Sulfide Stress Corrosion study of a super martensitic stainless steel: role of H_2S on metallic sulfur formation and hydrogen embrittlement

摘要

Due to their good corrosion resistance as well as a wide range of mechanical properties, super martensitic stainless steels are generally used in the petrochemical industry. In this context, the super martensitic stainless steel EN 1.4418 (15% Cr, 5% Ni 1%Mo), which exhibits good corrosion and mechanical properties in sour environment, could be an alternative grade to replace EN 1.4542, which presented some stress corrosion cracking problems in service. In this work, corrosion resistance and stress corrosion cracking of 1.4418 have been followed by electrochemical and physical techniques to understand the failure mechanism at low pH. This study focused on laboratory stainless steel heats containing different controlled amounts of Cr, Ni, Mo and various thermal treatments have been performed in order to define carefully the contents of martensite, ferrite and residual austenite. The corrosion mechanisms will be discussed in terms of pitting corrosion potentials, sulfide stress cracking and repassivation processes. Moreover, the effect of H_2S on 1.4418 corrosion properties has been correlated to the formation of metallic sulfur, which promotes hydrogen embrittlement. In order to determine the role of this metallic sulfur in the corrosion mechanism, XPS and hydrogen permeation measurements have been realized.