The Norse didn't have mythical metals, they had mythical artifacts. In some cases, a sword is described as forged by giants or some god, if that counts. Keep in mind that many myths, Norse or otherwise, simply were misunderstood or unknown science. Others were generationally migrated to different areas. Many are simply tales that were passed down for many years, thousands in some cases, and altered through time as the stories were retold.
Norse mythology has been referred to as gods versus giants with men as either sufferers or benefactors, depending on the tale. You might want to look at norse-mythology.net as a source. There's also a guy (gal?) who writes Norse mythology books, McCoy is the name I think (been a while).
I guess it depends on your story as to what you need to write but if you take a current metal commonly used and roll it back a thousand years you may find what you need.
Jeff