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 effective for reinforcing a super-large off-road tire wherein strands made by simultaneously twisting together 3 to 6 steel wires in the same twisting direction with the same pitch length are used and the steel cord is made by twisting together 3 to 6 such strands in the same direction as the twisting direction of the strands and with the same pitch length. Each of the steel wires constituting the strands continuously has a small wavy pattern of a pitch length smaller than the lay length of the strands and therefore each of the strands has a compound pattern comprising a wavy pattern formed by the twisting and said small wavy pattern and in a gap is formed between steel wires each of the strands by the small wavy pattern. The lay length P.sub.1 of the steel cord is 8 to 15 times the steel cord diameter D and the elongation on breakage by tension of the steel cord is over 5%.

Abstract: A high elongation compact helical steel cord with a high degree of elongation at break of not less than 5% has a (1.times.n) structure comprising three or more base wires which are helically preformed at a predetermined pitch and which are twisted in the same direction and at the same pitch so that the ratio P/D of the cord diameter D to the twisting pitch P is in the range of 8-15 with the base wire preforming pitch being shorter than the cord twisting pitch. The finished cord has a helical composite structure with its elongation under a load of 35 kgf/mm.sup.2 being 0.71%-1.00% and that under a load of 70 kgf/mm.sup.2 being 1.18%-1.57%. A radial tire is reinforced with the steel cord preferably as a steel belt cord. An apparatus for making the steel cord is provided with revolving preformers on the wire introducing portion of a bunching machine such that the bunching machine is rotated in a direction reverse to the rotational direction of the revolving preformers.

Abstract: A steel cord effective for reinforcing a super-large off-road tire wherein strands made by simultaneously twisting together 3 to 6 steel wires in the same twisting direction with the same pitch length are used and the steel cord is made by twisting together 3 to 6 such strands in the same direction as the twisting direction of the strands and with the same pitch length. Each of the steel wires constituting the strands continuously has a small wavy pattern of a pitch length smaller than the lay length of the strands and therefore each of the strands has a compound pattern comprising a wavy pattern formed by the twisting and said small wavy pattern and in a gap is formed between steel wires each of the strands by the small wavy pattern. The lay length P.sub.1 of the steel cord is 8 to 15 times the steel cord diameter D and the elongation on breakage by tension of the steel cord is over 5%.

Abstract: The steel cord has the 1.times.9 structure, in which three core wires and six thicker outer wires are twisted in the same direction with the same pitch, and has a flat shape in the section which is taken perpendicularly to the longitudinal section thereof. The six outer wires having at least two gaps between adjacent ones and the core wires have at least one gap between adjacent ones.