All the physical weapons mentioned in Harry Potter canon seem to be made out of silver. Voldemort conjures a silver shield in his duel with Dumbledore in OotP. The Sword of Godric Gryffindor is described as being silver, as is Bellatrix's knife. And in Tales of Beadle the Bard, the Warlock with the hairy heart cuts out his heart with a silver dagger.
Why are all of these weapons silver? Silver has to be just about one of the worst metals to make any sort of weapon out of, since it is a very soft metal. A silver blade will get dull and bend very quickly.
What's wrong with goblin-forged steel? Does silver have magical properties that would make it preferable to steel? Or did J.K. Rowling just think silver sounded cooler than steel?
Tim the Enchanter