Improvement of corrosion resistance of austenitic stainless steels by means of glow-discharge nitriding

Abstract

Austenitic stainless steels are employed in many industrial fi elds due to their very good resistance to general corrosion in several environments. However, their use is limited due to the fact that they suffer localised corrosion in specifi c environments, particularly in chloride-ion rich solutions. Low temperature nitriding treatments can improve both corrosion resistance in chloride-ion containing media and surface hardness, due to the formation of a metastable phase known as expanded austenite or S phase; this phase can be outlined as a supersaturated interstitial solid solution of nitrogen in the expanded and distorted γ -Fe f.c.c. lattice. We review the main experimental results obtained in our research on low temperature glow-discharge nitriding of austenitic stainless steels. By means of proper treatment parameters, low temperature glowdischarge nitriding is able to markedly improve the corrosion resistance of austenitic stainless steels, such as AISI 316L and AISI 202 in chloride-ion rich solutions in comparison with the untreated alloys.

In vitro response of human peripheral blood mononuclear cells to AISI 316L austenitic stainless steel subjected to nitriding and collagen coating treatments

“…Low temperature nitriding is particularly useful for increasing the corrosion resistance of austenitic stainless steels in chloride-ion containing solutions [6][7][8][9]13]. This treatment produces a modified surface layer, which consists mainly of S phase.…”

“…The formation of this phase affects also surface morphology and roughness of the nitrided samples. In fact, the peculiar surface morphology of low temperature glow-discharge nitrided samples is produced not only by plasma etching during sputtering and nitriding, but also by local plastic deformations, due to the high internal stresses caused by nitrogen solubilisation [6,13,25]. The high internal stresses may promote also the formation of nitrogen induced h.c.p.…”

“…Therefore, it would be necessary to modify the surface of the metallic implants, in order to obtain a better resistance to corrosion and a better biocompatibility. Among the surface treatment techniques, surface alloying with nitrogen by means of low temperature nitriding improves corrosion resistance of austenitic stainless steels in chloride-ion containing solutions, as body fluids are [6][7][8]. When treatment temperatures lower than 450°C are used, nitrogen is retained in a supersaturated solid solution, known as expanded austenite or S phase [9], and the precipitation of chromium nitrides, which usually decreases corrosion resistance, is avoided.…”

From Micro to Nano Scales -Recent Progress in the Characterization of Nitrided Austenitic Stainless Steels

“…Nitrogen alloyed austenitic stainless steels were reported to show increased strength and fatigue lifetime [6,17]. It also improves the corrosion resistance regarding localised pitting, crevice corrosion, inter granular corrosion, and the stress corrosion cracking failure [6,[18][19][20][21][22][23]. These advantages are especially promising if the low hardness and or the weak corrosion resistance of austenitic steels are concerned, e.g.…”

A comparative study of the corrosion performance of titanium (Ti), titanium nitride (TiN), titanium dioxide (TiO2) and nitrogen-doped titanium oxides (N–TiO2), as coatings for biomedical applications

“…The formation of a nitrogen supersaturated solid solution phase without CrN precipitations should maintain the good corrosion resistance of SS [29].…”