Abstract
Duplex and superduplex stainless steels have high strength and high corrosion resistance with a crescent demand in chemical and petrochemical industries. The best mechanical properties of this family of steels are obtained with approximately equal parts of ferrite and austenite. Grain refinement increases the toughness and resistance to environmentally assisted cracking. The precipitation of tertiary phases, such as σ, χ and secondary austenite, decreases the mechanical and corrosion resistance properties. The σ phase is the most dangerous of these deleterious phases and the one that precipitates in higher amounts. The majority of research works on deleterious phases in duplex and superduplex steels evaluate the kinetics of precipitation in specimens isothermally treated. In the present work, the precipitation of deleterious phases during continuous cooling from 1100°C was evaluated by optical and scanning electron microcopies, hardness measurements and electrochemical corrosion tests. Two superduplex stainless steel steels UNS S32750 with similar composition but quite different grain sizes were analysed in order to evaluate the influence of this microstructural feature.
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