Kinetics of Plasma Nitriding With Rare Earth In Nh3 At 440℃ On 2205 Duplex Stainless Steel

Abstract

This study investigates the kinetics of plasma nitriding of 2205 duplex stainless steel at 440°C, comparing samples treated with and without rare earth elements in ammonia. The combination of plasma nitriding technology with rare earth elements is expected to enhance the material properties, especially for complex metallic materials like duplex stainless steel. The thickness of the effective hardening layer after 24 hours of plasma nitriding with rare earth elements reached its maximum at 54.0 μm, showing a 30.1% increase compared to samples treated without rare earth elements. The hardness of the effective hardening layer after 24 hours of nitriding with rare earth elements (1245 HV0.025) was 5.4% higher than that of samples nitrided without rare earths (1181 HV0.025), which is 3.4 times greater than the hardness of untreated material (365 HV0.025). Energy-dispersive X-ray spectroscopy (EDS) analysis indicated that specimens treated with La had a higher nitrogen content in the austenite (FCC) phase than in the ferrite (BCC) phase. The diffusion coefficients of specimens with and without rare earth additions were 2.11×10-14 m2·s-1 and 3.34×10-14 m2·s-1, respectively. The addition of La significantly increases the intensity of the γN peak in the nitride layer, effectively reduces the formation of nitrides (γ′-Fe4N, ε-Fe2-3N, and CrN), and yields finer and more uniform grain sizes. The γN phase, with a higher nitrogen atom concentration, exhibited improved corrosion resistance. After 8 hours of plasma nitriding with rare earth elements, the wear rate was 1.14 × 10-7 g·N-1m-1, representing a 24.5% reduction compared to samples nitrided for 8 hours without rare earth elements. The primary wear mechanisms identified were adhesive wear and oxidation wear.

Keywords: 2205 duplex stainless steel, Plasma nitriding, Rare earth, kinetics, Wear resistance