Corrosion Behaviour of Stainless Steels Aner Plasma and Ammonia Nitriding

Abstract

Steels Cr17Ni2 and Cr18Ni9Ti were plasma nitrided and nitrided in ammonia at 585°C for 16h, and the layers obtained examined by X-ray diffraction and microhardness measurements. Corrosion properties were determined in 0.05M Na2SO4 at pH 3.0 and 5.0, with and without added chloride, using a potentiodynamic polarisation method. Nitriding resulted in a deterioration of corrosion resistance, especially in the acidic (pH 3.0) solutions, whereas in the near neutral (pH 5.0) chloride free solution the deterioration was slight and limitea to the transpassive region. Ammonia nitrided layers with ε +γ nitrides had lower corrosion resistances than plasma nitrided layers with γ nitride alone. This can be explained by the high porosity of the ε nitride layers and the resultant exposure of diffusion zones. The corrosion resistance of diffusion zones with CrN precipitates was markedly lower than that of outer nitride zones and of steel cores.

Corrosion and passivation of plasma nitrided stainless steels

“…6,7 The improvement of the mechanical properties is, however, accompanied by a deterioration of the corrosion resistance. [8][9][10][11] This is caused by the depletion of chromium around chromium nitride precipitates in the austenite matrix and by the heterogeneity of the precipitates/matrix system. It has been a great challenge for researchers and engineers to solve the problem of the adverse effect of nitriding on corrosion resistance of stainless steels.…”

Corrosion resistance improvement of nitrocarburised and post-oxidised steels by oil impregnation

“…1) shows a predominance of compact c9phase. 15 For the oxide layer, X-ray diffraction analysis of the surface of post-oxidised samples (20MnCr5_NCO and 42CrMo4_NCO) allows to identify magnetite (Fe 3 O 4 ) as the only oxide grown above the compound layer.…”

Duplex and Superduplex Stainless Steels: Microstructure and Property Evolution by Surface Modification Processes

“…Diffusion surface treatments including nitriding, carburizing, or nitrocarburizing can be performed under a controlled gas atmosphere as well as under plasma conditions [21][22][23]. Nitriding can be applied to unalloyed steels and irons to produce a corrosion and wear-resistant nitride layer.…”