Effects of low temperature aging on the mechanical properties and corrosion resistance of duplex and lean duplex stainless steels UNS S32205 and UNS S32304

Abstract

Duplex stainless steels (DSS) with austenite-ferrite microstructure are high strength and corrosion resistant steels frequently used as pipes and accessories in chemical/petrochemical on/and off-shore industries. Low temperature heat treatments (400-475ºC) may increase the hardness and wear resistance of duplex steels, due to a spinodal decomposition reaction of the ferrite, whose small particles α' precipitate in the matrix. In this work, several heat treatments at 400ºC and 475ºC with short duration (<24h) were performed on UNS S32304 and UNS S32205 grades. The kinetics of a' precipitation was studied by hardness measurements. Tensile tests were also carried out for some heat treatment conditions to evaluate the effect of the aging on the ductility of both grades. The hardening of duplex UNS S32205 was more intense than that of UNS S32304, although both steels have shown an interesting increase in tensile strength. Specimens of duplex steel heat treated at 475ºC for 4 h and 8 did not show any detectable decrease of corrosion resistance in anodic polarization and critical pitting temperature tests were carried out in NaCl media.