Actually, the US steel industry isn't what it was. It took a major hit in the 70's, especially in western PA and the midwest. Now the US is having to compete mightily with Japanese steel. There was actually quite the trade dispute about it for a while, with the US claiming that the Japanese were trying to flood the US market with Japanese steel.
While the steel industry took a hit, it didn't die by a long shot... The industry had to deal with foreign competition for the first time like Anton mentioned, and that forced an overinflated industry with a chokehold to deal with something it hadn't up till that point... It shut down a lot of various steel companies, forced others into combining, but it didn't spell doom for steel like history books sometime say. My home town still has two operational specialty steel mills in it, there is one of the nation's larger plants up the river in another town, and further down the Allegheny is the Allegheny Technologies headquarters plant...
That's just some of the plants in Western PA, which are still considered the top employers for the region. There's others... Others still simply moved to areas that would cost less to produce, but kept them in the U.S. The mills aren't one in every town in the area out near Pittsburgh anymore and that's the visible sign of the hit the industry did take, but they're still plentiful, and U.S. Steel is still a strong industry despite what competition they were forced to deal with.