Effect of Conventional and Cathodic Cage Plasma Nitriding on the Mechanical and Corrosion Behavior of AISI 420 Martensitic Stainless Steel

AISI 420 martensitic stainless steel was treated via conventional plasma nitriding (PN) and cathodic cage plasma nitriding (CCPN) at temperatures ranging from 400 to 500 °C for 5 h to enhance surface properties. X-ray diffraction and scanning electron microscopy analyses confirmed uniform nitride layer formation, and microhardness measurements showed a peak hardness of 1270 HV₀.₅ for PN at 500 °C. Notably, CCPN at 450 °C achieved similar hardness (1011 HV₀.₅) alongside excellent adhesion (HF1-HF2), highlighting the effectiveness of the cathodic cage technique. Electrochemical impedance spectroscopy and open-circuit potential tests in 3.5 wt % NaCl showed improved corrosion resistance in all nitrided samples compared to the untreated steel. These results indicate that specific nitriding conditions, particularly PN at 450 °C and CCPN at 400 °C, achieve an optimal balance of hardness, corrosion protection, and interfacial toughness while preserving the substrate's inherent microstructure.