Salt spray test on AISI 316L stainless steel

Abstract

Damage produced by rigorous working conditions can affect materials, especially when they are exposed to high temperatures, corrosive atmospheres and mechanical stresses. Austenitic stainless steels have variable chromium contents but greater than 16%, which allows the surface formation of a passivating thin layer of chromium oxide (Cr2O3) that protects the steel against corrosion during prolonged exposure to aggressive environments. From a metallurgical point of view, these steels meet the requirements to operate under prolonged exposures to high temperature and aggressive environments (depending on the steel grade), however attention must be paid to the precipitation of different carbides, such as M23C6 and M6C, and especially sigma () phase formation, since its precipitation produced chromium depleting zones which are very harmful in many applications, because it makes the material brittle and allows high corrosion penetration. Another consequence is sensitize hydrogen capture originated during corrosion. The aim of this work is to evaluate the corrosive behavior of an austenitic stainless steel (AISI 316L) that was first exposed to several heat treatments conditions and then was subjected to a spray saline solution of 5% NaCl, inside the chamber the temperature was set in 35ºC while the saturated air temperature was 47ºC. Characterization techniques such as optical and scanning electron microscopy were applied. Results allowed to establish the incidence on the corrosion rate of formed chromium carbides, that sensitize steel to the attack of chloride ions responsible of pitting corrosion by breaking of the passive layer thus helping a rapid corrosion rate.