I believe that the steel for the Sydney harbour bridge was made by Dorman Long Iron and Steel Company which was capable (at one time) of producing the longest steel beams in the world.

Technically not in Slaggy Island (which was South Bank) but in Grangetown (just down the road).

Dorman Long became British Steel and is now owned by Corus. Steel is still in production but in a much reduced capacity.

In its heyday a new town - Dormanstown - was built to house the Steelworkers. This town is now a part of Redcar.