Effect of annealing temperature on properties of H2/N2 rf plasma-treated stainless steel

Nitriding of AISI 304 austenitic stainless steel was prepared using inductively coupled radio frequency (ICRF) plasma with different H2/N2 ratios. Thickness of nitriding layer, microhardness, and structural phases of the compound layer, surface microstructure and cross-section morphology were studied before and after annealing treatment. Little change is found in the microhardness values and thickness of the compound layer when the treated samples are annealed up to 400 °C. With further increase in the annealing temperature, the microhardness values decrease while the thicknesses increase. Due to the low temperature plasma processing for the 50% N2 + 50% H2 sample, post-annealing over 500 °C has enormous influence on the structural phases of the sample. However, the 25% N2 + 75% H2 sample shows little variation on the structural phases due to annealing process.