Abstract
Simultaneous plasma nitriding and ageing were performed on 15-5 PH stainless steel, being the treatment time (2, 4 and 6 h) and temperature (390, 440 and 490 °C) the control variables. The highest value for core hardness was obtained at the longest time (6 h) and the lowest temperature (390 °C). A long treatment time (6 h) and high temperature (490 °C) have favoured the surface layer formation. The formation of expanded martensite α_N and expanded austenite γ_N was observed using low nitriding temperature, while raising the temperature favoured the formation of the γ’ and CrN phases. When the treatment was carried out at temperatures of 440 and 490 °C, a drop in the corrosion resistance was observed. Treatment at 390 °C led to an improvement in the corrosion potential (E_I = 0), however, the samples processed at 390 °C did not show a clear passive region.

Key words
plasma nitriding, ageing, 15-5 PH stainless steel, phase formation, corrosion

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