METE - A2 Advise Please

R

rlinger

Joined
Mar 29, 2002
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4,591
Mete,

Here is what I have and what I did:

A scandi A2 within about 1 thousanth edge before heat treat and 5/32 spine thickness (I took it to zero edge after HT with no noticable compromise in temper while grinding to zero edge after HT).

preheat: 1200 / 7 min.

austenitize: 1770 / 10 min.

rapid air quench to hand warm

snap temper: 325 / 1 hr.

cryo: >10 hr

temper 420 followed by 400 F / 2 hr per

The Scandi grind is about 50% on a 1 1/4 wide blade, so its fairlly steep.

My wondering about it is the edge seems to roll a little while chopping hard wood and when drilling a piece of seasoned cherry with the blade tip the tip broke off about 1/64 inch back. The chopping, and some slicing, into seasoned cherry seems not to have chipped the edge. Is my heat treat okay from what you can see of it? This is my very first A2 heat treat so I don't know much about it yet. Do you think I might have a problem with either my snap temperature or my soak time? (I can't break a sample to look at grain because the blade belongs to another and I have no A2 to experiment with).

Thanks Mete.

RL
 
I know I'm not Mete but this problem sounds familiar...

At work we make a lot of parts from cryo'd A2 and surface grind them to zero edges. I know there was a problem a while back with exactly what you describe: Finished parts rolling their edges over in hardwood. The HT was sound (though I'm pretty sure they were conventionally tempered, not snap tempered). We aim for Rc 60 (500º Temper), where A2 is toughest against impact. The problem ended up being the grinding. Even with coolant gushing everywhere, the older surface grinders were not taking even-enough cuts (and we're talking differences of a few tenths between cuts). You couldn't even see, but the edges were getting burned. We ended up having to put those parts on newer, more precise machinery to keep from drawing the hardness out of the edge.

I'll ask around today and see if I can dig up any more about what was going on and get back to you tonight.

Something to consider: RoseMill makes a modified PBC powder for up to 1800º called PBC Special. It might allow you to put that zero-edge on before HT.

-Allin
 
There are two main problems with edges; decarburization, and overheating when finish grinding .There is a third, grain growth because of overheating in austenitizing, but since you're using a proper furnace it's probably not the case. Your heat treating looks fine .A very fine edge has to be carefully watched ,things can happen very fast.
 
So Mete, perhaps I could drop the soak down a couple minutes and try again? It's plenty hard but seems not to edge chip so I kinda figure I might be close but not as close as I could be. That's my thinking anyhow. You think with such a thin edge I could go down a little in soak time and see what happens?? I sure can't see going up in soak time from what I have already done. If I drop the soak, what - about 2 minutes less than my 10 minutes(?).

As always, thanks Mete.

ALLIN, thank you for jumping in too. Knife geometry can be difficult to reliably hardness test with the equipment we use. Especially for me since my tangs are almost always tapered and I do not test on ricasso, I usually mix some experience with tester results to make my determination. That said, I believe the A2 blade of the above heat treat to be 59 - 60 HRc.


RL
 
Roger, I had exact problem when first started using A2 for small knives with fine edges. I have Wilson tester so I was pretty sure my process was correct based on hardness. Only solution I have found is a .015 minimum edge going into heat treat.
 
Thanks Gene but its a Scandi and I don't leave them that thick before HT. Some do. I don't. Don't make any difference now anyway - its at zero edge now. No biggie I suppose. It chops and cuts and if Mete doesn't see my last question about it I'll send the un-handled blade out for customer testing. He's going to handle the blade, not me, and if it does not pass his expectations I'll re-do for him.

Thanks.

RL
 
I wouldn't drop the soak time down , you wouldn't saturate the austenite with carbon.Either leave some material or do something better for decarb protection.
 
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