The strongest material on Earth, fictional substances included, is a hockey puck. It's true. After surviving against the red hot nickel ball and going toe to toe with liquid nitrogen, it totally edges out adamantium and whatever T-1000 was made out of. Here's another battle that it holds up admirably to: thermite, which is basically fire transported in from Mordor.
The essentially never ending hot hot fire burn of thermite (pyrotechnic composition of metal powder fuel and metal oxide) totally burns the hockey puck but the hockey puck still does an amazing job in surviving. Hockey puck material is boss.