nonchalance vs sangfroid

nonchalance

noun
  • Indifference, unconcern; carelessness; coolness; disregard, detachment. 

sangfroid

noun
  • Composure, self-possession or imperturbability especially when in a dangerous situation. 

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