Enhancement of Pitting Corrosion Resistance of Austenitic Stainless Steel Through Deposition of Amorphous/Nanocrystalline Oxy-nitrided Phases by Active Screen Plasma Treatment

Abstract

In this research, AISI 304 austenitic stainless steels were efficient treatment using active screen plasma oxy-nitriding technique. The modified layers were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopes, and atomic force microscopy. In addition, the pitting corrosion resistances of untreated and oxy-nitrided samples were analyzed by polarization method in 3.5 wt.% NaCl solution. The results showed that a duplex-layer consisting of a deposition layer and a diffusion layer (including CrN+α phase and nitrogen expanded austenite phase) was generated. Special concern has been given to the formation of an amorphous top layer for the deposition of nano sized oxy-nitrides. It believed that the deposition layer of oxy-nitrides formed on steel surface during active screen plasma oxy-nitriding that lead to improved corrosion resistance of AISI 304 austenitic stainless steel, so that the pitting corrosive attack can be avoided.

Simulation of hollow-cathode-nitriding plasma and design of diffusion equipment with DC and RF dual discharge

“…When ammonia is the only gas used in the nitriding process, the gas pressure can be understood as a function of the number of ammonia molecules. The optimized pressure determined by the model was in the range of 2-3 Torr, which is consistent with the pressure range used in practice [6,[31][32][33]. If the gas pressure is extremely low, there are too few gas molecules in the furnace; consequently, the probability of their collision with electrons is small, and the electron density is low.…”

Stainless steel corrosion in instrumentation pipe

“…Figure 1 shows the most critical points in which the material has suffered corrosion and is important for identifying the type of corrosion presented, in this case pitting. According to Telles (2003) and LI et al (2018), this type of corrosion occurs due to rupture of the passive fi lm and propagation of pitting when in the presence of halogen ions.…”