Board Thread:General Discussion/@comment-24.247.108.45-20130607213225/@comment-34316223-20180112235534

My first guess was going to be Manganese it's one of the most basic alloys and is present in nearly every modern 'good' steel. Tough as several users pointed out, Corundum is an actual mineral, so "corundum ingot" could just be a pet-name for aluminum. Other alloys in specialty steels are Chromium, Nickel, and Molybdenum. Might also be Silicon or another rare-earth metal.

Of course it is a little fictional, so we can't be TOO sure. Unless we get an official answer, I'm going to have to say Aluminum. Could be either Manganese or Silicon, which would explain its purpose as an alloy, but with nothing you can make out of just Corundum.

Maybe we'll find out in the next Elder Scrolls game