Comparative analysis on phase quantification methods in duplex stainless steels weldments

Duplex Stainless Steels (DSS) are biphasic steels of increasing interest, employment as structural materials in aggressive environments. In these steels, the austenite-to-ferrite phase ratio is maintained at about one-even if a slightly wider range between 40/60 and 60/40 is in any case accepted-giving the best combination of mechanical and corrosion-resistance properties. However, DSS must be handled with extreme care, especially if thermal cycles are involved, owing to the possible formation of dangerous secondary compounds that can highly worsen their excellent features. In industry, the production of big pipes requires manufacturing welding operations on steel plates or sheets and the end products must satisfy specific requirements. Therefore, since DSS properties depend on phase ratio, ferrite quantification at an industrial scale represents a topic of great interest, which must be as reliable as possible and, at the same time, of fast execution. In the present paper, different methods currently employed for ferrite estimation in DSS weldments are compared, in order to understand the limits deriving from each technique.