Effect of Alloying Elements on Anti-atmospheric Corrosion of High Strength Weathering Steel

In comparison with ordinary Q345B low-alloy high-strength steel, periodic wetting accelerated corrosion and electrochemical tests were carried out for weathering steels with different alloying elements. The effects of alloy elements on the atmospheric corrosion resistance of high strength weathering steels were studied. The morphology and structure of the rust layer were characterized with scanning electron microscopy (SEM) and X ray diffraction (XRD). The results show that the corrosion rate of Q345B without Cr is in a zigzag pattern during an experimental cycle. Meanwhile, as the corrosion time increases, the corrosion rate of No. 1 tested steel (mass fraction of Cr is 1.7%) first reduces slowly and then stabilizes, while the corrosion rate of No. 2 (mass fraction of Cr is 4.5%) first increases slowly and then stabilizes. After 120 h corrosion, the rust layer of the Cr free tested steel is thick and loose with a yellow-brown appearance. With the increase of Cr content, the rust layer gradually transforms into a dense dark brown color and the ratio of α/γ^* (α indicates mass fraction of α-FeOOH; γ^* indicates the total mass fraction of γ-FeOOH, β-FeOOH and Fe₃O₄) in the rust layer gradually increases. With the prolongation of corrosion time, the impedance value of tested steel with higher Cr content increasesmore significantly. At the later stage of corrosion, the protective effect of alloying element Cr on the matrix gradually appeared.