what is steel a mixture or a compound

Steel is an alloy and is considered as a mixture since it shows the properties of its constituents and can have variable composition.
 

Steel is considered a mixture rather than a compound because the iron does not chemically bond with the carbon and other components. Instead, in simple iron-carbon alloys, the carbon atoms are small enough to intersperse themselves within the open spaces of the iron crystal.

Steel is a mixture. It is a mixture because it contains atoms and molecules of varying types, making intermolecular bonds that are not as strong as those found in compounds.