A2 heat treat

rodriguez7

rodriguez7

Gila wilderness knife works
Joined
Feb 1, 2009
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Can someone here give me an idea where to start with this steel, I have an evenheat kiln, quench plates and access to liquid nitrogen! Just not sure where to start. I’m going to be building a knife around 6 1/2 inches in blade length, close to 1/4 in stock, maybe .20 thick. I’m looking for good toughness with some decent edge holding! I’m new to air hardening steels. Is there any way to get close to the toughness of 8670? I’m sure A2 won’t match it in toughness, but I would imagine I could get close from what I’ve read! Thanks
 
Start by looking at A2 data sheets from manufactures of A2. Also A2 will beat the pants off of 8670 and send it running home to mommy (5160).
 
I’ve read the data sheets, just wanted to ask here. So you’re saying it’s tougher than 8670? That’s hard to believe! If it is, it might be my go to carbon steel. I’m sure Edge retention is much better. Thanks JT.
 
I put 8670 on the same level as 5160. I’m not saying that A2 is tougher then 8670. But I would wadger a bet that at the hardness we like out knives st (60+rc) that A2 is tougher. I find 5160 at high hardness to not be very tough. A quick search turned up these numbers.

M4 - 15J @ 64
440C - 22J @ 58
CPM S90V - 26J @ 58
D2 - 30J @ 59
CPM M4 - 38J @ 63.5
S30V - 38J @ 58-60?
M390 - 41J/sq cm @ 58? and 32J/sq cm @ 63 (unknown test method)

O1 - 41J @ 62 (61 to 63)
3V - 53J @ 62 and 113 @ 58
A2 - 56J @ 60 and 42J @ 61
L6 - 58J @ 61 and 93J @ 57
S7 - 169J @ 57
S5 - 198J @ 58-59
4340 - 55J @ 57 (Charpy V notch test)
 
But with all that said, it’s just numbers. 5160 is a great steel when used correctly. To many people get caught up in numbers and think because x steel is harder or tougher or what ever that it means it’s better. Every steel has a use and when treated correctly it will preform very.
 
Sweet, thanks man. I just ordered a few bars of A2 to try out. I’ll run some tests along side some 8670 and see what I get. Do you have a recommended aust temp to start with? Hold times?
 
A2 really does need a cryo treatment to preform at its best. As for time and temp I will have to look in my ovens controller when I get home. Do you have stainless foil wrap? You need to protect the blades surface from oxygen on these air hardening steels. If all your planing on using is A2 then you don’t need the high temp foil.
 
I have access to cryo, and I forgot to order foil, I’ll put in another order for it now! Thanks for your help.
 
I think I fixed it, I hope
 
From the Tool Steel book I'm reading:

A2: 1740 F, 20-30 min soak, plate quench, 350-400 F x2
 
I’ve seen that, I’m gonna include cryo too! But I’m wondering what some of these guys are doing off the books!
 
This is where testing comes into play. Make a bunch of coupons and set up a testing schedule and try all the options to see what you get. I have spent a lot of time playing with heat treating to get the results I get. But even if I gave you everything I know (not much) it would still be different with your setup. There are a few tricks of the trade I have figured out along the way. One exzample has to do with keeping AEB-L straight. But those things stay in my shop. Not that I’m hoarding secrets it’s just my process and how I do stuff. But yes I will tell you that A2 really does need a cryo treatment and do it befor any tempering.
 
If you want a starting point, I found 1775 for 15 minutes, plate quench, cryo, temper at 425 to give a fairly good result. I don't remember the exact RC, but my personal carry knife I heavily abuse is old Starrett A2 done that way.
But as JT said your results will vary. All I can say is that works well with the older starrett A2 I had a bunch of, and my specific oven.
 
Last edited:
Geoff Flato said:
If you want a starting point, I found 1975 for 15 minutes, plate quench, cryo, temper at 425 to give a fairly good result. I don't remember the exact RC, but my personal carry knife I heavily abuse is old Starrett A2 done that way.
But as JT said your results will vary. All I can say is that works well with the older starrett A2 I had a bunch of, and my specific oven.
Click to expand...
Sweet, thanks for the reply! I appreciate it. I’m still new to heat treat, very limited on time! I just needed somewhere to start, and it seems like some people don’t like to help out much! I’ll give that a shot and see how it turns out.
 
1975f for A2??? I've never heard of such a high aus temp. Perhaps you mean 1775f. Other than that weirdly high aus temp that is probably a typo, this HT looks very good. I could totally get behind that.
 
Ok, thanks. Should that put me around 60rc? This is at least something I can start working off of. The main use of these knives will be skinners, up to around a 6 inch stout blade, heavy duty enough for batonning and chopping!
 
IIRC, I use 1750 with a 20 minute soak. Plate quench to room temp cryo for 4 hours or dry ice bath for 15 minutes. Temper at 400-425F for one hour twice. cool in running water between tempers.
 
I’ll try both of these. Stacey why do you do cryo for 4 hours? But dry ice for 15 minutes?
 
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