inflexibleness vs iron hand

inflexibleness

noun
  • The quality or state of being inflexible 

  • Obstinacy of will or temper; firmness of purpose that will not yield to importunity or persuasion; unbending pertinacity. 

iron hand

noun
  • Firmness, inflexibility, sternness. 

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