The Steelium Z (Japanese: ハガネＺSteel Z) is a type of Z-Crystal introduced in Pokémon Sun and Moon. It is the type-specific Z-Crystal associated with the Steel type and allows Pokémon to upgrade their Steel-type moves to Z-Moves.
A Steelium Z appeared in SM109, where Hapu presented Ash with a box full of type-specific Z-Crystals and allowed him to choose one of them as his prize for defeating her. Ash let Pikachu make the choice, and he chose the Steelium Z.
Another Steelium Z appeared in SM114, where it was one of the Z-Crystals stolen by a Pheromosa.