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 N2+Ar atmospheres under N2 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 N2 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.