Fracture is a critical factor for structural materials, which has been extensively investigated. For metallic materials with a body-centered cubic (bcc) crystal structure, brittle fracture is typically observed when the testing temperature is below the ductile to brittle transition temperature. However, a significant amount of plastic deformation has been observed in tensile tests of different bainitic and martensitic steels at –196 °C in this study, which is far below the ductile to brittle transition temperature of these materials. Both enormous ductility and high toughness have been reported in several nanostructured metals and ultra-fine grained steels with a bcc structure at cryogenic temperatures. The cryogenic fracture properties of the investigated commercial bainitic and martensitic steels are very distinguished from the ultra-fine grained steels, since only the tensile ductility is significantly improved with decreasing temperature and brittle fracture still occurs in the toughness tests. To understand the observed fracture phenomena in these bainitic and martensitic steels, a comprehensive experimental program is carried out to investigate the fracture properties covering a broad range of stress states. Tensile tests have been performed at different temperatures using flat specimens with various geometries, including shear, central hole, notched dog bone, side grooved plane strain. The fracture surface and through-thickness cross-section have been analyzed for several fractured specimens tested under different loading conditions. It is observed that the underlying failure mechanisms change with local stress states. In addition, finite element simulations of corresponding experiments have been performed to extract the local critical stress and strain variables. Based on the experimental and numerical results, a unified fracture criterion is applied to explain the observed diverse fracture properties and failure mechanisms of the investigated bainitic and martensitic steels.