The intermetallic phase precipitation, mainly sigma (σ) and chi (χ) phases, was studied in a comparative manner in two stainless duplex steels: a duplex type UNS S31803 and a superduplex type UNS S32520. The χ-phase precipitated at ferrite/ferrite grain boundaries prior to the σ-phase precipitation, which occurred preferentially at ferrite/austenite interfaces and at ferrite/ferrite grain boundaries. The χ-phase precipitation is a eutectoid type reaction of ferrite, leading to σ-phase and austenite (γ). The χ-phase precipitated at lower temperatures and in smaller amounts than sigma. The χ-phase is metastable in the studied steels and was consumed during the σ-phase precipitation. © (2010) Trans Tech Publications.