Samples of AISI 304 steel with layers nitrided at low temperature
(< 450°C) have been heated isothermally under neutral atmosphere for times ranging
from 4 to 3,000 h. The stability of the layers varies depending on holding temperature.
At temperatures greater than 450°C, the initial FCC disordered metastable solid
solution, supersaturated in nitrogen (
), decomposes in a relatively short time
(4 h). At lower temperatures, however, no change in supersaturation and no decomposition
occur, even for holding times exceeding 3,000 h. Nevertheless, an increase in layer
thickness is noted and the hardness within the layers remains high (800 HV10).