Nitrogen Surface Enrichment of Austenitic Stainless Steel ISO 5832-1: SHTPN vs Low-temperature Plasma Nitriding

Specimens of ISO 5832-1stainless steel were submitted to low temperature plasma nitriding treatment and Solution Heat Treatment after Plasma Nitriding (SHTPN) process aiming to obtain a S-phase, chromium precipitates-free, surface layer. The following techniques were used for analysis: scanning electron microscopy (SEM), optical microscopy (OM), microhardness, X-ray diffraction (XRD) and wavelength dispersive spectroscopy (WDS) microanalysis. Corrosion resistance was evaluated by means of potentiodynamic anodic polarization and open-circuit measurements of corrosion potential. Results indicated that the S-phase layer with N concentrations of about 0.9 wt% and 2 µm thick was formed during low temperature plasma nitriding, while layers with concentratios of about 0.45 wt% of N and up to 200 µm thick resulted from the SHTPN process. Results proved the increase in localized corrosion resistance caused by nitrogen in solid solution for both processes, as well as the deleterious effect caused by the precipitation of chromium nitride.

SHTPN; plasma nitriding; ISO 5832-1; corrosion behaviour