The Microstructure of Historic As-Cast Fe Alloys

This begins with 19th C AD Musket Barrel made at the Henry Gun Factory near Nazareth, Pennsylvania. The picture shows scale (iron oxide) at the surface due to hot forging the wrought iron. Below the surface scale is a zone of columnar ferrite grains due to decarburization. Below that zone, the ferrite grains are smaller and equiaxed in shape. At the bottom of the image, the ferrite grains are larger with evidence of segregation, probably due to less heat and forging deformation. Some small black particles are visible (easier to see if the specimen is not etched) in the ferrite grains. These are slag particles. Next is a Roman nail found near Vicenza, Italy. The first 2 pictures are as-polished and we can see carburization in the nail head, and then slag in the shaft with a fine ferrite matrix. The next image shows a change in the microstructure across the head. Some patches of as-quenched martensite are present in the carburized head, with pearlite. Some silicate inclusions are also present. The shaft contains equiaxed ferrite grains with Neumann bands and slag particles.

Next we see helmets and armour from various countries. The first is a 17th century Japanese helmet with some intergranular and transgranular brittle cleavage fractures. The helmet contained some large sections of slag. Etching the cross section revealed columnar and duplex grain structures ast the fracture face. The helmet also contained grain-boundary cementite films.