Well-made stainless steel will generally not rust under normal atmospheric conditions. A couple of factors lead to the corrosion of stainless.

1. Cheap stainless steel. Stainless steel uses chromium to produce an adhesive, non-scaling oxide. This provides the “stainless" effect. Most grades also contain a considerable content amount of nickel. Both chromium and nickel are expensive. People making cheap stainless will try to cut the amounts used to a minimum. If the overall chromium content is too low… or if localized variations in the chrome content create spots with depleted chrome, these spots will corrode.

2. There are conditions, such as severe acid rain, which can corrode some of the less resistant grades of stainless.

Although stainless steel is known for its corrosion resistance, it can still corrode under certain conditions. Some cleaning agents, especially those containing chlorides or abrasive particles, can damage the protective oxide layer on stainless steel and promote rusting. Besides, scratches, gouges, or other forms of mechanical damage to the stainless steel surface can compromise the protective layer and make the material more prone to rust. While stainless steel relies on oxygen to maintain its passive film, certain conditions that limit the availability of oxygen can lead to corrosion. It is known as anaerobic corrosion.

While stainless steel is known for its corrosion resistance, it can still corrode under certain conditions. Here are some common causes of rust in stainless steel, including exposure to chlorides, crevice and pitting corrosion, high temperatures, contamination during fabrication, and poor passive film formation.

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