If you’ve responded to your cat licking metal in the past by giving them food or a treat, then they may also begin licking metal every time they feel hungry or want a treat.
A curious cat is very likely to investigate something with her mouth. Cats have sensitive tongues, so licking or chewing on an object may provide them with some essential information on what the thing is.
A cat’s tongue is very sensitive to textures, so she may begin licking nearby metal objects because it is an easy way to both satisfy her boredom and feels good at the same time.
Of course, the best way to keep your cat from licking or consuming metal objects is to remove all access to the metal objects in the first place.
Providing them with plenty of toys and frequent playtime to keep them occupied can help prevent them from seeking out other ways (like licking metal) to cure their boredom.