Why Stainless Steel Never Rusts But a Nail Does

Leave an iron nail outside and it rots. Your stainless steel sink shrugs off water for decades.

They're both mostly iron. So why does one crumble into orange rust while the other stays mirror-bright?

Rust forms when iron meets oxygen and water, building flaky iron oxide that falls away and exposes fresh metal underneath. The rot never stops. Stainless steel cheats. It's iron blended with at least ten percent chromium. The moment chromium touches air, it grabs oxygen and forms an ultra-thin, invisible layer of chromium oxide across the whole surface. Unlike rust, this layer is dense, tightly bonded, and locks the metal away from the air. Scratch it, and it instantly reseals itself, because the fresh chromium underneath reacts again in seconds.

So stainless steel isn't rust-proof. It's actually rusting on purpose, constantly, in a microscopic skin too thin to see, that shields everything below it.

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