Nickel (8.0–10.5% in SUS304) is a critical element for three key performance traits:
Austenite Stabilization: Nickel promotes the formation of the FCC austenitic crystal structure, which is non-magnetic and highly ductile. Without nickel, SUS304 would form a ferritic (body-centered cubic) structure, losing its ductility and corrosion resistance.
Corrosion Resistance: Nickel enhances resistance to reducing acids (e.g., sulfuric acid) and chloride-induced pitting corrosion (e.g., seawater). It strengthens the passive chromium oxide layer, preventing localized breakdown of the surface.
Toughness: Nickel improves low-temperature toughness, allowing SUS304 to maintain ductility even at -196°C. This is essential for cryogenic applications like LNG storage tanks.While nickel increases material cost, its benefits make SUS304 irreplaceable for applications requiring a balance of corrosion resistance, ductility, and toughness. Lower-nickel alternatives (e.g., SUS201) have reduced corrosion resistance and are not suitable for harsh environments.