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

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 degrees C, 500 degrees C, and 550 degrees 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 gamma phase matrix into an expanded austenite (gamma (N)) phase, which is recognized with its high hardness and wear resistance. Furthermore, depending on the nitriding condition, chromium nitride (Cr1-2N) and iron nitride (epsilon -Fe2-3N and gamma ' -Fe4N) phases were detected, which can be detrimental to the corrosion resistance of the 316L austenite stainless steel. The gamma (N) phase was observed in all nitriding conditions, resulting in a significant increase in the surface hardness. However, decomposition of the gamma (N) 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 degrees C (higher than 450 degrees 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.

Automated summary

The ion nitriding behavior of AISI 316L austenite stainless steel was investigated at different nitriding times and temperatures. The study found that a nitriding temperature of 500 degrees C and time of 9 h led to optimal phase composition and hardness distribution for 316L austenite stainless steels, making it suitable for applications requiring a combination of wear and corrosion resistance.