AES study of passive films formed on a type 316 austenitic stainless-steels in a stress field

Abstract

The type AISI 316 stainless steel, in addition to the principal alloying elements chromium and nickel, contains 2.5–3.5% of molybdenum. This element is added to improve the mechanical properties and the pitting resistance of austenitic alloys. Concerning the Stress Corrosion Cracking (SCC) resistance of austenitic stainless steels, molybdenum additions to alloys have a variable effect: the effect is detrimental for small additions of Mo, and it is beneficial for the alloy containing more than 4% Mo. Thus the Mo concentration on passive film plays an important role on the SCC resistance of steels. On the other hand, in a previous investigation, it was shown that the composition of passive films formed on the stressed 302 alloy depended on the compressive or tensile nature of stresses. Consequently, the aim of the present work is to study the composition of passive films formed on 316 steel and the migration of molybdenum in a stress field. Thus, Auger electron spectroscopy spectra were recorded to determine the chemical composition of the passive films formed on both sides of the type AISI 316 stainless steel U-bend samples. The results obtained show that the behaviour of chromium and oxygen in passive films formed on 316 steel in the stress field was nearly similar to that formed on 302 steel. Concerning the molybdenum diffusion outwards the passive film formed on the 316 steel was reduced by either the tensile or compressive stress field.