Stress corrosion susceptibility of super martensitic stainless steels for oil gas industry: influence of microstructure and Mo additions

摘要

Today, requirements for super martensitic stainless steels in terms of mechanical and corrosion resistance properties increase continuously. To reach better material properties, alloying elements such as Cu or Mo are added and the microstructure is carefully controlled through various heat treatments. The complexity of sulfide stress corrosion mechanisms makes both the results and their interpretation a real challenge that needs to be addressed. In this context, this study focused on laboratory stainless steel heats containing different controlled amounts of Mo. After characterization of stress corrosion resistance on proof rings, slow strain rate traction measurements coupled with electrochemical impedance measurements have been performed in sour medium to highlight corrosion processes occurring at metal surface and hydrogen sulfide effects on mechanical properties. By varying thermal treatments, hydrogen embrittlement has been studied as function of retained austenite and its stability during mechanical testing. Moreover, hydrogen permeation analysis is used to compare hydrogen diffusion in the different heats. Besides the amount of hydrogen in samples after stress corrosion tests has also been determined with hydrogen analyzer based on thermal conductivity measurements.