Quote Originally Posted by Bruno View Post
Tamahagane is not necessarily harder. It all depends on the heat treatment. For a katana I thought the rule of thumb was 60-40. 60 HRC for the cutting edge and 40 for the spine.

67 would be virtually impossible to hone, and extremely brittle on a hollow ground razor. So has a knife or cutter that is HRC 67. IIRC he called it virtually defective. It was nearly impossible to hone and very brittle so the edge would crumble away when used incorrectly. I doubt a razors edge on 67 HRC would last long (if you could get it shaveready).
Yes this might or might not be true (I know there are traditional Japanese knives hardened to HRC67 which do not chip at all). I was hoping someone that owns one of those razors will fill us in