Microstructure and erosion-corrosion property of 304 stainless steel treated by salt bath nitriding at low temperature

Austenitic 304 stainless steel was nitrided in a salt bath at 430 °C. The effect of nitriding time on thickness, microstructure, microhardness, and erosion-corrosion resistance of the nitrided layer was studied by X-ray diffraction (XRD), optical microscopy (OM), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and microhardness tester. The results showed that the thickness and microhardness of nitrided layer are increased with extending nitriding time. The nitrided layer only contains a single S phase after nitriding for 1 h, but is composed of S phase and CrN for 16 h. The content of CrN in nitrided layer is increased with prolonging nitriding time. A larger amount of CrN segregates after nitriding for 40 h. The erosion-corrosion resistance of 304 stainless steel is improved by nitriding, and is the best by nitriding at 430 °C for 16 h, but is decreased with further increasing nitriding time.