Constituted oxides/nitrides on nitriding 304, 430 and 17-4 PH stainless steel in salt baths over the temperature range 723 to 923 K

The progressively developed oxides and nitrides that form on nitriding 304, 430 and 17-4 PH stainless steel are analysed by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) in this study. The experimental results show that the Cr contents and matrix structures (ferrite, austenite and martensite) play an important role in forming FeCr2O4, Cr2O3 and Fe2O3 oxides as well as nitrides. After a short immersion time, oxides of Cr2O3 and FeCr2O4 form in nitride films on 304 stainless steel samples. Fe2O3 oxide will subsequently form following an increasing immersion time. For the 430 stainless steel, Cr2O3 predominately forms after a short dipping time which hinders the growth of the nitride layer. As a result, this sample had the thinnest nitride film of the three for a given immersion time. After the formation of oxides, both CrN and Cr2N were detected near the surface of the nitride films of three samples while Cr2N phases formed in the deeper zone. The greatest amount of Fe2O3 oxide among the three samples was obtained on the nitriding 17-4 PH stainless steel which also had a high intensity count of N 1s.