Low-temperature plasma nitriding of AISI F51 duplex stainless steel

Development and microstructure characterization of single and duplex nitriding of UNS S31803 duplex stainless steel

“…Some "deformation bands" were observed, inside expanded ferrite, which were assigned to intense compressive residual stresses. On the other hand, the results reported in this manuscript are quite different from those given in reference[11]. Although the modulated structure reported in the previous paper was also formed after active screen LTPN, the results show that -Fe 3 N needles precipitate coherently inside the expanded ferrite regions of the nitrided layer, sharply increasing the hardness.The duplex HTGN + LTPN nitriding treatment, consisting of a 4 µm thick, nitrogen rich, 1227 ±78 HV 0.01 hard, expanded austenite layer, formed on top of a 550 µm thick, 0.9 wt% N, fully austenitic layer, ensures a more homogeneous microstructure and gentler hardness gradients.…”

“…calculated for the as received material 0.3613 nm. The calculated nitrogen content for  N (not considering the compressive residual stresses effects) is 13.7 at.% or 3.8 wt.%, very close to the reported 3.7 at.% N obtained by WDX for expanded austenite formed on a F51 duplex stainless steel[11]. This strong supersaturation and lattice expansion lead to strong hardening of the expanded austenite 1360  81 HV 0.01.…”

“…Nagatsuka et al (10) discussed the formation of a nitrided case on top of ferrite grains and concluded that S phase (expanded austenite) was uniformly formed on both austenitic and ferritic phases, after ASPN at 450 ºC. In a previous work, Pinedo et al [11] found that the nitrided layer was composed by a modulated structure developed on the surface of the specimen, containing expanded austenite and expanded ferrite, with the expanded ferrite layer being thicker than the neighboring expanded austenite layer. The expanded ferrite phase showed acicular structures crossing the layer, suggesting that deformation bands propagated inside this phase due to intense compressive stresses developed during nitriding [11].…”

Study of plasma nitriding and nitrocarburizing for higher corrosion resistance and hardness of 2205 duplex stainless steel

“…The reason why ferrite exhibits higher thickness than the austenite can be explained as follows. It has been reported that the diffusion of nitrogen in the ferrite phase of the duplex austenitic-ferritic steel is higher than in the austenite phase [23]. This is because the BCC structure is more open than the FCC structure and as a consequence nitrogen exhibits higher diffusion coefficient in BCC lattice of ferrite than in FCC lattice of austenite phase.…”

On the Nitrogen Diffusion in a Duplex Stainless Steel

“…Although the mechanism of diffusion of nitrogen in austenitic stainless steels (ASS) has been extensively studied [6][7][8] . In the case of DSS there are studies where nitrided layer properties are evaluated 5,9,10 , but the mechanism of formation and the morphology of the layer have not been deeply studied 11,12 . This study aims to study the kinetics of nitrided layer formation on DSS and its morphology.…”