Microstructure and Mechanical Properties of a Cold-Rolled Ultrafine-Grained Dual-Phase Steel

A new processing route to produce Ultrafine-Grained Dual-Phase steel has been proposed, involving cold-rolling and subsequent intercritical annealing of a fibrous ferrite–martensite starting structure. Ultrafine-grained DP (UFG-DP) steel with an average ferrite grain size of about ~2.7 μm and an average martensite island size of ~2.9 μm was achieved. Tensile testing revealed superior mechanical properties (the ultimate tensile strength of 1267 MPa and uniform elongation of 8.2%) for the new DP steel in comparison with the fibrous DP steels. The superior mechanical properties are attributed to the influence of microstructure refinement on the work-hardening and fracture behavior.