scrap iron vs Fe

scrap iron and Fe both are nouns.

Word	Noun	Adjective	Verb	Adverb
scrap iron	Yes	No	No	No
Fe	Yes	No	No	No

As nouns, Fe is a hypernym of scrap iron; that is, Fe is a word with a broader meaning than scrap iron:

scrap iron: iron to be melted again and reworked
Fe: a heavy ductile magnetic metallic element; is silver-white in pure form but readily rusts; used in construction and tools and armament; plays a role in the transport of oxygen by the blood

Other hypernyms of scrap iron include atomic number 26, iron, scrap metal.

scrap iron (noun)	Fe (noun)
iron to be melted again and reworked	a heavy ductile magnetic metallic element; is silver-white in pure form but readily rusts; used in construction and tools and armament; plays a role in the transport of oxygen by the blood