How To Heat treat for 01 in a kiln.

[Liam Ryan]

Hi everyone, as I get more involved in making new details I never considered start popping up, so I need your help.

A coworker and I are about to heat treat some O1 choppers, 1/4" thick. He had a nice sized plate of it, maybe not the best steel for a chopper but I believe far from the worst, and it's free.

So he's gone into the industrial heat treatment books and they all talk about pre soak, starting at 1200f and ramping up to 1450f or so and soaking for about 10 minutes. I knew this was different from what I thought I knew but I didn't specifically know why, or where I heard this as it's rarely mentioned, its just "heat to critical temp and quench."

Yet he has books specifically saying it needs a pre soak to reduce grain size. So why is it different with knives? Is it because industrial parts are generally big chunks that need time to heat up?

A second question is a bit simpler, after quench apparently it's important to not let the blade cool below 100f or so, is this true? How critical is that step? Last blade I made was a short gladius and I put it right on the welding table and clamped it to the table to reduce warping (which worked) but it went into the tempering oven barely warm to the touch. Should I re hear treat this blade?

Anyway thanks in advance for any help.

 

[DevinT]

Preheat is for large dies with varying cross section thickness to prevent undue stress. Knives are long and thin.

Set furnace to 1450’ , heat fully for 30 minutes, then heat treat blade.

Hoss

 

[Evan Wilson]

the heat soak is generally for large dies and thick pieces as mentioned by DevinT here is a link to some decent heat treat info:https://cdn.newjerseysteelbaron.com/wp-content/uploads/2020/07/O-1-Heat-Treat-7-20.pdf

the 2nd question is no in most cases it is just a good rule I've found to go strait to tempering It does not necessarily need to be done unless stated in the recommended heat treat data sheet,most recomend this because it can crack even after the quench and at room temperature. blades can continue to harden a small amount up to 24-48 hours after the quench this is why a blade can be put in cryo and gain a greater degree of hardness.that should be the caveman brain explanation for things.

 

[Liam Ryan]

the heat soak is generally for large dies and thick pieces as mentioned by DevinT here is a link to some decent heat treat info:https://cdn.newjerseysteelbaron.com/wp-content/uploads/2020/07/O-1-Heat-Treat-7-20.pdf

the 2nd question is no in most cases it is just a good rule I've found to go strait to tempering It does not necessarily need to be done unless stated in the recommended heat treat data sheet,most recomend this because it can crack even after the quench and at room temperature. blades can continue to harden a small amount up to 24-48 hours after the quench this is why a blade can be put in cryo and gain a greater degree of hardness.that should be the caveman brain explanation for things.

Thanks, I believe You've helped me convince him, lol. One more question if I may, I've been thinking of doing a differential temper, by which I mean softening the spine of the blade once it's tempered. Is this as simple as keeping the edge submerged in water and using a torch to heat up the spine to say a dark blue? It's something I'm sure I've seen done in the past, but when I search the only thing that comes up is people using clay during the heat treat.

 

[A.McPherson]

There are a couple ways of doing it...
1.You could edge quench, leave the edge below the oil until the spine isn't red, the quench the rest, then temper the whole thing.
2. You could quench the whole thing, temper the whole thing, then heat the back with a torch, or other heat source, keeping the edge under water.
3. You could quench the whole thing, then temper by heating the back of the blade and "running the colors" to the edge.
4. Clay
5. I'm sure there are others...

I think the first and second methods are probably the best, but I've not done any testing to confirm that

 

[Stacy E. Apelt - Bladesmith]

I don't like an edge quench. Too many variables to get consistent results.

Harden the whole blade and then temper as normal. It is always best to convert the blade to martensite and then temper because this gives a known and even structure to the blade before any differential zones are made. Do a differential temper by keeping the edge cool and heating the spine. I "run colors" when doing this with a small jeweler's torch. If you are drawing the spine back a lot more than the edge, a wet sponge with the edge pressed into it will also work as a heat sink for "bluing the spine".