plate iron vs tank iron

plate iron and tank iron both are nouns.

Word	Noun	Adjective	Verb	Adverb
plate iron	Yes	No	No	No
tank iron	Yes	No	No	No

As nouns, tank iron is a hyponym of plate iron; that is, tank iron is a word with a more specific, narrower meaning than plate iron:

plate iron: a plate of iron
tank iron: plate iron that is thinner than boilerplate but thicker than sheet iron or stovepipe iron

Other hyponyms of plate iron include boilerplate, sheet iron, stovepipe iron.

plate iron (noun)	tank iron (noun)
a plate of iron	plate iron that is thinner than boilerplate but thicker than sheet iron or stovepipe iron