Corrosion characteristics of duplex surface-treated spheroidal graphite cast iron

Spheroidal graphite cast iron was treated by a duplex surface treatment pro cess, which was combined plasma nitriding and oxidation. The surface and cr oss-sectional microstructures and corrosion characteristics were analyzed. Potentiodynamic polarization curves were obtained at room temperature from samples immersed in 3% NaCl solution. In the case of oxidation after nitrid ing, an oxide layer (double layers of Fe2O3 and Fe3O4) was found to be form ed on top of the compound layer (gamma ' -Fe4N). The value for the average roughness (R-a) of the plasma nitrided sample was higher than that of the p lasma oxidation-treated sample. The untreated sample showed typical graphit ic corrosion, and the plasma treatment was found to increase the corrosion resistance. (C) 2001 Elsevier Science B.V. All rights reserved.