<p>This research investigates the hot corrosion behavior of as-cast and heat-treated Haynes 25 samples (solution-annealed, single-step age-hardened, and double-step age-hardened) at 900&#xa0;°C under simulated turbine conditions. The samples were exposed to a molten salt mixture of 75% Na₂SO₄ and 25% NaCl for a prolonged period of 500&#xa0;h. The hot-corroded samples were examined using Field Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier-Transform Infrared Spectroscopy (FTIR) and Energy-Dispersive X-ray Spectroscopy (EDX) to assess microstructural changes, elemental distribution and corrosion mechanisms. This work introduces double-step aging as a novel approach to enhance the hot corrosion resistance of Haynes 25 by forming dense Cr₂O₃ and CoCr₂O₄ protective layers. The findings reveal that aged samples exhibited significantly improved corrosion resistance, with weight gain stabilizing after 300&#xa0;h, while as-cast and solution-annealed samples showed continuous weight gain up to 500&#xa0;h due to forming a non-protective Co₃O₄ oxide layer. The double-step aged sample, in particular, developed dense and continuous Cr₂O₃ and CoCr₂O₄ spinel oxide layers, leading to reduced corrosion penetration depths of 41 ± 0.13&#xa0;μm, compared to 61 ± 0.24&#xa0;μm in the as-cast sample. Moreover, finer grain structures (86 ± 0.17&#xa0;μm) in the double-step aged sample further improved corrosion resistance, whereas coarser grains (131 ± 1.58&#xa0;μm) in the solution-annealed sample decreased their resistance. This study underscores the importance of chromium in forming protective oxide layers. It demonstrates the effectiveness of optimized heat treatment in enhancing the corrosion resistance and longevity of Haynes 25 superalloy in high-temperature environments. These insights are vital for improving the alloy’s performance in aerospace and energy applications, where high-temperature corrosion is a critical concern.</p>