The city most famously known for steel production is Pittsburgh, Pennsylvania. Nicknamed the "Steel City," Pittsburgh became the powerhouse of steel manufacturing in the late 1800s through the mid-20th century. At its peak in the 1940s, Pittsburgh produced over 60% of all steel in the United States, largely propelled by innovations from Andrew Carnegie and the development of the Carnegie Steel Company. Its strategic location at the convergence of three rivers facilitated the easy transportation of raw materials and finished steel products. Pittsburgh's legacy in steel production is a defining part of its identity, with its economy, culture, and history deeply tied to the steel industry.

Currently, Gary, Indiana, is also known as a major steel production center in the U.S., hosting one of the largest integrated steel mills, Gary Works, operated by U.S. Steel. This city leads contemporary steel production due to its advantageous location on Lake Michigan and proximity to major transportation networks.

Summary

• Pittsburgh, PA: Historically the dominant city known as the "Steel City" for leading U.S. steel production especially in the 19th and 20th centuries.
• Gary, IN: Currently a leading city for steel production with major integrated mills active today.

Thus, Pittsburgh is most famously synonymous with steel production historically, while Gary is a present-day steel production hub.