The mills you're seeing reopen are mostly specialty casting mills which tend to be small in size. Pittsburgh has only a few steel mills anymore. USS closed mills all across the country from the mid seventies on, mostly due to technology improvements in the Iron and Steel making processes.What was once done all over the country is now done in maybe three or so mills now....tariffs hurt production output that's been siting idly by....for big steel, its like running a car at 40 mph.....with already operating mills....just ramp it up.
Which also brings up a question of why did our gov't do this to big steel in the first place? We allowed dumping here and this is why many mills closed.
At Edgar Thomson Works, where I did 12 years hard time, the Open Hearth furnaces, which made around 240 ton of steel in eight hours were replaced by the BOP (basic oxygen process) which placed an oxygen lance down into the steel, produced about 240 ton in only forty five minutes. They poured the molten steel into ingot molds which had to cool, then be reheated and rolled out into slabs in a slabbing mill (where I worked). They eliminated the rolling mill by directly pouring the molten steel into what is called a continuous caster which makes slabs continuously as long as you got molten steel feeding into it, slabs of different sizes and lengths are made to order....poured,cast, cooled and cut to about any size or length you want. Not all steel can be cast, but even at that, you only need maybe a couple mills in the country to do that function.
Even in the blast furnace, which Iron is made, has cut production time drastically using the 'direct reduction' process.
So, for the most part, any mill that's coming back most likely are making specialty alloys and such, on a small time basis, probably in electric arc furnaces.
). The inferior metal compromised our military might. 
