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Duplex stainless steels (DSS), with a microstructure of an approximately equal mixture of ferrite (a) and austenite (c) phases, are susceptible to the formation of undesirable phases if manufacturing processes are not carefully controlled. In particular, sigma phase (r) is a Cr-and Mo-rich intermetallic phase, formed generally when DSS are by the temperature range from 600 to 900°C, even for very short time periods. The precipitation of this phase induces detrimental effects in mechanical and corrosion resistance properties in the material, and even a low volume percentage of r phase can significantly affect these properties. The current paper presents the effect of thermal treatments on UNS S32760 superduplex stainless steel seamless tubes, applied in order to promote the precipitation of different r phase percentages in a ferrite/ austenite microstructure. The detection and quantification of the r phase using non-destructive ultrasounds testing has been one of the most relevant events of this study that contributes to improving the correlation of the results obtained using destructive and non-destructive techniques for the quantification of undesirable phases in superduplex seamless tubes during the manufacturing process.

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