Auger Electron Microprobe Investigation of Nitrided Austenitic Stainless Steel

Abstract

Auger electron microprobe observations on plasma nitrided 304 austenitic stainless steel samples have confirmed previous results obtained by scanning electron microscopy and wavelength dispersive X-ray spectroscopy and have also shown some marked differences in micrograin structure between NH3 and plasma nitrided samples. The N H3 nitrided layer appeared to consist of a single layer with precipitate grains, if any, > 0.1 μm size, nitrogen concentration decreasing exponentially with depth. The plasma nitrided layer, on the other hand, consisted of two layers: a near surface layer with constant nitrogen concentration and precipitate grains of B1 (CrN) 1-2 μm in size, beneath which is a layer in which the nitrogen content decreases exponentially with depth, this layer being thinner than its equivalent in the NH₃ nitrided material. The differences in nitrogen depth profile and nitriding rate between the two processes are explained in terms of the different resultant microstructures.