A lecture given by Shinji Munetoh, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. Uses molecular dynamics simulations to study the role of voids in determining the ductile fracture energy. Molecular dynamics (MD) simulations of the ductile fracture behaviour on the austenite and ferrite phases in steel were performed by using the MD cells including the voids due to the precipitates. The number of Fe atoms were around 30,000. Atomic movements were determined by solving Langevin equations with Finnis-Sinclair interatomic force. The tensile test was simulated by expanding the MD cell in one direction at?room temperature. In the case of the perfect crystalline MD cell, the shear fracture was observed in the austenite phase, and the ferrite phase caused the cup and cone fracture. In the case of the MD cell including the voids, the cup and cone fracture?were observed on both austenite and ferrite phases. The ductile fracture energy of austenite phase was the same level to that of?ferrite phase in the perfect crystalline MD cells.