Possible to differentially temper O1?

[psween]

I've made blades of O1 before, really like the steel for ease of heat treat and good edge holding. I'd like to try a differential temper on a kitchen knife to go for a harder edge, but not sure how to go about it. First inclination is to quench per usual, then protect the cutting edge with clay or ??, then torch or oven temper the spine. I'd like the edge to stay around 60-61 Rc, and draw the spine back down to 56-57. I think I could leave the whole blade at 60 without issue, but would like to try something new. Would also be cool to end up with a temper line or hamon after polishing, but that's not the main reason. Any ideas?

Patrick

 

[timekeeper01]

Sure it is possible. I use 01 for my folder blades, precision ground. I quench in olive oil and temper at 400 for a 2 hour cycle. You want a little more
hardness than I do so I would go 350 to 375 degrees for 2 hours. With the thickness of the folder blades a two hour cycle may be more than needed,but thats the way I do my straight blades so I just do my folders the same way.
As for the hamon..........not so much...........01 just does'nt lend itself to a very defined hamon. I have even used ferric chloride after final polish and the line shows up but not like one of the 10 steels, like 1084, 1095, ect.

 

[psween]

Thanks, good to know I'm not completely out in left field. Been doing some more research and looks like I should be able to maybe do a 350 oven temper after quench, then just submerge the cutting edge in a shallow pan of water while drawing the spine back with a torch. The blade shape is a santoku type, so the cutting edge is nearly straight and easy to protect in water while having good access to the spine and tang. I won't have high hopes for a hamon with this steel, sounds like it's nearly impossible, but will be happy if I can just get the hardness right.

Patrick

 

[cdhknives]

Yes. You don't get the sharp/severe temper line (hamon) you get with simpler steels, but you do get a line.

The easy way is to put a block of brick or similar in your oil tank so you can rock the edge in the oil and leave the spine in air as you quench...essentially only quenching the edge and air cooling the spine.

Clay coating the spine works too.

Finally, after overall temper you can torch temper the spine only with the edge in water. I've also heard of guys shaping a potato, planting the edge into the potato for heat protection, and then torch tempering the spine. Note that neither of these methods gives a temper line since the blade is hardened through!

For a kitchen knife I'd call it overkill unless you were just looking for the temper line. My little EDC got accidentally differentially tempered when I used a pair of propane torches to heat it..spine and edge were close to the flames and got to hardening heat, but there is an arc from the thumb past the plunge and back to the choil back through the handle that didn't make it to hardening heat. It shows in certain light but I never etched it to bring out the contrast.

 

[psween]

Cool, I may just have to try the edge quench alone and leave the spine and tang to air cool. Any guesses as to whether any hardening of the air cooled portions will occur, or just expect them to be in a soft/annealed state? I suppose if I want to have any real knowledge of the condition of the spine I'd have to fully quench, fully temper to my desired edge hardness, then draw back the spine by color while protecting the edge. You've given me some good ideas, this should be kind of fun to experiment. Thanks!

Patrick

 

[cdhknives]

I would assume no hardening of the spine from an edge quench. That can be a problem as it will scratch much easier...but you get a temper line as tradeoff.

 

[Hawkeye]

The Nepalis selectively harden Koukri blades by heating them to critical temperature, then quenching the edge only with a water stream from a teapot. It seems to work well. I tried it on mine. Of course, the traditional material isn't O1. These famous knives are normally made from truck leaf springs.

Another traditional method, previously used in sword-making, is to harden the blade by heating and quenching as usual. Then it is polished to remove scale. A bar of steel of suitable length is then heated to red hot and the blade is placed spine-first on the hot bar. This allows the heat to migrate evenly from the spine toward the edge, leaving the least hardness (and most toughness) along the spine. When the desired colour reaches the edge, you stop. Again, this method was used on carbon steel, not O1.

 

[cdhknives]

Post heat treat, before polish, and the scale line shows where the HT transition line.



You can just barely see the difference in the picture...a change in the 'frostiness' of the reflection. It is slightly more noticeable in person, but with a little etching it will show.

 

[psween]

Cool little knife, I like the lines. I decided proper hardness was more important to me than a nearly impossible temper line, so I think I'll do a full quench, oven temper to 350, then draw back the spine with the edge in water. Should have pretty good control that way, and can keep the spine more of a spring temper rather than soft. Time to get grinding!

Patrick