Abstract: The steel wire is made using a carbon steel wire rod material containing 0.70 to 0.75 wt % carbon and has the characteristics that its diameter is 0.10 to 0.40 mm and Y.gtoreq.-1960d+3580 ?Y: tensile strength (N/mm.sup.2), d: diameter (mm)!. Furthermore, the torque decrease factor of the steel wire is less than 7% in a torsion-torque curve in a torsion-torque test wherein forward twisting and then reverse twisting are applied. A preferred steel cord has two steel wires bundled together substantially in parallel and one steel wire is wound around this bundle. This steel cord is made from steel wires having the diameter, tensile strength and toughness characteristics set forth above, and also the ratio B/A of the strength B of the twisted steel cord to the aggregate strength A of the steel wires before they are twisted together into the steel cord is 0.935 or over.

Abstract: A steel cord has a core strand and an outer strand. The core strand includes three wire filaments located in a core portion and each having a same diameter, and nine wires located to enclose the three wires, twisted together with the three wire filaments, and each having a diameter smaller than that of each of the three wires. The outer strand has wires located to enclose the nine wires of the core strand, twisted in a direction reverse to the twisting direction of the core strand, and having a clearance between them.