Liquid, gaseous and plasma nitrocarburizing using three stainless steels types (austenitic, ferritic and duplex ferritic-austenitic) as a substrate: a comparative study

Three different stainless steels types have been studied: 1) austenitic (17 % Cr, 11 % Ni and 2 % Mo, DIN W. Nr. 1.4404 or AISI 316 L), 2) super-ferritic (28 % Cr, 4 % Ni and 2.5 % Mo, DIN W.Nr. 1.4575) and 3) duplex ferritic-austenitic (22 % Cr, 5.5 % Ni and 3 % Mo, DIN W. Nr. 1.4462). Samples of the three steels have been nitrocarburized under three typical industrial conditions : 1) plasma nitrocarburizing during 10 hours at 560degreesC (IONIT process); 2) gaseous nitrocarburizing under an atmosphere of nitrogen, ammonia and carbon dioxide for 6 h at 560degreesC (DEGANIT process) and 3) liquid nitrocarburizing for 1.5 h 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.