<p>This study investigates the influence of deformation-induced microstructures on the hot corrosion behavior of the γ’-strengthened Ni-based superalloy IN740H. Controlled cold rolling to thickness reductions of 5%, 15%, 30%, and 50% produced systematic microstructural evolution: grain elongation, progressive transformation of CSL boundaries into HAGBs, and increased defect density. A hot corrosion test was conducted at 760&#xa0;°C for 100&#xa0;h in simulated flue gas, both with and without a salt deposit (74%Na₂SO₄, 24% K₂SO₄, and 2% NaCl). Contrary to the conventional expectation that increased defect densities would promote protective chromia scale formation in a high-chromium (∼25 wt%) alloy such as IN740H, higher defect densities deteriorated the hot corrosion resistance. The cold-rolled samples exhibited greater mass gain under salt-free conditions and more severe mass loss under salt-deposited conditions. The increased defect density accelerated γ’ dissolution into the γ matrix, promoting extensive subsurface degradation. This was characterized by internal oxidation and sulfidation (i.e., Al₂O₃ and (Cr, Ti)S), accompanied by Ni enrichment and Cr and Al depletion in the subsurface region. Furthermore, the subsurface damage morphology exhibited a clear transition with increasing deformation. At low-to-intermediate deformation levels (5–15%), the subsurface damage region remained limited in extent, but localized percolation of corrosive species along grain boundaries promoted deep intergranular attack. At high strain levels (30–50%), increased defect densities led to extensive subsurface degradation dominated by uniform internal oxidation and sulfidation rather than deep grain boundary percolation.</p>