Effect of Mg-Ce Treatment on Inclusion Characteristics and Pitting Corrosion Behavior in EH420 Marine Steel

Abstract

Reasonable regulation of nonmetallic inclusions in steel can significantly improve its strength, toughness, and corrosion resistance. In this paper, EH420 marine steel was treated with Mg, Ce, and Mg-Ce to modify the inclusions. The effects of different treatments on the morphology, composition, size distribution, induced intragranular ferrite (IGF) nucleation, and pitting resistance of inclusions were systematically analyzed using various methods. The results show that the Mg-Ce composite treatment can modify irregular MgAl2O4 inclusions into spherical Mg-Ce-O composite inclusions and MgO-dominated inclusions. The density of inclusions is increased from 74.8/mm2 to 186.0/mm2, and the average size of inclusions is decreased from 2.60 μm to 1.07 μm. The Mg-Ce-O composite inclusions are effective inclusions for inducing IGF. Furthermore, the pitting potential is increased from −503 mV to −487 mV, and the corrosion rate is decreased. The order of average electronic work function is ΦMgO < ΦCe2O3 < Φα-Fe < ΦAl2O3. Ce2O3 is hard to induce pitting corrosion due to its similar electronic work function to the steel matrix. Thus, the Mg-Ce composite treatment is better than that for Mg and Ce treatment alone, and has better application prospects.