−6.22 ε+43)% for dies at which ε is more than 2.25 except for the final die,
• 4. reduction per die is set from 4% to (8.3 ε+40.6)% for the final die, and
• 5. ε at the final die is set from 3.0 to 4.3,
• wherein ε is drawing strain expressed by a formula ε=2ln(d0/d), d0 is diameter of the steel wire material in mm before drawing, d is diameter of the steel wire in mm after passing through a die, and ln means natural logarithm.

A steel wire comprising wire diameter ranging from 0.10 mm to 0.40 mm obtained by subjecting a high-carbon steel wire material having a carbon content ranging from 0.70% to 0.90% in weight to heat treatment and wire drawing,

• the steel wire manufactured by drawing a high-carbon steel wire material after heat treatment, wherein the drawing is carried out according to following condition;
• 1. reduction per die is set from (22.67 ε+3)% to 29% for dies at which ε is less than 0.75,
• 2. reduction per die is set from 20% to 29% for dies at which ε is not less than 0.75 and not more than 2.25,
• 3. reduction per dies is set from (−5.56 ε+32.5)% to (−6.22 ε+43)% for dies at which ε is more than 2.25 except for the final die,
• 4. reduction per die is set from 4% to (8.3 ε+40.6)% for the final die, and
• 5. ε at the final die is set from 3.0 to 4.3,
• wherein ε is drawing strain expressed by a formula ε=2ln(d0/d), d0 is diameter of the steel wire material in mm before drawing, d is diameter of the steel wire in mm after passing through a die, and ln means natural logarithm and the tensile strength TS (N/mm2) of the steel wire satisfies following formula,
• TS≧2250−1450 logD
• wherein D is the diameter of the steel wire in mm and log means common logarithm,
• and that repeated torsion value RT (turns/100D) of the steel wire, which is defined as sum of forward twisting and reverse twisting given until a crack is formed on a steel wire in a test wherein a steel wire is subjected to a repetition of forward twisting equivalent to 3 turns per 100D and reverse twisting to the original state with the axis of the steel wire kept straight, satisfies following formula,
• logRT≧2−0.001{TS−(2250−1450 logD)}.