As for fire, we have an open fire at home and I don't mind putting this test piece into it, I may be month or so until it gets cold enough in the house to light it, you may have to wait for those results, the best I can do is phone the supplier of the metal and ask what the metal spec was for our best guess at a melting point, although it will of course soften before that.
quick search says fireplaces can be 500F-1100F depending on fuel etc. house fires can be 1100F. a propane torch can hit 2000F. so if you can test it with propane torch (which are very cheap) and heat it to red hot say and have it survive that would be a good test.