Mechanical properties of austenitic high-nitrogen Cr-Ni and Cr-Mn steels at low temperatures

Mechanical properties of solution annealed austenitic 19Cr-8Ni-(0.26-0.5N), 22Cr-12Mn-1.0N and 19Cr-15Mn-0.8N steels were investigated by means of tensile and Charpy-V impact toughness tests between room temperature and 77 K. Solution annealing temperature was selected in order to prevent Cr₂N formation. Fracture surfaces were investigated using SEM (scanning electron microscope). Austenite stability against α′-martensite formation during cooling or deformation in tensile and Charpy-V tests was determined using magnetic measurements. Austenitic high-nitrogen Cr-Ni and Cr-Mn steels exhibited excellent strength, ductility and toughness at room temperature. At 77 K, yield strength was increased, but ductility and toughness were decreased markedly, and ductile-to-brittle behaviour associated with brittle transgranular and intergranular fracture was observed. Results are compared with AISI 304N steel (0.16wt% N) which retained excellent ductility and impact toughness at 77 K.