Will stainless steel rust?
Stainless steel is naturally corrosion-resistant, but it is not immune to rust. While it is less prone to rusting than conventional steels, exposure to damaging chemicals, saline, grease, moisture, or heat for extended periods of time can cause corrosion. The likelihood of corrosion depends on the chromium content of the stainless steel, with higher chromium content reducing the risk of rust formation.
Stainless steel basics
To understand why stainless steel is rust-resistant, and how this resistance breaks down, it is helpful to understand how these alloys are different than other steels.
Stainless contains a minimum of 10.5% chromium. This chromium reacts quickly with surrounding oxygen to form a thin oxide layer on the steel’s surface. Unlike iron oxide, which often is in the form of flaky and corrosive rust, the chromium oxide clings to the steel. It therefore acts as a protective barrier. The chromium oxide is known as a passive film which seals the iron in the alloy away from the air and water in the environment. This film gives stainless its rust-resistance.
Stainless steel is low maintenance, and its resistance to oxidation and staining makes it an ideal material for many applications.
There are four main types of stainless steels: austenitic, ferritic, martensitic, and duplex. Austenitic stainless steel is dominant in industry and comprises over 70% of total stainless steel production. Its properties include a maximum of 0.15% carbon and a minimum of 16% chromium, yielding very strong protection against rust. Ferritic stainless steel has reduced corrosion resistance compared to austenitic grades, but fares better than martensitic stainless steel. Duplex stainless steels have high resistance to localized corrosion particularly pitting, crevice corrosion, and stress corrosion cracking.
