Tribological Properties of AISI 420 ESR Stainless Steel Modified by Sequential Boriding and Nitriding

This study investigates the effects of surface thermochemical treatments using boriding, nitriding, and boronitriding on the microstructure and mechanical properties of martensitic stainless steel AISI 420 ESR. Powder-pack boriding, gas nitriding, and sequential boronitriding processes were applied to enhance surface hardness, wear resistance, and adhesion. The microstructural and mechanical properties of the surface samples were analyzed using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, microhardness, and nanoindentation testing. Tribological behavior was analyzed using a pin-on-disk tribometer under dry-sliding wear conditions, with applied normal loads of 5 N and 10 N and a sliding distance of 1000 m. The results showed that the borided samples exhibited the highest surface hardness, up to 1182 HV0.05, as well as brittle fracture and spallation with poor adhesion, while the boronitrided layer offered excellent adhesion. The boronitriding condition demonstrated a synergistic balance, combining high wear resistance (5.92 × 10−7 mm3N−1m−1 and 4.96 × 10−7 mm3N−1m−1) and reduced friction (~0.78 and ~0.67) for loads of 5 N and 10 N, respectively, without brittle fractures on the coating layer. These results confirm that duplex coating treatment is an effective strategy for improving the surface performance of AISI 420 ESR components subjected to severe operating conditions.