Combined niobizing and plasma nitriding of AISI 430 stainless steel

In this work, AISI430 ferritic stainless steel specimens were duplex treated by niobizing followed by plasma nitriding (Nb-PN) and plasma nitriding followed by niobizing (PN-Nb). Pack cementations were carried out for 2 h at two different temperatures of 850 ;C and 950 ;C for Nb-PN specimens and 950 ;C for PN-Nb samples. Plasma nitriding of all specimens was performed for 6 h at 450 ;C. The fabricated layers were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurement. Plasma nitriding of niobized layers resulted in formation of niobium nitride (NbN) on the surface layer; while the layer produced by reverse treatment composed of NbN, Fe2Nb and NbCr2 phases. Furthermore, AFM results revealed that PN-Nb specimen had a rougher surface than that of the Nb-PN. Contact angle measurements illustrated better hydrophobicity of the duplex treated samples as compared to the untreated 430 stainless steel.