This invention reveals steel alloys for use in manufacturing reinforcing wires for rubber products, such as tires. The steel filaments made with such steel alloys have an outstanding combination of strength and ductility. The steel alloys of this invention can be manufactured into filaments having a tensile strength in the range of 4000 MPa to 5000 MPa. Additionally, these can be patented in a low-cost process due to their having a very fast rate of isothermal transformation. This allows the steel in the steel wire being patented to transform from a face-centered cubic microstructure to an essentially body-centered cubic microstructure within a very short period. This invention more specifically discloses a steel alloy composition which is particularly suitable for use in manufacturing reinforcing wire for rubber products which consists essentially of (a) iron, (b) about 1.05 to about 1.7 weight percent carbon, (c) about 0.2 to about 0.8 weight percent manganese, (d) about 0.1 to about 0.8 weight percent silicon, (e) about 0.1 to about 0.7 weight percent chromium, (f) 0.0 to about 0.5 weight percent nickel, (g) 0.0 to about 0.3 weight percent copper, (h) 0.0 to about 0.5 weight percent molybdenum and (i) 0.0 to about 0.5 weight percent vanadium; with the proviso that the carbon equivalent of the steel alloy is within the range of 1.15 to 1.8 weight percent. It is highly preferred for the steel alloys of this invention to contain from about 0.02 to about 0.3 weight percent copper.