The researchers find that a plastic deformation surface layer with nanocrystalline grains can be produced on the surface of the important engineering material, AISI 321 austenitic stainless steel, by means of SMAT. The nano-structured sample and the coarse grain sample were then nitrided simultaneously using pulsed-DC glow discharge plasma technique at low temperature. The results show that the plasma nitriding of AISI 321 steel can be enhanced considerably by means of SMAT process before nitriding, and a much thicker nitrogen diffusion layer with higher hardness was obtained for the SMAT samples when compared with un-SMAT samples. In addition, the wear resistance and load capacity of the nitrided layers on the SMAT samples was much higher than that of the un-SMAT samples due to the thicker S phase case and the gradient nitrogen diffusion layer.
This research conducts nanocrystallization technique and combines the conventional nitriding treatment on strengthening of stainless steel and, as a result, the high brittleness and poor case depth of the nitrided layer can be eliminated. Our results exhibit an application potential of nanotechnology for commercial engineering materials.