Cryogenic Heat Treatment

Jon Siegel replies: A recent article in More Woodturning magazine contained an article on the scientific testing of various types of steel used in woodturning chisels.

The results showed that cryogenically treated steel, while better than M2 high speed steel was not better than the other high alloy or PM types.

Garrett Hack replies: Cryogenic treatment makes clarinets sound better, women’s nylon stockings last longer, and as part of the tempering process for certain high quality steels, makes edges that stay sharp longer. Noticeably longer, which is why Lie-Nielsen and Lee Valley are doing it on their A2 blades. Steel metallurgy is so complicated the guys that do this stuff can’t even give a reasonable explanation. The simple version: By cooling the steel to minus -300° (or thereabouts) the steel crystals condense and pack in more tightly. Denser steel makes for a tougher edge.

Dave Anderson replies: The short answer to your question is, “It depends on who you ask.”
Generally for woodworking edge tools like plane irons and chisels, cryogenic treatment is used only on A-2 tool steel. This is not to say it can’t be used on O-1 or any other steel, but it is rarely done in woodworking tools.

The most critical things about heat treating are getting the material to the right critical temperature for the correct dwell time (thermal soak) and then quenching the material quickly and correctly to “set” the hardness. Where cryo treating really shines is in completing the transition of the carbon (carbides) to the form necessary for the tool to take and hold an edge. It is the carbon in the tool steel which has the primary responsibility for providing the ability of the steel to harden.

Stated another way, cryo treatment can correct or complete the process when there has been a problem in the standard treatment process.

Another answer to your question is that some studies by metallurgists claim cryo treatment is beneficial and other studies claim it makes no difference provided the tool has been properly treated. This is a complex field and about the only definitive correct statement is that it might make a difference. The jury is still out and we might not see an answer for years.