The Study of Corrosion Behavior of Active Screen Plasma Nitrided Stainless Steels

Plasma nitriding is a surface treatment process which is increasingly used to improve wear, fatigue and corrosion resistance of industrial parts. Active screen plasma nitriding (ASPN) has both the advantages of the classic cold wall and the hot wall conventional dc plasma nitriding (DCPN) method and the parts to be nitrided are no longer directly exposed to the plasma, In this study, AS plasma nitriding has been used to nitride the UNS S31803 duplex stainless steel, AISI 304 and AISI 316 austenitic stainless steel, and AISI 420 martensitic stainless steel. Treated specimens were characterized by means of microstructural analysis, microhardness measurements and electrochemical tests in NaCl aerated solutions. Hardness of the nitride cases of AISI 420 stainless steel by Knoop test can get up to 1300 HK 0.1. From polarization tests, the corrosion current densities of AISI 420 and UNS S31803 specimens ASPN at 420 .deg. C were generally lower than those of their untreated substrates. The corrosion resistance of UNS S31803 duplex stainless steel can be enhanced by plasma nitriding at 420 .deg. C Cowing to the formation of the S-phase