Effect of heating rate on the microstructure formation during intercritical annealing of cold-rolled low-carbon steels

Abstract

Cold-rolled (80%) low-carbon steel samples having ferrite-pearlite or ferrite-martensite (blocky/fibrous morphology) starting structures were heated at two different heating rates (∼300 K/s & ∼1 K/s) to different sub/inter-critical annealing temperatures (773-1173 K) and immediately water quenched. Ferrite-fibrous martensite starting structure showed the finest ferrite grain sizes (3-6 μm) and uniform distribution of martensitic islands (∼1-2 μm) after annealing, offering the best tensile properties amongst the investigated samples. The microstructures obtained after the annealing treatment have been explained in view of the strain partitioning in cold-rolled starting structure (as determined by EBSD analysis) and the recrystallization-transformation interaction taking place during annealing as the function of heating rate.