They present higher corrosion resistance when compared to ferritic stainless steels, promoted by high content of chromium, nitrogen and molybdenum, and, due to the presence of austenite, the DSS present good ductility and toughness (250 J impact toughness) ( Young et al. KEYWORDS: Duplex stainless steels, Ferrite quantification, Ferritoscope, Quantitative metallography, X-ray diffraction, ThermoCalcВ®.Дuplex stainless steels (DSS) are characterized ideally by equal amounts of ferrite and austenite, which provides increased mechanical resistance (680 to 880 MPa ultimate tensile strength) due to the fine grain size, typical of these steels ( Sedriks 1996 Souza et al. Values obtained by quantitative metallography look more assertive as it is a direct measurement method but the ferritoscope technique should be considered mainly for in loco measurement. For all solution treatment temperatures, the ferrite volume fractions obtained by XRD measurements were higher than those achieved by the other two techniques and ThermoCalcВ® simulation, probably due to texturing effect of previous rolling process. The microstructure presents preferred grains orientation along the rolling directions even for a sample solution treated for 30 min at 1,200 вЊ.

As expected, the microstructure is composed only by austenite and ferrite phases, and ferrite content increases as the solution treatment temperature increases. In order to quantify ferrite content, three techniques, XRD, ferritoscope and optical metallography, were applied to a duplex stainless steel UNS S31803 solution-treated for 30 min at 1,000, 1,100 and 1,200 вЊ, and then compared to equilibrium of phases predicted by ThermoCalcВ® simulation.

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