<p>To investigate the effect of microstructure on the corrosion resistance of rail steel, different sizes of pearlite clusters and austenite grains were obtained via heat treatment of U75V rail samples at different temperatures. The effects of different pearlite cluster sizes and austenite grain sizes on the corrosion behavior and electrochemical properties of the rail samples were subsequently investigated via salt spray corrosion tests and electrochemical performance tests. The results show that the corrosion products of all the samples are composed of γ-FeOOH, α-FeOOH, and Fe₃O₄, and the microscopic morphology mainly manifests as clusters, needles, and flowers, indicating that the differences in microstructure do not affect the composition and morphology of the corrosion products. During the salt spray corrosion process, the average corrosion rate of all the samples decreased; however, with increasing corrosion time, there was still an overall increasing trend, and compared with that of the pearlite cluster samples, the average corrosion rate of the austenite samples exhibited relatively better corrosion resistance. In addition, for the same microstructure, samples with higher heat treatment temperatures that have larger austenite grains or smaller pearlite clusters exhibit higher average corrosion rates and self-corrosion current densities (<i>J</i>_<i>corr</i>), lower charge transfer resistances (<i>R</i>_<i>ct</i>), and poorer corrosion resistance owing to the decrease in the relative area of the grain boundaries of the austenite grains and the increase in the lamellar spacing within the pearlite clusters. A smaller grain boundary area and larger lamellar spacing result in a much greater probability of corrosion occurring, thereby increasing the susceptibility of the sample to corrosion in a salt spray environment.</p>