Definition
Crude iron as it comes from a blast furnace, cast into rough oblong blocks called pigs. Pig iron has a high carbon content (typically 3–4%) and various impurities, making it brittle and unsuitable for direct structural use. It serves as the raw stock for producing cast iron, wrought iron, and steel through further refining.
Plain English
The rough, basic form of iron that comes straight out of the furnace. It's not ready to use yet — it has to be refined into steel or other useful metals first.
Context Anchor
Seen in aircraft maintenance and materials discussions when explaining how iron and steel are produced.
Derivation
The name comes from the old method of casting molten iron into a row of small molds branching off a central channel. The arrangement looked like piglets feeding from a sow, so the central channel was called the 'sow' and the side blocks 'pigs.' The term stuck.
Why Pilots Care
A pilot or mechanic may see the term while studying aircraft materials. Knowing that pig iron is raw starting material helps prevent confusing it with finished steel or cast iron used in actual parts.
Intuition Check
Pig iron does not mean iron from an animal or a special aircraft part. Here, “pig” refers to the old mold shape used to cast raw iron into small bars.
Example Sentence 1
The steel used in aircraft engine crankshafts begins as pig iron, which is then refined and alloyed to achieve the required strength.
Example Sentence 2
Early radial engines often used pig iron for heavy structural sections before lighter alloys became common.