A2 heat treatment

S

skillgannon

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Apr 27, 2009
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I just got my new 27" oven. I'm pretty excited. I'm hoping to use A2 for some hunting and bushcrafters and then maybe a competition chopper. Any advice for heat treatment? Do I need SS wrap, sub zero quench? I have seen different things in different post.
 
I'll tell you what I do. Using ATP 641 anti scale
Pre-quench at 1575f, then temper at 1300 for 2 hours (this step not necessary, but is done for hopeful grain refinement and thus a slightly tougher edge)
Harden at 1750f, 20 minutes, warmed canola oil quench, then into plates for straightness
Immediately into sub zero dry ice/denatured alcohol slurry for a few hours (all you need to do is get it to that temp, approx -100f)
At least 2 tempers, 2 hours each. 350f-400f depending on application

Using foil is great, but I would just use quench plates if doing so.
 
samuraistuart said:
I'll tell you what I do. Using ATP 641 anti scale
Pre-quench at 1575f, then temper at 1300 for 2 hours (this step not necessary, but is done for hopeful grain refinement and thus a slightly tougher edge)
Harden at 1750f, 20 minutes, warmed canola oil quench, then into plates for straightness
Immediately into sub zero dry ice/denatured alcohol slurry for a few hours (all you need to do is get it to that temp, approx -100f)
At least 2 tempers, 2 hours each. 350f-400f depending on application

Using foil is great, but I would just use quench plates if doing so.
Click to expand...

I have quench plates.
What does the high temper do? Or is it just a grain refining cycle as well?
 
Precipitates more carbides that are nucleation sites for new aus grain. (Finer grain). At least that is my understanding.

And I meant to say that if using oil quench, the foil may be problematic. So if using foil, probably best just to use plates. They are plenty fast for a2.
 
samuraistuart said:
I'll tell you what I do. Using ATP 641 anti scale
Pre-quench at 1575f, then temper at 1300 for 2 hours (this step not necessary, but is done for hopeful grain refinement and thus a slightly tougher edge)
Harden at 1750f, 20 minutes, warmed canola oil quench, then into plates for straightness
Immediately into sub zero dry ice/denatured alcohol slurry for a few hours (all you need to do is get it to that temp, approx -100f)
At least 2 tempers, 2 hours each. 350f-400f depending on application

Using foil is great, but I would just use quench plates if doing so.
Click to expand...
What's the expected hardness with those tempers? I'm assuming that they might be a bit low for a large chopper.
 
samuraistuart said:
then temper at 1300 for 2 hours (this step not necessary, but is done for hopeful grain refinement and thus a slightly tougher edge)
warmed canola oil quench,
Click to expand...

Stuart I've never worked with A2 but I just got a new furnace and might try new steels and this all caught my eye.

Is this recipe something you have developed and tested yourself or do you have some reference for this?
I've not seen any industry guidelines for the 1300 temper step, and I thought A2 was an air hardening steel.

Developing or use of a proper HT method is very important, we can all agree to this, but so is efficiency and elimination of steps that don't yield real gains :), at least for me.
regards
 
Harbeer, this A2 heat treatment was given to me by one of the well known makers on this forum, Devin Thomas "Hoss". He and I were discussing AEBL pre-quench after his informative thread, and the subject of A2 came up. In full disclosure, I haven't done extensive testing with this HT, not sure if anyone has. I've only recently been interested in the alloy, the same time AEBL pre-quench was being discussed. I do remember him saying to me (concerning the A2 pre-quench) "School is still out on this one". I take that to mean that the "pre-quench" for this particular alloy may not be of much benefit, but the goal is grain refinement in an alloy that isn't usually cycled like we normally do with low alloy carbon steels, because of the microstructure you would have after a traditional "thermal cycle". Hence the pre-quench, and then the subsequent "temper" to help re-spheroidize the matrix, setting it up for the next and final hardening cycle. I like the idea of squeezing out as much performance as possible, but you make a perfectly valid point about efficiency. This is just one of those things that needs a harder looking into.

A2 is indeed an air hardening steel. Hence the letter "A". I believe "industry standard" is air or plate quench, but A2 is quenched in oil by some. I believe the theory goes that the faster quench might help in some retained austenite reduction. We're talking about splitting hairs, tho, and if the faster quench gives distortion issues, it probably isn't worth it. But an oil quench followed by plates seems to work very well for me. The A2 I received from SB Specialty has proven extremely stable in an oil/plate quench. I'm hardening 1/16" profiles, grinding post HT.

The heat treatment method for A2 that I think is most common for knife makers is along the lines of:
1750f-1775f 20 minute soak
plate quench until ambient
dry ice slurry or LN2
temper

I've done both the pre-quench and the regular approach. As to what is "best", I make NO claims, and the correct answer will be up to the individual maker. For now.
 
Has anyone used A2 in a large chopper like a competition style knife? How did it do and what heat treatment was used?
 
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