Fracture behavior of a tempered dual phase steel

The influence of tempering on the fracture of a dual phase steel was studied. The martensite in the as-quenched dual phase steel began to deform only after the steel had attained the maximum uniform strain, while the martensite in the tempered steel started contributing to deformation from the very beginning. The fracture process in the as-quenched dual phase structure began at a much lower strain compared to that in quenched and tempered steels by nucleation of microvoids at ferrite/martensite interfaces, followed by their growth and coalescence. This was due to the difference in hardness of the tempered and untempered martensite.