inflexible vs refractory

inflexible

adj
  • Not able to be changed or adapted to circumstances. 

  • Not willing to change, e.g. one's opinion or habits. 

  • Not flexible; not capable of bending or being bent. 

refractory

adj
  • Incapable of registering a reaction or stimulus. 

  • Obstinate and unruly; strongly opposed to something. 

  • Not affected by great heat. 

  • Difficult to treat. 

noun
  • A material or piece of material, such as a brick, that has a very high melting point. 

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