Influence of small amount and different morphology of secondary phases on impact toughness of UNS S32205 Duplex Stainless

Duplex Stainless Steels (DSSs) are biphasic austenite-ferrite stainless steels, with higher mechanical properties and corrosion resistance than the other stainless steels grades. Impact toughness is a very important mechanical property and even though DSSs have a lower impact toughness as compared to the austenitic grades, the transition to ductile to brittle behavior is more gradual and it occurs at lower temperature than ferritic grades. On the other hand, DSSs suffer from embrittlement due to secondary phase precipitation, which affects all mechanical and corrosion properties, in particular impact toughness, even in low amount. In this research paper, the influence of a small amount (< 2%) and different morphologies of secondary phases (coarse and finely dispersed) on the ductile to brittle transition of standard Duplex Stainless Steel UNS S32205 was studied. Two isothermal heat treatments were conducted on the solubilized DSS in order to precipitate the same amount but different morphologies of secondary phases. Charpy tests were conducted on a temperature range between 20 degrees C and - 196 degrees C. The wrought material retained a very good impact toughness even at - 90 degrees C (100 J), but a small volume fraction of secondary phases affected the impact toughness even at room temperature. Coarser secondary phases affect the impact toughness largely as compared to small and finely dispersed particles.