Improvement of hardness in Ti-stabilized austenitic stainless steel

The high passivation capacity of austenitic stainless steel results in their excellent corrosion resistance. There are many ways to improve the hardness of austenitic stainless steel such as cold rolling or grain refinement. Herein, we explore the possibility of improving the hardness of AISI316-Ti stainless steel by generating an amorphous-nanocrystalline microstructure. First, we have utilized our modified melt-spinning technique to fabricate AISI316-Ti stainless steel microfibers with a fully amorphous structure. Formation of a fully amorphous structure was confirmed by using X-ray diffraction (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). Thermal analysis revealed a glass transition temperature of 437 degrees C followed by a crystallization peak of 573 degrees C. Nanoindentation analysis showed a fourfold increase of hardness from the initial value of approximate to 2.5 +/- 0.1 GPa the starting AISI316-Ti stainless steel rod to the hardness of approximate to 8.2 +/- 0.5 GPa for the amorphous AISI316-Ti structure. Further step-size heat treatment on melt-spun (amorphous) stainless steel microfibers generated a microstructure compromising adjacent nanocrystalline and amorphous grains as observed by TEM. Nanoindentation analysis of those fibers has shown an even greater increase in hardness, reaching an average value of approximate to 14.2 +/- 1.0 GPa. We believe that both the confinement of dislocation movement in the nanocrystalline grains as well as the absence of dislocations in the amorphous grains contribute to this tremendous increase of hardness in stainless steel. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The hardness of AISI316-Ti stainless steel has been improved by generating an amorphous-nanocrystalline microstructure. The fully amorphous structure was obtained using a modified melt-spinning technique, and the hardness was characterized using thermal analysis and nanoindentation analysis.