Microstructure and Properties of Active Screen Plasma Nitrided Duplex Stainless Steel

Abstract

UNS S31803 duplex stainless steel (DSS) was nitrided using the active screen plasma nitriding (ASPN) technique at temperature ranging from 400 to 450°C. Microstructures and corrosion properties of the untreated substrate and AS plasma nitrided specimens were analyzed by means of X-ray diffractometry, scanning electron microscopy, microhardness measurement, anodic polarization test, and wear test using a ring-on-disc tester. The result shows that ASPN specimen surface nitrided at 420°C consisted of a dual phase nitrided layer of nitrogen expanded austenite (γ_N or S-phase) and expanded ferrite (α_N), which considerably improved the hardness, wear, and corrosion property of the UNS S31803 duplex stainless steel. For ASPN specimens nitrided at 435°C or 450°C, precipitated nitrides of Fe₃N, Fe₄N and chromium nitride (CrN) appeared in the nitrided layer. The results showed that the wear and corrosion resistance of the specimen nitrided at 420°C for 10 h were exceedingly improved, and the specimen exhibited the least wear mass loss and corrosion current density.

Keywords:

• Active screen plasma nitriding
• Corrosion
• Duplex stainless steel
• Wear

ACKNOWLEDGMENT

Financial support of this research by Tatung University, Taipei, under the grant E95-T11-082 is gratefully acknowledged.