step in vs supervene upon

step in and supervene upon both are verbs.

Word	Noun	Adjective	Verb	Adverb
step in	No	No	Yes	No
supervene upon	No	No	Yes	No

As verbs, supervene upon is a hypernym of step in; that is, supervene upon is a word with a broader meaning than step in:

Other hypernyms of step in include replace, supersede, supplant.

step in (verb)	supervene upon (verb)
get involved, so as to alter or hinder an action, or through force or threat of force	take the place or move into the position of
act as a substitute