Which element is the primary austenite-nucleating alloying addition for non-magnetic behavior in stainless steel when over 6%?

Which element is the primary austenite-nucleating alloying addition for non-magnetic behavior in stainless steel when over 6%?

• A. Chromium
• B. Nickel
• C. Iron
• D. Vanadium

Answer: (B)

Nickel is the element that primarily stabilizes the austenite (gamma) phase in stainless steels. When nickel content exceeds about 6%, the austenite phase is stabilized at room temperature, and the steel becomes non-magnetic because austenite is essentially non-magnetic compared to ferrite or martensite. This is why many austenitic stainless steels (like the common 300-series) use significant nickel, typically in the 8–12% range, to ensure non-magnetic, fully austenitic structure. Chromium mainly contributes corrosion resistance and can promote ferrite if used without nickel, iron is the base metal, and vanadium strengthens by forming carbides rather than stabilizing austenite.