rolling mill vs steelworks

rolling mill and steelworks both are nouns.

Word	Noun	Adjective	Verb	Adverb
rolling mill	Yes	No	No	No
steelworks	Yes	No	No	No

As nouns, steelworks is a hypernym of rolling mill; that is, steelworks is a word with a broader meaning than rolling mill:

Other hypernyms of rolling mill include steel factory, steel mill, steel plant.

rolling mill (noun)	steelworks (noun)
steel mill where metal is rolled into sheets and bars	a factory where steel is made