come forward vs step up

come forward

verb
  • Used other than figuratively or idiomatically: see come, forward. 

  • To offer help or information (especially, about a crime). 

step up

verb
  • To assume or take responsibility. 

  • To increase, augment, or advance, especially by one or more steps. 

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