Evolution of structure in austenitic steel powders during ball milling and subsequent sintering

The aim of this work was to obtain bulk nanocrystalline austenitic steel by ball milling of steel powders and their compaction. For powder compaction pulse plasma sintering method was used. Ball milling of 316L austenitic steel powders in a planetary Fritsch P5 mill resulted in the two-phase structure consisting of austenite and martensite. Both phases exhibited crystallite size in the range 10–20 nm. The maximum content of martensite reached 66% and was observed after short processing time. The decrease of its contribution was observed after prolonged milling and was explained by stabilization of nanocrystalline austenite and residual stresses. Pulse current sintering technique allowed obtaining fully dense samples exhibiting austenitic structure characterized by grain size in the range 150–300 nm and microhardness 400 HV0.3.