Abstract
The microstructure of the low-temperature plasma-nitrided layer on AISI 304 austenitic stainless steel was studied by transmission electron microscopy (TEM). The results show that the surface of the layer consists of a supersaturated solid solution (γ′N) based on the γ′-Fe4N phase whose electron diffraction pattern (EDP) has a strong diffuse scattering effect resulting from supersaturating nitrogen (above 20 at. pct) and 〈110〉 streaks arising from matrix elastic strain due to the formation of paired or clustered Cr-N. The latter is due to the N above the 20 at. pct γ′-Fe4N-phase value and leads to a lattice parameter that is greater than that of the γ′-Fe4N phase. The subsurface of the layer is composed of a supersaturated solid solution based on γ-austenite, which is an expanded austenite, γ N. Its morphology shows the basketweave or “tweedlike” contrast consisting of so-called stacking fault precipitates having twin relationships with the matrix whose EDP shows diffuse scattering streaks with certain directions. The ε martensite transformation was observed in the subsurface of the layer. The increase in stacking faults compared with the original stainless steel and formation of ε martensite in the subsurface of the layer indicate that nitrogen lowers the stacking fault energy of austenite.
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Xu, X., Wang, L., Yu, Z. et al. Study of microstructure of low-temperature plasma-nitrided AISI 304 stainless steel. Metall Mater Trans A 31, 1193–1199 (2000). https://doi.org/10.1007/s11661-000-0115-1
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DOI: https://doi.org/10.1007/s11661-000-0115-1