Tennessee Coal & Iron Company, Ensley Works, West of residential & commercial districts, Birmingham, Jefferson County, AL

Significance: The Ensley steel mill is historically significant for a variety of "firsts" which occurred there. The first duplex steel in the United States was made here in 1899. So named because it was first produced in a Bessemer convertor then transferred to open hearth furnaces, the duplex process was later adopted widely at many major steel mills including the Duquesne plant of U.S. Steel. This steel was made into the first railroad rails produced from the open hearth process in the United States. The Ensley open hearths were also some of the first tilting open hearths employed in the United States. While these features make the site nationally significant, historically, the blast furnace plant is also important. These furnaces were the first blast furnaces in the District to produce basic iron on a large scale and the product was so competitive that it was sold to the Carnegie Steel Company for their steel furnaces in Pittsburgh. Since they were used to make basic pig iron from Red Mountain ore, in contrast to most other furnaces in the District which produced foundry iron, they developed a body of practice and design that was different from their local counterparts as well as the basic iron blast furnaces from other regions. While the differences were subtle, they were substantive and by the time the plant was acquired by U.S. Steel, it had become a basis of comparison with furnace design in other regions. Several technical reports issued by U.S. Steel show the designs of the Ensley furnaces alongside such notable blast furnaces as those at South Chicago, Edgar Thomspon and Duquesne. When the thin-walled furnace design was introduced from Germany, U.S. Steel rebuilt one of the Ensley furnaces to these specifications making it an important prototype for the corporation.
Survey number: HAER AL-52
Building/structure dates: 1888 Initial Construction