steel
A staircase whose supporting framework is made from steel members, regardless of its nonstructural finish.
A steel staircase is a set of steps in a built object whose supporting framework is built of steel, a strong iron-based alloy containing carbon. The tensile strength of steel makes it suitable for almost any stairway configuration, and it is one of the best materials for freestanding staircases (like many helical stairways for example). It is also useful for staircases that bridge a wide space without supporting columns in the middle.
The steel members carry the steps and stabilize the stairway. A coating or covering over them does not change their structural material.
Steel is distinct from the cast or wrought iron covered by iron staircases. Both can provide metal framing, but their material identities differ.
