Improvement of the cavitation erosion resistance of an AISI 304L austenitic stainless steel by high temperature gas nitriding

An AISI 304L austenitic stainless steel was high temperature gas nitrided in N 2+Ar atmospheres under N 2 partial pressures up to 0.10 MPa at 1423 K for 21.6 ks. Nitrogen contents at the surface up to 0.48 wt.% and case depths up to 1 mm were obtained. All the samples showed fully austenitic microstructures free of precipitates. Solution treated AISI 304L as well as nitrided samples were tested in distilled water in a vibratory cavitation erosion (CE) equipment. Characterization of the test specimens was made by optical microscopy, electron back scattering diffraction coupled to a scanning electron microscope (EBSD–SEM), X-ray diffraction (XRD), wavelength dispersive spectroscopy (WDS) microanalysis and depth-sensing indentation tests. All the samples had almost the same mean grain diameter, ∼80 μm, similar mesotexture and microtexture, though the nitrogen contents differed. The nitrided samples exhibited much better cavitation erosion resistance and the erosion rate was reduced by almost 8.5 times. Increasing the N 2 partial pressure increased the nitrogen content at the surface, leading to an increase in the incubation period for damage and a decrease in the erosion rate.