Hardened O1 questions

Signalprick

Signalprick

Jason Ritchie
Gold Member
Joined
Apr 3, 2009
Messages
3,260
Howdy all,
I have a question or two regarding a few O1 blades I recently cooked up. Up till now I have been successful of hitting my mark for an RC of 59 - 60 for O1 blades but this recent batch all the blades came out 57 - 59. First question is 57 too low for O1 to be useful for a slip joint blade? 2nd question is can it be tempered for a 3rd cycle to possibly bring the hardness up a point or 2? Thanks for the help here.
 
As far as I know you can’t gain hardness on a temper for a steel like O1 if you tempered at 400 doing a 3rd cycle at 350 isn’t going to do anything for your hardness. I like to walk my tempers up to hit my target so I’ll do an initial cycle lower than my target in case I need to do my final temper lower than expected.
 
Joshua Fisher said:
As far as I know you can’t gain hardness on a temper for a steel like O1 if you tempered at 400 doing a 3rd cycle at 350 isn’t going to do anything for your hardness. I like to walk my tempers up to hit my target so I’ll do an initial cycle lower than my target in case I need to do my final temper lower than expected.
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Gotcha. Its weird, I tempered 2 - 2 hour cycles @375. Any idea if a 57 RC is useable?
 
I just went back and looked. I measured 58 - 59 on two of the blades and only just the one came out as low as 57 in a couple tested spots. So 57 - 58, is that an acceptable hardness for O1 blades?
 
Could be it didn’t harden correctly did you check your oven or tester to know those are still accurate or calibrated? Or did you get the O1 from a different source? To me I think 57 for small knife is a bit on the soft side but that doesn’t mean it wouldn’t make a decent blade
 
Joshua Fisher said:
Could be it didn’t harden correctly did you check your oven or tester to know those are still accurate or calibrated? Or did you get the O1 from a different source? To me I think 57 for small knife is a bit on the soft side but that doesn’t mean it wouldn’t make a decent blade
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I guess my assumption is my oven is fine, its brand new and I've only used it 6 times now. I do know my kitchen oven where I temper my blades varies my 30* or so. I was shooting for 375* for tempering. For my tester, I just got it and I dont have calibration blocks yet but I have tested a spring and blade that I had previously tested by a buddy who I know his tester is accurate and got the same exact readings.
 
Bill DeShivs said:
57 RC is fine.
There are millions of knives out there with 50 RC blades.
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Thanks Bill. I think worst case I will use them to practice my freehand hollow grinding. If one or all happens to turn out good at least I know I can still build a useable knife out of it.
 
All tempered together in same spot in the oven? A little overshoot on the temp oven getting to a stable temp could be the source but not if they were all in a batch. Like others Im sure its the decarb if you were testing "through" it and not the steel under. Can you come back and let us know if that was the problem?
 
David Schott said:
All tempered together in same spot in the oven? A little overshoot on the temp oven getting to a stable temp could be the source but not if they were all in a batch. Like others Im sure its the decarb if you were testing "through" it and not the steel under. Can you come back and let us know if that was the problem?
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We have one of those double compartment kitchen ovens and this is where I have been doing my blade tempering. I always temper them in the top smaller oven in the same spot. I also run an external thermometer because the oven isn't very accurate. Also it does vary by 25* as it cooks but it's never been an issue before. I'll clean the scale off and test them again and see if maybe that was the issue. I'll def. Let you know. Thanks!
 
I'm betting on decarb since it's O1, unless you used a foil pouch.
57-58Rc is pretty common for factory blades these days. If you specifically wanted them harder, then maybe do another one, but certainly you're in the ballpark. If it was 50Rc I'd re-harden it.
 
Cliff Carter Knives said:
Silly question but are you sure you ground through all the decarb on the spots you hardness tested?
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I owe you a beer!! I just profiled and surface ground one of the blades and retested, 59 - 60. I checked 4 spots just to make sure. It didn't even occur to me to clean the scale off first. I'll check the other 2 as I work up to them but I'm feeling pretty confident this was my issue. Thanks again for that tip!
 
Signalprick said:
I owe you a beer!! I just profiled and surface ground one of the blades and retested, 59 - 60. I checked 4 spots just to make sure. It didn't even occur to me to clean the scale off first. I'll check the other 2 as I work up to them but I'm feeling pretty confident this was my issue. Thanks again for that tip!
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really glad to have been able to help, and even happier that it was an easy fix for you!
 
Signalprick said:
Howdy all,
I have a question or two regarding a few O1 blades I recently cooked up. Up till now I have been successful of hitting my mark for an RC of 59 - 60 for O1 blades but this recent batch all the blades came out 57 - 59. First question is 57 too low for O1 to be useful for a slip joint blade? 2nd question is can it be tempered for a 3rd cycle to possibly bring the hardness up a point or 2? Thanks for the help here.
Click to expand...
I have been making throwing knives with O1 tool steel for several years. Since I started using graphite for decarb and scale protection, I have NO, NO decarb or scale issues. I just tested my latest batch of throwers using my new Grizzly Rockwell tester. I tested one direct from the 330-350° F oven (before the 750° F temper) and it tested at HRC 61 ± 0.5. After my final temper, I got a range of 50 - 52 on different areas of the knife. By the way, I test while the graphite is still on!!! No scale or decarb!!! I have written several papers regarding the process and results on my DIY sight (bellablades.com). You may find them useful.

Good luck,

Ratpack
Signalprick said:
Howdy all,
I have a question or two regarding a few O1 blades I recently cooked up. Up till now I have been successful of hitting my mark for an RC of 59 - 60 for O1 blades but this recent batch all the blades came out 57 - 59. First question is 57 too low for O1 to be useful for a slip joint blade? 2nd question is can it be tempered for a 3rd cycle to possibly bring the hardness up a point or 2? Thanks for the help here.
Click to expand...
 
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