Patent ID: 6949149

Claim:
A process for forming a drawn wire, comprising a) casting and rolling of a steel to form a wire of an initial diameter, said steel comprising iron and the following components in percent by weight: 0.95%≦carbon≦1.3%, 0.2%≦chromium≦1.8%, 0.2%≦manganese≦0.8% 0.2%≦silicon≦1.2% cobalt≦2.2% niobium≦0.1% 0.0006 parts per million (ppm)≦boron≦0.0025 pm sulfur<0.006% phosphorus<0.010%; b) rough drawing of the wire to reduce the diameter of the wire to an intermediate diameter; c) patenting the wire to obtain a predominantly pearlitic microstructure with a small globular size having an elongation greater than 7.5%, with the predominantly pearlitic microstructure providing a tensile strength determined by the following equation: Y 0 =A 1 [(1 −C/C c )( Y f +K f /((1 −C/C c ) L ) 0.5 +( Y c +K c /( C/C c L ) 0.5 C]+Hε where: A 1 =a constant varying from 0.1 to 1 depending on the content of alloying elements, C=the carbon content of the steel, in %, C c =the carbon content in cementite, in %, L=the thickness of ferrite lamellae, Y f , K f and Y c , K c =Hall-Petch constants for ferrite and cementite, respectively, H=the strain hardening of the wire, and ε=the total elongation of the wire; d) brass plating and fine drawing the wire to reduce the wire to a final diameter of about 0.1 to about 0.4 mm with a true strain from 3.6 to 4.5 to obtain an ultimate tensile strength determined by the following equation: Y=Y 0 exp( A 2 ε d ) where A 2 is a constant from 0.2 to 0.5 and ε d is total drawing strain wherein the wire has a tensile strength of at least 3800 MPa at a wire diameter of 0.35 mm.