Effect of RF plasma nitriding time on microhardness and corrosion resistance of 304 stainless steel

Abstract

Austenitic stainless steel (ASS) has been nitrided for different plasma times using an inductively coupled RF glow discharge. Different nitrided phases were created in the sample's surface during the first stage of the nitriding process (up to 7 min) whereas the sample temperature increases very rapidly. Once the temperature reaches the saturation level, the nitriding process is accompanied with annealing effects. The microhardness of the nitrided surface of austenitic stainless steel (NASS) increases with increasing plasma time up to a certain value and then decreases with a further increase of the nitriding plasma time. The weight loss of NASS, due to immersion in 5% HCl solution, versus nitriding time shows a similar trend as the microhardness does. The microhardness decreases and the corrosion resistance increases when either ASS or NASS were annealed up to 800°C.