Investigation of α to γ transformation in the production of a nanostructured high-nitrogen austenitic stainless steel powder via mechanical alloying

In this study, phase transformation of α to γ in a nanostructured high-nitrogen Fe-18Cr-11Mn austenitic stainless steel powder produced by mechanical alloying (MA) was investigated. MA was performed under nitrogen and argon atmospheres using a high-energy planetary ball mill. The obtained results from X-ray diffraction (XRD) and Oxygen/Nitrogen analyser revealed that nitrogen solubility in powders significantly increases by increasing the milling time under nitrogen atmosphere. Nitrogen solubility reaches to 0.65 wt% in samples milled for up to 100 h. The obtained results also indicated that MA in argon (Ar) atmosphere produces a ferrite structure after 120 h of milling. In contrast, a completely austenitic structure was obtained by performing MA for 100 h in nitrogen (N2) atmosphere. Nanostructured powders of below 10 nm grain sizes were obtained by MA under both Ar and N2 atmospheres.