|The two photomicrographs on this page are of the dark
masses in the specimen on the preceding page, but were each taken at
The material is wrought iron ... quite an anachronism even in 1960 when this specimen was obtained by M.I.T.
The first photomicrograph on the preceding page is a longitudinal section (note the aspect ratios of the slag stringers) while the second is a transverse section.
Wrought iron was made by forging or "puddling" a spongy ball of mixed slag and pig iron, which squeezes out excess oxide and oxidizes the carbon out of the pig iron at the same time as the iron is being consolidated.
|Eventually a red hot mass of low carbon iron is obtained,
once no more slag can be exuded. Hot working stretches the oxide
stringers while the workpiece is being elongated. The properties
are therefore quite anisotropic, the fracture of such a piece being as
fibrous as a piece of green wood.
On this page, the upper photomicrograph is a longitudinal section, while the one at left is a transverse section.
Why aren't these microstructures directional also ?
Pause to formulate an answer and then take a look.
|The slag is a two
phase mixture of iron oxide and silica, and it recrystallizes easily at
the hot working temperature.