Raw steel production in the country's Great Lakes region plunged to 648,000 tons after two Northwest Indiana blast furnaces went offline.
Overall U.S. output ticked down by 0.2 percent in the week that ended Saturday, according to an American Iron and Steel Institute estimate.
Local production declined by 44,000 tons, or 6.3 percent.
Output fell after ArcelorMittal idled the No. 7 furnace at ArcelorMittal Indiana Harbor East in East Chicago for a major maintenance project. The No. 8 blast furnace at Gary Works also went down after a disruption.
Most of the raw steel production in the Great Lakes region takes place in Indiana and the Chicago area.
Production in the Southern District, typically the country's second biggest steel-producing region, rose to 638,000 tons, up from 596,000 tons a week earlier.
Total domestic raw steel production last week was about 1.85 million tons, up from 1.845 million tons a week earlier.
U.S. steel mills had a capacity utilization rate of 76.9 percent last week, up from 76.7 percent a week earlier. The capacity utilization rate had been 76.1 percent at the same time last year.
Domestic mills have produced an estimated 43.2 million tons of steel this year, a 0.2 percent decrease from the 43.3 million tons produced during the same period last year.
U.S. steel exports rose by 3.8 percent to 1.08 million net tons in April, the second straight month of growth, according to the American Institute for International Steel.
Exports to Mexico grew 6.9 percent to 368,215 net tons, and exports to the European Union rose 16.4 percent to 34,942 net tons. U.S. exports to the Dominican Republic soared to 24,199 net tons, a 13-fold increase from March to April.