Microstructure and high-temperature oxidation resistance of wire and arc additively manufactured Si-containing 9Cr oxide dispersion strengthened steel

Three 9Cr oxide dispersion strengthened (ODS) steels with addition of 0.5-2 wt.% Si were fabricated by wire and arc additive manufacturing (WAAM) technique in this work. Their microstructures and oxidation behavior at 800°C were systematically studied. The WAAM-processed steels exhibited refined martensite lath bundles due to rapid solidification. Increasing Si content (1–2 wt.%) further refined martensitic laths, enhanced dislocation density, and promoted the formation of high-density (∼6.54 × 10 23 m -3 ) Y 2 SiO 5 nano-oxides (∼3.43 nm) within the matrix. Notably, the 2Si steel demonstrated exceptional oxidation resistance, with a rate of 0.36 × 10 -3 mg·cm -2 ·h -1 , surpassing most commercial heat-resistant steels. This improvement is attributed to a tri-layered Cr 1.5 Mn 1.5 O 4 /Cr 2 O 3 /SiO 2 (amorphous) oxide scale, which effectively inhibits oxygen inward diffusion.