casework vs welfare work

casework and welfare work both are nouns.

Word	Noun	Adjective	Verb	Adverb
casework	Yes	No	No	No
welfare work	Yes	No	No	No

As nouns, welfare work is a hypernym of casework; that is, welfare work is a word with a broader meaning than casework:

casework: close sociological study of a maladjusted person or family for diagnosis and treatment
welfare work: an organized activity to improve the condition of disadvantaged people in society

Other hypernyms of casework include social service.

casework (noun)	welfare work (noun)
close sociological study of a maladjusted person or family for diagnosis and treatment	an organized activity to improve the condition of disadvantaged people in society