Decreasing chromium precipitation in AISI 304 stainless steel during the plasma-nitriding process

Experiments were carried out to study the effects of ion nitriding of type 304 stainless steel in the temperature range from 450 to 600°C for different concentrations of N2, H2 and C2H2. The pressure of the gas (a mixture of nitrogen, hydrogen and acetylene) and the temperature during the nitriding process exert a profound influence on the surface hardness. The nature of the compound layer formed on the surface was studied by X-ray diffraction, microhardness and X-ray photoelectron spectroscopy (XPS). A high concentration of hydrogen species during the nitriding process decreases the chromium concentration on the surface. The deconvolution method (peak analysis fitting) and XPS analysis identified the phase Cr3Ni2. We observed a very high hardness (1635 kg mm−2) at 0.5% C2H2 concentration at 500°C.