<p>This study investigated the high-temperature corrosion behavior of ASTM A516 carbon steel exposed to KCl–CaCl₂ salt vapor environments at 600&#xa0;°C to evaluate the influence of salt composition on corrosion kinetics, oxide scale characteristics, and degradation mechanisms. Corrosion tests were conducted for 100&#xa0;h using salt mixtures containing 75% KCl–25% CaCl₂ and 75% CaCl₂–25% KCl in a three-hot-zone tube furnace. Kinetic analysis showed that the KCl-rich environment exhibited mixed corrosion kinetics, with a kinetic exponent of n ≈ 0.69 and an apparent rate constant of kₚ ≈ 5.28, indicating that the oxide scale provided partial resistance to further corrosion. In contrast, the CaCl₂-rich environment exhibited corrosion behavior approaching near-linear kinetics (n ≈ 0.86; kₚ ≈ 20.08), accompanied by substantially higher mass gain and mass loss throughout the exposure period. Cross-sectional SEM observations revealed that the oxide scale formed in the KCl-rich environment was relatively more compact, with a porosity of 8.6%, whereas the CaCl₂-rich environment produced a highly porous oxide scale with a porosity of 13.07%, extensive cracking, and severe spallation. XRD analysis identified Fe₂O₃ and Fe₃O₄ as the dominant corrosion products in both environments, together with chloride-containing phases including FeCl₂ and FeCl₃, indicating the occurrence of coupled oxidation and chlorination reactions. The more severe degradation observed in the CaCl₂-rich environment was associated with the formation of a porous and mechanically unstable oxide scale, which facilitated the transport of corrosive species and promoted repeated oxide breakdown during exposure. Consequently, the corrosion scale provided lower protection against further attack, resulting in accelerated material degradation at high temperatures.</p>