Problems with thicker 3V quenching???

M

MeatRobot

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Sep 22, 2012
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Just heat treated some thicker 3v bush knives One was 5/16" thick the other was just shy of 3/8". I sealed in heat treat foil.
took to 1500f soak for 20min then fast ramp to 1985F soak 30min. I then pulled from oven and plate quenched while blowing compressed air into the foil pack witch I cut the end off while clamped in plates, rockwell tested one and was 61rc.

soaked in Liq N02 for 20hr, then I tempered them at 425f twice for 3hr and now they are testing at 58-59rc

checked the toughness of the test blade by tapping on piece of mild steel flat bar and it started chipping out.

I was expecting alot more toughness from an un-sharpened edge at .025"

I'm wondering if the plates are not cooling it down fast enough and go to and oil quench for the thicker stuff.

going to try tempering again at 500F temper and check toughness, will up date,

Any suggestions on a proper low temper 3v recipe would be appreciated!
 
3v benefits from three 2h tempers, and even a fourth can help. I've read that the eta carbides can decrease toughness a bit. I'm no expert on this. I did a couple camp knives in 3/8" 3v, and the edges tested fine at 0.010". I did four 2h tempers at 400f. Rc60/61 was my test. I used cryo, but only for 1h to avoid the pitential eta carbide issue.
 
Thanks Willie! All is not lost will redo the heat treat with less of a soak in the Liq. N02 and add some more temper cycles
 
58-59rc 3v doesn't chipped out like that - regardless of how badly/mangled ht (your ht looked fine). I suspect (95+% likeliness) post-ht ground by very coarse (36-50 grit) & dulled belt, which cracked along the edge. In this case, cracked depth was much thicker than 0.025".
 
Willie those extra tempers worked wonders, I'm chopping big chunks out of mild steel 1" square hhs tubing.
Goal achieved!! Now for some more touchier testing:thumbup:
 
I would suggest oil quench for that thickness .
Why do you LN for 20 hours ?
Do you have documentation for eta carbide - toughness problems ?
 
mete said:
I would suggest oil quench for that thickness .
Why do you LN for 20 hours ?
Do you have documentation for eta carbide - toughness problems ?
Click to expand...

I'll look it up. I remember seeing it referenced recently.

Warren
 
Meet, I've been searching for the article I was reading. I'm co big up blank. I'm finding a few articles specific to tungsten eta carbides, but they don't apply to 3v. It was specific to 3v. Larrin referenced the same thing a few months back, but didn't cite his source. I'll keep looking. I see quite a few references to enhanced cohesion, so this isn't that straight forward.
 
I don't remember what I said before, but here is a paper that talks about eta carbide and toughness differences with 1h vs 24h cryo processing: http://www.airproducts.com/~/media/...-quenching-of-steel-revisited-33005019GLB.pdf

I have expressed skepticism in the past about there being a real difference in transition carbide distributions but there seems to be a consensus in the literature.

Edit: Here are a couple literature reviews:

http://s3.amazonaws.com/academia.ed...=Metallurgical_principles_of_cryogenicall.pdf

http://s3.amazonaws.com/academia.ed...=A_research_review_on_deep_cryogenic_trea.pdf
 
Last edited:
Larrin said:
I don't remember what I said before, but here is a paper that talks about eta carbide and toughness differences with 1h vs 24h cryo processing: http://www.airproducts.com/~/media/...-quenching-of-steel-revisited-33005019GLB.pdf

Some great info there, Thanks Larrin!

My latest test blade I cryoed for 2hr then triple tempered, I was able to hammer the blade into 3/16" mild steel plate with no chipping and only some slight distortion at the edge. Getting there with the 3v heat treat.
Thanks Guys!
Click to expand...
 
It was chuck from AKS who told me about the three tempers. He said the manufacturer recommended four, but that is a tough sell. I do four now. The extra 2h isn't a big deal at my production level. For industry, it might be.

For high hardness applications that need more wear resistance, 10h cryo probably helps. For tough applications, I would do 2-3h. Just my opinion. Ymmv.
 
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