Abstract
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.
Highlights
Due to their excellent corrosion resistance, austenitic stainless steels are widely used in many industrial applications [1]
XRD patterns of the nitride layers on AISI 316L samples obtained at different nitriding temperatures and times are given in Figure 1. γ, γN, γ, α, ε, CrN, and/or Cr2N are the major and minor phases detected in all patterns
The presence of the γN phase formed by the diffused nitrogen into the γ phase is crucial as it plays a critical role to obtain a combination of high hardness and good corrosion properties [17]
Summary
Due to their excellent corrosion resistance, austenitic stainless steels are widely used in many industrial applications [1]. Their surfaces can suffer from wear damages if they articulate on a counterpart surface, such as in dental implants, bone/joint replacements, etc. An increase in their surface hardness and corresponding wear resistance without losing their corrosion resistance could significantly broaden their utilization in several different applications [3]. [4,5], or diffusion processes, such as carburizing, nitriding, etc. Nitriding is a well-established thermochemical process to increase the surface hardness of the steels, their wear and corrosion resistance. Ion nitriding is recognized as a cost-effective and fast nitrogen diffusion process even at lower treatment temperatures and shorter times [7]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call