Low strain rate deformation behavior of a Cr–Mn austenitic steel at −80 °C Original Research Article

The deformation behavior of a Cr–Mn austenitic steel during interrupted low strain rate uniaxial tensile testing at −80 °C has been studied using X-ray diffraction (XRD), electron backscatter diffraction and transmission electron microscopy. Continuous γ → ε → α′ martensite transformation was observed until failure. High dislocation densities were estimated in the austenite phase (∼1015 m−2), and for the α′-martensite they were even an order of magnitude higher. Dislocation character analysis indicated that increasing deformation gradually changed the dislocation character in the austenite phase to edge type, whereas the dislocations in α′-martensite were predominantly screw type. XRD analyses also revealed significant densities of stacking faults and twins in austenite, which were also seen by transmission electron microscopy. At low strains, the deformation mode in austenite was found to be dislocation glide, with an increasing contribution from twinning, as evidenced by an increasing incidence of ∑3 boundaries at high strains. The deformation mode in α′-martensite was dominated by dislocation slip.