Nippon Steel to invest $3 billion in new U.S. Steel hot-strip mill

New York – United States Steel, which was acquired by Japan’s Nippon Steel, said Thursday that it plans to invest about $3 billion to build a hot-strip mill at its Mon Valley Works in Pennsylvania.

The project is expected to be the largest under Nippon Steel’s commitment — made as part of its acquisition of U.S. Steel — to invest $11 billion by 2028.

A hot-strip mill rolls steel slabs heated to high temperatures into thin sheets.

U.S. Steel aims to begin production at the mill in the second half of 2029. The site will allow for expanding output of automotive steel sheets, one of the areas in which Nippon Steel excels, and other products to bolster the U.S. company’s competitiveness.

Nippon Steel had initially planned to invest up to $2.5 billion in Mon Valley Works over three years. The projected cost has risen to reflect higher labor costs and inflation.

Nippon Steel completed its acquisition of U.S. Steel in June 2025.

The Japanese steelmaker’s domestic operations have struggled with weak market conditions caused by excess production in China and rising costs stemming from tensions in the Middle East.

Against this backdrop, U.S. Steel contributed to Nippon Steel’s return to the black in the April-June quarter of 2026, emerging as what the Japanese company called its biggest earnings driver. The acquisition appears to be beginning to pay off.