Influence of epitaxial ferrite on tensile properties of dual phase steel

Effect of epitaxial ferrite (epitaxial ferrite: ferrite formed by transformation of austenite by epitaxial growth on retained ferrite during cooling from intercritical annealing temperature, retained ferrite: ferrite present at intercritical annealing temperature) at constant volume fraction of martensite on tensile properties has been studied. The results showed that specimens with 20–25% epitaxial ferrite have low yield and tensile strengths but have superior ductility compared with specimens which were free of epitaxial ferrite. Studies in the necked region revealed that microvoids density and true fracture strain was higher and the form of fracture was dimple depression type in the presence of epitaxial ferrite. The specimens with no epitaxial ferrite were free from microvoids and less true fracture strain in the necked region and showed completely cleavage type of fracture. Elongation of martensite in the necked region of specimens having epitaxial ferrite showed that martensite deformed plastically before ultimate failure, resulting in ductile fracture.