Steel rusts.

You need to add chromium to it to make it stainless steel.

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However if you happen to pull a piece of metal out of a field and make it into a plough you may be lucky enough to have picked a piece of an iron meteorite.

Some people say that these are what have given rise to the magic swords of legend, the idea being that the iron meteorites have a good base metal low on carbon to make a nice steel sword just by being wrought into shape.