Properties of rapid arc discharge plasma nitriding of AISI 420 martensitic stainless: effect of nitriding temperatures

Abstract

Martensitic stainless steels (MSS) with excellent mechanical properties are potential candidates used in the nuclear, marine, aeronautical, and aerospace industries. However, surface treatments are needed to improve the wear performance of MSS. Arc discharge plasma nitriding (ADPN) was applied on selected AISI 420 stainless steel to improve the wear performance without reducing its original corrosion resistance. To avoid the formation of the CrN phase, the ADPN was performed at temperatures ranging from 400 °C to 460 °C for 1 h. The effects of nitriding temperature on the structural, mechanical, and tribological properties of the nitrided layers were examined by X-ray diffraction (XRD), Scanning electron microscope (SEM), Vickers microhardness tester, and ball-on-disk tribometer, respectively. Potentiodynamic polarization in a 3.5% NaCl solution was used to assess corrosion resistance. The surface of the specimen nitrided at 400 °C is ε-Fe2-3N phase while that of specimen nitrided at higher temperature is αN phase. The thickness of the nitrided layer could reach 15 μm in 1 h at 460 °C in virtue of the high-density and high-energy nitrogen plasma, which showed an extremely high nitriding efficiency. The brittle Fe2–3N phase layer on specimen nitrided at 400 °C contributes to unsatisfactory wear resistance with severe abrasive wear behavior, however, excellent corrosion properties. The specimen nitrided at 460 °C shows superior wear resistance but degraded corrosion property due to Ti particles covered microstructure. The specimen nitrided at 420 and 440 °C possess desirable wear and corrosion performance, as well as excellent surface quality.