Abstract
Nickel-free high-nitrogen austenitic stainless steels (HNSS) are increasingly considered for biomedical applications owing to their excellent biocompatibility, corrosion resistance, and favourable mechanical properties. Their mechanical behaviour is strongly influenced by interstitial alloying, which can enhance both strength and work-hardening capability. However, the deformation mechanisms governing work hardening in HNSS, particularly at high nitrogen contents, remain insufficiently understood. Here, we investigate the effect of nitrogen on the mechanical response and associated deformation mechanisms of a nickel-free austenitic stainless steel containing 1 wt.% nitrogen. Tensile tests revealed a combination of high strength, sustained work hardening, and good ductility, with further strengthening achievable through cold rolling. The annealed material exhibited a distinct constant strain-hardening regime during the early stages of deformation. Using electron backscatter diffraction and in situ tensile testing, planar dislocation slip, evidenced by slip traces, was identified as the predominant deformation mechanism, with no detectable strain-induced martensitic transformation or mechanical twinning in this regime. Mechanical twinning was observed only at higher strains (>15%) and appears to make a secondary, limited contribution to the overall deformation. Despite the relatively high calculated stacking-fault energy, the mechanical and microstructural observations are consistent with strongly restricted cross-slip and localized dislocation glide. These findings suggest that chemical short-range order may play an important role in governing the distinctive plasticity and sustained work-hardening behaviour of Ni-free HNSS.