Influence of Rare Earth Element Y on the Corrosion Resistance of Low Alloy Steel

To study the effect of rare earth Y on the corrosion resistance of low alloy steel， low alloy steel with different rare earth contents was obtained by adding rare earth Y to DH36 low alloy steel.Then， the effect of simulated marine environment on the corrosion resistance of DH36 ship plate steel was investigated using 3.5%NaCl solution as the corrosive medium.The effects of rare earth Y on the corrosion resistance of DH36 steel were investigated using immersion tests， laser confocal microscopy， scanning electron microscopy (SEM)， X-ray diffraction analyzer (XRD)，electrochemical testing and other methods.The residual stress between inclusions unmodified by rare earth and inclusions modified by rare earth and the steel substrate was investigated using electron backscatter diffraction (EBSD)， and the effect of inclusions on the corrosion resistance of low alloy steel was determined.Results showed that rare earths could refine grains， modify inclusions， reduce the peripheral stress of rare earth inclusions， reduce the occurrence of microcracks and micropores， and thus reduce the corrosion sensitivity of low alloy steel in simulated marine environments.The addition of Y could shift the corrosion potential positively， decrease the corrosion current density， and reduce the appearance of pitting pits on the surface of the test steel in the early stage of corrosion，thereby reducing the active area where corrosion occurred.Moreover， the addition of rare earth Y significantly declined the content of γ-FeOOH in the corrosion products， increased the content of Fe3O4 and α-FeOOH， and enhanced the stability and compactness of the rust layer.Furthermore， the addition of Y also increased the thickness of the rust layer， more effectively hindering the entry of Cl-.Hence，the addition of rare earth Y could effectively improve the corrosion resistance of low alloy steel.When the mass fraction of rare earth was 0.004 3%，the best corrosion resistance of the test steel was achieved.