LOW TEMPERATURE DEFORMATION BEHAVIOR OF HIGH-NITROGEN NICKEL-FREE AUSTENITIC STAINLESS STEELS

The low-temperature deformation behaviors of two high-nitrogen nickel-free austenitic stainless steels (HNSs) with different N content were investigated by impact test, tensile test, XRD and TEM. The results indicate that HNS shows apparent ductile-to-brittle transformation (DBT) and work-hardening at low temperature. In the range of the experimental steels' Mn content, the increase of Mn. content improved the plasticity and the toughness at low temperature, and decreased the DBT temperature of HNS. Deformation-induced martensite transformation occurs in steel 18Cr-12Mn-0.55N during tensile deformation at low temperature, but the content of martensite is low and the decrease of temperature has no obvious effect on its formation. Deformation-induced martensite enhances the work-hardening ability but decreases the plasticity and toughness of FINS at low temperature. The decreases of work-hardening ability and stacking fault energy with temperature decreasing are the main reasons for brittle fracture of Fe-Cr-Mn HNS at low temperature.