The present investigation on a designed high strength Fe-0.25C-1.48Mn-1.20Si-1.51Ni-0.05Nb （wt%） steel treated by a novel quenching-partitioning-tempering （Q-P-T） process was focused on deformation temperature dependence of mechanical properties and microstructures. The results indicate that the Q-P-T steel deformed at various deformation temperatures from -70 to 300 ℃ exhibits superior mechanical properties due to excellent thermal stability of retained austenite. The microstructural characterization by transmission electron microscopy （TEM） reveals that the high strength of the Q-P-T steel results from dislocation-type martensite laths and fcc NbC carbides or/and hcp ε-carbides precipitated dispersively in martensite matrix, while excellent ductility is attributed to the significant transformation induced plasticity （TRIP） effect produced by considerable amount of retained austenite. The relationship between mechanical properties and microstructures at different deformation temperatures was clarified.
