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

Abstract 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 N 2 , H 2 and C 2 H 2 . 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 Cr 3 Ni 2 . We observed a very high hardness (1635 kg mm −2 ) at 0.5% C 2 H 2 concentration at 500°C.