The Corrosion Enhancement due to Plasma Post-Oxidation Subsequent to Plasma Nitriding of a Steel AISI 4140

Abstract

The corrosion enhancement due to plasma post-oxidation subsequent to plasma nitriding of the samples of low alloy annealed steel AISI 4140 was evaluated. The plasma nitriding was carried out at ≈570• C for 1-3 h in an atmosphere of 75% H2 and 25% N2. After this process post-oxidation at ≈450• C in a gas mixture, air and dry air-like was conducted for an hour. The treated samples were characterized using the XRD, SEM, AFM, potentiodynamic polarization and Vickers microhardness tests. The outcome of combined processes showed the presence of ε and γ nitrided phases in the inner compound layer and in the outer one mostly of magnetite phase and barely visible of hematite one without using H2 in the post-oxidation process. Also in these processes, the corrosion potential proved to be lower in the treated specimens than the untreated ones, and the corrosion current decreased up to one order of magnitude when treated in environment air and air-like ambient.

An Experimental Study of Temperature Effect on Properties of Nitride Layers on X37CrMoV51 Tool Steel Used in Extrusion Aluminium Industry

“…The iron oxide phases of hematite (Fe 2 O 3 ) and magnetite (Fe 3 O 4 ) through the post-oxidizing treatment at 400 • C and 450 • C was found. The hematite has been also identified in work [34] after the postoxidation of plasma nitriding AISI 4140 steel. In contrast, in [35], after oxidation of nitride layer at 480 • C to 500 • C, Fe 3 O 4 (magnetite) was reported.…”