Structural Characterization of Ion Nitrided 316L Austenitic Stainless Steel: Influence of Treatment Temperature and Time

• Published in: Metals (Basel ) Vol. 12; no. 2; p. 306
• Main Authors: Gokcekaya, Ozkan, Ergun, Celaletdin, Gulmez, Turgut, Nakano, Takayoshi, Yilmaz, Safak
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 10.02.2022
• Subjects: 316L stainless steel; Austenite; Austenitic stainless steels; Chromium nitride; Corrosion resistance; Corrosive wear; Diffraction patterns; Diffusion; Gamma phase; Ion nitriding; Iron nitride; Microhardness; Microscopy; nitride layer; Nitrogen; Phase composition; Phase distribution; Process parameters; Residual stress; Software; Solid solutions; Stainless steel; Structural analysis; Surface hardness; Thickness; Wear resistance; Japan
• ISSN: 2075-4701; 2075-4701
• DOI: 10.3390/met12020306

The ion nitriding behavior of AISI 316L austenite stainless steel was investigated at different nitriding times (2 h, 4 h, and 9 h) and temperatures (450 °C, 500 °C, and 550 °C). The structural characterization has been assessed by several considerations which can be listed: (i) the evaluation of phase distribution through Rietveld analysis of X-ray diffraction patterns and accompanying peak fitting process, (ii) hardness profile and related nitride layer thickness by microhardness and microscopic measurements, and (iii) displacement measurements to assess the residual stress accumulation. The diffusion of nitrogen atomic species into the sample surface caused a transformation of the γ phase matrix into an expanded austenite (γN) phase, which is recognized with its high hardness and wear resistance. Furthermore, depending on the nitriding condition, chromium nitride (Cr1-2N) and iron nitride (ε-Fe2-3N and γ′-Fe4N) phases were detected, which can be detrimental to the corrosion resistance of the 316L austenite stainless steel. The γN phase was observed in all nitriding conditions, resulting in a significant increase in the surface hardness. However, decomposition of the γN phase with an increase in nitriding temperature eventually altered the surface hardness distribution in the nitriding layer. Considering the phase-type and distribution with the consequent hardness characteristics in the nitride layer, to our best knowledge, this is the first report in which an ion-nitriding temperature of 500 °C (higher than 450 °C) and time of 9 h can be proposed as ideal processing parameters leading to optimal phase composition and hardness distribution for 316L austenite stainless steels particularly for the applications requiring a combination of both wear and corrosion resistance.