1. Low temperatures (≤0°C): Stable but slow corrosion
Low temperatures reduce the activation energy of electrochemical reactions (anode dissolution, cathode oxygen reduction), slowing ion migration and oxygen diffusion-slashing overall corrosion rate to ~60% of that at 20°C.
The Cu/Cr-enriched protective rust layer forms slowly (2–3 years to mature) due to hindered element diffusion, but once formed, it resists thermal damage; freeze-thaw only causes minor local cracks (easily repaired by Cu/Cr).
2. Medium temperatures (10–30°C): Optimal corrosion resistance
Balanced electrochemical activity promotes uniform rusting, avoiding local pitting.
Cu and Cr diffuse efficiently, converting loose initial rust (γ-FeOOH) into dense α-FeOOH with a Cu₂O/Cr₂O₃ barrier (porosity ~5%). This rust layer blocks oxygen/moisture effectively, cutting annual corrosion rate to 0.01–0.03 mm/year.
3. High temperatures (≥35°C): Declining corrosion resistance
Excessive heat accelerates electrochemical reactions (corrosion current density doubles at 40°C vs. 20°C), leading to rapid but porous, loose rust (porosity ~15%) that fails to protect.
Thermal expansion mismatch between steel and rust causes microcracks/spalling; high humidity/contaminants (e.g., acid rain) further erode the Cu/Cr-enriched layer, triggering secondary corrosion.
