What makes stainless steel stainless

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The steel becomes stainless because any scratches or breaks in the layer are quickly repaired as new oxide forms, preventing corrosion.

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Q.� Is stainless steel completely untarnished

A.� Although stainless steel is amazing stuff, it does have its limitations mainly because its blemish free properties only really work in air where oxygen molecules are free. It isn't much use underwater because it needs to react with free oxygen to repair itself.

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Q.� Why would steel rust normally

A.� The reason chromium and oxygen form such a stable layer is because their atoms are of a similar size and sit comfortably together.

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Whereas without the addition of chromium, steel and oxygen have very uneven atoms that don't fit together easily. As a result, the oxide sits loosely on the steel, flaking off as rust.

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Q.� When was stainless steel invented

A.� In 1913, by accident. Its inventor, Harry Brearley, was working for Thomas Fearth and Sons, a company based in Sheffield. He came across the now famous alloy while experimenting with different ways of making rifle barrels. After much resistance from his employers the steel alloy was eventually used to make cutlery, making Sheffield the 'steel city'.

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by Lisa Cardy