key up vs steam up

key up

verb
  • To raise the intensity, excitement, tension, etc., of. 

  • To produce nervous tension in. 

  • To raise the pitch of. 

  • To raise (the whole ring of an arch) off its centering, by driving in the keystone forcibly. 

steam up

verb
  • To become steamy. 

  • To become coated with condensation. To fog up. 

  • To bring (a steam boiler) up to working steam pressure. 

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