intrude vs step in

intrude

verb
  • To force in. 

  • To thrust oneself in; to come or enter without invitation, permission, or welcome; to encroach; to trespass. 

step in

verb
  • To get involved; to act 

  • To act as a replacement or substitute. 

How often have the words intrude and step in occurred in a corpus of books? (source: Google Ngram Viewer )