HT 440c and ATS34 thin blades

Milt

Milt

Joined
Nov 16, 2008
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Lately I have been making fillet knives from ATS34, 1/16" stock. My blades taper from about .040 at the ricasso area to about .020 at the tip before HT. I have been soaking them for 30 minutes at 1900 degrees. No warpage problems. I plate quench.

I have been reading some info on HT and think that I may be over soaking these blades. I saw a chart on a popular website that said for a 1/8" blade, the soak time should be 8-10 minutes.

I have been tempering the ATS34 at 450 degrees, for 2 hours, 2 times. However, this same chart says I should be tempering at 400 degrees for just a single cycle of 2 hours (for RC 58).

I would like to hear opinions from guys that have actually HT'ed these steels.


Thanks,


Milt
 
You are not over soakingit tkes awhile for everything to get into solution,I soak 440-Cfor 35 min and ats 34 for 40min
On the ats 34 I quench from 1930 deg, to room temp into cryo for 4 hrs and temper twice at 400 and usually get 59-60 Rc.
Also the 440-C really like cryo improves edge holding quite a bit.
Stan
 
I'd say that if your temperature control is good, the extra soak time doesn't hurt. I found an industrial source that recommends a 30 minute soak for 1/8" sheet, but I've seen other sources that say X minutes per inch of thickness. Like I said, if your temperature control is good, the extra 15-20 minutes isn't going to hurt you. I usually start my soak of 30 minutes once the oven has equalized from putting the steel in. It's going to take 5-10 minutes for the blade to fully reach temperature, so I figure I'm getting a 20 minute soak at temperature for a 5/32" blade.

As for tempering, I do three cycles of 2 hours for my high alloy steels. It's probably overkill, but the first cycle will almost certainly convert retained austenite into martensite (unless you're doing a cryo, in which case there will be considerably less RA), and that newly formed martensite needs a temper as well.

Hardness results at 400 vs. 450 will vary depending on how you quenched (air vs plate vs oil) and if you performed a cryo. Crucible lists a 400F temper for 154CM (same as ATS34 for all intents and purposes) that has been oil quenched from 1900 as getting you 59RC. 600F drops that to 56 RC. Cryo can add anywhere from 1-3 pts hardness depending on your temper temperature. Labtrobe lists a 400F temper for 440C as geting you in the ball park of 57-58. In their material, they indicate about 1RC higher hardness when oil quenched vs. air quenched (for 440C, a 1900F plate quench will get you 60 as quenched, whereas dropping temperature to 1875 will get you around 61).

--nathan
 
What about blade thickness vs. soak time. These fillet knives are quite thin.

Milt
 
For these steels, you still want a longer soak to make sure everything is in solution. The smaller cross section will come to temp faster, but I'd still soak for 20 minutes at temperature just to be sure. That's just me, but I know that in that amount of time, if my temperature is controlled, I'm not going to do any harm.

--nathan
 
I don't start the timer until I reach 1900 degrees. I use a gas kiln and can control the temp quite well. So, I think I will try a 20 minute soak time tonight.

Thanks fellows,

Miltg
 
Nothing is wrong with a 30 minute soak! It's pretty much what everyone does, and ATS34 does not get grain growth even if you soak it for much longer.
 
Opinions are just that, but since you asked... :)

I've had people tell me that they can HT ATS34 just fine with a torch and a bucket of water. (No, I'm not suggesting that). I think what happens with shorter soaks is that the steel matrix may harden (at least somewhat) but the alloy advantages are just lost. They take time to get into solution.

In short, the blade may skate a file after a short soak HT, but I believe your long soak is correct to get the best out of the steel. There are exceptions, but the steels you mention are not among them.

Rob!
 
Thanks to all who responded. This forum has been invaluable to me as a new knifemaker. One hazard of any forum is that opinions vary widely. It is difficult to sort them all out at times. It is, however, obvious to me that are many smart fellows hanging around here. Sometimes the responses get very technical and hard for me to fully comprehend due to lack of background.

I guess it really boils down to developing your own techniques and practices. I really need to buy a hardness tester. That is the next item on the wish list.

Milt
 
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