Pig Iron is Iron as soon as it has been Smelted– melted away from the rock it was found in. The raw Iron; Pig Iron, is very high in Carbon content: 3.5 – 4.5%! which makes it very brittle. Pig Iron was cheap, so the American Colonists could use much of it for their farming needs.
The reason it was called Pig Iron is because when the melted Iron ran out, it ran through several “canals” to the mold. When it cooled, the canals resembled piglets suckling from a sow (the mold). The “piglets” were whacked off the “sow” and all were sent to the Blacksmith to be formed.
I originally thought they called it pig iron because it was so stubborn to work with; like a pig. I would never have guessed the real reason!