 Low-grade ore (taconite) shipments continued, boosted by new taconite pellet technology, but ore shipments were lower overall.In the 1970s the United States experienced a steel crisis, a recession in the global steel market, and like many American cities Duluth entered a period of industrial restructuring.In 1981, US Steel closed its Duluth Works plant, a blow to the city's economy whose effects included the closure of the cement company, which had depended on the steel plant for raw materials (slag).