High tensile steel filament member for rubber product reinforcement

A high tensile steel wire for rubber product reinforcement, said high tensile steel wire being made by a method comprising heat-treating and plating a carbon steel wire rod material containing 0.70 to 0.75% carbon and subsequently drawing the heat-treated and plated carbon steel wire rod to form the steel wire, wherein the steel wire has a diameter of from 0.10 to 0.40 mm, a tensile strength (Y) in N/mm.sup.2 not less than a lower limit given by the following equation I:

• Y.gtoreq.-(1960 N/mm.sup.3) d+3580 N/mm.sup.2 (I),
• wherein d is the diameter in mm, and a torque decrease factor of less than 7% in a torsion-torque curve as measured in a torsion torque test in which the steel wire is twisted forward and then reverse twisted.

A steel cord for reinforcement of rubber products, said steel cord being made by a method comprising bundling two steel wires together substantially in parallel to each other and winding another steel wire around the two steel wires substantially in parallel to each other, wherein a ratio of a steel cord strength to an aggregate strength of all of said steel wires before being twisted together to form the steel cord is not less than 0.935, and wherein the steel wire is high tensile steel wire for rubber product reinforcement, said high tensile steel wire being made by a method comprising heat-treating and plating a carbon steel wire rod material containing 0.70 to 0.75% carbon and subsequently drawing the heat-treated and plated carbon steel wire rod to form the steel wire, wherein the steel wire has a diameter of from 0.10 to 0.40 mm, a tensile strength (Y) in N/mm.sup.2 not less than a lower limit given by the following equation I:

• Y.gtoreq.-(1960 N/mm.sup.3) d+3580 N/mm.sup.2 (I),
• wherein d is the diameter in mm, and a torque decrease factor of less than 7% in a torsion-torque curve as measured in a torsion torque test in which the steel wire is twisted forward and then reverse twisted.