Effect of high content rare earth on inclusion modification and corrosion resistance in wind turbine tower steel

To improve the corrosion resistance of Q355 steel used in wind turbine towers in marine atmospheres, 0.010 wt.% rare earth (RE) content was added to this steel by feeding RE wire into its continuous casting mold under industrial production conditions. Inclusion characteristics and electrochemical behavior were studied using automated inclusion analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The measured RE content in the rolled product reached 0.0098 wt.%, and RE addition substantially changed the types and distributions of inclusions in steel. Compared with the base steel (without RE addition), the number densities of (Ca-)(Mg-)Al-O, TiN, and (Ca, Mn)S inclusions in RE-treated steel decreased from 5.3, 2.8, and 1.1 #·mm -2 to 0.5, 1.6, and 0.3 #·mm -2 , respectively, and stable RE-S, RE-O-S, and other RE-containing inclusions were formed under the action of RE. Additionally, RE-treated steel showed improved corrosion resistance, with the pitting potential shifting from -0.52 V in base steel to -0.47 V in RE-treated steel, and the corrosion current density falling from 4.13×10 -5 to 2.35×10 -5 A·cm -2 . The overall positive shift in the Tafel curve indicated that RE primarily inhibited anodic polarization. The EIS results verified a higher charge transfer resistance for RE-treated steel (230.8–500.2 Ω·cm 2 ) than for base steel (125.0–297.6 Ω·cm 2 ). Moreover, the rust layer resistance of the RE-treated steel reached 19.53 Ω·cm 2 , markedly above the 4.41 Ω·cm 2 measured for the base steel. The overall improvement of corrosion resistance of Q355 steel indicates the potential and value of mold feeding RE wire technology for large-scale industrial production.