The present work is aimed at determining the properties of 3.5Ni steels simulated to a condition in which they would be used for the manufacture of large turbine rotors. Samples were subjected to heat treatment schedules, particularly cooling rates, that would be experienced during manufacture. With increasing size, the cooling rate from the austenitizing temperature is reduced, leading to the formation of bainite with a coarse distribution of carbides. Since brittle fracture from the center of large forgings must be avoided, special emphasis has been placed on the fracture toughness and fracture mode and the way in which both are determined through the microstructure, particularly the carbide form and distribution.