440C treatment

Zuluninja

Zuluninja

Tuquito Leather & Steel Works
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Aug 25, 2009
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Hello folks. I tried searching here but a lot of stuff came up that is not really what I'm looking for...

I was wondering about the ht cycle of 440C. I decided to try my hand with some thin stock 440c from Aldo and try to make a paring knife for my grandma. From what I've been reading on other sites, it needs a cryogenic cycle after quench. I have several questions:

1> Does it need a specific soak time while austenitizing?

2> Can I use dry ice for the cryo after ambient temp has been reached?

3> How long is the cryogenic cycling?

4> And finally, how difficult is to treat 440c? I'm fairly new at this and have only been working with carbons. Should I try my hand first with another type of stainless?

Your help is deeply appreciated, thanks!
 
If you have a temperature controlled furnace, electric or gas or salt bath doesnt matter, you need to soak it at least 20 mins, isolated from oxygen (ht foil, vacuum furnace, argon gas, etc). Dry ice is Ok, but LN is better. Generally for all austenitic stainless same logic applies. Airtight soak, cool in air, oil or AL plate, cryo, then temper...
 
We need to know what equipment you have. If you have a coal forge then the advice will be completely different than if you have a HT oven and a liquid nitrogen dewar.
 
I'm guessing that if you have to ask this question....you will need to send it out for HT. They will know how to do 440C.
 
probably sending it off for ht would be the better way to do it, but I like to do things myself, I guess it's the good way to learn by trial and error... right now I have a rather crude forge but will be getting a gas open ends forge within the month.

how long does the cryo take?
 
Thanks! I printed it out, but still don't know how long do I have to leave in cryo...do I just take it out after reaching -100 F?
 
Send it out for heat treatment. Then buy some 1084 and your forge should work ok with that steel. You are not going to heat treat 440c successfully with a forge. The cryo wont even matter if it isnt heat treated correctly. I have a forge and there is no way I would try to ht 440c in it. 1084 you can bring it it to just above non magnetic and quench and you will have a useable knife. Texas knifemakers is the least expensive heat treater.

But if you must know, just leave it overnight in the dry ice and alcohol slurry.
 
I'll explain the HT for 440 ( and stainless in general).

It must be prepared by having the blade sanded to 400 grit and nearly finished. The edge should be about .010".
Place in a sealed HT foil packet and put in a HT oven ( almost aways electric) at 1200F for 15 minutes. ramp to 1900-1950F.
Hold at 1900-1950F for 30 to 45 minutes.
Remove packet and quench between heavy aluminum plates. Alternate quench is in oil. Cool to room temperature.
Snap temper at 300F for 30 minutes. Cool to room temperature.
Place in sub-zero bath of dry ice (-100F) and acetone/kerosene and hold for 30 minutes, or do cryo in liquid nitrogen (-300F) and hold for 2-3 hours. ( note: sub-zero quench and cryo are different things. Either one will work)
Temper at 375-400F for two hours. Cool to room temperature. Repeat temper at 375-400F for two hours.
Sand blade to final finish. Rc should be around 57-58 if done with sub-zero quench, and 58-59 if done with cryo.

This whole procedure requires a controlled oven with a programmer, HT foil, quench plates, and either a dry ice bath or a dewar of liquid nitrogen.
As you can see, a forge and a pair of tongs won't work.

It takes about 8 hours to do a proper stainless HT, and $2000 to $10,000 in equipment. That is why even the pros often send their stainless out for HT. You can get a blade done with cryo for about $10-15, or twenty pounds of blades done for $70-100.

Attempting to do this at home with a forge won't be trial and error...it will be trial and failure :)
Sending the blade out is not cheating, it is good knifemaking. It is the same as buying Micarta for handles. Let the folks who do it for a profession do that step.
 
Thanks bladsmth, very thorough explanation. I see the point now (hyuk hyuk). Guess I'll prep and send them, price for ht sounds like a good deal vs the work involved, which I am nowhere near equipped to do. Lol, I'll stick to the 1084...for now. Thanks again!

Before I let go... can the sub-zero bath be done with carbons? any benefits or not necessary?
 
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