deharden vs soften up

deharden

verb
  • To make or become less hard (resistant to pressure). 

soften up

verb
  • To become less committed to something. 

  • To make softer. 

  • To appease someone in order to make them more receptive to an idea or proposal. 

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