Steel Dynamics, Inc., sometimes abbreviated as "SDI", is a steel producer based in Fort Wayne, Indiana.

With a production capacity of 11 million tons, Steel Dynamics is the 4th largest producer of carbon steel products in the United States. SDI is among the most profitable American steel companies in terms of profit margins and operating profit per ton.

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 galvanizing plants in Pittsburgh that coat flat-rolled steel, and OmniSource Corporation.

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.

In 2012, Richard Sarver, an employee of the company's Roanoke Bar Division, wrote Taking the Heat - A Steelworker's Story, a 271-page memoir based on his 32 years of service at the Roanoke Electric Steel Corporation, which was acquired by Steel Dynamics in 2006.

Along with other steel producers, the company was a defendant in a price-fixing lawsuit. The case was settled and Steel Dynamics agreed to pay $4.6 million in 2016.