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 77K. Solution annealing temperature was selected in order to prevent Cr2N formation. Fracture surfaces were investigated using SEM (scanning electron microscope). Austenite stability against alpha'-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 tough ness were decreased markedly, and ductile-to-brittle behaviour associated with brittle transgranular and intergranular fracture was observed. Results are compared with AISI 3O4N steel (0.16wt% N) which retained excellent ductility and impact toughness at 77 K.