Investigation of the effects of shot peening, aging, and low temperature carburization on corrosion performance and hardness of custom 465 stainless steel

This study investigates the effects of shot peening, aging, and low-temperature carburization on the microstructure, corrosion performance, and hardness of Custom 465 stainless steel. Custom 465, a precipitation-hardenable martensitic stainless steel, offers high strength and corrosion resistance, yet surface treatments are often required to enhance wear performance in aggressive environments. Three material conditions were examined: untreated (as-received), low-temperature carburized, and shot-peened followed by aging (H950). Microstructural characterization showed that untreated samples contained uniform lath martensite with films of retained austenite. Carburized samples developed a ∼40 µm carbon-enriched surface layer, while shot peening produced a ∼45 µm plastically deformed layer with refined lath morphology. Corrosion testing was performed in an SO 2 -enriched salt spray environment (ASTM G85 Annex A4) under simultaneous galvanic-crevice, galvanic-only, and individual exposure conditions. Untreated samples were most susceptible to localized corrosion, exhibiting dense and deep pitting near the pin-contact region when galvanically coupled with Ti-6Al-4V. Carburized specimens showed markedly reduced pit density and severity, whereas shot-peened and aged samples displayed no visible pitting under any exposure scenario, indicating superior passive-film stability. Hardness measurements demonstrated a progressive increase from the untreated condition (∼285 HV) to carburized (∼550 HV), shot-peened (∼310 HV), and shot-peened plus aged (∼695 HV) samples. Surface hardening was confined to the near-surface region except for the shot-peened and aged condition, where both surface and core hardness increased. Overall, the results confirm that appropriately surface-engineered Custom 465 can provide enhanced corrosion resistance and hardness, demonstrating strong potential as a cadmium-free replacement material for corrosion-sensitive structural components.