Controlling the initial nanostructure by an innovative heat treatment to mitigate low temperature embrittlement of super duplex stainless steel 2507

An innovative heat treatment process at temperatures between 750 and 900 °C, i.e. above the upper limit of the miscibility gap (MG), is found to slow down the subsequent phase separation occurring in the bcc phase when a super duplex stainless steel (DSS) 2507 is further treated within the MG. This delayed phase separation postpones low temperature embrittlement of the DSS and provides unprecedented life time. The innovative heat treatment can be applied to other DSSs, and thus it could provide means to prolong the service life of DSS in general. The underlying mechanism of the delayed phase separation can be sought in the initial nanostructure, studied here through atom proble tomography and scanning transmission electron microscopy. The results lead us to suggest that the change in short-range order and solute interstitial elements are responsible for the reduced phase separation kinetic imposed by the innovative heat treatment.