On the divergent effects of stress on the self-organizing nanostructure due to spinodal decomposition in duplex stainless steel

Duplex stainless steels suffer from serious embrittlement due to the self-organization of the nanostructure caused by phase separation (PS) in ferrite. As duplex stainless steel (DSS) components are often subjected to stress during service, the effect of elastic tensile stress (ETS) on phase separation (PS) in alloy 2507 has been investigated in this study. The alloy was aged at 400 and 450 °C for different times under an applied ETS. The nanostructure evolution and mechanical properties were analyzed using small-angle neutron scattering and analytical transmission electron microscopy as well as Vickers-hardness and nanoindentation measurements. The results show that the applied ETS can suppress spinodal decomposition (SD) in ferrite in DSS 2507, which may be due to that ETS increases the critical compositional fluctuation wavelength for SD and thus increases the diffusion distance and barrier to the occurrence of SD. The suppressive effect is more obvious at longer aging time for the same level of applied stresses. It is also indicated that the suppressive effect of ETS seems to change non-monotonically with stress levels and the medium stress level is likely to have the largest suppressive effect. The suppressive effect of ETS on PS may significantly delay the embrittlement and extend the service longevity of DSS components within the miscibility gap. These results further the understanding of the effect of ETS on PS and elastic stress should be considered in the configurations of computational simulations of PS and evaluation of the service longevity of DSS components.