cast iron vs pot metal

cast iron and pot metal both are nouns.

Word	Noun	Adjective	Verb	Adverb
cast iron	Yes	No	No	No
pot metal	Yes	No	No	No

As nouns, pot metal is a hyponym of cast iron; that is, pot metal is a word with a more specific, narrower meaning than cast iron:

cast iron: an alloy of iron containing so much carbon that it is brittle and so cannot be wrought but must be shaped by casting
pot metal: cast iron used for making cooking wares

Other hyponyms of cast iron include alloy cast iron, alloy iron.

cast iron (noun)	pot metal (noun)
an alloy of iron containing so much carbon that it is brittle and so cannot be wrought but must be shaped by casting	an alloy of copper and lead used especially for making large pots
	cast iron used for making cooking wares