High-pressure torsion of metastable austenitic stainless steel at moderate temperatures

Abstract

We subjected samples of a 304 metastable austenitic stainless steel to high-pressure torsion (HPT) in the temperature range of 303–573 K, (i.e. at different austenite stabilities), to examine their microstructures and mechanical properties. HPT processing at room temperature led to the formation of a lamellar microstructure with austenitic and martensitic phases, of which sizes were characterised by prior austenite grains, whereas HPT processing at moderate temperatures produced nanostructured austenite grains through mechanical twinning. The nanostructured 304 steel with an average grain size of ~70 nm exhibited a fine balance between tensile strength (~1.7 GPa) and reduction of area (~55%).

Keywords:

• high-pressure torsion
• martensitic transformations
• twinning
• nanostructured materials
• austenite
• mechanical characterisation

Acknowledgements

The authors thank Mr N. Horita and Mr T. Ideguchi (Kumamoto University) for their assistance with the experiment.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported in part by a Grant-in-Aid for Scientific Research (C) 25420758 from the Japan Society for the Promotion of Science (JSPS) and by Grant-in-Aids for Scientific Research (S) (No. 26220909) and on the Innovative Area ‘Bulk Nanostructured Metals’ (No. 22102004) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. This study used facilities of severe plastic deformation in the International Research Centre on Giant Straining for Advanced Materials (IRC-GSAM) at Kyushu University.