Microstructure/Mechanical Characterization of Plasma Nitrided Fine-Grain Austenitic Stainless Steels in Low Temperature

• Published in: Nitrogen (Basel, Switzerland) Vol. 2; no. 2; pp. 244 - 258
• Main Authors: Farghali, Abdelrahman, Aizawa, Tatsuhiko, Yoshino, Tomoaki
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.06.2021
• Subjects: Austenitic stainless steels; Bias; biomedical applications; Core wire; Corrosion; Elongation; Evolution; fine-grained austenitic stainless steels; Gas flow; Grain size; hardening; Low temperature; low-temperature plasma nitriding; Mechanical properties; Microstructure; Nitrogen; Plasma; Scanning electron microscopy; Size effects; Stainless steel; Stiffness; strengthening; Supersaturation; Tensile tests; Titanium alloys; Ultimate tensile strength; Wire; Japan
• ISSN: 2504-3129; 2504-3129
• DOI: 10.3390/nitrogen2020016

Fine-grained austenitic stainless steels (FGSS) were plasma nitrided below 700 K to describe their microstructure evolution during the nitrogen supersaturation process and to investigate the post-stressing effect on the microstructure and mechanical properties of nitrided FGSS. Normal- and fine-grained AISI304 plates were nitrided at 623 K and 673 K to investigate the grain size effect on the nitrogen supersaturation process as well as the microstructure evolution during the nitriding process. Fine-grained AISI316 (FGSS316) wires were nitrided at 623 K to demonstrate that their outer surfaces were uniformly nitrided to have the same two-phase, refined microstructure with high nitrogen solute content. This nitrided FGSS316 wire had a core structure where the original FGSS316 core matrix was bound by the nitrided FGSS316 layer. The nitrided wire had higher stiffness, ultimate strength, and elongation in the uniaxial tensile testing than its un-nitrided wires. The core microstructure was refined and homogenized by this applied loading together with an increase of nitrided layer hardness.