Linking Microstructure and Processing Technology in Wrought Iron from the Turn of the Twentieth Century

Wrought iron is ubiquitously recognized in ornamental applications and is also known as a material of antiquity with archaeological evidence dating back approximately 5000 years. While this material is simply referred to as wrought iron, the raw materials, processing technologies, and final products varied drastically over the centuries that wrought iron was produced. Perhaps a lesser known period of wrought iron production is post Industrial Revolution, around the turn of the twentieth century. During this time period, wrought iron was produced by a transient liquid phase processing method, known as puddling. While the adoption of steel making technology eventually eclipsed production of puddled wrought iron in the first half of the twentieth century, there was a brief period when wrought iron, cast iron, and steel were distinct engineering materials. With improvement in steel making, the use-case for puddled wrought iron narrowed and some of the attributes associated with wrought iron were discovered to be less significant. The present work delves into the historical process of puddling and discusses effects that this process had on the microstructure of wrought iron making it distinct from cast iron and steel. Microstructure analysis and mechanical testing of wrought iron artifacts are presented to support discussion and showcase the microstructure and performance of puddled wrought iron. State of the art characterization techniques including light-optical microscopy and scanning electron microscopy with electron backscatter diffraction and energy dispersive x-ray spectroscopy reveal the anisotropic microstructure and chemical distribution in the ferrite and slag. X-ray diffraction techniques were used to verify phases in the microstructure and to provide a quantitative measurement of grain size and carbon concentration in ferrite. Mechanical testing results indicate the strength of the wrought iron samples. These modern characterization techniques are combined with a historical processing perspective to draw connections between processing, structure and properties.