How do I interpret the type of steel used in a tool?
There are many types of standards which provide Steel Grades. The one you mentioned seems to be of SAE Steel Grades. 


  400  --> is a 400 series steel 
  
  C    --> has Carbon 
  
  C    --> has Chromium


All steels of 4xx are usually Molybdenum steels and have Ni and Cr apart from Carbon