DESIGN OF LOW CARBON DUAL-PHASE STEELS FOR HIGH STRENGTH WIRE

An investigation has been made to produce high strength wire from low carbon dual-phase steel using its high strain hardening rate and superior formability. This dual-phase steel wire is an alternative to conventional high strength wire, which is produced by cold drawing high carbon pearlitic steel rod to large strains with several intermediate annealing or patenting heat treatments.; Some alloy design considerations were assessed to develop a dual-phase steel suitable for cold drawing into high strength wire. The effects of metallurgical variables such as martensite particle size, shape, volume fraction and ferrite grain size on controlling the strength-ductility balance were described, and their role during the wire drawing process characterized.; The dual-phase steel of composition Fe-2% Si-0.1% C, which has been developed according to the selected design guidelines, was found to be the most promising material for high strength wire application. This steel could be continuously drawn to strength levels found in commercial high carbon pearlitic wires without any intermediate patenting treatments during the drawing process, resulting in reductions of production cost and operation complexity. The attractive properties found in the silicon containing dual-phase steel are attributed to its microstructural feature; fine, fibrous and disconnected lath martensite particles in a fine ferrite matrix.; This desirable dual-phase microstructure can be produced by austenitizing and quenching to form 100% martensite, followed by two phase annealing and subsequent quenching or in the as-rolled condition by rolling in the two phase region and quenching after controlled deformation in the austenite region. It is recommended that the quench after two phase annealing or finish rolling be as rapid as possible to prevent austenite pool shrinkage or decomposition prior to its transformation to martensite.