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 FeCr ₂ O ₄ , Cr ₂ O ₃ and Fe ₂ O ₃ oxides as well as nitrides. After a short immersion time, oxides of Cr ₂ O ₃ and FeCr ₂ O ₄ form in nitride films on 304 stainless steel samples. Fe ₂ O ₃ oxide will subsequently form following an increasing immersion time. For the 430 stainless steel, Cr ₂ O ₃ 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 Cr ₂ N were detected near the surface of the nitride films of three samples while Cr ₂ N phases formed in the deeper zone. The greatest amount of Fe ₂ O ₃ 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.