Mechanical property restoration in embrittled ultra-super ferritic stainless steels through Laves phase redissolution

In this study, the Laves-phase precipitation embrittlement phenomenon in Al-modified ultra-super ferritic stainless steels (USFSSs) was laboratory-simulated. The dissolution kinetics of the Laves phase and the grain-coarsening kinetics during redissolution heat treatment were investigated, along with their effects on mechanical properties and fracture behavior. Laves-phase dissolution followed a modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetics model with an activation energy of 86.8 kJ·mol -1 . Significant grain coarsening occurred during high-temperature reheating, exhibiting an activation energy of 140.0 kJ·mol -1 . Mechanical properties showed temperature-dependent behavior: plasticity improved with increasing temperature up to 1050 °C but deteriorated at 1100 °C. Optimal mechanical properties were achieved after treatment at 1050 °C for 0.5–2 h, comprising an ultimate tensile strength of 550.0–557.5 MPa, a yield strength of 430.6–443.0 MPa, and an elongation of 25.4–30.0%. Fractographic analysis revealed dimpled morphologies in samples where Laves phase had dissolved; coarse Laves-phase particles induced brittleness below 1050 °C, while excessive grain growth reduced plasticity above 1100 °C. The results demonstrate that controlled redissolution treatment can effectively eliminate Laves-phase embrittlement in USFSSs, provided that grain growth is appropriately managed.