Phases Quantification in Duplex Stainless Steels Weldments

Abstract

Duplex Stainless Steels (DSS) are very attractive steels and their application is presently of increasing interest, especially as structural materials in aggressive environments. DSS are austeno-ferritic biphasic steels, having an austenite-to-ferrite phase ratio of about one, giving the best combination of mechanical and corrosion-resistance properties. However, these steels must be handled with extreme care, especially if thermal cycles are involved, owing to the formation of dangerous secondary compounds that highly worsen their excellent properties.The production of big pipes requires manufacturing welding operations on steel plates or sheets and the final products must satisfy specific requirements in terms of material properties. DSS approximately contain equal volume fraction of the phases that, in practice, cover a slightly wider range within 40/60 and 60/40. Therefore, since DSS properties depend on phase ratio, ferrite quantification on an industrial scale represents a topic of great interest, which must be as reliable as possible and, at the same time, quickly executable.The present paper gives a comparison of different methods currently employed for ferrite determination in DSS weldments, in order to understand the limits derived from the specific employed technique.