Understand the Thermal Aging Effect on Mechanical Response of a Duplex Stainless Steel by In Situ Synchrotron Wide-Angle X-Ray Scattering

Duplex stainless steels (DSSs) are widely used in the energy and chemical industries due to their favorable combination of mechanical strength and corrosion resistance. However, long-term thermal aging can degrade their performance by inducing microstructural changes, particularly in the ferrite phase. In this study, the deformation behavior of DSSs thermally aged at 475 °C for 400, 1000, and 3000 hours was investigated using in situ synchrotron Wide-Angle X-ray Scattering (WAXS) tensile testing, with calculated dislocation densities validated by post-mortem Transmission Electron Microscopy (TEM) analysis. Macroscopic tensile results show that thermal aging increases the ultimate tensile strength (UTS) and reduces ductility, with the UTS plateauing after 1000 hours. Phase-specific analysis reveals that austenite maintains a stable mechanical response with minimal change in lattice strain and yield strength (~194 MPa), while ferrite exhibits pronounced aging effects, including increased lattice strain, progressive hardening up to ~ 1837 MPa, and enhanced dislocation multiplication. Load partitioning becomes increasingly asymmetric with aging, shifting more stress to ferrite and intensifying interfacial constraints. And microstructural characterization further shows that long-term aging promotes pore formation at austenite–ferrite boundaries, contributing to earlier fracture and reduced ductility. Together, the in situ WAXS and TEM results provide a mechanistic understanding of how thermal aging selectively alters the ferrite response, driving embrittlement in DSSs.