cast iron vs pig iron

cast iron and pig iron both are nouns.

Word	Noun	Adjective	Verb	Adverb
cast iron	Yes	No	No	No
pig iron	Yes	No	No	No

cast iron (noun)	pig iron (noun)
an alloy of iron containing so much carbon that it is brittle and so cannot be wrought but must be shaped by casting	crude iron tapped from a blast furnace