Mechanical properties of austenitic high nitrogen steels at elevated temperatures

Mechanical properties of Cr-Mn and Cr-Ni type austenitic high nitrogen steels (HNSs) were investigated in solution annealed condition by means of tensile tests performed between room temperature and 800 degreesC. Nitrogen contents of the steels were between 0.26 and 1.00 wt.%. The strain rates used in the tensile tests varied between 0.0005 and 0.01 1/s. Fracture surfaces and deformation structures of the tensile test specimens were investigated using SEM and TEM, respectively. Internal friction measurements were used for calculating of activation enthalpy of nitrogen diffusion in austenitic HNSs. Austenitic HNSs have excellent strength and good ductility between room temperature and 400 degreesC, although strength and ductility decrease with increasing temperature. Austenitic HNSs show serrated yielding during tensile tests at small amount of plastic deformation. Activation enthalpy for nitrogen diffusion of about 1.947 eV was determined using internal friction measurements.