Supersteel bar

After obtaining a Broken Juggernaut Shell, putting one in the furnace with 90 Smithing will turn it into a Supersteel bar, which, with 99 Smithing, can be made into a Supersteel helmet, which is an item used in the quest Requiem for a Juggernaut. Alternatively, after the quest, it can be made into Supersteel bolts with 95 Smithing.