The low-temperature aging embrittlement in a 2205 duplex stainless steel

The effect of isothermal treatment (at temperatures ranging between 400 and 500 °C) on the embrittlement of a 2205 duplex stainless steel (with 45 ferrite–55 austenite, vol.%) has been investigated. The impact toughness and hardness of the aged specimens were measured, while the corresponding fractography was studied. The results show that the steel is susceptible to severe embrittlement when exposed at 475 °C; this aging embrittlement is analogous with that of the ferritic stainless steels, which is ascribed to the degenerated ferrite phase. High-resolution transmission electron microscopy reveals that an isotropic spinodal decomposition occurred during aging at 475 °C in the steel studied; the original δ-ferrite decomposed into a nanometer-scaled modulated structure with a complex interconnected network, which contained an iron-rich BCC phase (α) and a chromium-enriched BCC phase (α′). It is suggested that the locking of dislocations in the modulated structure leads to the severe embrittlement.