The decline of heavy industries happens mostly in the EU era.I was here (since 1977) and witnessed. The US pension funds moved in and bought all the medium sized companies they could, closed the factories and shipped the machines off to the eastern block countries before they even joined the EU. Textile factories went to North Africa. Nothing to do with the EU.
Hayange was an agricultural village before the De Wendels family started a steel mill there (Ignace de Wendel started 'Le Creusot'). At its peak, the mill employed about 30,000 people. The village became a town. When Fos-sur-Mer started, its fate was sealed. It was eventually sold to Mittal and renamed ArcelorMittal. 2,500 worked there. Now the mill is closed, but officially, mothballed.
That story is repeated across the EU hundreds times.