Development of a New Ultrafine/Nano Ferrite-Carbide Microstructure by Thermomechanical Processing

Abstract

The steel with the new microstructure, bimodal submicrometer equiaxed ferrite grains with uniformly distributed nanosized cementite particles, was manufactured by a new approach utilizing simple cold-rolling and subsequent annealing of a dual phase ferrite-martensite starting structure. The mean ferrite grain size and carbide size range of the specimen after 80% cold-rolling and subsequent annealing at 600 °C for 20 min were 0.35 µm and 70–140 nm, respectively. A combination of bimodal ultrafine ferrite and nanoscale carbides used as a more effective method for achieving an excellent balance in strength-ductility. The strength of the steel with the new microstructure increased to about 880 MPa (nearly 60% higher than that of the as-received state, e.g., 540 MPa), without significant loss of ductility.