Abstract: The influence of hot deformation conditions on static and dynamic recrystallization0 behaviour of 12CrNi3A and 18Ni maraging steels was studied. Using the Zener-Hollomon parameter in the dynamic recrystallization diagram for reference, a new parameter Y(=tZexp (- Qrec /RT)) is recommended and a static recrystallization diagram put forward. The occurrence of static re crystallization of hot deformed austenite in 18Ni maraging, steel was determined as a function of Y parameter (the holding time modified by temperature and strain rate). The microstructural changes during deformation in hot deformed austenite may be described by the dynamic re crystallization diagram (Z-ε diagram.), and that after deformation may be described by the static one (Y-ε diagram).