440c @ 75degrees over???

[David Loukides]

What is the proper way to deal with a 440c blade that went thru the hardening cycle at 1975deg? It went in with the CPM154 batch by mistake It hardened at Rc57 and after 3 tempers at 350deg and 1 cyro -95degs it was Rc61
What the heck do you think is going on???

 

[Barkes Knife Shop]

Well Now: 61Rc is good in my book. Somethings going on there. Have a great and safe knife day. :thumbup:

 

[David Loukides]

Doesn't tempering usually drop the Rc?

 

[RJ Martin]

Dave: Overheating before quench results in a lot of retained Austenite. That is why ths initial hardness was low. the cryo you did converted a lot of that retained Austenite to Martensite, and, so the hardness increased. Perfectly normal, metallurgical reaction.

Unfortunately, you probably have a larger grain size that normal. I'd re-temper the blade and bring the hardness back to Rc58, or whatever you use for 440C. then, see how it looks when you finish it and see how it performs once it's sharpened.