o1 rockwell

[Petie]

I made my first knife out of o1 and heat treated it friday night. Has anyone ever heard of o1 hitting 75 rockwell. Mine did. I drew it back saturday but haven't checked the rockwell yet.
Jon"Petie"Ross

 

[Nathan the Machinist]

...wait, what?

Are you sure your diamond isn't chipped? I don't think any steel will go to 75 HRC.

 

[Petie]

We tested it twice and both times the diamond made a barely visible mark.
Jon"Petie"Ross

 

[Barkes Knife Shop]

Temper it back some more. Temper 350 2 hours and check.

Terry

 

[David Loukides]

Try putting your test calibration gauge on the tester. Checking the tester 3 or more times to see if you get a consistent reading.
For O-1, 75rc sounds like a false reading.
Ferro-Tic carbide will go as hard as 72/74 rc. It is machinable in its pre hard state but needs a diamond wheel to grind it in post hard state.

 

[me2]

Check your scale. It sounds like your on the Rockwell D scale instead of the C scale. Similar loads, both use the diamond penetrator. The as quenched hardness of O1 should be about 64-65, maybe 66 on the C scale. The conversion to the D scale gives a HRD hardness in the mid 70's. Heres a chart with converted numbers:
http://www.hardnesstesters.com/hardness-conversion.htm
68 HRC is about the absolute max for common quenched and tempered steels, and O1 would certainly qualify as common.
Or check to be sure it's really O1. Mix ups happen.