A comparative study using three stainless steels types (austenitic, super-territic and duplex ferritic-austenitic) and three industrial nitrocarburizing processes (liquid, gaseous and plasma)

Three different stainless steels types have been studied: 1) austenitic (AISI 316 L), 2) superferritic (28%Cr, 4% Ni and 2.5% Mo, DIN W.Nr. 1.4575) and 3) duplex ferritic-austenitic (UNS S31803). Samples of the three steels have been nitrocarburized under three typical industrial conditions: a) plasma nitrocarburizing during 10 hours at 560degreesC (IONIT process); b) gaseous nitrocarburizing under an atmosphere of nitrogen, ammonia and carbon dioxide for 6 hours at 560degreesC (DEGANIT process) and c) liquid nitrocarburizing for 1.5 hours at 550degreesC in a molten mixture of cyanide, carbonate of sodium and potassium (TENIFER process). The nitrocarburized layers were studied by optical microscopy, electron scanning microscopy, energy-dispersive analysis (EDS), glow discharge optical spectrometry analysis (GDOS), X-ray diffraction and hardness measurements. The results have been compared and discussed in terms of roughness, thickness, hardness and the chemical composition of the formed layers.