Effect of addition of alumina and rare-earth oxide particles on the corrosion resistance and mechanism of low carbon low alloy steel

The corrosion mechanism of the low carbon low alloy steel with Al _2 O _3 particles and rare Earth (RE) oxide particles was compared in a simulated marine environment. It is shown that when the Al _2 O _3 -containing particles are introduced, the number density of nonmetallic particles of the steel increases twice, and the average particle size decreases from approximately 2.4 μ m to 1.4 μ m. With the introduction of Al _2 O _3 -containing particles, the amount of pitting corrosion increases. Furthermore, pitting corrosion occurs more uniformly owing to the fineness of the Al _2 O _3 particles, thereby leading to smaller, shallower pits after the Al _2 O _3 particles are shed. Hence, the corrosion performance of the steel with Al _2 O _3 particles is significantly improved than that of the steel without Al _2 O _3 particles. By adding RE oxide particles into steel, the nonmetallic particles in steel are refined but not as effectively as that achieved by adding the Al _2 O _3 -containing particles. Different from Al _2 O _3 particles, Cu is obviously enriched in the location of RE oxide particles at the initial corrosion stage, which makes the steel exhibit the best corrosion resistance. Cu enrichment is attributed to the mobile Cu present in the rust layer and to the micro acid region formed around the RE oxide particles.