Steel Dynamics, Inc. (SDI) is an American steel producer based in Fort Wayne, Indiana. With a production capacity of 13 million tons of steel, the company is the third largest producer of carbon steel products in the United States. It is among the most profitable American steel companies in terms of profit margins and operating margin per ton. Based on its 2021 revenue, the company ranked 196th on the 2022 edition of the Fortune 500.

Steel Dynamics was founded in 1993 by three former executives of Nucor with $370 million in funding. It began production at its $275 million Butler, Indiana, flat roll mill in 1996 and reported its first annual profit in 1997.

During the early 2000s recession, the company offered many incentive programs for employees to cut costs and improve standards and outperformed most other steel manufacturers.

In 2007, the company acquired The Techs, three hot-dip galvanization plants in Pittsburgh that coat flat-rolled steel, and OmniSource Corporation, a scrap metal processor and trader.

In 2014, the company acquired Severstal Columbus for $1.625 billion. The acquisition increased the company's production capacity to 11 million tons.

In 2016, the company acquired Vulcan Threaded Products for $126 million.

In 2016, the company began construction of a $100 million facility in Columbus, Mississippi.

In 2017, the company began a $28 million expansion of its Roanoke Bar Division.