Why quench them in liquid nitrogen before they go into temper cycles? These came out at 320 degrees below zero (F). Bill Harsey (who just recently finished his new shop - looks good sir!) advises, "The shop air hits the blades and cools, it's frozen fog falling from the blades."
According to Bill Harsey (the designer of the Yarborough Knife and the Neil Roberts Warrior Knife, and a man who has worked with Al Mar, Col. Rex Applegate and Col. Nick Rowe), you quench them in liquid nitrogen because:
- Tool steels harden or soften without changing chemical composition depending on how they are heated and cooled. How they are heated and cooled (times and temps) depends on the alloying elements like carbon, vanadium, chromium and in this case niobium too. Phases are the names given the particular molecular conditions the steel is in as a response to heating or cooling.
The below names describe some of these phases. - Heat treating is how we get optimum performance from a given tool steel for a given task.
- the deep freezing (cryogenic) step mechanically converts the retained austenite into martinsite and pearlite resulting in higher transverse bend fracture strength (pry bar strength) and better edge holding.