The term 'German Steel Center' refers to the city of Essen and the region of the Ruhr in Germany. Essen is a city located in the Ruhr region, which is known for its steel production. The city of Essen is the largest city in the Ruhr region and is home to many steel companies. The Ruhr region has been an important center of steel production since the 19th century and is still a major producer of steel today.