Effect of post-oxidizing time on corrosion properties of plasma nitrocarburized AISI 1020 steel

Plasma nitrocarbutized AIR 1020 steels are oxidized for 15, 30 and 60 min to evaluate the effect of post-oxidizing time on corrosion-behavior. After plasma nitrocarburizing for 3 h at 570 degreesC, the compound layer composed of epsilon-Fe2-3(N,C) and gamma'-Fe-4(N,C) phases and the diffusion. layer above the matrix are observed. The oxide top layer, mainly consisting of magnetite (Fe3O4) and, hematite (Fe2O3) phases, is formed after post-oxidation treatment at 500 degreesC. However, the oxide layer is degraded severely by spallation as a result of the prolonged oxygen plasma bombardment as the post-oxidizing time increases. The difference in corrosion resistance is mainly attributed to the thickness of the oxide top layer, which is governed by the post-oxidizing time. (C) 2002 Elsevier Science B.V All rights reserved.