Effect of tempering on corrosion behavior and mechanism of low alloy steel in wet atmosphere

Although tempering is an effective method to improve the mechanical properties of steel, its influence on corrosion behavior has been controversial. Therefore, we conducted this study to assess the effects of different tempering temperatures on the corrosion resistance of low alloy steel in wet atmosphere using an immersion test, salt spray test, electrochemical measurement, and morphology characterization and phase analysis. The results showed that defects and the highly reactive nature of high angle grain boundaries (HAGBs) of bare steels are preferentially corroded. In the initial stage of corrosion, the tempering temperature affects the distribution of low angle grain boundaries (LAGBs). The specimens tempered at low tempering temperatures corroded lightly because of low interface energy. In the later stage of corrosion, the corrosion resistance of the specimens still depends on the matrix due to the limited protection of the rust layer. Thus, the charge transfer resistance improves and the corrosion resistance becomes better with the decrease of tempering temperature.