Plasma Nitriding of ISO 5832-1 Stainless Steel at 425 ºC with Intermittent Nitrogen Flow

Abstract

The aim of this work was to study the influence of varying nitrogen potential during plasma nitriding of stainless steel ISO 5832-1. The control of nitrogen potential was achieved by pulsing the nitrogen flow for different times (01/19, 02/18, and 05/15), where the numbers represent the time (in minutes) of nitrogen flow on/off, thus creating an intermittent flow of nitrogen during the treatment. For all tested conditions-continuous and pulsed flow of nitrogen-the treatment temperature was kept at 425ºC during 2 and 8 hours. Specimens were characterized by means of X-ray diffraction, scanning electron microscopy, optical microscopy, energy-dispersive X-ray spectroscopy, and nanohardness. Results showed that the layer thickness increases with the increase of total treatment time, and decreased for shorter times of pulsed nitrogen flow. Smaller expansion of the austenite phase, as well as less precipitation of chromium nitrides, were also observed for shorter times of pulsed nitrogen flow. Hence, the use of intermittent nitrogen flow appears to be an efficient approach in order to control the nitrogen concentration within the layer, reducing its brittleness.

Mechanical Preparation Procedure for Characterizing by EBSD the Crystallographic Orientation in Surface Layers of Austenitic Stainless Steels Plasma Nitrided

“…Hardness reported elsewhere for the expanded austenite phase, obtained by diverse plasma nitriding processes of conventional ASSs, typically ranges between 7 and 16 GPa 21,22,[31][32][33][34] .…”

“…Plasma nitriding of ASSs is a thermochemical process that aims at improving anti-scratch and anti-wear properties of conventional ASSs. When carried out at temperatures lower than around 400 °C (673 K), plasma nitriding of ASSs allows one to obtain materials with an overall high toughness, and high hardness at the surface region, without meaningful deterioration of the corrosion resistance 17,[20][21][22] .…”